JP2019002380A - Internal Combustion Engine System - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an internal combustion engine system capable of reducing the NOx emission amount without using a special configuration even when the NOx reduction catalyst becomes high temperature by high load operation. An internal combustion engine system includes an engine, a three-way catalyst and a NOx reduction catalyst, a catalyst outlet concentration acquisition unit that acquires a catalyst outlet NOx concentration at an outlet of the NOx reduction catalyst, and an exhaust gas at an outlet of the NOx reduction catalyst. Temperature acquisition means for acquiring the temperature or a catalyst-related temperature which is the catalyst temperature thereof, an injection control section for controlling the fuel injection amount in the engine, an engine outlet concentration acquisition means for measuring or estimating the engine outlet NOx concentration, and a catalyst outlet NOx. Combustion switching that switches the combustion mode of the engine between the lean combustion mode and the stoichiometric combustion mode based on the NOx purification rate calculated from the concentration and the NOx concentration at the engine outlet, the catalyst-related temperature, the engine speed, and the fuel injection amount. And a control unit. [Selection diagram] Figure 1

Description

  The present invention relates to an internal combustion engine system, and more particularly to an internal combustion engine system including a three-way catalyst and a NOx reduction catalyst as exhaust gas purification catalysts.

  Conventionally, Patent Document 1 describes a compression ignition engine including a three-way catalytic converter for reducing harmful exhaust gas. In this compression ignition engine, in the first mode with low engine load, the engine is operated at a high exhaust gas recirculation (EGR) rate in normal diesel combustion conditions to reduce NOx emissions. Also, in the second mode with medium to high engine load, the engine is operated in a stoichiometric state that can reduce NOx emissions using a three-way catalytic converter. Also, in a third mode with very high engine load and / or engine speed, the engine is operated at normal diesel combustion conditions and low EGR rates to obtain maximum torque.

  Patent Document 2 describes a diesel engine in which a three-way catalyst, an HC trap catalyst, and a NOx trap catalyst (NSR) are sequentially arranged in an exhaust passage in order to reduce HC and NOx during cold weather. . This diesel engine includes an HC trap catalyst and a NOx trap catalyst temperature sensor and an exhaust air-fuel ratio sensor. In this diesel engine, after the cold start, first, rich operation in which the exhaust air-fuel ratio becomes rich is performed to reduce NOx and activate the catalyst early. HC at this time is trapped by the HC trap catalyst. When the catalyst temperature is such that HC is desorbed from the HC trap catalyst and can be purified, the rich operation is terminated. If the NOx trap catalyst does not reach a temperature at which NOx can be trapped, the stoichiometric operation is performed. If the temperature reaches a temperature at which NOx can be trapped, a lean operation is performed to promote NOx desorption purification.

JP 2012-197794 A JP 2004-285832 A

  In the technique of the above-mentioned Patent Document 1, an expensive NOx reduction catalyst is abolished and NOx purification is performed by stoichiometric combustion and a three-way catalyst. However, since normal lean combustion is performed in the third mode at high load, There is a problem that the amount of NOx emissions in lean combustion increases.

  Further, in the technique of Patent Document 2, since the NOx trap catalyst is not activated when it is cold, the NOx occlusion activity is increased if the NOx trap catalyst is heated to a certain extent by performing stoichiometric combustion and purifying NOx with a three-way catalyst. Therefore, after that, lean combustion is performed and NOx is occluded / reduced by the NOx trap catalyst. However, this technique does not take into consideration that the NOx emission amount increases due to the deterioration of the NOx purification characteristics when the diesel engine is operated at a high load and the NOx trap catalyst becomes high temperature.

  An object of the present invention is to provide an internal combustion engine system capable of reducing the NOx emission amount without using a special configuration even when the NOx reduction catalyst becomes high temperature due to high load operation.

  A first internal combustion engine system according to the present invention includes an engine, a three-way catalyst for purifying exhaust gas exhausted from the engine, a NOx reduction catalyst, and a catalyst for obtaining a catalyst outlet NOx concentration at an outlet of the NOx reduction catalyst. An outlet concentration acquisition means, a temperature acquisition means for acquiring an exhaust temperature at the outlet of the NOx reduction catalyst, or a catalyst-related temperature that is a catalyst temperature of the NOx reduction catalyst, and a rotation speed acquisition for acquiring the engine speed of the engine Means, an injection control unit for controlling the number, amount and timing of fuel injection in the engine, an engine outlet concentration acquisition means for measuring or estimating an engine outlet NOx concentration for NOx discharged from the engine, and the catalyst outlet The catalyst outlet NOx concentration acquired by the concentration acquisition means and the engine outlet concentration acquisition means acquired by the concentration acquisition means. Obtained from the NOx purification rate calculated from the engine outlet NOx concentration, the catalyst-related temperature obtained by the temperature obtaining means, the engine speed obtained by the rotational speed obtaining means, and the injection control unit And a combustion switching control unit that switches a combustion mode of the engine between a lean combustion mode and a stoichiometric combustion mode based on the fuel injection amount.

  Further, the second internal combustion engine system according to the present invention acquires the engine, a three-way catalyst for purifying exhaust gas exhausted from the engine, a NOx reduction catalyst, and a catalyst outlet NOx concentration at the outlet of the NOx reduction catalyst. A catalyst outlet concentration acquisition means, a time measurement unit that measures the operation time and operation stop time of the engine, an operation history storage unit that receives a signal from the time measurement unit and stores the operation history of the engine, Measure or estimate the engine speed NOx concentration for NOx discharged from the engine, and an engine speed control means for controlling the engine speed of the engine, an injection control unit for controlling the number, amount and timing of fuel injection in the engine Engine outlet concentration acquisition means, the catalyst outlet NOx concentration acquired by the catalyst outlet concentration acquisition means, and the catalyst outlet concentration acquisition means NOx purification rate calculated from the engine outlet NOx concentration acquired by the engine outlet concentration acquisition means, a signal representing the operation history of the engine acquired from the operation history storage unit, and the rotation speed acquisition means A combustion switching control unit that switches a combustion mode of the engine between a lean combustion mode and a stoichiometric combustion mode based on the engine speed and a fuel injection amount acquired from the injection control unit;

  According to the internal combustion engine system of the present invention, when it is determined that the temperature of the NOx reduction catalyst is high and the NOx purification rate by the portion including the NOx reduction catalyst becomes low, the engine combustion mode is changed from the lean combustion mode. By switching to the stoichiometric combustion mode, NOx purification by a three-way catalyst becomes possible. Therefore, even when the NOx reduction catalyst becomes high temperature due to high load operation of the engine and the NOx purification rate decreases, the NOx emission amount can be reduced. Moreover, it is not necessary to use a special configuration that requires a complicated and excessive cost as the exhaust gas aftertreatment system.

1 is a diagram schematically showing an overall configuration of an internal combustion engine system according to a first embodiment of the present invention. 2 is a flowchart showing a process executed in the combustion switching control device of the internal combustion engine system shown in FIG. 1. It is a graph which illustrates the map which shows an EGR rate. (A) is the temperature of the NOx reduction catalyst (SCR), (b) is the NOx purification rate in the SCR, (c) is the change in the air-fuel ratio by switching the combustion mode, (d) is the NOx of the three-way catalyst and the NOx reduction catalyst. The amount of purification, (e), is a graph showing the NOx value at the outlet of the NOx reduction catalyst. It is a figure which shows roughly the whole structure of the internal combustion engine system of 2nd Embodiment. 6 is a flowchart showing processing executed in the combustion switching control device of the internal combustion engine system shown in FIG. 5. (A) is an actual measurement value of the SCR temperature, (b) is an estimated value of the SCR temperature, and (c) is a graph showing changes in the NOx purification rate of the three-way catalyst and the SCR as a whole.

  Embodiments according to the present invention will be described below in detail with reference to the accompanying drawings. In this description, specific shapes, materials, numerical values, directions, and the like are examples for facilitating the understanding of the present invention, and can be appropriately changed according to the application, purpose, specification, and the like. In addition, when a plurality of embodiments and modifications are included in the following, it is assumed from the beginning that these characteristic portions are used in appropriate combinations.

  In the following, a case where the engine is a compression ignition type diesel engine will be described. However, the present invention is not limited to this, and the present invention may be applied to an internal combustion engine including a spark ignition type gasoline engine.

<First Embodiment>
FIG. 1 is a diagram schematically showing an overall configuration of an internal combustion engine system 10 according to a first embodiment of the present invention. The internal combustion engine system 10 includes an engine 12, a combustion switching control device (combustion switching control unit) 11, a fuel injection device 16, and an injection control device (injection control unit) 18. In the present embodiment, the engine 12 is a compression ignition type diesel engine and includes, for example, four cylinders 14. Each cylinder 14 is provided with a fuel injection device 16. In each fuel injection device 16, the number, amount, and timing of fuel injection are controlled by an injection control device 18 that has received a signal from the combustion switching control device 11.

  The internal combustion engine system 10 further includes a rotation speed sensor (rotation speed acquisition means) 20 attached to the engine 12. The rotation speed sensor 20 has a function of acquiring the rotation speed of the crankshaft connected to the piston in each cylinder of the engine 12 as the engine rotation speed Ne. The engine rotational speed Ne acquired by the rotational speed sensor 20 is transmitted to the combustion switching control device 11 for combustion mode switching in the engine 12 or the like.

  The internal combustion engine system 10 further includes an intake system 21, an exhaust system 30, an exhaust gas recirculation device 50, and a turbocharger (supercharger) 60.

  The intake system 21 is an air passage for supplying air to the engine 12. The direction of air intake in the intake system 21 is indicated by an arrow A. The intake system 21 includes a first intake passage 22 and a second intake passage 24. One end of the first intake passage 22 is opened to the atmosphere via a filter or the like (not shown), and the other end is connected to the compressor chamber 62 of the turbocharger 60. The second intake passage 24 has one end connected to the compressor chamber 62 and the other end connected to the intake port of the engine 12. An intake throttle valve 26 is provided in the second intake passage 24. The intake throttle valve 26 is preferably configured by, for example, an electromagnetic on-off valve. In the present embodiment, the intake throttle valve 26 is installed in the vicinity of the compressor chamber 62 of the turbocharger 60.

  The intake throttle valve 26 is an air amount adjusting device that adjusts the amount of air taken into the engine 12. The intake throttle valve 26 is adjusted in opening by receiving a signal from the intake / exhaust control device 28. The intake / exhaust control device 28 transmits / receives a signal to / from the combustion switching control device 11. The intake / exhaust control device 28 receives a command signal from the combustion switching control device 11 and transmits an opening degree signal to the intake throttle valve 26. In addition, the intake / exhaust control device 28 transmits a signal indicating the opening state of the intake throttle valve 26 to the combustion switching control device 11. The intake throttle valve 26 may constitute a part of a supercharging pressure adjusting device that adjusts the supercharging pressure by the turbocharger 60.

  The exhaust system 30 is an exhaust gas passage for exhausting exhaust gas exhausted from the engine 12 to the outside. The exhaust system 30 includes a first exhaust passage 32, a second exhaust passage 34, and a turbine bypass passage 36. The first exhaust passage 32 has one end connected to the exhaust port of the engine 12 and the other end connected to the turbine chamber 64 of the turbocharger 60. The second exhaust passage 34 has one end connected to the turbine chamber 64 and the other end open to the atmosphere via a muffler (or a silencer) not shown.

  A three-way catalyst 38 and a NOx reduction catalyst 40 are provided in the second exhaust passage 34. While the exhaust gas passes through the three-way catalyst 38 and the NOx reduction catalyst 40, HC (hydrocarbon), CO (carbon monoxide), NOx (nitrogen oxide), etc. are removed and purified from the exhaust gas to the atmosphere. Discharged. In the present embodiment, a catalyst (for example, an HC trap catalyst or a particulate filter (DPF)) is not provided in addition to the three-way catalyst 38 and the NOx reduction catalyst 40, but may be provided.

  The three-way catalyst 38 has a function of removing and purifying HC, CO, NOx contained in the exhaust gas by oxidation / reduction action, and the purification efficiency becomes high when the air-fuel ratio is stoichiometric, even at high temperatures. The purification efficiency can be maintained relatively high. On the other hand, the NOx reduction catalyst 40 mainly has a function of removing and purifying NOx in the exhaust gas by a reducing action, and its purification efficiency is very high even during the lean operation, but tends to be slightly lowered at a high temperature.

  In the present embodiment, the NOx reduction catalyst 40 is a selective reduction catalyst (SCR). By using a selective reduction catalyst as the NOx reduction catalyst 40, the catalyst can be configured at a low cost, unlike the configuration using an occlusion reduction catalyst (NSR).

  In the second exhaust passage 34, an exhaust temperature sensor (temperature acquisition means) 80 and a NOx sensor (catalyst outlet concentration acquisition) are located in the vicinity of the outlet of the NOx reduction catalyst 40 in the pipe downstream of the NOx reduction catalyst 40 in the exhaust gas discharge direction. Means) 81 is arranged. The exhaust temperature sensor 80 acquires the exhaust temperature (catalyst related temperature) at the outlet of the NOx reduction catalyst 40 by directly detecting the exhaust temperature in the vicinity of the outlet of the NOx reduction catalyst 40. The exhaust temperature sensor 80 is disposed in the vicinity of the outlet of the NOx reduction catalyst 40 so that the exhaust temperature at the mounting position can be regarded as the same as the exhaust temperature at the outlet of the NOx reduction catalyst 40. The exhaust gas temperature Tg acquired by the exhaust gas temperature sensor 80 is transmitted to the combustion switching control device 11.

  The NOx sensor 81 acquires the catalyst outlet NOx concentration in the vicinity of the outlet of the NOx reduction catalyst 40 by detection. The NOx sensor 81 is disposed in the vicinity of the outlet of the NOx reduction catalyst 40 so that the NOx concentration at the mounting position can be regarded as the same as the NOx concentration at the outlet of the NOx reduction catalyst 40. The catalyst outlet NOx concentration acquired by the NOx sensor 81 is transmitted to the combustion switching control device 11.

  In the present embodiment, the NOx reduction catalyst 40 is disposed on the downstream side of the three-way catalyst 38 with respect to the exhaust gas discharge direction (arrow E direction). In other words, the three-way catalyst 38 is arranged on the upstream side of the NOx reduction catalyst 40 with respect to the exhaust gas discharge direction E. The three-way catalyst 38 has a higher high temperature resistance than the NOx reduction catalyst 40 and maintains the purification characteristics of pollutants such as NOx even at a high temperature. Therefore, the three-way catalyst 38 is disposed on the upstream side exposed to higher temperature exhaust gas. Is preferred. However, the present invention is not limited to this, and the NOx reduction catalyst 40 may be disposed upstream of the three-way catalyst 38.

The internal combustion engine system 10 further includes a urea addition device (reducing agent addition device) 82, a urea addition amount control device 83, an NH ₃ adsorption amount estimation device (adsorption amount estimation unit) 84, and a NOx emission amount estimation device (engine outlet concentration acquisition). Means) 85. In the second exhaust passage 34, the urea addition device 82 is connected to a pipe upstream of the NOx reduction catalyst 40 and downstream of the three-way catalyst 38 in the exhaust gas discharge direction. The urea adding device 82 adds urea to the second exhaust passage 34 as urea water, for example. Thereby, the exhaust gas flowing through the second exhaust passage 34 is sent to the NOx reduction catalyst 40, whereby ammonia (NH ₃ ) as a reducing agent generated by the hydrolysis of urea is added to the NOx reduction catalyst 40.

The urea addition amount control device 83 controls addition of NH ₃ to the NOx reduction catalyst 40 by controlling the urea addition device 82 to control addition of urea to the exhaust gas upstream side of the NOx reduction catalyst 40. The urea addition amount control device 83 is controlled by the combustion switching control device 11.

The NH ₃ adsorption amount estimation device 84 estimates the current adsorption / reduction agent amount on the NOx reduction catalyst 40, that is, the amount of NH ₃ adsorbed on the NOx reduction catalyst 40, and calculates a saturated NH ₃ adsorption amount. . The saturated NH ₃ adsorption amount is calculated from the exhaust temperature Tg acquired from the exhaust temperature sensor 80. Adsorbed NH ₃ amount is adsorbed amount of reducing agent present time, the NH ₃ amount added to the predetermined time as will be described later, the amount of NH ₃ was reduced used for purifying NOx in the predetermined time, the saturation of the current NH ₃ adsorption, and determined from the amount of NH ₃ was not desorbed used for purification of NOx. The estimated value of the current adsorption reducing agent amount acquired by the NH ₃ adsorption amount estimation device 84 and the calculated value of the saturated NH ₃ adsorption amount are transmitted to the combustion switching control device 11.

  The NOx emission estimation device 85 estimates and acquires the engine outlet NOx concentration for NOx discharged from the engine 12. The engine outlet NOx concentration is estimated from the engine rotational speed acquired from the rotational speed sensor 20 and the acquired value of the fuel injection amount Q determined by the injection control device 18. For this purpose, the NOx emission amount estimation device 85 stores a map representing the relationship between the engine speed, the fuel injection amount Q, and the engine outlet NOx concentration in advance, and from the acquired engine speed and fuel injection amount Q, Estimate the engine outlet NOx concentration. The engine outlet NOx concentration may be estimated from a model obtained using the operation state of the engine 12. The estimated value of the engine outlet NOx concentration acquired by the NOx emission amount estimation device 85 is transmitted to the combustion switching control device 11.

  The turbine bypass passage 36 is connected to the first exhaust passage 32 on the upstream side of the turbine chamber 64 of the turbocharger 60, and the other end is connected to the second exhaust passage 34 on the upstream side in the exhaust gas discharge direction E of the three-way catalyst 38. Has been. A wastegate valve 42 is provided in the turbine bypass passage 36. The wastegate valve 42 has a function of adjusting the supercharging pressure of intake air by the turbocharger 60. Further, the wastegate valve 42 has a function of preventing the supercharging pressure from exceeding a specified value and protecting the engine 12 and the turbocharger 60 from being damaged.

  The wastegate valve 42 is preferably configured by, for example, an electromagnetic on-off valve. The wastegate valve 42 is adjusted in opening degree in response to a signal from the combustion switching control device 11. When the opening degree of the waste gate valve 42 increases, the exhaust gas bypassed to the second exhaust passage 34 through the turbine bypass passage 36 without flowing into the turbine chamber 64 increases. As a result, the engine 12 and the turbocharger 60 are protected from damage. The turbine bypass passage 36 and the waste gate valve 42 in the present embodiment correspond to the “supercharging pressure adjusting device” in the present invention.

  An exhaust gas recirculation device 50 is provided between the second intake passage 24 and the first exhaust passage 32. The exhaust gas recirculation device 50 includes an exhaust gas recirculation passage 52 that connects the first exhaust passage 32 and the second exhaust passage 34, and an exhaust gas recirculation amount adjustment valve (exhaust gas recirculation amount adjustment device) installed in the middle of the exhaust gas recirculation passage 52. 54. The exhaust gas recirculation amount adjustment valve 54 is adjusted in opening degree in response to a signal from the intake / exhaust control device 28. The intake / exhaust control device 28 receives an instruction from the combustion switching control device 11 and transmits an opening degree adjustment signal to the exhaust gas recirculation amount adjustment valve 54. By adjusting the opening degree of the exhaust gas recirculation amount adjustment valve 54 in this way, the amount of exhaust gas recirculated or recirculated from the first exhaust passage 32 to the second intake passage 24 via the exhaust recirculation passage 52 is adjusted.

  The turbocharger 60 includes a compressor wheel 63 accommodated in the compressor chamber 62, a turbine 65 accommodated in the turbine chamber 64, and a shaft 66 connecting the compressor wheel 63 and the turbine 65. The exhaust gas is sprayed from the first exhaust passage 32 to the turbine 65 in the turbine chamber 64, whereby the turbine 65 rotates, and this rotational power is transmitted to the compressor wheel 63 via the shaft 66. As a result, the compressor wheel 63 is driven to rotate, and the air supplied to the engine 12 via the second intake passage 24 is pressurized (ie, supercharged).

  The combustion switching control device 11 is preferably configured by, for example, a microcomputer including a processing device, a storage unit, and an I / O interface. The processing device reads and executes a program, data, or the like stored in the storage unit. The storage unit stores the program and the engine rotational speed Ne acquired and transmitted by the rotational speed sensor 20, the exhaust gas temperature Tg acquired by the exhaust gas temperature sensor 80, and the catalyst outlet NOx concentration acquired by the NOx sensor 81. Remember. The storage unit also stores the engine outlet NOx concentration, the map, and the predetermined value acquired by the NOx emission amount estimation device 85.

  Further, the combustion switching control device 11 transmits a command signal for controlling the number, amount, and injection timing of fuel injection to each cylinder 14 of the engine 12 to the injection control device 18. Further, the combustion switching control device 11 transmits a command signal for adjusting the opening degree of the intake throttle valve 26 and the exhaust gas recirculation amount adjusting valve 54 to the intake / exhaust control device 28. Further, the combustion switching control device 11 transmits an opening degree adjustment signal to the waste gate valve 42.

  Further, the combustion switching control device 11 calculates the NOx purification rate from the catalyst outlet NOx concentration acquired by the NOx sensor 81 and the engine outlet NOx concentration acquired by the NOx emission amount estimating device 85. The combustion switching control device 11 acquires from the calculated NOx purification rate, the exhaust temperature Tg acquired by the exhaust temperature sensor 80, the engine rotational speed Ne acquired by the rotational speed sensor 20, and the injection control device 18. On the basis of the fuel injection amount Q, the combustion mode of the engine 12 is switched between the lean combustion mode and the stoichiometric combustion mode. This mode switching will be described later with reference to FIG.

The combustion switching control device 11 is a chip integrated with at least one of the injection control device 18, the intake / exhaust control device 28, the urea addition amount control device 83, the NH ₃ adsorption amount estimation device 84, and the NOx emission amount estimation device 85. It may be configured, or may be configured as a separate chip.

  Next, control of the internal combustion engine system 10 of the present embodiment will be described with reference to FIG. FIG. 2 is a flowchart showing processing executed in the combustion switching control device of the internal combustion engine system 10 shown in FIG. FIG. 3 is a graph illustrating a map showing the EGR rate. The process shown in FIG. 2 is repeatedly executed in the combustion switching control device 11 every predetermined control period (for example, 1 second).

  As shown in FIG. 2, the combustion switching control device 11 first acquires the exhaust gas temperature Tg in step S1. As the exhaust temperature Tg, a value acquired by the exhaust temperature sensor 80 and stored in the storage unit can be used.

  Next, the combustion switching control device 11 acquires the catalyst outlet NOx concentration in step S2. As the catalyst outlet NOx concentration, a value acquired by the NOx sensor 81 and stored in the storage unit can be used.

  Next, the combustion switching control device 11 acquires the engine speed Ne in step S3. As the engine speed Ne, a value acquired by the speed sensor 20 and stored in the storage unit can be used.

Subsequently, in step S4, the combustion switching control device 11 estimates the current saturated NH ₃ adsorption amount Tan from the exhaust temperature Tg and also estimates the current NH ₃ adsorption amount Aan. The exhaust temperature at the outlet of the NOx reduction catalyst 40 is determined by the result of heat exchange between the catalyst bed and the exhaust gas. Thereby, the correlation between the exhaust temperature Tg and the bed temperature of the NOx reduction catalyst 40 is high. Further, since the saturated NH ₃ adsorption amount Tan has a strong correlation with the catalyst bed temperature, the correlation between the exhaust temperature Tg and the saturated NH ₃ adsorption amount Tan is also strong. As a result, the saturated NH ₃ adsorption amount Tan from the exhaust temperature Tg. Can be requested. Further, the NH ₃ adsorption amount Aan (t) at the present time (t) is the NH ₃ addition amount addNH ₃ (t) added between the time t-1 and the time t a predetermined time before the time t-1. NH ₃ amount NH ₃ rd (t) used in NOx purification from time t to time t, NH ₃ amount NH ₃ desorbed from the catalyst not used in NOx purification from time t-1 to time t sp (t), and saturated NH ₃ adsorption Tan (t) at the current time is determined using the following equation (1).

Aan (t) = minimum value (saturated NH ₃ adsorption amount Tan (t), Aan (t−1) + addNH ₃ (t) −NH ₃ rd (t) −NH ₃ sp (t)) (1)
Here, t is time, and the minimum value (a1, a2... Ai) means taking the minimum value from a1 to ai. In the equation (1), the NH ₃ addition amount addNH ₃ (t) can be obtained from the addition amount determined by the urea addition amount control device 83. NH ₃ rd (t) can be obtained from a change in the exhaust gas temperature Tg acquired from the exhaust gas temperature sensor 80 using a relational expression or a map obtained in advance. NH ₃ sp (t) can be obtained, for example, from the following equation (2).

NH ₃ sp (t) = f (engine speed Ne, fuel injection amount Q, injection timing, intake throttle valve opening, urea addition amount, NH ₃ adsorption amount Aan (t), gas temperature Tg (t)) (2)
Here, f is a function. For example, the expression (2) is described by the following expression (3).

NH ₃ sp (t) = A1 × NH ₃ adsorption amount Aan (t) (3)
Here, the coefficient A1 of the first term on the right side is described by the following equation (4).

A1 = a × (engine speed Ne) + b × (fuel injection amount Q) + c × (injection timing) + d × (intake throttle valve opening × engine speed Ne) + e × (urea addition amount) + f × (gas temperature) (4)
Here, a, b, c, d, e, and f are predetermined coefficients. In addition, (2)-(4) Formula is an illustration, and does not limit the number of a coefficient, a kind, and the form of a formula.

The initial value of the NH ₃ adsorption amount Aan is 0. When the engine 12 is stopped, the value of the NH ₃ adsorption amount Aan is held, and calculation is started from the value at the time of stop when restarting.

  In step S5, the fuel injection amount Q is acquired. As the fuel injection amount Q, a value transmitted from the injection control device 18 and stored in the storage unit can be used. In addition, the combustion switching control device 11 performs the normal lean in step S5 so that the operating conditions (target torque Tq_tag and target engine speed Ne_tag) input from the host control device (not shown) are realized. As the combustion conditions, the number of fuel injections, the injection timing, the target EGR rate, the supercharging pressure, and the opening of the intake throttle valve 26 are determined. For this determination, for example, various maps stored in the storage unit are referred to. For example, FIG. 3 illustrates a map for deriving the target EGR rate from the engine speed Ne and the fuel injection amount Q. A solid line UL shown in FIG. 3 is an upper limit line indicating an operation limit in the engine 12. Thus, the operating condition of the engine 12 is determined from the fuel injection amount Q and the engine speed Ne.

  Referring to FIG. 2 again, subsequently, the combustion switching control device 11 acquires the engine outlet NOx concentration in step S6. As the engine outlet NOx concentration, a value transmitted from the NOx emission estimating device 85 and stored in the storage unit can be used. As described above, the operating condition of the engine 12 is determined from the fuel injection amount Q and the engine speed Ne in S5. When the operating condition is determined, the combustion state is also determined, so that the gas component discharged from the engine 12 is also determined. As a result, the relationship between Q and Ne and the engine outlet NOx concentration can be expressed in a map in which the fuel injection amount Q and the engine speed Ne are two orthogonal axes. In step S6, a map prepared in advance from the relationship between the fuel injection amount Q and the engine speed Ne, which are engine operating states, and the engine outlet NOx concentration, which are obtained by measurement in advance, is used. The NOx emission amount estimation device 85 estimates the current engine outlet NOx concentration by using this map, and the combustion switching control device 11 acquires the estimated value.

  The engine outlet NOx concentration may be estimated using a map representing the relationship between the intake air amount, the EGR rate, the engine speed and the fuel injection amount Q as the engine operating state, and the engine outlet NOx concentration. .

  Further, as the engine outlet concentration acquisition means, a second NOx sensor (not shown) that acquires the engine outlet NOx concentration by measurement can be used instead of the NOx emission amount estimation device 85. The second NOx sensor can be provided in the first exhaust passage 32 near the outlet of the exhaust port of the engine 12. The measurement value of the second NOx sensor is transmitted to the combustion switching control device 11.

  Next, the combustion switching control device 11 determines whether or not the exhaust gas temperature Tg is higher than the first predetermined value K1 in step S7. As the first predetermined value K1 here, a value obtained in advance from experiments or simulations and stored in the storage unit can be used. If an affirmative determination (YES) is made in step S7, the process proceeds to the subsequent step S8, and if a negative determination (NO) is made, the process proceeds to step S14.

  When an affirmative determination is made in step S7, the combustion switching control device 11 calculates the NOx purification rate R in step S8. The NOx purification rate R is obtained by the following equation (5).

R = {(engine outlet NOx concentration) − (catalyst outlet NOx concentration)} / (engine outlet NOx concentration) (5)
In the equation (5), {(engine outlet NOx concentration) − (catalyst outlet NOx concentration)} corresponds to the amount of purified NOx purified by the exhaust purification unit including the three-way catalyst 38 and the NOx reduction catalyst 40. A high value of the NOx purification rate R means that the amount of purified NOx in the exhaust purification unit is large.

  In step S9, the combustion switching control device 11 determines whether or not the NOx purification rate R is smaller than the second predetermined value K2. As the second predetermined value K2 here, a value obtained in advance from experiments or simulations and stored in the storage unit can be used. When the NOx purification rate R is smaller than the second predetermined value K2, it is determined that the purification capability of the NOx reduction catalyst 40 has decreased. If an affirmative determination (YES) is made in step S9, the process proceeds to the subsequent step S10, and if a negative determination (NO) is made, the process proceeds to step S14.

Subsequently, in step S10, the combustion switching control device 11 determines whether or not the ratio Aan / Tan between the current NH ₃ adsorption amount Aan and the saturated NH ₃ adsorption amount Tan is greater than a third predetermined value K3. When the ratio Aan / Tan is larger than the third predetermined value K3, the amount of NH ₃ adsorption in the NOx reduction catalyst 40 is sufficiently large, and the reason for the decrease in the NOx purification rate R is not because the amount of NH ₃ adsorption is small, It is determined that the NOx purification amount has decreased due to the high temperature of the NOx reduction catalyst 40. On the contrary, when the ratio Aan / Tan is equal to or smaller than the third predetermined value K3, it is determined that the NOx purification rate R may have decreased due to the small amount of NH ₃ adsorbed by the NOx reduction catalyst 40.

If an affirmative determination (YES) is made in step S10, the process proceeds to the subsequent step S12, and if a negative determination (NO) is made, the process proceeds to step S11. In step S11, by controlling the urea addition amount control device 83, the urea addition device 82 adds a predetermined amount of urea to the exhaust gas upstream side of the NOx reduction catalyst 40, and the process proceeds to step S14. At this time, as the amount of urea added, for example, an amount corresponding to the amount of NH ₃ added obtained by the following equation (6) is used.

(NH ₃ addition amount) = (saturated NH ₃ adsorption amount Tan) × predetermined value K3a− (NH ₃ adsorption amount Aan)
... (6)
Here, the predetermined value K3a is preferably larger than the third predetermined value K3.

  In step S12, the combustion switching control device 11 determines the combustion mode in the engine 12 based on a predetermined map from the engine speed Ne acquired in step S3 and the fuel injection amount Q acquired in step S5. The target EGR rate, the target supercharging pressure, and the target intake throttle valve opening are determined so that becomes the stoichiometric combustion mode. Here, the target EGR rate, the supercharging pressure, and the intake throttle valve opening are determined so that the air-fuel ratio, which is the ratio of air to fuel, becomes the stoichiometric ratio (about 14.6: 1). It is set to perform stoichiometric combustion at the intake oxygen concentration. Then, in the subsequent step S13, the combustion switching control device 11 determines the number of injections and the injection timing based on a predetermined map from the engine speed Ne and the fuel injection amount Q.

  On the other hand, in step S14, the combustion switching control device 11 determines the fuel injection amount Q acquired in step S5, the number of fuel injections determined in step S5, the injection timing, the target EGR rate, the supercharging pressure, and the intake throttle valve. The opening is used as it is as a lean combustion condition. That is, the combustion switching control device 11 maintains the determination in step S5 without changing it.

  In step S15, the combustion switching control device 11 performs combustion under the conditions determined in steps S12 and S13 or step S14. That is, when the combustion of the engine 12 is executed under the conditions determined in steps S12 and S13, the combustion mode is switched from the lean combustion mode to the stoichiometric combustion mode, or the stoichiometric combustion mode is maintained. On the other hand, when the combustion in the engine 12 is executed under the conditions determined in step S14, the combustion mode becomes the lean combustion mode.

  Since the control is performed as described above, in the case of a negative determination in step S7, since the exhaust gas temperature Tg is low, it is determined that both the three-way catalyst 38 and the NOx reduction catalyst 40 have a low NOx purification rate, and the lean combustion mode is set. Leave. In other words, when the exhaust gas temperature Tg is high, it is determined that the purification activity of the NOx reduction catalyst 40 has decreased, and switching to the stoichiometric combustion mode is enabled.

  4, (a) is a graph showing the temperature of the NOx reduction catalyst 40, (b) is a NOx purification rate in the NOx reduction catalyst 40, and (c) is a graph showing changes in the air-fuel ratio due to switching of the combustion mode. 4, (d) is a graph showing the NOx purification amount of the three-way catalyst 38 and the NOx reduction catalyst 40, and (e) is a graph showing the NOx value at the outlet of the NOx reduction catalyst 40, respectively. In each graph of FIGS. 4A to 4E, the horizontal axis indicates time. FIG. 4 assumes that the three-way catalyst 38 and the NOx reduction catalyst 40 are sufficiently cooled before starting the engine.

  As shown in FIG. 4 (a), when the engine 12 is started, the lean combustion mode is executed as the normal combustion mode of the engine 12, and when time elapses, the high-temperature exhaust gas passes through the NOx reduction catalyst 40 to reduce NOx. The catalyst temperature (SCR temperature) gradually increases. At this time, in the period B1 up to time t1 (FIG. 4D), the NOx purification activity increases as the catalyst temperature increases. At this time, the lean combustion mode is executed until the temperature of the catalyst rises sufficiently. In a period B2 (FIG. 4 (d)) from time t1 to t2, the catalyst temperature becomes sufficiently high, and the high purification rate of NOx is maintained by improving the purification activity. On the other hand, when the high load operation of the engine is continued, in the period B3 after the time t2 (FIG. 4 (d)), the NOx reduction catalyst 40 becomes too high, so the NOx purification rate gradually decreases.

  At this time, the NOx purification rate in the NOx reduction catalyst 40 exceeds a predetermined value at time t1. At this time, the exhaust temperature Tg is still low and is equal to or lower than the first predetermined value K1. When the NOx reduction catalyst temperature (SCR temperature) further rises as time elapses, the exhaust temperature Tg is greater than the first predetermined value K1 at time t2, and the NOx purification rate at the NOx reduction catalyst 40 is less than the predetermined value. It becomes. At this time, it is determined that the NOx reduction catalyst 40 has become high temperature, and the NOx purification rate R in the exhaust purification unit including the three-way catalyst 38 and the NOx reduction catalyst 40 is less than the second predetermined value K2. At this time, as shown in FIG. 4C, the combustion mode of the engine is switched from the lean combustion mode to the stoichiometric combustion mode. In this case, as shown in FIG. 4D, the NOx purification amount of the NOx reduction catalyst 40 greatly decreases after time t2. On the other hand, as shown in FIG. 4 (d), the three-way catalyst 38 has a condition in which the air-fuel ratio is close to the stoichiometric ratio, so the amount of NOx purification increases. Further, the purification activity of the three-way catalyst 38 is maintained even at a high temperature. As a result, the NOx contained in the exhaust gas can be purified not by the NOx reduction catalyst 40 in which the purification efficiency is lowered, but by the three-way catalyst 38 in which the NOx purification efficiency is increased due to the stoichiometric ratio of the air-fuel ratio. . Therefore, according to the present embodiment, even when the NOx reduction catalyst 40 becomes high temperature due to a high load operation of the engine 12 and the NOx purification rate decreases, the three-way catalyst 38 can sufficiently purify NOx. The NOx emission amount of the internal combustion engine system 10 can be reduced. Further, in the internal combustion engine system 10 of the present embodiment, it is not necessary to use a special configuration that requires a complicated and excessive cost as the exhaust gas aftertreatment system.

  The solid line “with three-way catalyst” in FIG. 4E indicates the NOx value (exit NOx value) at the outlet of the NOx reduction catalyst 40 in the embodiment. As shown in FIG. 4E, in the embodiment, the outlet NOx value is kept low even after time t2. A broken line “no three-way catalyst” in FIG. 4E indicates a comparative example in which a three-way catalyst is not provided. The characteristics of the outlet NOx value in this comparative example are the same as the characteristics of the outlet NOx value when the combustion mode of the engine 12 is set to the lean combustion mode even after the time t2, and the outlet NOx value rapidly increases after the time t2. Yes.

  The temperature acquisition means for acquiring the catalyst-related temperature is not limited to the exhaust temperature sensor 80 disposed near the outlet of the NOx reduction catalyst 40. As the temperature acquisition means, a catalyst temperature sensor that is attached to the NOx reduction catalyst 40 and detects a catalyst bed temperature (catalyst temperature) that is a catalyst-related temperature may be used. At this time, in the lean combustion mode, the combustion switching control unit switches to the stoichiometric combustion mode when the catalyst bed temperature is higher than the first predetermined value K1a and the NOx purification rate R is lower than the second predetermined value K2. May be. Further, the catalyst bed temperature may be estimated using a predetermined model in which a change in the exhaust temperature is estimated from the operating state of the engine 12.

Second Embodiment
Next, an internal combustion engine system 10a according to a second embodiment will be described with reference to FIGS. FIG. 5 is a diagram schematically showing an overall configuration of the internal combustion engine system 10a of the second embodiment. Hereinafter, the same reference numerals are assigned to the same components as those of the internal combustion engine system 10 of the first embodiment described above, and the description thereof is omitted.

  As shown in FIG. 5, the internal combustion engine system 10 a includes a time measurement device (time measurement unit) 86, an operation history storage unit 87, an outside air temperature sensor 88, and a catalyst temperature estimation device (catalyst temperature estimation unit) 89. Unlike the internal combustion engine system 10 of the first embodiment, the internal combustion engine system 10a does not include the exhaust temperature sensor 80 (FIG. 1). The time measuring device 86 measures the operation time and the operation stop time of the engine 12. The operation history storage unit 87 receives signals from the time measuring device 86, the rotation speed sensor 20, and the injection control device 18 and stores the operation history of the engine 12. At this time, the operation history includes the engine speed and the engine load torque as the load, which is the operation state during the operation time from the current start of the engine 12. Further, the operation history includes the engine speed and the engine load torque as the load during the operation time before the previous operation stop of the engine 12, the operation time, and the engine 12 between the current time and the previous time. It also includes the stop time that was stopped at.

  Further, the operation history storage unit 87 stores a current operation history Qn (t) that is a time change of the product of the engine speed and the load during the current operation time of the engine 12, and the current operation history Qn (t) is stored. It transmits to the combustion switching control apparatus 11. Further, the operation history storage unit 87 stores a previous operation history Qpre (t) that is a time change of a product of the engine speed and the load during the previous operation time of the engine 12, and the previous operation history Qpre (t) is stored. It transmits to the combustion switching control apparatus 11.

  The outside air temperature sensor 88 acquires the outside air temperature T0 of the vehicle and transmits it to the combustion switching control device 11 and the catalyst temperature estimating device 89. The catalyst temperature estimation device 89 estimates the temperature of the NOx catalyst on the basis of the signal from the operation history storage unit 87 and the signal from the outside air temperature sensor 88, and sends the estimated temperature value of the NOx catalyst to the combustion switching control device 11. Send. The method for estimating the temperature estimated value will be described later with reference to FIG.

  The time measuring device 86 and the operation history storage unit 87 may be configured as an integrated device. The combustion switching control device 11 may be configured as a chip integrated with at least one of the time measurement device 86, the operation history storage unit 87, and the catalyst temperature estimation device 89, or may be configured as a separate chip. .

  The combustion switching control device 11 determines the combustion mode of the engine based on the signal representing the operation history of the engine 12 acquired from the operation history storage unit 87, the NOx purification rate, the engine speed Ne, and the fuel injection amount Q. Switch between lean combustion mode and stoichiometric combustion mode. The NOx purification rate is calculated from the catalyst outlet NOx concentration acquired by the NOx sensor 81 and the engine outlet NOx concentration acquired by the NOx emission estimation device 85. The switching of the mode will be described later with reference to FIG.

  Next, control of the internal combustion engine system 10a of the present embodiment will be described with reference to FIG. FIG. 6 is a flowchart showing processing executed in the combustion switching control device 11 of the internal combustion engine system 10a.

  In step S21, the combustion switching control device 11 acquires a previous operation history Qpre (t) that is a product of the engine speed and the load during the previous operation time from the time measuring device 86. The combustion switching control device 11 also acquires the current operation history Qn (t) that is the product of the engine speed and the load during the current operation time from the time measuring device 86. The combustion switching control device 11 also acquires the operation stop time tmst from the time measuring device 86.

  Next, the combustion switching control device 11 acquires the catalyst outlet NOx concentration from the NOx sensor 81 in step S22.

  Next, in step S23, the combustion switching control device 11 acquires the engine rotational speed Ne from the rotational speed sensor 20, and acquires the outside air temperature T0 of the vehicle from the outside air temperature sensor 88.

  Subsequently, in step S24, the combustion switching control device 11 obtains the fuel injection amount Q determined by the injection control device 18, and the number of fuel injections, the injection timing, the target EGR rate, the excessive fuel injection condition as the normal lean combustion conditions. The supply pressure and the opening degree of the intake throttle valve 26 are determined. The process of step S24 is the same as the process of step S5 (FIG. 2) of the first embodiment.

  In step S25, the combustion switching control device 11 acquires the engine outlet NOx concentration from the NOx emission amount estimating device 85. The process of step S25 is the same as the process of step S6 (FIG. 2) of the first embodiment.

  Next, in step S26, the combustion switching control device 11 time-integrates the current operation history Qn (t) in a predetermined time range from the start of the engine 12 during the current operation time to the present time, thereby integrating the current operation state integrated value. InQn is calculated. The predetermined time range is set in advance. If the predetermined time range has not elapsed immediately after the start of operation, the current operation state integration value InQn is calculated by time-integrating the current operation history Qn (t) from the operation start to the current time. Further, in the same step, the combustion switching control device 11 calculates the previous operation state integration value InQpre by time-integrating the previous operation history Qpre (t) in a predetermined time range during the previous operation time of the engine 12. At this time, if the previous operation time is less than the predetermined time range, the previous operation state integration value InQpre as a time integration value is calculated over the entire previous operation time.

  Further, in the same step, the catalyst temperature estimation device 89 calculates an estimated value of the catalyst bed temperature Tcpre of the NOx catalyst at the current time using the following equation (7).

Tcpre = max (β (InQpre−α × tmst + InQn), T0) (7)
Here, α and β are constants, and max (a, b) is a function that takes the larger value of a and b.

  In Expression (7), InQpre is a value related to the heat input amount of the NOx reduction catalyst 40 in a predetermined time range in the previous operation or in the entire operation time, and InQn is from a predetermined time range in the current operation or from the start of operation. This is a value related to the heat input amount of the NOx reduction catalyst 40 up to the current time. Α × tmst represents the amount of heat released from the NOx reduction catalyst 40 when the engine is stopped. (InQpre−α × tmst + InQn) corresponds to the amount of heat of the NOx reduction catalyst 40 at the current time. Further, β is a constant corresponding to the heat capacity of the NOx reduction catalyst 40, and becomes a value corresponding to the catalyst bed temperature of the NOx reduction catalyst 40 by multiplying β. The estimated value of the catalyst bed temperature Tcpre is a larger value of the outside air temperature T0 and β (InQpre−α × tmst + InQn) so that the catalyst bed temperature Tcpre does not become lower than the outside air temperature.

  In step S29, the combustion switching control device 11 determines whether or not the current operating state integral value InQn exceeds a fourth predetermined value K4. If an affirmative determination (YES) is made in step S27, the process proceeds to step S29, and if a negative determination (NO) is made, the process proceeds to step S28. Thereby, when it is determined that the temperature of the NOx reduction catalyst 40 is sufficiently high because a sufficiently high amount of heat has passed through the NOx reduction catalyst 40 in the current operation, the previous operation state is not considered. , S30 and S31 are switched to the stoichiometric mode on the assumption that an affirmative determination is made.

The process of steps S29 to S36 is the same as the process of steps S8 to S15 of the first embodiment described above. Here, in step S31, in the process of step S10 of the first embodiment, the NH ₃ adsorption amount estimation device 84 estimates the catalyst bed temperature Tcpre estimated by the catalyst temperature estimation device 89 instead of the exhaust gas temperature Tg. Is used to estimate the current saturated NH ₃ adsorption amount Tan. At the same time, the NH ₃ adsorption amount estimation device 84 estimates the current NH ₃ adsorption amount Aan. The estimation formulas in these estimations are the same as the formulas described in the first embodiment. In step S31, the combustion switching control device 11 compares the ratio Aan / Tan between the NH ₃ adsorption amount Aan and the saturated NH ₃ adsorption amount Tan with a third predetermined value K3.

  On the other hand, in step S28, the combustion switching control device 11 determines whether or not the catalyst bed temperature Tcpre is greater than a fifth predetermined value K5. If an affirmative determination (YES) is made in step S28, it is determined that the temperature of the NOx reduction catalyst 40 is sufficiently high, and the process proceeds to step S29. If a negative determination (NO) is made, the process proceeds to step S35. . Thereby, in step S27, even when it is not determined that a sufficiently high amount of heat passes through the NOx reduction catalyst 40 in the current operation, if the catalyst bed temperature Tcpre estimated in consideration of the previous operation is sufficiently high, , S30 and S31 are switched to the stoichiometric mode on the assumption that an affirmative determination is made. At this time, it is determined that the temperature of the NOx reduction catalyst 40 is sufficiently high due to heat from the previous operation and heat from the current operation.

  7A is an actual measurement value of the temperature of the NOx reduction catalyst 40, FIG. 7B is an estimated value of the temperature of the NOx reduction catalyst 40, and FIG. 7C is an overall view of the three-way catalyst 38 and the NOx reduction catalyst 40. It is a graph which shows the change of NOx purification rate. In each graph of FIGS. 7A to 7C, the horizontal axis represents time. FIG. 7 shows changes in the previous operation, the current operation, and the operation stop time therebetween.

  As shown in FIG. 7, a case is considered in which the engine 12 is stopped and restarted in a state where the NOx reduction catalyst 40 is sufficiently warmed during the previous operation time. In this case, the temperature of the NOx reduction catalyst 40 is sufficiently warmed in the previous operation, and a temperature drop is observed during the engine stop time. However, restart is performed before the engine completely cools down, and the catalyst temperature (catalyst bed temperature) is reduced. ) Will rise again. Thereafter, when the high load operation continues, the catalyst bed temperature becomes high and the NOx purification rate deteriorates. The broken lines in FIGS. 7B and 7C show a comparative example of the internal combustion engine system that does not consider the previous operating state. In this comparative example, the restart is determined to be a start from the initial state in a state where the NOx reduction catalyst 40 is completely cooled, and the catalyst bed is actually in spite of the high temperature of the NOx reduction catalyst 40. It does not switch to stoichiometric operation from the judgment that the temperature is low. As a result, in the comparative example, as shown by the broken line in FIG. 7C, the NOx purification rate deteriorates.

  On the other hand, in this embodiment, the estimated value of the catalyst bed temperature Tcpre reflects the change in the catalyst temperature due to the previous operation, the temperature decrease during engine stop, and the operation after restart. Thereby, the actual state in which the catalyst bed temperature is high can be accurately estimated, and by switching to stoichiometric combustion, it is possible to shift to high NOx purification by the three-way catalyst 38, and it is possible to maintain the reduction in the NOx emission amount.

  In the present embodiment, the upper limit value is not provided for the calculated values of InQpre and InQn. However, since there is heat dissipation in both the engine and the catalyst, upper limit values may be provided for the calculated values of InQpre and InQn. Further, in the equation (7), the equation for estimating the decrease in the catalyst bed temperature while the engine is stopped is in a linear form, but it can also be represented by a nonlinear equation. In this embodiment, other configurations and operations are the same as those in the first embodiment shown in FIGS.

  Note that the internal combustion engine system according to the present invention is not limited to the above-described embodiment and modifications thereof, and various modifications and improvements within the scope of matters described in the claims of the present application and their equivalent scope. Is possible.

  For example, in the above description, the example in which the turbocharger 60 is used as the supercharging device has been described. However, the present invention is not limited to this. Instead of the turbocharger 60 in each embodiment, a mechanical supercharger that performs supercharging operation with engine power may be used. Further, a supercharger may be provided in a plurality of stages by combining a turbocharger and a mechanical supercharger. Furthermore, an electric compressor may be added to the turbocharger or mechanical supercharger or a combination thereof.

  For example, the electric compressor has a compressor wheel and a motor. The compressor wheel is rotationally driven by this motor. The driving of the motor is controlled by an electric supercharging control device. The electric supercharging control device receives a command from the combustion switching control device 11 and rotationally drives the motor. The compressor wheel is driven to rotate by the motor, whereby the air supplied to the engine 12 is pressurized (ie, supercharged). In such a configuration, the supercharging pressure of the intake air is also controlled by the electric compressor. By providing such an electric compressor, a sufficient boost pressure can be obtained quickly when the operating state of the engine changes, and NOx generation can be reduced. In this configuration, the motor of the electric compressor constitutes a part of the supercharging pressure adjusting device.

  Further, the turbocharger 60 of the internal combustion engine system may have a turbine with a variable nozzle vane that varies the exhaust gas flow velocity. By making the exhaust gas flow velocity hitting the turbine variable with the variable nozzle vanes, the supercharging pressure by the turbocharger 60 can be adjusted. The opening adjustment of the variable nozzle vane is performed in response to a command from the combustion switching control device 11. In this configuration, in the turbocharger 60, it is possible to prevent the supercharging pressure from exceeding a specified value due to the variable nozzle vane, and therefore the turbine bypass passage 36 and the wastegate valve 42 can be omitted. In this configuration, the variable nozzle vane forms a part of the supercharging pressure adjusting device.

  Moreover, a pressure accumulation tank for storing compressed air can be provided, and the compressed air supplied from the pressure accumulation tank can be used for supercharging. For example, the supercharging pressure of intake air can be controlled by adjusting the opening of the valve of the pressure accumulating tank. At this time, the pressure accumulation tank constitutes a supercharging device, and the valve of the pressure accumulation tank constitutes a part of the supercharging pressure adjusting device. Moreover, it is good also as a structure which assists the supercharging by the turbocharger 60 with a pressure accumulation tank. At this time, the configuration may be such that the compressed air supplied from the pressure accumulating tank is introduced downstream of the intake throttle valve 26 in the intake direction or upstream of the turbine 65 in the exhaust direction to assist supercharging.

DESCRIPTION OF SYMBOLS 10,10a Internal combustion engine system, 11 Combustion switching control apparatus, 12 Engine, 14 Cylinder, 16 Fuel injection apparatus, 18 Injection control apparatus (injection control part), 20 Speed sensor (rotation speed acquisition means), 21 Intake system, 22 First intake passage, 24 Second intake passage, 26 Intake throttle valve, 28 Intake and exhaust control device, 30 Exhaust system, 32 First exhaust passage, 34 Second exhaust passage, 36 Turbine bypass passage, 38 Three-way catalyst, 40 NOx reduction catalyst, 42 Wastegate valve (supercharging pressure adjustment device), 50 Exhaust gas recirculation device, 52 Exhaust gas recirculation passage, 54 Exhaust gas recirculation amount adjustment valve (Exhaust gas recirculation amount adjustment device), 60 Turbocharger (supercharging device), 62 Compressor chamber, 63, 72 Compressor wheel, 64 Turbine chamber, 65 Turbine, 66 shaft, 80 Exhaust temperature sensor (temperature acquisition means) 81 NOx sensor (catalyst outlet concentration acquiring means), 82 urea addition device (reducing agent adding device), 83 urea addition amount control device, 84 NH ₃ adsorption amount estimating apparatus (adsorption amount estimating section) 85 NOx emissions estimator ( Engine outlet concentration acquisition means), 86 time measuring device (time measuring unit), 87 operation history storage unit, 88 outside air temperature sensor, 89 catalyst temperature estimating device (catalyst temperature estimating unit).

Claims (16)

Engine,
A three-way catalyst for purifying exhaust gas exhausted from the engine and a NOx reduction catalyst;
Catalyst outlet concentration acquisition means for acquiring the catalyst outlet NOx concentration at the outlet of the NOx reduction catalyst;
Temperature acquisition means for acquiring an exhaust temperature at the outlet of the NOx reduction catalyst or a catalyst-related temperature that is a catalyst temperature of the NOx reduction catalyst;
A rotational speed acquisition means for acquiring the engine rotational speed of the engine;
An injection control unit for controlling the number, amount and timing of fuel injection in the engine;
Engine outlet concentration acquisition means for measuring or estimating the engine outlet NOx concentration of NOx discharged from the engine;
The NOx purification rate calculated from the catalyst outlet NOx concentration acquired by the catalyst outlet concentration acquisition means and the engine outlet NOx concentration acquired by the engine outlet concentration acquisition means, and the catalyst acquired by the temperature acquisition means Based on the relationship temperature, the engine rotational speed acquired by the rotational speed acquisition means, and the fuel injection amount acquired from the injection control unit, the combustion mode of the engine is set to a lean combustion mode and a stoichiometric combustion mode. A combustion switching control unit that switches between,
Internal combustion engine system. The internal combustion engine system according to claim 1,
The combustion switching control unit
An internal combustion engine system that switches to a stoichiometric combustion mode when the catalyst-related temperature is higher than a first predetermined value and the NOx purification rate is lower than a second predetermined value in the lean combustion mode. Engine,
A three-way catalyst for purifying exhaust gas exhausted from the engine and a NOx reduction catalyst;
Catalyst outlet concentration acquisition means for acquiring the catalyst outlet NOx concentration at the outlet of the NOx reduction catalyst;
A time measuring unit for measuring the operation time and the operation stop time of the engine;
An operation history storage unit that receives a signal from the time measurement unit and stores an operation history of the engine;
A rotational speed acquisition means for acquiring the engine rotational speed of the engine;
An injection control unit for controlling the number, amount and timing of fuel injection in the engine;
Engine outlet concentration acquisition means for measuring or estimating the engine outlet NOx concentration of NOx discharged from the engine;
The NOx purification rate calculated from the catalyst outlet NOx concentration acquired by the catalyst outlet concentration acquisition means and the engine outlet NOx concentration acquired by the engine outlet concentration acquisition means, and the engine acquired from the operation history storage unit Based on the signal representing the operation history of the engine, the engine speed acquired by the speed acquisition means, and the fuel injection amount acquired from the injection control unit, the combustion mode of the engine is changed to the lean combustion mode and the stoichiometric mode. A combustion switching control unit that switches between the combustion modes,
Internal combustion engine system. The internal combustion engine system according to claim 3,
The internal combustion engine system, wherein the engine operating history includes the engine speed and load that are operating states during the current operating time of the engine. The internal combustion engine system according to claim 4, wherein
The engine operating history includes an internal combustion engine system that includes the engine speed and load that are the operating state during the previous operating time of the engine, the operating time, and the time during which the engine has been stopped. The internal combustion engine system according to claim 4 or 5,
The combustion switching control unit calculates a current operating state integral value by time-integrating a product of the engine speed and a load in a predetermined time range during the current operating time of the engine, and in the lean combustion mode, An internal combustion engine system that switches the combustion mode of the engine to a stoichiometric combustion mode when the operating state integrated value exceeds a fourth predetermined value this time. The internal combustion engine system according to any one of claims 4 to 6,
The combustion switching control unit calculates a previous operation state integral value by time-integrating a product of the engine speed and a load in a predetermined time range during the previous operation time of the engine, and in the lean combustion mode, An internal combustion engine system that switches a combustion mode of the engine to a stoichiometric combustion mode based on a previous operation state integral value and an operation stop time of the engine. The internal combustion engine system according to any one of claims 1 to 7,
The NOx reduction catalyst is a selective reduction catalyst,
A reducing agent addition device for adding a reducing agent to the NOx reduction catalyst;
An adsorption amount estimation unit for estimating the amount of adsorption reducing agent on the NOx reduction catalyst;
With
The combustion switching control unit
An internal combustion engine system that switches to the stoichiometric combustion mode when the amount of adsorption reducing agent estimated by the adsorption amount estimation unit exceeds a third predetermined value in the lean combustion mode. The internal combustion engine system according to any one of claims 1 to 7,
The NOx reduction catalyst is a selective reduction catalyst,
A reducing agent addition device for adding a reducing agent to the NOx reduction catalyst;
An adsorption amount estimation unit for estimating the amount of adsorption reducing agent on the NOx reduction catalyst;
A reducing agent addition controller for controlling the reducing agent addition device;
With
The reducing agent addition control unit is
An internal combustion engine system, wherein when the adsorption reducing agent amount estimated by the adsorption amount estimating unit is equal to or less than a third predetermined value, the reducing agent addition device adds a reducing agent to the NOx reduction catalyst. The internal combustion engine system according to any one of claims 1 to 9,
The combustion switching control unit is an internal combustion engine system that controls an intake state of the engine so that an air-fuel ratio becomes a stoichiometric ratio in a stoichiometric combustion mode. The internal combustion engine system according to any one of claims 1 to 10,
The internal combustion engine system, wherein the NOx reduction catalyst is arranged on the downstream side of the three-way catalyst in the exhaust gas discharge direction. The internal combustion engine system according to any one of claims 1 to 11,
An exhaust gas recirculation device for recirculating part of the exhaust gas of the engine;
An exhaust gas recirculation amount adjusting device for adjusting the amount of exhaust gas recirculated to the engine;
A supercharging device for supercharging air sucked into the engine;
A supercharging pressure adjusting device for adjusting a supercharging pressure by the supercharging device;
An internal combustion engine system, further comprising: an air amount adjustment device that adjusts an amount of air taken in. The internal combustion engine system according to claim 12,
The supercharger is an internal combustion engine system including at least one of a turbocharger, a mechanical supercharger, an electric compressor, and an accumulator tank. The internal combustion engine system according to claim 12 or 13,
The supercharging pressure adjusting device is an internal combustion engine system configured by a wastegate valve provided in a turbine bypass flow path, a variable nozzle vane that varies an exhaust gas flow velocity hitting the turbine, a motor of an electric compressor, or a valve of an accumulator tank. The internal combustion engine system according to any one of claims 12 to 14,
The combustion switching control unit controls the exhaust gas recirculation amount adjusting device and the air amount adjusting device so as to obtain a predetermined intake oxygen concentration and supercharging pressure according to engine operating conditions in the stoichiometric combustion mode, and engine operating conditions An internal combustion engine system that performs predetermined fuel injection control according to the engine. The internal combustion engine system according to any one of claims 12 to 14,
The combustion switching control unit includes an exhaust gas recirculation amount adjusting device, the air amount adjusting device, and the supercharging pressure so that a predetermined intake oxygen concentration and a supercharging pressure are obtained in a stoichiometric combustion mode according to engine operating conditions. An internal combustion engine system that controls a regulator and performs predetermined fuel injection control according to engine operating conditions.

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