JP2006220019A - Exhaust emission control device for engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device for an engine capable of stably maintaining excellent exhaust emission control performance regardless of an operating situation and obtaining excellent drivability by ensuring a quick accelerating response or the like by rich burning even when applied to an engine of a motorcycle of small displacement. <P>SOLUTION: The exhaust emission control device 31 for the engine 3 is provided with a first catalyst 7 disposed in an exhaust gas passage 5 of the engine 3 to mainly perform reduction action; a second catalyst 9 disposed downstream of the first catalyst 7 to mainly perform oxidation action; a first secondary air supply line 11 connected between the first and second catalysts 7, 9 of the exhaust gas passage 5; and a linear air-fuel ratio sensor 33 disposed downstream of the second catalyst 9. A supply air-fuel ratio to the engine 3 is feedback-controlled based on detection values of the linear air-fuel ratio sensor 33. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to an engine exhaust gas purification apparatus that purifies NOx, CO, and THC in exhaust gas discharged from an engine.

Conventionally, an engine exhaust gas purification apparatus having the configuration shown in FIG. 5 has been proposed (see, for example, Patent Document 1).
In the engine exhaust gas purification apparatus 1 shown here, a catalytic converter 66 is mounted between a front exhaust pipe 63 connected to an exhaust manifold 62 of an engine 61 and an exhaust pipe 64 provided with a muffler 65 on the downstream side thereof. Has been.

The catalytic converter 66 is a three-way catalyst (first catalyst) 68 mainly disposed for the purpose of reducing action disposed on the upstream side inside the housing 67, and mainly intended for an oxidizing action disposed on the downstream side inside the housing 67. An oxidation catalyst (second catalyst) 69. This three-way catalyst 6
A secondary air supply port 71, which is one end of the secondary air supply path 72, opens in the space 70 between 8 and the oxidation catalyst 69.
A reed valve device 80 is connected to the other end of the secondary air supply path 72. The reed valve device 80 includes a reed valve 82 inside the housing 81 and an air element 83 on the atmosphere port 84 side.
It has.
An oxygen sensor 90 attached to the exhaust manifold 62 detects the oxygen concentration in the exhaust gas.

The exhaust gas purification apparatus 1 of this type feeds back the fuel injection amount to the engine 61 so that the detected air-fuel ratio obtained based on the oxygen concentration in the exhaust gas detected by the oxygen sensor 90 becomes stoichiometric (theoretical air-fuel ratio). And controlling the NOx in the exhaust gas by the three-way catalyst 68.
NOx, CO, and THC in the exhaust gas are purified by oxidizing the CO and THC in the exhaust gas by the oxidation catalyst 69.

Further, by supplying secondary air to the space 70 according to the operating state of the engine 61, for example, exhaust gas that is richer than the stoichiometric air-fuel ratio passes through the three-way catalyst 68, so that CO and THC were not sufficiently purified. Even in this case, the exhaust gas in which the CO and THC are not sufficiently purified is mixed with the secondary air to form an oxidizing atmosphere, so that the exhaust gas in which the CO and THC in the exhaust gas is sufficiently purified by the oxidation catalyst 69 is obtained. The gas can be discharged from the exhaust pipe 4 through the muffler 65 to the atmosphere.

Japanese Utility Model Publication No. 58-156115

However, the exhaust gas passage three-way catalyst 68 as in the engine exhaust gas purification device 1 described above.
Based on the detection value of the oxygen sensor 90 disposed upstream of the fuel supply device, the fuel supply device
In the method in which the air-fuel ratio supplied to 1 is feedback controlled, it is not possible to cope with changes in the amount of secondary air supplied downstream from the three-way catalyst 68.

Therefore, when operating conditions where stoichiometric combustion cannot be maintained, for example, when rich burn with an increased fuel ratio is required, such as during warm-up operation or high-speed high-load operation, or when medium-high speed low-load operation is performed When lean burn with a reduced fuel ratio is desirable, such as when, etc., NOx, CO, and THC in exhaust gas cannot be sufficiently purified, and excellent exhaust gas purification performance is achieved regardless of operating conditions. However, there is a problem that it cannot be maintained stably.

In the case of feedback control based on stoichiometric operation, agile acceleration response due to rich burn is lost, and when applied to engines such as small displacement motorcycles, drivability is significantly deteriorated and practical use is reduced. There was also a problem of poor sex.
Therefore, an object of the present invention is to solve the above-mentioned problems, and it is possible to stably maintain an excellent exhaust gas purification performance regardless of operating conditions, and when applied to an engine such as a small displacement motorcycle. Another object of the present invention is to provide an engine exhaust gas purification device that can secure a quick acceleration response by rich burn and obtain good drivability.

The above-described object of the present invention is to provide a first catalyst mainly for the purpose of reduction disposed in the exhaust gas passage of the engine, and a second catalyst mainly for the purpose of oxidation disposed downstream of the first catalyst. A first secondary air supply path connected between the first and second catalysts in the exhaust gas passage;
And an exhaust gas concentration sensor disposed downstream of the second catalyst, wherein the exhaust gas concentration sensor controls an air / fuel ratio supplied to the engine. .

According to the exhaust gas purification apparatus for an engine configured as described above, the exhaust concentration sensor for feedback control of the air-fuel ratio supplied to the engine is further downstream than the second catalyst disposed downstream of the first catalyst in the exhaust gas passage. Even if the amount of secondary air supplied between the first catalyst and the second catalyst changes in accordance with the temperature state of the engine and each catalyst, the change in the amount of secondary air is reduced. The included exhaust concentration can be detected.

Therefore, an exhaust gas component at the outlet of the second catalyst that varies depending on a change in the amount of secondary air supplied between the first catalyst and the second catalyst is provided in advance without adding a correction sensor or the like. Compared with a conventional exhaust gas purification apparatus that can measure the exhaust gas concentration upstream of the first catalyst, it can be detected accurately only by the exhaust gas concentration sensor, and the air / fuel ratio supplied to the engine is more preferable. The ratio can be controlled with high accuracy.

Further, in an exhaust gas purification apparatus of a type in which secondary air is supplied between a first catalyst and a second catalyst that are arranged in series apart from each other in the flow path direction of the exhaust gas passage, an empty air-fuel mixture is supplied to the engine. At the position where the fuel ratio deviates from the stoichiometric (about 14.6) to the rich side, the three components (NOx, CO,
There is an exhaust component decreasing region where THC) decreases. And this exhaust component decreasing area is the second
It substantially matches the stoichiometric region of the detected air-fuel ratio obtained based on the exhaust concentration detected in the downstream region from the catalyst.

Therefore, the amount of secondary air supplied from the first secondary air supply passage to the exhaust gas passage and the engine so that the detected air-fuel ratio obtained from the detection value of the exhaust concentration sensor is on the lean side including the stoichiometric region. By controlling the air-fuel ratio supplied to the engine, the actual air-fuel ratio supplied to the engine is in a rich region, and rich burn required during warm-up operation or high-speed high-load operation can be realized. Moreover, the three components of exhaust gas (NOx, CO, THC) can be suppressed to the same small amount as in the stoichiometric operation, and the three components of exhaust gas (NOx, CO, THC) as in the case of stoichiometric operation of the engine. All of the above can be purified well by the first and second catalysts to produce clean exhaust.

That is, even when the engine is rich burned, the exhaust gas purification performance similar to that at the time of stoichiometric combustion can be maintained, and the excellent exhaust gas purification performance can be stably maintained regardless of the operating conditions. As a result, even when applied to an engine such as a motorcycle with a small displacement, for example, an agile acceleration response by the rich burn can be ensured and good drivability can be obtained.

In the exhaust gas purification apparatus for an engine having the above-described configuration, it is desirable that the first secondary air supply path be connected closer to the first catalyst between the first and second catalysts.
According to this configuration, part of the secondary air supplied between the first catalyst and the second catalyst passes through the second downstream catalyst while once flowing into the first catalyst due to exhaust pulsation, Also in the first catalyst, CO and THC can be oxidized by a part of the secondary air that flows in, and the first catalyst can be used effectively.

In the engine exhaust gas purification apparatus having the above-described configuration, it is preferable that the supply air-fuel ratio is controlled by increasing or decreasing the fuel supply amount.
According to this configuration, a device such as a fuel injection valve that increases or decreases the fuel supply amount can be configured relatively easily, and the supply amount can be controlled more easily than when the air supply ratio is controlled by increasing or decreasing the air supply amount.

Further, in the engine exhaust gas purification apparatus having the above-described configuration, at least the second catalyst is disposed in a muffler attached to the downstream end of the exhaust gas passage, and the exhaust concentration sensor is attached to the muffler. desirable.
According to this configuration, since the second catalyst that is disposed downstream from the first catalyst and is not easily activated is disposed in the muffler, the activation temperature is easily maintained, so that the exhaust gas can be quickly and stably purified. Can do.

In the engine exhaust gas purification apparatus having the above configuration, it is preferable that the exhaust concentration sensor is a linear air-fuel ratio sensor or an oxygen sensor.
According to this configuration, for example, by using a relatively inexpensive oxygen sensor as the exhaust concentration sensor, the cost of the exhaust gas purification device can be reduced.

On the other hand, when a linear air-fuel ratio sensor is used as the exhaust gas concentration sensor, the cost of the exhaust gas purification device increases as the sensor becomes expensive, but the amount of information that can be detected increases. For example, it is possible to deal with variations in individual engines including the fuel supply system, fluctuations in detected values due to secular changes, changes in fuel properties, and the like. For this reason, it is possible to accurately detect information regardless of variations in individual engines including the fuel supply system, changes over time, changes in fuel properties, etc., and improve control accuracy and responsiveness of the air-fuel ratio supplied to the engine. be able to.
As a result, it is possible to stably maintain excellent exhaust gas purification performance and improve the reliability of exhaust gas purification performance, and to stably maintain the air / fuel ratio supplied to the engine as intended, Performance can also be stabilized.

In the engine exhaust gas purification apparatus having the above-described configuration, it is preferable that a second secondary air supply path is connected to the upstream side of the first catalyst.
According to this configuration, for example, when the supply air-fuel ratio to the engine is set to the rich side in order to increase the engine output during high speed and high load operation, the amount of CO and THC in the exhaust gas increases. During the stoichiometric operation, the secondary air is supplied from the second secondary air supply path upstream of the first catalyst that is responsible for NOx purification, so that the upstream side of the first catalyst can also be maintained in an oxygen-excess state. As a result, both the first and second catalysts function as an oxidation catalyst that purifies CO and THC by oxidation, so that the purification treatment capacity for CO and THC is improved, and CO and THC are reduced due to insufficient purification treatment capacity. The contained exhaust gas is not released.

In other words, even when the supply air-fuel ratio to the engine is set to the rich side, excellent purification performance can be exhibited, and by increasing the engine output performance by setting the supply air-fuel ratio to the engine to the rich side, high drivability is achieved. It can also be obtained. Furthermore, even when the supply air-fuel ratio to the engine is set to the rich side for warm-up operation, by supplying secondary air from the second secondary air supply path upstream of the first catalyst, Both the first and second catalysts can be activated early, and the purification performance during warm-up operation can be improved.

In the exhaust gas purification apparatus for an engine having the above-described configuration, it is desirable that an on-off valve capable of shutting off the secondary air supply is provided in the second secondary air supply path.
According to this configuration, for example, when the engine is operated at a medium to high speed and low load, if the secondary air supply from the second secondary air supply path is cut off by the operation of the on-off valve, the first catalyst is The NOx purification processing performance that was initially assumed can be properly demonstrated, and the second catalyst that receives the supply of secondary air from the first secondary air supply path exhibits the CO and THC purification processing performance. All of NOx, CO, and THC in the exhaust gas can be purified well.

Furthermore, in the engine exhaust gas purification apparatus having the above-described configuration, it is preferable that a linear air-fuel ratio sensor is disposed between the inlet of the second secondary air supply path and the first catalyst.
According to this configuration, a linear air-fuel ratio sensor capable of dealing with variations in individual engines including the fuel supply system, fluctuations in detected values due to secular changes, changes in fuel properties, etc. is introduced into the second secondary air supply path. Arranged between the mouth and the first catalyst. As a result, the exhaust concentration taking into account the amount of secondary air supplied from the second secondary air supply path is corrected based on variations in individual engines including the fuel supply system, the effects of secular changes, changes in fuel properties, etc. Can be detected more accurately.

Therefore, the detection value of the linear air-fuel ratio sensor is used to control on / off of secondary air supply from the second secondary air supply path, control of the secondary air supply amount from the first secondary air supply path, and By utilizing the control of the air-fuel ratio supplied to the engine, the upstream region of each catalyst is always maintained in a suitable atmosphere in which each catalyst can efficiently perform purification performance regardless of changes in engine operating conditions. can do. That is, it is possible to obtain stable exhaust gas purification performance under various operating conditions including operating conditions such as rich burn and lean burn.

In the exhaust gas purification apparatus for an engine having the above-described configuration, it is preferable that a linear air-fuel ratio sensor is disposed upstream of the first catalyst.
According to this configuration, the linear air-fuel ratio sensor that can cope with variations in individual engines including the fuel supply system, fluctuations in detected values due to secular changes, changes in fuel properties, etc. is arranged upstream of the first catalyst. Thus, correction based on the variation of individual engines including the fuel supply system, the influence of secular change, the change in fuel properties, and the like can be added to the feedback control by the exhaust concentration sensor arranged on the downstream side of the second catalyst. As a result, the supply air-fuel ratio to the engine can be controlled more accurately as desired, and thus the exhaust gas composition variation can be suppressed and the reliability of the exhaust gas purification performance of the first catalyst and the second catalyst can be further improved.

Further, the above object of the present invention is to provide a first catalyst mainly for the purpose of reducing action disposed in the exhaust gas passage of the engine and a second object mainly for the purpose of oxidizing which is disposed downstream of the first catalyst. A catalyst, a first secondary air supply path connected between the first and second catalysts in the exhaust gas passage, and a linear air-fuel ratio sensor disposed upstream of the first catalyst. The engine exhaust gas purifying apparatus is characterized in that the air-fuel ratio supplied to the engine is controlled in the rich region only by the linear air-fuel ratio sensor.

According to the exhaust gas purification apparatus for an engine having the above-described configuration, a linear air-fuel ratio sensor that can cope with variations in individual engines including the fuel supply system, fluctuations in detected values due to secular changes, changes in fuel properties, etc. Arranged upstream. Therefore, compared with the conventional one using an oxygen sensor, information is accurately detected without being influenced by variations in individual engines including the fuel supply system, changes over time, changes in fuel properties, etc. Control accuracy and responsiveness within the rich range of the fuel ratio can be improved, and exhaust gas purification performance can be improved.

According to the exhaust gas purification apparatus for an engine of the present invention described above, the exhaust concentration sensor for feedback control of the air-fuel ratio supplied to the engine is more than the second catalyst disposed downstream of the first catalyst in the exhaust gas passage. Even when the amount of secondary air supplied between the first catalyst and the second catalyst changes in accordance with the temperature state of the engine and each catalyst, the amount of the secondary air is reduced. The exhaust concentration including the change can be detected.

Therefore, an exhaust gas component at the outlet of the second catalyst that varies depending on a change in the amount of secondary air supplied between the first catalyst and the second catalyst is provided in advance without adding a correction sensor or the like. It can be accurately detected only by the exhaust concentration sensor. In addition, compared with a conventional exhaust gas purification device that measures the exhaust concentration upstream of the first catalyst, the air-fuel ratio supplied to the engine can be controlled to a more preferable ratio with high accuracy.

Further, the amount of secondary air supplied from the first secondary air supply passage to the exhaust gas passage and the engine so that the detected air-fuel ratio obtained from the detection value of the exhaust concentration sensor is on the lean side including the stoichiometric region. By controlling the air-fuel ratio supplied to the engine, the actual air-fuel ratio supplied to the engine is in a rich region, and rich burn required during warm-up operation or high-speed high-load operation can be realized. Moreover, the three components (NOx, CO, THC) of the exhaust gas can be suppressed to the same small amount as in the stoichiometric operation, and the exhaust gas 3 as in the case of the stoichiometric operation.
All of the components (NOx, CO, THC) can be well purified by the first and second catalysts, and clean exhaust can be achieved.

Therefore, the excellent exhaust gas purification performance can be stably maintained regardless of the operating conditions. In addition, even when applied to an engine such as a motorcycle with a small displacement, it is possible to provide an engine exhaust gas purification device that can ensure a quick acceleration response by rich burn and obtain good drivability.

Hereinafter, an engine exhaust gas purification apparatus according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a schematic configuration diagram of an engine exhaust gas purification device 31 according to a first embodiment of the present invention.

As shown in FIG. 1, an exhaust gas purification device 31 for an engine according to the first embodiment is disposed in an exhaust gas passage 5 connected to an exhaust port of an engine 3 suitable for a motorcycle, and the exhaust gas passage 5. A first catalyst 7 mainly for the purpose of reduction, a second catalyst 9 mainly for the purpose of oxidation disposed downstream from the first catalyst 7, and the first and second catalysts 7 in the exhaust gas passage 5.
, 9 and a linear air-fuel ratio sensor (A / F sensor) which is an exhaust concentration sensor disposed downstream of the second catalyst 9 in the exhaust gas passage 5 and the first secondary air supply passage 11 connected between 33, and the air-fuel ratio supplied to the engine 3 is controlled by the linear air-fuel ratio sensor 33.

The downstream end of the exhaust gas passage 5 is opened in the muffler 13 for silencing. In the case of the present embodiment, the second catalyst 9 is disposed in the muffler 13, and the linear air-fuel ratio sensor 33 is installed in the muffler 13 downstream from the downstream end of the exhaust gas passage 5. The air-fuel ratio (fuel / air mixing ratio) of the exhaust gas discharged from the downstream end is detected.
Here, since the second catalyst 9 that is disposed downstream from the first catalyst 7 and is not easily activated can be easily maintained at the activation temperature by being disposed in the muffler 13, the exhaust gas can be purified quickly and stably. Can do.

An intake passage 15 is connected to the intake port of the engine 3, and an air cleaner 17 is connected to the opening end side of the intake passage 15. A fuel supply device 19 such as a fuel injection valve for mixing fuel gas with air supplied to the intake port of the engine 3 through the intake passage 15 is provided in the middle of the intake passage 15.

In the fuel supply device 19, the fuel supply amount is controlled by an engine control unit (control unit) 35 so that fuel corresponding to the operating state of the engine is supplied to the engine 3.
The engine control unit 35 feedback-controls the fuel supply device 19 based on the air-fuel ratio of the exhaust gas detected by the linear air-fuel ratio sensor 33 so that the air-fuel ratio supplied to the engine 3 becomes the air-fuel ratio that matches the operating conditions. To do.
Note that the supply air-fuel ratio in the present embodiment is controlled by increasing or decreasing the fuel supply amount by the fuel supply device 19, so that the device can be configured relatively easily, and the air supply amount can be increased or decreased. The supply amount is easier to control than when the fuel ratio is controlled.

The first secondary air supply path 11 converts the air purified by the air cleaner 17 into the exhaust gas path 5.
This is a conduit that leads to the space 5 a between the first catalyst 7 and the second catalyst 9. And on the way,
A reed valve 21 as a check valve is provided, and secondary air is supplied to the space 5a by using a negative pressure that acts by pulsation of exhaust gas flowing in the exhaust gas passage 5.
In addition, the 1st secondary air supply path 11 in this embodiment is connected near the 1st catalyst 7 between the 1st, 2nd catalysts 7 and 9. FIG. Therefore, a portion of the secondary air supplied between the first catalyst 7 and the second catalyst 9 passes through the second downstream catalyst 9 while once flowing into the first catalyst 7 due to exhaust pulsation, Also in the first catalyst 7, CO and THC can be oxidized by a part of the secondary air that has flowed in, and the first catalyst 7 can be used effectively.

That is, in the exhaust gas purification device 31 of the first embodiment described above, the first catalyst 7 disposed in the exhaust gas passage 5 is basically similar to the conventional exhaust gas purification device 1 shown in FIG. The NOx in the exhaust gas is reduced, and the CO, T in the exhaust gas is further reduced by the second catalyst 9 disposed on the downstream side.
By oxidizing HC, NOx, CO, and THC in the exhaust gas are purified.
However, in the exhaust gas purification apparatus 31 of the first embodiment, the linear air-fuel ratio sensor 33 for feedback control of the air-fuel ratio supplied to the engine 3 is located downstream of the first catalyst 7 disposed in the exhaust gas passage 5. The first catalyst 7 is disposed further downstream than the second catalyst 9 disposed.
Even when the amount of secondary air supplied to the space 5a between the second catalyst 9 and the second catalyst 9 changes in accordance with the temperature state of the engine 3 and the catalysts 7, 9, the change in the secondary air amount is included. The air-fuel ratio of exhaust gas can be detected.

Therefore, according to the exhaust gas purifying device 31, fluctuation is caused by a change in the amount of secondary air supplied to the space 5 a between the first catalyst 7 and the second catalyst 9 without adding a correction sensor or the like. The exhaust gas component at the outlet of the second catalyst 9 to be detected can be accurately detected only by the linear air-fuel ratio sensor 33 equipped in advance. Compared with the conventional exhaust gas purification apparatus 1 that detects the oxygen concentration in the exhaust gas upstream of the three-way catalyst (first catalyst) 68, the supply air-fuel ratio to the engine 3 is controlled to a more preferable ratio with high accuracy. can do.

Furthermore, in the exhaust gas purification apparatus of the type in which secondary air is supplied between the first catalyst 7 and the second catalyst 9 that are arranged in series apart from each other in the flow path direction of the exhaust gas passage 5, as shown in FIG. In addition, there is an exhaust component reduction region R in which the exhaust gas three components (NOx, CO, THC) are reduced at a position where the air-fuel ratio of the air-fuel mixture supplied to the engine 3 is shifted to the rich side from the stoichiometric (about 14.6). To do. The exhaust component reduction region R substantially coincides with the detected air-fuel ratio stoichiometric region detected downstream from the second catalyst 9.

Therefore, the engine control unit 35 of the exhaust gas purifying device 31 makes the detected air-fuel ratio obtained from the detected value of the linear air-fuel ratio sensor 33 to be on the lean side including the stoichiometric region (that is, the exhaust component reducing region R). In addition, the amount of secondary air supplied from the first secondary air supply passage 11 to the exhaust gas passage 5 and the air-fuel ratio supplied to the engine 3 are controlled. As a result, the engine 3
As shown in FIG. 2, the actual air-fuel ratio supplied to the engine is in a rich region, and the rich burn required during warm-up operation or high-speed and high-load operation can be realized. Moreover, the three components of exhaust gas (
NOx, CO, THC) can be suppressed to the same small amount as when stoichiometric operation is performed, and all the three components of exhaust gas (NOx, CO, THC) are the same as when the engine 3 is stoichiometrically operated. The second catalyst 7 and 9 can be used to purify well and produce a clean exhaust.

Therefore, the exhaust gas purification device 31 can maintain the same exhaust gas purification performance as that during stoichiometric combustion even when the engine 3 is rich burned, and can stably maintain the excellent exhaust gas purification performance regardless of the operating conditions. it can. Moreover, even when applied to an engine such as a motorcycle with a small displacement, it is possible to ensure a quick acceleration response by rich burn and obtain good drivability.

The above-described first secondary air supply path 11 is equipped with a reed valve 21, and the supply of secondary air is realized by the pulsation of the exhaust gas in the exhaust gas passage 5. However, in the supply of secondary air using the pulsation of exhaust gas, the amount of secondary air supplied varies. The first catalyst 7
The back pressure of the space (secondary air introduction part) 5a provided between the second catalyst 9 and the second catalyst 9 rises with the temperature of the catalyst, and a phenomenon that the amount of supplied secondary air gradually decreases occurs.

Therefore, in order to maintain the detected air-fuel ratio downstream of the second catalyst 9 on the lean side including the stoichiometric region as described above, the fuel supply device 19 provided in the intake passage 15 of the engine 3 is detected by the detected air-fuel ratio. It is essential to perform feedback control based on the above.
In order to facilitate this feedback control, an air pump 37 is connected to the intake passage 15 instead of the reed valve 21 as shown in FIG. Control the operation. Accordingly, the secondary air supply to the space 5a between the first catalyst 7 and the second catalyst 9 is preferably forced supply.

Thus, if forced supply using the air pump 37 is used, fluctuations in the supply amount due to exhaust gas pulsation can be prevented. Further, a sufficient amount of secondary air can be introduced into the space 5a between the first catalyst 7 and the second catalyst 9 without being affected by the increase in back pressure caused by the temperature rise of the catalyst. As a result, the second
The detected air-fuel ratio in the downstream area from the catalyst 9 can be easily maintained on the lean side, and feedback control based on the detected air-fuel ratio can be simplified.

In the exhaust gas purifying apparatus 31 described above, the linear air-fuel ratio sensor 33 is used as an exhaust concentration sensor disposed on the downstream side of the second catalyst 9, so that the amount of information that can be detected is increased compared to the oxygen sensor. For example, it is possible to deal with variations in individual engines including the fuel supply system, fluctuations in detected values due to secular changes, changes in fuel properties, and the like. For this reason, it is possible to accurately detect information regardless of variations of individual engines including the fuel supply system, changes over time, changes in fuel properties, etc., thereby improving control accuracy and responsiveness of the air-fuel ratio supplied to the engine 3 Can be made.

As a result, excellent exhaust gas purification performance can be stably maintained to improve the reliability of exhaust gas purification performance, and the supply air-fuel ratio to the engine 3 can be stably maintained as intended. Etc. can also be stabilized.
Note that an oxygen sensor can also be used as the exhaust concentration sensor, and in this case, the cost of the exhaust gas purification device can be reduced.

In the exhaust gas purifying device 31 described above, a linear air-fuel ratio sensor is also arranged upstream of the first catalyst 7 so that the engine control unit 35 can supply air to the engine 3 based on the detection data of the linear air-fuel ratio sensor. You may make it correct | amend an air-fuel ratio and the amount of secondary air from the 1st secondary air supply path 11 to the space 5a.

In this case, a linear air-fuel ratio sensor that can cope with variations in individual engines including the fuel supply system, fluctuations in detected values due to secular changes, changes in fuel properties, etc. is arranged upstream of the first catalyst. The feedback control by the linear air-fuel ratio sensor 33 arranged on the downstream side of the two catalysts 9 can be corrected based on variations of individual engines including the fuel supply system, the influence of secular change, changes in fuel properties, and the like. As a result, the supply air-fuel ratio to the engine 3 can be controlled more accurately as intended, and the reliability of the exhaust gas purification performance of the first catalyst 7 and the second catalyst 9 can be further improved by suppressing variations in the exhaust gas composition. Can do.

FIG. 3 is a schematic diagram of an engine exhaust gas purification device 41 according to the second embodiment of the present invention.
The exhaust gas purification device 41 for an engine according to the second embodiment is different from the exhaust gas purification device 31 according to the first embodiment shown in FIG. 1 in the second two upstream of the first catalyst 7 in the exhaust gas passage 5. The difference is that a secondary air supply path 43 is connected and a linear air-fuel ratio sensor 45 is additionally provided between the introduction port 43 a of the second secondary air supply path 43 and the first catalyst 7. In addition, about the structure which is common in the exhaust gas purification apparatus 31 which concerns on 1st Embodiment, the same code | symbol is attached | subjected and detailed description is abbreviate | omitted.

The second secondary air supply passage 43 according to the second embodiment is a conduit that guides the air purified by the air cleaner 17 from the introduction port 43a into the exhaust gas passage 5. A reed valve 47 as a check valve is provided in the middle of the second secondary air supply passage 43, and uses the negative pressure that acts due to the pulsation of the exhaust gas flowing in the exhaust gas passage 5. Secondary air is supplied to

However, on the upstream side of the reed valve 47 of the second secondary air supply path 43, an on / off switch that opens and closes the flow path of the second secondary air supply path 43 based on a control signal from the engine control unit 35. An off valve (open / close valve) 49 is provided so that the secondary air supply from the second secondary air supply passage 43 can be shut off according to the operating conditions.

Therefore, according to the engine exhaust gas purification apparatus 41 according to the second embodiment described above, for example, when the air-fuel ratio supplied to the engine 3 is set to the rich side in order to increase the engine output during high speed and high load operation or the like. The amount of CO and THC in the exhaust gas increases, but the secondary air is supplied from the second secondary air supply passage 43 upstream of the first catalyst responsible for NOx purification during normal stoichiometric operation. The upstream side of the first catalyst 7 can also be maintained in an oxygen-excess state. As a result, both the first and second catalysts 7 and 9 function as an oxidation catalyst for purifying CO and THC by oxidation, so that the purification treatment capacity for CO and THC is improved, and the CO treatment capacity is insufficient due to the lack of purification treatment capacity. And exhaust gas containing THC is not released.

That is, even when the supply air-fuel ratio to the engine 3 is set to the rich side, excellent purification performance can be exhibited, and by increasing the engine output performance by setting the supply air-fuel ratio to the engine 3 to the rich side, a high driver You can also get the ability. Further, even when the supply air-fuel ratio to the engine 3 is set to the rich side for warm-up operation, the secondary air is supplied from the second secondary air supply path 43 upstream of the first catalyst 7. Thus, both the first and second catalysts 7 and 9 can be activated early, and the purification performance during the warm-up operation can be improved.

Since the second secondary air supply passage 43 according to the second embodiment is equipped with an on / off valve 49, for example, during the middle / high speed low load operation of the engine 3, etc. If the secondary air supply from the second secondary air supply passage 43 is cut off by the operation of the off valve 49, the first catalyst 7 can properly exhibit the NOx purification processing performance originally assumed, The second catalyst 9 that receives the supply of secondary air from the first secondary air supply path 11 exhibits CO and THC purification processing performance, thereby favorably purifying all of NOx, CO, and THC in the exhaust gas. be able to.

Further, in the engine exhaust gas purification device 41 according to the second embodiment, a linear air-fuel ratio sensor that can cope with variations in individual engines including the fuel supply system, fluctuations in detected values due to secular changes, changes in fuel properties, and the like. 45 is disposed between the inlet 43 a of the second secondary air supply passage 43 and the first catalyst 7. As a result, the detected air-fuel ratio taking into account the amount of secondary air supplied from the second secondary air supply passage 43 can be used for the variation of individual engines including the fuel supply system, the influence of secular change, the change in fuel properties, etc. It is possible to detect more accurately by adding correction based on it.

Therefore, the detected value of the linear air-fuel ratio sensor 45 is determined based on the ON / OFF control of the secondary air supply from the second secondary air supply path 43 and the secondary air supply amount from the first secondary air supply path 11. And the control of the air-fuel ratio supplied to the engine, the first and second catalysts 7 and 9 are always efficient in the upstream region of each catalyst regardless of changes in the operating conditions of the engine 3. It can be maintained in a suitable atmosphere that can well exhibit purification performance. As a result, it becomes possible to obtain stable exhaust gas purification performance under various operating conditions including operating conditions such as rich burn and lean burn.

FIG. 4 is a schematic configuration diagram of an engine exhaust gas purification device 51 according to a third embodiment of the present invention.
As shown in FIG. 4, an exhaust gas purification device 51 for an engine according to the third embodiment is disposed in an exhaust gas passage 5 connected to an exhaust port of an engine 3 suitable for a motorcycle, and the exhaust gas passage 5. A first catalyst 7 mainly for the purpose of reduction, a second catalyst 9 mainly for the purpose of oxidation disposed downstream from the first catalyst 7, and the first and second catalysts 7 in the exhaust gas passage 5.
, 9, and a linear air-fuel ratio sensor (A / F sensor) 53 disposed upstream of the first catalyst 7 in the exhaust gas passage 5. Thus, the air-fuel ratio supplied to the engine 3 is feedback-controlled within the rich region using only the linear air-fuel ratio sensor 53.

In the case of this exhaust gas purifying device 51, the first linear air-fuel ratio sensor 53 that can cope with variations in individual engines including the fuel supply system, fluctuations in detected values due to changes over time, changes in fuel properties, etc.
Arranged upstream of the catalyst 7. Therefore, the conventional exhaust gas purification apparatus 1 using the oxygen sensor 90.
The exhaust gas purification device 51 accurately detects information without being influenced by variations in individual engines including the fuel supply system, changes over time, changes in fuel properties, etc., and the richness of the supply air-fuel ratio to the engine 3 is detected. Control accuracy and responsiveness within the region can be improved, and exhaust gas purification performance can be improved.

The engine exhaust gas purification devices 31, 41, 51 of the present invention described above can exhibit good exhaust gas purification performance even when the supply air-fuel ratio of the engine 3 is set to the rich side. Also,
The engine exhaust gas purification devices 31, 41, 51 of the present invention can ensure agile acceleration response and the like by increasing the output by enriching the supply air-fuel ratio, and therefore can be applied to motorcycles having a relatively small displacement. This is particularly effective when

1 is a schematic configuration diagram of an exhaust gas purification apparatus for an engine according to a first embodiment of the present invention. FIG. 4 is a correlation diagram between an air-fuel ratio and each exhaust gas characteristic in an exhaust gas purification apparatus in which secondary air is supplied between a first catalyst and a second catalyst that are spaced apart in the flow path direction of the exhaust gas passage. It is a schematic block diagram of the exhaust gas purification apparatus of the engine which concerns on 2nd Embodiment of this invention. It is a schematic block diagram of the exhaust gas purification apparatus of the engine which concerns on 2nd Embodiment of this invention. It is a schematic block diagram of the exhaust gas purification apparatus of the conventional engine.

Explanation of symbols

3 Engine 5 Exhaust gas passage 5a Space 7 First catalyst 9 Second catalyst 11 Secondary air supply passage 13 Muffler 15 Intake passage 17 Air cleaner 19 Fuel supply device 21 Reed valve 31 Exhaust gas purification device 33 Linear air-fuel ratio sensor (exhaust concentration sensor)
35 Engine control unit (control unit)

Claims (11)

A first catalyst arranged mainly in the exhaust gas passage of the engine for mainly reducing action;
A second catalyst mainly disposed for the purpose of oxidizing action disposed downstream of the first catalyst;
A first secondary air supply path connected between the first and second catalysts in the exhaust gas passage;
An exhaust concentration sensor disposed downstream of the second catalyst,
An exhaust gas purification apparatus for an engine, wherein the exhaust air concentration sensor controls an air / fuel ratio supplied to the engine. The exhaust gas purification apparatus for an engine according to claim 1, wherein the first secondary air supply path is connected between the first and second catalysts closer to the first catalyst. The engine exhaust gas purification apparatus according to claim 1, wherein the supply air-fuel ratio is controlled by increasing or decreasing a fuel supply amount. 2. The engine exhaust gas according to claim 1, wherein at least the second catalyst is disposed in a muffler attached to a downstream end of the exhaust gas passage, and the exhaust concentration sensor is attached to the muffler. Purification equipment. The exhaust gas purification device for an engine according to claim 1, wherein the exhaust concentration sensor is a linear air-fuel ratio sensor or an oxygen sensor. 2. The engine exhaust gas purification apparatus according to claim 1, wherein a second secondary air supply path is connected to an upstream side of the first catalyst. The exhaust gas purification apparatus for an engine according to claim 6, wherein the second secondary air supply path is provided with an on-off valve capable of shutting off the secondary air supply. The exhaust gas purification apparatus for an engine according to claim 6, wherein a linear air-fuel ratio sensor is disposed between the inlet of the second secondary air supply path and the first catalyst. The exhaust gas purification apparatus for an engine according to claim 1, wherein a linear air-fuel ratio sensor is disposed upstream of the first catalyst. A first catalyst arranged mainly in the exhaust gas passage of the engine for mainly reducing action;
A second catalyst mainly disposed for the purpose of oxidizing action disposed downstream of the first catalyst;
A first secondary air supply path connected between the first and second catalysts in the exhaust gas passage;
A linear air-fuel ratio sensor disposed upstream of the first catalyst,
An exhaust gas purification apparatus for an engine, wherein the air-fuel ratio supplied to the engine is controlled within a rich region only by the linear air-fuel ratio sensor. 11. The engine exhaust gas purification apparatus according to claim 10, wherein the first secondary air supply path is connected between the first and second catalysts and closer to the first catalyst.

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