JP5510237B2 - Control device for internal combustion engine - Google Patents

Description

  The present invention relates to a control device for an internal combustion engine equipped with an EGR system.

  In Patent Document 1, an EGR system that recirculates part of exhaust gas to an intake passage is improved, and a mixed gas obtained by adding a part of fuel to recirculated exhaust gas (EGR gas) is used for the heat of the exhaust gas. In addition, there is described a method in which an endothermic reforming reaction is performed by passing a reforming catalyst to reform the reformed gas containing hydrogen, and the reformed gas is recirculated to the intake passage. In this case, when knocking occurs, the recirculation amount of the reformed gas is increased in accordance with the retarded timing of the ignition timing to prevent deterioration of fuel consumption.

JP 2004-92520 A

  However, in the above-mentioned Patent Document 1, since it is necessary to provide an injection valve for supplying fuel to exhaust gas, a reforming catalyst for generating reformed gas, etc., the number of parts is increased and the system is complicated. This leads to an increase in weight and an increase in size. In addition, fuel consumption is deteriorated by the amount of fuel supplied to the exhaust gas.

  Therefore, in the present invention, hydrogen is generated using an exhaust purification catalyst such as a three-way catalyst, and this hydrogen is configured to be supplied to the intake passage along with the exhaust gas using the EGR system. The hydrogen supply amount can be adjusted by controlling the equivalent ratio of the air-fuel mixture supplied to.

  That is, the present invention is provided in an exhaust passage of an internal combustion engine, in which hydrogen is generated by a water gas shift reaction under a predetermined condition, and a part of the exhaust gas is sucked from an exhaust passage downstream of the catalyst through an EGR passage. An EGR system having an EGR system that recirculates to a passage and controls the EGR rate in accordance with an engine operating state. In an EGR region in which a part of the exhaust gas is recirculated to an intake passage, the EGR An equivalence ratio control means for controlling the equivalence ratio of the air-fuel mixture in the combustion chamber according to the EGR rate so as to optimize the amount of hydrogen supplied to the intake passage through the passage is characterized.

  According to the present invention, in the EGR region, a part of the hydrogen generated by the catalyst is supplied to the intake passage side together with a part of the exhaust gas through the EGR passage in the EGR system. By suppressing the self-ignition of the fuel, it is possible to suppress the occurrence of knocking, and since the combustion becomes faster due to the addition of hydrogen, the EGR rate (EGR amount) for slowing the combustion is increased, Fuel consumption can be improved.

  Particularly, since a part of hydrogen generated by the catalyst provided in the exhaust passage is supplied to the intake passage side through the EGR passage, the hydrogen supply amount to the intake passage side varies depending on the EGR rate. That is, the higher the EGR rate, the greater the amount of hydrogen supplied to the intake passage side through the EGR passage. Conversely, the lower the EGR rate, the smaller the hydrogen supply amount. However, in the present invention, the EGR rate is reduced. Accordingly, the amount of hydrogen supplied to the intake passage can be optimized by controlling the equivalence ratio of the air-fuel mixture.

The system block diagram which shows an example of the control apparatus of the internal combustion engine which concerns on this invention. The flowchart which shows the flow of control which concerns on one Example of this invention. The characteristic view which shows the setting map of an EGR rate. The characteristic view which shows the setting map of the equivalence ratio in a 1st driving | operation area | region. The characteristic view which shows the setting map of the equivalence ratio in a 2nd driving | operation area | region. Explanatory drawing which shows two setting examples (A) and (B) of the EGR rate and equivalence ratio according to a request torque. Explanatory drawing which similarly shows two setting examples (A) and (B) of the EGR rate and the equivalence ratio corresponding to the required torque. Explanatory drawing which similarly shows the example of a setting of the EGR rate and equivalence ratio according to a request torque. Explanatory drawing which similarly shows the example of a setting of the EGR rate and equivalence ratio according to a request torque. Explanatory drawing which similarly shows the example of a setting of the EGR rate and equivalence ratio according to a request torque.

  FIG. 1 schematically shows a system configuration of an internal combustion engine to which a control device according to an embodiment of the present invention is applied. The internal combustion engine 10 is a spark ignition internal combustion engine typified by a gasoline internal combustion engine in which a fuel / air mixture injected and supplied into the intake passage 11 or the cylinder by a fuel injection valve 31 is ignited by an ignition plug 32.

  A three-way catalyst 13 is provided in the exhaust passage 12 of the internal combustion engine 10. As is well known, this three-way catalyst 13 uses a noble metal such as platinum, palladium, rhodium, etc., and contains hydrocarbons (HC), carbon monoxide (CO), nitrogen oxides contained in the exhaust gas near the theoretical air-fuel ratio. It removes harmful components such as (NOx) simultaneously by reduction and oxidation.

  The internal combustion engine 10 is provided with a turbocharger 14 that supercharges intake air by exhaust energy. The turbocharger 14 is provided in the exhaust passage 12 and rotationally drives the rotor 15 by the energy of the exhaust gas. The turbocharger 14 is fixed to the rotor 15 back to back with the exhaust turbine 16, and the rotor 15 rotates as the rotor 15 rotates. And a compressor 17 for supercharging the intake air in the intake passage 11.

  Further, an EGR system 18 is provided that extracts a part of the exhaust gas from the exhaust passage 12 downstream of the three-way catalyst 13 and recirculates it to the intake passage 11. That is, in the EGR passage 19 connecting the exhaust passage 12 on the downstream side of the three-way catalyst 13 and the intake passage 11 on the upstream side of the compressor 17, the EGR rate of exhaust gas (exhaust gas flowing into the cylinder) depends on the engine operating state. An EGR valve 20 that adjusts the gas amount divided by the sum of the amount of air flowing into the cylinder and the amount of exhaust gas) and an EGR cooler 21 that cools high-temperature exhaust gas (EGR gas) are provided. . Further, an auxiliary catalyst 22 described later may be provided in the EGR passage 19.

  The intake passage 11 is provided with a throttle valve 23 for adjusting the amount of intake air, and an intake module 24 in which an air cooler 25 for cooling intake air and an intake collector 26 are integrated on the downstream side of the throttle valve 23 is an internal combustion engine. 10 is attached to the intake side.

  The control unit 30 stores and executes various controls, and the throttle valve 23 is based on signals representing the engine operating state detected by various sensors, that is, the accelerator opening, the engine speed, the engine temperature, and the like. In addition to the EGR valve 20, a control signal is output to the fuel injection valve 31 that injects and supplies fuel into the intake passage 11 or the cylinder, the spark plug 32 provided in the combustion chamber, etc., and the throttle opening, EGR rate, fuel The injection timing, fuel injection amount, ignition timing, etc. are controlled.

  Here, in the above-described three-way catalyst 13, the air-fuel ratio of the exhaust gas supplied to the three-way catalyst 13 in a low temperature range (for example, 250 to 700 ° C.) where the catalyst temperature is lower than the specified temperature. Is made richer than the stoichiometric air-fuel ratio, so that carbon monoxide (CO) is supplied to the three-way catalyst 13 and the water gas shift reaction (to the hydrogen generation side) with the water (H 2 O) remaining on the catalyst ( CO + H2O → CO2 + H2) is generated, and hydrogen (H2) is generated. In the temperature range on the high temperature side exceeding 700 ° C., the reaction (CO + H 2 O ← CO 2 + H 2) is opposite to that on the hydrogen generation side, but in a general internal combustion engine, this temperature is in the high temperature range. There is nothing.

  In this embodiment, in the EGR region in which the EGR valve 20 is opened and a part of the exhaust gas is recirculated to the intake passage 11, hydrogen is generated by the three-way catalyst 13 by the water gas shift reaction. The exhaust gas is supplied to the intake passage 11 side through the EGR passage 19. Then, the equivalence ratio of the air-fuel mixture (the stoichiometric air-fuel ratio is divided by the air-fuel ratio of the air-fuel mixture) based on the EGR rate so that the hydrogen supply amount to the intake passage 11 side is appropriate according to the engine operating state. Value), specifically, the amount of hydrogen produced by the three-way catalyst 13 is adjusted by controlling the fuel injection amount (equivalent ratio control means).

  In this way, by supplying an appropriate amount of hydrogen together with the exhaust gas to the intake passage 11 side, self-ignition can be suppressed and occurrence of knocking can be suppressed. For this reason, for example, the retard of the ignition timing for avoiding the occurrence of knocking can be suppressed, and the fuel consumption can be improved. In addition, as the EGR rate increases, combustion slows down and the combustion stability decreases. However, by adding hydrogen, the combustion becomes faster, and the EGR rate (EGR) while ensuring the combustion stability. Amount) can be increased.

  FIG. 2 is a flowchart showing the flow of control according to the present embodiment, and this routine is stored and executed by the control unit 30 described above. In step S11, the engine operating state detected by various sensors, that is, the accelerator opening degree of the accelerator pedal operated by the driver, the engine speed, the catalyst temperature of the three-way catalyst 13, and the like are read. The catalyst temperature may be detected directly by providing a sensor, or may be estimated from the engine water temperature or the engine operating state.

  In step S12, the EGR rate is set based on the engine speed Ne and the engine required torque (load) Te with reference to a preset EGR rate setting map as shown in FIG. 3, for example. As shown in FIG. 3, in this embodiment, the region on the high load side corresponding to the supercharging region is an EGR region R0 in which the EGR rate is made larger than 0 and EGR gas is recirculated to the intake passage. Thus, by performing EGR in the supercharging region on the high load side, NOx emission is suppressed, an increase in exhaust temperature due to supercharging is suppressed, deterioration of the three-way catalyst 13 etc. is prevented, and exhaust temperature Fuel consumption can be improved by suppressing fuel increase for suppression. In the low to medium load range, for example, a known variable valve device is used to control the opening and closing timing of the intake valve and exhaust valve, thereby providing so-called internal EGR that returns exhaust gas discharged from the cylinder into the cylinder. Like to do.

  In step S <b> 13, as described above, it is determined whether or not it is an operation region in which hydrogen generated by the three-way catalyst 13 is supplied to the intake passage 11 via the EGR passage 19. Specifically, it is determined whether it is the EGR region R0 in the supercharging region.

  If it is not a hydrogen supply region, that is, a low / medium load region that is not the EGR region R0, the process proceeds to step S14, and the equivalence ratio of the air-fuel mixture supplied into the cylinder without considering hydrogen addition (the stoichiometric air-fuel ratio is supplied). Set the value divided by the air-fuel ratio of the mixture. In this embodiment, in order to obtain the desired exhaust purification performance by the three-way catalyst 13, the equivalent ratio in the low / medium load range is set to “1” corresponding to the stoichiometric air-fuel ratio. However, the equivalence ratio may be changed / adjusted according to the engine rotation speed, the engine required torque, and the like.

  If it is determined in step S13 that the region is a hydrogen supply region, that is, the EGR region R0, the process proceeds to step S15, and in the EGR region R0, the first operation region R1 on the high load side where the occurrence of knocking may occur. Alternatively, it is determined whether the second operating region R2 is on the lower load side than the first operating region R1.

  When it determines with it being 1st driving | running area | region R1 of the high load side, it progresses to step S16, and with reference to the setting map for 1st driving | running area R1 shown in FIG. 4 preset, an EGR rate (EGR ratio) Equivalence ratio is set based on the catalyst temperature (Temperature). In the first operating region R1 on the high load side, it is desirable to supply a certain amount of hydrogen suitable for combustion into the cylinder so as to suppress the occurrence of knocking. Here, when the EGR rate increases, the amount of hydrogen supplied to the intake passage 11 through the EGR passage 19 increases with respect to the amount of hydrogen produced by the three-way catalyst 13, and conversely, the EGR rate When the engine speed becomes lower, the amount of hydrogen supplied to the intake passage 11 through the EGR passage 19 also decreases with respect to the amount of hydrogen produced by the three-way catalyst 13. Therefore, as shown in FIG. 4, the equivalence ratio is increased as the EGR rate is increased so that a constant amount of hydrogen is supplied regardless of the EGR rate, that is, the air-fuel ratio is increased to the rich side, and the EGR rate is decreased. The equivalent ratio is made smaller, that is, the richness of the air-fuel ratio is made smaller.

  Further, the amount of hydrogen produced by the three-way catalyst 13 by the water gas shift reaction described above tends to increase as the catalyst temperature decreases and decrease as the catalyst temperature increases. Therefore, the equivalence ratio is increased to the rich side as the catalyst temperature is increased so that the hydrogen supply amount is constant, and the equivalence ratio is decreased as the catalyst temperature is decreased.

  On the other hand, if it is determined in step S15 that the second operating region R2 is on the lower load side than the first operating region R1 in the EGR region R0 instead of the first operating region R1, the process proceeds to step S17. The equivalence ratio (Equivalence ratio) is set based on the EGR rate (EGR ratio) and the catalyst temperature (Temperature) with reference to the setting map for the second operation region R2 shown in FIG. In the first operation region R1 described above, in order to suppress the occurrence of knocking, a fixed amount of hydrogen is supplied mainly for the purpose of suppressing self-ignition by hydrogen addition. However, in this second operation region R2, Is less likely to cause knocking, and therefore aims to increase the EGR rate by improving the combustion rate by hydrogenation. That is, as shown in FIG. 5, the EGR rate is increased by increasing the hydrogen supply amount. As a result, the higher the EGR rate, the larger the equivalent ratio, and the lower the EGR rate, the smaller the equivalent ratio. It is set. Further, as in the case of the first operation region R1, the equivalence ratio is increased as the catalyst temperature is increased, and the equivalence ratio is decreased as the catalyst temperature is decreased so as to suppress the increase and decrease of the hydrogen supply amount due to the catalyst temperature. Yes.

  In step S18, the throttle opening, the opening of the EGR valve 20, the ignition timing, and the like, based on the equivalence ratio set in step S14, S16 or S17, the EGR rate set in step S12, and the like. The fuel injection amount is set. Specifically, the EGR opening is set according to the EGR rate, and the fuel injection amount is set according to the equivalence ratio. The fuel injection amount increases as the equivalence ratio increases, and the fuel injection increases as the equivalence ratio decreases. The amount is decreasing.

  Next, FIGS. 6 to 10 show setting examples of the EGR rate (EGR ratio) and the equivalence ratio (Φ) according to the engine required torque (load) Te. In the setting example of FIG. 6A, the required torque Te is set to a predetermined EGR rate in the EGR region where the required torque Te is equal to or greater than the first predetermined value Te1, and the equivalence ratio is set to a richer side than 1 according to the EGR rate. It is set large.

  On the other hand, in the setting example of FIG. 6B, when the required torque Te is in the EGR region equal to or greater than the first predetermined value Te1, the predetermined EGR rate is set as in the setting example of FIG. However, with regard to the equivalence ratio, in order to suppress the occurrence of knocking only in the high load side region where the required torque is higher than the first predetermined value Te1 and higher than the second predetermined value Te2 in the EGR region, the equivalent ratio Φ Is increased to the rich side to perform hydrogenation. That is, in the low load side region (Te1 to Te2) where the required torque is relatively low in the EGR region, the equivalence ratio Φ is set to “1” corresponding to the stoichiometric air-fuel ratio so as not to deteriorate fuel consumption and exhaust. keeping.

  FIG. 7 shows an example in which the EGR rate is changed according to the required torque Te. In the setting example of FIG. 7A, the torque is secured in the high load side region where the required torque is equal to or greater than the second predetermined value Te2, as compared to the low load side region where the required torque is less than the second predetermined value Te2. Therefore, the EGR rate is reduced and the equivalent ratio Φ is increased so as to suppress the occurrence of knocking.

  In the setting example in FIG. 7B, the setting of the equivalence ratio Φ is changed with respect to the setting example in FIG. That is, until the required torque reaches a third predetermined value Te3 that is higher than the second predetermined value Te2, the equivalence ratio Φ is maintained at “1” to suppress deterioration of fuel consumption and exhaust, and the required torque is the third predetermined value. Only in the region on the higher load side that exceeds Te3, hydrogen supply is performed with an equivalent ratio larger than 1 so as to suppress the occurrence of knocking.

  In the setting example of FIG. 8, among the EGR regions where the required torque Te is equal to or greater than the first predetermined value Te1, in the high load side region where the required torque is equal to or greater than the second predetermined value Te2, a predetermined EGR rate is given. In order to suppress the occurrence of knocking, the equivalence ratio Φ is set to be larger than 1 so as to obtain a constant amount of hydrogen supply. On the other hand, in the EGR region, the low load side region where the required torque is less than the second predetermined value Te2 is less likely to cause knocking and the combustion is stable compared to the high load side region. In order to increase the equivalent ratio Φ, the hydrogen addition amount is increased. As a result, the EGR rate in the low load region can be increased, and fuel consumption can be improved.

  FIG. 9 shows an example of setting in a transition period in which a transition is made from the non-EGR region to the EGR region as in acceleration. In such a transition period, at the time of switching so that the EGR gas rapidly increases at the time t1 when switching to the EGR region, the combustion stability does not deteriorate or the torque changes suddenly and does not impair the operability. The EGR rate is gradually increased from t1. On the other hand, with respect to the equivalence ratio, the equivalence ratio is increased to the rich side stepwise at the switching time t1 to the EGR region so that knocking does not occur immediately after the switching to the EGR region, and the intake passage side Hydrogen is supplied promptly.

  FIG. 10 shows an example of setting in a transition period in which a transition is made from a low load side region with a high EGR rate to a high load side region with a low EGR rate in the EGR region. Also in this case, the EGR rate is gradually decreased from the switching time t2 so as not to cause a decrease in drivability due to a sudden change in torque, and the equivalent ratio is knocked immediately after the switching time t2. The equivalence ratio is increased stepwise to the rich side so that hydrogen is quickly supplied to the intake passage side.

  Although the present invention has been described based on the illustrated embodiments as described above, the present invention is not limited to the above-described embodiments, and includes various modifications and changes. For example, in the above embodiment, the present invention is applied to an internal combustion engine provided with a turbocharger. However, the present invention can also be applied to a naturally aspirated internal combustion engine not provided with a turbocharger.

  Further, as shown in FIG. 1, an auxiliary catalyst 22 that is separate from the exhaust purification three-way catalyst 13 may be provided in the EGR passage 19 or the exhaust passage 12 downstream of the three-way catalyst 13. Similar to the above three-way catalyst 13, the auxiliary catalyst 22 generates hydrogen by a water gas shift reaction under a predetermined condition. Since the auxiliary catalyst 22 is provided on the downstream side farther from the cylinder than the three-way catalyst 13, the catalyst temperature is lower than that of the three-way catalyst 13, so that hydrogen is generated by the water gas shift reaction. It is easy to be done, the increase of the equivalent ratio for ensuring the hydrogen supply amount can be suppressed, and the deterioration of fuel consumption and exhaust can be suppressed. In addition, when the auxiliary catalyst 22 is provided in the EGR passage 19 as shown in FIG. 1, since the entire amount of generated hydrogen is supplied to the intake passage 11 side, it is easier to secure the hydrogen supply amount. Become.

DESCRIPTION OF SYMBOLS 10 ... Internal combustion engine 11 ... Intake passage 12 ... Exhaust passage 13 ... Three-way catalyst 14 ... Turbocharger 18 ... EGR system 20 ... EGR valve 22 ... Auxiliary catalyst 30 ... Control part

Claims (6)

A catalyst that is provided in an exhaust passage of an internal combustion engine and generates hydrogen by a water gas shift reaction under a predetermined condition;
An EGR system that recirculates part of the exhaust gas from the exhaust passage downstream of the catalyst to the intake passage through the EGR passage, and controls the EGR rate according to the engine operating state;
In a control device for an internal combustion engine having
In the EGR region where a part of the exhaust gas is recirculated to the intake passage, the equivalent amount of the air-fuel mixture in the combustion chamber according to the EGR rate so as to optimize the amount of hydrogen supplied to the intake passage through the EGR passage. A control apparatus for an internal combustion engine, comprising equivalence ratio control means for controlling the ratio.   The control apparatus for an internal combustion engine according to claim 1, wherein the equivalence ratio control means increases the equivalence ratio as the catalyst temperature increases.   The equivalence ratio control means increases the equivalence ratio as the EGR rate decreases so as to keep the hydrogen supply amount constant in a predetermined first engine operation region in the EGR region. Item 3. The control device for an internal combustion engine according to Item 1 or 2.   The equivalence ratio control means increases the equivalence ratio so as to increase the EGR rate in a predetermined second engine operation region in the EGR region. The internal combustion engine control device described.   An auxiliary catalyst separate from the catalyst is provided in the exhaust passage or the EGR passage downstream of the catalyst, and the auxiliary catalyst is such that hydrogen is generated by a water gas shift reaction under a predetermined condition. The control device for an internal combustion engine according to claim 1, wherein the control device is an internal combustion engine. It has a turbocharger that supercharges intake air by exhaust energy,
The supercharging region on the high load side is an EGR region, and in this EGR region, the equivalence ratio is controlled to the rich side by the equivalence ratio control means, and hydrogen is supplied to the intake passage through the EGR passage. Item 6. The control device for an internal combustion engine according to any one of Items 1 to 5.

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