JPH09137716A - Emission control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To raise the temperature of a catalyst by heating of an electric heater in a short time without increasing buttery load when the emission temperature is low. SOLUTION: An oxidizing catalyst 5 provided with an electric heater 5a is provided on an exhaust passage 3 of a diesel engine 1, and a bypass passage 6 for connecting the upstream part to the downstream part from the oxidizing catalyst of the exhaust passage is provided. A bypass control valve 8 for opening and closing the bypass passage 6 is provided on the bypass passage 6, and a catalyst temperature sensor 10 for detecting the catalyst floor temperature is provided on the oxidizing catalyst 5. An engine control circuit(ECU) 20 calculates the emission temperature from the engine accelerator opening and the engine speed. When both the exhaust gas temperature and the catalyst temperature are not more than the prescribed value, the bypass control valve 8 is opened, the flow rate of the emissions to flow to the oxidizing catalyst is decreased, and the electric heater 5a is electrified. Therefore, the temperature of the oxidizing catalyst can be raised to the activation temperature without taking heat of the heater by low-temperature exhaust gas.

Description

Detailed Description of the Invention

[0001]

The present invention relates to an exhaust gas purification device for an internal combustion engine.

[0002]

2. Description of the Related Art As an example of this type of exhaust gas purification apparatus,
For example, the one described in JP-A-6-108826 is
is there. In this publication, NO is added to the exhaust passage of the internal combustion engine._XAbsorbent
NO in exhaust_XExhaust purification device to remove
It is shown. NO_XAbsorbent is the air-fuel ratio of the inflowing exhaust gas
NO in the exhaust when is lean_XAbsorbs and inflows
NO absorbed when the oxygen concentration in the air decreased_XRelease
NO_XPerforms the absorption and release action. Exhaust gas purification device of the same publication
Is the NO in the exhaust gas of the engine performing lean air-fuel ratio operation. _XOn
Note NO_XAbsorb with absorbent and then NO_XFor absorbent
Decrease the oxygen concentration of the inflowing exhaust gas, and at the same time, reduce the H in the exhaust gas.
NO by increasing C and CO components_XAbsorbent or
NO absorbed from_XAnd released NO
_XIs reduced with HC and CO components.

By the way, in the device of the above publication, HC, CO
Liquid hydrocarbons such as fuel oil are used as a supply source of components. In this case, if the temperature of the NO _x absorbent has risen sufficiently, the supplied hydrocarbons burn on the NO _x absorbent and produce a large amount of unburned HC and CO components, so NO from the NO _x absorbent is generated. Release and reduction of _X occurs. However, the engine exhaust temperature is low, deposition of liquid hydrocarbons is supplied to _the NO _X absorbent surface without burning the supplied liquid hydrocarbons on _the NO _X absorbent when _the NO _X absorbent temperature is not high enough because of its tendency to release of the nO _X from _the nO _X absorbent, there is a problem that reduced to nO _X absorbing capacity of only either _the nO _X absorbent can not reduced.

[0004] In the exhaust gas purifying apparatus of the above publication, the oxidation catalyst causes supported on the upstream side portion of the NO _X absorbent, so as to heat the oxidation catalyst part in the electric heater, thereby achieving a solution to this problem. That is, in the exhaust emission control device of the publication, when the engine exhaust temperature is low, the electric heater of the catalyst on the upstream side is energized at the same time when the supply of the hydrocarbon component is started, and the catalyst is heated by the heater to raise the catalyst temperature in a short time. The supplied hydrocarbon component is burned by the catalyst carried on the upstream side of the NO _x absorbent so as to reach the activation temperature. When the hydrocarbon component burns with the catalyst, the oxygen concentration in the exhaust gas decreases, and a large amount of unburned HC,
CO component is generated. Also, since the exhaust temperature rises due to combustion, the oxygen concentration is low in the downstream side of the NO _x absorbent,
Large amount of unburned HC, the hot exhaust containing CO component becomes to flow, so that the reduction and NO _X emission from _the NO _X absorbent even when the engine exhaust temperature is low is performed. Further, in the apparatus of the above publication, even when a liquid hydrocarbon containing a large amount of HC component having a large molecular weight, such as fuel oil, is used as the HC and CO supply source, the high molecular weight component of the fuel oil is decomposed by combustion with the catalyst, since so HC components in the low molecular weight frequently occur, the effect of the reduction and release of the NO _X in _the NO _X absorbent is promoted.

[0005]

However, there is a problem in that the temperature rise of the catalyst is delayed if heating is performed by the electric heater while the exhaust gas is flowing through the catalyst when the exhaust gas temperature is low, as in the device of the above publication. That is, when the exhaust gas temperature is low, a part of the heat generated by the electric heater is taken by the exhaust gas, so that the temperature rise of the catalyst becomes slow. Therefore, if the hydrocarbon is supplied to the catalyst at the same time when the electric heater is energized, the combustion of the hydrocarbon in the catalyst does not occur because the catalyst has not reached the activation temperature. Further, when the liquid hydrocarbon is supplied, the heat of the electric heater is taken away by the evaporation of the liquid hydrocarbon, which further delays the temperature rise of the catalyst. Therefore, catalyst release of the NO _X in _the NO _X absorbent until it reaches the activation temperature, the reduction does not occur, the supplied hydrocarbons be released into the atmosphere without being consumed by _the NO _X absorbent Therefore, there arises a problem that exhaust emission is deteriorated.

For example, if the amount of heat generated by the heater is increased by greatly increasing the current supplied to the heater, this problem can be solved to some extent, but the increase in the heater current causes a problem that the battery load increases. Will end up. Also,
If the hydrocarbon component is not supplied until the catalyst is heated by the heater and the temperature rises sufficiently, it is possible to prevent the deterioration of exhaust emission, but in this case as well, the heater is heated with the exhaust flowing to the catalyst. I went to
Since it takes a long time to raise the temperature of the catalyst, NO _{x is} generated after the engine is started.
There is a problem that the release of NO _X from the absorbent and the start of reduction can be delayed.

The above is the HC, C supplied to the NO _x absorbent.
The problem in the case of generating the O component in the catalyst with the electric heater has been described, but the similar problem occurs in other cases. For example, a catalyst with an electric heater is arranged on the upstream side of the particulate filter of a diesel engine, and the temperature of the particulate filter is raised by supplying fuel to the catalyst with the electric heater and burning it, and the catalyst is collected by the particulate filter. The same problem may occur in the case of an exhaust gas purification device that burns soot if the exhaust gas temperature is low.

In view of the above problems, the present invention provides an exhaust gas purification apparatus having a structure for burning a hydrocarbon component on a catalyst with an electric heater, by heating the catalyst in a short time without increasing the heater current, An object of the present invention is to provide an exhaust emission control device for an internal combustion engine that can start the combustion of hydrogen components.

[0009]

According to the present invention, a catalyst arranged in an exhaust passage of an internal combustion engine, an electric heater for heating the catalyst, and a hydrocarbon component are supplied to the exhaust passage upstream of the catalyst. An HC supply device, a bypass passage that bypasses the catalyst and connects an exhaust passage on the upstream side of the catalyst and an exhaust passage on the downstream side of the catalyst, a bypass control valve that controls an exhaust flow rate through the bypass passage, and a temperature of the catalyst. And temperature detection means for respectively detecting the engine exhaust temperature, when both the catalyst temperature and the engine exhaust temperature are below a predetermined temperature, the bypass control valve is opened to at least a part of the engine exhaust. There is provided an exhaust gas purification device for an internal combustion engine, comprising: a control unit that supplies a current to the electric heater while flowing in a bypass passage.

In the exhaust gas purification apparatus of the present invention, both the catalyst temperature and the exhaust gas temperature are predetermined temperatures (for example, the catalyst activation temperature).
In the following cases, the control means energizes the electric heater with at least a part of the engine exhaust flowing in the bypass passage. Therefore, heating by the electric heater is performed in a state where the exhaust flowing into the catalyst is blocked or reduced, the amount of heat taken from the catalyst by the low-temperature exhaust is reduced, and the temperature of the catalyst rises in a short time.

[0011]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a diagram showing a configuration of an exhaust emission control device of the present invention. In FIG. 1, 1 is a diesel engine (only one cylinder is shown in the drawing), 2 is an intake passage of the engine 1, 3 is an exhaust passage, and 4 is an engine 1.
Fuel injection valves for injecting fuel into the combustion chambers of the respective cylinders are shown.

Further, in the present embodiment, the exhaust passage 3 of the engine 1 is provided with an oxidation catalyst 5, a DPF 7 for collecting soot in the exhaust gas, and a NO _x absorbent 9 for absorbing NO _x in the exhaust gas from the upstream side. Each is arranged. These elements will be described later. Further, in the present embodiment, a bypass passage 6 that bypasses the oxidation catalyst 5 and connects the exhaust passage on the inlet side of the oxidation catalyst 5 and the exhaust passage on the outlet side is provided, and the exhaust gas passing through the bypass passage 6 is provided on the bypass passage 6. A bypass control valve 8 that controls the flow rate is provided. The bypass control valve 8 is
An actuator 8a of an appropriate type such as a step motor or a negative pressure actuator is provided, and an opening degree according to a control signal from an engine control circuit 20 which will be described later is taken to control an exhaust flow rate passing through the bypass passage 6.

Reference numeral 20 in FIG. 1 is an engine control circuit (ECU). The ECU 20 is a central processing unit (CP
U) 21, random access memory (RAM) 22, read only memory (ROM) 23, input port 24 and output port 25 are connected to each other by a bidirectional bus 26.
In addition to performing the basic control such as fuel injection control, combustion (hereinafter referred to as "DPF regeneration operation") of soot collected by DPF7 in this embodiment and the reduction and release of the NO _X from _the NO _X absorbent 9 (hereinafter “Regeneration operation of NO _x absorbent”) is controlled.

For these controls, signals such as engine speed and accelerator opening are input to the input port 24 of the ECU 20 from sensors (not shown), respectively, and also provided on the catalyst bed of the oxidation catalyst 5. Catalyst temperature sensor 1
A signal corresponding to the temperature of the catalyst 5 is input from 0. The output port 25 of the ECU 20 is connected to the fuel injection valve 4 of the engine 1 and the actuator 8a of the bypass control valve 8 via a drive circuit (not shown), and bypasses the fuel injection amount of the engine, the injection timing, and the exhaust temperature at low temperature. The exhaust gas flow rate passing through the passage 6 is controlled.

As the oxidation catalyst 5, for example, a monolithic carrier made of cordierite is coated with an alumina catalyst supporting layer, and a catalyst component such as platinum Pt or palladium Pd is supported on this supporting layer. Oxidation catalyst 5
Oxidizes the HC and CO components in the exhaust when the exhaust air-fuel ratio is leaner than the stoichiometric air-fuel ratio, and oxidizes the NO component contained in the exhaust to produce the NO ₂ component. In this specification, the ratio of the amount of air and the amount of fuel supplied upstream from a certain portion of the exhaust system is referred to as the exhaust air-fuel ratio of that portion. That is, when the secondary air or fuel is not supplied to the exhaust passage, the exhaust air-fuel ratio in each part of the exhaust system becomes equal to the combustion air-fuel ratio of the engine (the ratio of air and fuel in combustion in the combustion chamber). .

Further, in this embodiment, an electric heater 5a for heating the oxidation catalyst 5 to start a catalytic reaction in a state where the exhaust gas temperature is low immediately after the engine is started is provided on the upstream end surface of the oxidation catalyst 5. Has been. A control signal from the output port 25 of the ECU 20 is input to the relay 5b of the electric heater 5a, and the ECU 20 controls ON / OFF of the electric heater 5a. As will be described later, the heater 5a heats the catalyst 5 when the exhaust temperature is low, raises the temperature to an activation temperature (for example, about 250 ° C.), and is also used to raise the exhaust temperature when the DPF 7 is regenerated. .

In this embodiment, the catalyst 5 and the heater 5
Although a and a are separately formed, for example, a metal monolithic carrier may be used as a carrier, and a catalyst with a heater may be used in which the carrier itself is directly energized to function as a heater. The DPF 7 uses a cordierite honeycomb filter in which a number of exhaust passages are formed in parallel with each other. The exhaust passages in the DPF 7 are alternately arranged with the upstream end portion and the downstream end portion closed, and the exhaust gas flows into the exhaust passage opening at the upstream end portion, From the porous wall that separates the gas into the exhaust passage whose downstream end is open and flows out to the downstream. Therefore, fine particles such as soot in the exhaust gas are collected on the exhaust wall surface when passing through the wall surface. Further, in this embodiment, an alumina layer supporting platinum Pt is formed on the wall surface of the DPF 7 so that the collected soot can be easily burned by NO ₂ as described later.

Next, the NO _x absorbent 9 used in the present invention will be described. As the NO _x absorbent 9, for example, a monolith carrier made of cordierite is formed with a carrier layer of alumina or the like, and potassium K, sodium N, etc. are formed on the carrier layer.
At least one selected from a, an alkali metal such as lithium Li and cesium Cs, an alkaline earth such as barium Ba and calcium Ca, and a rare earth such as lanthanum La and yttrium Y, and a noble metal such as platinum Pt. Use the supported one. _The NO _X absorbent 9 absorbs NO _X in the case the air-fuel ratio of the exhaust gas flowing is lean, the oxygen concentration is carried out to absorbing and releasing action of the NO _X that releases NO _X when lowered.

For example, platinum Pt and barium B are formed on the supporting layer.
O To explain by taking an example that by supporting a, the exhaust air-fuel ratio when the lean, NO occupying most of the NO _X in the engine exhaust (nitrogen oxides) is deposited on the platinum Pt
₂ ^- or O ^2-, etc. are oxidized by nitric acid ions NO ₃
^- to generate. Next, this nitrate ion NO ₃ ⁻ diffuses into BaO while combining with barium oxide BaO, so that NO in the exhaust gas is absorbed in the NO _x absorbent 9 in the form of nitrate ion NO ₃ ⁻ . Further, when the exhaust air-fuel ratio becomes the stoichiometric air-fuel ratio or the rich air-fuel ratio, the oxygen concentration in the inflowing exhaust gas decreases and the amount of NO ₂ produced on platinum Pt decreases. As a result, the reaction proceeds in the direction of NO ₃ ⁻ → NO ₂ contrary to the above, and the nitrate ion NO ₃ ^{− in} BaO is released in the form of NO ₂ . That is, the oxygen concentration in the inflowing exhaust gas is released NO _X from _the NO _X absorbent 9 when lowered.

On the other hand, the reducing agent and unburned HC, C are contained in the inflowing exhaust gas.
When components such as O are present, these components react with oxygen O ₂ ⁻ or O ^{2 −} on the platinum Pt to be oxidized and consume oxygen in the exhaust gas to reduce the oxygen concentration in the exhaust gas. Further, NO ₂ released from the NO _X absorbent 9 due to the decrease in oxygen concentration in the exhaust gas reacts with HC and CO to be reduced, and N ₂ and CO
₂ , H ₂ O, etc. are generated. Therefore, when NO ₂ is reduced on the surface of platinum Pt by the HC and CO components, NO ₂ is released one after another from the absorbent, and HC and CO in the exhaust gas are discharged.
It will react with the ingredients.

That is, the NO _X absorbent 9 removes the NO _X in the exhaust gas flowing in at the lean air-fuel ratio, releases the absorbed NO _X in the rich air-fuel ratio, and reacts with the HC and CO components in the exhaust gas flowing in. Perform the action of causing. That is,
The NO _X absorbent can purify HC and CO components and NO _X components in the exhaust gas at the same time. Next, the operation of this embodiment will be described.

In the present embodiment, since the diesel engine 1 is used, the exhaust air-fuel ratio during normal operation is considerably lean (for example, the air-fuel ratio is about 30). Further, the exhaust in the engine outlet contains relatively large amounts of soot and small amounts of NO _X (mainly NO). This exhaust gas first passes through the oxidation catalyst 5, the NO in the exhaust gas is oxidized, and NO ₂ is produced by the reaction of 2NO + O ₂ → 2NO ₂ .

Next, this exhaust gas flows into the DPF, and the soot in the exhaust gas is collected in the DPF. Soot collected in the DPF is partially reacted with NO ₂ generated by the, NO ₂ + C → NO + CO and NO produced reaction of CO is generated. However, since the amount of soot is larger than the amount of NO generated in the engine, and the exhaust temperature during normal operation of the diesel engine is low (for example, about 200 ° C.), the above reaction does not actually occur so much. The collected soot is gradually accumulated on the DPF 7. On the other hand, the exhaust containing NO generated by the above reaction and NO ₂ that has passed through the DPF 7 without reacting with soot next flows into the NO _x absorbent 9. During normal operation, since the exhaust air-fuel ratio of the diesel engine 1 is lean, NO and NO _{2 in} this exhaust are absorbed by the NO _x absorbent 9 and removed from the exhaust. As a result, during normal operation, the exhaust gas is discharged from the NO _X absorbent 9 in a state where it contains almost no soot and NO _X.

As described above, the soot in the engine exhaust during normal operation is due to the DPF 7, and the NO _X (NO, NO ₂ ) is NO.
_{The X-} absorbent 9 removes the soot, respectively, whereby the DPF 7 gradually accumulates soot, and the NO _X absorbent 9 gradually accumulates NO _X. When the amount of soot accumulated in the DPF 7 increases, the exhaust pressure loss in the DPF 7 increases, so that an increase in exhaust back pressure causes a problem such as a decrease in engine output. Further, NO _X absorbing capacity of the NO _X absorbent 9 when the amount of NO _X accumulated in _the NO _X absorbent 9 is increased is reduced, problems amount of the NO _X released to the atmosphere increases occurs.

Therefore, in the present embodiment, as will be described below, the above-mentioned NO _x absorbent regeneration operation is periodically performed and N
The NO _X absorbed from the O _X absorbent 9 is released to restore the NO _X absorption capacity, and the DPF is periodically regenerated so that the soot collected in the DPF 7 is burned to reduce the pressure loss. ing. First, the operation of regenerating the NO _X absorbent 9 will be described. In the present embodiment, the ECU 20
The regeneration operation of the NO _X absorbent 9 is executed by a routine (not shown) executed by. During the regeneration operation of the NO _x absorbent 9, the ECU 20 supplies a hydrocarbon component to the oxidation catalyst 5 for a short time and burns it on the catalyst 5 to reduce the oxygen concentration in the exhaust gas and unburned HC and CO. The components are produced and supplied to the NO _X absorbent 9. The exhaust gas having a low oxygen concentration containing HC and CO components, which has passed through the oxidation catalyst 5, becomes D
It passes through the PF 7 and reaches the NO _X absorbent 9. Therefore, as described above, NO _X is released from the NO _X absorbent 9 and is reduced and purified by the HC and CO components in the exhaust gas.

In this embodiment, the fuel injected into the combustion chamber of the engine 1 is used as a hydrocarbon supply source. That is, the ECU 20 performs the fuel injection from the fuel injection valve 4 of the engine 1 twice per cycle of each cylinder when the NO _X absorbent 9 is regenerated. During normal operation, the ECU 20 calculates the fuel injection amount based on a predetermined relationship from the depression amount (accelerator opening) of the engine accelerator pedal and the engine speed, and supplies the calculated amount of fuel from the fuel injection valve 4 to each. The fuel is injected into the cylinder in the latter half of the compression stroke of the cylinder. During normal operation, the fuel injection keeps the engine air-fuel ratio significantly lean (for example, the air-fuel ratio is about 30). However, when supplying hydrocarbons to the oxidation catalyst 5, the ECU 20 re-injects fuel from the fuel injection valve 4 not only in the normal compression stroke late fuel injection but also in the exhaust stroke of each cylinder.

The fuel injected into the cylinder during the exhaust stroke is
Although some of them burn in the cylinder, they do not contribute to the increase in output of the engine. Further, most of the fuel that has not burned is vaporized in the cylinder and is discharged to the exhaust passage together with the exhaust gas and supplied to the oxidation catalyst 5. If the oxidation catalyst 5 has reached the activation temperature, most of this vaporized fuel is burned by the oxidation catalyst, and a large amount of HC and CO components are generated. In addition, the remaining fuel that has not been burned in the oxidation catalyst 5 is also thermally decomposed when passing through the catalyst 5 that has become hot due to combustion, and the high-boiling point hydrocarbon component having a large molecular weight is converted to a low-boiling point unburned HC component having a small molecular weight. To be done. Thus, low oxygen concentration in the NO _X absorbent 9, a large amount of unburned HC, will be exhausted comprising CO component flows in a short time regeneration of the NO _X absorbent 9 is completed.

Next, the reproduction operation of the DPF 7 will be described. In this embodiment, as described above, NO ₂ and D in the exhaust gas
The soot (carbon) deposited on the PF is reacted to burn the soot. Further, the NO component generated at this time is changed to DPF7.
It is necessary to absorb the NO _x absorbent 9 on the downstream side to prevent the release to the atmosphere. Therefore, when reproducing the DPF 7,
The exhaust air-fuel ratio must be lean. Further, in order to promote the reaction between NO ₂ and soot, the exhaust temperature is preferably higher. Therefore, in the present embodiment, the ECU 2
In the range 0 where the exhaust air-fuel ratio does not become rich, as in the case of regeneration of the NO _X absorbent 9, fuel is injected in the exhaust stroke in addition to the injection in the latter half of the normal compression stroke by a routine (not shown). Exhaust temperature is raised by burning with the oxidation catalyst 5. In addition, in order to raise the exhaust temperature, the electric heater 5a of the oxidation catalyst 5 is energized as needed during regeneration of the DPF 7. Since the exhaust gas passing through the oxidation catalyst 5 is heated by the electric heater 5a, and the fuel injected during the exhaust stroke is burned by the oxidation catalyst 5, the DPF 7 has a temperature higher than usual (for example, about 400 to 500 ° C.). Exhaust gas will flow in. Therefore, NO ₂ in the exhaust gas easily reacts with the soot accumulated on the DPF 7, the soot is burned and removed, and the pressure loss of the DPF 7 is reduced. Also, DP
Since the exhaust gas passing through F7 is still a lean air-fuel ratio as a whole, NO generated by the reaction between NO ₂ and soot is
Is absorbed by _the NO _X absorbent 9 on the downstream side and is removed from the exhaust.

In the present embodiment, the number of DPF 7 regeneration operations is several.
The air-fuel ratio at the time of regeneration is about 20.
Maintained at a lean air-fuel ratio. At this time, the DPF
Playback of 7 is completed in a few minutes. As mentioned above,
NO_XThe regeneration operation of the absorbent 9 is performed at intervals of several tens of seconds to several minutes.
However, in the present embodiment, N is set during the regeneration operation of the DPF 7.
O_XWhen it is time to regenerate the absorbent 9
Increases the fuel injection amount during the exhaust stroke to increase the exhaust air-fuel ratio.
Reduce to about 13. As a result, the DPF7 regeneration operation
During production, normal NO _XIn addition to absorbent 9 regeneration operation, usually
The regeneration operation will be performed at a higher exhaust temperature,
NO_XRegeneration of the absorbent 9 is more complete.

However, the above NO _x absorbent 9 and DPF
Since it is necessary to burn the fuel with the oxidation catalyst 5 when executing the regeneration operation of No. 7, it is necessary that the oxidation catalyst 5 is at the catalyst activation temperature (for example, about 250 ° C.) when executing the regeneration operation. To be done. During normal operation, the oxidation catalyst 5 is heated by the passing exhaust gas and is heated to a temperature according to the exhaust gas temperature, but the exhaust gas temperature becomes considerably lower than the activation temperature of the catalyst in idle operation after cold start of the engine. There is. Further, generally, the exhaust temperature of a diesel engine during normal operation is lower than that of a gasoline engine, and it may be lower than the catalyst activation temperature during low load operation. In such a state, the temperature of the oxidation catalyst 5 is also below the activation temperature, and in this state, the NO _x absorbent 9 and DP
Even if the fuel injection in the exhaust stroke is executed to execute the regeneration operation of F7, the fuel does not burn in the oxidation catalyst 5,
As described above, problems such as deterioration of exhaust emission occur. In this case, a large amount of low-temperature exhaust gas is used as the oxidation catalyst 5.
Therefore, even if the electric heater 5a is energized to raise the temperature of the oxidation catalyst 5, the electric heater 5
The heat generated by a is taken by a large amount of exhaust gas passing through the oxidation catalyst 5, and the temperature of the oxidation catalyst 5 cannot be raised rapidly.

Therefore, in the present embodiment, when both the engine exhaust temperature and the temperature of the oxidation catalyst 5 are lower than the predetermined temperature, the bypass control valve 8 is opened to remove most of the exhaust gas from the oxidation catalyst 5. The electric heater 5a is energized in a state of bypassing and flowing. When the bypass control valve 8a is opened, most of the exhaust gas flows through the bypass passage 6 and almost no exhaust gas flows into the oxidation catalyst 5. Therefore, the heat generated by the electric heater 5a can be used only for heating the oxidation catalyst 5, and the oxidation catalyst 5 can be heated to the activation temperature in a short time. In this embodiment, since the bypass control valve 8 is provided on the bypass passage 6, a small amount of exhaust gas passes through the oxidation catalyst 5 even when the bypass control valve 8 is opened. If the exhaust switching valve is provided at the connection portion so that the exhaust gas flows into the bypass passage 6 when the exhaust temperature is low to completely block the inflow of the exhaust gas to the oxidation catalyst 5, the temperature of the catalyst 5 is further increased. It is possible to speed up.

Even when the exhaust gas temperature is low, when the catalyst temperature reaches the activation temperature as described above, unburned H in the exhaust gas is reduced.
The C and CO components and the vaporized fuel by the exhaust stroke injection are catalysts 5.
The temperature of the catalyst 5 rises because it becomes burned in
Will be maintained at a high temperature. FIG. 2 is a flowchart showing a catalyst heating control routine using the bypass control valve 8 and the electric heater 5a when the exhaust temperature is low. This routine is executed by the ECU 20 at regular intervals.

In FIG. 2, when the routine starts,
In step 201, from the sensors corresponding to the accelerator opening A _CC of the engine 1 and the engine speed NE,
Further, the temperature THC of the oxidation catalyst 5 is read from the catalyst temperature sensor 10. Next, at step 203, the engine exhaust temperature T _EX is calculated from the accelerator opening A _CC and the engine speed NE read as described above. In the present embodiment, the engine exhaust temperature is previously obtained by actually measuring under various conditions of the accelerator opening and the engine speed, and the RO of the ECU 20 is a numerical map using the accelerator opening A _CC and the engine speed NE.
It is stored in M23. In step 203, using this map, the exhaust temperature T _EX is calculated using A _CC and NE read in step 201. In the present embodiment, as described above, the accelerator opening A _CC and the engine speed N
Although the engine exhaust temperature is indirectly detected by using E and E, it is possible to directly detect the exhaust temperature by providing an exhaust temperature sensor at the oxidation catalyst inlet portion of the exhaust passage 3.

Based on the above, after the exhaust gas temperature T _{EX is} calculated, the exhaust gas temperature T _EX
EX and oxidation catalyst 5 temperature THC read in step 201
Is determined to be a predetermined value T ₀ or less. Here, T ₀ is the activation temperature of the oxidation catalyst or a temperature higher than it, and is set to a temperature of about the activation temperature (250 ° C.) of the oxidation catalyst 5 in this embodiment, for example.

In steps 205 and 207, the exhaust temperature T _EX
If both the catalyst temperature THC and the catalyst temperature THC are equal to or lower than the predetermined temperature T ₀ , that is, if the exhaust gas temperature is low and the catalyst 5 has not reached the activation temperature, the catalyst is brought to the activation temperature early. There is a need. Therefore, in this case, step 2
At 09, the relay 5b of the electric heater 5a is turned on, the electric heater 5a is energized, and step 21
At 1, the bypass control valve 8 is opened. As a result, the heater 5 is energized with the exhaust gas flowing into the catalyst 5 being restricted, so that the temperature of the catalyst 5 quickly rises and reaches the activation temperature.

On the other hand, if at least one of the exhaust temperature T _EX and the catalyst temperature THC exceeds the predetermined temperature T ₀ in steps 205 and 207, step 21
3 and step 215 are executed, the power supply to the heater 5a is stopped, and the bypass control valve 8 is closed. As a result, the entire amount of exhaust gas from the engine will pass through the catalyst 5. Even when the catalyst temperature THC is equal to or lower than the predetermined value T ₀ , when the exhaust temperature is equal to or higher than T ₀ , the heater energization is stopped and the entire amount of exhaust gas is allowed to flow to the catalyst 5 because the exhaust temperature is T 0. _This is because the temperature exceeds ₀ and is high, so that the temperature of the catalyst 5 rises quickly by flowing the entire amount of exhaust gas to the catalyst 5 without heating with the heater 5a.

As described above, the exhaust temperature T _EX is T
If ₀ temperature of the catalyst 5 even at was the following cases becomes T ₀ or more, the HC in the exhaust gas at the catalyst 5, an oxidation reaction of CO component caused by supplying the exhausted catalyst 5, catalyst 5 Temperature Will be maintained at a high temperature. According to the routine of FIG. 2, when both the exhaust gas temperature and the catalyst 5 temperature are low, heating is performed by the electric heater 5a with the exhaust flow rate passing through the catalyst being limited, and the catalyst 5 temperature is quickly increased. Since the activation temperature is reached, the supplied hydrocarbon component can be burned even when the exhaust temperature is low. When the exhaust gas temperature or the catalyst 5 temperature becomes high, the electric heater is de-energized, and at the same time, the entire amount of exhaust gas passes through the catalyst 5. Therefore, according to the present embodiment, it is possible to shorten the energization time of the electric heater 5 and reduce the battery load.

In the above embodiment, the fuel injection valve of the engine is used as the HC and CO supply device to perform the fuel injection in the exhaust stroke of the diesel engine, but the present invention is not limited to this, and the catalyst is not limited thereto. An HC and CO supply device for supplying a hydrocarbon component (for example, light oil, gasoline, etc.) to the exhaust passage on the upstream side may be provided separately from the fuel injection valve. In this case, for example, a pressurized hydrocarbon supply source such as a pump and an injection valve for injecting hydrocarbons are provided in the exhaust passage, a flow control valve is provided in a pipe connecting these, and the ECU controls opening / closing of this flow control valve. By doing so, the supply of the hydrocarbon component to the catalyst may be controlled.

[0039]

According to the present invention, the exhaust gas flow into the catalyst is restricted when the catalyst is heated by the electric heater, so that the catalyst can reach the activation temperature in a short time without increasing the battery load. This makes it possible to quickly burn the supplied hydrocarbon component even when the exhaust gas temperature is low.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a schematic configuration of an embodiment of an exhaust emission control device of the present invention.

FIG. 2 is a flowchart illustrating a catalyst temperature raising operation in the exhaust gas purification method of the present invention.

[Explanation of symbols]

1 ... diesel engine 2 ... intake passage 3 ... exhaust passages 4 fuel injection valves 5 ... oxidation catalyst 6 ... bypass passage 8 ... bypass control valve 7 ... DPF 9 ... NO _X absorbent 20 ... engine control circuit (ECU)

Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI Technical display location F01N 3/10 ZAB F01N 3/10 ZABA 3/24 3/24 E ZAB ZABL F02D 45/00 310 F02D 45/00 310R (72) Inventor Koichi Kojima 1 Toyota-cho, Toyota-shi, Aichi Toyota Motor Co., Ltd.

Claims (1)

[Claims] 1. A catalyst arranged in an exhaust passage of an internal combustion engine, an electric heater for heating the catalyst, and H for supplying a hydrocarbon component to the exhaust passage upstream of the catalyst.
A C supply device, a bypass passage that bypasses the catalyst and connects an exhaust passage on the upstream side of the catalyst and an exhaust passage on the downstream side of the catalyst, a bypass control valve that controls an exhaust flow rate through the bypass passage, and a temperature of the catalyst Temperature detecting means for detecting the engine exhaust temperature and the engine exhaust temperature, respectively, when both the catalyst temperature and the engine exhaust temperature are below a predetermined temperature, the bypass control valve is opened to at least a part of the engine exhaust. An exhaust emission control device for an internal combustion engine, comprising: a control unit that supplies a current to the electric heater while flowing in a bypass passage.