JP2944371B2 - Air introduction device in exhaust pipe of internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for introducing air into an exhaust pipe of an internal combustion engine, which activates a catalyst for purifying exhaust gas by introducing air into the exhaust pipe of the internal combustion engine.

[0002]

2. Description of the Related Art FIG. 6 is a block diagram showing a conventional air introduction device in an exhaust pipe similar to that shown in, for example, Japanese Utility Model Laid-Open No. 47-21018. In FIG. 1, an internal combustion engine 1 is connected to an intake pipe 2 for introducing air and an exhaust pipe 3 for discharging harmful exhaust gas generated by combustion to the atmosphere. An air cleaner 4 for removing dust in the atmosphere is provided at an upstream portion of the intake pipe 2. Downstream of the air cleaner 4, a throttle valve 5 for changing the passage area of the intake pipe 2 to adjust the amount of air taken into the internal combustion engine 1 is provided.

[0003] In the middle of the exhaust pipe 3, a first catalyst accommodating portion 6 accommodating a first three-way catalyst (hereinafter simply referred to as a first catalyst) for purifying harmful exhaust gas by a chemical reaction.
Is provided. A second three-way catalyst (hereinafter simply referred to as a second catalyst) that purifies exhaust gas is stored downstream of the first catalyst storage unit 6 in the same manner as the first catalyst. Is provided. An air introduction pipe 8 is connected between the intake pipe 2 and the exhaust pipe 3. The air introduction pipe 8 is branched into two parts on the way, and one of the branches is connected to the upstream part of the first catalyst storage part 6 and the other is connected to the upstream part of the second catalyst storage part 7.

[0004] The first and second air inlet pipes 8 are provided at a branch portion.
Air is introduced upstream of both of the catalyst storage sections 6 and 7 of
A switching valve 9 for switching whether to introduce air only upstream of the second catalyst storage unit 7 is provided. An air pump 10 for forcibly introducing air into the exhaust pipe 3 is provided upstream of the switching valve 9 of the air introduction pipe 8. The air pump 10 is driven by the internal combustion engine 1 via a belt (not shown).

[0005] A temperature sensor 11 for detecting the temperature of the second catalyst is attached to the second catalyst accommodating section 7. The temperature sensor 11 and the switching valve 9 include the temperature sensor 1
1 for controlling the switching valve 9 in accordance with information from the control unit 1
2 are connected. Note that an injector for supplying fuel to the internal combustion engine 1 and a control system thereof are omitted here.

Next, the operation will be described. Internal combustion engine 1
During the choke operation at the time of starting, since the air-fuel ratio is rich and a large amount of HC and CO is generated, a part of the purified air passing through the air cleaner 4 is forcibly forced into the air introduction pipe 8 by the air pump 10. And is introduced upstream of both catalyst storage sections 6,7. As a result, HC and CO generated in large amounts are converted into H ₂ O and CO ₂ by an oxidation reaction in both the first and second catalyst housing sections 6 and 7, thereby purifying exhaust gas.

When the temperature of the second catalyst becomes high and becomes activated, the temperature is detected by the temperature sensor 11, and
The switching valve 9 is switched by the control unit 12, and the second
The air is introduced only upstream of the catalyst storage section 7. In this state, NO _X in the exhaust gas, is changed to N ₂ by a reduction reaction of the first catalyst and HC, CO can be varied in H ₂ O and CO ₂ only the second catalyst side, Exhaust gas purification is performed.

[0008]

In the conventional exhaust-pipe air introduction device configured as described above, since the first and second catalysts are at a low temperature, normal-temperature air at a lower temperature than the exhaust gas is supplied. Due to the introduction, the temperature of the exhaust gas passing through each of the catalyst storage units 6 and 7 decreases, and the activation of the catalyst is delayed, thereby causing a problem that the purification efficiency of the exhaust gas decreases. . Further, the distribution ratio of the amount of air introduced into the first and second catalysts is constant until the temperature of the second catalyst reaches a set value and the introduction of air into the first catalyst is stopped. since the emission of the nO _X is gradually increases with increasing temperature of the internal combustion engine 1 against, until switches the switching valve 9, there is a problem that can not be efficiently purify nO _X.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has an object to provide an internal combustion engine capable of promoting catalyst activation and improving harmful exhaust gas purification efficiency. It is intended to obtain an air introduction device in an exhaust pipe.

[0010]

According to a first aspect of the present invention, there is provided an air introduction device in an exhaust pipe of an internal combustion engine, wherein air is introduced into each of the first and second three-way catalysts by the air introduction means, and the distribution means is provided. by introducing air into the first and second three-way catalyst and partitioned, the first and second the air introduced into the three-way catalyst was heated separately by further heater, these air introduction means, the dispensing means and the heater Is controlled by the control unit.

According to a second aspect of the present invention, the control unit determines the amount of air to be introduced based on the amount of intake air of the internal combustion engine, and sets the amount of introduced air to the injection pulse width of the injector. Based on the correction, the air introduction means is controlled.

According to a third aspect of the present invention, the control unit determines the distribution ratio of the introduced air based on the capacity ratio of the first and second three-way catalysts. The distribution means is controlled so that the amount of air introduced into the first three-way catalyst is gradually reduced and the amount of air introduced into the second three-way catalyst is gradually increased with an increase in the water temperature. is there.

According to a fourth aspect of the present invention, the control unit determines the distribution ratio of the introduced air based on the capacity ratio of the first and second three-way catalysts. Controlling the distribution means so as to gradually reduce the amount of air introduced into the first three-way catalyst and gradually increase the amount of air introduced into the second three-way catalyst with time from the start. It is.

According to a fifth aspect of the present invention, in the exhaust pipe air introduction device for an internal combustion engine, the control unit may control the first three-way catalyst before a predetermined time before the amount of air introduced into the first three-way catalyst becomes zero. This is to stop the heating of the air introduced into the chamber.

[0015]

According to the first aspect of the present invention, the temperature of the exhaust gas entering the first and second three-way catalysts is prevented by lowering the temperature of the exhaust gas entering the first and second three-way catalysts by heating the air introduced into the exhaust pipe with the heater . Promotes activation of the three-way catalyst.

According to the second aspect of the present invention, the amount of introduced air is determined based on the amount of intake air of the internal combustion engine, so that the amount of introduced air is matched with the amount of exhaust gas. By performing correction based on the pulse width, the amount of introduced air is adjusted to the amount of HC and CO in the exhaust gas.

According to the third and fourth aspects of the present invention,
By determining the distribution ratio of the introduced air to the first and second three-way catalysts from the capacity ratio of each catalyst, an amount of air corresponding to the purifying ability of each catalyst is introduced, and further, the water temperature of the internal combustion engine or The distribution ratio is changed so that the amount of air introduced into the first three-way catalyst is gradually reduced and the amount of air introduced into the second three-way catalyst is gradually increased with the passage of time from the start. Accordingly, gradually raise the purification rate of the first three-way catalyst for NO _X emissions from an internal combustion engine with an increase in temperature of the internal combustion engine is increased, the NO _X in the first three-way catalyst, the second
HC and CO are each efficiently purified by the three-way catalyst.

In the invention of claim 5, the heating of the air introduced into the first three-way catalyst is stopped before the amount of air introduced into the first three-way catalyst becomes zero, so that the heating means Prevent excessive heating.

[0019]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. Embodiment 1 FIG. FIG. 1 is a configuration diagram showing an air introduction device in an exhaust pipe of an internal combustion engine according to Embodiment 1 of the present invention. The same or corresponding parts as those in FIG. 6 are denoted by the same reference numerals, and description thereof will be omitted.

In FIG. 1, an injector 21 for supplying fuel by spraying fuel in a mist toward an intake valve (not shown) is provided for each cylinder on the intake pipe 2 side of the internal combustion engine 1. ing. An airflow sensor 22 for detecting the amount of air taken into the internal combustion engine 1 is provided upstream of the throttle valve 5 in the intake pipe 2. In the exhaust pipe 3,
An air-fuel ratio sensor 23 for detecting the air-fuel ratio in the internal combustion engine 1 from the concentration of oxygen contained in the exhaust gas is provided.

The air pump 24 serving as the air introducing means of the first embodiment is constituted by, for example, an electric pump or the like, so that the rotation speed can be adjusted independently of the rotation of the internal combustion engine 1 without synchronization. Has become. Further, the air introduction pipe 8
Distribution valve 25 which is a distribution means provided at a branch portion of
Can linearly change the distribution ratio of the amount of air introduced into the first and second catalysts. Downstream from the branch of the air introduction pipe 8, heaters 26 as heating means for heating the air introduced into the first and second catalysts, respectively,
27 are provided. Check valves 28 and 29 for preventing backflow of air are provided between the heaters 26 and 27 and the distribution valve 25, respectively.

A control unit (control unit) 30 is connected to each of the injectors 21, the air flow sensor 22, the air-fuel ratio sensor 23, and the like. This control unit 3
0 indicates the basic fuel injection pulse width based on the intake air amount detected by the air flow sensor 22 and the engine speed, corrects the temperature such as water temperature, and further adjusts the air-fuel ratio so that the air-fuel ratio becomes the stoichiometric air-fuel ratio. The air-fuel ratio feedback correction is performed based on the output of the sensor 23, the injection pulse width is determined, and the injector 21 is driven by the fuel injection signal to perform fuel control.

The control unit 30 controls the number of revolutions of the air pump 24 to adjust the flow rate, controls the distribution valve 25 according to the water temperature of the internal combustion engine 1 and the like, and controls the first and second catalysts. Adjust the distribution ratio of the introduced air. Further, the control unit 30 controls the power supply to the heaters 26 and 27 to adjust the temperature of the introduced air.

Next, the operation will be described. Internal combustion engine 1
Is in a cold state immediately after the start, the fuel injection amount by the injector 21 is controlled by the control unit 30 in an open loop so as to be richer than the stoichiometric air-fuel ratio.
Therefore, in this case, harmful substances such as HC,
A lot of CO is mixed. However, immediately after starting, the first
Since both the first and second catalysts are in an inactive state, the control unit 30 activates the air pump 24 and controls the distribution valve 25 simultaneously with the start of the internal combustion engine 1 to control the first and second catalysts. Air is introduced to both. Further, the introduced air is heated by both the heaters 26 and 27.

Thus, the temperature of the exhaust gas is prevented from being lowered by the introduced air, and the activation of the first and second catalysts is promoted by the exhaust gas flowing in without the temperature drop and the heat generated by the oxidation reaction. Is done. As a result, HC and CO are efficiently oxidized by oxygen in the introduced air, and CO ₂ and H ₂ O
become. Here, in such a cold state immediately after the start, N
Since O _X hardly occurs mainly immediately after starting to a first catalyst arranged for reduction of the NO _X introducing air, H
Purification of C and CO can be performed.

Next, FIG. 2 is a relationship diagram showing an example of a method of controlling the distribution valve 25 and the heaters 26 and 27 by the control unit 30 of FIG. The control unit 30 estimates the temperature condition of the first catalyst based on, for example, the water temperature of the internal combustion engine 1, and controls the distribution valve 25 when it is determined that the first catalyst has been activated, so that air is supplied only to the second catalyst. To introduce. At this time, since the second catalyst is disposed downstream of the first catalyst, the temperature of the exhaust gas entering the second catalyst storage unit 7 is always low, and therefore, the activation of the second catalyst is caused by the first catalyst. It is behind the catalyst. Therefore, the air introduced into the second catalyst is supplied to the heater 2
Continue heating with 7 .

After the introduction of air into the first catalyst is stopped, HC and CO are continuously purified by the introduced air in the second catalyst storage section 7, and the internal combustion engine 1 is warmed up. NO _X which Runishitagatte emissions increases is converted into harmless N ₂ by the reducing action of the first catalyst storage section 6.

Thereafter, when it is determined that the internal combustion engine 1 has been further warmed up and the second catalyst has also been activated, the control unit 30 stops energizing the heater 27, whereby the second catalyst is heated. Not room temperature air is introduced. Therefore, N
O _X and some HC, CO are purified by oxidation-reduction reaction at the first catalyst, H which has not been purified in the first catalyst
C and CO are purified by an oxidation reaction with the second catalyst.

As described above, immediately after the start of the internal combustion engine 1, the first
By heating the air introduced into the second catalyst and the heaters 26 and 27, the activation of the first and second catalysts is promoted, and the purification efficiency of HC and CO is improved. Conventionally, since the air pump 10 was driven by the internal combustion engine 1 via a belt or the like, the amount of air introduced into the exhaust pipe 3 was not appropriate in some cases. Since the control is performed independently of the engine 1, the amount of air introduced into the first and second catalysts can be made appropriate, thereby also improving the purification efficiency.

Embodiment 2 FIG. Next, a second embodiment of the present invention will be described. In the second embodiment, in addition to the first embodiment, the control unit 30 controls the amount of air introduced into the exhaust pipe 3 to an amount corresponding to the amount of exhaust gas and the concentrations of HC and CO, so that the first and second parts are controlled. 2 further promotes the activation of the catalyst and further improves the exhaust gas purification efficiency.
That is, the amount of exhaust gas is proportional to the amount of intake air, and the control unit 30 detects the amount of intake air based on information from the air flow sensor 22, and according to the amount of intake air, the air pump 24
Determine the output value to.

Further, by making a correction based on the value of the injection pulse width of the injector, the difference in the emission concentration of HC and CO between the presence and absence of the air-fuel ratio feedback and the difference in the air-fuel ratio feedback based on the output of the air-fuel ratio sensor 23 are obtained. The air corresponding to the difference in the emission concentration of HC and CO due to the rich / lean fluctuation of the air-fuel ratio can be introduced into the exhaust pipe 3.

Referring to FIG. 3, when the acceleration is started at the point A and the throttle valve 5 of FIG. 1 is opened, the intake air amount (a) increases and the exhaust gas amount (d) increases accordingly. Therefore, the control unit 30 increases the introduced air amount (f) in proportion to the exhaust gas amount (d). Also, even if the intake air amount (a) is constant, the injector pulse width (b), for example, when air-fuel ratio feedback is being performed, when switching from the air-fuel ratio feedback mode to the enriched mode, or vice versa. Is constantly changing.
For this reason, A / F (air-fuel ratio) (c) always fluctuates, and H
The C and CO concentrations (e) also fluctuate.

Therefore, as shown in FIGS.
Assuming that the injector pulse width at which F becomes 14.7 (theoretical air-fuel ratio) is 100%, the intake air amount (b) obtained from the intake air amount (a) is a value corresponding to the injector pulse width (b) increased or decreased therefrom. ), HC, C
The amount of air corresponding to the O concentration (e) can be introduced.

Embodiment 3 FIG. Next, a third embodiment of the present invention will be described. In the third embodiment, the control unit 30
The distribution ratio of the introduced air in the distribution valve 25 is continuously changed according to the water temperature of the internal combustion engine 1 as shown in FIG. 4, for example. That is, immediately after the start of the internal combustion engine 1,
The above-mentioned distribution ratio is set to the volume ratio of the first and second catalysts. Thereafter, as the water temperature of the internal combustion engine 1 increases, the amount of air introduced into the first catalyst is gradually reduced, and The amount of air introduced into the first catalyst is gradually increased, and is set such that the amount of air introduced into the first catalyst becomes zero when the water temperature reaches a temperature at which it is determined that the first catalyst has been activated.

[0035] By performing the control unit 30 controls such distribution valve 25, with respect to emissions of the NO _X increasing with the warm-up of the internal combustion engine 1 progresses, the first with an increase in the emissions It is possible to increase the NO _X purification rate of the catalyst, and thereby limit the NO _X emission amount to a certain value or less.

Embodiment 4 FIG. In the third embodiment, the first
And the distribution ratio of the introduced air to the second catalyst is changed in accordance with the water temperature of the internal combustion engine 1. For example, as shown in FIG. 5, the distribution ratio may be changed with the lapse of time from the start of the internal combustion engine 1. Alternatively, the same effect as in the third embodiment can be obtained.

Embodiment 5 FIG. Next, a fifth embodiment of the present invention will be described. In the fifth embodiment, in addition to the above-described third embodiment, as shown in the heater energization relation diagrams of FIGS. 4 and 5, the point B at which the distribution ratio of the introduced air to the first catalyst becomes zero is higher than the point B. At an early time point A, the power supply to the heater 26 for heating the air introduced into the first catalyst is stopped according to the water temperature of the internal combustion engine 1 (FIG. 4) or the time from the start (FIG. 5).

Thus, the heater 26 can be prevented from excessively increasing in temperature due to a decrease in the air flow rate, and a failure such as disconnection can be prevented. Further, since the introduced air after the heater 26 is stopped is heated by the residual heat of the heater 26, the exhaust gas is not cooled by the introduced air. Conversely, the time between A and B may be set so that heating can be performed by residual heat.

[0039]

As described above, the air introduction device in the exhaust pipe of an internal combustion engine according to the first aspect of the present invention is provided with the first heater by the heater .
In addition, since the air introduced into the second three-way catalyst is separately heated, it is possible to promote the activation of each catalyst and to improve the purification efficiency of harmful exhaust gas.

According to the second aspect of the present invention, the control unit determines the amount of air to be introduced based on the amount of intake air of the internal combustion engine, and determines the amount of air to be introduced by the injection pulse width of the injector. To control the air introduction means, in addition to the same effects as the first aspect of the present invention, the amount of introduced air is reduced by the amount of exhaust gas and the amount of HC,
The effect is that the amount can be adjusted to the CO concentration and the purification efficiency can be further improved.

Further, in the exhaust pipe air introduction device for an internal combustion engine according to the third and fourth aspects of the present invention, the control unit determines the distribution ratio of the introduced air based on the capacity ratio of the first and second three-way catalysts. And the amount of air introduced into the first three-way catalyst is gradually reduced and the amount of air introduced into the second three-way catalyst is gradually increased with the rise of the water temperature of the internal combustion engine or the time from the start. Since the distribution means is controlled so as to cause the same effect as in the first aspect of the present invention, it is possible to introduce an amount of air commensurate with the purifying ability of each catalyst.
It is possible to prevent an increase in the amount of emission of NO _X due to a rise in the temperature of the internal combustion engine, and it is possible to further improve the purification efficiency.

Further, according to the fifth aspect of the present invention, in the exhaust pipe air introduction device for an internal combustion engine, the control unit may control the first three-way catalyst to perform the first three-way catalyst before the predetermined time before the amount of air introduced into the first three-way catalyst becomes zero. Since the heating of the introduced air to the source catalyst is stopped, in addition to the same effect as the above-mentioned claim 1, by heating in the absence of air, it is possible to prevent the heating means from excessively rising. Thus, there is an effect that the failure of the heating means can be prevented.

[Brief description of the drawings]

FIG. 1 is a configuration diagram illustrating an air introduction device in an exhaust pipe of an internal combustion engine according to a first embodiment of the present invention.

FIG. 2 is a relationship diagram illustrating an example of a method of controlling a distribution valve and a heater by a control unit in FIG. 1;

FIG. 3 is a relationship diagram showing a time change of an intake air amount, an injector pulse width, an air-fuel ratio, an exhaust gas amount, HC, CO concentration, and an introduced air amount when a control unit according to a second embodiment of the present invention is used. .

FIG. 4 is a relationship diagram showing a change over time in a water temperature, an introduced air distribution ratio, and a heater energized state of an internal combustion engine when the control units according to Embodiments 3 and 5 of the present invention are used.

FIG. 5 is a relationship diagram showing a change over time in an introduced air distribution ratio and a heater energized state when the control units according to Embodiments 4 and 5 of the present invention are used.

FIG. 6 is a configuration diagram showing an example of a conventional air introduction device in an exhaust pipe of an internal combustion engine.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 internal combustion engine 3 exhaust pipe 6 first catalyst storage section 7 second catalyst storage section 21 injector 24 air pump (air introduction means) 25 distribution valve (distribution means) 26 heater (heating means) 27 heater (heating means) 30 control Department

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) F01N 3/30 F01N 3/22 F01N 3/32 F01N 3/20

Claims (5)

(57) [Claims] 1. An air introducing means for introducing air into first and second three-way catalysts arranged in series with each other in an exhaust pipe of an internal combustion engine, and introducing air into the first and second three-way catalysts. Distributing means for distributing air, heaters for separately heating the air introduced into the first and second three-way catalysts, and a control unit for controlling the air introducing means, the distributing means and the heater are provided. An air introduction device in an exhaust pipe of an internal combustion engine. 2. The control unit determines an amount of air to be introduced based on the amount of intake air of the internal combustion engine, corrects the amount of air to be introduced based on the injection pulse width of the injector, and controls the air introduction means. 2. The air introduction device in an exhaust pipe of an internal combustion engine according to claim 1, wherein: 3. The control unit determines a distribution ratio of the introduced air based on a capacity ratio of the first and second three-way catalysts, and controls the first three-way catalyst as the water temperature of the internal combustion engine rises. And controlling the distributing means so as to gradually reduce the amount of air introduced into the second three-way catalyst and gradually increase the amount of air introduced into the second three-way catalyst. Item 3. An air introduction device in an exhaust pipe of an internal combustion engine according to Item 2. 4. The control unit determines a distribution ratio of the introduced air based on a capacity ratio of the first and second three-way catalysts, and the first three-way catalyst according to time from the start of the internal combustion engine. The distribution means is controlled so as to gradually reduce the amount of air introduced into the second three-way catalyst and gradually increase the amount of air introduced into the second three-way catalyst. An air introduction device in an exhaust pipe of an internal combustion engine according to claim 2. 5. The control unit stops heating of the air introduced into the first three-way catalyst before a predetermined time when the amount of air introduced into the first three-way catalyst becomes zero. 5. The exhaust pipe introduction device for an internal combustion engine according to claim 3, wherein: