JPH0322505Y2 - - Google Patents

Description

[Detailed description of the invention] [Field of industrial application] The present invention is a diesel exhaust purification device that collects diesel particulates contained in the exhaust gas of a diesel engine and purifies the exhaust gas, particularly the structure of a ceramic heater for regenerating the device. Regarding.

[Conventional technology]

A filter made of a ceramic honeycomb structure or a ceramic foam structure is used to collect particulates in the exhaust gas. Such filters become clogged due to accumulated particles when used for a long period of time, so an electric heater is placed upstream of the filter and electricity is applied to the electric heater at an appropriate time to remove the accumulated particles on the filter. The filter is burnt and processed to regenerate the filter's function.
It has been proposed to use a ceramic heater as a heater in such a diesel exhaust purification system for reasons such as weight reduction and high degree of freedom in design (for example, Japanese Patent Application Laid-Open No. 111014/1983).

Ceramic heaters are generally constructed by radially arranging a plurality of segment-shaped ceramic heater elements, and each heater element is formed with an electrode hole for attaching a pair of electrodes connected to a battery power source. Due to the arrangement of the heater element, these electrodes are formed near the corners of the fan-shaped outer periphery so as to be located on the same circumference.
Further, it is preferable that the electrode be attached as close to the outer periphery of the heater as possible so as not to be exposed to exhaust gas, that is, to be outside the cross section of the exhaust passage.

[Problem that the invention attempts to solve]

However, as is well known, ceramic material is a brittle material and has the disadvantage of being easily broken. Due to the unique properties of ceramic materials, cracks and chips often occur in the above-mentioned ceramic heaters.

The present inventor investigated cracks and chips in a large number of ceramic heaters and found that almost all of the cracks occurred in the same direction at the electrode holes. Based on these facts, it was confirmed that the cause of chipping and cracking was as follows. In other words, a brazing material is filled between the upper and lower joining surfaces (upper electrode and lower electrode) of the electrode inserted into the electrode hole and the heater element body, but the brazing material is not inserted into the electrode hole. Flows in and sticks. However, ceramic heaters are generally exposed to high-temperature exhaust gas,
Also, when the heater is energized, the entire area is heated, so
The heat oxidizes and expands the brazing material within the electrode hole. This expansion of the brazing material causes the ceramic heater to crack. This can be supported by the fact that cracks occur only at the electrode holes.

The reason why the cracking directions are the same is simple.
That is, the cracking direction is along the shortest transverse line passing through the electrode hole, since that direction is the weakest in terms of strength.

The purpose of the present invention is to prevent cracking or chipping in the electrode holes of a ceramic heater as described above.

[Means for solving problems]

According to the present invention to achieve the above objectives,
A plate-shaped heater element that constitutes the heater body is inserted into the electrode hole, and an electrode pin having a plate-shaped electrode surface portion that clamps both surfaces of the heater element is inserted, and the plate-shaped electrode surface portion and both surfaces of the heater element are connected to each other. In between, a barrier means is provided around the electrode hole to prevent a bonding material for bonding the two from flowing into the electrode hole.

[Effect]

As mentioned above, by providing a barrier means around the electrode hole to prevent the bonding material such as the soldering material from flowing into the electrode hole, the soldering material no longer flows into the electrode hole, and therefore the soldering material inside the electrode hole is prevented from flowing into the electrode hole. Stress due to expansion of the material does not act on the heater element.

〔Example〕

FIG. 4 shows a diesel exhaust purification system 10 equipped with a ceramic heater according to the present invention, which is installed as a part of an exhaust passage through which exhaust gas flows as shown by arrow G. That is, the diesel exhaust purification device 10 is connected to an exhaust manifold (not shown) by the flange 12 provided on the upstream side.
It can be connected to a turbine housing (not shown) of a turbocharger or a turbocharger, and further connected to an exhaust pipe (not shown) on the downstream side by a flange 14 provided on the downstream side.

The diesel exhaust purification device 10 has a main pipe portion 16, and this main pipe portion has the flanges 12 and 1 described above.
It has passages 18 and 20 that are bifurcated between the passages 18 and 20. One passage 18 is the main passage and the other passage 20 is the bypass passage. An electric heater (ceramic heater according to the present invention) 22 is provided in the main passage 18.
A heater case 24 containing a ceramic filter 26 and a trap case 28 containing a ceramic filter 26 are connected. The exhaust gas passing through the main passage 18 passes through the electric heater 22 and the filter 26, then makes a U-turn, and then passes through the partition wall 30.
Thus, the air passes through a passage 32 separated from the electric heater 22 and the filter 26, and passes through the main pipe part 16 again through the confluence passage 34 of the main pipe part 16.
A normally closed bypass control valve 36 is disposed in the bypass passage 20 of the main pipe section 16, and is driven by a known negative pressure diaphragm actuator 38. Energization of electric heater 22 and actuator 3
The switching of the operating negative pressure of 8 is controlled by an electric control unit (ECU) 42 that operates based on the signal a from the sensor that detects the engine rotation speed, the signal b from the back pressure sensor 40, and other detection signals. When the time comes to regenerate the filter 26, the electric heater 22 is energized and the bypass control valve 36 is opened. The control of the ECU 42 itself is well known and is not directly related to the present invention, so it will not be described in detail.

The above-described features of trap case 28 will be apparent with reference to FIGS. 4 and 5. moreover,
Trap case 28 has a flange 28 for connection to heater case 24. and,
Filter 2 housed in trap case 28
6. It is formed in a known manner as a ceramic honeycomb structure or a ceramic foam.

FIG. 6 shows details of the heater case 24 of FIG. 4 and the electric heater 22 housed therein. The electric heater 22 includes a plurality of (for example, six) ceramic heater elements 2 arranged in the circumferential direction.
Consisting of 2a. Each heater element 22a is a generally V-shaped segment, suitably deformed from the V-shape and suitably provided with slits so as not to provide resistance to the passage of exhaust gas. Each heater element 22a is arranged such that the central acute corner of the V-shape faces the center of the heater case 24, and the tips of two legs expanding from the central acute corner are supported by the inner diameter part of the heater case 24. be done. Each heater element 22a is supported insulated from the heater case 24, and the tips of the two leg portions form electrode portions. That is, as shown in FIG. 7, the heater case 24 has an inner flange 44 in the axially intermediate portion, and each heater element 2
2a is sandwiched between this inner flange 44 and an insulating lower ring 46 via an insulating material and a cushioning material, respectively. The lower ring 46 is connected to the inner flange 44 at the discontinued position of the heater element 22a.
It is held by bolts etc.

An insulating upper ring 48 is attached above the inner flange 44 of the heater case 24. A groove extending in the circumferential direction is formed on the upper surface of this upper ring 48, and an inner lead wire 5 is provided in this groove.
0 is embedded. This inner lead wire 50
The tips of the heater elements 22a are connected to two electrode holes 52 formed in the V-shaped legs of each heater element 22a by electrode pins 54 (only one of which is shown). The other electrode pin is body grounded to the heater case 24. Therefore, by connecting the inner lead wire 50 to the positive electrode of an external power source, each heater element 22a is energized. The arrangement of the ceramic heaters forming each heater element 22a may be as described in, for example, Japanese Patent Laid-Open No. 111014/1983. Furthermore, a cover ring 56 is attached above the upper ring 48.

Referring to FIG. 6, the heater case 24 is located in the fifth
Flange 28 of trap case 28 shown in the figure
A flange 24a similar to a is provided, and these flanges 24a and 28a connect the heater case 24.
and the trap case 28 can be connected with bolts. And, as shown in Figure 4,
A similar flange is provided on the main pipe portion 16, and these three parts are integrated by a through bolt (not shown). Flange 2 of heater case 24
4a further includes a flange portion 24b bulging outward, as shown in FIG. 6, and the inner lead wire 50 is gathered at this flange bulging portion 24b.

2 is an enlarged view of the electrode hole 52 in FIG. 7, and the electrode pin 54 is connected to the heater element 2.
It is composed of an upper electrode 54A that holds 2a from above and below, and a lower electrode 54B in the form of a nut. The lower end of the upper electrode 54a is configured as a screw shaft, into which the lower electrode 54B is screwed.
The upper electrode 54a and the lower electrode 54b constitute a plate-shaped electrode surface portion for the plate-shaped heater element 22a, and a bonding material such as a brazing material W is filled between the upper and lower sides of the opposing heater element 22a. This provides electrical connection and fixation between the two. It was difficult to avoid a portion of the brazing material W flowing into the electrode hole 52 during processing and assembly.

However, in order to regenerate the filter 26, the brazing material W, which is heated at the electrode section by energizing each heater and flows into the electrode hole 52, is oxidized and expands, compressing the hole wall, resulting in stress on the ceramic heater body. It takes a lot of time and eventually cracks occur. Note that expansion of the brazing material also occurs due to high temperature exhaust gas. As mentioned above, this crack always passes in the same direction, that is, through the hole 52, at the corner 7 of the heater element 22a.
It occurs along the shortest line L that crosses both edges of the 4 [Fig. 10]. In other words, line L is the weakest direction.

In this invention, the heater element 22a
Taking note of the fact that the cracking is caused by the expansion of the brazing material W flowing into the electrode hole 52, a device was devised to prevent the brazing material W from flowing into the electrode hole 52.

Therefore, according to the present invention, a barrier means is provided around the electrode hole 52 to prevent the brazing material W from flowing into the electrode hole 52.

Three examples of barrier means are shown in Figures 2, 8 and 9, respectively. First, in the embodiment shown in FIGS. 1 to 3, the barrier means is constituted by an annular ridge 81 formed on the heater element 22a. The annular protuberance 81 preferably surrounds the electrode hole 52 as close as possible to the electrode hole 52 so as not to reduce the bonding area between the lower and upper electrodes and the upper and lower surfaces of the heater element.
The protuberance 81 preferably has a circular shape that is concentric with the electrode hole 52, but it does not necessarily have to be concentric or circular in shape. The protuberances 81 are preferably provided on both sides of the upper electrode 54A and the lower electrode 54B. The bump 81 is the ceramic heater 22a.
It can be molded integrally when forming.

In the embodiment shown in FIG. 8, the protuberances 85 are formed not on the heater element but on the lower surface of the upper electrode 54A and the upper surface of the lower electrode 54B, respectively. bump 8
The position 5 is preferably a position corresponding to the periphery of the electrode hole 52 of the heater element 22a.

In the embodiment shown in FIG. 9, the barrier means is an atsushi washer 8 pressed against the lower surface of the atspa electrode 54a.
7A and a lower washer 87B located on the upper surface of the lower electrode 54B when assembled. The washers 87A and 87B are shown as circular rings that fit into the threaded rod 54A of the electrode 54, but C-rings or the like may also be used. Washiya 8
It is preferable that the outer diameters of the electrode holes 7A and 87B are slightly larger than the diameter of the electrode hole 52.

With the above configuration, in any embodiment, when the electrode pin 54 is fitted into the electrode hole 52 of the heater element 22a, the electrode hole 52
There are ridges 81, 85 or washer 8 around 2.
A wall is formed by 7A and 87B, and the upper electrode 54
A. The brazing material W filled between the lower electrode 54B and the upper and lower surfaces of the heater element 22a is obstructed by this wall and cannot flow into the electrode hole 52.

In the present invention, the shape of the heater element and the shape of the electrode hole are not limited to those shown in the drawings, and can be applied to any shape.

[Effect of idea]

As explained above, according to the present invention, cracks and chips that occur in the electrode holes of the heater element can be prevented without reducing the bonding strength between the ceramic heater and the electrodes, and therefore, highly reliable diesel exhaust purification can be achieved. You can get the equipment.

[Brief explanation of the drawing]

FIG. 1 is a front view of a ceramic heater element according to the present invention, FIG. 2 is an enlarged sectional view of the electrode hole portion of the ceramic heater element according to the present invention, and FIG. 3 is a view showing the main part of FIG. 4 is a cross-sectional view of the diesel exhaust purification device having the ceramic heater element shown in FIG. 1, FIG. 5 is an end view of the trap case shown in FIG. 4, FIG. 6 is an end view of the heater case, and FIG. A cross-sectional view along the line -,
FIG. 8 is a diagram showing a different embodiment from FIG. 2, FIG. 9 is a diagram showing still another embodiment, and FIG. 10 is a diagram showing cracks in the ceramic heater element. 22... Heater, 22a... Heater element, 26... Filter, 52... Electrode hole, 54...
...Electrode pin, 54A...Atsupa electrode, 54B...
Lower electrode, 81, 85... Protrusion, 87A, 87B
...Watsiya.

Claims (1)

[Scope of utility model registration request] A ceramic heater that periodically regenerates the filter of an exhaust purification device that collects exhaust particulates from a diesel engine, and includes a plate-shaped heater element that constitutes the heater body, and a plate-shaped electrode surface that sandwiches both sides of the heater element. The heater element has an electrode hole through which the electrode pin is inserted, and a joint is provided around the electrode hole between the plate-shaped electrode surface portion and both surfaces of the heater element to join the two. 1. A ceramic heater for a diesel exhaust purification device, characterized in that a barrier means is provided to prevent material from flowing into an electrode hole.