JP4998221B2 - Control device for internal combustion engine - Google Patents

Description

  The present invention relates to an internal combustion engine in which a mixed fuel of gasoline and alcohol is preferably used, and more particularly to an internal combustion engine configured to add a combustible gas generated from fuel to an air-fuel mixture.

  2. Description of the Related Art Conventionally, as disclosed in, for example, Patent Document 1 (Japanese Patent Laid-Open No. 2006-132354), an internal combustion engine configured to reform a fuel into a combustible gas using heat of exhaust gas is known. A control apparatus for an internal combustion engine according to this type of prior art includes a fuel reforming catalyst that generates combustible gas from fuel by a steam reforming reaction or the like. The combustible gas generated by the fuel reforming catalyst is recirculated to the intake system of the internal combustion engine and contributes to combustion in the cylinder.

  In addition, the fuel reforming catalyst may be poisoned by sulfur due to adhesion of sulfur in the fuel during the reforming reaction. When sulfur poisoning occurs, the reforming reaction is hindered, and the amount of combustible gas produced decreases.

  For this reason, in the prior art, it is determined that sulfur poisoning has occurred when the amount (concentration) of combustible gas decreases below the allowable level. And at the time of this determination, it is set as the structure which performs a poisoning recovery process by supplying the fuel with a low sulfur concentration to a fuel reforming catalyst.

JP 2006-132354 A

  By the way, in the prior art mentioned above, it is set as the structure which determines sulfur poisoning by the fall of the production amount of combustible gas, and performs poisoning recovery processing. In this case, since it is considered that the degree of sulfur poisoning and the speed of progress vary depending on the sulfur concentration in the fuel, it is preferable to implement appropriate measures depending on the level of the sulfur concentration, if possible.

  However, at present, it is difficult to develop a small and inexpensive sulfur concentration sensor suitable for use in an internal combustion engine. Further, in the prior art, when the amount of combustible gas produced decreases, this is detected as a sulfur poisoning state. However, this state is a state in which sulfur poisoning of the catalyst has already progressed. For this reason, the internal combustion engine of the prior art has a problem that the sulfur concentration in the fuel cannot be easily detected before the sulfur poisoning of the fuel reforming catalyst proceeds.

  The present invention has been made to solve the above-described problems. The present invention can quickly detect the sulfur concentration in the fuel with a simple configuration without using a sulfur concentration sensor or the like. An object of the present invention is to provide a control device for an internal combustion engine.

1st invention is provided with the heating means, The fuel reforming catalyst which produces | generates combustible gas from reformed fuel with the heat of the said heating means,
Reformed fuel supply means for supplying fuel containing at least gasoline to the fuel reforming catalyst as the reformed fuel;
Reforming amount detecting means for detecting the amount of combustible gas generated from the reformed fuel;
A reduction rate calculation means for calculating a gas reduction rate that is a temporal reduction rate of the amount of combustible gas generated using the detection result of the reforming amount detection unit;
Sulfur concentration calculating means for calculating a sulfur concentration in the reformed fuel using at least the gas reduction rate;
It is characterized by providing.

  According to 2nd invention, the said sulfur concentration calculation means is set as the structure which calculates the said sulfur concentration as a high value, as the said gas reduction ratio becomes large.

  According to a third invention, the sulfur concentration calculating means calculates the sulfur concentration using the gas reduction ratio and other parameters, and the other parameters include gasoline and alcohol in the reformed fuel. At least one parameter of the mixing ratio, the temperature of the fuel reforming catalyst, the supply amount of the reformed fuel supplied to the fuel reforming catalyst, and the flow rate of the exhaust gas supplied to the fuel reforming catalyst It is set as the structure which is.

  According to the fourth invention, the sulfur concentration calculating means corrects the calculated value of the sulfur concentration to increase as the alcohol concentration in the reformed fuel and / or the temperature of the fuel reforming catalyst increases. The correction means is provided.

  According to a fifth aspect of the present invention, when the amount of combustible gas generated is detected by the reforming amount detection means, the amount of reformed fuel supplied to the fuel reforming catalyst and the exhaust supplied to the fuel reforming catalyst Reference state holding means for holding at least two parameters including the gas flow rate in a constant reference state is provided.

  According to a sixth aspect of the invention, the heating means is a heat exchanger that heats the fuel reforming catalyst with the heat of exhaust gas.

  According to the first aspect of the invention, when the fuel contains sulfur, the performance of the fuel reforming catalyst is lowered according to the duration of the reforming reaction. The production amount of gas) gradually decreases. At this time, the reduction ratio calculation means can calculate the gas reduction ratio by obtaining a temporal change in the reformed gas generation amount detected by the reforming amount detection means. Since there is a correlation between the gas reduction rate and the sulfur concentration in the fuel, the sulfur concentration calculation means can easily calculate the sulfur concentration according to the gas reduction rate.

  In this case, since the sulfur concentration calculating means obtains the sulfur concentration using the gas reduction rate, the sulfur concentration in the fuel should be calculated promptly at or near the time when the amount of hydrogen gas generated starts to decrease. Can do. For this reason, the sulfur concentration can be reliably detected before the production amount of hydrogen gas is greatly reduced by sulfur poisoning.

  Therefore, even when the sulfur concentration in the fuel is high, it is possible to take a quick and appropriate measure according to the sulfur concentration before the sulfur poisoning of the fuel reforming catalyst proceeds. Thereby, a catalyst can be protected from a sulfur content and reforming control can be performed smoothly. Moreover, since the sulfur concentration can be detected with a simple configuration, it is possible to avoid complication of the apparatus and an increase in cost due to the use of a concentration detection sensor or the like.

  According to the second aspect of the invention, the gas reduction rate increases as the sulfur concentration in the fuel increases, so that these relationships can be stored in advance as data. Then, the sulfur concentration calculation means can accurately calculate the sulfur concentration as a higher value as the gas reduction ratio increases by referring to this data.

  According to the third aspect, the sulfur concentration calculating means can calculate the sulfur concentration using not only the gas reduction rate but also other parameters. As a result, a required parameter change among the fuel mixing ratio, the catalyst temperature, the reformed fuel supply amount, and the exhaust gas flow rate supplied to the catalyst can be reflected in the calculated value of the sulfur concentration. Therefore, the error of the calculated value due to these changes can be reliably corrected, and the sulfur concentration can be obtained more accurately in an arbitrary control state.

  According to the fourth aspect of the invention, when the alcohol concentration in the fuel is high, the reforming reaction is accelerated by that amount, and the influence of the sulfur content is canceled out, so that the apparent sulfur concentration becomes lower than actual. Even when the temperature of the fuel reforming catalyst is high, the reforming reaction is promoted, so that the apparent sulfur concentration becomes low. In these cases, the correction means can correct the calculated value of the sulfur concentration to be high. Thereby, the change of alcohol concentration or catalyst temperature can be reflected in the calculated value of sulfur concentration.

  According to the fifth aspect of the invention, the reference state holding means holds the supply amount of the reformed fuel to the fuel reforming catalyst and the flow rate of the exhaust gas at a constant reference state when detecting the amount of combustible gas generated. can do. As a result, the reforming amount detection means can stably detect the amount of hydrogen gas produced under certain conditions, and can prevent detection errors due to variations in preconditions.

  According to the sixth aspect, the heat exchanger can heat the fuel reforming catalyst using the heat of the exhaust gas. As a result, an exhaust heat recovery type system can be configured, and a heating device and heating energy dedicated to the catalyst are not required, so that high operating efficiency can be realized.

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 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 including an electromagnetic valve or the like for injecting fuel is provided at each intake port of each 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 as a heating unit 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 generated by the reforming reaction is recirculated into the intake pipe 12 through the reformed gas passage 36 and mixed with the intake air. The reformed gas passage 36 is provided with a cooler 38 for cooling the reformed gas, and an electromagnetic flow rate adjusting valve 40 for adjusting the recirculation amount of the reformed gas to the intake pipe 12.

  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 the 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, a fuel property sensor 54, a catalyst temperature sensor 56, a reforming amount sensor 58 and the like is connected to the input side of the ECU 50.

  The exhaust gas sensor 52 is provided in the exhaust pipe 20 and outputs a detection signal corresponding to the oxygen concentration in the exhaust gas to the ECU 50. The fuel property sensor 54 is provided, for example, in the fuel pipe 46, and constitutes the mixing ratio detection means of the present embodiment. That is, the fuel property sensor 54 detects the mixing ratio of gasoline and alcohol in the fuel (hereinafter referred to as ethanol concentration 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 reforming amount sensor 58 constitutes the reforming amount detecting means of the present embodiment, and is provided in the reforming gas passage 36. The reforming amount sensor 58 is constituted by, for example, a hydrogen concentration sensor or the like, and detects the hydrogen concentration in the combustible gas (reformed gas) generated by the fuel reforming catalyst 28. The ECU 50 can detect the amount of reformed gas generated using the reformed gas concentration detected by the reforming amount sensor 58 and the reformed gas flow rate set by the flow rate adjusting valve 40.

  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 fuel injection amount is calculated according to the intake air amount and the like, and the fuel for the injection amount is injected from the fuel injection device 18. Further, by performing air-fuel ratio feedback control using the detection signal of the exhaust gas sensor 52, control is performed so that the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst 42 becomes substantially the stoichiometric air-fuel ratio.

(Reforming control)
Further, as described below, the ECU 50 performs reforming control for returning the reformed gas generated by the reforming reaction between the exhaust gas and the reformed fuel into the intake pipe 12. In the reforming control, the reformed fuel is injected from the reformed fuel injection valve 34 to the exhaust gas flowing through the branch pipe 32, and the mixed gas is 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, and the reformed fuel can be converted into substances having a larger amount of heat (H ₂ and CO).

  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 occur efficiently.

The reformed gas obtained by the above reforming reaction flows into the intake pipe 12 through the reformed gas passage 36 and is mixed with the intake air. At this time, the ECU 50 controls the flow rate of the reformed gas flowing into the intake pipe 12 by the flow rate adjustment valve 40. The reformed 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.

In addition, refluxing the reformed gas to the intake system also has an effect as EGR (Exhaust Gas Recirculation). In general, when the EGR rate is increased, combustion becomes unstable, so there is a limit to the EGR rate. On the other hand, in the system according to the present embodiment, the reformed gas that becomes the EGR gas contains H ₂ having high combustibility, so that the limit of the EGR rate can be increased. As a result, a large amount of reformed gas can be recirculated to the intake system, so that fuel efficiency and emission can be improved.

[Characteristics of Embodiment 1]
In the reforming control described above, when the reformed fuel contains a sulfur content, coking or the like is likely to occur in the fuel reforming catalyst 28, and the catalyst performance may be reduced due to sulfur poisoning. In order to avoid such a state of sulfur poisoning, in the present embodiment, the sulfur concentration in the reformed fuel is calculated, and the following measures are implemented according to the calculated value.

(Calculation of sulfur concentration)
When the fuel contains a sulfur content, the performance of the fuel reforming catalyst 28 is lowered according to the duration of the reforming reaction. As a result, the generation amount of the reformed gas gradually decreases from the time when the reforming control is started. In this case, since there is a correlation between the sulfur concentration in the fuel and the reduced state of the reformed gas, the sulfur concentration can be calculated according to the reduced state of the reformed gas.

  When calculating the sulfur concentration, first, a gas reduction rate ΔH that is an index of the state of reduction of the reformed gas is calculated. The gas reduction rate ΔH is an amount (ratio) in which the amount of reformed gas generated is reduced over a certain period of time. More specifically, the gas reduction rate ΔH is defined as the difference between the amount of reformed gas produced at a certain point in time and the amount of gas produced after a certain reference time Δt has passed. In the following description, the amount of hydrogen gas generated is used as an example of a numerical value representative of the amount of reformed gas generated.

  FIG. 2 shows how the amount of hydrogen gas produced gradually decreases due to the influence of sulfur contained in the fuel. FIG. 2 illustrates specific values ΔH ′ and ΔH ″ of the gas reduction ratio for each of the cases where the sulfur concentration is high and low. As can be seen from this figure, the sulfur concentration in the fuel is high. In this case, the gas reduction rate (specific value ΔH ″) is larger than the gas reduction rate (specific value ΔH ′) when the sulfur concentration is low.

  Therefore, it can be seen that the gas reduction rate ΔH increases as the sulfur concentration in the fuel increases. For this reason, if a specific relationship between the two is obtained through experiments or the like, reference data indicating the relationship between the gas reduction rate ΔH and the sulfur concentration can be obtained as shown by the solid line in FIG.

  This relationship of the reference data is established when other parameters that affect the calculation of the sulfur concentration are in a constant reference state. Examples of other parameters include the ethanol concentration in the fuel, the temperature of the fuel reforming catalyst 28 (catalyst temperature), the amount of reformed fuel supplied to the fuel reforming catalyst 28, and the reformed gas passage 36. For example, the flow rate of exhaust gas (EGR flow rate).

  The reference data is stored in advance in the storage circuit of the ECU 50. Therefore, when the reforming control is started, the ECU 50 calculates the hydrogen gas reduction rate ΔH using the detection result of the reforming amount sensor 58, and refers to the reference data in FIG. 3 according to the calculated value. Thus, the sulfur concentration in the reference state can be obtained.

  When calculating the sulfur concentration, among the above-described parameters, for example, the supply amount of reformed fuel and the flow rate of exhaust gas are maintained in the above-described reference state. These reference states are realized by maintaining the valve opening time (fuel injection time) of the reformed fuel injection valve 34 and the opening of the flow rate adjusting valve 40 at a predetermined magnitude. Regarding the ethanol concentration and the catalyst temperature, which are the remaining parameters, the calculated value of the sulfur concentration is corrected according to these values.

  Since ethanol has a higher reactivity to the reforming reaction than gasoline, when the ethanol concentration is high, the reforming reaction is accelerated accordingly. As a result, the influence of the sulfur content that reduces the production amount of hydrogen gas is canceled out by the presence of ethanol, so that the apparent sulfur concentration is calculated as a lower value than the actual value without considering the ethanol concentration. On the other hand, when the ethanol concentration is low, the apparent sulfur concentration becomes higher than actual.

  Therefore, in the present embodiment, correction is made so that the calculated value of the sulfur concentration increases as the ethanol concentration in the fuel increases. As an example of this correction, for example, when the ethanol concentration is higher than the above-described reference state, the reference data indicated by a solid line in FIG. 3 is corrected to data at a high ethanol concentration indicated by a virtual line.

  Even when the temperature of the fuel reforming catalyst 28 is high, the reforming reaction is promoted, so that the apparent sulfur concentration becomes low. On the other hand, when the temperature of the catalyst 28 is low, the apparent sulfur concentration increases. For this reason, in the present embodiment, correction is made so that the calculated value of the sulfur concentration increases as the temperature of the fuel reforming catalyst 28 increases. As shown in FIG. 3, the content of this correction is almost the same as the correction according to the ethanol concentration.

  As described above, according to the present embodiment, since the sulfur concentration is obtained using the gas reduction rate ΔH, the sulfur concentration in the fuel is set at or near the time when the production amount of hydrogen gas starts to decrease. It can be calculated quickly. For this reason, the sulfur concentration can be reliably detected before the production amount of hydrogen gas is greatly reduced by sulfur poisoning.

  Therefore, even when the sulfur concentration in the fuel is high, it is possible to implement a quick and appropriate measure according to the sulfur concentration before the sulfur poisoning of the catalyst 28 proceeds. Thereby, the fuel reforming catalyst 28 can be protected from the sulfur content, and reforming control can be performed smoothly. Moreover, since the sulfur concentration can be detected with a simple configuration, it is possible to avoid complication of the apparatus and an increase in cost due to the use of a concentration detection sensor or the like.

  Further, when calculating the sulfur concentration, while maintaining the injection amount of the reformed fuel and the EGR flow rate in the reference state, for example, using three parameters (gas reduction ratio ΔH, ethanol concentration, and catalyst temperature), a final value is obtained. The sulfur concentration is calculated. For this reason, even when the execution state of the reforming control changes, the sulfur concentration can be accurately and easily calculated according to the state of each parameter.

  Further, when the sulfur concentration is calculated, the amount of hydrogen gas produced can be stably detected under certain conditions by maintaining the reformed fuel injection amount and the EGR flow rate at the reference state. For this reason, it is possible to prevent detection errors due to variations in preconditions. In addition, changes in ethanol concentration and catalyst temperature can be reflected in the calculated value of sulfur concentration. Therefore, the error of the calculated value due to these changes can be reliably corrected, and the sulfur concentration can be obtained more accurately in an arbitrary control state.

(Measures according to sulfur concentration)
In the present embodiment, appropriate measures can be taken in accordance with the sulfur concentration in the fuel, as described below. First, when the temperature of the fuel reforming catalyst 28 is low, the reforming reaction does not occur smoothly. Therefore, when the temperature of the fuel reforming catalyst 28 is lower than the reforming lower limit temperature, the reformed fuel injection is stopped (reforming lower limit temperature control). Here, the reforming lower limit temperature is the lowest temperature necessary for the fuel reforming catalyst 28 to stably cause the reforming reaction.

  When the sulfur concentration in the fuel is high, coking or the like is likely to occur and the reforming reaction in the low temperature region becomes unstable. For this reason, in the reforming lower limit temperature control, the reforming lower limit temperature is set to a higher temperature as the calculated value of the sulfur concentration increases. Thus, in the present embodiment, the reforming control can be performed only in an appropriate temperature range corresponding to the sulfur concentration. For example, in the temperature range where the reforming reaction becomes unstable due to the influence of the sulfur content, the reforming can be performed. Quality control can be stopped.

  Further, the fuel reforming catalyst 28 is more likely to be deteriorated due to coking or the like as the fuel having a higher sulfur concentration is supplied in a larger amount. For this reason, in the present embodiment, as the sulfur concentration in the fuel becomes higher, a reduction correction for reducing the injection amount of the reformed fuel is performed (injection amount reduction control). According to this injection amount reduction control, when the sulfur concentration is high, the injection amount of the reformed fuel can be reduced by that amount, and a large amount of high sulfur concentration fuel is prevented from being supplied to the catalyst 28. can do.

  Furthermore, when the sulfur concentration in the fuel is extremely high, it is difficult to cope with it by changing the lower limit temperature or correcting the injection amount. For this reason, in the present embodiment, when the sulfur concentration S is higher than the predetermined upper limit determination value Sx, the reforming control is forcibly stopped and the subsequent reforming control is prohibited (reforming prohibiting control). According to this reforming prohibition control, the fuel reforming catalyst 28 can be protected from a high concentration of sulfur.

[Specific Processing for Realizing Embodiment 1]
4 and 5 are flowcharts of routines executed by the ECU 50 in order to realize the system operation of the present embodiment. Note that the routines shown in these drawings are started when the internal combustion engine is started, and are repeatedly executed at regular intervals.

  First, in step 100 in FIG. 4, the detection signal of the fuel property sensor 54 is read. In step 102, the ethanol concentration in the fuel is calculated using this detection signal. In step 104, for example, the basic injection amount of the reformed fuel is calculated according to 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. In step 106, fuel corresponding to the calculated value is injected from the reformed fuel injection valve 34.

  Next, in step 108, a sulfur concentration calculation process shown in FIG. 5 described later is executed to calculate a sulfur concentration S in the fuel. In step 110, it is determined whether the sulfur concentration S is equal to or less than an upper limit determination value Sx stored in the ECU 50 in advance. Here, when the determination is “YES”, the sulfur concentration S in the fuel is below the allowable limit, so the routine proceeds to step 112.

  In step 112, reformed fuel injection is executed, and thereafter, the process ends. In the reformed fuel injection, as described above, the reforming lower limit temperature control and the injection amount decrease control are executed according to the sulfur concentration in the fuel, and the reformed fuel is injected according to these control results.

  On the other hand, when it is determined as “NO” in step 110, the sulfur concentration S in the fuel exceeds the allowable limit. Therefore, in step 114, the reforming prohibition control is forcibly terminated by executing the above-described reforming prohibition control, and the reforming prohibition flag provided in the storage circuit of the ECU 50 is set to ON. When the reforming prohibition flag is set to ON, reforming control can be prohibited regardless of the operating state of the internal combustion engine 10, the temperature state of the catalyst 28, and the like.

  Next, the sulfur concentration calculation process will be described with reference to FIG. First, in step 120, as described above, the opening time of the reformed fuel injection valve 34 and the opening degree of the flow rate adjustment valve 40 are maintained at a predetermined size. As a result, the injection amount of the reformed fuel and the EGR flow rate are maintained at a constant reference state assuming the calculation of the sulfur concentration. Next, in step 122, the detection signal of the reforming amount sensor 58 is read, and in step 124, the amount of hydrogen gas generated is calculated using this detection signal.

  Then, in step 126, it is determined whether or not it is the time to start the measurement of the reference time Δt, and when it is determined “YES”, in step 128, the calculated value of the hydrogen gas generation amount is sent to the ECU 50 as the initial generation amount. Remember. If “NO” is determined in the step 126, the process proceeds to the step 130 without storing the calculated value.

  In step 130, it is determined whether or not the reference time Δt has elapsed since the first calculation of the hydrogen gas generation amount. Here, when it is determined as “YES”, since two hydrogen gas generation amounts separated by the reference time Δt are obtained, the process proceeds to step 132. If it is determined “NO” in step 130, steps 122 and 124 are repeated until the reference time Δt has elapsed.

  In step 132, the gas reduction rate ΔH is calculated by obtaining the difference between the two hydrogen gas generation amounts described above. In step 134, as described above, the sulfur concentration S in the basic state is estimated by referring to the map data of FIG. 3 using the gas reduction rate ΔH.

  In step 136, as described above, the sulfur concentration S is corrected according to the ethanol concentration obtained in step 102 and the temperature of the fuel reforming catalyst 28 detected by the catalyst temperature sensor 56, and then the process returns.

  In the above-described embodiment, steps 122 to 132 in FIG. 5 show a specific example of the reduction ratio calculation means. Step 134 shows a specific example of the sulfur concentration calculating means. Further, step 120 shows a specific example of the reference state holding means, and step 136 shows a specific example of the correction means.

  In the embodiment, among four parameters (ethanol concentration in fuel, catalyst temperature, reformed fuel injection amount, EGR flow rate) that affect the calculation of the sulfur concentration, the reformed fuel injection amount and the EGR flow rate are Was maintained in the reference state, and the calculated value of the sulfur concentration was corrected according to the ethanol concentration and the catalyst temperature.

  However, in the present invention, it is not always necessary to maintain the injection amount and the EGR flow rate in the reference state, and instead, for example, the calculated value of the sulfur concentration may be corrected by all four parameters. According to this configuration, when calculating the sulfur concentration, it is not necessary to switch the injection amount of the reformed fuel and the EGR flow rate from a normal state to a specific reference state. For this reason, the reforming control can be performed smoothly. Further, in the present invention, the calculated value of the sulfur concentration may be corrected by two parameters that are a combination different from the embodiment described above, or the calculated value of the sulfur concentration may be corrected by one or three parameters. Good.

  In the embodiment, a hydrogen concentration sensor is used as the reforming amount sensor 58, and the amount of reformed gas generated is obtained by detecting the hydrogen concentration in the reformed gas. However, the present invention is not limited to this, and it is also possible to use a carbon monoxide concentration sensor as a reforming amount detection means and detect the carbon monoxide concentration in the reformed gas to obtain the reformed gas generation amount. Good.

  Furthermore, 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.

  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. It is a characteristic diagram which shows the relationship between the production amount of hydrogen gas produced | generated by reforming reaction, and time. It is a characteristic diagram which shows the relationship between the gas reduction rate of hydrogen gas, and the sulfur concentration in a fuel. It is a flowchart of the routine performed in Embodiment 1 of the present invention. It is a flowchart which shows the sulfur concentration calculation process in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Internal combustion engine 12 Intake pipe 14 Intake manifold 16 Throttle valve 18 Fuel injection apparatus 20 Exhaust pipe 24 Heat exchanger (heating means)
26 Reforming chamber 28 Fuel reforming catalyst 30 Exhaust passage 32 Branch pipe 34 Reformed fuel injection valve (reformed fuel supply means)
36 reformed gas passage 38 cooler 40 flow rate adjusting valve 42 exhaust purification catalyst 44 fuel tank 46 fuel piping 50 ECU
52 Exhaust gas sensor 54 Fuel property sensor 56 Catalyst temperature sensor 58 Reforming amount sensor (reforming amount detecting means)
ΔH Gas reduction rate

Claims (6)

A fuel reforming catalyst comprising heating means, and generating a combustible gas from the reformed fuel by heat of the heating means;
Reformed fuel supply means for supplying fuel containing at least gasoline to the fuel reforming catalyst as the reformed fuel;
Reforming amount detecting means for detecting the amount of combustible gas generated from the reformed fuel;
A reduction rate calculation means for calculating a gas reduction rate, which is an amount by which the amount of combustible gas produced is reduced during a certain period of time, using the detection result of the reforming amount detection means;
Sulfur concentration calculating means for calculating a sulfur concentration in the reformed fuel using at least the gas reduction rate at a time before detecting that sulfur poisoning has occurred in the fuel reforming catalyst ;
A control device for an internal combustion engine, comprising:   The control device for an internal combustion engine according to claim 1, wherein the sulfur concentration calculation means is configured to calculate the sulfur concentration as a higher value as the gas reduction ratio increases.   The sulfur concentration calculation means is configured to calculate the sulfur concentration using the gas reduction ratio and other parameters, the other parameters being a mixing ratio of gasoline and alcohol in the reformed fuel, the fuel The temperature of the reforming catalyst, the supply amount of the reformed fuel supplied to the fuel reforming catalyst, and the flow rate of the exhaust gas supplied to the fuel reforming catalyst are at least one parameter. The control apparatus of the internal combustion engine described in 1.   The sulfur concentration calculating means includes a correcting means for correcting so that the calculated value of the sulfur concentration increases as the alcohol concentration in the reformed fuel and / or the temperature of the fuel reforming catalyst increases. The control device for an internal combustion engine according to any one of claims 1 to 3.   When the amount of combustible gas generated is detected by the reforming amount detection means, it comprises the amount of reformed fuel supplied to the fuel reforming catalyst and the flow rate of exhaust gas supplied to the fuel reforming catalyst. The control device for an internal combustion engine according to any one of claims 1 to 4, further comprising reference state holding means for holding at least two parameters in a constant reference state.   The control device for an internal combustion engine according to any one of claims 1 to 5, wherein the heating means is a heat exchanger that heats the fuel reforming catalyst by heat of exhaust gas.

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