JP2009144555A - Control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stably maintaining an air-fuel ratio, in start or stop of supply of reformed fuel, or increase or decrease of the reformed fuel. <P>SOLUTION: An internal combustion engine 10 has a fuel reformable catalyst 28 generating combustible gas by the supply of the reformed fuel. In execution of reformed EGR control, the reformed fuel is supplied to the catalyst 28 by the reformed fuel injection valve 34 and the combustible gas generated in the catalyst 28 is circulated in an intake system. The ECU 50 reduces an amount of main fuel injected by the fuel injection device 18, when an exhaust air-fuel ratio is changed on a rich side from the start of the supply of the reformed fuel or the increase of the reformed fuel amount. Therefore, a temporary excessive lean air-fuel ratio of air-fuel mixture, caused by reduction in injection amount of the main fuel before supply change of the reformed fuel (combustible gas) is reflected on the combustion, is prevented. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a control device for an internal combustion engine configured to generate a combustible gas from fuel by a fuel reforming catalyst and to recirculate the combustible gas to an intake system.

  2. Description of the Related Art Conventionally, as disclosed in, for example, Patent Document 1 (Japanese Patent Laid-Open No. 2006-291775), an internal combustion engine configured to reform a fuel into a combustible gas using heat of exhaust gas is known. A control device for an internal combustion engine according to this type of prior art includes a fuel reforming catalyst for generating a combustible gas from the reformed fuel by a steam reforming reaction or the like.

  The combustible gas generated by the fuel reforming catalyst is recirculated to the intake system together with the exhaust gas, whereby reforming EGR control is performed. In the reformed EGR control, the combustible gas recirculated to the intake system contributes to combustion together with the air-fuel mixture (main fuel). For this reason, at the start of reforming EGR control, the injection amount of the main fuel is often reduced by the amount that the combustible gas contributes to combustion.

  However, there is a certain time delay between the supply of the reformed fuel to the catalyst and the arrival of the combustible gas in the combustion chamber. For this reason, if the main fuel is immediately reduced when the supply of reformed fuel is started, the air-fuel mixture may temporarily become an excessive lean air-fuel ratio. Therefore, in the prior art, the main fuel is reduced when a time (estimated arrival time) at which it is predicted that the combustible gas has reached the combustion chamber has elapsed after the supply of the reformed fuel is started.

JP 2006-291775 A

  By the way, in the above-described conventional technology, the main fuel is reduced when the estimated arrival time has elapsed after the supply of the reformed fuel is started. In setting this predicted arrival time, it is necessary to consider the time required for each process of reforming EGR control. Here, the time required for each process refers to, for example, the time required for the reformed fuel to reach the catalyst on the exhaust gas flow, the time required for the reforming reaction to proceed on the catalyst, and the catalyst. The time until the generated combustible gas reaches the combustion chamber through the intake passage or the like.

  However, these times vary depending on the operating state of the internal combustion engine (for example, exhaust gas flow rate, pressure, catalyst temperature, etc.). For this reason, in the prior art, when the reforming EGR control is started or the supply amount of the reformed fuel is increased, it is difficult to appropriately set the predicted arrival time according to the operating state. And, when the arrival prediction time is set inappropriately, for example, the air-fuel mixture becomes an excessive lean air-fuel ratio, fuel efficiency and drivability are deteriorated, and the effect of reforming EGR control is not sufficiently exhibited. become.

  On the other hand, when the reforming EGR control is stopped or the supply amount of the reformed fuel is reduced, problems similar to those described above occur. That is, during the reforming EGR control, as described above, the injection amount of the main fuel is often reduced by the amount that the combustible gas contributes to the combustion. In this state, if only the stop or reduction of the reformed fuel is performed carelessly, the air-fuel mixture becomes an excessive lean air-fuel ratio, resulting in a problem that fuel efficiency and drivability deteriorate.

  The present invention has been made to solve the above-described problems. When starting, stopping, increasing or decreasing the supply of reformed fuel, the main fuel injection state is appropriately set in any operation state. An object of the present invention is to provide a control device for an internal combustion engine that can be switched at a proper timing and can stably maintain an air-fuel ratio.

A first invention is a main fuel injection means for injecting main fuel toward a combustion chamber of an internal combustion engine;
A fuel reforming catalyst that generates combustible gas from the reformed fuel when the reformed fuel is supplied;
Reformed fuel supply means for supplying reformed fuel to the fuel reforming catalyst;
EGR means for recirculating EGR gas, which is a mixed gas of the exhaust gas of the internal combustion engine and the combustible gas, to the intake system of the internal combustion engine;
Air-fuel ratio detecting means for detecting the air-fuel ratio of the exhaust gas;
Reformed fuel increasing means for starting or increasing the supply of reformed fuel by the reformed fuel supplying means according to the operating state of the internal combustion engine;
Rich determination means for determining whether or not the air-fuel ratio has changed to the rich side by the operation of the reformed fuel increasing means;
A main fuel reduction means for reducing the injection amount of the main fuel by the main fuel injection means when the rich determination means determines that the air-fuel ratio has changed to the rich side;
It is characterized by providing.

  According to the second aspect of the present invention, it is configured to include the determination prohibiting unit that prohibits the determination operation of the rich determination unit from the time when the reformed fuel increasing unit is activated until the determination prohibition period elapses.

A third invention comprises a main fuel injection means for injecting main fuel toward a combustion chamber of an internal combustion engine,
A fuel reforming catalyst that generates combustible gas from the reformed fuel when the reformed fuel is supplied; and
Reformed fuel supply means for supplying reformed fuel to the fuel reforming catalyst;
EGR means for recirculating EGR gas, which is a mixed gas of the exhaust gas of the internal combustion engine and the combustible gas, to the intake system of the internal combustion engine;
Main fuel increasing means for increasing the amount of main fuel injected by the main fuel injecting means when stopping or reducing the supply of reformed fuel by the reformed fuel supplying means;
Reformed fuel reducing means for stopping or reducing the supply of the reformed fuel by the reformed fuel supplying means at the time when the main fuel increasing means is operated or thereafter,
It is characterized by providing.

4th invention, the air fuel ratio detection means which detects the air fuel ratio of the said exhaust gas,
Rich determination means for determining whether or not the air-fuel ratio has changed to the rich side by the operation of the main fuel increasing means,
The reformed fuel reducing means is configured to stop or reduce the reformed fuel when the rich determining means determines that the air-fuel ratio has changed to the rich side.

  According to the first invention, when the supply of the reformed fuel is started, it can be confirmed accurately and easily by the change of the exhaust air-fuel ratio that the combustible gas has reached the combustion chamber. Thus, after the combustible gas actually contributes to the combustion, the main fuel injection amount can be reduced by that amount. For this reason, even when the delay time until the combustible gas contributes to combustion changes according to the operating state of the internal combustion engine, the main fuel reduction timing can be set appropriately in any operating state.

  Therefore, it is possible to reliably prevent the main fuel from being reduced before the combustible gas contributes to the combustion, and thereby to prevent the air-fuel mixture from becoming an excessive lean air-fuel ratio. The air-fuel ratio can be stabilized. Also, when the supply amount of the reformed fuel is once increased and then increased, the injection amount of the main fuel can be reduced when the exhaust air-fuel ratio changes to the rich side. Accordingly, in this case as well, the same effect as when fuel supply is started can be obtained.

  According to the second aspect of the present invention, even when the output of the air-fuel ratio detecting means is disturbed due to a disturbance such as noise during the determination prohibition period, the disturbance of the output can be ignored. For this reason, it is possible to reliably prevent erroneous determination due to disturbance at a timing when the combustible gas should not reach the combustion chamber. In addition, after the determination prohibition period has elapsed, the determination operation can be reliably performed according to the output of the air-fuel ratio detection means. Therefore, reliability against disturbances such as noise can be improved.

  According to the third invention, by stopping the supply of the reformed fuel, even if the combustible gas is not recirculated to the intake system, the injection amount of the main fuel can be increased in advance. That is, it is possible to switch the injection state of the main fuel at an appropriate timing in preparation for stopping the reformed fuel. As a result, when the reformed fuel is stopped, the air-fuel mixture can be reliably prevented from having an excessive lean air-fuel ratio, and the air-fuel ratio can be stably maintained. In addition, when the supply amount of the reformed fuel is decreased, the main fuel injection amount can be increased in advance. Therefore, also in this case, the same effect as when the fuel supply is stopped can be obtained.

  According to the fourth aspect, by increasing the main fuel, the supply of the reformed fuel can be stopped or reduced after the exhaust air-fuel ratio has changed to the rich side. Thereby, it can be confirmed by the change in the exhaust air-fuel ratio that the increase in the main fuel is reflected in the combustion. Therefore, for example, when the increase in the main fuel is insufficient, the supply stop of the reformed fuel can be delayed, and the timing of the supply stop or the decrease can be surely grasped.

Embodiment 1 FIG.
[Configuration of Embodiment 1]
The first embodiment of the present invention will be described below with reference to FIGS. First, FIG. 1 shows an overall configuration diagram for explaining the system configuration of the first embodiment. The system of this embodiment includes a multi-cylinder internal combustion engine 10, for example. The internal combustion engine 10 is operated by, for example, a fuel in which alcohol and gasoline are mixed. In the present embodiment, a mixed fuel of ethanol and gasoline is used as an example.

  An intake pipe 12 of the internal combustion engine 10 is connected to an intake port of each cylinder via an intake manifold 14. In the middle of the intake pipe 12, an electric throttle valve 16 for adjusting the amount of intake air is installed. A fuel injection device 18 as a main fuel injection means is provided at each intake port of each cylinder. These fuel injection devices 18 are composed of electromagnetic valves and the like, and inject fuel (hereinafter referred to as main fuel) toward the combustion chamber in the cylinder.

  An exhaust pipe 20 of the internal combustion engine 10 is connected to an exhaust port of each cylinder via an exhaust manifold 22. A heat exchanger 24 is provided in the middle of the exhaust pipe 20. A plurality of reforming chambers 26 are formed at intervals in the heat exchanger 24, and these reforming chambers 26 contain a metal material such as Rh, Pt, Co, Ni, and the like. A fuel reforming catalyst 28 is supported.

  Between each reforming chamber 26, an exhaust passage 30 that is disconnected from the reforming chamber 26 is provided. These exhaust passages 30 are connected in the middle of the exhaust pipe 20. According to the heat exchanger 24 configured as described above, the reforming chamber 26 (the fuel reforming catalyst 28) can be heated by the heat of the exhaust gas passing through the exhaust passage 30. By this heating, the fuel reforming catalyst 28 can cause a reforming reaction described later.

  The exhaust pipe 20 is provided with a branch pipe 32 that branches on the upstream side of the heat exchanger 24. The downstream side of the branch pipe 32 is connected to the reforming chamber 26 of the heat exchanger 24. In the middle of the branch pipe 32, a reformed fuel injection valve 34 is provided as reformed fuel supply means. The reformed fuel injection valve 34 is composed of an electromagnetic valve or the like, and injects and supplies fuel (hereinafter referred to as reformed fuel) into the exhaust gas flowing through the branch pipe 32.

  With this configuration, a part of the exhaust gas flowing through the exhaust pipe 20 is introduced into the reforming chamber 26 by the branch pipe 32 and supplied with the reformed fuel by the reformed fuel injection valve 34. A mixed gas of these exhaust gas and reformed fuel flows into the reforming chamber 26 and causes a reforming reaction described later by the action of the fuel reforming catalyst 28.

  The reformed gas (combustible gas) generated by this reforming reaction becomes EGR gas mixed with the exhaust gas. Then, the EGR gas is recirculated into the intake pipe 12 through the EGR passage 36 and mixed with the intake air. The EGR passage 36 is provided with a cooler 38 for cooling the EGR gas, and an electromagnetic flow rate adjusting valve 40 that variably sets the recirculation amount of the EGR gas to the intake pipe 12 (hereinafter referred to as EGR amount). It has been. The EGR passage 36 and the flow rate adjustment valve 40 constitute the EGR means of the present embodiment.

  Further, of the exhaust gas flowing through the exhaust pipe 20, the remaining exhaust gas that has not flowed into the branch pipe 32 passes through the exhaust passage 30 of the heat exchanger 24 and supplies heat to the reforming chamber 26. The exhaust gas is purified by an exhaust purification catalyst 42 made of a three-way catalyst or the like provided in the exhaust pipe 20 and discharged to the outside.

  On the other hand, in the internal combustion engine 10, the mixed fuel of ethanol and gasoline is stored in the fuel tank 44. The fuel tank 44 is provided with a fuel pump (not shown) for sending the fuel in the tank to the outside in a pressurized state. Connected to the discharge side of the fuel pump is a fuel pipe 46 for supplying fuel (main fuel and reformed fuel) discharged from the pump to the fuel injection device 18 and the reformed fuel injection valve 34, respectively.

  Further, the system of the present embodiment includes an ECU (Electronic Control Unit) 50. The ECU 50 is constituted by a microcomputer provided with a storage circuit such as a ROM and a RAM. A sensor system including an exhaust gas sensor 52 as an air-fuel ratio detection means, a fuel property sensor 54, and a catalyst temperature sensor 56 is connected to the input side of the ECU 50.

  The exhaust gas sensor 52 is constituted by an A / F sensor or the like, for example, and is provided in the exhaust pipe 20. The exhaust gas sensor 52 detects the air-fuel ratio of the exhaust gas and outputs a detection signal to the ECU 50. The fuel property sensor 54 is provided, for example, in the fuel pipe 46 and detects the mixing ratio of gasoline and alcohol in the fuel. The catalyst temperature sensor 56 is provided in the reforming chamber 26 of the heat exchanger 24 and detects the temperature of the reforming chamber 26 (fuel reforming catalyst 28).

  The sensor system connected to the input side of the ECU 50 includes, for example, a rotation sensor that detects the engine speed, an air flow meter that detects the intake air amount, a water temperature sensor that detects the coolant temperature, and an accelerator that detects the accelerator opening. A general sensor used for operation control of the internal combustion engine 10 such as an opening sensor is included.

  On the other hand, on the output side of the ECU 50, various actuators including the throttle valve 16, the fuel injection device 18, the reformed fuel injection valve 34, the flow rate adjustment valve 40, the fuel pump and the like are connected. The ECU 50 controls the operation by driving the actuators while detecting the operation state of the internal combustion engine 10 using the sensor system.

  In this operation control, the injection amount of the main fuel is calculated according to the intake air amount, the accelerator opening, etc., and the main fuel corresponding to the injection amount is injected from the fuel injection device 18. Further, air-fuel ratio feedback control is executed using the output of the exhaust gas sensor 52 so that the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst 42 is substantially the stoichiometric air-fuel ratio.

(Reformed EGR control)
Further, as described below, the ECU 50 performs reforming EGR control for returning the reformed gas generated by the reforming reaction between the exhaust gas and the reformed fuel into the intake pipe 12 together with the exhaust gas. In this reforming EGR control, first, reformed fuel is injected from the reformed fuel injection valve 34 to the exhaust gas flowing in the branch pipe 32, and these mixed gases are caused to flow into the reforming chamber 26. At this time, the ECU 50 determines an appropriate injection amount (supply amount) of the reformed fuel according to, for example, the operating state of the internal combustion engine 10, the ethanol concentration in the fuel, the temperature of the fuel reforming catalyst 28, and the like.

Thereby, in the reforming chamber 26, due to the action of the fuel reforming catalyst 28, ethanol in the mixed gas and steam and carbon dioxide in the exhaust gas cause a reforming reaction (steam reforming reaction). By this steam reforming reaction, hydrogen (H ₂ ) and carbon monoxide (CO) are generated as shown in the following formula (1).

C ₂ H ₅ OH + 0.4CO ₂ + 0.6H ₂ O + 2.3N ₂ + Q1 → 3.6H ₂ + 2.4CO + 2.3N ₂ (1)

  Further, the gasoline in the mixed gas also undergoes a reforming reaction with water vapor and carbon dioxide in the exhaust gas as shown in the following equation (2).

1.56 (7.6CO ₂ + 6.8H ₂ O + 40.8N ₂ ) + 3C _7.6 H _13.6 + Q2
→ 31H ₂ + 34.7CO + 63.6N ₂ (2)

  The amount of heat Q1 in the above equation (1) and the amount of heat Q2 in the equation (2) are reaction heat absorbed by the reforming reaction. That is, since these reforming reactions are endothermic reactions, the calorific value of the reformed gas represented by the right side in the above formulas (1) and (2) is the value before the reaction described on the left side of each formula. It becomes larger than the amount of heat that the substance has.

Therefore, according to the heat exchanger 24, the heat of the exhaust gas passing through the exhaust passage 30 can be transmitted to the fuel reforming catalyst 28 and absorbed by the reforming reaction. That is, in the system of the present embodiment, the heat of the exhaust gas can be recovered and used to convert the reformed fuel into a substance (H ₂ and CO) having a larger amount of heat.

  Since the amount of heat Q2 required for the reforming reaction of gasoline is extremely large, for example, the fuel reforming catalyst 28 needs to be at a high temperature of 600 ° C. or higher in order to cause this reforming reaction. For this reason, during the operation of the internal combustion engine 10, the ethanol reforming reaction occurs stably in a wide operating range, whereas the gasoline reforming reaction is performed in a high rotation / high load operating range in which, for example, the exhaust temperature rises. Etc., it will be generated efficiently.

The reformed gas obtained by the above reforming reaction becomes EGR gas when mixed with exhaust gas. The EGR gas is recirculated into the intake pipe 12 through the EGR passage 36 and mixed with the intake air. At this time, the ECU 50 controls the recirculation amount of the EGR gas recirculated to the intake pipe 12 by the flow rate adjustment valve 40. The EGR gas flows into the cylinder of the internal combustion engine 10 together with the intake air, and H ₂ and CO in the reformed gas are combusted in the cylinder together with the fuel injected from the fuel injection device 18.

  In this case, as described above, the amount of heat of the reformed gas is greater than that of the original fuel by the amount of heat recovered from the exhaust gas by the heat exchanger 24. For this reason, by burning the reformed gas in the internal combustion engine 10, the thermal efficiency of the entire system is improved, so that the fuel efficiency performance of the internal combustion engine 10 can be improved. Moreover, according to the heat exchanger 24, the fuel reforming catalyst 28 can be heated using the heat of the exhaust gas without using a heating device or heating energy dedicated to the catalyst. As a result, an exhaust heat recovery type system with high operating efficiency can be configured.

  Further, the reforming EGR control can enhance the effect as EGR (Exhaust Gas Recirculation) by recirculating the EGR gas containing the reformed gas to the intake system. Generally, as the EGR rate is increased, combustion becomes unstable, so there is an upper limit for the EGR rate. On the other hand, when the reforming EGR control is executed, the combustion state is improved as much as the combustible gas is included in the EGR gas.

  For this reason, in reformed EGR control, the upper limit of the EGR rate can be increased and the amount of EGR can be increased as compared with normal EGR control in which only exhaust gas is recirculated to the intake system. Therefore, according to the reformed EGR control, a large amount of EGR gas can be recirculated to the intake system, so that the fuel efficiency can be further improved and the emission can be improved.

[Characteristics of Embodiment 1]
As described above, during the reforming EGR control, the reformed gas contributes to combustion. Therefore, if the main fuel is injected in a normal amount, the air-fuel mixture tends to have an excessive rich air-fuel ratio. Therefore, when the reforming EGR control is started or the reformed fuel injection amount (reforming injection amount) is increased, the main fuel injection amount is decreased by that amount. In the following description, the case of starting reforming injection will be described as an example.

  FIG. 2 is a time chart when the reforming EGR control is started, and this time chart shows a temporal relationship between the reforming injection amount, the air-fuel ratio, and the main fuel injection amount. As shown in this figure, when the reforming injection is started, the reformed gas generated by the injected fuel reaches the combustion chamber with a certain delay time. As a result, after the delay time has elapsed, the air-fuel mixture becomes a rich air-fuel ratio due to the main fuel and the reformed gas, and the exhaust air-fuel ratio also changes to the rich side accordingly.

  For this reason, in the present embodiment, the main fuel is not reduced when the reforming injection is started, and at this time, the injection amount of the main fuel is maintained at the level before the reforming injection. Then, whether the exhaust air-fuel ratio has changed to the rich side due to the reformed injection being reflected in the combustion is determined based on the output of the exhaust gas sensor 52.

  Here, “the exhaust air / fuel ratio changes to the rich side” means that the exhaust air / fuel ratio after the reformed injection changes to the rich side as compared to the exhaust air / fuel ratio before the reformed injection. . When the exhaust air-fuel ratio changes to the rich side, it is determined that the reformed injection is reflected in the combustion. Therefore, the injection amount of the main fuel is reduced, and this injection amount is set to a level corresponding to the reforming EGR control. To do.

  According to this configuration, when the reforming injection is started, it can be confirmed accurately and easily by the change in the exhaust air-fuel ratio that the reformed gas has reached the combustion chamber. As a result, the injection amount of the main fuel can be reduced by that amount after the reformed gas actually contributes to the combustion regardless of the delay time. For this reason, even when the delay time changes according to the operating state of the internal combustion engine, the main fuel reduction timing can be appropriately set in any operating state.

  Therefore, according to the present embodiment, it is possible to reliably prevent the main fuel from being reduced before the reformed fuel contributes to combustion, and thereby the air-fuel mixture to become an excessive lean air-fuel ratio. As a result, the air-fuel ratio of the air-fuel mixture can be stabilized at the start of reforming injection, and the effect of reforming EGR control can be sufficiently exhibited.

  Next, a case where the reforming injection amount is increased during the reforming EGR control will be described. Also in this case, there is a time delay until the increased amount of the reformed fuel is reflected in the combustion. Thus, almost in the same manner as in the case of the injection start described above, after the reformed injection amount is increased, the injection amount of the main fuel is decreased when the exhaust air-fuel ratio changes to the rich side. The reduction level at this time is set according to the increase level of the reforming injection amount. Therefore, even when the reforming injection amount is increased, the same effect as that at the start of injection can be obtained.

[Specific Processing for Realizing Embodiment 1]
FIG. 3 is a flowchart of a routine executed by the ECU 50 in order to realize the system operation of the present embodiment. Note that the routine shown in FIG. 3 is started when the internal combustion engine is started, and is repeatedly executed at regular intervals.

  First, in step 100, the operating state (for example, intake air amount, load state, engine speed, etc.) of the internal combustion engine is detected by a sensor system. In step 102, an EGR amount suitable for the current operating state is calculated by referring to an EGR control map or the like according to, for example, the load state and the engine speed.

  Next, in step 104, the temperature of the exhaust gas (or the fuel reforming catalyst 28) is detected by the catalyst temperature sensor 56 or the like. In step 106, reforming EGR control is started when a reforming start condition set in accordance with, for example, the operating state of the internal combustion engine, the exhaust gas flow rate, the catalyst temperature, or the like is satisfied. That is, the reformed fuel is injected from the reformed fuel injection valve 34 into the branch pipe 32. In this case, the reforming injection amount is set according to, for example, the operating state of the internal combustion engine, the opening degree of the flow rate adjustment valve 40, the temperature and pressure of the exhaust gas, and the like.

  Next, in step 108, it is determined using the output of the exhaust gas sensor 52 whether or not the exhaust air-fuel ratio has changed to the rich side. If “YES” is determined here, it is determined that the reformed fuel injected in step 106 has reached the combustion chamber. Therefore, in this case, the injection amount of the main fuel is reduced in step 110, and this injection amount is set to a level corresponding to the reforming EGR control. In step 112, air-fuel ratio feedback control is executed, and then the process ends.

  On the other hand, when “NO” is determined in step 108, it is determined that the reformed fuel has not yet reached the combustion chamber because the exhaust air-fuel ratio has not changed due to the reforming injection. In this case, therefore, the routine waits at step 108 until the exhaust air-fuel ratio changes to the rich side. As a result, the timing at which the reformed gas contributes to combustion can be reliably grasped, and the main fuel can be reduced in accordance with this timing.

Embodiment 2. FIG.
Next, Embodiment 2 of the present invention will be described with reference to FIGS. Since the present embodiment has the same system configuration (FIG. 1) as that of the first embodiment, description of the basic system configuration will be omitted.

[Characteristics of Embodiment 2]
In the present embodiment, at least a part of the period from the start of reforming injection until the exhaust air-fuel ratio changes to the rich side is set as the determination prohibition period. Then, during the determination prohibition period, a determination is made as to whether or not the exhaust air-fuel ratio has changed to the rich side.

  The delay time from the start of reforming injection until the exhaust air-fuel ratio changes to the rich side changes according to the operating state of the internal combustion engine. The determination prohibition period is a time set as a time shorter than the shortest delay time that can occur in practice. That is, the exhaust air-fuel ratio is set so as not to change within the determination prohibition period, no matter how fast it changes after the start of reforming injection.

  According to this configuration, even when the output of the exhaust gas sensor 52 is disturbed due to a disturbance such as noise during the determination prohibition period, the disturbance of the output can be ignored. For this reason, it is possible to reliably prevent erroneous determination due to disturbance at the timing when the reformed gas should not reach the combustion chamber. Further, after the elapse of the determination prohibition period, the determination operation can be reliably performed according to the output of the exhaust gas sensor 52. Therefore, according to the present embodiment, it is possible to obtain substantially the same operational effects as those of the first embodiment, and it is possible to improve the reliability against disturbances such as noise.

[Specific Processing for Realizing Embodiment 2]
FIG. 5 is a flowchart of a routine executed by the ECU 50 in order to realize the system operation of the present embodiment. The routine shown in FIG. 5 is started when the internal combustion engine is started, and is repeatedly executed at regular intervals.

  First, in steps 200 to 204, processing similar to that in steps 100 to 104 in the first embodiment is performed. Next, in step 206, the determination prohibition period is set to an appropriate length according to, for example, the operating state of the internal combustion engine, the exhaust gas flow rate, the pressure, the catalyst temperature, and the like. In step 208, as in the first embodiment, reforming injection is started when the conditions for executing reforming EGR control (whether the catalyst temperature is appropriate, etc.) are met. At this time, the ECU 50 starts a timer for measuring the determination prohibition period.

  Next, in step 210, it is determined whether or not the determination prohibition period has elapsed by referring to the timer. If "YES" is determined here, the process proceeds to step 212 in order to determine the air-fuel ratio. If “NO” is determined in the step 210, it is a timing at which it is not necessary to determine the air-fuel ratio yet, so that the process waits until the determination prohibition period elapses.

  In steps 212 to 216, processing similar to that in steps 108 to 112 in the first embodiment is performed, and the process ends. Thus, when the determination prohibition period has elapsed since the start of reforming injection, the determination of the exhaust air-fuel ratio can be started, and the injection amount of the main fuel can be reduced according to the determination result. .

Embodiment 3 FIG.
Next, Embodiment 3 of the present invention will be described with reference to FIGS. Since the present embodiment has the same system configuration (FIG. 1) as that of the first embodiment, description of the basic system configuration will be omitted.

[Characteristics of Embodiment 3]
In the present embodiment, when the reforming EGR control is stopped or the reforming injection amount is decreased, the main fuel injection amount is increased prior to this. In the following description, a case where the reforming injection is stopped will be described as an example.

  During the reforming EGR control, the injection amount of the main fuel is reduced by the amount that the reformed gas contributes to combustion. If the reforming injection is stopped in this state, the air-fuel mixture may become an excessive lean air-fuel ratio. Therefore, in the present embodiment, the main fuel is increased in advance, and the reforming injection is stopped simultaneously with the increase or after the increase is performed.

  FIG. 6 is a time chart when the reforming EGR control is stopped, and this time chart shows a temporal relationship between the EGR amount, the main fuel injection amount, the air-fuel ratio, and the reforming injection amount. As shown in this figure, when the reforming EGR control is stopped, the EGR amount is first reduced from the setting amount by the reforming EGR control to the setting amount by the normal EGR control. Here, normal EGR control is control in which only exhaust gas that does not contain reformed gas is recirculated to the intake system. The EGR amount by the reforming EGR control is set to be larger than that in the normal EGR control.

  After the EGR amount is returned to the normal state, the main fuel injection amount is increased. In this case, the increase level of the main fuel is calculated by the ECU 50 as an amount that can compensate for a decrease in the air-fuel ratio caused by, for example, stopping the reforming injection. When the injection amount of the main fuel is increased, this increase operation is reflected in the air-fuel ratio of the air-fuel mixture in a relatively short time, and the exhaust air-fuel ratio also changes to the rich side accordingly.

  At this time, the ECU 50 determines from the output of the exhaust gas sensor 52 whether or not the exhaust air-fuel ratio has changed to the rich side by increasing the injection amount of the main fuel. When the exhaust air-fuel ratio changes to the rich side, even if the reforming injection is stopped, the excessive lean air-fuel ratio is not reached, so the reforming injection is stopped.

  Thus, according to the present embodiment, even if the reformed gas is not recirculated to the intake system by stopping the reforming injection, the injection amount of the main fuel is increased in advance prior to this. be able to. That is, it is possible to switch the injection state of the main fuel at an appropriate timing in preparation for stopping the reforming injection. Thereby, when the reforming EGR control is stopped, it is possible to reliably prevent the air-fuel mixture from becoming an excessive lean air-fuel ratio. Therefore, the reforming EGR control can be smoothly stopped while the air-fuel ratio is stably maintained.

  Moreover, in the present embodiment, the reforming injection is stopped after the exhaust air-fuel ratio is changed to the rich side by increasing the main fuel. Thereby, it can be confirmed by the change in the exhaust air-fuel ratio that the increase in the main fuel is reflected in the combustion. Therefore, for example, when the increase in the main fuel is insufficient, it is possible to delay the stop of the reforming injection, and the timing of the stop of the injection can be reliably grasped.

  Next, a case where the reforming injection amount is reduced without stopping the reforming EGR control will be described. Also in this case, before reducing the reforming injection amount, the main fuel injection amount is increased in advance by that amount. Then, the reformed injection amount is decreased after the exhaust air-fuel ratio changes to the rich side by increasing the main fuel. Therefore, even when the reforming injection amount is reduced, the same effect as when the reforming injection is stopped can be obtained.

[Specific Processing for Realizing Embodiment 3]
FIG. 7 is a flowchart of a routine executed by the ECU 50 in order to realize the system operation of the present embodiment. Note that the routine shown in FIG. 7 is started when the internal combustion engine is started, and is repeatedly executed at regular intervals.

  First, in step 300, it is determined whether or not the reforming stop flag is ON. The reforming stop flag is set to an ON state during reforming EGR control when, for example, a reforming stop condition set according to the operating state of the internal combustion engine, the exhaust gas flow rate, the catalyst temperature, or the like is satisfied. Is.

  When it is determined “YES” in step 300, stop processing is performed in step 302 and subsequent steps in order to stop the reforming EGR control currently being executed. If “NO” is determined in the step 300, the processing ends as it is.

  Next, in step 302, the operating state (for example, intake air amount, load state, engine speed, etc.) of the internal combustion engine is detected by a sensor system. In step 304, the EGR amount is returned to the level at the time of normal EGR control by decreasing the opening degree of the flow rate adjusting valve 40 and reducing the EGR amount.

  In step 306, the injection amount of the main fuel is calculated according to, for example, the intake air amount, the accelerator opening, the cooling water temperature, and the like. This injection amount includes an increase amount for compensating for a decrease in the air-fuel ratio caused by stopping the reforming injection. In step 308, main fuel corresponding to the injection amount is injected from the fuel injection device 18 toward the combustion chamber. As a result, the injection amount of the main fuel increases as compared with the injection amount before starting the reforming injection stop process.

  Next, in step 310, it is determined using the output of the exhaust gas sensor 52 whether or not the exhaust air-fuel ratio has changed to the rich side. If “YES” is determined here, it is determined that the increase in the main fuel is reflected in the combustion, and the reforming injection is stopped in step 312. In step 312, the reforming injection amount does not necessarily have to be zero at a time. For example, the reforming injection amount may be reduced by a predetermined amount. In this case, the processing in steps 308 to 312 may be repeated until the reforming injection amount becomes zero.

  On the other hand, when it is determined “NO” in step 310, it is determined that the increase in the main fuel is not yet reflected in the combustion. Therefore, in this case, the process waits at step 310 until the exhaust air-fuel ratio changes to the rich side. Thus, according to the present embodiment, the reforming EGR control can be stopped in a state where the injection amount of the main fuel is increased, and at this time, the air-fuel ratio can be stabilized.

  In each of the above embodiments, steps 106 and 208 in FIGS. 3 and 5 show specific examples of the reformed fuel increasing means. Steps 108 and 212 show a specific example of the rich determination means in claim 1, and steps 110 and 214 show a specific example of the main fuel reduction means. Step 210 in FIG. 5 shows a specific example of determination prohibiting means. On the other hand, step 308 in FIG. 7 shows a specific example of the main fuel increasing means, and step 312 shows a specific example of the reformed fuel reducing means. Step 310 shows a specific example of the rich determination means in claim 4.

  In the third embodiment, the reforming injection is stopped or reduced when the air-fuel ratio changes to the rich side in step 310 in FIG. However, the present invention is not limited to this. For example, the present invention may be configured as a modification shown in FIG. In this modification, in step 310 ′, the reformed injection is stopped or reduced when the exhaust air-fuel ratio reaches the target value. This target value has a value corresponding to, for example, a rich air-fuel ratio, and is variably set according to the operating state of the internal combustion engine. According to this configuration, it is possible to appropriately change the determination condition of the air-fuel ratio according to the operating state and the like, and it is possible to improve the determination accuracy.

  In the present invention, the above-described target value may be used also in the first and second embodiments. That is, in steps 108 and 212 in FIGS. 3 and 5, the main fuel injection amount may be reduced when the exhaust air-fuel ratio reaches the target value. Thereby, the same effect as the said modification can be obtained.

  In the first and second embodiments, the control performed when the reforming EGR control is started has been described. In the third embodiment, the control performed when the reforming EGR control is stopped has been described. In this case, the present invention may be configured to combine the first and third embodiments, or may be configured to combine the second and third embodiments.

  In the embodiment, a mixed fuel of gasoline and ethanol is used as the reformed fuel. However, the present invention is not limited to this. For example, a mixed fuel of gasoline and other alcohols including methanol may be used as the reformed fuel.

  Moreover, the fuel applied to this invention should just be a fuel containing at least gasoline, and is not limited to the fuel containing alcohol. That is, the present invention can also be applied to a fuel composed only of gasoline, for example, and a fuel in which a material other than alcohol is mixed in gasoline.

  Furthermore, in the embodiment, the fuel reforming catalyst 28 is heated using the heat of the exhaust gas. However, the present invention does not necessarily use the heat of the exhaust gas, and may be applied to a non-exhaust heat recovery type internal combustion engine. That is, the present invention may be configured such that the fuel reforming catalyst 28 is heated by a heat source other than the exhaust gas (for example, a dedicated heating device).

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an overall view for explaining a system configuration according to a first embodiment of the present invention. 6 is a time chart showing a temporal relationship between a reforming injection amount, an air-fuel ratio, and a main fuel injection amount. It is a flowchart of the routine performed in Embodiment 1 of the present invention. In Embodiment 2 of this invention, it is a time chart which shows the temporal relationship of the reforming injection quantity, the air fuel ratio, and the injection quantity of the main fuel. It is a flowchart of the routine performed in Embodiment 2 of this invention. In Embodiment 3 of this invention, it is a time chart which shows the temporal relationship of the amount of EGR, the injection amount of the main fuel, the air fuel ratio, and the reforming injection amount. It is a flowchart of the routine performed in Embodiment 3 of the present invention. It is a flowchart of the routine performed in the modification of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Internal combustion engine 12 Intake pipe 14 Intake manifold 16 Throttle valve 18 Fuel injection apparatus (main fuel injection means)
20 Exhaust pipe 24 Heat exchanger 26 Reforming chamber 28 Fuel reforming catalyst 30 Exhaust passage 32 Branch pipe 34 Reformed fuel injection valve (reformed fuel supply means)
36 EGR passage (EGR means)
38 Cooler 40 Flow control valve (EGR means)
42 Exhaust purification catalyst 44 Fuel tank 46 Fuel piping 50 ECU
52 Exhaust gas sensor (air-fuel ratio detection means)
54 Fuel property sensor 56 Catalyst temperature sensor

Claims (4)

Main fuel injection means for injecting main fuel toward the combustion chamber of the internal combustion engine;
A fuel reforming catalyst that generates combustible gas from the reformed fuel when the reformed fuel is supplied;
Reformed fuel supply means for supplying reformed fuel to the fuel reforming catalyst;
EGR means for recirculating EGR gas, which is a mixed gas of the exhaust gas of the internal combustion engine and the combustible gas, to the intake system of the internal combustion engine;
Air-fuel ratio detecting means for detecting the air-fuel ratio of the exhaust gas;
Reformed fuel increasing means for starting or increasing the supply of reformed fuel by the reformed fuel supplying means according to the operating state of the internal combustion engine;
Rich determination means for determining whether or not the air-fuel ratio has changed to the rich side by the operation of the reformed fuel increasing means;
A main fuel reducing means for reducing the amount of main fuel injected by the main fuel injection means when the rich determination means determines that the air-fuel ratio has changed to the rich side;
A control device for an internal combustion engine, comprising:   2. The control device for an internal combustion engine according to claim 1, further comprising a determination prohibiting unit that prohibits the determination operation of the rich determination unit from the time when the reformed fuel increasing unit operates until the determination prohibition period elapses. . Main fuel injection means for injecting main fuel toward the combustion chamber of the internal combustion engine;
A fuel reforming catalyst that generates combustible gas from the reformed fuel when the reformed fuel is supplied; and
Reformed fuel supply means for supplying reformed fuel to the fuel reforming catalyst;
EGR means for recirculating EGR gas, which is a mixed gas of the exhaust gas of the internal combustion engine and the combustible gas, to the intake system of the internal combustion engine;
A main fuel increasing means for increasing an injection amount of the main fuel by the main fuel injection means when stopping or reducing the supply of the reformed fuel by the reformed fuel supply means;
Reformed fuel reducing means for stopping or reducing the supply of the reformed fuel by the reformed fuel supplying means at the time when the main fuel increasing means is operated or thereafter,
A control device for an internal combustion engine, comprising: Air-fuel ratio detecting means for detecting the air-fuel ratio of the exhaust gas;
Rich determination means for determining whether or not the air-fuel ratio has changed to the rich side by the operation of the main fuel increasing means,
The internal combustion engine control according to claim 3, wherein the reformed fuel reducing means is configured to stop or reduce the reformed fuel when the rich determining means determines that the air-fuel ratio has changed to the rich side. apparatus.

Images