JP2012163058A - Catalytic converter device and method for energizing catalyst carrier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a catalytic converter device that can prevent a damage caused by a local overheat of a catalyst carrier.SOLUTION: The catalyst carrier has a property the electrical resistance decreases as the temperature rises. An energization power applied to the catalyst carrier is gradually reduced at an end stage of energization TE' including at least an end of energization TE.

Description

  The present invention relates to a catalytic converter device provided in an exhaust pipe of an internal combustion engine and a catalyst carrier energization method for energizing a catalyst carrier.

  In a catalytic converter device provided in an exhaust pipe for purifying exhaust gas generated in an internal combustion engine, it is desirable to energize a catalyst carrier carrying a catalyst to raise the temperature so that a sufficient catalytic effect can be obtained. However, if a locally overheated portion is generated inside the catalyst carrier, the catalyst carrier may be damaged.

  On the other hand, Patent Document 1 describes an energization control system for an electrically heated catalyst device that performs energization control on a catalyst carrier based on information from a temperature sensor disposed on the catalyst carrier.

  The energization control system described in Patent Document 1 switches between energization and non-energization of the catalyst carrier, and further measures are desired to actually suppress the damage of the catalyst carrier.

JP 2009-189921 A

  In view of the above facts, an object of the present invention is to obtain a catalytic converter device capable of suppressing breakage due to local overheating of a catalyst carrier.

  In the first aspect of the present invention, the catalyst carrier is provided with a characteristic that the electric resistance decreases as the temperature rises, carries a catalyst for purifying exhaust gas discharged from the internal combustion engine, and is heated by energization, An energization means capable of energizing the catalyst carrier by controlling the energization power, and the energization means gradually reduces the energization power toward the end of energization at least at the energization end stage including the end of energization to the catalyst carrier. Let

  In this catalytic converter device, when the catalyst carrier is energized by the energizing means, the catalyst carrier is heated and heated up, so that the purification effect by the supported catalyst can be exhibited more highly.

  Since the catalyst carrier has the characteristic that the electric resistance decreases as the temperature rises, the temperature unevenness due to local overheating of the catalyst carrier tends to increase with the passage of time to the catalyst carrier. The power supplied to the catalyst carrier by the means is gradually reduced toward the end of energization at least in the energization end stage including the end of energization. That is, energization is terminated while the energization power gradually decreases. Therefore, local overheating of the catalyst carrier is suppressed as compared with a configuration in which the energized power gradually increases at the end of energization or a configuration in which the energized power is constant. Thereby, the temperature unevenness of the catalyst carrier is also reduced, so that damage to the catalyst carrier can be suppressed.

  The “gradual decrease” mentioned here includes, of course, those in which the energization power decreases monotonically without increasing at the end of energization, but for example, substantially increases in the temperature of the catalyst carrier. Even if the configuration is such that the energization power takes a maximum value in a short time that does not contribute, or the energization power takes a constant value for a certain time in the energization end stage, the energization is performed when the energization end stage is viewed as a whole. If the electric power gradually decreases, it is included in the “gradual decrease” here.

  In the invention according to claim 2, in the invention according to claim 1, the energization means sets the energization power to a maximum value after the start of energization to the catalyst carrier and before the end of energization. The energization end stage is set from the time of the value to the end of energization to gradually decrease the energization power.

  Thus, the catalyst carrier can be effectively heated by setting the energization power to the maximum value after the start of energization to the catalyst carrier and before the end of energization.

  Moreover, since the energized power is gradually reduced as the energization end stage from the time of the maximum value (hereinafter referred to as “maximum power”) to the end of energization, local overheating of the catalyst carrier is suppressed.

  In the invention according to claim 3, in the invention according to claim 2, the time point of the maximum value is set before (3/4) of the total energization time from the energization start.

  That is, since the maximum power is before (3/4) of the total energization time from the start of energization, the energized power is surely gradually reduced after (3/4) of the total energization time. For this reason, it is possible to more reliably suppress damage before the end of energization of the catalyst carrier (particularly immediately before the end of energization).

  According to the fourth aspect of the present invention, the catalyst carrier energization is performed by heating the catalyst carrier carrying the catalyst for purifying the exhaust gas discharged from the internal combustion engine with the characteristic that the electrical resistance decreases as the temperature rises. In the method, the energization power is gradually reduced toward the end of energization at least in the energization end stage including the end of energization of the catalyst carrier.

  In this catalyst carrier energization method, when the catalyst carrier is energized, the catalyst carrier is heated and raised in temperature, so that the purification effect by the supported catalyst can be exhibited more highly.

  Since the catalyst carrier has a characteristic that the electric resistance decreases as the temperature rises, the temperature unevenness due to local overheating of the catalyst carrier tends to increase with the passage of time to the catalyst carrier. The energization power to the carrier is gradually reduced toward the end of energization at least at the energization end stage including the end of energization. That is, energization is terminated while the energization power gradually decreases. Therefore, local overheating of the catalyst carrier is suppressed as compared with a configuration in which the energized power gradually increases at the end of energization or a configuration in which the energized power is constant. Thereby, the temperature unevenness of the catalyst carrier is also reduced, so that damage to the catalyst carrier can be suppressed.

  Since the present invention is configured as described above, it is possible to suppress breakage due to local overheating of the catalyst carrier.

1 shows a catalytic converter device according to a first embodiment of the present invention, in which (A) is a cross-sectional view along the flow direction of exhaust gas, and (B) is a cross-sectional view in a direction orthogonal to the flow direction of exhaust gas. The catalytic converter device of the first embodiment of the present invention is shown in the same cross section as FIG. 1B, (A) is an explanatory diagram conceptually showing the magnitude of the current of the catalyst carrier, and (B) is the catalyst carrier. It is explanatory drawing which shows temperature distribution. In the embodiment pattern A of the present invention and the pattern E of the comparative example, (A) is a graph showing the time change of the energized power, and (B) is a graph showing the time change of the temperature of the catalyst carrier. It is a graph which shows the time change of the thermal energy made to act on a catalyst support | carrier in the pattern of the implementation pattern A, B, C of this invention, and a comparative example. It is a graph which shows the time change of the electricity supply in the implementation patterns B and C of this invention. It is a graph which shows the time change of the energization electric power in the implementation pattern D of this invention.

  FIG. 1A shows a catalytic converter device 12 according to a first embodiment of the present invention. The catalytic converter device 12 is mounted in the middle of the exhaust pipe. Exhaust gas from the engine flows in the exhaust pipe. FIG. 1B shows a catalytic converter device in a cross-section in the direction orthogonal to the flow direction of the exhaust gas (cross-section BB in FIG. 1A). 12 is shown.

  As shown in FIG. 1, the catalytic converter device 12 includes a catalyst carrier 14 formed of a material having conductivity and rigidity. The surface area of the material is increased by making the catalyst carrier 14 into a honeycomb shape, for example. A catalyst (platinum, palladium, rhodium, etc.) is supported on the surface of the catalyst carrier 14 in an attached state. The catalyst has an action of purifying harmful substances in the exhaust gas flowing in the exhaust pipe (the flow direction is indicated by an arrow F1). The structure for increasing the surface area of the catalyst carrier 14 is not limited to the above honeycomb shape, and may be, for example, a lattice shape or a wave shape.

  As a material constituting the catalyst carrier 14, a conductive ceramic, a conductive resin, a metal, or the like can be applied. In the present embodiment, a material containing SiC (silicon carbide) is particularly used. This SiC is an example of a material having a characteristic (NTC characteristic) in which the electrical resistance decreases as the temperature rises. In this embodiment, since the material constituting the catalyst carrier 14 contains silicon carbide, high strength and heat resistance can be obtained.

  Furthermore, if the electrical resistivity of the catalyst carrier 14 is 10 to 200 Ω · cm, the temperature of the supported catalyst can be increased efficiently when energized as described later, which is preferable. The porosity of the catalyst carrier 14 is preferably in the range of 30 to 60%. When the porosity is 30% or more, a necessary surface area is secured and a large amount of catalyst can be supported. Moreover, it becomes possible to maintain the intensity | strength calculated | required as the catalyst support | carrier 14 by making a porosity into 60% or less.

  Two electrodes 16A and 16B are attached to the catalyst carrier 14, and terminals 18A and 18B are connected to the centers of the electrodes 16A and 16B, respectively. The electrodes 16A and 16B are arranged in contact with the catalyst carrier 14 in a range having a predetermined spread along the outer peripheral surface of the catalyst carrier 14, and the catalyst carrier 14 is energized from the terminals 18A and 18B through the electrodes 16A and 16B. Thus, the catalyst carrier 14 can be heated. Then, by heating, the temperature of the catalyst carried on the catalyst carrier 14 is raised, so that the exhaust gas purifying action of the catalyst can be exhibited to a higher degree.

  The cross-sectional shape of the catalyst carrier 14 (the cross-sectional shape orthogonal to the exhaust flow direction) is not particularly limited, but is circular in this embodiment. The electrodes 16A and 16B are arranged at positions facing each other across the center of the circle.

  A holding member 24 formed in a cylindrical shape by an insulating material is disposed on the outer periphery of the catalyst carrier 14. Further, a case cylinder 28 formed in a cylindrical shape with a metal such as stainless steel is disposed on the outer periphery of the holding member 24. That is, the catalyst carrier 14 is accommodated inside the cylindrical case cylinder 28, and the catalyst carrier 14 is placed in the case cylinder 28 by the holding member 24 disposed between the case cylinder 28 and the catalyst carrier 14. It is held without gaps inside. Since the insulating holding member 24 is disposed between the catalyst carrier 14 and the case cylinder 28, the flow of electricity from the catalyst carrier 14 to the case cylinder 28 is prevented.

  A power supply device 30 capable of supplying power to the catalyst carrier 14 is connected to the electrodes 16A and 16B. The power supply device 30 is controlled by a control device 32. The power supply start time and end time can be set at a predetermined timing, and the power supply amount can be adjusted. The power supply device 30 and the control device 32 constitute the energizing means of the present invention.

  Next, the operation of the catalytic converter device 12 of this embodiment will be described.

  In the catalytic converter device 12, the case cylinder 28 is attached in the middle of the exhaust pipe, and the exhaust passes through the inside of the catalyst carrier 14 in the direction of the arrow F1. At this time, harmful substances in the exhaust gas are purified by the catalyst supported on the catalyst carrier 14. In the catalytic converter device 12 of the present embodiment, the catalyst carrier 14 is energized by the terminals 18A and 18B and the electrodes 16A and 16B, and the catalyst carrier 14 is heated, whereby the temperature of the catalyst supported on the catalyst carrier 14 is raised and purified. The effect can be exhibited earlier. For example, when the temperature of the exhaust gas is low, such as immediately after starting the engine, the catalyst purification performance in the initial stage of engine starting can be ensured by conducting energization heating to the catalyst carrier 14 in advance.

  Here, FIG. 3 (A) shows a pattern example of change in power supplied to the catalyst carrier 14 over time (example pattern A and pattern E of the comparative example). Further, FIG. 3B shows temperature changes at the highest temperature portion and the lowest temperature portion of the catalyst carrier in Example Pattern A and Pattern E of Comparative Example (in this graph, the temperature of the catalyst carrier 14 is expressed as “ EHC temperature ”). Further, FIG. 4 shows a temporal change in the amount of heat energy applied to the catalyst carrier 14 in Example Patterns B and C described later in addition to Example Pattern A and Comparative Example Pattern E. These power supply patterns are set so that the time integration values of the supplied power are substantially the same. For this reason, as shown in FIG. 4, the total amount ES of heat energy applied to the catalyst carrier 14 by the end of energization TE is substantially the same.

  And about each embodiment pattern of this invention, it is set as the electric power supply pattern which can suppress the local overheating (temperature nonuniformity) of the catalyst support | carrier 14, and can also suppress the failure | damage of the catalyst support | carrier 14 resulting from this local overheating. This will be described in detail below.

  Since SiC used as the catalyst carrier 14 in this embodiment has low strength, it may be damaged (for example, cracked or chipped) when an excessive force is applied. In particular, when a difference (temperature gradient or temperature unevenness) occurs in the internal temperature depending on the portion of the catalyst carrier 14, a thermal stress proportional to this temperature difference is generated in the catalyst carrier 14, so that the catalyst carrier 14 Cause damage. In order to prevent such damage to the catalyst carrier 14, it is only necessary to reduce the electric power supplied to the catalyst carrier 14. In this case, the time required to raise the temperature of the catalyst carrier 14 to the target temperature. Becomes longer.

  In the configuration in which the catalyst carrier 14 is heated by energization as in this embodiment, the temperature distribution of the catalyst carrier 14 may be biased due to the current distribution during energization. That is, as shown in FIG. 1B, when the cross-sectional shape of the catalyst carrier 14 is circular and the electrodes 16A and 16B are attached to positions facing each other with the catalyst carrier 14 interposed therebetween, In comparison, since the electric resistance of the catalyst carrier 14 is large, the current tends to concentrate on a path where the distance flowing through the catalyst carrier 14 becomes relatively short. Therefore, the current distribution is as shown by an arrow EC in FIG. 2A (in FIG. 2A, the magnitude of the current value is made to correspond to the magnitude of the arrow EC). Even if the catalyst carrier 14 has a different cross-sectional shape or a structure in which the arrangement of the electrodes 16A and 16B is different from this, a current distribution corresponding to each structure occurs.

  Further, SiC used as the catalyst carrier 14 in this embodiment has NTC characteristics. As shown in FIG. 2A, the temperature of the portion where a large amount of current flows is higher than that of the surrounding area, so that the electrical resistance is low and the current flows more easily. That is, the current is further concentrated on the portion where a large amount of current flows, and the local heating is promoted. In addition, since the degree of current concentration is proportional to the supplied power, local heating becomes more conspicuous as the power increases. Although heat conduction (heat transfer from a relatively high temperature part to a low temperature part) also occurs in the inside of the catalyst carrier 14, if this current concentration becomes large, the heat conduction will not be in time, and the temperature distribution of the catalyst carrier 14 will be large. Become. For example, in the case of the structure of the catalyst carrier 14 and the electrodes 16A and 16B shown in FIG. 1 (A), as shown in FIG. 2 (B), the high-temperature part HT near the current concentration part and the distance from the concentration part are separated. The temperature distribution is such that a low temperature portion LT is generated. And if this temperature deviation becomes large, it will cause damage to the catalyst carrier 14.

  The power supply pattern A of this embodiment shown in FIG. 3A and the power supply patterns B and C shown in FIG. 5 both start supplying power at time TS (at the start of energization) and time TE (energization end). However, at least for a predetermined time including the energization end TE (referred to as energization end stage TE ′), the energization power gradually decreases.

  In the material having the NTC characteristics described above, the temperature unevenness inside tends to increase with the elapse of time from energization. Therefore, for example, if the catalyst carrier 14 is energized so that the energized power becomes large immediately before the energization end TE, the internal temperature difference is further increased. Further, as in the power supply pattern E of the comparative example, even when the energization power is constant from the energization start time TS to the energization end time TE, as shown by a two-dot chain line in the graph of FIG. The temperature difference inside the catalyst carrier 14 tends to be larger than the power supply pattern A of the present embodiment.

  On the other hand, in the present embodiment, the energization power is increased at a stage where the temperature unevenness of the catalyst carrier 14 is small (initial stage of energization), and the energization power is gradually reduced at least at the energization end stage TE ′ including the energization end TE. Yes. Therefore, local overheating of the catalyst carrier 14 can be suppressed while the temperature of the catalyst carrier 14 is raised. That is, as compared with the configuration in which the energized power increases immediately before the end of energization TE, temperature unevenness in the catalyst carrier 14 can be reduced, and damage due to thermal stress of the catalyst carrier 14 can be suppressed.

  In the power supply pattern A, the energization power is maximized at the energization start time TS, and the energization power is changed linearly (linear function of time) as time passes. In short, the energization end time TE is included. It is only necessary that the energized power is gradually reduced in the energization end stage TE ′. From this viewpoint, for example, the following power supply patterns B and C as shown in FIG. 5 may be used.

  In the power supply pattern B, the energization power gradually increases for a predetermined time from the energization start time TS. And between energization start time TS and energization end time TE, energization electric power becomes the maximum value (the time of this electric power maximum value is made into electric power maximum time TM). The energization power gradually decreases from the maximum power TM to the energization end TE. Even in such a power supply pattern B, the energized power gradually decreases in the energization end stage TE ′, and it is possible to reduce the temperature unevenness in the catalyst carrier 14.

  In addition, in the energization end stage TE ′, if there is no substantial change in the supply of thermal energy to the catalyst carrier 14, the energization end stage even if there is a time during which the energized power is increasing (or decreasing). It is included in the configuration in which the energized power “decreases” in TE ′. For example, in the power supply pattern C of FIG. 5, there is a time ΔT ′ at which the energized power reaches a maximum value at the energization end stage TE ′. However, if this time ΔT ′ is sufficiently short, the temperature of the catalyst carrier 14 does not rise excessively, so that the energized power is gradually reduced in the energization end stage TE ′. Temperature unevenness can be reduced. It should be noted that the maximum value of the energization power at the time ΔT ′ (the height of the convex portion on the graph) is not particularly limited.

  Further, the power supplied to the catalyst carrier 14 does not need to change continuously, and may be intermittent (step-like) change. For example, in the power supply pattern D shown in FIG. 6, the energized power is constant for a predetermined time ΔT1 from the energization start time TS, and the energized power is temporarily lowered (substantially set to zero) for the subsequent predetermined time ΔT2. ) Thereafter, the energization power is maximized (a constant value) at a predetermined time ΔT3, and the energization power (constant value) is lower than the maximum value at a predetermined time ΔT4 until the subsequent energization end TE. In the power supply pattern D, the period from the end of the predetermined time ΔT3 to the end of energization TE after the predetermined time ΔT4 corresponds to the energization end stage TE ′ in the present invention. That is, in the energization end stage TE ′, the energization power gradually decreases (decreases in stages), so that it is possible to reduce the temperature unevenness in the catalyst carrier 14.

  In addition, in this power supply pattern D, the time ΔT2 during which the energized power is temporarily reduced is set between the energization start time TS and the energization end time TE, so that the heat conduction inside the catalyst carrier 14 is performed during this time. This makes it possible to promote the uniformity of the temperature and to more effectively suppress the occurrence of temperature unevenness.

  In any of the power supply patterns of the present embodiment, the energized power takes a maximum value after the energization start time TS (including the energization start time TS) to the energization end time TE, The catalyst carrier 14 can be efficiently heated. In particular, it is preferable to set the energization power to the maximum value in the initial stage of energization, because the catalyst support 14 can be heated with large power at a stage where the temperature of the catalyst support 14 is low. For example, the electrode supply pattern A is preferable in terms of efficient heating of the catalyst carrier 14 because the energization power has the maximum value at the start of energization TS. Of course, the present invention includes a configuration in which the energized power is made constant for a predetermined time from the energization start time TS, and then the energized power is gradually reduced toward the energization end time TE.

  In the present invention, the “energization end stage TE ′” includes at least the energization end TE, but in an extremely short time, the energization power is gradually reduced only immediately before the energization end TE. Therefore, the substantial time during which the energization voltage is gradually reduced is shortened, and the effect of reducing temperature unevenness in the catalyst carrier 14 is reduced. Therefore, when the “energization end stage TE ′” is started before TC (see FIGS. 3, 5, and 6) at the time of (3/4) of the total energization time to the catalyst carrier 14, Sufficient time can be secured. For example, in the power supply pattern A, the energized power becomes the maximum value at the energization start time TS, and thereafter, the energized power is gradually reduced, so this condition is satisfied. Also in the power supply patterns B and C, the power maximum time TM at which the energized power is the maximum value may be set before the above-described (3/4) elapsed time TC. Similarly, also in the power supply pattern D, the end of the time ΔT3 when the energized power is the maximum value may be set before the above-described (3/4) elapsed time TC.

  The start point of the “energization end stage” of the present invention may be determined in advance by time. As described above, the configuration in which the stage after the TC at the time when (3/4) of the total energization time to the catalyst carrier 14 is “the energization end stage” is an example of this. Instead of this (or in combination), the temperature of the catalyst carrier 14 is detected by a temperature sensor or the like, and when this temperature reaches a predetermined range of the target temperature of the catalyst carrier 14, the process proceeds to the “energization end stage”. You may do it.

  In the above description, the catalyst carrier 14 has a circular cross section perpendicular to the exhaust flow direction (arrow F1 direction), but the shape of the catalyst carrier 14 is not limited to a circle. That is, if the catalyst carrier 14 has NTC characteristics, the temperature unevenness in the catalyst carrier 14 can be reduced regardless of the shape of the catalyst carrier 14, and damage due to thermal stress of the catalyst carrier 14 can be suppressed.

12 catalytic converter device 14 catalyst carrier 24 holding member 28 case cylinder 30 power supply device (energizing means)
32 Control device (energization means)
TS When energization starts TE When energization ends TE 'Energization end stage

Claims (4)

A catalyst carrier that has a characteristic that electric resistance decreases as the temperature rises, carries a catalyst for purifying exhaust gas discharged from an internal combustion engine, and is heated by energization;
Energization means capable of energizing the catalyst carrier by controlling energization power;
Have
A catalytic converter device in which the energization means gradually reduces energized power toward the end of energization at least in the energization end stage including the end of energization of the catalyst carrier.   The energization means sets the energization power to a maximum value after the start of energization to the catalyst carrier and before the end of energization, and sets the energization end stage from the time of this maximum value to the end of energization. The catalytic converter device according to claim 1, wherein the electric power is gradually reduced.   The catalytic converter device according to claim 2, wherein the time point of the maximum value is set before (3/4) of the total energization time from the energization start. A catalyst carrier energization method comprising heating a catalyst carrier carrying a catalyst for purifying exhaust gas discharged from an internal combustion engine, with a characteristic that electric resistance decreases with increasing temperature,
A catalyst carrier energization method for gradually reducing energization power toward the end of energization at least at the energization end stage including the end of energization of the catalyst carrier.

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