JP2004176675A - Control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control device for an internal combustion engine capable of more securely emitting NOx in forcedly setting an exhaust air-fuel ratio rich to emit NOx from NOx absorbing material by use of a turbo charger with a motor. <P>SOLUTION: This control device for an internal combustion engine is provided with the NOx absorbing material (NOx storage reduction catalyst) 29 which absorbs nitrogen oxide NOx when an exhaust air-fuel ratio is lean, and which emits NOx when it is rich or stoichiometric, a turbo charger 11 disposed to be attached on the internal combustion engine, the motor 11b capable of changing supercharge pressure by rotating a turbine/compressor 11 by exhaust currents, and performing regenerative power generation by exhaust energy, and motor control means 16 and 21 to control the motor 11b. The motor control means 16 and 21 controls the motor 11b to reduce intake air quantity when the exhaust air-fuel ratio is set rich to emit NOx from the NOx absorbing material 29. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a control device for an internal combustion engine having a NOx absorber on an exhaust passage and a turbocharger having an electric motor incorporated in a turbine / compressor.
[0002]
[Prior art]
In recent years, there has been a strong demand for improved fuel efficiency and cleaner exhaust gas, and lean burn engines and the like have been put to practical use. In a lean burn engine, a NOx absorbent is used in combination with a three-way catalyst to purify NOx emitted during lean burn, or a NOx storage reduction type exhaust purification catalyst is employed to reduce NOx in exhaust gas. The purification rate has been improved. The NOx absorbent has the property of absorbing nitrogen oxides NOx when the exhaust air-fuel ratio of the inflowing exhaust gas is lean, and releasing the absorbed nitrogen oxides NOx when the exhaust air-fuel ratio is rich or stoichiometric. NOx discharged at the time of leaning is temporarily absorbed and stored, released when the exhaust air-fuel ratio becomes rich or stoichiometric, and purified by a three-way catalyst (in the case of a NOx storage reduction type exhaust purification catalyst itself). In order to forcibly purify the stored NOx, a so-called rich spike for forcibly enriching the exhaust air-fuel ratio for a short time may be performed.
[0003]
[Patent Document 1]
JP 2001-55946 A
[Problems to be solved by the invention]
As an internal combustion engine that performs a rich spike, the one described in Patent Literature 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 the atomization of the injected fuel in an increased amount during a rich spike. When a rich spike is performed in an internal combustion engine having a turbocharger, the exhaust energy increases and the supercharging pressure increases. In Patent Literature 1, the boost pressure is further increased (increased intake air amount) to further promote atomization, so that the exhaust air-fuel ratio cannot be made sufficiently rich and the effect of the rich spike cannot be sufficiently obtained. Is concerned.
[0005]
The internal combustion engine according to the present invention is provided with a turbocharger with a motor in which a motor (motor) is incorporated in a turbine / compressor, and drives the motor to forcibly drive the turbine / compressor to perform supercharging. It is possible to assist or to make the electric motor perform regenerative power generation using the exhaust energy. An object of the present invention is to use a turbocharger with a motor to forcibly make the exhaust air-fuel ratio rich and release NOx from the NOx absorbent (for example, at the time of rich spike). It is an object of the present invention to provide a control device for an internal combustion engine that can release the internal combustion engine.
[0006]
[Means for Solving the Problems]
The control device for an internal combustion engine according to claim 1 is disposed on an exhaust passage of the internal combustion engine, and absorbs nitrogen oxides NOx when the exhaust air-fuel ratio of the inflowing exhaust gas is lean, and absorbs nitrogen oxide NOx when the exhaust gas is rich or stoichiometric. A NOx absorbent that releases nitrogen oxide NOx, a turbocharger provided in association with the internal combustion engine, and a turbocharger that is rotated by the exhaust gas to change the supercharging pressure and exhaust gas. An electric motor capable of performing regenerative power generation with energy and motor control means for controlling the driving and regenerative power generation of the motor are provided. The electric motor control means forcibly makes the exhaust air-fuel ratio rich and absorbs NOx absorbed from the NOx absorbent. It is characterized in that the electric motor is controlled so as to reduce the amount of intake air when being discharged.
[0007]
According to a second aspect of the present invention, in the control apparatus for an internal combustion engine according to the first aspect, the motor control means reduces the amount of drive current supplied to the motor to reduce the amount of intake air. And
[0008]
According to a third aspect of the present invention, in the control device for an internal combustion engine according to the first aspect, the electric motor control means reduces an intake air amount by increasing a regenerative power generation amount recovered from the electric motor. I have.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of the control device of the present invention will be described below. FIG. 1 shows an engine 1 having a control device according to the present embodiment.
[0010]
The engine 1 described in the present embodiment is a multi-cylinder engine, but here only one cylinder is shown in FIG. 1 as a cross-sectional view. The engine 1 is of a type in which fuel is injected into the upper surface of a piston 4 in a cylinder 3 by an injector 2. This engine 1 is capable of performing stratified combustion, and is a so-called lean burn engine. By supercharging a larger amount of intake air by a turbocharger described later and performing lean burn, not only high output but also low fuel consumption can be realized.
[0011]
The engine 1 compresses air sucked into the cylinder 3 through the intake passage 5 by the piston 4, injects fuel into a hollow formed on the upper surface of the piston 4, and moves a rich mixture to the vicinity of the ignition plug 7. It can be collected and ignited by the spark plug 7 to burn (stratified combustion). If fuel is injected during the intake stroke, normal homogeneous combustion can also be performed. The interior of the cylinder 3 and the intake passage 5 are opened and closed by an intake valve 8. The exhaust gas after combustion is exhausted to the exhaust passage 6. The interior of the cylinder 3 and the exhaust passage 6 are opened and closed by an exhaust valve 9. 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 on the intake passage 5 from the upstream side.
[0012]
The air cleaner 10 is a filter that removes dust and dirt from the intake air. The air flow meter 27 of the present embodiment is of a hot wire type, and detects an intake air amount 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]
Further, the turbocharger of the present embodiment is a turbocharger with an electric motor in which the electric motor 11b is incorporated so that the rotation shaft of the turbine / compressor 11a becomes the output shaft. The motor 11b can also function as a generator that generates power using exhaust energy. The turbo unit 11 can 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]
In addition, by using the exhaust energy, the electric motor 11b is rotated via the turbine / compressor 11a to generate regenerative electric power, and the generated electric power can be collected. The electric motor 11b has, as main components, a rotor fixed to the rotating shaft of the turbine / compressor 11a and a stator arranged around the rotor. On the downstream side of the turbo unit 11 on the intake passage 5, an air-cooled intercooler 12 that lowers the temperature of the intake air whose temperature has increased due to a pressure increase due to supercharging by the turbo unit 11 is arranged. The intercooler 12 lowers the temperature of the intake air to improve the charging efficiency.
[0015]
Downstream of the intercooler 12, a throttle valve 13 for adjusting the amount of intake air is arranged. The throttle valve 13 of the present embodiment is a so-called electronically-controlled throttle valve. The operation amount of an accelerator pedal 14 is detected by an accelerator positioning sensor 15, and the ECU 16 controls the throttle valve 13 based on the detection result and other information amounts. Is determined. The throttle valve 13 is opened and closed by a throttle motor 17 provided in association therewith. In addition to the throttle valve 13, a throttle positioning sensor 18 for detecting the opening degree is also provided.
[0016]
Downstream of the throttle valve 13, a pressure sensor 19 for detecting the pressure (supercharging pressure / intake pressure) in the intake passage 5 is provided. These sensors 15, 18, 19, 27 are connected to the ECU 16 and send the detection results to the ECU 16. The ECU 16 is an electronic control unit including a CPU, a ROM, a RAM, and the like. The above-described injector 2, the ignition plug 7, the electric motor 11b, and the like are connected to the ECU 16, and these are controlled by signals from the ECU 16. In addition, the ECU 16 is also connected to a hydraulic pressure of a variable valve timing mechanism 20 for controlling the opening / closing timing of the intake valve 8, a controller 21 connected to the electric motor 11b, a battery 22, and the like.
[0017]
The controller 21 not only controls the driving of the electric motor 11b, but also has a function as an inverter that performs voltage conversion of the electric power regenerated by the electric motor 11b. The power generated by the regenerative power generation is converted into a voltage by the controller 21 and then charged in the battery 22. On the other hand, on the exhaust passage 6, an air-fuel ratio sensor 28 that detects an exhaust air-fuel ratio is disposed upstream of the turbo unit 11. The air-fuel ratio sensor 28 is connected to the above-described ECU 16, and sends the detection result to the ECU 16. The air-fuel ratio sensor 28 according to the present embodiment is a so-called linear air-fuel ratio sensor capable of linearly detecting the air-fuel ratio from a lean region to a rich region.
[0018]
An exhaust purification catalyst 23 for purifying exhaust gas is attached downstream of the turbo unit 11. The exhaust gas purifying catalyst 23 is a normal three-way catalyst, which is disposed upstream of the exhaust passage 6, and is quickly heated to the activation temperature by the exhaust gas temperature at the time of a cold start, so that the catalytic function is exhibited earlier. Things. On the downstream side of the exhaust purification catalyst 23, an NOx absorption reduction type exhaust purification catalyst (hereinafter, also simply referred to as a NOx storage reduction type catalyst) 29 is disposed. The NOx storage reduction catalyst 29 is a catalyst in which a NOx absorbent is also carried 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 storage reduction catalyst 29 is also a NOx absorbent.
[0019]
The NOx occlusion reduction type catalyst 29 is provided on a carrier whose surface is coated with a thin film layer of alumina, on an alumina coating layer in addition to a noble metal such as platinum, palladium and rhodium, and on an alumina coating layer. ), An alkaline earth metal (Ba, Ca, etc.) or a rare earth element (La, Y, etc.) are further supported to absorb NOx contained in exhaust gas when the engine is operated at a lean air-fuel ratio. Is made possible. Therefore, as described above, the NOx storage reduction catalyst 29 functions as a normal three-way catalyst, that is, a function of purifying HC, CO, and NOx in the exhaust gas when the fuel is burned near the stoichiometric air-fuel ratio. In addition, NOx not reduced contained in the exhaust gas can be stored.
[0020]
The NOx stored in the NOx storage reduction catalyst 29 is released when burned at a rich air-fuel ratio or a stoichiometric air-fuel ratio (stoichiometric air-fuel ratio), and is reduced and purified by HC and CO in the exhaust gas. At this time, HC and CO are simultaneously oxidized and purified). For this reason, when it is determined that the NOx storage amount of the NOx storage reduction catalyst 29 is almost full, for example, when the operation in the lean burn region is continued, the engine is stored for a short time by operating the engine at the rich air-fuel ratio. In some cases, a so-called rich spike operation for reducing NOx is forcibly performed.
[0021]
Also, 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 formed downstream of the pressure sensor 19) is provided. It is arranged. An EGR valve 25 for adjusting the amount of exhaust gas recirculation is mounted on the EGR passage 24. The opening 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 near 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]
The control in the above-described internal combustion engine will be described. FIG. 2 shows a flowchart of control in the present embodiment.
[0023]
The control in the flowchart of FIG. 2 is executed in parallel with the air-fuel ratio control and the normal electric motor control. The motor control is executed in such a manner as to interrupt the normal motor control. The normal motor control means that the supercharging assist amount by the electric motor 11b (the amount of current supplied to the electric motor 11b) is determined from the target supercharging pressure and the actual supercharging pressure. This is a control for performing regenerative power generation without power. 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 a rich spike request has been generated (step 200). The rich spike request is generated in the air-fuel ratio control being executed in parallel. In the 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 the request. 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 storage reduction catalyst 29. Therefore, if the operation in the lean burn region continues for several tens of seconds, a rich spike will be separated by a few seconds. From about 1 second.
[0025]
If there is no rich spike request, the control of the flowchart shown in FIG. 2 is finished. However, if there is a rich spike request, first, the electric motor 11b is being driven in order to control the electric motor 11b and reduce the intake air amount. It is determined whether or not (step 210). The state where the electric motor 11b is being driven means that the driving power is being supplied to the electric motor 11b and the supercharging assist by the electric motor 11b is being performed. When step 210 is affirmative, first, the supply of the driving power to the electric motor 11b is stopped to stop the supercharging assist by the electric motor 11b (step 220), and the regenerative power generation is started (step 230).
[0026]
By stopping the supercharging assist and starting the regenerative power generation, resistance occurs 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 and more. 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 electric motor 11b is controlled to directly reduce the intake air amount, a rich state can be realized earlier, so that the effect of the rich spike can be obtained earlier.
[0027]
On the other hand, if step 210 is denied, then it is determined whether regenerative power generation by the electric motor 11b has already been performed (step 240). If step 240 is denied, that is, if neither supercharging assistance nor regenerative power generation is performed by the electric motor 11b, regenerative power generation is started (step 230) to reduce the amount of intake air. Also in this case, the effect of the rich spike can be obtained more reliably and earlier. If 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 be reduced by increasing the regenerative power generation amount as in the present embodiment.
[0028]
If the maximum power generation 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 amount of power generation has been increased in step 250 is continued for a predetermined time (step 260). As the predetermined time, for example, a time corresponding to the time of the rich spike can be considered. Note that, if the state is shifted to rich earlier, the situation can be maintained. Therefore, it is sufficient to simply reduce the intake air amount by the electric motor 11b for a predetermined time and shift to the rich state as in this embodiment. can get. The predetermined time is determined in advance by an experiment. Further, 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 executing the rich spike, the air-fuel ratio before and after the rich spike, etc.).
[0029]
After the intake air amount is reduced for a predetermined time by the electric motor 11b, the operation returns to the normal state (step 270). That is, as described above, the amount of supercharging assist by the electric motor 11b (the amount of power to the electric motor 11b) is determined from the target supercharging pressure and the actual supercharging pressure, and depending on the condition of the engine 1, regeneration is performed instead of supercharging assist. The electric motor 11b is controlled based on the control for generating electric power. Thereafter, when the rich spike is performed again, the control of the above-described flowchart of FIG. 2 is performed. In the present embodiment, the regenerative power generation is started or the regenerative power generation amount is increased with a reduction in the amount of intake air by the electric motor 11b, so that there is also an advantage that energy efficiency can be improved by collecting electric energy. .
[0030]
At the time of a rich spike, a step may occur in the output torque of the engine 1. 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, and the torque step tends to be remarkable. Therefore, in the present embodiment, this torque step adjusts the ignition timing (retards) so that the output torque before and after the execution of the rich spike becomes substantially equal.
[0031]
The present invention is not limited to the embodiments described above. For example, in the above-described embodiment, when the rich spike is executed (when the exhaust air-fuel ratio is forcibly made rich and the NOx is released from the NOx absorbent), the electric motor of the turbocharger is being driven (during the supercharging assist). In some cases, the motor was stopped and regenerative power generation by the motor was started. However, simply stopping the motor being driven has the effect of reducing the amount of intake air, so it is only necessary to stop the motor being driven.
[0032]
Further, the NOx absorbent (NOx storage reduction type catalyst) has a property that the sulfur oxide SOx is stored more stably than NOx. For this reason, the sulfur component in the fuel or the engine oil is stored as SOx in the NOx storage reduction catalyst, and so-called SOx poisoning, in which the capacity of storing NOx is reduced, may occur. Although a rich spike can be performed to eliminate this SOx poisoning, NOx is also released at the same time as SOx in the rich spike. In this case, the electric motor is controlled to reduce the intake air amount. It is 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 and the NOx is released 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 shifted to rich, and the effect of releasing NOx can be obtained earlier and more reliably. Here, if the amount of intake air is reduced by reducing the amount of electricity supplied to the electric motor, wasteful consumption of electric energy can be suppressed and energy efficiency can be improved. Here, if the amount of regenerative power generated by the motor is increased, electric energy can be recovered, and energy efficiency can be improved.
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing a configuration of an internal combustion engine having one embodiment of a control device of the present invention.
FIG. 2 is a flowchart of electric 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, 11a: Turbine, 11b: Electric motor, 12: Intercooler, 13: Air cleaner, 13: Throttle valve, 14: Accelerator pedal, 15: Accelerator positioning sensor, 16: ECU (motor control means), 17: Throttle motor, 18: Throttle positioning Sensor 19 pressure sensor 20 variable valve timing mechanism 21 controller (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 (3)

A NOx absorbent disposed on the exhaust passage of the internal combustion engine, absorbing the nitrogen oxides NOx when the exhaust air-fuel ratio of the inflowing exhaust gas is lean, and releasing the nitrogen oxides NOx absorbed when the exhaust gas is rich or stoichiometric;
A turbocharger arranged in association with the internal combustion engine,
An electric motor capable of changing a supercharging pressure by rotating a turbine / compressor of the turbocharger by an exhaust gas flow and performing regenerative power generation by exhaust energy;
Motor control means for performing drive and regenerative power generation control of the motor,
The electric motor control means controls the electric motor to reduce the intake air amount when the exhaust air-fuel ratio is forcibly made rich and the NOx absorbed from the NOx absorbent is released. Control device for internal combustion engine. 2. The control device for an internal combustion engine according to claim 1, wherein the electric motor control means reduces an amount of drive air supplied to the electric motor to reduce an intake air amount. 3. 2. The control device for an internal combustion engine according to claim 1, wherein the motor control unit increases the amount of regenerative power generated by the motor to reduce the amount of intake air. 3.

Images