JP4042546B2 - Control device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a control device for an internal combustion engine having a turbocharger having a NOx absorber on an exhaust passage and an electric motor incorporated in a turbine / compressor.
[0002]
[Prior art]
In recent years, there has been a growing demand for improved fuel economy and cleaner exhaust gas, and lean burn engines and the like have been put into practical use. In lean burn engines, NOx absorbents are used in combination with a three-way catalyst to purify NOx emitted during lean burn, and NOx storage reduction type exhaust purification catalysts are used. The purification rate is improved. The NOx absorber has the property of absorbing nitrogen oxide NOx when the exhaust air-fuel ratio of the inflowing exhaust gas is lean and releasing the nitrogen oxide NOx absorbed when it is rich or stoichiometric. NOx discharged during lean is absorbed and occluded once, and released when the exhaust air-fuel ratio becomes rich or stoichiometric, and is purified by a three-way catalyst (in the case of a NOx occlusion reduction exhaust purification catalyst). In order to forcibly purify the stored NOx, a so-called rich spike or the like that forcibly enriches the exhaust air-fuel ratio for a short time may be performed.
[0003]
[Patent Document 1]
JP-A-2001-55946
[Problems to be solved by the invention]
As an internal combustion engine that performs rich spike, one described in [Patent Document 1] is known. In the internal combustion engine described in [Patent Document 1], the supercharging pressure by the turbocharger is increased so as to promote atomization of the injected fuel that is increased during a rich spike. When a rich spike is performed in an internal combustion engine having a turbocharger, exhaust energy increases and the boost pressure rises, so that there is a tendency that it is difficult to become rich. In [Patent Document 1], the supercharging pressure is further increased to increase atomization (intake air amount is increased), so that the exhaust air / fuel ratio cannot be made sufficiently rich and the effect of rich spike cannot be obtained sufficiently. Is concerned.
[0005]
In the internal combustion engine of the present invention, a turbocharger with an electric motor in which an electric motor (motor) is incorporated in a turbine / compressor is attached, and the electric motor is driven to forcibly drive the turbine / compressor to perform supercharging. It is possible to assist or make the electric motor perform regenerative power generation using exhaust energy. The object of the present invention is to use a turbocharger with an electric motor to make the exhaust air-fuel ratio rich and to release NOx from the NOx absorbent (for example, during a rich spike) more reliably and earlier. An object of the present invention is to provide a control device for an internal combustion engine that can be discharged.
[0006]
[Means for Solving the Problems]
The control apparatus for an internal combustion engine according to claim 1 is disposed on an exhaust passage of the internal combustion engine and absorbs nitrogen oxide NOx when the exhaust air-fuel ratio of the inflowing exhaust gas is lean and absorbs when it is rich or stoichiometric. NOx absorber that emits nitrogen oxides NOx, a turbocharger that is attached to the internal combustion engine, and the turbocharger's turbine / compressor can be rotated by the exhaust flow to change the supercharging pressure and exhaust An electric motor capable of performing regenerative power generation by energy and a motor control means for controlling driving / regenerative power generation of the motor, the motor control means forcing the exhaust air-fuel ratio to be rich and the NOx absorbed from the NOx absorbent when released, the motor state drive state, regenerative power generation state, to determine which of the drive stop and regeneration power generation stop state, if the electric motor is determined to be in the driving state, Motor is characterized in that when it is determined that the drive is stopped and regeneration power generation stop state, controls the electric motor so as to change the state of the electric motor to reduce the intake air amount.
[0007]
According to a second aspect of the present invention, in the control apparatus for an internal combustion engine according to the first aspect, when it is determined that the electric motor is in a driving state, the electric motor control means drives the motor to stop / regenerate the state of the electric motor. It is characterized in that the amount of intake air is reduced by changing to a power generation stop state.
The invention according to claim 3 is the control device for an internal combustion engine according to claim 2, wherein the motor control means further changes the state of the motor to a regenerative power generation state to reduce the intake air amount. It is said.
According to a fourth aspect of the present invention, in the control device for an internal combustion engine according to the first aspect, when the electric motor is in a drive stop / regenerative power generation stop state, the motor control means changes the state of the motor into the regenerative power generation state This is characterized in that the intake air amount is reduced by changing to.
In the control device for an internal combustion engine according to claim 3 or 4, the motor control means increases the regenerative power generation amount recovered from the motor to reduce the intake air amount. It is a feature.

[0008]
The control device for an internal combustion engine according to claim 6 is disposed on the exhaust passage of the internal combustion engine , absorbs nitrogen oxide NOx when the exhaust air-fuel ratio of the exhaust gas flowing in is lean , and is rich or stoichiometric. The supercharging pressure can be changed by rotating the turbine / compressor of the turbocharger by the NOx absorbent that discharges nitrogen oxide NOx that is sometimes absorbed, the turbocharger attached to the internal combustion engine, and the exhaust flow. And an electric motor capable of performing regenerative power generation using exhaust energy and a motor control means for controlling driving / regenerative power generation of the motor, and the motor control means forcibly made the exhaust air-fuel ratio rich and absorbed from the NOx absorbent. when NOx is released, it is determined to motor state drive state, regenerative power generation state, to determine which of the drive stop and regeneration power generation stop state, the motor is in regenerative power generation state If the is characterized by controlling the electric motor so as to increase the regenerative power generation amount of recovered from the electric motor to reduce the intake air amount.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the control device of the present invention will be described below. An engine 1 having a control device of the present embodiment is shown in FIG.
[0010]
The engine 1 described in the present embodiment is a multi-cylinder engine, but only one cylinder is shown in FIG. 1 as a sectional view. The engine 1 is a type of engine in which fuel is injected onto the upper surface of a piston 4 in a cylinder 3 by an injector 2. The engine 1 is capable of stratified combustion and is a so-called lean burn engine. By supercharging more intake air with a turbocharger, which will be described later, and performing lean burn, not only high output but also low fuel consumption can be realized.
[0011]
The engine 1 compresses the air sucked into the cylinder 3 through the intake passage 5 by the piston 4, and injects fuel into a recess formed in the upper surface of the piston 4 to bring a rich air-fuel mixture near the spark plug 7. These can be collected and ignited by a spark plug 7 and burned (stratified combustion). If fuel is injected during the intake stroke, normal homogeneous combustion can also be performed. An intake valve 8 opens and closes the inside of the cylinder 3 and the intake passage 5. The exhaust gas after combustion is exhausted to the exhaust passage 6. An exhaust valve 9 opens and closes the inside of the cylinder 3 and the exhaust passage 6. On the intake passage 5, an air cleaner 10, an air flow meter 27, a turbo unit 11, an intercooler 12, a throttle valve 13 and the like are arranged from the upstream side.
[0012]
The air cleaner 10 is a filter that removes dust and dirt in the intake air. The air flow meter 27 of this embodiment is of a hot wire type and detects the amount of intake air as a mass flow rate. The turbo unit 11 is disposed between the intake passage 5 and the exhaust passage 6 and performs supercharging. In the turbo unit 11 of the present embodiment, the turbine side impeller and the compressor side impeller are connected by a rotating shaft (hereinafter, this portion is simply referred to as a turbine / compressor 11a).
[0013]
In addition, the turbocharger of this embodiment is a turbocharger with an electric motor in which an electric motor 11b is incorporated so that the rotating shaft of the turbine / compressor 11a becomes an output shaft. The electric motor 11b can also function as a generator that generates electric power using exhaust energy. The turbo unit 11 can also function as a normal supercharger that performs supercharging only by exhaust energy, but can further perform supercharging by forcibly driving the turbine / compressor 11a by the electric motor 11b. .
[0014]
Further, by using the exhaust energy, the electric power can be regenerated by rotating the electric motor 11b through the turbine / compressor 11a, and the generated electric power can be recovered. The electric motor 11b has a rotor fixed to the rotating shaft of the turbine / compressor 11a and a stator disposed around the rotor as main components. On the downstream side of the turbo unit 11 on the intake passage 5, an air-cooled intercooler 12 is disposed that lowers the temperature of the intake air whose temperature has increased as the pressure has increased due to supercharging by the turbo unit 11. The temperature of the intake air is lowered by the intercooler 12 to improve the filling efficiency.
[0015]
A throttle valve 13 that adjusts the amount of intake air is disposed downstream of the intercooler 12. The throttle valve 13 of the present embodiment is a so-called electronically controlled throttle valve, and an operation amount of the accelerator pedal 14 is detected by an accelerator positioning sensor 15, and the ECU 16 detects the throttle valve 13 based on this detection result and other information amounts. Is determined. The throttle valve 13 is opened and closed by a throttle motor 17 that is provided in association therewith. Further, a throttle positioning sensor 18 that detects the opening degree of the throttle valve 13 is also provided.
[0016]
A pressure sensor 19 for detecting the pressure (supercharging pressure / intake pressure) in the intake passage 5 is disposed on the downstream side of the throttle valve 13. These sensors 15, 18, 19, and 27 are connected to the ECU 16, and the detection results are sent to the ECU 16. The ECU 16 is an electronic control unit that includes a CPU, a ROM, a RAM, and the like. The ECU 16 is connected to the injector 2, the spark plug 7, the electric motor 11b, and the like described above, and these are controlled by signals from the ECU 16. In addition to this, the hydraulic pressure of the variable valve timing mechanism 20 that controls the opening / closing timing of the intake valve 8, the controller 21 connected to the electric motor 11 b, the battery 22, and the like are also connected to the ECU 16.
[0017]
The controller 21 not only controls the drive of the electric motor 11b but also has a function as an inverter that performs voltage conversion of electric power regenerated by the electric motor 11b. The electric power generated by the regenerative power generation is voltage-converted by the controller 21 and then charged to the battery 22. On the other hand, an air-fuel ratio sensor 28 for detecting the exhaust air-fuel ratio is disposed on the exhaust passage 6 upstream of the turbo unit 11. The air-fuel ratio sensor 28 is connected to the ECU 16 described above, and the detection result is sent to the ECU 16. The air-fuel ratio sensor 28 in the present embodiment is a so-called linear air-fuel ratio sensor that can linearly detect the air-fuel ratio from the lean region to the rich region.
[0018]
Further, an exhaust purification catalyst 23 for purifying exhaust gas is attached to the downstream side of the turbo unit 11. The exhaust purification catalyst 23 is a normal three-way catalyst, and is disposed upstream of the exhaust passage 6. The exhaust purification catalyst 23 is heated to the activation temperature earlier by the exhaust temperature at the cold start, and exhibits the catalyst function earlier. Is. A NOx absorption reduction type exhaust purification catalyst (hereinafter also simply referred to as a NOx occlusion reduction type catalyst) 29 is disposed downstream of the exhaust purification catalyst 23. The NOx occlusion reduction type catalyst 29 has a NOx absorbent supported on a three-way catalyst, and has both a function as a normal three-way catalyst and a function as a NOx absorbent. That is, the NOx occlusion reduction type catalyst 29 is also a NOx absorbent.
[0019]
The NOx occlusion reduction type catalyst 29 has an alkali metal (K, Na, Li, Cs, etc.) on a support whose surface is coated with a thin film layer of alumina, in addition to a noble metal such as platinum, palladium and rhodium. ), Alkaline earth metals (Ba, Ca, etc.) or rare earth elements (La, Y, etc.) are further supported, and NOx contained in the exhaust gas is occluded when the engine is operated at a lean air-fuel ratio. It is made to be able to. Therefore, as described above, the NOx occlusion reduction catalyst 29 functions as a normal three-way catalyst, that is, a function of purifying HC, CO, NOx in the exhaust gas when burned in the vicinity of the theoretical air-fuel ratio. In addition, it is possible to occlude unreduced NOx contained in the exhaust gas.
[0020]
The NOx occluded in the NOx occlusion reduction catalyst 29 is released when burned at a rich air-fuel ratio or stoichiometric air-fuel ratio (stoichiometric air-fuel ratio), and is reduced and purified by HC and CO in the exhaust gas (this When HC and CO are simultaneously oxidized and purified). For this reason, when it is determined that the NOx occlusion amount of the NOx occlusion reduction type catalyst 29 is almost full, such as when the operation in the lean burn region is continued, the engine is operated for a short time with the rich air-fuel ratio and occluded. There is a case where a so-called rich spike operation for reducing NOx is forcibly performed.
[0021]
Further, an EGR (Exhaust Gas Recirculation) passage 24 for recirculating exhaust gas from the exhaust passage 6 (upstream of the air-fuel ratio sensor 28) to the intake passage 5 (surge tank portion formed downstream of the pressure sensor 19) is provided. It is arranged. On the EGR passage 24, an EGR valve 25 for adjusting the exhaust gas recirculation amount is attached. The opening degree control of the EGR valve 25 is also performed by the ECU 16 described above. A crank positioning sensor 26 that detects the rotational position of the crankshaft is attached in the vicinity of the crankshaft of the engine 1. The crank positioning sensor 26 can also detect the engine speed from the position of the crank position.
[0022]
Control in the above-described internal combustion engine will be described. FIG. 2 shows a flowchart of control in this embodiment.
[0023]
The control of the flowchart in FIG. 2 is executed in parallel with air-fuel ratio control and normal motor control. And about motor control, it is performed in the form which interrupts with respect to normal motor control. The normal motor control is to determine the supercharging assist amount (the energization amount to the electric motor 11b) by the electric motor 11b from the target supercharging pressure and the actual supercharging pressure. This is a control that causes regenerative power generation. The electric motor 11b is controlled by the ECU 16 and the controller 21 in cooperation with each other, and these function as electric motor control means.
[0024]
First, it is determined whether or not a rich spike request has been generated (step 200). The rich spike request is generated in the air-fuel ratio control that is executed in parallel. In this air-fuel ratio control, a rich spike may be performed as described above. At this time, a rich spike request is generated, and the fuel injection amount is controlled based on this. At this time, if necessary, the intake air amount is controlled by the throttle valve 13 or the exhaust gas recirculation amount is controlled by the EGR valve 25. For example, when the operation in the lean burn region is continued, NOx is accumulated in the NOx occlusion reduction type catalyst 29. Therefore, if the operation in the lean burn region is continued for several tens of seconds, the rich spike is a few seconds of commas. For about 1 second.
[0025]
If there is no rich spike request, the control of the flowchart shown in FIG. 2 ends. If there is a rich spike request, the motor 11b is first driven to control the motor 11b to reduce the intake air amount. Whether or not (step 210). The fact that the electric motor 11b is being driven means that driving electric power is being supplied to the electric motor 11b and supercharging assistance by the electric motor 11b is being performed. When step 210 is affirmed, first, the supply of drive power to the motor 11b is stopped to stop supercharging assist by the motor 11b (step 220), and regenerative power generation is started (step 230).
[0026]
By stopping the supercharging assist and starting the regenerative power generation, resistance is generated in the rotation of the turbine / compressor 11a, and as a result, the intake air amount is reduced. By reducing the amount of intake air during a rich spike, the degree of richness can be increased, and more NOx can be released more reliably. In the present embodiment, the NOx released from the NOx storage reduction catalyst 29 is purified by the NOx storage reduction catalyst 29 itself. Further, since the intake air amount is directly reduced by controlling the electric motor 11b, a rich state can be realized earlier, so that the effect of rich spike can be obtained earlier.
[0027]
On the other hand, if step 210 is negative, it is then determined whether regenerative power generation by the electric motor 11b has already been performed (step 240). When step 240 is denied, that is, when neither supercharging assist nor regenerative power generation is performed by the electric motor 11b, regenerative power generation is started (step 230), and the intake air amount is reduced. Also in this case, the effect of the rich spike can be obtained more reliably and earlier. When step 240 is affirmed, the regenerative power generation amount is increased (step 250). Although depending on the control, when the regenerative power generation amount is variably controlled by the controller 21, the intake air amount can also be reduced by increasing the regenerative power generation amount as in this embodiment.
[0028]
If the maximum power generation amount has already been generated, the opening of the throttle valve 13 may be reduced. The regenerative power generation started in step 230 or the regenerative power generation in which the power generation amount is increased in step 250 is continued for a predetermined time (step 260). As the predetermined time, for example, a time corresponding to the rich spike time can be considered. In addition, since the situation can be maintained if the rich state is shifted earlier, a sufficient effect can be obtained simply by reducing the intake air amount by the electric motor 11b and shifting to the rich state for a predetermined time as in the present embodiment. can get. The predetermined time is determined in advance by experiments. The predetermined time may be a fixed value, or may be variably controlled based on the supercharging pressure or the rich degree (the air-fuel ratio at the time of rich spike execution, the air-fuel ratio difference before and after that).
[0029]
After the intake air amount is reduced for a predetermined time by the electric motor 11b, the normal state is restored (step 270). That is, as described above, the supercharging assist amount by the electric motor 11b (the energization amount to the electric motor 11b) is determined from the target supercharging pressure and the actual supercharging pressure. The electric motor 11b is controlled based on the control for generating power. Thereafter, when the rich spike is performed again, the control of the flowchart of FIG. 2 described above is executed. In the present embodiment, regenerative power generation is started or the regenerative power generation amount is increased as the intake air amount is reduced by the electric motor 11b, so that there is an advantage that energy efficiency can be improved by collecting electric energy. .
[0030]
Note that a step may occur in the output torque of the engine 1 during a rich spike. In particular, if a rich spike is executed during operation in the lean burn region, the air-fuel ratio becomes rich at once from lean, so that the torque step is likely to become noticeable. Therefore, in the present embodiment, this torque step adjusts (retards) the ignition timing so that the output torque before and after execution of the rich spike becomes substantially equal.
[0031]
The present invention is not limited to the embodiment described above. For example, in the above-described embodiment, when the rich spike is executed (when the exhaust air-fuel ratio is forced to be rich and NOx is released from the NOx absorbent), the turbocharger motor is being driven (during supercharging assist). In some cases, the motor was stopped and regenerative power generation using the motor was started. However, since the effect of reducing the amount of intake air can be achieved simply by stopping the motor that is being driven, it is also possible to simply stop the motor that is being driven.
[0032]
Further, the NOx absorbent (NOx occlusion reduction type catalyst) has a property that the sulfur oxide SOx is occluded more stably than NOx. For this reason, the sulfur component in the fuel or engine oil is stored as SOx in the NOx storage-reduction catalyst, and so-called SOx poisoning in which the capacity to store NOx decreases can occur. Rich spikes can also be performed to eliminate this SOx poisoning, but NOx is also released at the same time as SOx in this rich spike, so at this time the motor can be controlled to reduce the amount of intake air Within the scope of the present invention.
[0033]
【The invention's effect】
According to the control device for an internal combustion engine of the present invention, when the exhaust air-fuel ratio is forcibly made rich to release NOx from the NOx absorbent, the amount of intake air is reduced by the electric motor, so that the exhaust air can be more reliably and earlier. The fuel ratio can be made richer, and the NOx release effect can be obtained earlier and more reliably. Here, if the amount of intake air is reduced by reducing the energization amount to the motor, it is possible to suppress wasteful consumption of electrical energy and improve energy efficiency. Here, if the amount of regenerative power generation by the electric motor is increased, the electrical energy can be recovered and the energy efficiency can be improved.
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing a configuration of an internal combustion engine (engine) having an embodiment of a control device of the present invention.
FIG. 2 is a flowchart of motor control according to an embodiment of the control device of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Engine, 2 ... Injector, 3 ... Cylinder, 4 ... Piston, 5 ... Intake passage, 6 ... Exhaust passage, 7 ... Spark plug, 8 ... Intake valve, 9 ... Exhaust valve, 10 ... Air cleaner, 11 ... Turbo unit, DESCRIPTION OF SYMBOLS 11a ... Turbine, 11b ... Electric motor, 12 ... Intercooler, 13 ... Air cleaner, 13 ... Throttle valve, 14 ... Accelerator pedal, 15 ... Accelerator positioning sensor, 16 ... ECU (electric motor control means), 17 ... Throttle motor, 18 ... Throttle positioning Sensor: 19 ... Pressure sensor, 20 ... Variable valve timing mechanism, 21 ... Controller (electric motor control means), 22 ... Battery, 23 ... Exhaust purification catalyst (three-way catalyst), 24 ... EGR passage, 25 ... EGR valve, 26 ... Crank positioning sensor, 27 ... Air flow meter, 2 ... fuel ratio sensor, 29 ... NOx storage reduction catalyst (NOx absorber).

Claims (6)

A NOx absorbent that is disposed on the exhaust passage of the internal combustion engine, absorbs nitrogen oxide NOx when the exhaust air-fuel ratio of the inflowing exhaust gas is lean, and releases nitrogen oxide NOx absorbed when rich or stoichiometric,
A turbocharger disposed along with the internal combustion engine;
An electric motor capable of changing the supercharging pressure by rotating the turbine / compressor of the turbocharger by an exhaust flow and performing regenerative power generation by exhaust energy;
Electric motor control means for performing drive / regenerative power generation control of the electric motor,
When the motor control means forcibly makes the exhaust air-fuel ratio rich and releases NOx absorbed from the NOx absorbent , the state of the motor is in a drive state, a regenerative power generation state, a drive stop / regenerative power generation stop The state of the motor is changed when it is determined that the motor is in a driving state, or when it is determined that the motor is in a driving stop / regenerative power generation stopping state. And controlling the electric motor so as to reduce the amount of intake air. 2. The motor control unit, when it is determined that the motor is in a driving state, changes the state of the motor to a driving stop / regenerative power generation stopping state to reduce the intake air amount. The control apparatus of the internal combustion engine described in 1. The control apparatus for an internal combustion engine according to claim 2, wherein the motor control means further changes the state of the motor to a regenerative power generation state to reduce the intake air amount. The said motor control means changes the state of the said motor to a regenerative power generation state, and reduces intake air amount when the said motor is a drive stop and regenerative power generation stop state. Control device for internal combustion engine. 5. The control device for an internal combustion engine according to claim 3 , wherein the motor control means increases a regenerative power generation amount recovered from the motor to reduce an intake air amount. 6. Nitrogen oxide when the exhaust air-fuel ratio of the exhaust gas that is disposed on the exhaust passage of the internal combustion engine is lean NOx Nitrogen oxide absorbed when rich or stoichiometric NOx Release NOx An absorbent material;
A turbocharger disposed along with the internal combustion engine;
An electric motor capable of changing the supercharging pressure by rotating the turbine / compressor of the turbocharger by an exhaust flow and performing regenerative power generation by exhaust energy;
Electric motor control means for performing drive / regenerative power generation control of the electric motor,
The electric motor control means forcibly makes the exhaust air-fuel ratio rich and the NOx Absorbed from the absorbent material NOx Is determined when the state of the motor is a driving state, a regenerative power generation state, a drive stop / regenerative power generation stop state, and when the motor is determined to be in a regenerative power generation state, A control device for an internal combustion engine, wherein the motor is controlled to increase a regenerative power generation amount recovered from the motor to reduce an intake air amount.

Images