JP3613681B2 - 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 such as a diesel engine, and more particularly to a control device for an internal combustion engine having a catalyst for purifying exhaust gas in an exhaust system.
[0002]
[Prior art]
An internal combustion engine such as a diesel engine burns fuel and outputs power, so exhaust is inevitably generated. However, from the viewpoint of global environmental conservation, the exhaust generated from the internal combustion engine should be cleaned as much as possible. Is required. An example of the pollutant contained in the exhaust gas of an internal combustion engine is nitrogen oxide (NOx), and it is required to reduce the emission amount.
[0003]
NOx is likely to occur when the combustion conditions of the fuel are relatively high and in an oxidizing atmosphere. Therefore, the ratio of the air-fuel ratio of the air-fuel mixture burned in the internal combustion engine, that is, the air-fuel ratio is the stoichiometric air-fuel ratio (14.5). It tends to occur when the value is larger and close to the theoretical air-fuel ratio (16 to 17). Therefore, in order to reduce the NOx emission amount, the air-fuel ratio may be made smaller or larger than this value. However, when the air-fuel ratio is lowered, the fuel supply amount increases, so that the fuel consumption deteriorates. Moreover, if it enlarges, it will become unstable combustion according to the grade, and a fuel consumption will deteriorate. As described above, the fuel efficiency characteristic and the NOx emission characteristic are in a contradictory relationship, and when one characteristic is improved, the other characteristic is deteriorated.
[0004]
Therefore, conventionally, attention has been paid to the fact that the rotational speed of the internal combustion engine can be controlled to some extent by connecting a continuously variable transmission to the output side of the internal combustion engine, and attempts have been made to achieve both fuel efficiency characteristics and NOx emission characteristics. . One example thereof is described in JP-A-4-255541. The device described in this publication obtains fuel consumption characteristics and NOx emission characteristics for each of an operation state in which the air-fuel ratio is the stoichiometric air-fuel ratio or richer and a lean operation state in which the air-fuel ratio is greater than the stoichiometric air-fuel ratio. In addition, the fuel consumption characteristic and the NOx emission characteristic are evaluated for the driving state that obtains the output based on the traveling state, the required drive amount, and the like, and the driving state in which both these characteristics are compatible is selected.
[0005]
[Problems to be solved by the invention]
According to the control device described in the above publication, either the lean operation or the stoichiometric air-fuel ratio operation (stoichiometric operation) on the iso-output line corresponding to the actual output, the fuel consumption rate and the NOx emission rate, It is possible to evaluate whether to achieve better compatibility and to select a driving state with good evaluation. However, recently, the emission control of environmental pollutants such as NOx is becoming more and more strict, and as described in the above-mentioned publication, the latest emission can be changed by changing the operation state or combustion state. Clearing regulations is becoming difficult. In order to comply with such strict NOx emission regulations, it is attempted to purify the exhaust gas of the internal combustion engine using a catalyst while controlling the driving state of the vehicle so as to achieve both the fuel consumption characteristic and the NOx emission characteristic. It has been.
[0006]
As such a catalyst, a NOx occlusion reduction type catalyst is known. This catalyst, for example, absorbs NOx in exhaust gas generated when an internal combustion engine is operated in a lean state with a large air-fuel ratio as nitrate nitrogen, and the amount of absorption increases to a predetermined amount. By making the reaction atmosphere a reducing atmosphere, the stored nitrate nitrogen is reduced and released as nitrogen gas. In that case, since nascent oxygen (active oxygen) is generated, soot adhering to the catalyst can be oxidized.
[0007]
When this type of catalyst is used, the atmosphere needs to be temporarily reduced when the NOx storage amount increases to some extent. As a control for reducing the atmosphere, there are known a method of supplying a reducing agent such as fuel and ammonia into the exhaust, a method of increasing the amount of fuel supplied to the internal combustion engine and lowering the air-fuel ratio, etc. Since it is not preferable that the ammonia is discharged from the vehicle, fuel is usually used as a reducing agent. Therefore, when the NOx occlusion reduction type catalyst described above is used, fuel is consumed to reduce and release the stored NOx.
[0008]
As described above, when the NOx storage reduction catalyst is used, the fuel burned in the internal combustion engine and the fuel for purifying NOx are consumed. Conventionally, only the former fuel consumption is considered. Since only control is performed, there is room for further improvement in terms of improving fuel consumption. Further, the device described in the above publication is consumed to remove pollutants in exhaust gas such as NOx, although it provides a basis for selecting either lean operation or stoichiometric operation on the iso-output line. Since the optimum operating state is not determined in consideration of the amount of fuel, there is a possibility that the fuel efficiency may not necessarily be optimum when the above-described NOx storage reduction catalyst is used.
[0009]
The present invention has been made paying attention to the above technical problem, and an object of the present invention is to provide a control device capable of improving fuel consumption including the use of a reducing agent for purifying exhaust gas. Is.
[0010]
[Means for Solving the Problem and Action]
In order to achieve the above object, the present invention is characterized in that the excess air ratio of the air-fuel mixture burned in the internal combustion engine at the time of supplying the reducing agent for purifying exhaust gas is reduced. Is. More specifically, according to the invention of claim 1 , the continuously variable transmission is connected to the output side of the internal combustion engine, the air- fuel ratio can be changed, and the catalyst for purifying predetermined pollutants in the exhaust is exhausted. the controller of an internal combustion engine provided in the system, the catalytic, the air-fuel ratio occludes said contaminant when the stoichiometric air-fuel ratio greater than, reducing the pollutant in the presence of changing Motozai tactile form configured by medium, when the operating condition in which the catalyst is occluding the contaminants, so that the internal combustion engine is operated at an operating point of optimal fuel consumption line, said of the internal combustion engine and the gear ratio of the continuously variable transmission when a first control means for controlling the fuel injection quantity, Ru reduces the excess air ratio of the mixture burned in the internal combustion engine to the time for supplying the pre-Symbol reducing agent, the output of the internal combustion engine at that time On the iso-power line that matches Second control means for controlling the speed ratio of the continuously variable transmission and the fuel injection amount of the internal combustion engine so that the operating point has an excess air ratio smaller than the excess air ratio in the operating state of storing a control apparatus characterized by being e Bei.
[0011]
The invention of claim 2 is the previous SL second control means in claim 1, in reducing the excess air ratio, so that the rotational speed of the internal combustion engine is decreased, the gear ratio of the continuously variable transmission And a means for increasing the fuel injection amount of the internal combustion engine . Further, in the invention of claim 3, the first control means in claim 1 obtains a target rotational speed that is on the optimum fuel consumption line from the target output of the internal combustion engine, and the rotational speed of the internal combustion engine is determined as the target rotational speed. Means for controlling the speed ratio of the continuously variable transmission so as to obtain the fuel injection amount from the target output and the target rotational speed so that the torque of the internal combustion engine becomes the target torque. It is a control device.
[0012]
Thus in the present invention, exhaust gas generated by the internal combustion engine burning a fuel-air mixture is supplied to the catalyst provided in the exhaust system, the predetermined contaminant is purified. Specifically, the contaminant is temporarily occluded in the catalyst, and then reduced and released in a reducing atmosphere. The reducing atmosphere is generated by supplying a reducing agent, but the excess air ratio at the time when the reducing agent is supplied is reduced. Lowering the excess air ratio may include an increase in the fuel supply amount to the internal combustion engine, the output of the internal combustion engine is a reducing agent so as not to be changed is supplied. As a result, the atmosphere at the time when the reducing agent is supplied is an atmosphere with a low degree of oxidation, so that the reducing agent supplied for exhaust purification is oxidized before reducing the pollutants. As a result, it is possible to improve the overall fuel consumption including consumption of the reducing agent.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Next, the present invention will be described based on specific examples. The internal combustion engine targeted by the present invention is a power device that outputs power by burning fuel such as a diesel engine or a gasoline engine, and is mounted on a vehicle as an example and used mainly as a power source for traveling. It is an internal combustion engine. FIG. 4 schematically shows an example in which a direct injection type diesel engine (hereinafter simply referred to as an engine) 1 is used as a power source of a vehicle. The engine 1 is an internal combustion engine of a type that directly injects fuel into a cylinder, and is provided with a common rail type electronically controlled fuel injection system 2 in order to enable fuel injection at high pressure. ing. This electronically controlled fuel injection system 2 can be of a known structure.
[0014]
Further, the engine 1 shown in FIG. 4 includes an exhaust turbine supercharger, that is, a turbocharger 3. An intake pipe 6 with an air cleaner 5 interposed is connected to the intake port of the compressor 4, and an intake manifold 8 is connected to the discharge port of the compressor 4 via an intercooler 7 for lowering the intake air temperature. ing.
[0015]
Further, an exhaust manifold 9 communicating with each cylinder is connected to an inlet of a turbine 10 in the turbocharger 3. Further, a catalytic converter 11 having an exhaust purification catalyst is connected to an outlet of the turbine 10. An air-fuel ratio sensor 12 and a pressure sensor 13 that detects the pressure of the exhaust gas flowing into the catalytic converter 11 are disposed upstream of the catalytic converter 11. Furthermore, a temperature sensor 14 for detecting the catalyst temperature is provided.
[0016]
Here, the exhaust purification catalyst will be described. In the example shown in FIG. 4, a NOx occlusion reduction type catalyst is used. This is the function of storing NOx, which is one of the pollutants in the exhaust in an oxidizing atmosphere, in the form of nitrate nitrogen, and reducing the released nitrate nitrogen as nitrogen gas in a reducing atmosphere. I have. Further, since active oxygen is generated during NOx occlusion and reduction, it has a function of oxidizing and removing soot (PM) adhering to the surface by the active oxygen and oxygen in the exhaust. Therefore, it is necessary to change the atmosphere of the exhaust purification catalyst between an oxidizing atmosphere and a reducing atmosphere at predetermined intervals. (Fuel ratio) and a rich air-fuel ratio (air-fuel ratio smaller than the stoichiometric air-fuel ratio) in which the amount of fuel is relatively increased. Note that the control to enrich the air-fuel ratio in order to release nitrogen from the exhaust purification catalyst may be temporary, and such temporary enrichment of the air-fuel ratio is referred to as “rich spike”.
[0017]
Further, the engine 1 shown in FIG. 4 is provided with an exhaust gas recirculation device in order to reduce NOx in the exhaust gas. That is, the exhaust manifold 9 and the EGR cooler 15 that cools the exhaust gas to be recirculated and the EGR valve 16 that controls the execution / stop of recirculation and the recirculation rate (EGR rate) to be constant are connected to the exhaust manifold 9. An intake manifold 8 is connected.
[0018]
A continuously variable transmission (CVT) 17 is connected to the output side of the engine 1. The continuously variable transmission 17 is basically a transmission capable of continuously changing a gear ratio, and a belt type continuously variable transmission or a traction type (toroidal) continuously variable transmission is adopted. .
[0019]
Engine electronic control unit (E-ECU) for electrically controlling the fuel injection amount and its injection timing, execution / stop of exhaust gas recirculation, throttle valve (not shown), etc. in the engine 1 18 and a transmission electronic control unit (T-ECU) 19 for controlling the continuously variable transmission 17 are provided. These electronic control units 18 and 19 are mainly composed of a microcomputer, and the required output amount, vehicle speed, engine water temperature, oil temperature of the continuously variable transmission 17, each sensor 12, and the like expressed by the accelerator opening. , 13, 14 based on detection signals and the like, the throttle opening, the fuel injection amount (that is, engine load), or the gear ratio in the continuously variable transmission 17 (that is, engine speed) is controlled. Yes.
[0020]
In the engine 1 described above, fuel is injected into each cylinder and burned, and mechanical energy generated in association with the fuel is output as a driving force. Therefore, the amount of fuel consumed is controlled to be as small as possible within a range that satisfies the required output amount. Further, pollutants such as NOx generated by the combustion of fuel in the cylinder are occluded by the catalyst in the catalytic converter 11, and before the occlusion amount is saturated, the amount of fuel in the exhaust gas is increased to form a reducing atmosphere. The nitrate nitrogen stored in is reduced and released as nitrogen gas. That is, fuel is consumed by increasing the amount of fuel supplied for purifying exhaust gas. Thus, fuel is consumed to drive the engine 1 and purify the exhaust, in other words, to reduce the amount of air pollutants emitted from the vehicle. The fuel in this case corresponds to a reducing agent that makes the catalyst a reducing atmosphere.
[0021]
The engine 1 is controlled so that the fuel consumption is minimized according to the required drive amount. An example of the control will be briefly described. The target driving force is obtained based on the accelerator opening representing the required driving amount and the vehicle speed, and the target output is obtained based on the target driving force and the vehicle speed. On the one hand, the target engine speed is determined on the basis of this target output. This may be performed, for example, by preparing a map obtained in advance for the engine speed at which the fuel consumption is minimized for each output, and obtaining the target engine speed from the target output and the map. Then, the gear ratio of the continuously variable transmission 17 is controlled so as to achieve the target engine speed.
[0022]
On the other hand, the target engine torque is obtained based on the target output and the engine speed. Then, the engine load (specifically, the throttle opening or the fuel injection amount) is controlled so as to output the target engine torque.
[0023]
The operating point determined by the engine speed and the engine load set as described above is an operating point on the optimum fuel consumption line at which the fuel consumption is minimized, and its air-fuel ratio (the fuel amount of the air-fuel mixture combusted in the engine 1 and The ratio to the air amount is larger than the stoichiometric air-fuel ratio. That is, air becomes an excessive air-fuel mixture. Therefore, since the engine 1 is operated at the operating point on the optimum fuel consumption line during normal traveling, the air-fuel ratio during normal traveling is a leaner (lean) air-fuel ratio than the stoichiometric air-fuel ratio.
[0024]
As the fuel burns in the engine 1, NOx is generated, and the NOx is stored by the above-described storage reduction catalyst provided in the exhaust system. As the operation of the engine 1 continues, the amount of NOx occluded by the catalyst increases. Therefore, by supplying a reducing agent every predetermined time to create a reducing atmosphere, that is, by executing a rich spike, The stored nitrate nitrogen is reduced to nitrogen gas and released to the outside air. This rich spike is executed, for example, when the fuel injection time is integrated and the integrated value reaches a preset reference value. In that case, the control device according to the present invention controls the air excess ratio (air-fuel ratio) of the air-fuel mixture when supplying the reducing agent to be different from that during normal traveling. An example of the control will be described below.
[0025]
FIG. 1 is a flowchart showing an example of the control, which is executed every predetermined short time Δt. First, it is determined whether or not a reducing agent supply process is in progress (step S1). This is a determination of whether or not the NOx occlusion amount by the catalyst has reached a predetermined value, and control for supplying a reducing agent to reduce and release the nitrogen content is started. The determination can be made based on the integrated value of time or a predetermined signal output when the integrated value reaches the reference value.
[0026]
When a negative determination is made in step S1, that is, when the reducing agent supply process is not in progress, a normal engine target speed is set (step S2), and a normal engine load is set (step S3). . The control in step S2 and step S3 is control for operating the engine 1 at the operating point on the optimum fuel consumption line described above, and the accelerator opening indicating the required drive amount, the vehicle speed at that time, the map, It is calculated and executed by the electronic control units 18 and 19 based on the engine speed and the like.
[0027]
On the other hand, if the determination in step S1 is affirmative, that is, if it is determined that the reducing agent supply process is in progress, the target engine speed at the time of reducing agent charging is set (step S4). . At the same time, the target engine load when the reducing agent is charged is set (step S5). The control in step S4 and step S5 is control for reducing the excess air ratio of the air-fuel mixture without changing the engine output at the time when the determination of the reducing agent supply process is established. Specifically, the engine at that time is controlled. The equal output line corresponding to the output has an equal excess air ratio line (an excess air ratio line corresponding to an air / fuel ratio equal to or higher than the theoretical air / fuel ratio) smaller than the equal excess air ratio line corresponding to the excess air ratio during normal operation. The target engine speed and the target engine load are set so as to be an operating point obtained as an intersecting point.
[0028]
This is shown in FIG. In FIG. 2, during normal operation until the determination of the reducing agent supply process is established, the vehicle is operated at the operating point (point A) on the optimum fuel consumption line. When the determination of the reducing agent supply process is established in this state, an operating point (point B) with a small excess air ratio is set as an operating point on the iso-output line to which point A belongs, and the engine speed corresponding to point B is set. And the engine torque is controlled. In this case, the engine speed is specifically controlled by controlling the speed ratio of the continuously variable transmission 17 described above. The engine torque is controlled by controlling the throttle opening or the fuel injection amount.
[0029]
Such control is executed for each normal driving state on the optimum fuel consumption line. Therefore, the operating line (line connecting the operating points) when the reducing agent is charged is more than the optimum fuel consumption line as shown in FIG. The line is drawn almost parallel to the high load side. The operating line or operating line that is set in advance based on experiments or the like is the operating point or operating line when the point B or reducing agent is charged.
[0030]
The supply of the reducing agent is executed in the state in which the control in step S4 and step S5 is executed, that is, in the state where the air excess ratio of the air-fuel mixture is reduced and the air-fuel ratio is brought close to the stoichiometric air-fuel ratio. An example of the supply of the reducing agent is the above-described rich spike, and the fuel supply amount (injection amount) is temporarily increased to such an extent that the air-fuel ratio becomes smaller than the stoichiometric air-fuel ratio. As a result, unburned fuel remains in the exhaust gas discharged from the cylinder of the engine 1 and is carried to the catalyst described above, and the catalyst is placed in a reducing atmosphere. Therefore, nitrate nitrogen stored in the catalyst is reduced and released as nitrogen gas, and the amount stored in the catalyst is reduced.
[0031]
In the process of reduction by the rich spike, the excess air ratio in the engine 1 is reduced, so that the amount of fuel supplied as the reducing agent is burned before reaching the catalyst. That is, since the fuel supplied as the reducing agent is prevented or suppressed from functioning as an increase in engine load, the increase in engine load and the accompanying fuel consumption are prevented or suppressed, and deterioration of fuel consumption is avoided or suppressed. The Further, since the engine load does not increase, the engine torque or the drive torque can be increased, and behavioral changes such as shock and vibration can be prevented or suppressed.
[0032]
Further, by reducing the excess air ratio, the amount of air that absorbs heat generated by combustion is reduced, and the amount of heat generated is increased by the relative increase in the amount of fuel, so that the catalyst temperature is increased. Accordingly, the activity of the catalyst is promoted. In this case, the exhaust gas purification rate is improved, and it becomes easier to clear exhaust gas emission regulations.
[0033]
In the control example described above, the functional means of Step S2 and Step S3 is a first control means of the present invention, functional means of Step S4 and Step S5, i.e. by reducing the transmission ratio engine speed means for increasing the engine load with a decrease in the engine speed with decreasing has become a second control hand stage of the present invention. In the present invention, instead of this, the excess air ratio may be reduced by other means. An example is shown in FIG.
[0034]
The example shown in FIG. 3 is an example in the case where supercharging is performed during normal operation, and the flowchart shown in FIG. 3 is executed every predetermined short time Δt. In the control example shown in FIG. 3, it is first determined whether or not a reducing agent supply process is in progress (step S11). This is the same control as step S1 in FIG. 1 described above. When a negative determination is made in step S11, that is, in a normal operating state, a normal target boost pressure is set (step S12). As an example, the supercharging pressure is set so that the air-fuel ratio corresponds to the operating point on the optimum fuel consumption line described above.
[0035]
On the other hand, when it is determined affirmatively in step S11 because the reducing agent is being supplied, the supercharging pressure when the reducing agent is charged is set as the supercharging pressure (step S13). This is, for example, a supercharging pressure that achieves the air-fuel ratio at point B shown in FIG. 2, and is a supercharging pressure that is lower than the supercharging pressure at the time when the determination in step S11 was made. The pressure value can be determined in advance. When the variable nozzle turbo is adopted, the supercharging pressure is controlled by the nozzle angle, and may be controlled by opening / closing or opening of the waste gate valve.
[0036]
Thus, if the supercharging pressure is lowered to reduce the excess air ratio, the fuel supplied as the reducing agent is burned with the air in the exhaust gas and consumed, as in the control example shown in FIG. As a result, fuel consumption can be improved by preventing or suppressing wasteful consumption of fuel. Further, when the catalyst temperature is low, the exhaust gas purification performance can be improved by increasing the temperature.
[0037]
Each of the above specific examples is configured to reduce the excess air ratio by reducing the engine speed and increasing the engine load, or by reducing the supercharging pressure. However, according to the present invention, in addition to these means, the excess air ratio is reduced by adjusting the opening / closing timing of the intake valve and exhaust valve of the engine to reduce the amount of air sucked into the cylinder. You can also Further, the reducing agent for making the exhaust purification catalyst into a reducing atmosphere may be fuel supplied to the inside of the cylinder for the generation of the air-fuel mixture, or injected into the cylinder with the exhaust valve opened. It may be a fuel mixed in the exhaust gas, or an appropriate reducing agent that is directly supplied to any of the exhaust systems. Furthermore, the engine targeted by the present invention is not limited to a turbocharger driven by exhaust gas, but may be an engine provided with an engine or a supercharger driven by a motor. The catalyst in the present invention may be a catalyst other than the above-described storage reduction catalyst, and the purification target substance is not limited to NOx.
[0038]
【The invention's effect】
As described above, according to the present invention, the excess air ratio at the time when the reducing agent for making the exhaust purification catalyst into the reducing atmosphere is supplied is reduced with respect to the normal operating state before that, In addition, since the reducing agent is supplied so that the output of the internal combustion engine does not change, the reducing agent supplied for exhaust purification is prevented or suppressed from being oxidized before the pollutant is reduced. As a result, the overall fuel consumption can be improved including the consumption of the reducing agent. Moreover, since the temperature rise of the catalyst can be promoted by the reduction of the excess air ratio, when the catalyst temperature is low, the activation thereof can be promoted and the exhaust purification efficiency can be improved.
[Brief description of the drawings]
FIG. 1 is a flowchart showing an example of control by a control device of the present invention.
FIG. 2 is a diagram showing changes in operating points when the excess air ratio is lowered.
FIG. 3 is a flowchart showing another example of control by the control device of the present invention.
FIG. 4 is a diagram schematically showing an example of a power system of a vehicle equipped with an internal combustion engine targeted by the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine, 11 ... Catalytic converter, 17 ... Continuously variable transmission, 18 ... Electronic controller for engines, 19 ... Electronic controller for transmissions

Claims (3)

In a control device for an internal combustion engine , a continuously variable transmission is connected to the output side of the internal combustion engine, the air- fuel ratio can be changed, and a catalyst for purifying predetermined pollutants in the exhaust is provided in the exhaust system.
Said catalysts, the air-fuel ratio occludes said contaminant when the stoichiometric air-fuel ratio greater than, instead of forms configured by catalysts for reducing the pollutants in the presence of Motozai, the catalyst is the contamination First control means for controlling a gear ratio of the continuously variable transmission and a fuel injection amount of the internal combustion engine so that the internal combustion engine is operated at an operating point on an optimum fuel consumption line in an operation state in which a substance is stored. If, before SL when the reducing agent Ru reduces the excess air ratio of the mixture burned in the internal combustion engine at the time supplies, an equal output line and the catalyst matches the output of the internal combustion engine at that time is the Second control means for controlling the gear ratio of the continuously variable transmission and the fuel injection amount of the internal combustion engine so that the operating point has an excess air ratio that is smaller than the excess air ratio in the operating state in which contaminants are occluded. control of the internal combustion engine, characterized in that door, and are e Bei Apparatus. Before Stories second control means, in reducing the excess air ratio, so that the rotational speed of the internal combustion engine is decreased, and controls the speed ratio of the continuously variable transmission, a fuel injection amount of the internal combustion engine 2. The control apparatus for an internal combustion engine according to claim 1, further comprising means for increasing the amount . The first control means obtains a target rotational speed that is on an optimum fuel consumption line from the target output of the internal combustion engine, and controls the gear ratio of the continuously variable transmission so that the rotational speed of the internal combustion engine becomes the target rotational speed. 2. The control apparatus for an internal combustion engine according to claim 1, further comprising means for obtaining the fuel injection amount from the target output and the target rotational speed so that the torque of the internal combustion engine becomes the target torque.

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