JP2004076643A - Exhaust gas purification device - Google Patents

Abstract

In an exhaust gas purification apparatus using an HC adsorbent, HC desorption from the HC adsorbent is started before the three-way catalyst reaches an activation temperature after the engine is cold started, so that HC which is easily exhausted after the start is sufficiently removed. Can not be purified.
The catalysts are arranged adjacent to each other such that a three-way catalyst (carrier 33) is located on an upstream side and an HC trap catalyst (carrier 21) is located on a downstream side. Is formed so as to traverse. Since the slit has a function of blocking heat transfer in the carrier before and after the slit, heat conduction to the downstream of the slit is suppressed, and the temperature rise and HC desorption timing of the catalyst carrier as a whole are delayed. During this time, the temperature of the catalyst metal rises and the conversion rate increases, so that the processing efficiency at the time of HC desorption is improved and the conversion efficiency of the upstream three-way catalyst is also improved.
[Selection diagram] Fig. 4

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an exhaust gas purification device mainly applied to exhaust gas purification of an engine, and more particularly to an improvement of an exhaust gas purification device having an HC trap function.
[0002]
[Conventional technology and problems to be solved]
In an exhaust gas purification system provided with a three-way catalyst, there is a problem of treating HC during cold operation of the engine. This is because HC that is easily discharged during combustion under low-temperature conditions cannot be sufficiently purified until the catalyst reaches the activation temperature. To cope with this problem, there is known a system in which an HC trap catalyst having a function of temporarily adsorbing HC in exhaust gas with an HC adsorbent such as zeolite is provided adjacent to a three-way catalyst ( JP-A-10-317949). This is intended to suppress HC emission until the catalyst metal reaches an activation temperature by using an HC trapping agent. However, even when the temperature of the trapped HC reaches the temperature at which desorption is started from the adsorbent, at this time, the effect of suppressing HC emission is not necessarily sufficient because the catalytic metal is usually not yet sufficiently activated. .
[0003]
Summary of the Invention
In the present invention, the catalysts are arranged adjacent to each other in the exhaust system of the engine such that the three-way catalyst is located upstream and the HC trap catalyst is located downstream. Further, a slit is formed in the honeycomb-shaped carrier of the HC trap catalyst located on the downstream side so as to cross the cell.
[0004]
In the configuration of the HC trap catalyst in which the slit is formed in the carrier, the slit has a function of blocking heat transfer in the carrier before and after the slit, so that heat conduction to the downstream of the slit is suppressed, and the temperature of the catalyst carrier as a whole rises. Slows down. That is, the timing until HC desorbs is also delayed. In this way, while the HC desorption timing in the HC trap catalyst is delayed, the temperature of the catalyst metal of the three-way catalyst adjacent on the upstream side rises and the conversion rate increases, so that it is equivalent to the early activation of the three-way catalyst. The effect described above can be obtained, so that the size of the three-way catalyst can be reduced or the amount of the catalyst metal carried can be reduced.
[0005]
Further, normally, the HC desorbed from the HC trap agent is purified by the catalytic metal layer of the HC trap catalyst. By activating the catalyst earlier than the HC desorption timing, when the exhaust gas flows backward from the HC trap catalyst to the three-way catalyst due to the pulsation of the exhaust gas, the desorbed HC is supplied to the slit portion of the HC trap catalyst. It can be reliably purified by the upstream three-way catalyst while diffusing.
[0006]
When a slit is provided in the catalyst carrier, the gas flow is disturbed at the slit. This turbulence increases the chance of the exhaust gas coming into contact with the HC adsorbent, thus improving the HC trap performance itself. Further, in the configuration having the slits, the gas flow distribution in the cross-sectional direction of the carrier can be made uniform by the turbulent flow action, so that the controllability is improved and the original performance of the exhaust gas purification device can be sufficiently exhibited.
[0007]
A configuration in which a three-way catalyst and further another HC trap catalyst are disposed adjacent to the downstream side of the HC trap catalyst may be added, so that each configuration can have unique beneficial characteristics.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 shows an example of an engine system to which an exhaust gas purification device according to the present invention is applied. In the figure, 1 is an engine, 2 is an intake passage, and 3 is an exhaust passage. Reference numeral 4 denotes an EGR passage for recirculating a part of the exhaust gas from the exhaust passage 3 to the intake passage 2. Reference numeral 5 denotes an EGR control valve for controlling the exhaust gas recirculation amount. 7 is a fuel injection valve, and 8 is a spark plug.
[0009]
Reference numerals 9 and 10 denote HC trap catalysts interposed in the exhaust passage 3. These two catalysts 9 and 10 function as a three-way catalyst having both an oxidizing action of CO and HC and a reducing action of NOx, and also have a function of temporarily trapping HC by an HC adsorbent such as zeolite. Have. The catalyst 9 located on the upstream side is attached to the outlet of the exhaust manifold 3a that forms a part of the exhaust passage. On the other hand, the catalyst 10 located on the downstream side is provided at a position separated from the upstream catalyst 9 via the exhaust pipe 3b. When this engine system is mounted on a vehicle, the catalyst 10 on the downstream side is usually located under the floor of the vehicle body or at the height of the engine oil pan.
[0010]
Reference numerals 12 and 13 denote exhaust gas sensors for detecting the air-fuel ratio or oxygen concentration of the exhaust gas upstream and downstream of the upstream catalyst 9, respectively. Reference numeral 14 denotes a temperature sensor for detecting the catalyst temperature of the downstream catalyst 10. Reference numeral 15 denotes a controller for controlling an air-fuel ratio, an ignition timing, and the like based on an operating state signal such as an engine rotation speed and an intake air amount, and is configured by a microcomputer including a CPU and its peripheral devices.
[0011]
FIG. 2 shows an embodiment of the catalyst carrier with slits 21 accommodated in the catalyst 9 or 10. In the present invention, at least the catalyst 9 located on the upstream side is formed by forming one or more slits 22 so as to cross the gas flow (in the direction of the arrow) of the catalyst carrier 21 as shown in FIG. In the drawing, the slit 22 is formed so as to be orthogonal to the gas flow from one side of the catalyst, and the non-slit portion 23 is left on the other side. Adjacent slits 22 are formed at an angle different from each other by 180 degrees around the catalyst carrier 21 and at equal intervals in the gas flow direction so that slits and non-slit portions are alternately arranged.
[0012]
FIG. 3 is a detail of the cell 24 formed as a gas flow path in the catalyst carrier 21, and is a partially enlarged view of a passage cross section of the catalyst carrier 21 viewed from the direction of the arrow in FIG. Many cells 24 are formed in a honeycomb shape. On the surface of the cell 24, an HC trap layer 25 made of an HC trapping agent such as zeolite is formed on the deep side by coating, and a catalytic metal layer 26 made of Pt, Rh or the like which functions as a three-way catalyst is formed on the surface side by coating.
[0013]
FIG. 4 shows an example of the support structure of the carrier 21 of the catalyst 9. In the figure, reference numeral 33 denotes a honeycomb catalyst carrier of a three-way catalyst, reference numeral 34 denotes a catalyst container, and reference numeral 35 denotes a heat-resistant mat made of ceramic fibers or alumina fibers. The left side in the figure is the upstream side, and the arrows indicate the flow direction of the exhaust gas. The catalyst carrier 21 of the HC trap catalyst is disposed adjacent to the downstream side of the three-way catalyst carrier 33, and each of the carriers 33 and 21 is placed in the catalyst container 34 via a heat-resistant mat 35 wound around the outer periphery thereof. Fixed to. In this embodiment, the outer periphery of the open portion of the slit 22 and the gap between the adjacent three-way catalyst carrier 33 is filled with a filler 36 having the same linear expansion coefficient as that of the catalyst carrier 21. By providing the filler 36 in this way, it is possible to prevent a problem that the mat 35 is worn away due to wind erosion due to exhaust gas that has passed through the slit 22. The use of the filler 36 having the same linear expansion coefficient as the catalyst carrier 21 ensures the strength of the catalyst carrier 21.
[0014]
Immediately after the start of the engine, a large amount of HC is discharged from the combustion chamber due to unignited fuel or incomplete combustion, as compared with during the steady idling operation. Most of this HC is trapped in the HC trap layer of the catalyst, and then when the temperature of the HC trap layer reaches about 150 ° C., the trapped HC starts to desorb from the HC trap layer. At this time, if the catalytic metal layer has reached an activation temperature of about 300 ° C., the desorbed HC is oxidized by a catalytic reaction.
[0015]
In the present invention, the provision of the slits 22 in the catalyst carrier 21 suppresses heat transfer in the carrier, so that the temperature rise of the entire carrier is delayed as compared with a carrier having no slit, and the HC trap layer is accordingly desorbed by HC. The time required to reach the separation temperature also increases. This increases the amount of HC trapped in the carrier and increases the amount of temperature rise of the catalytic metal layer of each of the catalysts 9 and 10 until the start of HC desorption, thereby improving HC purification performance. Further, since the trapping agent carried on the catalytic converter is more effectively used by the action of the turbulent flow when the exhaust gas passes through the slit 22, the performance of trapping HC is also improved as compared with the case without the slit. .
[0016]
In the upstream catalyst 9 located immediately after the exhaust manifold 3a in FIG. 1, the slit 22 is formed particularly by the configuration in which the HC trap layer 25 is laminated on the deep side of the cell 24 and the catalyst metal layer 26 is laminated on the surface side. This increases the time required for the HC trap layer 25 to reach the HC desorption temperature, increases the amount of temperature rise of the catalyst metal layer 26 until the desorption of HC is started, and further increases the amount of HC by the action of the turbulence. Since the activity of the catalytic metal layer 26 can be made uniform while ensuring the effect of trapping HC in the trap layer 25, high purification performance is exhibited. As described above, since the transfer of the reaction heat generated in the catalyst metal layer 26 to the downstream side of the slit 22 is suppressed, the temperature rise of the downstream HC trap layer 25 is slowed, and the HC trapping performance is improved. Since the catalyst metal layer 26 has a small heat capacity for each carrier block partitioned by the slit 22, the catalyst metal layer 26 is activated in order from the upstream side as the exhaust gas flows, thereby improving the purification performance at the time of HC desorption.
[0017]
Since the three-way catalyst is located immediately after the exhaust manifold 3a, the temperature rise is fast, while the HC trap catalyst is located on the downstream side, so that the temperature can be delayed to ensure the HC adsorption performance. In this configuration, by setting the heat capacity of the HC trap catalyst to be larger than that of the three-way catalyst located on the upstream side, the temperature rise of the HC trap catalyst is further delayed. It will be easier to satisfy the conflicting demands for faster catalyst activation.
[0018]
Next, another embodiment of the present invention will be described. 5 to 12 schematically show second to ninth embodiments of the present invention, respectively.
[0019]
FIG. 5 shows a configuration in which a second three-way catalyst 33a is provided adjacent to the downstream side of the HC trap catalyst (carrier) 21. Since the delay of HC desorption in the slitted carrier 21 promotes the activation of the catalytic metal of the three-way catalyst 33a adjacent to the downstream side, even if HC that cannot be completely processed by the upstream side catalyst is released. This can be reliably processed at the three-way catalyst 33a. Further, the chance of contact between the catalyst and the exhaust gas in the three-way catalyst 33a increases due to the turbulence in the slit, so that the temperature rise and purification performance of the three-way catalyst are also improved.
[0020]
By making the heat capacity of the HC trap catalyst 21 larger than that of the three-way catalyst 33a, it is possible to satisfy the conflicting requirements of delaying the temperature rise in the HC trap catalyst 21 and promoting the temperature rise in the three-way catalyst 33a. Further, by making the heat capacity of the three-way catalyst 33 located at the uppermost stream smaller than that of the downstream three-way catalyst 33a, the temperature rise and activation of the three-way catalysts 33, 33a are suppressed while the temperature rise of the HC trap catalyst is suppressed. Can be further promoted. Alternatively, if the heat capacity of the downstream three-way catalyst 33a is set smaller than that of the upstream three-way catalyst 33, the activation of the downstream three-way catalyst 33a is accelerated, and HC that cannot be completely processed by the upstream catalyst is generated. The purification performance at the time can be improved.
[0021]
FIG. 6 shows a configuration in which a second HC trap catalyst 21a is provided adjacent to the downstream side of the second three-way catalyst 33a in the configuration of FIG. According to this embodiment, in addition to the effects of the embodiment shown in FIG. 5, by providing the second HC trap catalyst 21a, the reliability of the HC treatment can be further improved. The HC adsorption performance of the second HC trap catalyst 21a is also improved by the gas turbulence caused by the slit.
[0022]
FIG. 7 shows a second HC trap catalyst (carrier) 21a of FIG. 6 in which a slit 22 is formed as in FIG. According to this embodiment, in addition to the effects of the embodiment shown in FIG. 6, the delay time until HC desorption and the chance of gas contact are further increased to increase the amount of adsorbed HC, to promote the activation and conversion of the catalytic metal. Efficiency can be improved.
[0023]
FIG. 8 shows a configuration in which the HC trap catalyst 21b is arranged on the upstream side and the three-way catalyst 33b is arranged on the downstream side so as to be adjacent to each other as the second catalyst 10 at the underfloor position in the configuration of FIG. According to this embodiment, a high HC adsorption performance can be obtained in the second catalyst 10 that is separated downstream from the first catalyst 9 in the manifold position by the above-described temperature increase suppression action. In addition, the adjacent three-way catalyst 33b can process HC that could not be completely processed by the catalytic metal layer of the HC trap catalyst 21b.
[0024]
FIG. 9 shows a configuration in which a slit 22 is formed in the HC trap catalyst (carrier) 21b in the configuration of FIG. According to this embodiment, in addition to the effects of the embodiment shown in FIG. 8, the HC adsorption performance of the HC trap catalyst 21 b can be further improved by the heat transfer suppressing action and the gas turbulence action at the slit 22. .
[0025]
FIG. 10 shows a configuration in which an HC trap catalyst 21c is further arranged adjacent to the downstream side of the three-way catalyst 33b in the configuration of FIG. According to this embodiment, even if HC that cannot be processed by the upstream catalyst is released, it can be surely adsorbed and purified.
[0026]
FIG. 11 shows a configuration in which a slit 22 is formed in the downstream HC trap catalyst (carrier) 21c in FIG. 9 similarly to FIG. According to this embodiment, in addition to the effects of the embodiment shown in FIG. 10, the HC adsorption performance of the downstream HC trap catalyst 21c can be further improved.
[0027]
FIG. 12 shows a configuration in which a three-way catalyst 33c is further arranged adjacent to the downstream side of the downstream HC trap catalyst carrier 21c in the configuration of FIG. According to this embodiment, in addition to the effects of the embodiment shown in FIG. 11, the purification performance when HC that cannot be processed is generated can be further enhanced. In particular, in the most downstream three-way catalyst 33c, two slit HC trap catalysts 21b and 21c are located on the upstream side and exert a large heat transfer suppressing action, so that sufficient time for catalyst activation is secured. Therefore, the performance as a three-way catalyst can be improved accordingly.
[0028]
FIGS. 13 and 14 show an embodiment relating to the structure of the exhaust pipe 3 b connecting the manifold side catalyst 9 and the underfloor side catalyst 10. FIG. 13 shows a case where a bellows-shaped flexible tube 3c having flexibility is applied to an intermediate part of the exhaust pipe 3b. FIG. 14 shows a universal pipe joint 3d which enables relative rotation of the catalysts 9 and 10 in the middle of the pipe 3b. Is applied. By applying the flexible tube 3c or the universal pipe joint 3d, the relative movement between the catalyst 9 and the catalyst 10 during the operation of the engine can be tolerated, and in addition, the flexible tube 3c or the pipe joint 3d increases the heat capacity of the exhaust pipe 3b. This is advantageous in improving the purification performance of the downstream HC trap catalyst.
[0029]
In each of the above embodiments, it is assumed that a plurality of catalyst carriers adjacent to each other in the catalyst 9 or 10 are housed in a common container. However, the present invention is not limited to this. It can also be configured. However, by adopting a configuration in which a plurality of carriers are arranged adjacent to each other in a common container, the entire apparatus can be reduced in size, and the turbulence of exhaust gas can be obtained due to the gap between the adjacent carriers. Alternatively, the effect of increasing the conversion efficiency of the catalyst can be obtained.
[0030]
In addition, each of the above drawings is a drawing for explaining the formation mode of the slit and the structure of the catalytic converter, and the size of the catalyst carrier, the width and the pitch of the slit, etc. are different from actual dimensions or dimensions for convenience of explanation. It is drawn in proportions.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing an example of an engine system to which an exhaust purification device according to the present invention is applied.
FIG. 2 is an explanatory view showing a catalyst carrier shape of the first embodiment of the exhaust gas purification apparatus according to the present invention.
FIG. 3 is a cross-sectional view showing details of a cell portion of the catalyst carrier.
FIG. 4 is a longitudinal sectional view showing an example of a support structure of the catalyst carrier.
FIG. 5 is a schematic view of a second embodiment of the present invention.
FIG. 6 is a schematic view of a third embodiment of the present invention.
FIG. 7 is a schematic diagram of a fourth embodiment of the present invention.
FIG. 8 is a schematic diagram of a fifth embodiment of the present invention.
FIG. 9 is a schematic view of a sixth embodiment of the present invention.
FIG. 10 is a schematic view of a seventh embodiment of the present invention.
FIG. 11 is a schematic view of an eighth embodiment of the present invention.
FIG. 12 is a schematic view of a ninth embodiment of the present invention.
FIG. 13 is a schematic configuration diagram of a tenth embodiment of the present invention.
FIG. 14 is a schematic configuration diagram of an eleventh embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Engine 2 Intake passage 3 Exhaust passage 3a Exhaust manifold 3b Exhaust pipe 3c Flexible tube 3d Fittings 9, 10, 19 HC trap catalyst 17, 18 Three-way catalyst 21 HC trap catalyst (carrier)
22 Slit 24 Cell 25 HC trap layer 26 Catalyst metal layer 33 Three-way catalyst (carrier)
34 catalyst container

Claims (17)

In the exhaust system of the engine, the respective catalysts are arranged adjacently so that the three-way catalyst is located on the upstream side and the HC trap catalyst is located on the downstream side,
An exhaust purification device, characterized in that a slit is formed in the honeycomb-shaped carrier of the HC trap catalyst located on the downstream side so as to cross the cell. The exhaust gas purifying apparatus according to claim 1, further comprising a three-way catalyst provided adjacent to a downstream side of the HC trap catalyst. 3. The exhaust gas purification apparatus according to claim 2, further comprising an HC trap catalyst adjacent to the downstream side of the downstream three-way catalyst. The exhaust purification device according to claim 3, wherein a slit is formed in the honeycomb-shaped carrier of the downstream HC trap catalyst so as to cross the cell. 2. The exhaust gas purification apparatus according to claim 1, wherein the adjacent three-way catalyst and HC trap catalyst are provided near an exhaust manifold of the engine. 2. The exhaust gas purification apparatus according to claim 1, wherein the heat capacity of the HC trap catalyst is larger than that of a three-way catalyst located on the upstream side thereof. The exhaust purification device according to claim 2, wherein the heat capacity of the HC trap catalyst is larger than that of a three-way catalyst located downstream thereof. The exhaust gas purifying apparatus according to claim 2, wherein the heat capacity of the catalyst is increased in the order of the HC trap catalyst, the downstream three-way catalyst, and the upstream three-way catalyst. The exhaust gas purifying apparatus according to claim 2, wherein the heat capacity of the catalyst is increased in the order of the HC trap catalyst, the upstream three-way catalyst, and the downstream three-way catalyst. 6. The catalyst according to claim 5, wherein the HC trap catalyst is arranged on the upstream side and the three-way catalyst is arranged on the downstream side so that the catalysts are located near the height under the floor of the vehicle when the vehicle is mounted. Exhaust gas purification device. The exhaust purification system according to claim 10, further comprising an HC trap catalyst adjacent to the downstream side of the three-way catalyst. The exhaust purification device according to claim 10 or 11, wherein a slit is formed in the honeycomb-shaped carrier of the HC trap catalyst so as to cross the cell. The exhaust purification system according to claim 11, further comprising a three-way catalyst provided adjacent to the downstream side of the downstream side HC trap catalyst. The exhaust gas purifying apparatus according to claim 1, wherein the adjacent HC trap catalyst and the three-way catalyst are housed in a common catalyst container. The exhaust gas purifying apparatus according to claim 1, wherein the HC trap catalyst is formed in a layered manner such that an HC trap layer containing an HC adsorbent is located on a deep side and a catalytic metal layer containing a catalyst metal is located on a surface layer. 7. The exhaust gas purification apparatus according to claim 6, wherein a catalyst provided near the exhaust manifold and a catalyst provided at a position below the floor are connected via a flexible exhaust pipe. 7. The exhaust gas purifying apparatus according to claim 6, wherein a catalyst provided near the exhaust manifold and a catalyst provided at a position under the floor are connected via an exhaust pipe provided with a universal pipe joint that allows relative movement of each catalyst. .

Images