JP2013249769A - Control device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inexpensive control device of an internal combustion engine, the device capable of effectively reducing an amount of generation of corrosive substances such as NHwithout decreasing an effect of suppressing NOx.SOLUTION: A control device of an internal combustion engine is mounted in an internal combustion engine that includes a catalyst unit for cleaning exhaust gas when an exhaust air-fuel ratio is a specific air-fuel ratio and an exhaust recirculation passage enabling a part of the exhaust gas downstream of the catalyst unit to be recirculated to an intake side. The control device controls the exhaust air-fuel ratio to the specific air-fuel ratio and suppresses an amount of generation of corrosive substances in exhaust gas. When an amount of generation of corrosive substances in the catalyst unit differs depending on whether the temperature Tof the catalyst unit is at a higher side or lower side than a specific temperature T, the control device controls the exhaust air-fuel ratio to a value in a lean combustion side than the specific air-fuel ratio (step S13) provided that the temperature Tof the catalyst unit is at a low temperature side in which an amount of generation of the corrosive substances increases (YES in step S12).

Description

  The present invention relates to a control device for an internal combustion engine, and more particularly to a control device for an internal combustion engine that suppresses an increase in the amount of corrosive substances generated due to the catalytic action of an exhaust purification catalyst.

  In an internal combustion engine (hereinafter referred to as an engine) mounted on a vehicle or the like, an exhaust gas recirculation (hereinafter referred to as EGR) system that is effective in reducing nitrogen oxides (NOx) is frequently used. Further, various exhaust purification apparatuses, for example, exhaust purification apparatuses using a three-way catalyst unit capable of simultaneously removing hydrocarbons (HC) and carbon monoxide (CO) in addition to NOx by an oxidation-reduction reaction in a gasoline engine or the like are frequently used. ing.

In an engine equipped with such an exhaust purification device and an EGR system, the exhaust gas when the air-fuel ratio is rich contains a lot of unburned fuel, and nitrogen in the exhaust gas reacts with hydrogen in the vicinity of the catalyst. NH ₃ (ammonia) is easily generated. Then, the NH ₃ and other components in the exhaust gas may react to form a salt (eg, ammonium chloride (NH ₄ Cl)), in which case the salt is generated in the EGR system. A high-concentration chlorine ion solution is generated in the EGR system by dissolving in the condensed water or evaporating the condensed water. Therefore, there is a concern that corrosion will occur in the EGR system.

Therefore, conventionally, in order to suppress the generation of NH _{3 which} is a corrosion factor, a catalyst in which Cu is supported on a carrier mainly composed of SiO ₂ , Al ₂ O ₃ , and H ₂ O is prepared, and NH 3 is used as the catalyst. _There has been proposed an exhaust emission control device in which exhaust gas containing ₃ is brought into contact with and NH ₃ is combusted (see, for example, Patent Document 1). In this apparatus, NH ₃ contained in the exhaust gas introduced into the first chamber is oxidized by being brought into contact with the catalyst under heating to become N ₂ and H ₂ O. In the product during this reaction, May contain small amounts of NOx. Therefore, the combustion exhaust gas is mixed with new NH ₃ gas necessary for NOx reduction in the second chamber, and further, NH ₃ and NOx are completely reacted in the third chamber filled with the selective NH ₃ reduction denitration catalyst. , Clean exhaust gas containing almost no NH ₃ or NOx is discharged from the third chamber.

Conventionally, a NOx storage reduction catalyst, the NH ₃ detection means for detecting the NH ₃ supply means for supplying NH ₃ to the NOx storage reduction catalyst, the NH ₃ in the exhaust downstream of from the NOx storage reduction catalyst, There is also known an exhaust purification control device including an exhaust temperature raising means for raising the temperature of the exhaust (for example, see Patent Document 2). In this apparatus, the NH ₃ is supplied to the NOx storage reduction catalyst by the NH ₃ supply means, and the NH ₃ detection means detects NH ₃ exceeding a predetermined allowable amount in the exhaust gas flowing downstream from the NOx storage reduction catalyst. Is detected, the exhaust air temperature ratio is temporarily made rich by the exhaust gas temperature raising means to raise the exhaust gas temperature and suppress the NH ₃ generation amount.

JP-A-56-108516 JP 2009-97471 A

However, in the former former exhaust gas purification apparatus described above, a dedicated catalyst is required for the removal of NH ₃ , so that the exhaust gas treatment system is expensive.

Further, in the above-described conventional exhaust purification control apparatus for the internal combustion engine, although the generation of NH ₃ can be suppressed without separately providing an NH ₃ removal catalyst, the exhaust temperature is raised by the exhaust temperature raising means. When the NH ₃ generation amount is suppressed, there is a concern that the NOx generation amount increases to suppress the generation of NH ₃ and the NOx suppression effect by the EGR system decreases.

The present invention has been made in view of such conventional problems, and is an inexpensive internal combustion engine that can effectively reduce the amount of corrosive substances such as NH ₃ without reducing the NOx suppression effect. A control device is provided.

  In order to solve the above problems, the control device for an internal combustion engine according to the present invention provides (1) a catalyst unit for purifying exhaust when the exhaust air-fuel ratio of the internal combustion engine is a specific air-fuel ratio, and exhaust gas downstream of the catalyst unit. Equipped in an internal combustion engine having an exhaust gas recirculation passage capable of partially recirculating to the intake side, controlling the exhaust air / fuel ratio to the specific air / fuel ratio and suppressing the amount of corrosive substances generated in the exhaust gas A control device for an internal combustion engine, wherein the amount of the corrosive substance generated in the catalyst unit differs depending on whether the temperature of the catalyst unit is higher or lower than a specific temperature. When the temperature is on the low temperature side that increases the generation amount of the corrosive substance, the exhaust air / fuel ratio is controlled to a value on the lean combustion side than the specific air / fuel ratio.

In the present invention, the generation amount of corrosive substances such as NH ₃ depends on the catalyst temperature and the air-fuel ratio, and the generation amount of such corrosive substances increases as the catalyst temperature is lower. When the temperature is lower than a specific temperature, the exhaust air fuel ratio of the engine is adjusted to the lean combustion side from the specific air fuel ratio, so that the oxygen concentration in the exhaust gas is increased and the amount of unburned fuel in the exhaust gas is reduced. Reduced. Therefore, when the amount of corrosive substances generated is expected to increase due to the catalyst temperature on the low temperature side, the increase in the amount of corrosive substances generated can be reliably suppressed by diluting the exhaust air-fuel ratio. Will be. As a result, an inexpensive internal combustion engine that can effectively suppress the generation of corrosive substances such as NH ₃ without reducing the NOx suppression effect while adopting an apparatus configuration that does not use a catalyst for removing corrosive substances. It becomes the control device.

  In the control device for an internal combustion engine of the present invention, (2) the catalyst unit has both the amount of the corrosive substance generated and the rate of change of the amount of the corrosive substance generated with respect to the temperature change of the catalyst unit. Depending on whether the temperature of the catalyst unit is the high temperature side or the low temperature side of the specific temperature, the rate of change of the amount of the corrosive substance generated with respect to the unit temperature change of the catalyst unit is switched. It is set within the temperature range.

  In this case, when the magnitude of the amount of corrosive substances begins to change, the exhaust air-fuel ratio of the internal combustion engine can be accurately adjusted to the lean combustion side from the specific air-fuel ratio, and the increase in the amount of corrosive substances generated is early. It is predicted and accurately suppressed.

  In the control apparatus for an internal combustion engine having the configuration described in (2) above, (3) the temperature range preferably includes 550 degrees Celsius.

In this case, while using a conventional catalyst unit in which the amount of NH ₃ generated increases at 550 degrees Celsius or less, it is possible to effectively suppress the generation within the temperature range on the low temperature side where the amount of corrosive substances generated increases. It will be possible.

  In the control device for an internal combustion engine according to the present invention, (4) the ignition timing of the internal combustion engine is a spark ignition type, and the ignition timing of the internal combustion engine is controlled based on at least the engine speed and the intake air amount. A control mechanism, and an exhaust gas recirculation control mechanism that is disposed on the exhaust gas recirculation path and variably controls the opening degree of the exhaust gas recirculation path, wherein the ignition timing control mechanism is configured such that the temperature of the catalyst unit is When the temperature is lower than a specific temperature, the ignition timing of the internal combustion engine is corrected to an ignition timing that is retarded from the normal ignition timing calculated based on at least the engine speed and the intake air amount. Good.

  With this configuration, it is possible to effectively suppress an increase in the NOx concentration in the exhaust gas when the combustion air-fuel ratio of the internal combustion engine is controlled to a value closer to the lean combustion side than the specific air-fuel ratio.

  More preferably, the control device for an internal combustion engine according to the present invention further includes (5) an exhaust gas recirculation control mechanism that variably controls an exhaust gas recirculation rate for recirculation to the intake side through the exhaust gas recirculation passage. When the temperature of the catalyst unit is on the low temperature side from the specific temperature, the exhaust gas recirculation rate is increased from the exhaust gas recirculation rate when the temperature of the catalyst unit is on the high temperature side from the specific temperature. is there.

  With this configuration, it is possible to effectively suppress an increase in the NOx concentration in the exhaust gas when the combustion air-fuel ratio of the internal combustion engine is controlled to a value closer to the lean combustion side than the specific air-fuel ratio.

  In the control apparatus for an internal combustion engine of the present invention, (6) the catalyst unit is constituted by a three-way catalyst, and an air-fuel ratio sensor for detecting an exhaust air-fuel ratio of the internal combustion engine, and detection information of the air-fuel ratio sensor are used. A feedback control mechanism that feedback-controls the fuel consumption of the internal combustion engine so that the exhaust air-fuel ratio matches the specific air-fuel ratio on the basis of the exhaust air-fuel ratio may be further provided.

  In this case, when the catalyst temperature exceeds a specific temperature, the catalytic action of the three-way catalyst can simultaneously remove HC and CO in addition to NOx by the oxidation-reduction reaction by matching the exhaust air-fuel ratio to the specific air-fuel ratio. Can be sufficiently exerted to ensure the required exhaust purification performance.

According to the present invention, it is possible to provide a control apparatus for an inexpensive internal combustion engine that can effectively reduce the generation amount of corrosive substances such as NH ₃ without reducing the NOx suppression effect.

1 is a schematic configuration diagram of an internal combustion engine equipped with a control device for an internal combustion engine according to an embodiment of the present invention. It is a flowchart which shows the general | schematic process sequence of the exhaust gas purification control program performed with the control apparatus of the internal combustion engine which concerns on one Embodiment of this invention. FIG. 4 is a graph showing the relationship between the amount of NH ₃ generated in a catalyst unit and the catalyst temperature in an embodiment of the present invention, where the vertical axis represents the amount of NH ₃ generated in the catalyst unit, and the horizontal axis represents the catalyst temperature. Represents. It is a graph showing the relationship between the rate of increase in the amount of NH ₃ generated in the catalyst unit and the air-fuel ratio of the internal combustion engine in one embodiment of the present invention, and the vertical axis represents the amount of NH ₃ generated in the catalyst unit, The horizontal axis represents the air-fuel ratio. 3 is a graph showing the relationship between the amount of NOx generated in the exhaust gas of the internal combustion engine and the correction of the ignition timing of the internal combustion engine in one embodiment of the present invention, where the vertical axis represents the NOx generation amount, and the horizontal axis represents the ignition timing. Represents an ignition timing correction coefficient for correcting. 4 is a graph showing the relationship between the NOx generation amount in the exhaust gas of the internal combustion engine and the EGR rate of the internal combustion engine in one embodiment of the present invention, the vertical axis represents the NOx generation amount, and the horizontal axis represents the EGR valve. It represents an EGR opening correction coefficient for correcting the opening. It is explanatory drawing of the catalyst temperature calculation map explaining the different aspect of the catalyst temperature detection method in the control apparatus of the internal combustion engine which concerns on one Embodiment of this invention, a vertical axis | shaft represents volumetric efficiency and a horizontal axis represents an engine speed. ing.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 1 shows a schematic configuration of an internal combustion engine equipped with a control device for an internal combustion engine according to an embodiment of the present invention. The internal combustion engine of the present embodiment is a spark ignition type multi-cylinder internal combustion engine that constitutes a travel drive source for a vehicle (not shown), and performs lean combustion exclusively.

  First, the configuration will be described.

  An engine 10 of the present embodiment shown in FIG. 1 is configured by, for example, an in-line four-cylinder four-stroke cycle gasoline engine, and has four cylinders 11 (only one is schematically shown in FIG. 1). Yes. Each cylinder 11 is formed with a combustion chamber 13 partitioned by a piston 12, and an intake valve 16 and an exhaust valve 17 are provided so as to be opened and closed by a valve mechanism (not shown) and exposed to the combustion chamber 13. A spark plug 14 is arranged. Further, the piston 12 in each cylinder 11 is connected to a corresponding crank-through portion of the crankshaft 15 via a connecting rod (not indicated).

  An injector 21 (fuel injection valve) is attached to an intake port portion (not shown in detail) corresponding to each cylinder 11 of the engine 10, and a plurality of injectors 21 corresponding to a plurality of cylinders 11 are delivered to each other, not shown. Connected to a pipe. Fuel, for example, gasoline, is supplied to the delivery pipe by a fuel pump in a fuel tank (not shown) mounted on the vehicle.

  Further, the engine 10 includes an intake device 30 having an intake passage 18 that can suck air into the combustion chamber 13 when the intake valve 16 is opened, and a gas after combustion from the combustion chamber 13 when the exhaust valve 17 is opened. And an exhaust device 40 having an exhaust passage 19 through which exhaust gas can be discharged.

  The intake device 30 forms an intake passage 18 and has an intake pipe 31 having a surge tank (not shown) in the middle thereof, and an air flow meter 32 that detects an intake air amount in the vicinity of an air cleaner (not shown) on the upstream end side of the intake pipe 31. And a throttle valve 33 located between the air flow meter 32 and the surge tank, and a throttle opening sensor 34 for detecting the opening of the throttle valve 33 (hereinafter referred to as throttle opening).

  The intake flow rate of fresh air detected by the air flow meter 32 is taken into the ECU 100 as an electronic control device as an intake air amount signal Qa representing the intake air amount, and the opening of the throttle valve 33 detected by the throttle opening sensor 34 is The throttle opening signal Athv is taken into the ECU 100.

  The exhaust device 40 includes an exhaust pipe 41 that forms the exhaust passage 19, an exhaust purification catalyst unit 42 that is composed of a three-way catalyst and is attached to the exhaust pipe 41, and a vicinity of the catalyst unit 42, for example, a catalyst unit 42. An air-fuel ratio sensor 43 that detects the exhaust air-fuel ratio in the downstream exhaust passage 19 and a catalyst temperature sensor 44 that detects the catalyst temperature of the catalyst unit 42 are configured.

  The exhaust pipe 41 has a plurality of exhaust branch pipes 41a (only one is shown in FIG. 1) so that exhaust gas can be discharged from the combustion chamber 13 corresponding to the opening of the exhaust valve 17 of each cylinder 11. And a collecting pipe portion 41b.

The catalyst unit 42 incorporates a known three-way catalyst 42a, and the exhaust air / fuel ratio of the engine 10 is specified by controlling the air / fuel ratio (combustion air / fuel ratio) in the combustion chamber 13 of the engine 10 to the stoichiometric air / fuel ratio. When the air-fuel ratio is controlled, nitrogen oxides (NOx), hydrocarbons (HC) and carbon monoxide (CO) in the exhaust gas of the engine 10 can be highly purified together by an oxidation-reduction reaction. . Specifically, the three-way catalyst 42a of the catalyst unit 42 is formed by coating alumina (Al ₂ O ₃ ) on a carrier having a monolith structure in which a porous cell wall forms a honeycomb shape, platinum (Pt), rhodium ( Rh), an alkali metal oxide, an alkaline earth oxide, a rare earth oxide, and the like. This catalyst unit 42 has a chemical equivalent of H ₂ , CO, and HC that are reducing gases with respect to NOx and O ₂ that are oxidizing gases under the condition of a theoretical air-fuel ratio (equivalent ratio φ = 1 described later). Therefore, the NOx, HC, and CO that are pollutants can be rendered harmless as N ₂ , H ₂ O, and CO ₂ by sufficiently oxidizing and reducing both gases with the three-way catalyst 42a.

Further, the three-way catalyst 42a of the catalyst unit 42 can store NOx at a lean air-fuel ratio that becomes an excessive oxidation atmosphere, and can reduce and purify NOx at a rich air-fuel ratio, so-called lean NOx. It is a catalyst. That is, when the three-way catalyst 42a comes into contact with exhaust gas during operation at a lean air-fuel ratio, for example, NO is oxidized to NO ₂ on Pt, and the basic substance on the catalyst is occluded in the form of nitrate. In addition, when contacting the exhaust gas during operation at a rich air-fuel ratio, nitrate is efficiently reduced to nitrogen (N ₂ ) by unburned HC, H ₂ , CO in the exhaust gas in a state where the oxygen concentration is low, and NOx It comes to purify.

The air-fuel ratio sensor 43 is composed of, for example, a known concentration cell type exhaust oxygen concentration sensor (O ₂ sensor), and the electromotive force rises sharply on the rich side where unburned fuel gas remains with the theoretical air-fuel ratio as a boundary. It has characteristics.

  The engine 10 is further equipped with an EGR device 50.

  The EGR device 50 includes an exhaust gas recirculation passage 51 that can recirculate part of the exhaust gas downstream of the catalyst unit 42 from the exhaust passage 19 to the intake air passage 18, and an end portion of the exhaust gas recirculation passage 51 on the intake air passage 18 side. And an EGR valve 52 provided in the vicinity.

  The exhaust gas recirculation passage 51 is formed by, for example, an EGR pipe and a part of an exhaust manifold, although details are not shown.

  The EGR valve 52 has a variable EGR rate (exhaust recirculation rate = recirculation exhaust flow rate / total intake air flow rate (including fresh air intake amount and exhaust recirculation amount)) indicating the magnitude of the exhaust gas recirculation flow rate through the exhaust gas recirculation passage 51. The valve opening Aev can be changed in accordance with the input opening control signal so as to be controlled.

  The EGR device 50 further includes an EGR cooler 53 that can cool the recirculated exhaust gas that passes through the exhaust recirculation passage 51 while forming a part of the exhaust recirculation passage 51 on the exhaust passage 19 side from the EGR valve 52. The EGR cooler 53 cools the recirculated exhaust gas passing through the exhaust recirculation passage 51 by heat exchange with the cooling water of the engine 10.

On the other hand, the ECU 100 described above receives the exhaust air-fuel ratio signal AF from the air-fuel ratio sensor 43 and the catalyst temperature sensor 44 in addition to the intake air amount signal Qa from the air flow meter 32 and the throttle opening signal Athv from the throttle opening sensor 34. Temperature detection signal (catalyst temperature T _CN ) is input. The ECU 100 further includes a crank angle signal CA from the crank angle sensor 61, a cooling water temperature signal Tw from the water temperature sensor 62 that detects the cooling water temperature of the engine 10, a required opening signal Accp from the accelerator opening sensor 63, A request signal from the in-vehicle ECU is input. The ECU 100 has a function of electronically controlling the engine 10 based on these input signals.

  ECU 100 includes a central processing unit (CPU), a read only memory (ROM), a random access memory (RAM), a backup memory, and further includes an A / D converter, although a specific hardware configuration is not illustrated. It includes an input interface circuit, an output interface circuit including a driver and a relay switch, and a communication interface with other in-vehicle ECUs.

  The ECU 100 realizes outputs (torque and engine speed) required for the engine 10 while executing so-called multitask processing, for example, according to a control program stored in a ROM or a backup memory (hereinafter referred to as a ROM or the like). Thus, the opening degree of the throttle valve 33 of the engine 10, the ignition timing, the fuel injection timing, the fuel injection amount, and the like are each controlled.

  For example, the ECU 100 is an ignition timing control mechanism that controls the ignition timing tp in each cylinder 11 of the engine 10 by an ignition signal to the ignition plug 14 based on at least the engine speed Ne [rpm] and the intake air amount Qa of the engine 10. Function. Further, the ECU 100 calculates a required torque from map data acquired by a preliminary test or the like based on the accelerator opening Accp detected by the accelerator opening sensor 63 and the engine speed Ne, and fuel injection corresponding to the required torque is performed. Set the amount. Further, the ECU 100 also functions as an exhaust gas recirculation control mechanism that variably controls by a control signal of the opening degree Aev to the EGR valve 52.

  The ECU 100 also corrects the amount of fuel supplied from the injector 21 to each cylinder 11 based on the detection value of the air-fuel ratio sensor 43 in accordance with an air-fuel ratio feedback control program stored in a ROM or the like. That is, the ECU 100 controls the amount of fuel supplied to each cylinder 11 based on the detection value of the air-fuel ratio sensor 43, so that the combustion air-fuel ratio, which is the mixing ratio of intake air and fuel in each cylinder 11, is set to its target air-fuel ratio. The feedback control mechanism executes feedback control that matches the exhaust air / fuel ratio of the engine 10 with the specific air / fuel ratio by matching the stoichiometric air / fuel ratio.

  The ECU 100 further detects the engine rotation speed of the engine 10 by taking in a pulse signal corresponding to the rotation speed Ne [rpm] of the crankshaft 15 from the crank angle sensor 61, and also detects the crank angle sensor 61 and a cylinder discrimination not shown. Based on the output signal from the sensor, the cylinder speed can be determined by grasping the engine speed Ne and the rotational angle position of the crankshaft 15.

  In addition, the ROM of the ECU 100 stores control programs such as air-fuel ratio correction control, ignition retardation control, EGR rate control, etc. based on the catalyst temperature, which will be described later, and various data. The RAM of the ECU 100 stores various controls. The CPU calculation results and control values in the processing are temporarily stored.

The ECU 100 executes such a control program to control the exhaust air / fuel ratio of the engine 10 to a specific air / fuel ratio and to suppress the generation amount of corrosive substances such as NH ₃ in the exhaust gas of the engine 10. (The control procedure itself will be described later with reference to FIG. 2).

By the way, the catalyst unit 42 has a temperature in the vicinity of the surface where the three-way catalyst 42a comes into contact with the exhaust gas (catalyst bed temperature; hereinafter referred to as catalyst temperature _TCN ) is higher or lower than a specific temperature. Thus, the amount of corrosive substances generated in the catalyst unit 42 and the rate of change of the amount of corrosive substances generated with respect to the change in the catalyst temperature _TCN have a temperature characteristic that is remarkably different.

Specifically, as shown in FIG. 3, in the catalyst unit 42, the amount of corrosive substances generated is significantly different depending on whether the catalyst temperature _TCN is higher or lower than the specific temperature T1. It has temperature characteristics. Here, the specific temperature T1, the vicinity temperature range of the temperature T _NH3 which the NH ₃ generating rate of change with respect to changes in the generation amount and the catalyst temperature T _CN in NH ₃ in the catalyst unit 42 differs significantly on both sides In Rt, for example, 550 [° C.] equal to the temperature T _NH3 is set. Further, the temperature range Rt (see FIG. 3) in the vicinity of the temperature T _NH3 here indicates that the rate of change of the amount of NH ₃ generated relative to the unit temperature change of the catalyst unit 42 is larger or smaller in the operating temperature range of the catalyst unit 42. The temperature range is switched from one to the other. Hereinafter, the specific temperature T1 set to the temperature _TNH3 is referred to as a specific temperature _TNH3 .

That is, as shown on the right side of the temperature T _NH3 in FIG. 3, when the catalyst temperature T _CN is within the temperature range of the high temperature side than the specified temperature T _NH3 in the catalyst unit 42, a constant elevated temperature ΔT in the catalyst temperature rising Reduction rate of NH ₃ generation amount Q _NH3 [ppm] per _CN (reduction amount ΔQ _NH3 / ΔT _CN ), or increase rate of NH ₃ generation amount Q _NH3 per constant decrease temperature ΔT _CN during catalyst temperature decrease ( Both the increase amount ΔQ _NH3 / ΔT _CN ) become smaller.

On the other hand, as shown on the left side of the temperature T _NH3 in FIG. 3, when the catalyst temperature T _CN is within the temperature range lower than the specific temperature T _NH3 , NH per constant increase temperature ΔT _CN during the catalyst temperature increase. _{3 The} rate of reduction of the generated amount Q _NH3 or the rate of increase of the generated amount Q _NH3 of NH ₃ per constant decrease temperature ΔT _CN during the catalyst temperature decrease is the temperature at which the catalyst temperature T _CN is higher than the specific temperature T _NH3 Both are larger than when they are within range. That is, in the catalyst unit 42, the NH ₃ generation amount Q _NH3 which is a corrosive substance and the change rate of the NH ₃ generation amount Q _NH3 with respect to the change in the catalyst temperature T _CN are notably _separated from the specific temperature T _NH3. It has changing temperature characteristics.

As shown in FIG. 4, the increase rate [%] of the NH ₃ generation amount accompanying the catalytic action of the three-way catalyst 42 a in the catalyst unit 42 is the combustion air-fuel ratio A / F in the combustion chamber 13 of the engine 10 and It also depends on the equivalent ratio φ corresponding thereto. Here, the equivalent ratio φ is a value representing the fuel concentration, and is a value obtained by dividing the theoretical air-fuel ratio by the actual air-fuel ratio of the air-fuel mixture, that is, a value corresponding to the reciprocal of the excess air ratio.

Specifically, in the range of the lean air-fuel ratio on the right side in FIG. 4 where the equivalence ratio φ <1 and the range of the rich air-fuel ratio on the left side in FIG. The increase rate CQ [%] of the NH ₃ generation amount is significantly different. That is, within the lean air-fuel ratio range where the equivalence ratio φ <1, the increase rate CQ of the NH ₃ generation amount in the catalyst unit 42 becomes small, and conversely, the rich air-fuel ratio range where the equivalence ratio φ> 1. The increase rate CQ of the NH ₃ generation amount in the catalyst unit 42 increases.

Further, in the range near the equivalent ratio φ = 1 in the rich air-fuel ratio range where the equivalent ratio φ> 1, the change amount ΔCQ of the NH ₃ generation amount increase rate CQ per constant air-fuel ratio change amount ΔAF is shown in FIG. It becomes very large as shown in the inside. That is, when the equivalence ratio φ starts to change from 1 to the rich side, the NH ₃ generation rate increase rate CQ rises sharply in the vicinity of the equivalence ratio φ = 1, and when the equivalence ratio φ approaches the equivalent ratio φ = 1 from the rich side. The increase rate CQ of the amount of NH ₃ generation falls steeply in the vicinity of the ratio φ = 1.

Therefore, in the operating condition of the air-fuel ratio AF2 in FIG. 4 within the range of φ <1, for example, in the operating state of A / F = 15.5, the operating condition of the air-fuel ratio AF1 in FIG. For example, compared with the operation state of A / F = 14.5, the increase rate CQ of the NH ₃ generation amount in the catalyst unit 42 can be reduced by about 70%.

In consideration of the catalyst temperature dependency and the air-fuel ratio dependency regarding the NH ₃ generation amount of the catalyst unit 42 as described above, in the ECU 100, the catalyst temperature T _CN of the catalyst unit 42 is the generation amount of corrosive substances such as NH _3. When the temperature falls within the above-mentioned temperature range on the low temperature side, the combustion air-fuel ratio A / F in the combustion chamber 13 of the engine 10 is controlled so that the exhaust air-fuel ratio of the engine 10 is controlled to a value on the lean combustion side from the specific air-fuel ratio. Is controlled to a value larger than the air-fuel ratio AF1.

Further, when the lean air-fuel ratio is controlled so that the equivalence ratio φ <1, the O ₂ concentration in the gas exhausted from the engine 10 increases, so the NOx reduction rate at the three-way catalyst 42a decreases. . On the other hand, the amount of NOx produced by combustion in the engine 10 depends on the temperature of the combustion, so the amount of NOx generated can be reduced by lowering the combustion temperature. The combustion temperature in the engine 10 and the amount of NOx generated depending on the combustion temperature can be reduced by retarding the ignition timing or increasing the EGR valve opening Aev (increasing the EGR rate) in the EGR device 50.

Therefore, ECU 100, when the catalyst temperature T _CN in the catalyst unit 42 is on the low temperature side than the specified temperature T1, the ignition by the function as a timing control mechanism, the ignition timing tp the ignition timing correction as shown in FIG. 5 of the engine 10 By correcting using the coefficient β, it is corrected to an ignition timing that is retarded from the normal ignition timing calculated based on at least the engine speed Ne and the intake air amount Qa. Here, the normal ignition timing is an ignition timing calculated under the same setting conditions as the ignition timing when the catalyst temperature _TCN is equal to or higher than the specific temperature T1.

Further, ECU 100, when the catalyst temperature _{T CN} in the catalyst unit 42 is on the low temperature side than a particular temperature T1, by the function of the exhaust gas recirculation control system, the valve opening Aev of the EGR valve 52 of the EGR device 50 in FIG. 6 by correcting using the EGR opening correction coefficient γ as shown, to increase the EGR rate when the EGR rate of the EGR device 50 is catalyst temperature T _CN in the catalyst unit 42 is on the high temperature side than a particular temperature T1 It is like that.

Specifically, a basic EGR amount map and an EGR correction map are stored in the ROM or the like of the ECU 100. In the basic EGR amount map, the vertical axis represents the fuel injection amount fq, the horizontal axis represents the engine speed Ne of the engine 10, and the EGR opening corresponding to the basic EGR amount for each operation state specified by them is determined by a preliminary operation test. It is obtained and mapped. Further, EGR correction map, the basic EGR amount obtained based on the engine speed Ne and the fuel injection amount fq, corrected on the basis of the advance is identified other parameters were coolant temperature Tw and the catalyst temperature T _CN etc. The EGR amount data is determined, and only the EGR opening correction coefficient γ with the basic EGR amount or the basic EGR opening as 1 may be determined. In this case, the final EGR opening = the basic EGR opening × the EGR opening correction coefficient γ.

  Next, the operation will be described.

  FIG. 2 shows the flow of exhaust purification control executed in the present embodiment.

  This control is repeatedly executed every predetermined time while the engine 10 is in operation.

First, the first, the catalyst temperature sensor 44 detects the catalyst temperature _{T CN} is (step S11), and then whether or not the catalyst temperature _{T CN} is below a specific temperature _{T NH3} is determined (step S12).

At this time, if the catalyst temperature _{T CN} is below a specific temperature _{T NH3} (YES in step S2), the then range air-fuel ratio A / F of the engine 10 is equivalent ratio phi <1 become lean air-fuel ratio Thus, control is performed to suppress the amount of NH ₃ generated in the catalyst unit 42 and the rate of increase thereof (step S13).

As shown in FIG. 4, the NH ₃ generation amount in the catalyst unit 42 depends on the air-fuel ratio A / F, and the NH ₃ generation amount greatly decreases under lean combustion where the equivalence ratio φ <1. It is possible to suppress the amount of NH ₃ generated and the rate of increase thereof.

Next, an ignition timing correction coefficient β for retarding the ignition timing tp is set according to the operating state of the engine 10 such as the catalyst temperature _TCN and the air-fuel ratio A / F in order to reduce the amount of NOx generated depending on the combustion temperature. The Then, a correction value tp ₀ × βp _{0 obtained} by multiplying the basic ignition timing tp ₀ calculated based on the engine speed [rpm] of the engine 10 and the intake air amount Qa by the ignition timing correction coefficient β is calculated, and this correction value is calculated. tp ₀ × βp ₀ is set as the retarded ignition timing tp (step S14).

Then, in order to reduce the NOx generation amount which depends on the combustion temperature, the catalyst temperature _{T CN} and EGR opening correction coefficient increase side according to the operating state of the engine 10 to expand the valve opening Aev of the EGR valve 52 gamma (> 1) is calculated using the above-mentioned EGR correction map, and the final EGR opening is calculated using the EGR opening correction coefficient γ larger than 1 and the basic EGR opening obtained from the basic EGR amount map. (Step S15).

On the other hand, if the catalyst temperature _{T CN} detected by the catalyst temperature sensor 44 is not less than a specific temperature _{T NH3} (case of NO in step S12), the then combustion air-fuel ratio A / F of the engine 10 and the equivalence ratio phi = 1 Feedback control is performed so that the stoichiometric air-fuel ratio is achieved (step S16). Therefore, the exhaust air-fuel ratio of the engine 10 is controlled to a specific air-fuel ratio, and NOx, HC and CO in the exhaust gas of the engine 10 are highly purified and removed by the catalytic action of the three-way catalyst 42a in the catalyst unit 42. The

In this case, if there is no change in parameters other than the catalyst temperature T _CN that affects the ignition timing, the ignition timing correction coefficient β = 1, and the calculation is based on the engine speed [rpm] of the engine 10 and the intake air amount Qa. The basic ignition timing tp ₀ is set as the current ignition timing tp (step S17).

Further, if there is no change in other parameters than the catalyst temperature _{T CN} affecting the EGR opening, EGR opening correction coefficient gamma = 1, and the basic EGR opening Aev ₀ obtained from the basic EGR amount map described above, The current final EGR opening is calculated (step S18).

In the present embodiment, by an exhaust gas purification control shown in FIG. 2 is repeated in a short cycle, the catalyst temperature T _CN is in the operating region becomes lower than a specific temperature T _NH3, air-fuel ratio as shown in step S13-15 A / Control is performed to dilute F, retard the ignition timing tp, and increase the EGR opening Aev. On the other hand, in the operation region where the catalyst temperature T _CN does not fall below the specific temperature T _NH3 , the process control as shown in Step S16-18 is executed.

Thus, in the present embodiment, when the catalyst temperature T _CN is the low temperature side than a particular temperature T _NH3, although the amount of generated corrosive substances such as NH ₃ is increased as the cold side of the catalyst temperature T _CN On the other hand, by adjusting the combustion air-fuel ratio A / F of the engine 10 to the lean combustion side from the air-fuel ratio AF1, the oxygen concentration in the exhaust gas is increased and the amount of unburned fuel in the exhaust gas is reduced. increased incidence of the corrosive substances that rely on fuel quantity and the catalyst temperature T _CN is advance to the restrained appropriately. That is, when the catalyst temperature T _CN becomes equal to or lower than the specific temperature T _NH3 , an increase in the amount of corrosive substances is predicted, so that the air-fuel ratio A / F is changed from stoichiometric to lean according to the catalyst temperature T _CN . By selecting the air / fuel ratio A / F, the increase in the amount of corrosive substances such as NH ₃ is effectively suppressed. Therefore, while adopting an apparatus configuration that does not use a catalyst for removing corrosive substances, the generation of corrosive substances such as NH ₃ can be effectively suppressed without reducing the NOx suppression effect, and the corrosion of the EGR apparatus 50 can be suppressed. It becomes an inexpensive control device for the engine 10 that can be prevented.

Further, in the present embodiment, the specific temperature T _NH3, generation rate of change of the corrosive substance to a unit temperature change of the catalyst unit 42 is set in the temperature range Rt. Therefore, the combustion air-fuel ratio A / F of the engine 10 can be accurately adjusted to the lean combustion side from the air-fuel ratio AF1 before the amount of corrosive substances generated increases, and the amount of corrosive substances generated becomes more effective. Will be reduced. In addition, since the temperature range Rt includes 550 degrees Celsius, while using the conventional catalyst unit in which the amount of NH ₃ generated increases at 550 degrees Celsius or less, the temperature range within the low temperature range where the amount of corrosive substances generated increases. Therefore, the occurrence can be effectively suppressed.

Further, ECU 100 serving as the ignition timing control mechanism, when the catalyst temperature _{T CN} is in the low temperature side than a particular temperature _{T NH3,} based on ignition timing tp of the engine 10, at least the engine speed Ne and the intake air amount Qa calculated The ignition timing is corrected to a retarded ignition timing than the normal ignition timing (basic ignition timing tp ₀ or an ignition timing obtained by correcting the basic ignition timing tp ₀ based on a parameter other than the catalyst temperature). Therefore, an increase in the NOx concentration in the exhaust gas when the exhaust air-fuel ratio of the engine 10 is controlled to a value on the lean combustion side than the specific air-fuel ratio can be effectively suppressed.

EGR when addition, ECU 100 serving as the exhaust gas recirculation control mechanism, when the catalyst temperature _{T CN} is in the low temperature side than a particular temperature _{T NH3,} the EGR rate is catalyst temperature _{T CN} in the high temperature side than a particular temperature _{T NH3} Therefore, as in the case of retarding the ignition timing tp, the increase in the NOx concentration in the exhaust gas when the exhaust air-fuel ratio of the engine 10 is controlled to a value closer to the lean combustion side than the specific air-fuel ratio is effective. Can be suppressed.

Thus, in the present embodiment, when the catalyst temperature T _CN is the low temperature side than the specified temperature T _NH3, together with suppressing the occurrence of NH ₃ in the lean combustion air-fuel ratio from the stoichiometric, the ignition timing By increasing the EGR amount while retarding, the increase in the generation of NOx can be effectively suppressed.

In the present embodiment, the catalyst unit 42 is constituted by the three-way catalyst 42a, and the exhaust air / fuel ratio is set to the specific air / fuel ratio based on the detection information of the air / fuel ratio sensor 43 that detects the exhaust air / fuel ratio of the engine 10. Air-fuel ratio feedback control for matching is executed. Thus, during normal operation of the catalyst temperature T _CN is the high temperature side than the specified temperature T _NH3 is sufficiently exhibit catalytic action of the three-way catalyst 42a can be removed simultaneously by the oxidation-reduction reactions of HC and CO in addition to NOx And high exhaust purification performance can be obtained.

As described above, in this embodiment, it is possible to provide an inexpensive control device for an internal combustion engine that can effectively reduce the amount of corrosive substances such as NH ₃ generated without reducing the NOx suppression effect. .

  In the above-described embodiment, the air-fuel ratio sensor 43 is composed of a concentration cell type exhaust oxygen concentration sensor. However, the air-fuel ratio sensor 43 detects the exhaust air-fuel ratio upstream of the catalyst unit 42. A limiting current type may be used, or an air-fuel ratio sensor upstream of the catalyst unit 42 and an oxygen sensor downstream of the catalyst unit 42 may be provided.

In the above-described embodiment, the catalyst temperature _TCN of the catalyst unit 42 is detected by the catalyst temperature sensor 44. However, the present invention is not limited to the direct temperature detection by the sensor, and a map as shown in FIG. 7 is used. catalyst temperature detection mechanism may be configured to indirectly detect the approximate value of the catalyst temperature T _CN based on the engine speed Ne and the volumetric efficiency KL of the engine 10.

Here, the volumetric efficiency KL is an index representing the intake capacity of fresh air by the exhaust of the burned gas and the intake of the unburned gas, and is the ratio of the substantial intake fresh air volume to the cylinder displacement (stroke volume). It corresponds to. The substantial intake fresh air volume is a volume converted into temperature and pressure at the air intake of the engine. This volumetric efficiency KL varies depending on operating conditions even in the same engine, for example, because the pressure resistance of the intake system increases in a high rotation range. Therefore, to calculate the volumetric efficiency KL from the intake air quantity Qa and EGR rate or the like in the engine speed of the engine 10 [rpm] and the air-fuel ratio feedback control, the change in the catalyst temperature T _CN in accordance with the map shown in FIG. 7 I can know.

In Figure 7, the temperature Ta to a temperature Tb, the catalyst temperature _{T CN} and from the temperature Tb to a temperature Tc gradually increases, the temperature Tg is the highest catalyst temperature _{T CN.} Further, the temperature Tc in FIG. 7 corresponds to a specific temperature _TNH3 .

Further, in the above-described embodiment, when the catalyst temperature _TCN becomes lower than the specific temperature _TNH3 , the ignition timing is retarded in addition to the air-fuel ratio A / F being changed from stoichiometric to lean. Although the NOx suppression control using the increase in the EGR amount is performed in combination, only one of the retarding of the ignition timing and the increase in the EGR amount may be executed, or other control parameters may be set. It is also conceivable to execute NOx suppression control by changing it.

In the above-described embodiment, the corrosive substance is NH ₃ , but the present invention is applicable even if the amount of the other corrosive substance generated depends on the catalyst temperature and the air-fuel ratio. is there.

As described above, the present invention, the amount of NH ₃ in the exhaust gas purifying catalyst depends on the catalyst temperature and the air-fuel ratio, and focusing on the fact that the amount of generated particularly NH ₃ in a temperature range of less than a predetermined temperature T _NH3 increases Te, based on the catalyst temperature T _CN in anticipation of an increase in NH ₃ emission under catalytic unit 42, in which effectively reduces in advance the increase of the generation amount of NH _3. As a result, it is possible to provide an inexpensive control device for an internal combustion engine that can effectively reduce the generation amount of corrosive substances such as NH ₃ without reducing the NOx suppression effect. The present invention as described above is useful for all control devices for internal combustion engines that suppress an increase in the amount of corrosive substances generated with the catalytic action of the exhaust purification catalyst.

10 Engine (Internal combustion engine)
11 Cylinder 14 Spark plug 16 Intake valve 17 Exhaust valve 18 Intake passage 19 Exhaust passage 19 Injector 30 Intake device 31 Intake pipe 32 Air flow meter 33 Throttle valve 34 Throttle opening sensor 40 Exhaust device 41 Exhaust pipe 42 Catalyst unit 42a Three-way catalyst 43 Air-fuel ratio sensor 44 Catalyst temperature sensor (catalyst temperature detection mechanism)
50 EGR device 51 Exhaust gas recirculation passage 52 EGR valve 61 Crank angle sensor 100 ECU (ignition timing control mechanism, exhaust gas recirculation control mechanism, feedback control mechanism)
AF1, AF2 Air-fuel ratio Aev ₀ Basic EGR opening Aev EGR opening Q _NH3 NH ₃ generation amount T1, T _NH3 specific temperature tp ₀ Basic ignition timing tp Ignition timing ΔAF Constant air-fuel ratio change ΔT _CN Catalyst temperature change β Ignition timing correction coefficient γ EGR opening correction coefficient φ Equivalent ratio (1 / air excess ratio)

Claims (6)

An internal combustion engine having a catalyst unit for purifying exhaust when the exhaust air-fuel ratio of the internal combustion engine is a specific air-fuel ratio and an exhaust gas recirculation passage capable of recirculating a part of exhaust gas downstream of the catalyst unit to the intake side An internal combustion engine control device that is equipped and controls the exhaust air-fuel ratio to the specific air-fuel ratio and suppresses the amount of corrosive substances generated in the exhaust;
When the amount of the corrosive substance generated in the catalyst unit differs depending on whether the temperature of the catalyst unit is higher or lower than a specific temperature,
When the temperature of the catalyst unit is on the low temperature side that increases the generation amount of the corrosive substance, the exhaust air / fuel ratio is controlled to a value on the lean combustion side than the specific air / fuel ratio. Control device. In the catalyst unit, both the generation amount of the corrosive substance and the rate of change of the generation amount of the corrosive substance with respect to the temperature change of the catalyst unit are such that the temperature of the catalyst unit is higher than the specific temperature. Depending on whether it is on the low temperature side or
2. The control device for an internal combustion engine according to claim 1, wherein the specific temperature is set in a temperature range in which a rate of change of the generation amount of the corrosive substance with respect to a unit temperature change of the catalyst unit is switched.   The control device for an internal combustion engine according to claim 2, wherein the temperature range includes 550 degrees Celsius. The internal combustion engine is a spark ignition type;
An ignition timing control mechanism for controlling the ignition timing of the internal combustion engine based on at least the engine speed and the intake air amount of the internal combustion engine;
An exhaust gas recirculation control mechanism that is disposed on the exhaust gas recirculation path and variably controls the opening degree of the exhaust gas recirculation path;
When the temperature of the catalyst unit is on the lower temperature side than the specific temperature, the ignition timing control mechanism is configured to calculate the ignition timing of the internal combustion engine based on at least the engine speed and the intake air amount. The control apparatus for an internal combustion engine according to any one of claims 1 to 3, wherein the ignition timing is corrected to an ignition timing that is retarded from the timing. An exhaust gas recirculation control mechanism that variably controls an exhaust gas recirculation rate of recirculation to the intake side through the exhaust gas recirculation passage;
The exhaust gas recirculation control mechanism determines the exhaust gas recirculation rate when the temperature of the catalyst unit is on the lower temperature side than the specific temperature, and the exhaust gas when the temperature of the catalyst unit is on the higher temperature side than the specific temperature. The control device for an internal combustion engine according to any one of claims 1 to 4, wherein the control rate is higher than a recirculation rate. The catalyst unit is composed of a three-way catalyst;
An air-fuel ratio sensor that detects the exhaust air-fuel ratio of the internal combustion engine, and feedback that feedback-controls the fuel consumption of the internal combustion engine so that the exhaust air-fuel ratio matches the specific air-fuel ratio based on detection information of the air-fuel ratio sensor 6. The control apparatus for an internal combustion engine according to claim 1, further comprising a control mechanism.

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