JP2014074385A - Control device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control device of an internal combustion engine capable of suppressing generation of NHin a three-way catalyst with an inexpensive constitution without increasing costs.SOLUTION: A control device of an internal combustion engine including an EGR system having an EGR passage communicating an exhaust passage at a downstream side with respect to a catalyst unit, with an intake passage, and an EGR valve for opening and closing the EGR passage, and allowing a part of exhaust from the exhaust passage to flow back to the intake passage through the EGR passage, further includes an ECU executing, as NOx concentration decrease control, at least one of ignition delay control, opening increase control of the EGR valve, injection sharing ratio increase control, and valve overlap quantity increase control under a condition that a catalyst temperature Tis a predetermined temperature Tor less.

Description

  The present invention relates to a control device for an internal combustion engine equipped with an EGR system that recirculates a part of exhaust gas to an intake passage from the downstream side of a three-way catalyst.

In this type of internal combustion engine, NH ₃ (ammonia) generated by the three-way catalyst and chlorine in the fuel combine to produce NH ₄ Cl (ammonium chloride) that causes a strong corrosion reaction, which is generated in the EGR system. May remain. When the remaining NH ₄ Cl is dissolved by the condensed water generated in the EGR system, a highly concentrated chlorine ion solution is generated, which may cause corrosion of the components of the EGR system. In an internal combustion engine equipped with an EGR system, it has been desired to reduce NH ₃ which can be a corrosion factor.

Conventionally, as a method for removing NH ₃ , a catalyst in which Cu (copper) is supported on a carrier mainly composed of SiO ₂ (silicon dioxide), Al ₂ O ₃ (aluminum oxide), and H ₂ O (water) is used. There is known a method for purifying NH _{3 in} a gas in which NH ₃ is combusted by contacting a gas containing ₃ (see, for example, Patent Document 1).

JP-A-56-108516

However, the NH ₃ purification method described in Patent Document 1 described above has a problem that the manufacturing cost increases because a catalyst for removing NH ₃ is required.

The present invention has been made to solve the above-described problems, and provides a control device for an internal combustion engine that can suppress generation of NH _{3 in} a three-way catalyst with an inexpensive configuration without increasing costs. The purpose is to do.

  In order to achieve the above object, the control apparatus for an internal combustion engine according to the present invention includes: (1) an EGR passage that connects an exhaust passage downstream of a three-way catalyst and an intake passage; and an EGR valve that opens and closes the EGR passage. And a control device for an internal combustion engine having an EGR system that recirculates a part of the exhaust gas from the exhaust passage to the intake passage through the EGR passage, wherein the temperature of the three-way catalyst is predetermined. On the condition that the temperature is equal to or lower than the temperature, the control unit includes a control unit that executes NOx concentration reduction control for reducing the NOx concentration on the upstream side of the three-way catalyst.

With this configuration, the control apparatus for an internal combustion engine according to the present invention provides NOx concentration reduction control for reducing the NOx concentration on the upstream side of the three-way catalyst on condition that the temperature of the three-way catalyst is equal to or lower than a predetermined temperature. Execute. For this reason, the control apparatus for an internal combustion engine according to the present invention controls the NOx concentration on the upstream side of the three-way catalyst by controlling, for example, the operating state of the internal combustion engine in a temperature region where the amount of NH ₃ generated in the three-way catalyst increases. Can be reduced. As a result, the amount of NH ₃ generated that increases as the NOx concentration increases can be reduced. Therefore, the control apparatus for an internal combustion engine according to the present invention does not need to be provided with a dedicated catalyst for suppressing NH ₃ as in the prior art, and therefore can be a corrosion factor of the EGR system with an inexpensive configuration without increasing the cost. Generation of NH _{3 in} the original catalyst can be suppressed.

  The control apparatus for an internal combustion engine according to the present invention is the control apparatus for an internal combustion engine according to the above (1), wherein (2) the control means retards the ignition timing of the internal combustion engine as the NOx concentration reduction control. It has a configuration for performing retardation control.

With this configuration, the control apparatus for an internal combustion engine according to the present invention performs the ignition delay control for retarding the ignition timing of the internal combustion engine as the NOx concentration reduction control, so that the combustion temperature in the internal combustion engine can be reduced. Thus, it is possible to reduce the generation amount of NOx becomes a cause of NH _3.

  The control apparatus for an internal combustion engine according to the present invention is the control apparatus for an internal combustion engine according to (1) or (2), wherein (3) the control means controls the opening of the EGR valve as the NOx concentration reduction control. It has the structure which performs the opening degree increase control to increase.

With this configuration, the control device for an internal combustion engine according to the present invention performs opening degree increase control for increasing the opening degree of the EGR valve as NOx concentration reduction control, so that the combustion temperature in the internal combustion engine can be reduced. Thus, it is possible to reduce the generation amount of NOx becomes a cause of NH _3.

  An internal combustion engine control apparatus according to the present invention is the internal combustion engine control apparatus according to any one of (1) to (3), wherein (4) the internal combustion engine has an opening / closing timing of at least one of an intake valve and an exhaust valve. The control means controls the variable valve timing mechanism so as to increase the valve overlap amount between the intake valve and the exhaust valve of the internal combustion engine as the NOx concentration lowering control. It has a configuration for performing overlap amount increase control.

With this configuration, the control device for an internal combustion engine according to the present invention performs the valve overlap amount increase control for increasing the valve overlap amount between the intake valve and the exhaust valve of the internal combustion engine as the NOx concentration reduction control. The combustion temperature can be lowered. Thus, it is possible to reduce the generation amount of NOx becomes a cause of NH _3.

  An internal combustion engine control apparatus according to the present invention is the internal combustion engine control apparatus according to any one of (1) to (4), wherein (5) the internal combustion engine includes a cylinder injection valve and a port injection valve as fuel injection valves. The control means has a configuration for performing an injection distribution rate increase control for increasing an injection distribution rate in the in-cylinder injection valve and the port injection valve as the NOx concentration reduction control.

With this configuration, the control device for an internal combustion engine according to the present invention performs fuel injection by the port injection valve by performing injection ratio increase control for increasing the injection distribution ratio in the in-cylinder injection valve and the port injection valve as NOx concentration reduction control. The ratio of the fuel injection amount by the cylinder injection valve to the injection amount is increased. As a result, the combustion temperature in the internal combustion engine can be lowered, and as a result, the amount of NOx that becomes the cause of the generation of NH ₃ can be reduced.

  An internal combustion engine control apparatus according to the present invention is the internal combustion engine control apparatus according to any one of (1) to (5), wherein (6) the control means reduces the compression ratio as the NOx concentration reduction control. It has a configuration for performing the drop control.

With this configuration, the control device for an internal combustion engine according to the present invention performs the compression ratio reduction control for reducing the compression ratio as the NOx concentration reduction control, so that the combustion temperature in the internal combustion engine can be reduced. Thus, it is possible to reduce the generation amount of NOx becomes a cause of NH _3.

  An internal combustion engine control apparatus according to the present invention is the internal combustion engine control apparatus according to any one of (1) to (6), wherein (7) the predetermined temperature is 550 ° C.

With this configuration, the control apparatus for an internal combustion engine according to the present invention, only in the temperature region where the generation amount of NH ₃ is significantly increased, it is possible to execute the NOx concentration reduction control for reducing the generation amount of NOx.

According to the present invention, it is possible to provide a control apparatus for an internal combustion engine capable of suppressing the generation of NH ₃ in the three-way catalyst with an inexpensive configuration without increasing the cost.

1 is a schematic configuration diagram of an internal combustion engine according to an embodiment of the present invention. It is a graph which shows the relationship between the generation amount of NH3 and the catalyst temperature in the catalyst unit which concerns on embodiment of this invention. It is a graph which shows the relationship between the generation amount of NH3 in the catalyst unit which concerns on embodiment of this invention, and NOx density | concentration of a catalyst upstream. It is a flowchart of NOx concentration fall control performed by ECU which concerns on embodiment of this invention. It is a graph which shows the relationship between the NOx density | concentration of the catalyst upstream in embodiment of this invention, and ignition timing. It is a graph which shows the relationship between the NOx density | concentration of the catalyst upstream in embodiment of this invention, and an EGR opening degree. It is a graph which shows the relationship between NOx generation amount in the exhaust gas of the internal combustion engine which concerns on embodiment of this invention, and an in-cylinder / port injection ratio. It is a graph which shows the relationship between the NOx generation amount in the exhaust gas of the internal combustion engine which concerns on embodiment of this invention, and a valve overlap period. It is a graph which shows the relationship between NOx generation amount and the compression ratio in the exhaust gas of the internal combustion engine in the modification of embodiment of this invention. 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 embodiment of this invention.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 shows a schematic configuration of an internal combustion engine equipped with a control device for an internal combustion engine according to the present embodiment. The internal combustion engine according to the present embodiment is a spark ignition type multi-cylinder internal combustion engine equipped with a dual injection system.

  First, the configuration will be described.

  As shown in FIG. 1, an engine 10 as an internal combustion engine according to the present embodiment is constituted by, for example, an in-line four-cylinder four-stroke cycle gasoline engine, and constitutes a travel drive source for a vehicle (not shown). The engine 10 has four cylinders 11 (only one is schematically shown in FIG. 1).

  Each cylinder 11 is formed with a combustion chamber 13 partitioned by a piston 12. Each cylinder 11 is equipped with an intake valve 16 and an exhaust valve 17 that can be opened and closed by a valve operating mechanism including an intake camshaft and an exhaust camshaft (not shown). Further, a spark plug 14 is disposed in each cylinder 11 so as to be exposed in the combustion chamber 13.

  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).

  The engine 10 includes a port injection valve 21 and a cylinder injection valve 22 as fuel injection valves. The port injection valve 21 injects fuel in the intake port. The in-cylinder injection valve 22 directly injects fuel in the combustion chamber 13. The port injection valve 21 and the in-cylinder injection valve 22 are supplied with fuel such as gasoline 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 post-combustion from the combustion chamber 13 when the exhaust valve 17 is opened. An exhaust device 40 having an exhaust passage 19 through which gas can be discharged is mounted.

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

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

  The exhaust device 40 includes an exhaust pipe 41, a catalyst unit 42, an air-fuel ratio sensor 43, and a catalyst temperature sensor 44.

  The exhaust pipe 41 forms the exhaust passage 19. Further, 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 is composed of a three-way catalyst, and is mounted on the exhaust pipe 41 as an exhaust purification unit. The catalyst unit 42 incorporates a known three-way catalyst 42a, and the air-fuel ratio (combustion air-fuel ratio) in the combustion chamber 13 is controlled to the stoichiometric air-fuel ratio, so that the exhaust air-fuel ratio of the engine 10 becomes a specific air-fuel ratio. When 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.

  The air-fuel ratio sensor 43 detects the exhaust air-fuel ratio in the vicinity of the catalyst unit 42, for example, in the exhaust passage 19 on the downstream side of the catalyst unit 42. The air-fuel ratio sensor 43 is composed of, for example, a known concentration cell type exhaust oxygen concentration sensor (O2 sensor), and has a characteristic that the electromotive force rises sharply on the rich side where unburned fuel gas remains with the theoretical air-fuel ratio as a boundary. have. The catalyst temperature sensor 44 detects the catalyst temperature of the catalyst unit 42.

  The engine 10 is further equipped with an EGR device (EGR system) 50. The EGR device 50 includes an EGR passage 51, an EGR valve 52, and an EGR cooler 53.

  The EGR passage 51 communicates the exhaust passage 19 and the intake passage 18 on the downstream side of the catalyst unit 42. Therefore, the EGR device 50 can recirculate part of the exhaust gas from the exhaust passage 19 downstream of the catalyst unit 42 to the intake passage 18 via the EGR passage 51. Although not shown in detail, the EGR passage 51 is formed by, for example, an EGR pipe and a part of an exhaust manifold.

The EGR valve 52 is provided near the end of the EGR passage 51 on the intake passage 18 side, and opens and closes the EGR passage 51. Further, the EGR valve 52 indicates an 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 EGR passage 51. The valve opening, that is, the EGR valve opening A _egr can be changed according to the input opening control signal so as to be variably controlled.

  The EGR cooler 53 cools the recirculated exhaust gas passing through the EGR passage 51 by heat exchange with the cooling water of the engine 10.

  Further, the engine 10 includes an intake camshaft and an exhaust camshaft that are not shown as variable valve timing (VVT) mechanisms capable of changing the opening / closing timing of at least one of the intake valve 16 and the exhaust valve 17. Are provided with an intake side VVT 25 and an exhaust side VVT 26. Such a variable valve timing mechanism can change the opening / closing timing of at least one of the intake valve 16 and the exhaust valve 17, and the length of the period during which the intake valve 16 and the exhaust valve 17 are simultaneously open (the valve overlap amount). Size) can be controlled. Specifically, the intake side VVT 25 and the exhaust side VVT 26 change the valve opening / closing timing by changing the rotation phase of the intake cam shaft or the exhaust cam shaft with respect to the crankshaft 15, respectively. In the present embodiment, for example, a vane type is adopted as the intake side VVT 25 and the exhaust side VVT 26.

On the other hand, in addition to the intake air amount signal Qa and the throttle opening signal Athv, the ECU 100 receives the exhaust air / fuel ratio signal AF from the air / fuel ratio sensor 43 and the temperature detection signal (catalyst temperature T _SC ) from the catalyst temperature sensor 44. The Further, the ECU 100 receives a crank angle signal CA from the crank angle sensor 61, a cooling water temperature signal Tw indicating the cooling water temperature of the engine 10 from the water temperature sensor 62, a required opening signal Accp from the accelerator opening sensor 63, and other in-vehicle ECUs (not shown). Request signal or the like 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), and a backup memory, and further includes an input interface circuit including an A / D converter and the like, a driver and a relay switch. An output interface circuit and a communication interface with other vehicle-mounted ECUs are included.

  The ECU 100 opens the throttle valve 33 and determines the ignition timing so as to realize the output (torque and engine speed) required for the engine 10 in accordance with a control program stored in a ROM or a backup memory (hereinafter referred to as a ROM). The fuel injection timing, the fuel injection amount, and the like are each controlled.

For example, the ECU 100 functions as an ignition timing control mechanism that controls the ignition timing τ in each cylinder 11 by an ignition signal to the ignition plug 14 based on at least the engine speed Ne [rpm] and the intake air amount Qa. 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. Furthermore, the ECU 100 also functions as an exhaust gas recirculation control mechanism that variably controls the control signal based on the opening degree A _egr to the EGR valve 52.

  Further, the ECU 100 obtains the required fuel injection amount of the engine 10 as a whole based on the engine operating state such as the engine speed Ne and the engine load, and the port injection valve 21 so as to obtain the required fuel injection amount according to the injection distribution ratio described later. In addition, fuel injection from the in-cylinder injection valve 22 is performed.

  In the present embodiment, the above-described injection division ratio is expressed as a ratio of the in-cylinder injection amount to the total injection amount. Therefore, when the value is “1.0”, all fuel is injected into the cylinder, and when the value is “0”, all fuel is injected into the intake port. Hereinafter, such an injection ratio is referred to as an in-cylinder / port injection ratio.

  The in-cylinder / port injection ratio is mapped and stored in advance as an injection ratio map in accordance with, for example, the operation region set based on the engine load and the engine speed Ne.

  The ECU 100 further detects the engine speed Ne of the engine 10 by taking in a pulse signal corresponding to the rotational speed Ne [rpm] of the crankshaft 15 from the crank angle sensor 61.

Moreover, ECU 100 is a condition that the catalyst temperature _{T SC} inputted from the catalyst temperature sensor 44 is below a predetermined temperature _{T NH3} predetermined, NOx concentration reduction control for reducing the NOx concentration on the upstream side of the catalyst unit 42 Is supposed to run.

  Specifically, the ECU 100 performs ignition delay control for retarding the ignition timing of the engine 10, opening increase control for increasing the opening of the EGR valve 52, and the intake valve 16 of the engine 10 as the NOx concentration reduction control described above. At least one of the valve overlap amount increase control for increasing the valve overlap amount between the exhaust valve 17 and the exhaust valve 17 and the injection ratio increase control for increasing the in-cylinder / port injection ratio in the in-cylinder injection valve 22 and the port injection valve 21. Is supposed to run. ECU 100 in the present embodiment constitutes a control means according to the present invention. Each control described above will be described later.

Next, the relationship between the amount of NH ₃ generated as a corrosive substance in the catalyst unit 42 and the catalyst temperature will be described with reference to FIG.

As shown in FIG. 2, the catalyst unit 42, the temperature of the surface portion near the three-way catalyst 42a is in contact with the exhaust gas (a catalyst bed temperature; hereinafter, referred to as the catalyst temperature T _SC) is the predetermined temperature T _{NH3 [°} C.] or less Then, NH ₃ generation amount Q _NH3 which is a corrosive substance in the catalyst unit 42 has a temperature characteristic that increases rapidly.

Specifically, the catalyst unit 42, while the predetermined temperature _{T NH3} [° C.] rate of change in generation amount _{Q NH3} of NH ₃ to a unit temperature change of the catalyst temperature _{T SC} in higher temperature range is relatively small , the predetermined temperature _{T NH3} [° C.] or less in the temperature range change rate of the generation amount _{Q NH3} of NH ₃ to a unit temperature change of the catalyst temperature _{T SC} becomes remarkably large. Thus, the amount _{Q NH3} of NH ₃ depends on the catalyst temperature _{T SC.} Here, the predetermined temperature T _NH3 [° C.] is 550 [° C.].

When the amount of NH ₃ generated Q _NH3 increases, NH ₃ Cl that is generated combines with chlorine in the fuel to generate NH ₄ Cl that causes a strong corrosion reaction, which may remain in the EGR device 50. Residual NH ₄ Cl may cause corrosion of, for example, an EGR pipe that forms the EGR passage 51 of the EGR device 50.

Further, as shown in FIG. 3, the NH ₃ generation amount Q _NH3 in the catalyst unit 42 depends on the NOx concentration upstream of the catalyst unit 42, and the NOx concentration upstream of the catalyst unit 42 becomes high. There is a tendency to increase. Therefore, if the NOx concentration on the upstream side of the catalyst unit 42 can be reduced, the NH ₃ generation amount Q _NH3 can be reduced.

  Here, the NOx concentration is the ratio of NOx contained in the exhaust gas, and the NOx concentration increases as the amount of NOx generated per unit time increases. The NOx concentration or the amount of NOx generated per unit time depends on the combustion temperature of the engine 10 and increases as the combustion temperature of the engine 10 increases. Therefore, in order to reduce the NOx concentration or the amount of NOx generated per unit time, it is necessary to lower the combustion temperature of the engine 10.

Therefore, in the present embodiment, when the catalyst temperature _{T SC} is that reaches a predetermined temperature _{T NH3 [℃] (= 550} [℃]) or less, NOx concentrations as described above in order to suppress the generation amount _{Q NH3} of NH ₃ Lowering control is executed.

  Next, with reference to FIG. 4, the NOx concentration lowering control executed by ECU 100 according to the present embodiment will be described. This control is repeatedly executed every predetermined time while the engine 10 is in operation. Here, in the present embodiment, a case will be described in which all of the above-described ignition retard control, opening increase control, injection ratio increase control, and valve overlap amount increase control are executed as NOx concentration reduction control. Needless to say, it is not necessary to execute all these controls, and it is possible to execute one or a plurality of controls in combination as necessary.

As shown in FIG. 4, ECU 100, first detecting the catalyst temperature _{T SC} based on the input value from the catalyst temperature sensor 44 (step S11).

Then, ECU 100 is detected catalyst temperature _{T SC} is equal to or a predetermined temperature _{T NH3 (= 550 [℃]} ) or less (step S12).

ECU100, when the detected catalyst temperature _{T SC} is determined that the predetermined temperature _{T NH3 (= 550 [℃]} ) not below _{(T SC>} T _NH3), the process is ended without executing the NOx concentration reduction control . That is, the ECU 100 sets the ignition timing τ of the engine 10 to the normal ignition timing τ ₀ (step S17), and sets the EGR valve opening A _egr of the EGR valve 52 to the normal EGR valve opening A _egr0 (step S17). S18) Further, the in-cylinder / port injection ratio ζ in the engine 10 is set to the normal in-cylinder / port injection ratio ζ ₀ (step S19), and the intake VVT advance amount ν _{in is set} to the normal intake VVT advance angle. set the amount _{[nu in0,} and sets the exhaust VVT advancement amount _{[nu out} the normal intake VVT advancement amount _{[nu out0} (step S20).

Here, the normal ignition timing τ ₀ is an ignition timing calculated based on at least the engine speed Ne and the intake air amount Qa. Further, the normal EGR valve opening A _egr0 is obtained by previously storing the EGR valve opening corresponding to the basic EGR amount for each operation state specified from the fuel injection amount and the engine rotational speed Ne. This is the EGR valve opening calculated based on the basic EGR amount map. The normal in-cylinder / port injection ratio ζ ₀ is an in-cylinder / port injection ratio calculated by referring to a pre-stored injection ratio map based on the engine load and the engine speed Ne. . Further, the normal intake VVT _{advance amount} ν _in0 and the normal intake VVT _{advance amount} ν _out0 are set so that the valve overlap amount (period) between the intake valve 16 and the exhaust valve 17 is normally set based on the operating state of the engine 10. The intake VVT advance amount and the exhaust VVT advance amount are such that the valve overlap amount (period) is set.

Meanwhile, ECU 100 is in the case where the catalyst temperature _{T SC} is determined to be the predetermined temperature _{T NH3 (= 550 [℃]} ) or less in step _{S12 (T SC ≦ T NH3)} , step S13~ step as NOx concentration reduction control Each control of S16 is performed and this process is complete | finished.

That is, the ECU 100 performs ignition delay control that retards the ignition timing τ of the engine 10 with respect to the normal ignition timing τ ₀ (step S13). By this ignition retardation control, the combustion temperature of the engine 10 is lowered, and the NOx concentration on the upstream side of the catalyst unit 42 is lowered as shown in FIG.

Next, the ECU 100 performs opening degree increase control for increasing the EGR valve opening degree A _egr from the normal EGR valve opening degree A _egr0 (step S14). For example, the ECU 100 calculates the final EGR valve opening by multiplying the normal EGR valve opening A _egr0 calculated based on the basic EGR amount map by a predetermined correction coefficient, and uses this as the EGR valve opening A _egr. be able to. By this opening degree increase control, the EGR rate increases, and the flow rate of the exhaust gas recirculated to the intake passage 18 increases. As a result, the combustion temperature of the engine 10 decreases, and the NOx concentration on the upstream side of the catalyst unit 42 is decreased as shown in FIG.

Next, the ECU 100 performs an injection ratio increase control for increasing the in-cylinder / port injection ratio ζ in the engine 10 from the normal in-cylinder / port injection ratio ζ ₀ (step S15). By this injection division ratio increase control, the ratio of the in-cylinder injection amount to the total injection amount for the engine 10 is increased. As a result, the combustion temperature of the engine 10 is lowered, and the amount of NOx generated per unit time is reduced as shown in FIG. 7, and as a result, the NOx concentration on the upstream side of the catalyst unit 42 is lowered.

  Next, the ECU 100 controls the intake side VVT 25 and the exhaust side VVT 26 so that the valve overlap amount (period) between the intake valve 16 and the exhaust valve 17 is increased (longer) than the normally set valve overlap amount (period). The valve overlap amount increase control is performed (step S16).

Specifically, the ECU 100 controls the intake side VVT ₂₅ to increase the intake VVT _{advance amount} ν _in from the normal intake VVT _advance amount ν _in0 , that is, advance the opening timing of the intake valve 16. At the same time, the ECU 100 controls the exhaust side VVT _{26 so as} to reduce the exhaust VVT advance amount ν _out from the normal intake VVT _{advance amount} ν _out0 , that is, retard the valve closing timing of the exhaust valve 17. Thereby, the valve overlap amount (period) between the intake valve 16 and the exhaust valve 17 is increased (longer). Note that the valve overlap amount (period) described above may be increased (longened) only by either advancement of the valve opening timing of the intake valve 16 or delay of the valve closing timing of the exhaust valve 17. .

When the valve overlap amount (period) is increased (longer) by this valve overlap amount increase control, the amount of exhaust gas remaining in the air-fuel mixture increases, and the inert gas such as CO ₂ contained in the exhaust gas is increased. The combustion temperature in the fuel chamber 13 is lowered by the gas. As a result, as shown in FIG. 8, the amount of NOx generated per unit time is reduced, and as a result, the NOx concentration on the upstream side of the catalyst unit 42 is reduced. In addition, the dotted line in FIG. 8 is the valve overlap amount (period) set normally.

Thus, in the present embodiment, by the NOx concentration reduction control shown in FIG. 4 is repeated at a short cycle, the operation region where the catalyst temperature T _SC is equal to or less than a predetermined temperature T _NH3, as shown in step S13-S16 Ignition retardation control, opening degree increase control, injection split ratio increase control, and valve overlap amount increase control are executed as NOx concentration reduction control.

On the other hand, the catalyst temperature _{T SC} is in the operation region which is not less than the predetermined temperature _{T NH3,} so that the control of the consequences shown in step S17-S20 are performed.

As described above, the control apparatus for an internal combustion engine according to the present embodiment reduces the NOx concentration on the upstream side of the catalyst unit 42 on condition that the catalyst temperature T _SC is equal to or less than the predetermined temperature T _NH3 predetermined The NOx concentration lowering control is executed. For this reason, the control apparatus for an internal combustion engine according to the present embodiment controls, for example, the operating state of the engine 10 in the temperature region where the amount of NH ₃ generated in the three-way catalyst 42a increases, thereby upstream of the catalyst unit 42. NOx concentration can be reduced. As a result, the amount of NH ₃ generated that increases as the NOx concentration increases can be reduced. Therefore, the control device for the internal combustion engine according to the present embodiment does not need to be provided with a dedicated catalyst for suppressing NH ₃ as in the prior art, and therefore, the corrosion factor of the EGR device 50 with an inexpensive configuration without increasing the cost. The generation of NH ₃ in the possible three-way catalyst 42a can be suppressed. In particular, according to the control apparatus for an internal combustion engine according to the present embodiment, in the catalyst temperature T _SC is below the predetermined temperature T _NH3 state, reducing the generated amount of NH ₃ in substantially three-way catalyst 42a as compared with the conventional Can be made.

Further, the control device for the internal combustion engine according to the present embodiment performs ignition delay control for retarding the ignition timing τ of the engine 10 as NOx concentration reduction control, so that the combustion temperature in the engine 10 can be reduced. Thus, it is possible to reduce the generation amount of NOx becomes a cause of NH _3.

Further, the control device for the internal combustion engine according to the present embodiment performs the opening degree increase control for increasing the EGR valve opening degree A _egr as the NOx concentration reduction control, so that the combustion temperature in the engine 10 can be reduced. Thus, it is possible to reduce the generation amount of NOx becomes a cause of NH _3.

Further, the internal combustion engine control apparatus according to the present embodiment performs the valve overlap amount increase control for increasing the valve overlap amount between the intake valve 16 and the exhaust valve 17 of the engine 10 as the NOx concentration reduction control. The combustion temperature at 10 can be reduced. Thus, it is possible to reduce the generation amount of NOx becomes a cause of NH _3.

In addition, the control device for an internal combustion engine according to the present embodiment performs port injection rate increase control by increasing the injection distribution rate ζ in the in-cylinder injection valve 22 and the port injection valve 21 as NOx concentration reduction control. The ratio of the fuel injection amount by the in-cylinder injection valve 22 to the fuel injection amount by the valve 21 is increased. As a result, the combustion temperature in the engine 10 can be lowered, and as a result, the amount of NOx that becomes the cause of the generation of NH ₃ can be reduced.

  In the present embodiment, the configuration in which the compression ratio of the engine 10 is not variable has been described. However, the present invention is not limited to this. For example, the engine 10 may be configured to change the compression ratio.

  As a configuration capable of changing the compression ratio, for example, a variable compression ratio variable mechanism that can change the compression ratio mechanically is provided, or a configuration in which the substantial compression ratio is changed by changing the closing timing of the intake valve 16 Etc. can be adopted.

  As the variable compression ratio mechanism, various configurations for changing the cylinder volume and changing the stroke of the piston 12 can be adopted. For example, the relative position between the cylinder head and the cylinder block of the engine 10 is changed by an actuator. Thus, a mechanism for changing the cylinder length can be used. Such a mechanism has a simple configuration and can simplify the overall configuration. Of course, other variable mechanisms such as a configuration using a bent connecting rod or a configuration using an eccentric piston pin may be employed.

  In the configuration in which the compression ratio is changed without using the variable compression ratio mechanism, the closing timing of the intake valve 16 is utilized by utilizing the fact that the substantial compression stroke is between the position where the intake valve 16 is closed and the top dead center. The substantial compression ratio can be changed by changing.

In the engine 10 in which the compression ratio can be changed, as the above-described NOx concentration reduction control, the compression ratio reduction control for reducing the compression ratio η of the engine 10 to be lower than the normal compression ratio η ₀ is performed using the above-described controls (ignition delay). (Angle control, opening increase control, injection division rate increase control, and valve overlap amount increase control). In this case, in addition to performing all the controls including the compression ratio lowering control, it goes without saying that the compression ratio lowering control may be performed alone or in combination with other controls. Here, the above-described normal compression ratio η ₀ is a compression ratio by event control set based on, for example, the intake air amount Qa of the engine 10 or the like.

  When the compression ratio η of the engine 10 is reduced by the compression ratio reduction control, the combustion temperature of the engine 10 is reduced, and the NOx concentration on the upstream side of the catalyst unit 42 is reduced as shown in FIG.

When the engine 10 is configured to change the compression ratio in this way, the combustion temperature in the engine 10 can be lowered because the compression ratio reduction control for reducing the compression ratio is performed as the NOx concentration reduction control. Thus, it is possible to reduce the generation amount of NOx becomes a cause of NH _3.

  Further, in the present embodiment, the air-fuel ratio sensor 43 is constituted by a concentration cell type exhaust oxygen concentration sensor, but the limit of the air-fuel ratio sensor 43 detecting the exhaust air-fuel ratio upstream of the catalyst unit 42 is used. A 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.

Further, in this embodiment, the catalyst temperature T _SC of the catalyst unit 42 has been assumed to be detected by the catalyst temperature sensor 44 is not limited to direct temperature detection by the sensor, using the map shown in FIG. 10, approximate value of the catalyst temperature T _SC based on the engine speed Ne and the volumetric efficiency KL of the engine 10 may be indirectly detected constituting.

  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.

In Figure 10, the temperature Ta to a temperature Tb, and the temperature Tb to a temperature Tc catalyst temperature _{T SC} is gradually increased, shows the temperature Tg is the highest catalyst temperature _{T SC.} Further, the temperature Tc in FIG. 10 corresponds to the specific temperature _TNH3 .

As described above, the control device for an internal combustion engine according to the present invention can suppress the generation of NH ₃ in the three-way catalyst with an inexpensive configuration without increasing the cost, and exhausts from the downstream side of the three-way catalyst. This is useful for a control device for an internal combustion engine equipped with an EGR system that recirculates a part of the engine to the intake passage.

DESCRIPTION OF SYMBOLS 10 ... Engine (internal combustion engine), 16 ... Intake valve, 17 ... Exhaust valve, 18 ... Intake passage, 19 ... Exhaust passage, 21 ... Port injection valve, 22 ... In-cylinder injection valve, 25 ... Intake side VVT (variable valve timing) Mechanism), 26 ... exhaust VVT (variable valve timing mechanism), 42 ... catalyst unit, 42a ... three-way catalyst, 44 ... catalyst temperature sensor, 50 ... EGR device (EGR system), 51 ... EGR passage, 52 ... EGR valve , 100 ... ECU (control means)

Claims (7)

An EGR passage that communicates an exhaust passage downstream of the three-way catalyst and an intake passage, and an EGR valve that opens and closes the EGR passage, and a part of the exhaust from the exhaust passage through the EGR passage. A control device for an internal combustion engine provided with an EGR system for refluxing a passage,
Control means for performing NOx concentration reduction control for reducing the NOx concentration on the upstream side of the three-way catalyst, provided that the temperature of the three-way catalyst is equal to or lower than a predetermined temperature. A control device for an internal combustion engine.   2. The control device for an internal combustion engine according to claim 1, wherein the control means performs ignition retard control for retarding an ignition timing of the internal combustion engine as the NOx concentration reduction control.   The control device for an internal combustion engine according to claim 1 or 2, wherein the control means performs opening degree increase control for increasing the opening degree of the EGR valve as the NOx concentration reduction control. The internal combustion engine includes a variable valve timing mechanism capable of changing an opening / closing timing of at least one of an intake valve and an exhaust valve,
The control means performs a valve overlap amount increase control for controlling the variable valve timing mechanism so as to increase a valve overlap amount between an intake valve and an exhaust valve of the internal combustion engine as the NOx concentration reduction control. The control device for an internal combustion engine according to any one of claims 1 to 3. The internal combustion engine includes a cylinder injection valve and a port injection valve as fuel injection valves,
5. The control unit according to claim 1, wherein the control unit performs injection ratio increase control for increasing an injection ratio in the cylinder injection valve and the port injection valve as the NOx concentration reduction control. The control device for an internal combustion engine according to claim 1.   6. The control device for an internal combustion engine according to claim 1, wherein the control unit performs compression ratio reduction control for reducing a compression ratio as the NOx concentration reduction control.   The control apparatus for an internal combustion engine according to any one of claims 1 to 6, wherein the predetermined temperature is 550 ° C.

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