JPH053698Y2 - - 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 a ceramic heater for regenerating the device. Regarding the structure of

[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. The arrangement of the heater elements and these electrode holes 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 causes of chipping and cracking were 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, the entire ceramic heater is exposed to high-temperature exhaust gas, and the entire ceramic heater is heated when the heater is energized, so that the brazing material in the electrode hole oxidizes and expands due to the heat. This expansion of the brazing material causes the ceramic heater to crack. This can also be explained 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 direction of cracking is along the shortest transverse line passing through the electrode hole, since that direction is the weakest in terms of strength.

In order to prevent the ceramic heater from cracking or chipping due to expansion of the brazing material, the diameter of the electrode hole 52' relative to the electrode pin 54 of the upper electrode 54A shown in FIG. 8 is increased to increase the clearance between the two. It is also possible to do so.

However, since the lower electrode 54B is usually nut-shaped, if the diameter of the electrode hole 52' is increased, the contact area with the lower electrode 54B becomes smaller. Since this electrode portion is repeatedly heated and cooled by energizing the heater, the brazing material W is likely to peel off if the contact clarity with the lower electrode 54B is small. Furthermore, the contact resistance increases, and the temperature tends to rise when electricity is applied. For this reason, the brazing material W
is easily oxidized and may eventually cease to function as a heater.

Therefore, there is naturally a limit to increasing the size of the electrode 52'.

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,
In the heater element that constitutes the ceramic heater that periodically regenerates the filter of the exhaust purification device that collects the exhaust particulates of the diesel engine,
An electrode hole for inserting an electrode pin having an upper electrode and a lower electrode that sandwich the heater element between the joint surfaces with the heater element through a brazing material has a diameter larger on the upper electrode side than on the lower electrode side. It is formed as a hole with different diameters.

[Effect]

As mentioned above, by making the electrode hole a stepped hole or an inclined hole with a larger diameter on the upper electrode side, even if the brazing material flows into the electrode hole, there is a space for expansion during heating, so there is no need for the heater element. The stresses that cause cracking cease to act.

〔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 can be connected to an exhaust manifold (not shown) or a turbine housing (not shown) of a turbocharger by a flange 12 provided on the upstream side, and a flange 12 provided on the downstream side thereof. 14, it is further connected to an exhaust pipe (not shown) 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 a main passage, and the other passage 20 is a bypass passage. A heater case 24 containing an electric heater (ceramic heater according to the present invention) 22 and a trap case 28 containing a ceramic filter 26 are connected to the main passage 18.
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.
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 via a 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 speed, the signal b from the back pressure sensor 40, and other detection signals. When it is time 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,
The trap case 28 has a flange 28a for connection to the heater case 24. The filter 26 housed within the trap case 28 is formed of a ceramic honeycomb structure or a ceramic foam in a known manner.

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 has a V-shaped central acute corner facing the center of the heater case 24, and the tips of two legs that expand from the central acute corner are facing the heater case 24.
It is arranged so that it is supported by the inner diameter part of. 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 22a has an insulating material between the inner flange 44 and the insulating lower ring 46. and sandwiched with a cushion material interposed therebetween. The lower ring 46 is connected to the inner flange 4 at the discontinuous position of the heater element 22a.
4 with bolts or the like.

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 grounded to the body of 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.

FIG. 2 is an enlarged view of the electrode hole 52 in FIG. 7. The electrode pin 54 is connected to the heater element 2.
The upper electrode 54A holds the electrode 2a from above and below, and the lower electrode 54B has a nut shape. The lower end of the upper electrode 54A is configured as a screw shaft, onto which the lower electrode 54B is screwed.
Brazing material W is filled between the upper electrode 54a and the lower electrode 54b and the upper and lower surfaces of the opposing heater elements 22a, thereby electrically connecting and fixing the two together. It is difficult to avoid that some of this brazing material W flows into the electrode holes 52 during processing and assembly. Also, it is difficult to increase the size of the joint surfaces of the upper electrode 54A and the lower electrode 54B due to the demand for a compact and lightweight device as a whole, and the size of the lower electrode 54B, which is in the form of a nut, is particularly limited due to space restrictions.

However, in order to regenerate the filter 26, the brazing material W heated by each heater electrode portion and poured into the electrode hole 52 is oxidized and expands, compressing the hole wall, and as a result, stress is applied to the ceramic heater 22 body. Eventually, cracks will occur. Note that expansion of the brazing material also occurs due to high temperature exhaust gas. As described above, this crack always occurs in the same direction, that is, along the shortest line L passing through the hole 52 and crossing both edges of the corner portion 74 of the heater element 22a (FIG. 9).
In other words, line L is the weakest direction.

In this invention, the heater element 22a
Focusing on the fact that the cracking is caused by the expansion of the brazing material W flowing into the electrode hole 52, the problem is how to prevent cracking of the heater element even if the brazing material W flows into the electrode hole 52. This paper proposes a solution to the problem.

Therefore, according to the present invention, the diameters of the electrode holes 52 are made different between the upper electrode 54A side and the lower electrode side 54B, as shown in FIGS. 1 and 2. In other words, according to the present invention, the electrode holes 52 have different diameters, with a larger diameter on the upper electrode side and a smaller diameter on the lower electrode side. Specifically, it may be a bevel-shaped inclined hole whose diameter decreases from the upper electrode side toward the lower electrode side as shown in FIG. 2, a stepped hole as shown in FIG. 3, or any other shape. be able to. Generally, the upper electrode 54A can secure a larger bonding surface than the lower electrode 54B, so by making the electrode hole 52 on the upper electrode side larger in diameter, the upper electrode 54A can secure a larger bonding surface than the lower electrode 54B.
Although the bonding area of the heater element 22a to the heater element 22a is slightly smaller than that of the conventional uniform small diameter hole (FIG. 8), this has almost no effect on the bonding force.

By increasing the diameter of the electrode hole on the upper electrode side in this way, even if the brazing material W flows into the electrode hole 52, as shown in FIGS. 2 and 3, the brazing material W will occupy the space created by the large diameter hole. It is absorbed and can ensure sufficient expansion. Therefore, even if the brazing material W inside the electrode 52 expands, stress due to the brazing material W hardly acts on the hole wall of the heater element 22a, and therefore cracking of the heater element is reliably prevented.

This becomes even clearer when comparing FIGS. 2 and 3, which show the present invention, and FIG. 8, which shows the prior art. That is, while the conventional electrode hole 52' was a round hole with a uniform diameter, the electrode hole 52 of the present invention is a hole with different diameters that widen toward the upper electrode side. As a result, in the present invention, a space for expansion of the brazing material W is secured by the enlarged diameter portion, and cracking or chipping of the ceramic heater element does not occur.

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, cracking and chipping that occur in the electrode hole of the heater element can be prevented without substantially reducing the adhesion force between the ceramic heater and the electrode pin, and therefore reliability can be improved. A high-quality diesel exhaust purification device can be obtained.

[Brief explanation of drawings]

FIG. 1 is a ceramic heater element according to the present invention, FIG. 2 is an enlarged cross-sectional view of the different diameter electrode holes of the ceramic heater element according to the present invention, and FIG. 3 is a similar embodiment showing a different embodiment from FIG. 2. Figure 4 is a cross-sectional view of the diesel exhaust purification system having the ceramic heater element shown in Figure 1, and Figure 5 is a cross-sectional view of the diesel exhaust purification system having the ceramic heater element shown in Figure 1.
6 is an end view of the heater case, FIG. 7 is a sectional view taken along the line - in FIG. 6, FIG. 8 is a view similar to FIG. 2 showing the prior art, and FIG. Figure 9 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.

Claims (1)

[Scope of utility model registration request] A heater element that constitutes a ceramic heater that periodically regenerates the filter of an exhaust purification device that collects exhaust particulates of a diesel engine, and the heater element is sandwiched between the joint surfaces with the heater element via a brazing material. A ceramic having an electrode hole through which an electrode pin having an upper electrode and a lower electrode is inserted, and the electrode hole is a hole of different diameters in which the upper electrode side has a larger diameter than the lower electrode side. Structure of heater element.