JP5811394B2 - Diesel particulate filter - Google Patents

Description

  The present invention relates to a collection filter for exhaust gas. Specifically, the present invention relates to a diesel particulate filter in which occurrence of defects such as cracks due to thermal stress during use and regeneration is suppressed.

In order to collect particulate matter (particulate matter, hereinafter referred to as “PM”) discharged from a diesel engine, a diesel particulate filter (hereinafter also referred to as “DPF”) is provided in a diesel engine vehicle. . In general, a DPF includes a honeycomb structure (honeycomb base material) having regularly arranged cells in order to increase the contact area with exhaust gas, and the honeycomb structure is a ceramic having high heat resistance and porosity (typically In particular, cordierite, silicon carbide, etc.) are often the main constituents. For this reason, the brittleness and impact resistance of the DPF itself are relatively low, and in order to use it in an actual automobile exhaust system, the entire DPF is covered with a holding case that restricts the movement of the DPF. It will be necessary. In general, in the exhaust gas purification system using the DPF, a holding member (buffer member) such as a mat or metal net made of an inorganic material (typically alumina fiber) is wound around the outer periphery of the DPF. These are housed in a metal catalytic converter case (metal shell) to form a catalytic converter, which is used in the exhaust passage.
Patent Document 1 and Patent Document 2 describe the configuration of the exhaust gas collecting filter and a catalytic converter containing the filter. Specifically, Patent Document 1 discloses a diesel particulate filter that includes a holding seal material disposed between a diesel particulate filter and a metal shell that covers the outside. Patent Document 2 discloses an exhaust gas purifying device in which an auxiliary body provided on the outer periphery of a filter body and a holding element arranged in a compressed state between the filter and the case are engaged.

By the way, in the process of using the DPF in the exhaust system, the particulate matter (PM) collected on the surface and pores of the partition wall of the DPF and accumulated with time increases the flow resistance of the exhaust gas and decreases the output of the internal combustion engine. Bring. For this reason, it is necessary to regenerate the DPF by appropriately removing the particulate matter deposited on the DPF (hereinafter also referred to as “PM regeneration”) to recover the exhaust gas circulation capacity. As this regeneration treatment, techniques such as a continuous regeneration method using an oxidation catalyst and a heating regeneration method using a heater or a burner are known.
However, during the PM regeneration, a non-uniform temperature rise is likely to occur in the DPF, and in this case, there is a problem that defects such as cracks and cracks are likely to occur in the DPF due to local generation of thermal stress.
Conventional techniques described in, for example, Patent Document 3 and Patent Document 4 are known as techniques for suppressing the occurrence of defects due to thermal stress during DPF regeneration. That is, Patent Document 3 discloses a ceramic honeycomb structure in which the thermal expansion coefficient of the outer peripheral wall portion of the ceramic honeycomb structure is smaller than the radial thermal expansion coefficient of the cell wall portion. Patent Document 4 describes a ceramic filter that is used while applying a compressive stress in a direction connecting both the gas inflow surface and the gas outflow surface.

Japanese Patent No. 4465792 JP 2008-8162 A JP 2004-75523 A JP 2003-31114 A

However, in the conventional DPF as described above, cracks and the like during use (that is, when PM is collected and removed from the exhaust gas) and when PM is regenerated (that is, when PM accumulated in the DPF is removed by combustion) There is still room for improvement regarding the suppression of defects, which is not sufficient.
In particular, in a state where a large amount of collected PM is accumulated in the DPF, when the automobile suddenly decelerates or stops suddenly, a phenomenon may occur in which the PM suddenly burns (abnormal combustion). When such abnormal combustion of PM occurs, it is no longer difficult to control the temperature of the entire DPF within the temperature range optimal for PM regeneration, so to speak, the DPF may be in a state of thermal runaway. At this time, it was inevitable that a sudden temperature increase more than expected occurred locally near the downstream end face of the DPF, and cracks occurred in the DPF due to the thermal stress generated by the thermal expansion difference.

On the other hand, in the above-described conventional technology, for example, as described in Patent Document 1 and Patent Document 2, a mat, a net, or the like is wound around the DPF outer periphery as a holding member and accommodated in a metal case while compressing it. It is possible to apply a certain amount of pressure to the DPF (that is, a surface pressure in an in-plane direction perpendicular to the axis of the DPF). Due to the pressure load applied to the DPF by the holding member in the in-plane direction, the thermal stress generated in the DPF at the time of abnormal combustion during PM regeneration can be relieved to some extent, and there is a certain crack generation suppressing effect. it is conceivable that.
However, the DPF has a problem in that the mat fiber and the net, which are holding members, are deteriorated during traveling, so that the surface pressure applied in the initial stage of use is remarkably lowered and the effect of suppressing the occurrence of cracks is easily lost. Further, since the magnitude of the surface pressure loaded by the holding member depends on the dimensional accuracy of the honeycomb structure and the holding member, there is a problem that there is a variation depending on each catalytic converter, and the crack suppressing effect may be small. .

  On the other hand, by reducing the porosity of the honeycomb structure constituting the DPF, or increasing the wall thickness of the honeycomb structure, the heat capacity of the honeycomb structure itself is increased, thereby causing cracks due to thermal stress. Can be suppressed. However, in this case, there is a problem that pressure loss due to exhaust gas increases and fuel consumption is deteriorated.

  The present invention has been created to solve such problems, and an object thereof is to suppress the occurrence of defects such as cracks in the DPF without affecting the performance such as pressure loss and fuel consumption. It is another object of the present invention to improve the soot accumulation limit amount (Soot Mass Limit, hereinafter also referred to as “SML”) against crack generation. The larger the SML value is, the longer the interval until DPF regeneration can be set, which is important because it leads to improvement in fuel consumption and reliability.

The present inventors have studied from various angles and have come to create the present invention capable of realizing the above object.
That is, the diesel particulate filter (DPF) disclosed here is a cylindrical DPF that is used in the exhaust passage of the diesel engine in order to purify the exhaust gas of the diesel engine. Here, in the exhaust passage, when the exhaust gas flows into the DPF as an upstream side, and when the exhaust gas passes through the DPF and flows out as a downstream side, the upstream side and the downstream side of the DPF. A compression force is locally applied from the outside toward the center in at least one of the outer peripheral end portions.
According to such a DPF, even when there is a sudden temperature change in the DPF when the DPF is used or during PM regeneration, the thermal stress is alleviated and the generation of cracks is suppressed. Further, according to such a DPF, the SML is improved, thereby improving the fuel consumption and the reliability. In particular, when a wall flow type DPF is used, a sealing material is applied, and the compressive force is applied to the upstream end portion or the downstream end portion of the DPF having a relatively large strength compared to other portions. Therefore, a relatively large compressive force (or pressure) can be applied, and a higher thermal stress relaxation effect can be obtained. Furthermore, since the compressive force is applied independently of the holding member for holding the case, it is possible to suppress variations and lowering of the SML derived from the dimensional accuracy, and the reliability is improved.

  Here, when the compressive force is locally loaded at the outer peripheral end of the DPF downstream end (that is, when the compressive force is locally applied to the outer peripheral end of the DPF downstream end) Since the DPF can relieve the thermal stress due to the difference in thermal expansion during the abnormal combustion of the PM in a state where the PM is deposited, the occurrence of cracks at the downstream end of the DPF can be suppressed. For this reason, the soot accumulation limit amount (SML) with respect to crack generation is improved, and the interval until PM combustion (DPF regeneration) can be lengthened. Therefore, improvement in fuel consumption and improvement in reliability are achieved.

  Further, when the compressive force is applied at the outer peripheral end of the DPF upstream end (that is, when the compressive force is locally applied to the outer peripheral end of the DPF upstream end), during DPF regeneration The thermal stress generated by the rapid temperature increase of and the rapid cooling due to the subsequent rapid regeneration stop can be alleviated, and the generation of cracks at the upstream end of the DPF can be suppressed.

In a preferred aspect of the DPF disclosed herein, the local compressive force is applied substantially uniformly over the entire outer periphery at the outer peripheral end of the DPF.
According to such a DPF, a compressive force is uniformly applied almost uniformly in the in-plane direction of the surface orthogonal to the axis of the DPF at the outer peripheral edge of the outer peripheral end of the DPF. Thereby, the higher suppression effect with respect to the crack generation by a thermal stress is achieved.

In another preferable aspect of the DPF disclosed herein, the substantially uniform compressive force is realized by tightening an outer periphery of the DPF with a restraining band.
According to such a DPF, it is possible to selectively apply a substantially uniform compressive force to the downstream end or the upstream end, which is a place where thermal stress is particularly likely to occur, by the restraining band (band-shaped instrument). it can. For this reason, the compression force of an appropriate magnitude can be easily applied in accordance with the crack generation mode, position, or degree that varies depending on the material and scale of the honeycomb structure. Further, when such a restraining band is used, it is possible to apply the compressive force to the end portion of the DPF and not apply the compressive force to the body portion of the DPF. For this reason, it is possible to prevent the occurrence of cracks such as ring-off cracks originating from an excessive compressive force applied to the body portion of the DPF.

In another preferred aspect of the DPF disclosed herein, the DPF is installed so that a part of the restraint band overlaps with an outer peripheral end region closer than at least 20 mm from the end face of the DPF.
According to such a DPF, it is possible to effectively suppress the generation of cracks in the vicinity of the outer peripheral end portion derived from thermal stress generated by a rapid temperature change such as abnormal combustion of PM.

In another preferred aspect of the DPF disclosed herein, the width of the restraining band (that is, the width of the portion restraining the outer peripheral end region of the DPF) is 5 mm or more and 20 mm or less.
According to such a DPF, it is possible to appropriately apply a compressive force to the main generation site of thermal stress generated by a rapid temperature change by the restraining band, and thus it is possible to suppress the generation of cracks.

In another preferable aspect of the DPF disclosed herein, the pressure applied to the DPF by applying the compressive force is 1 MPa or more and 5 MPa or less at 25 ° C.
According to such a DPF, even when the internal combustion engine operates at a high load or when the DPF is heated to a high temperature (typically 400 ° C. or more and 900 ° C. or less) due to abnormal PM combustion in the DPF, the DPF In a state in which the pressure (or compressive force) that is a positive value is loaded (more preferably in a state in which a pressure of 0.2 MPa or more is loaded when the temperature at the outer peripheral portion of the DPF is 500 ° C.) Can be kept. For this reason, generation | occurrence | production of the crack by a thermal stress can be suppressed also in this high temperature state.

The exhaust gas purifying apparatus disclosed herein uses any of the DPFs disclosed in this specification.
According to such an exhaust gas purifying apparatus, since SML is improved, an interval until PM regeneration is extended, and fuel efficiency and reliability are improved.

It is the schematic of the exhaust gas purification apparatus which concerns on one Embodiment. It is the figure which demonstrated typically the structure of the control part in the exhaust gas purification apparatus which concerns on one Embodiment. It is a perspective view of the honeycomb structure used in DPF concerning one embodiment. It is a perspective view of DPF concerning one embodiment. It is a perspective view of the restraint band used in DPF concerning one embodiment. It is a perspective view of DPF concerning one embodiment. It is a perspective view of DPF concerning one embodiment. It is sectional drawing of the exhaust gas purification part which concerns on one Embodiment. It is a figure explaining the installation place of the thermocouple installed when performing the unsteady forced regeneration test about DPF which concerns on Example 1, 3 and Comparative Example 1. FIG. It is the figure which showed the temperature behavior in the unsteady forced regeneration test in case the soot accumulation amount is 8.3 g / piece | unit about the DPF which concerns on Example 1. (A vertical axis | shaft: Temperature (degreeC), A horizontal axis: Time (second) )). It is the figure which showed the temperature behavior in the unsteady forced regeneration test in case the soot accumulation amount is 6.7 g / piece | unit about the DPF which concerns on the comparative example 1 (a vertical axis | shaft: temperature (degreeC), a horizontal axis: time (second). )). It is a photograph of the downstream end face after the unsteady forced regeneration test about DPF (soot accumulation amount: 6.7 g / piece) concerning comparative example 1. It is a photograph of the upstream end face after the rapid cooling test about DPF concerning the comparative example 1.

  Hereinafter, preferred embodiments of the present invention will be described. Note that matters other than matters specifically mentioned in the present specification and necessary for the implementation of the present invention can be grasped as design matters of those skilled in the art based on the prior art in this field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field.

  An embodiment of the DPF disclosed herein and an exhaust gas purification apparatus including the DPF will be described with reference to the drawings. As shown in FIGS. 1 and 2, the exhaust gas purification apparatus 100 according to this embodiment is roughly an engine unit 1 mainly composed of a diesel engine (the engine unit 1 includes an accelerator for driving the engine and other operations. An exhaust gas purification unit 40 provided in an exhaust system communicating with the engine unit 1, and an ECU (electronic control unit) 30 that controls the exhaust gas purification unit 40 and the engine unit 1. It is comprised by.

  The engine unit 1 typically includes a plurality of combustion chambers 2, a fuel pump 23 communicating with a fuel tank 24, and a fuel injection valve 3 that injects fuel supplied via a fuel supply pipe 22 into each combustion chamber 2. And. Each combustion chamber 2 communicates with an intake manifold 4 and an exhaust manifold 5. The intake manifold 4 is connected to the outlet of the compressor 7 a of the exhaust turbocharger 7 via the intake duct 6. An inlet of the compressor 7 a is connected to an air cleaner 9 via an intake air amount detector 8. A throttle valve 10 is disposed in the intake duct 6. Around the intake duct 6, a cooling device 11 for cooling the air flowing in the intake duct 6 is arranged. The exhaust manifold 5 is connected to the inlet of the exhaust turbine 7 b of the exhaust turbocharger 7. The outlet of the exhaust turbine 7 b is connected to the exhaust pipe 12.

  The exhaust manifold 5 and the intake manifold 4 are connected to each other via an exhaust gas recirculation (hereinafter referred to as EGR) passage 18. An electronically controlled control valve 19 is disposed in the EGR passage 18. A cooling device 20 for cooling the EGR gas flowing in the EGR passage 18 is disposed around the EGR passage 18.

  A fuel supply valve 15 that supplies (injects) fuel into the exhaust gas is disposed in the exhaust pipe 12, and an exhaust gas purification unit 40 is disposed further downstream. The exhaust gas purification unit 40 includes an oxidation catalyst 50 for oxidizing CO and HC in the exhaust gas, and a diesel particulate filter (DPF) 60 that collects PM in the exhaust gas.

As shown in FIG. 2, the ECU 30 is a unit that performs control between the engine unit 1 and the exhaust gas purification unit 40, and includes a digital computer. The ECU 30 has a ROM (read-on memory), a RAM (random access memory), a CPU (microprocessor), an input port, and an output port that are connected to each other via a bidirectional bus.
A load sensor that generates an output voltage proportional to the amount of depression of the accelerator pedal is connected to an accelerator pedal (not shown). The output voltage of the load sensor is input to the input port via the corresponding AD converter. Further, a crank angle sensor that generates an output pulse every time the crankshaft rotates by a predetermined angle (for example, 15 °) is connected to the input port.

Output signals from the temperature sensor and the differential pressure sensor in the exhaust gas purification unit 40 are input to the input port via corresponding AD converters. On the other hand, the output port is connected to the fuel injection valve 3, the step motor for driving the throttle valve 10, the control valve 19, the fuel pump 23 communicating with the fuel tank 24, and the fuel supply valve 15 through corresponding drive circuits. . In this way, the fuel injection valve 3, the fuel supply valve 15, and the like are controlled by the ECU 30.
The above-described control system itself does not characterize the present invention, and may be conventionally employed in this type of internal combustion engine (diesel engine), and further detailed description thereof is omitted.

Next, the DPF 60 provided in the exhaust gas purification unit 40 characterizing the present invention will be described. The DPF 60 disclosed herein includes a tubular honeycomb structure.
As shown in FIG. 3, the honeycomb structure 70 has regularly arranged cells 72. Here, as the honeycomb structure 70, a wall flow type honeycomb structure 70 characterized in that the cells 72 adjacent to each other on both end faces of the honeycomb structure 70 are sealed at opposite end faces. Used for. The wall flow type honeycomb structure 70 is a structure in which PM is collected while the exhaust gas flows between the cells 72 through the porous partition walls of the honeycomb structure 70, and the collection efficiency is good. Is also easy.
The honeycomb structure 70 only needs to have a stable property even when it is suddenly exposed to high-temperature exhaust gas (for example, 400 ° C. or more) generated when the diesel engine is operated under a high load condition. Conventionally, the material used for this kind of honeycomb structure 70 can be used. Examples of the material include cordierite, aluminum titanate, ceramics such as silicon carbide (SiC), and metals (alloys) such as stainless steel. Among them, cordierite and aluminum titanate have a relatively small thermal expansion coefficient, and an excellent effect by the technique disclosed in the present specification, that is, an effect of suppressing the occurrence of cracks due to a compressive force load at the outer peripheral end of the DPF 60. Since it is easy to express, it can be particularly preferably used.

Further, in the DPF 60 disclosed herein, a compressive force is applied from the outside toward the center at at least one outer peripheral end of the upstream end or the downstream end.
The means for applying the compressive force is not particularly limited as long as the compressive force (or pressure) can be applied toward the center at the outer peripheral end of the DPF 60. Specific means are described below. Illustrate. In addition, the following illustration is not described in order to limit the load means of the said compression force.
Examples of the compressing force loading means include tightening the outer periphery of the DPF 60 with a restraining band. That is, it can be performed by winding the restraining band around the outer periphery of the DPF 60 while applying a certain pulling force, and fixing the restraining band with a band fixing device (band clamp) so as to maintain the pulling force. The use of the restraining band as a compressive force loading means is preferable because the compressive force can be applied substantially uniformly over the entire outer peripheral end of the DPF 60.
In another example, a hose clamp or a hose band is installed on the outer periphery of the DPF 60, and a compressive force is applied to the outer periphery of the DPF 60 by tightening an attached screw or fixing with a spring-type fixing device. Can do.
The material used for applying the compressive force described above (typically, the above-mentioned restraint band) has a melting point of approximately 900 ° C. or higher (more preferably 1000 ° C. or higher, such as titanium, copper, stainless steel, shape memory alloy). More preferably, a metal or alloy at 1300 ° C. or higher is preferably used.

FIG. 4 is a diagram for explaining an embodiment in which the compressive force is locally applied by locally wrapping the restraining band around the downstream end of the DPF 60. That is, in the DPF 60A shown in FIG. 4, when the DPF 60A is placed in the exhaust passage, the restraining band 80 is locally wound around the outer peripheral edge in the vicinity of the end surface on the side from which the exhaust gas flows (described as “Rr side” in the drawing) Therefore, the compression force is applied.
FIG. 5 illustrates the configuration of the restraining band 80. That is, the restraining band 80 includes a band portion 82 having a certain width and thickness, and a band fixing device (band clamp) 84 for fixing the band portion 82.

6 is a diagram illustrating the DPF 60B when the compressive force is locally applied to the upstream end portion of the DPF 60. FIG. That is, in the DPF 60B disclosed herein, the restraining band 80 is locally disposed on the outer peripheral edge in the vicinity of the end face on the side (referred to as “Fr side” in the drawing) into which the exhaust gas flows when the DPF 60B is placed in the exhaust passage. By being wound around, the compressive force is locally applied.
FIG. 7 is a diagram illustrating the DPF 60C when the compressive force is locally applied to both the upstream end and the downstream end of the DPF 60. That is, in the DPF 60C disclosed herein, the restraining band 80 is locally wound around the outer peripheral edges in the vicinity of both the upstream side (Fr side) and the downstream side (Rr side), and the upstream end and The compressive force is locally applied to both downstream ends.

The restraint band 80 is preferably installed so that a part of the restraint band 80 overlaps with an outer peripheral end region closer than at least 20 mm from the end face of the DPF 60. That is, it is not preferable that the end of the restraining band 80 that is closer to the end face is wound in a state where it is separated from the end face of the DPF 60 by 20 mm or more. When the distance from the end face of the DPF 60 to the end of the restraining band 80 closer to the end face is greater than 20 mm, the temperature is rapidly increased and a portion near the DPF end face where thermal stress is likely to occur, and the load of the compressive force Therefore, the effect of suppressing the occurrence of cracks tends to be reduced because the overlap with the portion where thermal stress relaxation is possible is reduced. Further, when the wall flow type DPF 60 is used, since the overlap between the portion near the end face of the DPF to which the sealing material is applied and the strength is relatively increased and the portion where the restraint band 80 is wound is reduced, the compression is large. There is a possibility that the force cannot be applied, and the crack generation suppressing effect is reduced.
It is more preferable that the distance between the end face of the DPF 60 and the end of the restraining band 80 closer to the end face is 15 mm or less (more 10 mm or less, further 5 mm or less, for example, 0 mm or more and 3 mm or less).

  The width of the restraining band 80 is preferably 5 mm or more and 20 mm or less (more preferably 6 mm or more and 15 mm or less, and further preferably 8 mm or more and 13 mm or less). When the width of the restraint band 80 is too narrow than 5 mm, the crack generation suppression effect tends to decrease because the width of the load portion of the compressive force is too small with respect to the portion of the DPF 60 where the thermal stress is generated. Further, when the width of the restraint band 80 is too wide than 50 mm, the effect of thermal stress relaxation is saturated, and there is a risk of inducing another mode crack (for example, ring-off crack) derived from the load of compressive force. . Here, the ring-off crack is likely to occur when the expansion and contraction of the DPF 60 in the axial direction is restricted.

  The pressure (or compressive stress) applied to the DPF 60 by applying the compressive force is 0.5 MPa to 6 MPa (more preferably 1 MPa to 5 MPa, more preferably 1.5 MPa to 4 MPa at 25 ° C. For example, 2 MPa or more and 3 MPa or less). When the pressure at 25 ° C. is too smaller than 0.5 MPa, the effect of suppressing the occurrence of cracks may be reduced. Further, in this case, when the means for applying the compressive force is a metal restraining band as will be described later, when the compressive force load device is more easily thermally expanded than the DPF 60, the DPF 60 is When heated to a high temperature, there is a risk that an appropriate compressive force will not be applied. On the other hand, if the pressure at 25 ° C. is more than 6 MPa, the compressive force may be applied exceeding the strength of the honeycomb structure constituting the DPF 60, which may cause defects such as cracks or cracks.

  The instrument used for the compressive force load (typically, the restraining band 80) can be installed so as to directly touch the outer peripheral edge of the DPF 60. On the other hand, a heat-resistant mat (typically mainly composed of an inorganic material) or the like may be sandwiched between the device and the DPF 60 as a buffer material. It is more preferable that the cushioning material not only has a function of uniformizing the compressive force applied by the instrument at the contact portion between the DPF and the instrument (that is, a cushioning function) but also has a heat insulating function. . According to such a cushioning material (and further a heat insulating material), it is possible to suppress an increase in temperature of the device due to heat transfer from the DPF 60 that becomes a high temperature (for example, about 500 ° C.) during PM regeneration, etc., and thermal expansion of the device Compressive force drop due to is suppressed. As the buffer material, a ceramic mat mainly composed of alumina fiber or silica fiber, or ceramic wool is preferably used.

Next, an embodiment of the exhaust gas purification unit 40 formed using the DPF 60 is shown in FIG. The exhaust gas purification unit 40 disclosed herein includes the DPF 60, an oxidation catalyst (DOC) 50 installed on the upstream side of the DPF 60, and a catalytic converter 90 formed by housing these. The catalytic converter 90 is formed by press-fitting and storing the DPF 60 and the oxidation catalyst 50 in a catalytic converter case 94 after a holding member 92 such as a mat or a net is disposed on the outer periphery of each body portion.
In the DPF 60, the holding member 92 is preferably wound around a portion that does not overlap with the portion around which the restraining band 80 is wound. Specifically, the holding member 92 is preferably used on the outer periphery of the body portion that is 15 mm or more and 30 mm or less (more preferably 20 mm or more and 25 mm or less) away from both end faces of the DPF 60.
The holding member 92 prevents cracks, cracks, etc. of the DPF 60 or the oxidation catalyst 50 generated when the DPF 60 or the oxidation catalyst 50 moves in the catalytic converter case 94 and collides with the catalytic converter case 94. It is used as a main purpose, and those conventionally used for this type of purpose can be used. As the holding member 92, for example, a ceramic mat mainly composed of alumina fibers or silica fibers, or a metal net can be preferably used.

  The method for regenerating PM of the DPF 60 disclosed herein can be performed by techniques such as a conventionally known continuous regeneration method using an oxidation catalyst or a heating regeneration method using a heater or a burner. In the exhaust gas purification unit 40 shown in FIG. 8, the fuel is added to the oxidation catalyst 50 disposed on the upstream side of the DPF 60, so that oxidation heat is generated in the oxidation catalyst 50, and the downstream side DPF 60 is generated by the oxidation heat. Is heated. When the DPF 60 reaches a sufficiently high temperature, the deposited PM burns and PM regeneration of the DPF 60 is performed.

Several examples relating to the present invention will be described below, but the present invention is not intended to be limited to those shown in the specific examples.

<Example 1>
Cordierite wall flow DPF with a cell count of 300 cpsi (cells per square inch), cell wall thickness of 0.3 mm, cell wall pitch of 1.47 mm, capacity of 3 L, total length of 150 mm, outer diameter of 160 mm, and porosity of 48% Prepared. A predetermined amount of alumina and a predetermined amount of noble metal were coated on the cell wall surface of the DPF.
Next, a restraining band was wound and fixed at the downstream end of the DPF in order to load a compressive force in the center direction. Specifically, among the end faces orthogonal to the axial direction of the DPF, a width of 9.6 mm and a thickness are formed on the outer peripheral edge in the vicinity of the downstream end face that becomes the exhaust gas outflow side when the DPF is installed in the exhaust passage of the automobile. A 0.5 mm stainless steel band (manufactured by BAND-IT) was wound. At this time, the DPF was disposed so that the distance between the downstream end surface of the DPF and the band end portion closer to the end surface was not larger than 5 mm. The band is tightened at a normal temperature (25 ° C.) with a pulling force of S = 163.5 kg / cm per unit width, and the band is fixed by a band clamp attached to the band. The band was attached to the DPF while maintaining the above. At this time, a small amount of ceramic wool was sandwiched between the contact surface (or contact point) between the band clamp portion and the DPF to obtain a cushioning material.

As described above, when a compressive stress is applied to a part of the outer periphery of a DPF having a cylindrical shape (cylindrical shape) using a band material having a certain width, the pressure (surface pressure) applied to the DPF in the band mounting portion ( q) is calculated as follows using the pulling force (S) per unit width and the radius (r) of the cross section perpendicular to the axis of the DPF.
q = S / r = 163.5 (kg / cm) / 8 (cm) = 20.4 (kg / cm ² )
= 2.0 MPa
When the above pressure (2.0 MPa) is applied at room temperature (25 ° C.) as in this embodiment, the temperature of the DPF outer wall of the band mounting portion is raised to 500 ° C. due to abnormal combustion of PM, etc. It was confirmed that the pressure (500 ° C.) did not fall below 0.5 MPa even when the pressure applied to the DPF was lowered due to the thermal expansion of (stainless steel).
The band-mounted DPF manufactured by the above manufacturing method is defined as a DPF according to the first embodiment.

<Example 2>
In the above-described method for manufacturing a DPF according to Example 1, a DPF was manufactured in which the band mounting portion was not the downstream end of the DPF, but only the upstream end. Specifically, among the end faces of the DPF, the outer periphery in the vicinity of the upstream end face that becomes the exhaust gas inflow side when the DPF is installed in the exhaust passage of the automobile is the same as that used in the first embodiment. Band material was wound and fixed. At this time, the distance between the upstream end face of the DPF and the end of the band closer to the end face was set so as not to be larger than 5 mm. The pulling force by the band and the pressure applied to the band mounting part at room temperature (25 ° C.) were the same as in Example 1. The band-mounted DPF manufactured by such a manufacturing method is defined as a DPF according to the second embodiment.
<Example 3>
In the manufacturing method of the DPF according to Example 1, a DPF was manufactured in which a band was attached to the upstream end in addition to the downstream end of the DPF (that is, the band was attached to both ends of the upstream and downstream portions). . Specifically, it is the same as the DPFs according to the first and second embodiments except that the bands are attached to the two downstream ends as in the first embodiment and the upstream end as in the second embodiment. DPF was manufactured by the manufacturing method of. The band-mounted DPF manufactured by the manufacturing method is referred to as a DPF according to the third embodiment.
<Comparative Example 1>
In Example 1 above, a DPF was produced in the same manner as Example 1 except that no band was attached to the DPF. This is the DPF according to Comparative Example 1.

<Powder (PM) deposition test>
In order to reproduce the state in which a sufficient amount of PM accumulates in the DPF and the DPF needs to be regenerated by burning the PM, the DPF according to the embodiment and the comparative example is attached to the engine exhaust pipe and the PM is collected. I let you. Specifically, first, about 50 g (thickness: about 8 mm) of holding alumina mat is wound around the outer periphery of the DPF according to the above-described examples and comparative examples, and the DPF in a state where the alumina mat is wound is wound. It was press-fitted and held in a metal converter case.
Next, the DPF held by the catalytic converter is mounted on the exhaust pipe of the 2.2 L engine so that the engine speed is 1800 rpm, the main injection amount is 15 mm ³ / st, the torque is 55 N · m, and the input gas temperature is 250 ° C. By rotating the engine and flowing exhaust gas into the DPF, PM was collected in the DPF so that the amount of soot accumulated was a predetermined amount (for example, a predetermined amount within a range of 5 to 10 g of soot per DPF). Thereafter, the DPF was heat treated at 300 ° C. for 2 hours to remove soluble organic components (SOF components) from the deposited PM.

<Unsteady forced regeneration test; DPF temperature measurement and cracking observation>
For the DPF in which a predetermined amount of soot was accumulated, a thermocouple was installed at a predetermined position (to be described in detail later) in order to measure the temperature in the DPF, and was attached to the exhaust pipe of the engine again. At this time, as shown in FIG. 8, an oxidation catalyst (DOC) was placed in the exhaust passage upstream of the DPF.
The above oxidation catalyst is coated with a slurry of alumina and zeolite as the main component (120 g / L), platinum 2 g / L, and palladium 1 g / L mixed on a honeycomb substrate with 400 cpsi cells, φ160 mm × L100 mm and 2 L capacity. And dried and then fired at 350 ° C. for 1 hour.
Next, the engine was rotated to cause exhaust gas to flow through the exhaust passage, thereby generating oxidation heat with the oxidation catalyst (DOC), thereby heating the downstream DPF. Specifically, the engine is first connected to the bypass exhaust pipe, the engine is rotated so that the engine speed is 2000 rpm, the torque is 100 N · m, and the air mass flow rate (Ga) is 75 ± 3 g / second. Switch to main drain and hold for 3 minutes. Thereafter, in a state where the base bed temperature, which is the catalyst bed temperature before fuel addition, is 290 ° C., fuel addition is started from the upstream of the oxidation catalyst to the exhaust pipe, and the DPF is heated by burning with the oxidation catalyst.
After that, when the exhaust gas temperature at the DPF inlet reached 680 ° C., the fuel addition was stopped immediately, and the engine speed was reduced to 800 rpm and the air mass flow rate (Ga) was reduced to 9 g / sec (so-called idling state). . As a result of the above operation, a gas having a relatively low flow rate and a high oxygen concentration flows into the DPF. Therefore, the PM accumulated in the DPF burns all at once, and the DPF bed temperature rapidly rises.
The above test condition is that when the DPF starts to be regenerated in actual vehicle running (that is, when the temperature of the gas containing the DPF becomes around 680 ° C. with PM accumulated), the soot in the DPF is suddenly decelerated or stopped. Simulates the worst conditions of burning and causing thermal runaway.
The temperature behavior in the DPF during the unsteady forced regeneration test and the occurrence of cracks after the test was observed were observed. Regarding the observation of crack generation, the DPF is taken out after the test, and the entire DPF (particularly near the downstream end and the outer periphery) is visually observed or observed with a microscope (an optical microscope or a scanning electron microscope). It was.

<DPF temperature distribution and crack generation>
The temperature change inside and outside the DPF during the unsteady forced regeneration test was measured. Here, the positions (16 places) of the thermocouples installed in the DPF according to the example and the comparative example are as shown in FIG. That is, in the vicinity of the upstream end face (Fr side) of the DPF, there are five thermoelectrics in the order of (1) to (5) from the center of the circle, which is a cross section perpendicular to the axis of the DPF, to the end. A pair was installed. Further, in a cross section (hereinafter, also referred to as “intermediate cross section”) perpendicular to the axis of the DPF that is an intermediate point between the upstream end face and the downstream end face of the DPF (6) to (10 ) Thermocouples were installed at a total of 5 locations in the order. Furthermore, in the vicinity of the end face on the downstream side (Rr side) of the DPF, thermocouples are installed in a total of five locations in the order of (11) to (15) from the center of the circular cross section perpendicular to the axis of the DPF toward the end. did. At the same time, in order to measure the gas temperature in the vicinity of the inlet where the exhaust gas flows into the DPF, a thermocouple is placed outside the DPF and at a position of (16) at a distance of about 1 cm from the upstream end face of the DPF. installed.
FIG. 10 (Example 1) and FIG. 11 (Comparative Example 1) show the temperature behavior of the DPF during the unsteady forced regeneration test measured by the thermocouple.
FIG. 10 shows the temperature behavior in the DPF according to Example 1 when the soot accumulation amount is relatively large at 8.3 g / piece. In FIG. 10, about 110 seconds after the start of the test, the incoming gas temperature (16) reaches 680 ° C. At this point, the temperature at each location tended to decrease once the fuel addition was stopped immediately. However, in (6) to (8) near the center of the intermediate section of the DPF and (11) to (13) near the center of the downstream end face, the temperature tends to rise again, and the test The maximum value of temperature was shown in the vicinity of 160 to 220 seconds from the start. The highest temperature in the DPF was (11) or (12) near the center of the downstream end face, and the maximum temperature reached about 900 ° C. From these results, it was confirmed that in the rapid burning of soot when a certain amount of soot is deposited, the center part of the downstream end face of the DPF is the part that is most likely to be heated to the highest temperature.

  The DPF according to Example 1 (soot accumulation amount: 8.3 g / piece) was taken out after the test and observed for occurrence of cracks. As a result, it was confirmed that no defects such as cracks occurred in any part of the DPF. That is, when a band is attached to the downstream end (Example 1), the temperature in the DPF rises rapidly, and cracks due to thermal stress do not occur even when the maximum temperature reaches about 900 ° C. Was confirmed. In addition, it was confirmed that the soot deposition limit (SML) in this test condition was at least 8.3 g / piece.

  FIG. 11 shows the temperature behavior when the soot accumulation amount is 6.7 g / piece in the DPF according to Comparative Example 1. About 110 seconds after the start of the test, the inlet gas temperature (16) reached 680 ° C., and then the fuel addition was stopped, so that the central sections (6) to (8) of the intermediate section of the DPF and the downstream section In the central portions (11) to (13), a high temperature increase was shown. The highest temperature was (11) or (12) near the center of the downstream end face, and the maximum temperature was about 850 ° C.

The DPF (soot accumulation amount: 6.7 g / piece) according to Comparative Example 1 was taken out after the test and observed for occurrence of cracks. As a result, it was confirmed that cracks were generated from the outer peripheral portion to the central portion of the downstream end face. A photograph of the downstream end face at this time is shown in FIG. In FIG. 12, an arrow indicates a portion where a crack has occurred.
From the above results, it was confirmed that when the band was not attached, even if the maximum temperature in the DPF was about 850 ° C., cracks occurred on the downstream end face of the DPF due to thermal stress. Moreover, it became clear that the soot deposition limit amount (SML) in this test condition is less than 6.7 g / piece.

  From these results, it was confirmed that by attaching the band to the downstream end face, the occurrence of cracks was suppressed against the temperature increase near the downstream end face due to the rapid combustion of PM (or soot). It was also confirmed that the SML was improved (at least 1.24 times) by mounting the downstream end face of the band.

<Rapid cooling test>
Next, particularly severe conditions were observed for the occurrence of cracks at the upstream end face of the DPF, that is, a rapid temperature drop from a high temperature at the upstream end face was realized, and the crack generation behavior near the end face was observed.
Specifically, a total of three types of DPFs according to Examples 2 and 3 and Comparative Example 1 (that is, band attachment at the upstream end (Example 2), and band attachment at the upstream and downstream ends (implementation) A predetermined amount of soot (5 to 20 g / piece) was deposited in the same manner as in the soot deposition test for Example 3) and no band (Comparative Example 1)). After that, as in the unsteady forced regeneration test, the DPF and DOC are mounted on the exhaust pipe of the engine and the engine is started to raise the temperature of the DPF gas to 680 ° C. and immediately after reaching 680 ° C. The engine was stopped by turning off the ignition switch. In general, when the DPF is heated to the regeneration temperature (680 ° C.) and the engine is immediately stopped as described above, the vicinity of the upstream end face of the DPF is rapidly cooled and a maximum temperature gradient is generated in the upstream outer peripheral portion. . Therefore, in this case, cracks due to thermal stress are likely to occur at the upstream end of the DPF.

<Observation results of crack generation behavior>
After the rapid cooling test, the DPF was taken out from the exhaust passage and observed for occurrence of cracks. As a result, in the DPFs according to Example 2 and Example 3, it was confirmed that cracks did not occur in any case regardless of the amount of soot accumulated. On the other hand, in the DPF according to Comparative Example 1, it was confirmed that cracks occurred on the upstream end face in any case regardless of the amount of soot accumulated.
FIG. 13 shows a photograph of the upstream end face of the DPF according to Comparative Example 1 after the rapid cooling test. In FIG. 13, a crack is generated at a part indicated by an arrow. That is, it can be seen that the DPF according to Comparative Example 1 is cracked in a portion near the outer periphery of the upstream end face.
From these results, it was confirmed that by attaching the band to the upstream end face, cracking of the upstream end face can be suppressed even when the high-temperature (680 ° C.) DPF is rapidly cooled. It was.

  Further, in the DPF according to Example 3 (that is, DPF in which pressure is applied to both end faces on the upstream side and the downstream side), the maximum soot deposition amount (SML) is obtained from the results of the unsteady forced regeneration test and the rapid cooling test. It was confirmed that the cracks on the downstream end face and the upstream end face were suppressed.

DESCRIPTION OF SYMBOLS 1 Engine part 2 Combustion chamber 12 Exhaust pipe 30 ECU (electronic control unit)
40 Exhaust gas purification unit 50 Oxidation catalyst (DOC)
60 Diesel particulate filter (DPF)
60A Diesel particulate filter (DPF)
60B Diesel particulate filter (DPF)
60C Diesel particulate filter (DPF)
70 honeycomb structure 72 cell 80 restraint band 82 band part 84 band fixture (band clamp)
DESCRIPTION OF SYMBOLS 90 Catalytic converter 92 Holding member 94 Catalytic converter case 100 Exhaust gas purification apparatus

Claims (7)

In order to purify the exhaust gas of a diesel engine, a cylindrical diesel particulate filter that is installed and used in the exhaust passage of the diesel engine,
In the exhaust passage, when the exhaust gas flows into the diesel particulate filter as an upstream side, and when the exhaust gas passes through the diesel particulate filter and flows out as a downstream side,
The outer peripheral edge portion of the upstream side of the particulate filter, and substantially uniformly compressive force is multiplied over the entire periphery toward the center from locally outward,
The substantially uniform compressive force is realized by tightening the outer periphery of the diesel particulate filter with a restraining band,
Here, the restraint band includes a band portion having a certain width and thickness, and a band clamp for fixing the band portion,
The diesel engine is characterized in that the band part is wound around the outer periphery of the diesel particulate filter while applying a constant tensile force, and the band part is fixed by the band clamp so that the tensile force is maintained. Particulate filter. Between the front Symbol diesel particulate filter and the restraining bands, wherein the buffer material is sandwiched, diesel particulate filter according to claim 1. The diesel particulate filter according to claim 2 , wherein the buffer material is ceramic mat or ceramic wool . Wherein the portion of the diesel particulate said constraining band to the outer peripheral end region closer than at least 20mm from the end face of the filter is placed so as to overlap, as claimed in any one of claims 1 to 3 Diesel particulate filter. The diesel particulate filter according to any one of claims 1 to 4, wherein a width of the restraint band is 5 mm or more and 20 mm or less. The diesel particulate filter according to any one of claims 1 to 5 , wherein a pressure applied to the diesel particulate filter by applying the compressive force is 1 MPa or more and 5 MPa or less at 25 ° C. . An exhaust gas purification apparatus comprising the diesel particulate filter according to any one of claims 1 to 6 .