JPS6327056Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field] The present invention generally relates to an exhaust gas purification device for a diesel engine, and more specifically, to an exhaust back pressure measuring device for a diesel exhaust solid particulate collector capable of regenerating a filter. This invention relates to a cap structure for introducing back pressure.

[Background technology]

BACKGROUND OF THE INVENTION Exhaust gas purification devices for purifying diesel engine exhaust gas by collecting solid particulate emissions, such as exhaust black particulates contained in the diesel engine exhaust gas, are well known in the art. Such a purification device usually consists of a trap using a heat-resistant porous filter made of ceramic or the like. An example of a conventional exhaust solid particulate collector will be described with reference to FIG. 1, where 10 is a diesel engine, 12 is an exhaust manifold, 14 and 16 are exhaust pipes, and 18 is a collector. A monolithic filter 22 is housed within the housing 20 of the collector 18, and is adapted to collect solid particulates in diesel exhaust gas mainly based on the principle of collision collection. In order to withstand the high heat of exhaust gas and effectively collect solid particles, the filter 22 is generally made of a monolith body made of cordierite ceramic molded into a three-dimensional network structure or porous foam. The size of the micropores in is approximately 2
The size of the pores is selected to be approximately 1.5 mm, and the inner surface of the micropores is coated with fine particles of gamma alumina or the like to increase the pore surface area, thereby making it possible to easily collect exhaust particulates.

If the solid particles collected during use of the collector accumulate in the filter, the filter will become clogged, increasing ventilation resistance and reducing the collection efficiency, so the filter must be regenerated at an appropriate time or periodically. Must be. Since the solid particulates in diesel exhaust are mainly composed of carbon and are therefore flammable, the filter can be regenerated by igniting some of the solid particulates that have accumulated in the filter and causing the fire to spread and blow over the entire area of the filter. Is possible. Various filter regeneration methods are known, including a method in which solid particulates are ignited by throttling the engine intake system to reduce the amount of intake air and raising the exhaust gas temperature; There is a method of igniting particulates by increasing the fuel injection amount and raising the exhaust gas temperature, but in the conventional example shown in FIG. The control circuit 26 closes the relay 28 at an appropriate time and energizes the heater 24 for a certain period of time to heat it, thereby igniting the solid particles in the filter.

There are two methods to determine when to regenerate the filter: one is to integrate the number of engine revolutions with an integrator and regenerate the filter when the total number of revolutions reaches a set value, and the other is to add up the distance traveled by the vehicle and regenerate the filter every predetermined distance traveled. A method of detecting the exhaust gas back pressure upstream of the collector and regenerating when the back pressure reaches a set value, a method of detecting the exhaust gas back pressure upstream and downstream of the collector and detecting the difference. There are methods to regenerate when the pressure reaches the set value, etc.
Since the former two methods do not necessarily accurately reflect the clogging state of the filter, the latter two methods using back pressure are the most rational. For example, in the example in Figure 1,
A back pressure detection port 30 is bored in the exhaust pipe 14, the back pressure is guided to the back pressure sensor 34 through the back pressure transmission pipe 32, and the back pressure value is measured as a current value using a piezoelectric resistance element or strain gauge built into the sensor. The control circuit 26 compares this with a set value to detect the reproduction timing. Generally, an introduction cap for taking in exhaust back pressure is attached to the detection port, and a back pressure transmission pipe is connected to this cap.

In this method of determining the filter regeneration timing by detecting the back pressure of exhaust gas, the structure of the back pressure introduction cap that is attached to the back pressure detection port bored in the exhaust pipe is extremely important. That is, during long-term use, solid particles and corrosive condensed components in the exhaust gas may act on the resistance element of the back pressure sensor, deteriorating the performance of the element. In addition, solid particulates and condensate also adhere to the inner walls of detection ports and back pressure transmission pipes, and if the amount of adhesion increases, the ports and pipes will eventually become clogged, making it difficult for the back pressure sensor to detect accurate pressure. This is because the reliability of the back pressure sensor is significantly impaired. Therefore, on the one hand, the back pressure introduction cap must be able to transmit exhaust gas pressure smoothly, and on the other hand, it must be able to completely block out solid particles and condensable components in the exhaust gas. .

Therefore, recently, a back pressure introduction structure has been proposed in which a honeycomb filter is loaded into the detection port and an electric heater is wound around the outer periphery of the honeycomb filter (Utility Application No. 57-61024). According to this, exhaust particulates in the exhaust gas are filtered by the honeycomb filter, and only clean exhaust gas enters through the detection port. Fine particles and the like that adhere to the honeycomb filter due to filtration are incinerated by heating the electric heater, and the honeycomb filter is thus properly regenerated. In this introduction part structure, a honeycomb filter made of ceramic is elastically supported between the introduction part housing and the honeycomb filter via a cushioning material such as a wire net.

However, in this introduction part structure, since the filter is honeycomb-shaped and has multilayered internal passages, it is difficult to heat the inside. Furthermore, since the electric heater is provided on the outer periphery of the filter, heat is dissipated to the outside, resulting in poor heat utilization efficiency of the heater. Therefore, a large amount of electric power is required to heat the honeycomb filter to a temperature necessary for its regeneration, and there is a risk that the regeneration may be insufficient.

To solve this problem, a hollow cylindrical ceramic filter with an open top end and a closed bottom end is attached to the bottom of the cylindrical mouthpiece body, which has a back pressure transmission passage inside. The electric heater may be provided inside the filter or directly on the filter. However, in this case, the above-described method of elastically supporting the filter cannot be used. In particular, a porous, hollow cylindrical ceramic filter has lower strength than dense ceramic, and when locally supported, there is a risk that the supporting portion may be damaged by engine vibration or the like.

[Purpose of invention]

The overall purpose of the present invention is to further improve this type of back pressure introduction cap structure, and to effectively block solid particulates and harmful components in the exhaust gas while reducing the pressure of the exhaust gas. Simple and compact structure that allows accurate transmission of back pressure to the back pressure measuring device.
To provide a back pressure introducing base structure capable of reliably regenerating a filter with a small amount of power consumption.

The present invention is particularly aimed at supporting porous and relatively brittle ceramic filters without fear of damage.

Another purpose is to support the filter without compromising its effective area.

[Structure of the idea]

The back pressure introduction cap of the present invention consists of a cap body that can be attached to a back pressure detection port and has a back pressure transmission passage inside, and a hollow cylindrical porous breathable ceramic filter that is open at the top end and closed at the bottom end. and an electric heater for heating and regenerating the ceramic filter, and the ceramic filter has a flange at its upper end, and is supported by the base body by the flange. The flange is preferably elastically supported via a cushioning material.

〔Example〕

Embodiments of the present invention will be described with reference to FIG. 2 and the following drawings. FIG. 2 shows a back pressure introduction mouthpiece 50 according to an embodiment of the present invention on an exhaust pipe 5 of a diesel engine.
It is shown attached to the detection port 54 of No. 2. The cap 50 has a substantially cylindrical cap body 56, to which a flange 58 is secured by interference fit or welding. The flange 58 is connected to the exhaust pipe 5 by the bolt 62 via the gasket 60.
2, the cap 50 is airtightly fixed to the exhaust pipe.

A filter 64 is attached to the lower part of the base body 56. As shown in FIG. 3, the filter 64 is a hollow cylindrical body whose upper end is open and whose lower end is closed.
A flange 66 is formed on the top thereof.

The filter 64 is made of an air permeable porous ceramic such as cordierite, and has minute pores of 10 to 100 microns in size to allow solid particles in the exhaust gas to pass through. Such a ceramic filter is known, and a ceramic filter having a desired pore size can be obtained by mixing carbon particles of the above-mentioned size into a semi-mixed ceramic material made of cordierite and sintering the mixture.

As shown in FIG. 2, the base body is formed with a shoulder extending radially inward, and a flange 66 of a filter 64 is seated on this shoulder via a cushioning ring 68 made of goose wire or the like. ing. After placing another buffer ring 70 over this flange 66, a filter retaining ring 72 is fitted.

A filter cover 74 is fixed to the lower part of the base body 56 by screwing or snap fitting. The filter cover 74 protects the ceramic filter 64 from the impact of the exhaust gas shown by the arrow and solid matter accompanying it, and has multiple openings (not shown) to allow the exhaust gas to freely enter and exit the filter surface. ) is provided.

The lower end of an elongated tubular housing 76 is inserted into the upper opening of the mouthpiece body 56 above the filter holding ring 72, and after a sealing material 78 such as a heat-resistant resin is injected and solidified, the upper edge of the housing 76 is inserted as shown in the figure. By crimping radially inward, the tubular housing 76 is hermetically connected to the base body 56. Inside the housing 76 is a heater holding cylinder 80 made of a heat-resistant insulating material such as ceramic.
is inserted in advance, and the electric heater 82 is seated on this heater holding cylinder 80. Electric heater 82
One end of the heating resistor (see FIG. 4) is connected to a positive lead wire 84, and the other end is grounded to the tubular housing 76 by a ground terminal 86. The heater 82 and the heater holding cylinder 80 are fixed by caulking a portion 90 of the housing 76 via the buffer ring 88.

A pressure extraction pipe 94 is inserted into the upper part of the tubular housing 76 via a packing 92, and by caulking the upper part of the housing 76, the space between the housing 76 and the pipe 94 is airtightly sealed. A flexible hose 96 is connected to the pressure extraction pipe 94 and communicates with a back pressure sensor (not shown). A positive lead wire 84 is connected to the pressure extraction pipe 94, and another positive lead wire 98 is connected to a DC power source via a switch (not shown). Therefore, this pressure takeoff pipe 94 not only forms part of the pressure transmission path, but also forms part of the electrical path to the heater. 100 is an insulating boot.

The electric heater 82 is tubular as shown in FIG. 2, and its inside forms a part of the back pressure transmission path leading to the back pressure sensor (not shown).
The ceramic filter 64 can be formed, for example, by printing an electric resistance wire 104 on the surface of a ceramic cylinder 102 by screen printing or the like, and then sintering the same, as shown in FIG.
In order to heat only the resistance wire 10
It is preferable to arrange the filter 64 so that the majority of the filter 64 faces the filter 64 .

The function of this back pressure introduction cap is as follows. Exhaust gas flowing through the exhaust pipe 52 comes into contact with the filter 64 through an opening in the filter cover 74 . Solid particles and condensed liquid droplets in the exhaust gas are filtered out, and only clean gas flows into the filter. The pressure of this gas is transmitted to the back pressure sensor via a back pressure transmission passage consisting of the inner passage of the tubular electric heater 82, the tubular housing 76, the pressure takeoff pipe 94, and the hose 96. In this way, only clean gas enters and exits the back pressure transmission path, so there is no risk of the path becoming clogged or the back pressure sensor element deteriorating even after long-term use.
Accurate back pressure can be measured at all times.

By periodically supplying electricity to the electric heater from a power source (not shown) via an interrupter, the filter 64
is heated from the inside. As a result, the solid particles adhering to the filter are incinerated, and the filter is regenerated. Note that if the electric heater 82 is formed of a PTC (Positive Temperature Coefficient) heater whose electrical resistance value increases as the temperature rises, a weak current is constantly supplied to the heater to constantly heat and regenerate the filter. You can also.

[Effect of idea]

As is clear from the above, according to the present invention, solid particulates and harmful components in exhaust gas can be effectively blocked, but the back pressure of exhaust gas can be freely and accurately introduced into the back pressure measuring device. A simple and compact base structure can be obtained.

In addition, a wide flange is formed on the ceramic filter, and it is supported by the mouthpiece body through the flange, so the filter can be held relatively softly while avoiding excessive local loads. It is possible to hold fragile ceramic filters without damaging them. This effect becomes even more reliable when a buffer material is used.

Furthermore, since the filter is held by its flanges, the excess surface of the filter can be used effectively without compromising its effective area.

Further, since the ceramic filter is held only by its upper part and its lower end is free, there is no risk of the filter being damaged due to thermal expansion.

[Brief explanation of the drawing]

Fig. 1 is a conceptual diagram of the exhaust solid particulate collection device, Fig. 2 is a sectional view of the back pressure introducing base of the present invention, Fig. 3 is a perspective view of the ceramic filter, and Fig. 4 is a perspective view of the electric heater. It is. 50... back pressure introduction cap, 56... cap body,
64...Ceramic filter, 66...Filter flange, 68, 70...Buffer ring, 72
... Filter retaining ring, 74 ... Filter cover, 82 ... Electric heater.

Claims (1)

[Scope of Claim for Utility Model Registration] 1. A back pressure sensor installed in a back pressure detection port of a diesel engine exhaust system in order to introduce exhaust gas back pressure into an exhaust gas back pressure measuring device of a filter regeneration type diesel exhaust solid particulate collector. It is a pressure introduction mouthpiece that can be attached to a back pressure detection port and has a substantially cylindrical mouthpiece body with a back pressure transmission passage inside, and a hollow cylindrical porous breathable body with an open top end and a closed bottom end. It includes a ceramic filter and an electric heater for heating and regenerating the ceramic filter, and the ceramic filter has a flange at its upper end, and is supported by the flange inside the mouthpiece body. Base for introducing back pressure. 2. The back pressure introduction cap according to claim 1 of the utility model registration, characterized in that a cushioning material is interposed between the cap body and the flange.