JP2006291813A - Exhaust emission control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device capable of increasing an exhaust emission control efficiency by utilizing the reverse flow of exhaust gases flowing in an exhaust pipe. <P>SOLUTION: This exhaust emission control device comprises a catalyst converter 13 having a casing 18 disposed on the exhaust pipe 12 extending from the body of an engine 1, a carrier 21 installed in the casing 18, and catalyst components carried on the catalyst. Based on a variation in the volume of exhaust gases due to the release of heat from the exhaust pipe 12, the length Lf of the carrier is set smaller than the length Lrf of the reversely flowing exhaust gas rf passed through the carrier 21. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an exhaust gas purifying apparatus that is provided in an exhaust passage of an internal combustion engine and includes a catalyst for purifying a combustion product in exhaust gas discharged from the internal combustion engine by oxidation or reduction.

  In order to protect the environment, exhaust gas purification regulations for internal combustion engines mounted on vehicles have been strengthened, and as a result, it has been required to further increase the purification efficiency of catalysts installed in the exhaust passages of internal combustion engines. ing. Conventionally, as a typical catalyst system provided on an exhaust passage of an internal combustion engine, there are a single catalyst system (single carrier) and a tandem catalyst system (two carriers). In the case of a tandem catalyst system, a gap is secured between the upstream catalyst and the downstream catalyst, and the exhaust gas that reaches here is mixed and then flows to the downstream catalyst. It becomes. For this reason, the tandem catalyst is generally superior to the single catalyst, and it is considered that the mixing of the gas generated in the gap is the main factor for improving the performance.

  JP-A-9-195757 (Patent Document 1) discloses a catalytic converter. In this catalytic converter, catalyst carriers are arranged in three stages in the casing along the exhaust gas flow direction via gaps, and the flow resistance of each carrier is set so as to increase toward the outlet side. The exhaust gas is agitated in the section to disperse the exhaust gas throughout the region, thereby improving the purification efficiency.

JP-A-9-195757

The present inventor further studied to improve the exhaust gas purification function. The examination process and results are described below.
Here, as shown in FIGS. 9A and 9B, two locations A and B on a carrier 101 of a single catalyst system (single carrier) 100 and a carrier 201 of a tandem catalyst system (two carriers) 200, Each temperature at two locations C and D on 202 was measured. Here, the temperature distribution in the catalyst during actual vehicle operation was measured. At this time, the temperature distribution of the tandem and the single brick catalyst system of 20 km / h in the 10.15 mode and the steady running of 20 km / h was sampled as the operating state, and FIGS. 9C and 9D were obtained.

  Furthermore, as shown in FIG. 10, at 20 km / h in the 10 · 15 mode, the average temperatures (336, 373 ° C.) at the two positions C and D on the front stage and the rear stage supports 201 and 202 of the tandem catalyst system are as follows. Both were higher than the average temperature (310, 366 ° C.) at two locations at the same positions A and B on the carrier 101 of the single brick catalyst system. Here, it should be noted that in the tandem catalyst system 200, the temperature rise uf of the front carrier 201 is larger than the temperature rise ur of the rear carrier 202 compared to the single brick catalyst system 100. In continuous running at 20 km / h, the average temperatures of the front and rear carriers 201 and 202 of the tandem catalyst system 200 were both higher than the same position of the single brick catalyst system.

  In consideration of this data characteristic, since the capacity of the front and rear catalyst carriers 201 and 202 is smaller in the tandem catalyst system 200 than in the single brick catalyst system 100, the temperature of each tandem catalyst is higher in the transient operation region. May increase faster. However, the above-mentioned data characteristics are characterized in that the catalyst temperature is higher in tandem not only in the rear but also in the front, even in steady operation without the influence of heat capacity. It is presumed that this indicates that the influence of exhaust backflow described is large. It has also been confirmed that the catalyst temperature is higher in the tandem catalyst system even in the cold state.

Here, further investigation was made on the exhaust backflow. The exhaust reverse flow can be defined as exhaust flowing from the tail pipe to the cylinder head in the opposite direction of the normal forward (cylinder head to tail pipe) exhaust flow. Here, not the pressure wave such as pressure pulsation but the material movement of the exhaust gas fluid itself is a reverse flow.
The following three points can be considered as factors of the exhaust backflow.
1) Backflow of exhaust into cylinder due to difference between in-cylinder pressure and exhaust pressure 2) Blow back to intake side due to valve overlap 3) Volume reduction due to gas cooling in exhaust pipe Therefore, the present inventor shows FIG. Using the backflow measuring device 300 to which such a discharge tuft method was applied, the backflow generation characteristics of the tandem gap were measured. Here, a spark plug 302 is mounted in a casing 301 of a tandem catalyst system, and a spark generator 305 including a coil 303, a pulse generator 304, and a power source 305 is connected to the spark plug. A part of the central wall portion of the casing 301 is formed of heat resistant glass (quartz glass) 306, and a spark image (see FIG. 12) of the spark plug 302 is photographed by the video camera 307 which is a high speed camera through the heat resistant glass 306. And a recording device 310 that records the image in the data storage unit 308 and reproduces the image on the monitor 309.

  Using such a backflow measuring device 300, under the conditions shown in FIG. 13A, the forward direction of the arc during discharge (showing the forward flow of exhaust gas) f1 and the backflow direction as shown in the spark image (see FIG. 12). F2 (indicating the backflow of exhaust gas) and f0 when the flow was stopped were measured, and a backflow ratio as shown in FIG. 13B was obtained. As is apparent here, the reverse flow rate when the engine motoring drive of A, B, C is 30% or less when operating at 750 rpm, whereas the reverse flow ratio when the engine is driven (fireing) is D. It is a high level of about 45%. It is clear that the exhaust gas backflow when the engine is driven is greatly affected by the exhaust gas volume fluctuation due to the heat radiation of the exhaust gas in the exhaust pipe (reference numeral 400 in FIG. 9A).

As described above, in the conventional apparatus and the catalyst apparatus of Patent Document 1 or the like, the tandem catalyst system having the front stage catalyst and the rear stage catalyst is simply adopted, so that the space between the front stage catalyst and the rear stage catalyst in the casing of the catalyst apparatus is reduced. Exhaust gas purification efficiency is improved by strengthening the exhaust gas agitating function using the exhaust gas agitation characteristics in the gaps.
The present invention has been made paying attention to the point that it is possible to improve the exhaust gas purification efficiency by utilizing the exhaust gas reverse flow of the exhaust gas flowing through the exhaust pipe as described above. An exhaust gas purification device that can be improved is provided.

  In order to achieve the above object, an exhaust gas purifying apparatus according to claim 1 is supported on a casing disposed on an exhaust pipe extending from a main body of an internal combustion engine, a carrier housed in the casing, and the carrier. In the exhaust gas purifying apparatus including a catalytic converter having a catalytic component, the length of the carrier is set to be equal to or smaller than the length of the backflow generated in the casing.

  The exhaust gas purifying device according to claim 2 is sequentially arranged in series in the casing along the exhaust passage direction along the exhaust passage direction through the space between the casing and the casing disposed on the exhaust pipe extending from the main body of the internal combustion engine. In an exhaust gas purification apparatus including a catalytic converter having a plurality of carriers and a catalyst component supported on each of the carriers, the length of the carrier at least upstream of the plurality of carriers is reduced in the reverse flow generated in the casing. It is characterized by being set equal to or smaller than the length.

  The exhaust gas purifying apparatus according to claim 3 is the exhaust gas purifying apparatus according to claim 1 or 2, wherein the length of the backflow is based on a volume variation of the exhaust gas due to heat radiation from at least the exhaust pipe. Exhaust gas purification device.

  The exhaust gas purifying apparatus according to claim 4 is the exhaust gas purifying apparatus for an internal combustion engine according to any one of claims 1 to 3, wherein the reverse flow is generated at least during cold idling, or an exhaust gas inlet. The length of the carrier on the side is set.

  The exhaust gas purifying apparatus according to claim 5 is the exhaust gas purifying apparatus for an internal combustion engine according to any one of claims 1 to 4, wherein the carrier capacity is set according to the length of the backflow. Is set to be equal to or smaller than the amount of exhaust gas flowing out from the casing to the internal combustion engine side.

  According to the first aspect of the present invention, the exhaust gas that has passed through the carrier is once stirred outside the carrier and then flows back as long as it covers the entire carrier. Therefore, the purification reaction between the catalyst component of the carrier and the exhaust gas can be promoted. As a result, the temperature of the carrier can be increased and the purification efficiency can be improved.

  According to the second aspect of the present invention, the exhaust gas that has passed through the carrier on at least the upstream side of the casing is once stirred in the space and then backflowed again to cover the entire exhaust gas inlet side carrier. The purification reaction of the catalyst component and the exhaust gas can be promoted, the catalyst temperature of the upstream side catalyst and the downstream side catalyst can be increased accordingly, and the purification efficiency by this can be promoted.

  According to the third aspect of the present invention, the length of the backflow of the exhaust gas is considered at least due to the volume fluctuation of the exhaust gas due to heat dissipation from the exhaust pipe, and therefore the length of the carrier can be set appropriately.

  According to the fourth aspect of the present invention, warm-up can be promoted by the temperature rise of the catalyst during cold idling, and the purification efficiency is further promoted.

  According to the fifth aspect of the present invention, the exhaust gas that flows backward efficiently covers the entire carrier, so that the purification reaction of the catalyst component of the carrier and the exhaust gas can be promoted, the temperature of the carrier can be increased accordingly, and the purification efficiency can be improved. It can be improved.

  FIG. 1 shows an exhaust gas purifying apparatus as an embodiment of the present invention and an internal combustion engine equipped with the apparatus. The internal combustion engine is an in-cylinder injection type four-cycle multi-cylinder gasoline engine (hereinafter simply referred to as the engine 1), and a cylinder 3 having a piston 2 that slides up and down in the body of the engine 1 has a number of cylinders (in the figure, (Only one is shown) deployed. When the engine 1 is driven, the combustion chamber 4 in the cylinder 3 sucks intake air from the intake passage 5 through the air cleaner AC and the throttle valve SV, and the engine control unit (ECU) 10 sets the fuel injection timing at a predetermined fuel injection timing. The electromagnetic fuel injection valve 6 is driven to perform fuel injection, and the spark plug 7 is driven in a timely manner to perform an ignition process. As a result, the engine 1 performs an output generating operation by the combustion of the air-fuel mixture, and the exhaust gas is discharged to the exhaust passage 8 to drive in the 4-cycle operation mode.

Here, from the engine body, an exhaust port 9 is formed in a substantially horizontal direction for each cylinder, and an exhaust manifold 11 that forms an exhaust passage 8 is formed in each exhaust port (only one is shown in FIG. 1), and an exhaust passage 8. , A catalytic converter 13 that forms the main part of the exhaust gas purification device disposed at the end of the exhaust pipe 12, a downstream exhaust pipe 14, and a muffler (not shown) are connected in this order to It is formed along the exhaust path 8 so as to be discharged to the outside.
An air-fuel ratio sensor 16 that detects an air-fuel ratio A / F is provided in the exhaust pipe 12 upstream of the catalytic converter 13.

  As shown in FIGS. 1 and 2, the catalytic converter 13 forms a tandem catalyst system disposed under the vehicle floor 17, and the inner diameter is expanded so as to be continuous with the exhaust pipe 12 and the downstream exhaust pipe 12. A cylindrical casing 18 having a shape, a front carrier 21 and a rear carrier 22 having a honeycomb structure arranged without deviation in the casing 18, a gap portion 20 between the front carrier 21 and the rear carrier 22, and front and rear carriers 21 and 22. And a plurality of through-holes 23 that pass through in the axial direction, an inner wall 24 made of a refractory inorganic oxide in the through-hole 23, and a noble metal catalyst component (not shown) supported on the inner wall 24.

  The length of the exhaust pipe (hereinafter referred to as the exhaust officer length) Le consisting of an exhaust manifold 11 and an exhaust pipe 12 that guides exhaust from the main body of the engine 1 to the catalytic converter 13 below the floor 17 of the vehicle is relatively long. The heat dissipation area is also relatively large. For this reason, the high-temperature exhaust gas discharged from the engine main body is instantaneously cooled, and when reaching the catalytic converter 13, the volume is relatively reduced. The exhaust pipe length Le here is set to a length that can generate an exhaust gas backflow, as will be described later.

  The main carrier 21 and the rear carrier 22 are cordierite as a main component, whereby the entire honeycomb structure including the supporting layer in the vicinity of the inner surface of each through hole 23 is formed. A three-way catalyst is supported on each supporting layer of the front carrier 21 and the rear carrier 22. That is, an oxygen storage material such as ceria and zirconia is supported as an additive using alumina as a base material, and Pt (platinum) and Pd (palladium) are used as catalyst components 35 of noble metals having high NOx reduction treatment, HC and CO oxidation treatment performance. ), Rh (rhodium) is supported. The upstream and downstream three-way catalysts have a three-way function of oxidizing CO and HC in the exhaust gas and reducing and purifying NOx in an atmosphere near the stoichiometric air-fuel ratio. At this time, with respect to the catalyst in the previous stage, it is preferable to place a high amount of noble metal on the basis of the importance of reducing HC in the cold state. On the other hand, for the latter stage catalyst, in order to attach importance to the reduction of NOx in the warm state, the precious metal may be less than the former stage and may have a lower loading amount, but the catalyst capacity should be increased as much as necessary and at least larger than the preceding stage. Is preferred.

  Here, the lengths Lf and Lr in the direction of the exhaust path 8 that define the volume of the front and rear carriers 21 and 22 are set in consideration of the exhaust gas purification capability. In particular, the front carrier 21 has an exhaust path 8 as described later. It is set in consideration of the backflow length Lrf (see FIG. 3B) of the generated exhaust gas backflow.

  As shown in FIG. 3 (a), when exhaust gas flows through the exhaust pipe 12, in the forward direction nf flow, the casing 18 is enlarged in the diameter of the pipe at the entrance portion, so that the radial velocity distribution is different. As shown in FIGS. 3B and 3C, in the case of the reverse flow rf, the flow velocity distribution in the catalyst is considered to be uniform because it is not affected by the exhaust pipe diameter change. In addition, when the exhaust flow reverses from the forward flow nf to the reverse flow rf, the gas temporarily stops, but at that time, there is no inertia in the upstream-downstream direction. A radial flow is generated by a radial pressure difference or the like, and gas diffusion proceeds by a radial gas concentration difference or the like, and the gas concentration and temperature are made uniform in the subsequent flow. In this case, the heat of the gas in the gap 20 and the unreacted substance move uniformly into the pre-catalyst 21 to promote the catalytic reaction. For this reason, the activity of the front catalyst increases, and the reaction heat increases the exhaust gas temperature at the inlet of the rear catalyst 22 and improves the purification performance of the rear catalyst. That is, if only the forward flow nf is in the state shown in FIG. 3A, the purification efficiency is low because the amount of gas flowing into the outer peripheral portion of the catalyst is small and the temperature of the catalyst is low. That is, the precious metal on the outer periphery of the catalyst is not effectively used and is wasted, and the substantial utilization efficiency of the catalyst as a whole is low.

  On the other hand, as shown in FIGS. 3B and 3C, in the case of the backward flow rf, the amount of gas at the outer periphery of the catalyst increases, and at the same time, the high-temperature gas that has passed through the center of the catalyst during forward flow flows. Since the outer peripheral portion also passes when flowing in the reverse direction, the temperature of the outer periphery of the catalyst rises. Thereby, the purification efficiency of the catalyst outer peripheral portion is increased. That is, due to the reverse flow of the exhaust gas, the precious metal on the outer periphery of the catalyst is also effectively used, and the substantial utilization efficiency of the entire catalyst is increased. In addition, the exhaust gas that has passed through the outer periphery of the catalyst during forward flow is not sufficiently purified because the catalyst temperature at the outer periphery is low, and blows up to the tandem gap in a state where a large amount of unpurified material is contained. Become. However, due to gas diffusion and mixing in the gap when the exhaust gas is reversed, the unreacted substance passes through the center of the catalyst, which is already at a high temperature due to the reaction heat of the forward flow, during reverse flow. . As a result, the unreacted substance is well purified, and the temperature at the center of the catalyst is further increased by the reaction heat of the unreacted substance.

  Next, measurement of the backflow length Lrf of the exhaust gas backflow of the engine 1 will be described. As described above, the exhaust backflow is effective in improving the catalyst purification performance regardless of the operating state such as warm, cold, transient, steady, etc., as described above, but it contributes most to the total exhaust gas value. As an operation state in which a large catalyst purification performance is desired, there is a cold idling immediately after starting. Thus, cold start refers to start from an ambient temperature of about 25 ° C.

  Here, an exhaust gas backflow length measuring device 40 as shown in FIG. 4 is used. The exhaust gas backflow length measuring device 40 includes many members similar to the backflow measuring device 300 to which the discharge tuft method described with reference to FIG. 11 is applied. Here, the duplicate description is simplified, and the same members are denoted by the same reference numerals. The exhaust gas backflow length measuring device 40 is mounted on the exhaust pipe 12 of the engine 1 and a measurement catalytic converter (hereinafter referred to as a measurement converter 41) having the same configuration as that of the engine 1. In the measurement converter 41, a part of the central body of the casing 42 is formed of heat-resistant glass (quartz glass) 43, and is disposed in the gap 39 between the front carrier 21 and the rear carrier 22 in the central body of the casing 42. A spark plug 44 that is visible through the glass 43 and a hot-wire anemometer 45 that is mounted immediately before the front carrier 21 are provided.

A spark generator 305 including a coil 303, a pulse generator 304, and a power source 305 is connected to the spark plug 44.
A video camera 46 that captures a spark image through a heat-resistant glass (quartz glass) 43 is provided, and the image of the video camera 46 is recorded in a data storage unit 47, and the data storage unit 47 is connected to a recording operation device 50 for recording operation. A recorded image or the like can be reproduced on the monitor 48 by a reproducing unit 49 in the apparatus 50.

  As shown in FIGS. 5A and 5B, the hot-wire anemometer 45 provided immediately before the front carrier 21 is provided at the center of the exhaust passage 8 and fixed to the casing 42. A heating wire 52 supported between both ends of the heating wire, a constant current circuit 53 for supplying a constant current to the heating wire 52, and a wind speed which is a resistance measuring device for measuring a change in electrical resistance accompanying cooling of the heating wire due to passage of exhaust gas. And a measuring instrument 54. In addition, even if the flow rate is zero, the electric resistance does not become zero, and the value depends on the atmosphere temperature of the heating wire when there is no cooling due to exhaust gas passage. Therefore, a temperature sensor for measuring the ambient temperature is provided (not shown). A C-shaped cross section (see FIG. 5B) is formed at the center of the frame 51 so that the exhaust gas is cooled by the forward flow nf and the heating wire 52 is not cooled, but is cooled by the reverse flow rf. The electric resistance value of the hot-wire anemometer 45 is output to the recording operation device 50, and the display control unit 55 of the recording operation device 50 compares and displays the electric resistance value and the spark image on the monitor. Thereby, the flow characteristics before and after the front carrier 21 can be measured.

  The recording operation device 50 is connected to an ECU 10 that is a control device of the engine 1 via a signal line so that signals can be exchanged with each other. The ECU 10 captures engine operation information, performs fuel injection control of the injection nozzle 6, ignition control of the spark plug 7, and opening control of the throttle SV, and the engine 1 is in the warm-up mode in the cold state, the steady operation mode, and the transient operation mode. It can be controlled to drive.

In such an exhaust gas backflow length measuring device 40, the spark generator 305 drives the spark plug 44 with a predetermined pulse width while driving the engine 1, and measures the flow direction of the spark, for example, FIG. ) And (c), it was measured over time whether the exhaust gas was in the forward direction f1 or the reverse direction f2.
On the other hand, as shown in FIG. 6, when the data of the hot wire anemometer 45 is in the forward flow nf, the cooling of the heating wire 52 by the forward flow does not depend, and the resistance value R is also small. On the other hand, when the backflow rf occurs, the degree of cooling of the heating wire 52 increases. At this time, the relationship between the resistance value and the flow velocity is experimentally obtained in advance.
For example, when the length of the first front carrier 21 attached in the measurement converter 41 in the flow path direction is Lc1 or Lc2, the data of the first front carrier 21 is shown in FIG. And so on.
Here, the case where the length of the first front carrier 21 in the flow path direction is Lf (= Lc1: see FIG. 3C) will be described with reference to the data of FIG. In the data of the first front carrier 21, based on the spark image, the region where the flow in the gap portion 20 between the front carrier 21 and the rear carrier 22 reversely flows f <b> 2 was sequentially measured. The data of the resistance value R of the hot-wire anemometer 45 measured in synchronization with the reverse flow region indicates that the heating wire 52 is not cooled in the flow region in the forward direction nf, shows a low resistance value R0, and enters the reverse flow region. In the meantime, the resistance value increases to Ra.

  Here, the high-temperature gas flowing into the exhaust pipe 12 from the cylinder in the exhaust stroke instantaneously reduces its volume due to heat dissipation, and the flow at the tip reaches the gap 20 after passing through the pre-stage catalyst. At that time, the forward velocity component Reaches zero f0 (see FIG. 12B). In addition, immediately after that, the cooling and reduction of the exhaust gas in the exhaust pipe 12 further proceeds, and a backflow rf is generated. The reverse flow rf is canceled out by the forward flow nf due to the outflow of the high-temperature exhaust gas from the cylinder in the next exhaust stroke, and the reverse flow rf is completed by returning to the forward flow again.

  Here, for simplification, it is assumed that the flow velocity during the backflow is constant and the resistance value during that time is also constant. From the resistance value Ra during the reverse flow, the flow velocity of the reverse flow is calculated based on the experimental result on the relationship between the resistance value and the flow velocity obtained in advance as described above. It is assumed that the flow velocity at the resistance value Ra is the reverse flow velocity Xa (mm / ms). In addition, as shown in FIG. 6, the backflow time ta (ms) during which the backflow has continued can be obtained based on the data of the hot-wire anemometer 45. The backflow length Lrf (mm) can be obtained from the backflow velocity Xa (mm / ms) and the backflow time ta (ms) obtained above. Here, since the flow velocity during the backflow is constant at Xa, the backflow length Lrf can be calculated by the following equation.

Lrf = Xa × ta
By comparing the backflow length Lrf and the carrier length, it is possible to determine how far the backflow is flowing back through the carrier.
Here, the length Lf in the long flow direction in the flow direction of the first first stage carrier 21 from the backflow length Lrf is too long as shown in FIG. Backflow exhaust gas that covers the entire area cannot be received, the temperature rise of the first pre-stage carrier 21 is relatively small, and the purification efficiency cannot be sufficiently improved.

  Next, when the length of the first front carrier 21 in the flow path direction is Lf (= Lc2: see FIG. 3B), as shown in FIG. 3B, the backflow length Lrf and the first front carrier 21 The lengths Lf in the flow path direction of 21 substantially coincide with each other, and a reverse flow in which the exhaust gas covers the entire area of the first front carrier 21 can flow.

  For this reason, the temperature rise of the first front carrier 21 can be sufficiently promoted, and the purification efficiency can be sufficiently improved. Accordingly, the temperature of the exhaust gas flowing into the rear stage rises due to the reaction heat of the front stage, and the rear carrier The temperature can be increased by 22 and the purification efficiency of the three-way catalyst at the front and rear stages can be improved. If the length Lf of the first front carrier 21 in the flow path direction is excessively shortened, the capacity of the catalyst is insufficient, and exhaust gas purification by the first catalyst of the first front carrier 21 is not sufficiently performed. , Dripping occurs downstream. Therefore, when the length Lf in the flow path direction of the first front carrier 21 when the backflow is obtained in this way is excessively short, the length Le of the exhaust pipe 12 or the diameter of the exhaust pipe 12 can be changed or the two exhaust pipes can be changed. It is possible to correct the amount of heat radiation by making a double pipe, installing a heat insulating material in the exhaust pipe, etc., and securing an appropriate length Lf in the flow path direction of the first front carrier 21. A supplementary explanation will be given for correcting the heat release amount by changing the length Le of the exhaust pipe 12 and controlling the reverse flow length Lrf.

  Since the exhaust backflow is generated by reducing the gas volume due to the exhaust gas being cooled in the exhaust pipe, it is affected by the length of the exhaust pipe, that is, the catalyst mounting position from the engine. Therefore, instead of determining the length Lf of the first front carrier in the flow path direction based on the backflow length after fixing the catalyst mounting position, the backflow length Lrf is changed by changing the catalyst mounting position, that is, the exhaust pipe length Le. It may be changed so that the backflow covers the entire area of the first front carrier. More specifically, as shown in FIGS. 14A, 14B, and 14C, the backflow length is changed by changing the exhaust pipe length. In the case of FIG. 14B, the back flow does not reach the entire catalyst because the back flow is too small. On the other hand, in the case of FIG. 14C, there is no problem with the use of the backflow, but there is a possibility that other disadvantages due to the catalyst position being too far, such as a problem of a decrease in the catalyst temperature, may occur. Therefore, in the case of FIG. 14A, the backflow length Lrf and the length Lf of the first front carrier 21 in the flow path direction substantially coincide with each other, and the backflow can be used effectively. In FIG. 14, the length of the catalyst in the flow path direction is the same in (a), (b), and (c).

  Further, not only the length Lf of the upstream carrier 21 in the flow path direction substantially coincides with the reverse flow length Lrf, but also the capacity of the upstream carrier 21 is set to be equal to or smaller than the exhaust gas capacity flowing from the casing 18 to the exhaust pipe 12 during the backward flow. It is preferable. In this case, the reverse flow surely reaches the entire catalyst. In particular, when the capacity of the upstream carrier 21 and the exhaust gas capacity flowing out to the exhaust pipe 12 are substantially matched, all the exhaust reverse flow can be brought into contact with the catalyst. Promotion of purification reaction due to gas backflow The temperature rise of the support can be maximized.

As described above, based on the actual measurement using the measurement converter 41, in the catalytic converter 13 of the engine 1 of FIG. 1, the length in the flow path direction of the front carrier 21 inside thereof substantially coincides with the backflow length Lrf. The length Lf (= Lc2) described in (1) was adopted.
In the engine 1 of FIG. 1 equipped with such an exhaust gas purification device having the catalytic converter 13, at the initial stage when the high temperature exhaust gas flowing out in the exhaust stroke of each cylinder flows down the exhaust pipe 12 at the cold start. The exhaust gas on the downstream side is pressed as the exhaust gas, and the volume is instantaneously reduced by cooling with the exhaust pipe 12, and the flow rate of the exhaust gas on the downstream side is reduced. In particular, after the exhaust gas that has passed through the upstream carrier 21 in the catalytic converter 13 and has reached the gap portion 20 maintains the flow velocity at zero at that time, the gas concentration and temperature are equalized and drawn back upstream of the exhaust pipe 12. It is.

  In this case, since the length Lf of the upstream carrier 21 in the flow path direction is equal to the length of the reverse flow length Lrf at the time of cold start of the engine 1, the gap 20 is once dispersed in the radial direction in a state of zero flow velocity. The stirred exhaust gas flows backward through the upstream carrier 21 at the same speed. At this time, as shown in FIG. 3B, the backflow exhaust gas flows back until it completely covers the entire area of the front carrier 21 and flows out to the inlet side of the casing 18. Next, the pressing force of the high-temperature exhaust gas from the cylinder that has reached the next exhaust stroke is applied to return to the forward flow nf, thereby repeating the exhaust pulsation including the reverse flow.

  As a result, the catalytic reaction of the front stage catalyst of the front stage carrier 21 is performed in the catalytic converter 13 without deviation in the radial direction, thereby warming up the engine by raising the temperature of the front stage catalyst at the time of cold start of the engine 1. The activation of the catalyst can be promoted and the purification efficiency can be improved. In addition, as the temperature of the upstream carrier 21 is increased quickly, the temperature of the exhaust gas flowing into the downstream catalyst 22 increases due to the reaction heat, and the temperature of the three-way catalyst that is the downstream catalyst 22 can be increased quickly. The purification efficiency of 13 as a whole can be improved. Further, even if the amount of the precious metal as the pre-stage catalyst is reduced due to the rapid increase in temperature of the pre-stage carrier 21, the NOx reduction treatment and HC oxidation performance are not deteriorated, and the cost of the precious metal of the catalyst can be reduced in this respect. .

  Here, as the exhaust gas backflow length measuring device 40, in addition to the hot-wire anemometer 45, a device similar to the backflow measuring device 300 to which the discharge tuft method is applied is used in combination, but only the hot-wire anemometer 45 may be used. Good. Further, when the backflow velocity is obtained by the hot wire anemometer 45, the measurement accuracy may be increased by performing density correction or the like by the exhaust gas temperature or the exhaust pressure.

  Further, the method for obtaining the reverse flow velocity is not limited to the hot-wire anemometer 45 used here. As a hot-wire anemometer, in addition to obtaining the flow velocity directly from the electric resistance change of the heating wire used here, a current is passed through the heating wire so that the temperature of the heating wire becomes constant even when the heating wire is cooled, The flow velocity may be obtained based on the current value. Here, the frame material 51 having a C-shaped cross section is used when measuring the reverse flow using a hot-wire anemometer, but a flow direction detection device may be provided. Furthermore, the current meter need not be limited to a hot-wire current meter, and any device that can measure the flow rate may be used. For example, a Karman vortex type may be used, or a measuring device such as a laser Doppler velocimeter may be used.

Here, the backflow length of the exhaust gas is actually measured by the exhaust gas backflow length measuring device, but the backflow length of the catalyst may be determined by calculating the backflow length. Specifically, since the exhaust backflow is generated by reducing the gas volume by cooling the exhaust gas in the exhaust pipe, the following method can be considered.
・ Estimated back flow length based on exhaust pipe volume and exhaust pipe surface area (heat release from the exhaust pipe).
-Estimate the backflow length based on the exhaust pipe volume and the amount of temperature drop in the exhaust pipe (for example, the amount of reduction from the cylinder head outlet to the catalyst inlet).
As for the temperature drop amount of the exhaust gas in the exhaust pipe, for example, the relationship between the distance from the cylinder head and the exhaust temperature can be obtained, and the exhaust backflow length may be obtained based on this.

  In the above description, the catalytic converter 13 used in the exhaust gas purifying apparatus of FIG. 1 employs a tandem catalyst system in which the front and rear carriers 21 and 22 are arranged via the gap portion 20, but the present invention may be used in some cases. Alternatively, it may be configured as the front-stage catalytic converter 70 in the catalyst system in which the rear stage is not close and the distance is long. In this case, as shown in FIG. 7, a front-stage catalytic converter 70 made of a single carrier is provided on the downstream end side of the exhaust pipe 12, and a rear-stage catalyst 71 is provided on the downstream exhaust pipe 14.

  In this case, the pre-stage catalytic converter 70 uses a single carrier similar to the pre-stage carrier 21 of the catalytic converter 13 of FIG. 1, and adopts the shape and trap material that is the pre-stage catalyst in the same manner. Similarly, a single support similar to the post-stage carrier 22 of the catalytic converter 13 of FIG. 1 is used for the post-catalyst converter 71, and a three-way catalyst that is a shape and a post-stage catalyst is employed in the same manner. Also in this case, the pre-stage catalyst can promote warm-up by early temperature increase at the time of cold start of the engine 1, promote activation, and improve the purification efficiency. The warming-up can be promoted by the conversion, the activation can be promoted, and the purification efficiency of the exhaust emission control device as a whole can be improved.

  In the above description, the catalytic converter 13 used in the exhaust gas purification apparatus of FIG. 1 employs a tandem catalyst system in which two carriers 21 and 22 are arranged in the front and rear in the casing 18, but as shown in FIG. Alternatively, a three-stage catalytic converter 76 in the front-rear direction in which three carriers 72, 73, 74 are sequentially disposed in the casing 75 in the front-rear direction of the exhaust passage via a gap 76 may be used.

In this case, as shown in FIG. 8, the front carrier 72 has the same shape as the front carrier 21 of FIG. 1, the shape and material are determined by the same method, and a small capacity three-way catalyst is adopted as the front catalyst, A medium capacity three-way catalyst is employed as the middle catalyst, and a large capacity three-way catalyst is employed as the rear catalyst.
Also in this case, when the engine 1 is cold-started, exhaust gas completely reversely flows across the entire front carrier 72, and the temperature rise due to early activation of the small-capacity three-way catalyst supported on the front carrier 72 is increased. Accordingly, early activation of the intermediate carrier 73 is achieved, and early activation of the latter three-way catalyst is also achieved. In this case, in particular, the early activation of the three-way catalyst in the previous stage can be achieved at the time of cold start, and the purification efficiency of the exhaust gas purification apparatus as a whole can be further improved. Note that the number of catalysts is not limited to three, and the same applies to a larger number of stages.

  The internal combustion engine to which the present invention is applied is not limited to the in-cylinder injection type 4-cycle multi-cylinder gasoline engine as in the embodiment as long as the exhaust pipe is provided with a catalyst. For example, an intake pipe fuel injection type or carburetor type gasoline engine or a diesel engine may be used. Moreover, not a 4-cycle but a 2-cycle engine may be sufficient. That is, as long as the exhaust pipe is provided with a catalyst and exhaust gas is completely discharged from the engine into the exhaust pipe, the internal combustion engine is not limited.

As the carrier, in addition to a ceramic such as cordierite, a metal carrier made of a metal such as stainless steel may be used.
The catalyst type is not limited to a three-way catalyst. NOx trap catalyst, HC trap catalyst, selective reduction type NOx catalyst (iridium catalyst, zeolite catalyst, urea SCR, etc.), oxidation catalyst, catalyst carrying purification substances other than noble metals, etc. Something like that.

1 is an overall schematic configuration diagram of an engine having the same exhaust gas purifying apparatus as an embodiment of the present invention. It is an expansion schematic sectional drawing of the catalytic converter used with the exhaust gas purification apparatus of FIG. FIG. 2 is an exhaust gas flow characteristic diagram of a front carrier in a catalytic converter used in the exhaust gas purification apparatus of FIG. 1, (a) shows a forward flow state, (b) shows a complete backflow state, and (c) shows a partial backflow state. It is a whole block diagram of the exhaust gas backflow length measuring apparatus used for the shape setting of the front | former stage support | carrier in FIG. The hot-wire anemometer used with the exhaust gas backflow length measuring apparatus of FIG. 4 is shown, (a) shows a plane sectional view, and (b) shows a side sectional view. The waveform diagram of the exhaust gas flow velocity and the resistance value in the exhaust gas back flow length measuring device of FIG. 4 is shown, and the data in the case of generating back flow is shown. It is the schematic of the exhaust-gas purification apparatus as other embodiment of this invention. It is the schematic of the exhaust-gas purification apparatus as other embodiment of this invention. It is a schematic operation characteristic explanatory view of an intake valve driven by the variable valve operating apparatus. FIG. 1 is a schematic diagram of a conventional exhaust gas purification device, where (a) is a schematic diagram of a single catalyst system, (b) is a schematic diagram of a tandem catalyst system, (c) is a temperature distribution diagram at positions A and B, and (d) is a schematic diagram of (d). It is a temperature distribution figure of C and D position. It is a temperature comparison diagram in the A, B, C, D position in the support | carrier of the conventional exhaust gas purification apparatus. It is a whole block diagram of a backflow measuring device. It is a backflow state visual observation figure by a backflow measuring apparatus, (a) shows a backflow, (b) shows no wind, (c) shows a forward flow. FIG. 12 is a diagram for explaining a backflow measurement example in the backflow measurement device of FIG. 11, (a) is an explanatory diagram of measurement condition values, and (b) is a comparison diagram of the backflow ratio. The relationship between the length of the backflow and the length of the carrier with respect to the length of the exhaust pipe is shown.

Explanation of symbols

1 Engine 12 Exhaust pipe 13 Catalytic converter 18 Casing 21 Front stage carrier 22 Rear stage carrier rf Backflow Lf Length of carrier

Claims (5)

In an exhaust gas purifying apparatus comprising a catalytic converter having a casing disposed on an exhaust pipe extending from a main body of an internal combustion engine, a carrier housed in the casing, and a catalyst component carried on the carrier,
An exhaust gas purification apparatus characterized in that the length of the carrier is set to be equal to or smaller than the length of the backflow generated in the casing. A casing disposed on an exhaust pipe extending from the main body of the internal combustion engine, a plurality of carriers sequentially disposed in series in the casing along a direction of the exhaust path along the exhaust passage direction, and supported by each of the above carriers In an exhaust gas purifying apparatus comprising a catalytic converter having a catalyst component that has been
An exhaust gas purification apparatus characterized in that the length of at least the upstream side of the plurality of carriers is set to be equal to or smaller than the length of the backflow generated in the casing. The exhaust gas purification device according to claim 1 or 2,
The length of the reverse flow is based on a change in the volume of exhaust gas due to heat radiation from at least the exhaust pipe. The exhaust gas purification apparatus for an internal combustion engine according to any one of claims 1 to 3,
The exhaust gas purifying apparatus is characterized in that the length of the exhaust pipe or the length of the carrier on the exhaust gas inlet side is set so that the reverse flow occurs at least during cold idling. The exhaust gas purifying device for an internal combustion engine according to any one of claims 1 to 4, wherein a capacity of the carrier whose length is set according to the length of the backflow flows out from the casing to the internal combustion engine side. An exhaust gas purifying device characterized in that it is set to be equal to or smaller than the amount of exhaust gas to be produced.

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