JP2011099405A - Exhaust emission control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device in which a carrier for catalyst is heated uniformly, whereby capable of raising the temperature of the catalyst borne by the carrier to the activation temperature even when the engine is going to make a cold start. <P>SOLUTION: The exhaust emission control device 100 is arranged so that the carrier 20 in cylindrical shape is heated electrically through electrodes 30 and 40 to raise the temperature of the catalyst borne by the carrier 20 to the activation temperature, the carrier 20 being formed in honeycomb structure with a plurality of bulkheads 21, 21... through which the current for heating the carrier 20 flows between the electrodes 30 and 40, wherein the thickness of the bulkheads 21, 21... is set so that the electric resistances of all current paths between terminals 50 and 60 are the same. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an exhaust purification device, and more particularly to an exhaust purification device that purifies exhaust gas discharged from an engine.

  2. Description of the Related Art Conventionally, an electrically heated catalyst (EHC) is known as an exhaust purification device that is provided on an exhaust path of an automobile or the like and purifies exhaust gas exhausted from an engine.

  As shown in FIG. 8, a conventional exhaust purification device 100, which is an EHC, has a hollow case 110 that forms an exterior, and a honeycomb structure that is housed in the case 110 and that supports a catalyst such as platinum or palladium. A cylindrical carrier 120 and electrodes 130 and 140 that are provided on the outer peripheral surface of the carrier 120 so as to face each other and are electrically connected to the carrier 120, and are electrically connected to the electrodes 130 and 140, respectively. And terminals 150 and 160 electrically connected to a power source such as a battery via a wire harness or the like. The exhaust gas purification apparatus 100 energizes and heats the carrier 120 with a current supplied from the power source and flows from the electrode 130 toward the electrode 140, thereby raising the temperature of the catalyst supported on the carrier 120 to the activation temperature. Harmful substances such as HC (unburned hydrocarbons), CO (carbon monoxide), and NOx (nitrogen oxides) in the exhaust gas discharged are purified by catalytic reaction.

  As described above, the catalyst supported on the carrier 120 can purify the exhaust gas by a catalytic reaction when it reaches the activation temperature. However, when the temperature of the catalyst does not reach the activation temperature at the time of starting the engine, particularly at the cold start, there arises a problem that harmful substances in the exhaust gas are discharged into the atmosphere without being purified.

  Therefore, the carrier 120 is efficiently and evenly heated by partially changing the thickness of the partition walls forming the honeycomb structure of the carrier 120 and partially changing the electric resistance, so that the catalyst supported on the carrier 120 is supported. A technique for raising the temperature is known (see, for example, Patent Document 1).

In the exhaust purification apparatus 100, the current that has passed through the terminal 150 does not immediately flow from the electrode 130 to the carrier 120, but flows to both ends of the electrode 130 that has a lower electrical resistance than the carrier 120 (see arrows in the figure). Therefore, the current density is higher in the vicinity of both ends of the electrodes 130 and 140 in the circumferential direction of the carrier 120 than in the vicinity of the center thereof, and the temperature of the carrier 120 as a whole varies.
In the technique described in Patent Document 1, such a problem is not taken into consideration, and the carrier 120 cannot be heated uniformly so as not to cause temperature variations. For this reason, there is a possibility that a portion of the catalyst supported on the carrier 120 at the cold start does not reach the activation temperature, and purification of harmful substances in the exhaust gas is not sufficient.

Japanese Patent Laid-Open No. 8-232647

  An object of the present invention is to provide an exhaust emission control device that can heat a carrier evenly and raise the temperature of a catalyst supported on the carrier to an active temperature even when the engine is cold-started.

The exhaust emission control device of the present invention includes a hollow case forming an exterior, a carrier housed in the case and carrying a catalyst, a pair of electrodes provided on an outer peripheral surface of the carrier, and the pair of electrodes. A pair of terminals electrically connected and projecting to the outside of the case; and an exhaust gas purification device that heats the carrier through the pair of electrodes and heats the catalyst to an activation temperature, The carrier is formed in a honeycomb structure by a plurality of partition walls, and an electric current for energizing and heating the carrier flows between the pair of electrodes through the plurality of partition walls, and is calculated from the following equation (1). The thickness of the partition wall of the carrier is set so that the electric resistances of all the current paths are equal.

  According to the present invention, the support can be heated evenly, and the temperature of the catalyst supported on the support can be raised to the activation temperature even when the engine is cold started.

1 is a front sectional view of an exhaust emission control device according to the present invention. The partial side sectional view of the exhaust emission control device according to the present invention. The figure which shows the electric current path which passes along a partition. The figure which showed the support | carrier, the electrode, and the terminal on the two-dimensional coordinate. The figure which shows the electric current path which passes along one partition which is not located in the range in which the electrode in the circumferential direction of the support | carrier was provided. The figure which shows the electric current path | route which passes along one partition in case the terminal is not arrange | positioned in the center part of the electrode in the circumferential direction of a support | carrier. The figure which shows the setting of the thickness of the partition when a support | carrier is inclined in the circumferential direction with respect to the electrode. Front sectional drawing of the conventional exhaust gas purification apparatus.

Below, with reference to FIGS. 1-2, the exhaust gas purification apparatus 1 is demonstrated.
The exhaust purification device 1 is an electrically heated catalyst (EHC) that is provided on an exhaust path of an automobile or the like and purifies exhaust gas discharged from an engine.

  As shown in FIGS. 1 and 2, the exhaust emission control device 1 includes a hollow case 10 that forms an exterior, a carrier 20 housed inside the case 10, and electrodes 30 and 40 provided on the outer peripheral surface of the carrier 20. And terminals 50 and 60 electrically connected to the electrodes 30 and 40, respectively.

  The case 10 is a member that forms an exterior of the exhaust purification device 1 and that forms part of an exhaust pipe through which exhaust gas discharged from the engine flows, and is formed in a substantially cylindrical shape.

The carrier 20 is a cylindrical member made of ceramics such as SiC (silicon carbide) or cordierite, and supports a catalyst such as platinum or palladium. The carrier 20 is formed in a honeycomb structure by a plurality of partition walls 21.
The outer diameter of the carrier 20 is set slightly smaller than the inner diameter of the case 10. The carrier 20 has a predetermined gap between the inner peripheral surface of the case 10 and the electrodes 30 and 40 provided on the outer peripheral surface of the carrier 20 within the case 10. ) And exhaust gas exhausted from the engine is disposed so as to pass through the inside of the carrier 20 in the axial direction. Note that a holding member (not shown) made of alumina or the like is provided between the inner peripheral surface of the case 10 and the outer peripheral surface of the carrier 20 to prevent the carrier 20 from being displaced, A gap between the peripheral surface and the outer peripheral surface of the carrier 20 is sealed.

  The partition wall 21 divides the internal space of the carrier 20 into a plurality of parts, and the plurality of partition walls 21, 21,... The carrier 20 is configured in a lattice-like honeycomb structure by the partition walls 21, 21. The thickness of the partition walls 21, 21... Is different for each partition wall 21 and is set so that the carrier 20 is heated evenly by partially changing the electric resistance. The setting of the thickness of each partition wall 21 will be described later.

The electrodes 30 and 40 are a pair of electrodes made of copper, aluminum, or the like formed in layers on the outer peripheral surface of the carrier 20 by thermal spraying. The electrodes 30 and 40 are respectively provided in a predetermined range in the circumferential direction of the carrier 20 and extend in parallel with the axis of the carrier 20 over both ends in the axial direction of the carrier 20 in a state of facing each other with a phase difference of 180 degrees. Has been issued. The lengths of the electrodes 30 and 40 in the circumferential direction of the carrier 20 are set to be the same, and the lengths of the electrodes 30 and 40 in the axial direction of the carrier 20 are also set to be the same. The electrodes 30 and 40 are electrically connected to the carrier 20 and function as electrodes for supplying current to the carrier 20 for heating. Between the pair of electrodes 30 and 40, a current for energizing and heating the carrier 20 flows through the plurality of partition walls 21 and 21.
In the present embodiment, the electrode 30 is a plus side electrode and the electrode 40 is a minus side electrode so that a current flows from the electrode 30 toward the electrode 40.

The terminals 50 and 60 are rod-shaped members for electrically connecting the electrodes 30 and 40 and a power source such as a battery provided outside the case 10. The terminals 50 and 60 are respectively arranged in accordance with the positions where the electrodes 30 and 40 are provided on the carrier 20, and in the present embodiment, the terminals 50 and 60 are arranged at the center of the electrodes 30 and 40 so as to face each other with a phase difference of 180 degrees. Has been placed. The terminals 50 and 60 are fixed in a state of penetrating the case 10 so that one end portions thereof protrude to the outside of the case 10.
The terminals 50 and 60 are electrically connected to the power source via a connecting member such as a wire harness outside the case 10, and are electrically connected to the electrodes 30 and 40, respectively, inside the case 10. That is, one end of the terminals 50 and 60 and the connecting member are connected, and the other end of the terminals 50 and 60 and the electrodes 30 and 40 are connected, respectively. In this way, the power supply and the electrodes 30 and 40 can be electrically connected by the terminals 50 and 60.
In the present embodiment, the terminal 50 is a plus side terminal and the terminal 60 is a minus side terminal, and the current flows in the order of the terminal 50, the electrode 30, the carrier 20, the electrode 40, and the terminal 60 (see FIG. 1).

  As described above, in the exhaust gas purification apparatus 1, the catalyst carried on the carrier 20 is heated to the activation temperature by heating the carrier 20 by energizing the electrode 30 toward the electrode 40 using the power source. Thus, harmful substances such as HC (unburned hydrocarbon), CO (carbon monoxide), and NOx (nitrogen oxide) in the exhaust gas discharged from the engine and passing through the carrier 20 are purified by a catalytic reaction.

Below, with reference to FIGS. 3-5, the setting of the thickness of each partition 21 in the support | carrier 20 is demonstrated in detail.
In the following description, the vertical direction in FIG. 3 is defined as the vertical direction of the carrier 20. Further, the partition walls 21, 21... Are parallel or orthogonal to a line connecting the center positions of the electrodes 30 40 in the circumferential direction of the carrier 20 (line connected in the vertical direction in FIG. 3). The length in the left-right direction of the partition walls 21, 21... Arranged along the vertical direction will be described as the thickness of each partition wall 21.
That is, here, since the current hardly flows in the direction (left-right direction) orthogonal to the arrangement direction of the electrodes 30, 40, the thickness of the partition walls 21, 21,. Thus, the carrier 20 is set to be heated evenly.

  As described above, when setting the thickness of each partition wall 21, the electrical resistance in the current path between the terminals 50, 60 passing through each partition wall 21 and flowing in the order of the terminal 50, the electrode 30, the electrode 40, and the terminal 60 is set. The electric resistance in all the current paths is made equal by calculating from the following equation (1). That is, by appropriately changing the thickness of each partition wall 21 having a different current path length (L), the current path cross-sectional area (A) is increased or decreased to equalize the electric resistance.

Here, as shown in FIG. 3, any one of the vertical partition wall 21 partitions 21a, and then its thickness and t _1, positioned at the radially outer side of the carrier 20 than the partition wall 21a adjacent to the partition wall 21a the partition wall 21 partition wall 21b which, and the thickness and _{t 2.} Furthermore, the starting point of the current path is a point A where the terminal 50 is located in the circumferential direction of the carrier 20, both ends of the partition wall 21 a are the points B and C, and the end point of the current path is the terminal 60 in the circumferential direction of the carrier 20. Let it be point D.
At this time, the current path passing through the partition wall 21a is a path that follows point A, point B, point C, and point D in order.
The partition walls 21a and 21b are located in a range where the electrodes 30 and 40 in the circumferential direction of the carrier 20 are provided. Further, the partition wall 21 in the left-right direction is not considered.

The current path passing through the partition wall 21 a can be divided into a current path on the electrode 30, a current path on the partition wall 21 a, and a current path on the electrode 40. The electric resistance of the carrier 20 is larger than the electric resistance of the electrodes 30 and 40. In the range where the electrodes 30 and 40 are provided on the outer peripheral surface of the carrier 20, the electric current gives priority to the electrodes 30 and 40 over the carrier 20. This is because it flows.
At this time, the current path on the electrode 30 is an arc AB in the circumferential direction of the carrier 20, the current path on the partition wall 21 a is a straight line BC, and the current path on the electrode 40 is an arc CD in the circumferential direction of the carrier 20. Become.
Here, the result of the addition of the lengths of the arc CD arc AB, that is, the current path length of the electrodes 30, 40 and L _e. Further, the length of the straight line BC, that is, the current path length of the partition wall 21a and _{L c.}

The center of the carrier 20 viewed from the axial direction will be further described as an origin O of two-dimensional coordinates (xy coordinates).
Here, as shown in FIG. 4, when the diameter of the carrier 20 is d, the coordinates (x, y) of the outer periphery of the carrier 20 are expressed by the following formula 2.

First, the current path length _{L c} of the partition wall 21a.
The x-coordinate in the thickness direction central portion of the partition wall 21a and x _1, when the y-coordinate of the outer circumference of the carrier 20 corresponding to the x-coordinate and y _1, is expressed as the number 3 than the number 2 below the The

In this case, _{y 1} is a half of (vertical length of the partition wall 21a in FIG. 4) _{L c} current path length of the partition wall 21a. Therefore, it is possible to represent the current path length L _c of the partition wall 21a as in equation 4 below.

Next, determine the current path length _{L e} of the electrodes 30, 40.
When angle theta ₁ of the center angle with respect to the arc from the center of the terminal 50 in the carrier 20 to the center portion in the thickness direction of the partition wall 21a (arc in Figure 3 AB), the number 5 below is established.

The above equation 5 is converted into the following equation 6.

Since the partition wall 21a is arranged in parallel with the y-axis, the angle of the central angle with respect to an arc (arc CD in FIG. 3) from the central portion of the carrier 20 in the thickness direction of the partition wall 21a to the center portion of the terminal 60 is also θ. ₁ and the length of the arc (arc AB in FIG. 3) from the center portion of the terminal 50 in the carrier 20 to the center portion in the thickness direction of the partition wall 21a, and the terminal from the center portion in the thickness direction of the partition wall 21a in the carrier 20 The length of the arc to the center of 60 (arc CD in FIG. 3) is the same. Therefore, it is possible to represent the current path length L _e of the electrodes 30, 40 as the number 7 below than the number 3, and 6 above.

As described above, the current path length _{L c} of the partition wall 21a, and on the current path length _{L e} of the electrodes 30, 40 is determined, the electrical resistance in the partition wall 21a of the carrier 20 and _{R c,} the electrical resistance of the carrier 20 rates and [rho _c, and the cross-sectional area of the current path in the partition wall 21a of the carrier 20 and a _c, the number 8 the following from the number 1, and number 4 above is satisfied.
In the present embodiment, the current path cross-sectional area _Ac of the partition wall 21a is obtained by multiplying the thickness t ₁ of the partition wall 21a by z (see FIG. 2) which is the axial length of the carrier 20. is there.

Further, the electrical resistance of the electrode 30 · 40 and _{R e,} the electrical resistivity of the electrode 30, 40 and [rho _e, and the cross-sectional area of the current path in the electrode 30 · 40 and _{A e,} the number of the 1, and the number From 7, the following formula 9 is established.

Current path through the partition wall 21a when the electrical resistance of the (points in FIG. 3 A, point B, point C, the route to follow the point D in this order) and _{R 1, R 1} is be regarded as a combined resistance of the _{R c} and _{R e} Can do. Therefore, R ₁ can be expressed as in the following Expression 10 from Expression 8 and Expression 9 above.
Note that the electrical resistivity ρ _e of the electrodes 30 and 40 is extremely small as compared with the electrical resistivity ρ _c of the carrier 20, and accordingly, the electrical resistance R _e of the electrodes 30 and 40 is also the electrical resistance of the partition wall 21 a of the carrier 20. because in comparison with R _c becomes extremely small, it may be ignored electrical resistance _{R e} of the electrode _{30 · 40 (R 1 = R} c).
Thereby, the setting of the thickness of the partition 21 in the vertical direction can be further simplified.

Similarly to obtaining R ₁ which is the electric resistance of the current path passing through the partition wall 21a, the x coordinate at the central portion in the thickness direction of the partition wall 21b is x ₂ and the y coordinate of the outer periphery of the carrier 20 corresponding to this x coordinate. Y _2, and the angle of the central angle with respect to the arc from the center of the terminal 50 to the center of the partition 21 b in the thickness direction is θ ₂ , and the electrical resistance of the current path passing through the partition 21 b is obtained. At this time, the electrical resistance of the current path through the partition wall 21b and R _2.
Then, t ₁ and t ₂ are set so that R ₁ and R ₂ are equal.
As described above, the partition walls 21 a and 21 b are located in a range where the electrodes 30 and 40 are provided in the circumferential direction of the carrier 20, and the thickness of the partition wall 21 in the vertical direction in the range is the same as that of the carrier 20. It is set smaller as it goes radially outward. That is, as shown in FIGS. 3 and 4, the thicknesses of the partition walls 21a and 21b are set to be smaller in order (t ₁ > t ₂ ).

Next, the vertical partition 21 that is not located in the range where the electrodes 30 and 40 in the circumferential direction of the carrier 20 are provided will be described.
Here, as shown in FIG. 5, any one of the vertical partition wall 21 partitions 21c, and the thickness and t _3, located radially inward of the carrier 20 than the partition wall 21c adjacent to the partition wall 21c the partition wall 21 partition wall 21d that, and the thickness and _{t 4.} Further, the starting point of the current path is a point A where the terminal 50 is located in the circumferential direction of the carrier 20, and the contact position between one end portion (the right end portion in FIG. 5) of the electrode 30 in the circumferential direction of the carrier 20 and the outer circumference of the carrier 20 is defined. Point E, both end portions of the partition wall 21c are point F and point G, and the contact position between one end portion of the electrode 40 in the circumferential direction of the carrier 20 (right end portion in FIG. 5) and the outer periphery of the carrier 20 is point H. The end point of the current path is a point D where the terminal 60 is located in the circumferential direction of the carrier 20.
At this time, the current path passing through the partition wall 21c is a path that sequentially follows point A, point E, point F, point G, point H, and point D.
The partition walls 21c and 21d are located in a range where the electrodes 30 and 40 in the circumferential direction of the carrier 20 are not provided. Further, the partition wall 21 in the left-right direction is not considered.

The current path passing through the partition wall 21c can be divided into a current path on the electrode 30, a current path on the carrier 20, and a current path on the electrode 40. The electric resistance of the carrier 20 is larger than the electric resistance of the electrodes 30 and 40. In the range where the electrodes 30 and 40 are provided on the outer peripheral surface of the carrier 20, the electric current gives priority to the electrodes 30 and 40 over the carrier 20. This is because it flows.
At this time, the current path on the electrode 30 is an arc AE in the circumferential direction of the carrier 20, the current path on the carrier 20 is an arc EF, a straight line FG, and an arc GH, and the current path on the electrode 40 is the carrier 20. The arc HD in the circumferential direction. That is, the current path (point A, point E in FIG. 5) passing through the partition wall 21c is compared with the current path passing through the partition wall 21a (path following points A, B, C, and D in FIG. 3 in order). , Points F, G, H, and D) in order, it is necessary to consider the outer periphery of the carrier 20 in a range where the electrodes 30 and 40 are not provided.
Since the setting of the thickness t _{3 of} the partition wall 21c and the thickness t ₄ of the partition wall 21d is substantially the same as the setting of the thickness t ₁ of the partition wall 21a and the thickness t ₂ of the partition wall 21b, details are omitted. .
As described above, the partition walls 21c and 21d are located in a range where the electrodes 30 and 40 are not provided in the circumferential direction of the carrier 20, and the thickness of the partition wall 21 in the vertical direction in the range is determined by the carrier 20 It is set larger as it goes outward in the radial direction. That is, as shown in FIG. 5, the thicknesses of the partition walls 21d and the partition walls 21c are set to increase in order (t ₃ > t ₄ ).

As described above, the electric resistance in the current path between the terminals 50 and 60 that passes through each partition wall 21 and flows in the order of the terminal 50, the electrode 30, the electrode 40, and the terminal 60 is calculated from the above formula 1, and all The thicknesses of all the partitions 21 in the vertical direction in the carrier 20 are set so that the electric resistances in the current paths are equal.
In this way, the vertical partition walls 21, 21,... In the range where the electrodes 30, 40 in the circumferential direction of the carrier 20 are provided, the thickness decreases toward the outside in the radial direction of the carrier 20. In a range where the electrodes 30 and 40 in the circumferential direction are not provided, the thickness increases toward the outer side in the radial direction of the carrier 20.
This allows current to flow evenly in all the vertical partition walls 21, 21..., And the current density near the ends of the electrodes 30 40 in the circumferential direction of the carrier 20 is higher than the current density near the center. Variations in current density in the carrier 20 can be prevented without increasing. Therefore, the carrier 20 can be heated uniformly, and the temperature of the catalyst supported on the carrier can be raised to the activation temperature even when the engine is cold started.

  As shown in FIG. 6, even when the terminals 50 and 60 are not arranged at the center of the electrodes 30 and 40 in the circumferential direction of the carrier 20, the terminals 50 and 60 are connected to the electrodes 30 and 60 in the circumferential direction of the carrier 20. As in the case of being arranged in the central portion of 40, it is possible to set the thickness of the partition wall 21 in the vertical direction. Further, as described above, when calculating the combined resistance of the electrical resistance of the current path on the carrier 20 and the electrical resistance of the current path on the electrodes 30 and 40, the electrical current of the current path on the electrodes 30 and 40 is calculated. By ignoring the resistance, the setting of the thickness of the partition wall 21 in the vertical direction can be further simplified.

As shown in FIG. 7, the partition walls 21, 21... Are not parallel to the line connecting the center positions of the electrodes 30, 40 in the circumferential direction of the carrier 20 (line connected in the vertical direction in FIG. 7). The thickness of each partition wall 21 can be set even when it is not or not orthogonal, that is, when the carrier 20 is inclined in the circumferential direction with respect to the electrodes 30 and 40.
More specifically, assuming that there is a vertical partition wall 21 at an arbitrary position (for example, a straight line α and a straight line β shown in FIG. 7), the thickness of the partition wall 21 is set to the electrodes 30 and 40. As opposed to the case where it is not inclined in the circumferential direction (when the partition walls 21, 21... Are parallel or orthogonal to the line connecting the center positions of the electrodes 30 and 40 in the circumferential direction of the carrier 20). The partition 21 that actually exists in the vicinity of the assumed partition 21 (the partition 21 intersecting the straight line α and the straight line β shown in FIG. 7 and indicated by a thick line) is set. Thickness.

DESCRIPTION OF SYMBOLS 1 Exhaust purification device 10 Case 20 Carrier 21 Partition 21a, 21b, 21c, 21d Partition 30, 40 Electrode 50, 60 Terminal

Claims (1)

A hollow case that forms the exterior;
A carrier housed in the case and carrying a catalyst;
A pair of electrodes provided on the outer peripheral surface of the carrier;
A pair of terminals electrically connected to the pair of electrodes and projecting to the outside of the case;
An exhaust gas purification apparatus that heats the carrier through the pair of electrodes and heats the catalyst to an activation temperature,
The carrier is formed into a honeycomb structure by a plurality of partition walls,
Through the plurality of partition walls, a current for energizing and heating the carrier flows between the pair of electrodes,
An exhaust emission control device in which the thickness of the partition wall of the carrier is set so that the electric resistances of all the current paths between the terminals calculated from the following formula 1 are equal.

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