JPH0681628A - Exhaust particulate eliminator - Google Patents

Abstract

PURPOSE:To keep upstream and downstream temperature balance constant so as to prevent cracking and the fusing of filters by detecting the upstream and downstream temperature of a particulate trap, and controlling current application to heating means on the temperature lowered side separately according to the detected temperature CONSTITUTION:Cylindrical filters 13 are provided inside of the external wall of a particulate trap 10. A first temperature sensor 17 is provided upstream of the filters 13, and a second temperature sensor 18 is provided downstream of the filters 13. The detected temperature is outputted to a control circuit 11 so as to control heaters 141-144 separately. Engine speed becomes high to activate the heaters, and the temperature is stabilized to the degree of 800 deg.C, and when the upstream temperature is lowered after that, a current is applied with priority only to the heaters 141, 142. When the downstream temperature is lowered, a current is applied only to the heaters 143, 144. The upstream and downstream temperature is thus kept stably to at least 800 deg.C or higher so as to prevent the damage of the external wall caused by temperature difference.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a particulate matter removing device for removing exhaust particulates (particulates) generated in a diesel engine.

[0002]

2. Description of the Related Art Exhaust gas emitted from a diesel engine contains particulates such as carbon. If particulate matter is discharged outside the vehicle as it is, it may cause pollution. Therefore, a particulate matter removing device that collects and burns the particulate matter to remove it is installed in a diesel engine vehicle.

FIG. 4 is a block diagram showing a conventional particulate removing device. The structure of the particulate removing device will be described below with reference to FIG. 41 is an engine, 42
Is a first exhaust pipe for sending the exhaust gas discharged from the engine 41 to the particulate trap 43, and 44 is a second exhaust pipe for sending the exhaust gas from the particulate trap 43 to the outside of the vehicle. The particulate trap 43 is provided with a filter 432 that collects only particulates inside a cylindrical outer wall 431, and the periphery of the outer wall is covered with a band heater (not shown). The exhaust gas from the engine flowing along the first exhaust pipe 42 is
It enters the particulate trap 43, but the filter 4
32 collects only particulates. Then, when the inside of the trap 43 is heated by the heater (about 800 ° C.), the particulates accumulated in the filter 432 are heated and burned to become carbon dioxide, which flows out of the vehicle through the second exhaust pipe 44.

[0004]

As described above, a heater is required to burn particulates, but conventionally, a heater is provided around the outer wall 431 of the particulate trap. Cause problems. Since heat is not transferred to the vicinity of the center of the particulate trap 43, the temperature reaches the set temperature (800 ° C.) only near the outer periphery where the heater is installed, and the temperature does not rise to the set temperature near the center. Therefore, the particulates in the vicinity of the outer periphery burn well, but the particulates in the vicinity of the center hardly burn because the temperature is low. To prevent this, if the temperature of the heater itself is further increased, the particulate trap 43
Becomes too hot and cracks occur.

Actually, the filter 432 is formed by the wall 532 and the collecting hole 632, and the flow of exhaust gas is suppressed by this wall 532, so that the engine 41 is upstream on the upstream side.
The exhaust gas winds from are directly affected. On the other hand, the flow velocity of exhaust gas increases as the engine speed increases,
When the flow velocity of the exhaust gas hitting the wall 532 and the outer wall 411 is increased, a kind of cooling effect is generated on the outer wall 431 and the wall 532. Therefore, a temperature difference occurs between the upstream and the downstream of the outer wall 431 (the flow velocity of the exhaust gas at the downstream is suppressed by the filter 31, so there is no cooling effect). When the temperature difference occurs in the outer wall 431 in this way, the outer wall 431 is cracked. In addition, the filter 432 may also melt.

In order to prevent this, there is a conventional one in which a plurality of rod-shaped heaters are provided in the filter, as disclosed in, for example, Japanese Patent Laid-Open No. 4-47108. If such a means is applied to the particulate trap 43, since the heater is provided directly near the center of the particulate trap 43, the temperature of the filter near the center also rises reasonably, and The particulates in can be completely burned, and the problem of can be solved.

However, even with such means, the above problems cannot be solved yet. That is, since the exhaust gas from the engine directly impinges on the outer wall 431 near the upstream side, a cooling effect is also produced, and a temperature difference between the upstream and downstream sides is inevitably generated.
31 will be cracked. The present invention aims to prevent the outer wall from being damaged by making the temperature difference between the upstream and the downstream of the particulate trap the same.

[0008]

In order to achieve the above object, the present invention provides a filter which is covered with a cylindrical outer wall and collects exhaust fine particles in exhaust gas, and the filter is provided in the filter. And a heating unit that operates by energization to heat the exhaust particulates, and in an exhaust particulate removal device that burns and removes the exhaust particulates by the heating unit, a rotational speed detection unit that detects the rotational speed of the internal combustion engine, A first temperature detecting means provided upstream of the filter for detecting a temperature of exhaust gas upstream thereof, and a second temperature detecting means provided downstream of the filter for detecting a temperature of exhaust gas downstream thereof. The heating means comprises at least a first heating means provided near the upstream side of the filter and a second heating means provided at least near the downstream side of the filter, and further comprising: A detection signal from the temperature detection means and the second temperature detection means is input, and a control means for controlling the energization of the first heating means or the second heating means based on the upstream temperature and the downstream temperature is provided. According to the first feature, the control means inputs the detection signals from the rotation speed detection means and the second temperature detection means, and based on the rotation speed and the downstream temperature of the internal combustion engine, the first heating means or the second heating means. The second feature is to control the energization of each means.

[0009]

The control means energizes the first heating means when the upstream temperature decreases or the internal combustion engine rotational speed increases based on the upstream and downstream temperatures or the internal combustion engine rotational speed and downstream temperature. , The second heating means is de-energized to raise the upstream temperature. On the contrary, when the downstream temperature is lowered, the second heating means is energized and the first heating means is de-energized to raise the downstream temperature. In this way, the energization of the first and second heating means is individually controlled to prevent the temperature decrease on the upstream side of the outer wall due to the increase in the number of revolutions, and to keep the temperature balance upstream and downstream constant. It is possible to prevent cracking and melting of the filter.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure of the particulate removing device of the present invention will be described with reference to FIG. FIG. 1 is a block diagram of a particulate removing device 1 showing an embodiment of the present invention. still,
The particulate trap described later is shown in a sectional view. The engine 3 rotates due to the explosion of the air-fuel mixture. The exhaust gas after the explosion flows from the engine 3 to the particulate trap 10 via the first exhaust pipe 4. The particulate removing device 1 is roughly composed of the particulate trap 10 and a control circuit 11 including a microcomputer. Further, the particulate trap 10 includes four rod-shaped heaters (141, 142, 143) which are installed by inserting the outer wall 12, a cylindrical filter 13 in the particulate trap 10, and a central portion of the filter 13. , 144), a first pressure sensor 15 provided on the upstream side of the particulate trap 10 for detecting the pressure value of the exhaust gas upstream thereof, and a second pressure sensor 16 for detecting the pressure value on the downstream side thereof, A first temperature sensor 17, which is provided on the upstream side of the filter 13 of the particulate trap 10, detects the temperature of the exhaust gas upstream thereof, and outputs a detection signal corresponding to this temperature to the control circuit 11, and the exhaust gas downstream thereof as well. The second temperature sensor that detects the temperature of the gas and outputs a detection signal corresponding to this temperature to the control circuit 11. And a 18.

The above-mentioned cylindrical filter 13 is made of ceramic and has a plurality of collecting holes 131 extending in the upstream-downstream direction.
And a sponge type wall portion 132 having a small hole. A cross-sectional view of the filter 13 taken along the line AB is shown in FIG. Exhaust gas enters the collecting holes 131, and the gas (oxygen or the like) contained in the exhaust gas flows to the downstream side, that is, the second exhaust pipe 16 through the hole of the wall portion 132, but is included in the exhaust gas. Particulates (exhaust particles) cannot pass through this hole because they are relatively large.
It will be accumulated in 31, and the particulates will not flow downstream. It should be noted that when the particulates are accumulated in the filter 13 by a predetermined amount or more, the particulates suppress the flow of the exhaust gas, so that there is a difference between the pressure of the exhaust gas on the upstream side and the pressure of the exhaust gas on the downstream side. If this pressure difference is detected, it can be determined that the particulates have accumulated in the filter 13 by a predetermined amount or more.

Four heaters 141, 142, 143
144 are arranged in order from upstream to downstream.
These filters are the particulate trap 10 in the figure.
Of the filters, the filters are arranged at equal intervals, and the first heater 141 is closest to the upstream side, and then the second heater 142 and the third heater 14 are arranged.
3, and the fourth heater 144 is closest to the downstream side.

The heater is actually like a kind of glow plug, in which a coil is inserted in a heat-resistant tube, and an insulating powder is filled around the coil. When a current flows through this coil, heat is generated. To insert the heater into the filter 13, for example, a hole is made in the filter 13 with a drill or the like, each heater is inserted therein, and fixed to the outer wall 12 with a nut or the like.

When the heater is heated, the particulates accumulated in the collecting hole 131 for a certain amount or more are burnt into carbon dioxide, which is discharged to the outside of the collecting hole 131, so that the inside of the collecting hole 131 is so-called empty. It becomes the state of. By doing so, the particulates can be stored in the filter 13 again, and the filter 13 can be reused (regenerated).

In this example, the heat generation of each heater is individually controlled by the control circuit 11 described later,
And by controlling each of these heaters individually,
The temperature in the upstream and the downstream of the outer wall 12 and the filter 13 can be made uniform while increasing the temperature in the vicinity of the upstream and the temperature in the vicinity of the downstream in particular.

The control circuit 11 includes an engine speed sensor 6 mounted on the engine 3 (hereinafter referred to as NE sensor).
The engine speed is input by the detection signal from. Further, the pressure values from the first and second pressure sensors 15 and 16 and the temperatures from the first and second temperature sensors 17 and 18 are input, respectively. Each input data is taken in by a microcomputer (not shown) in the control circuit 11, and the microcomputer uses each data as a basis for each heater 141, 1
On / off of energization is controlled for each of 42, 143, and 144.

The operation of this example will be described below. First, the operation when the engine is idle (the flow velocity of exhaust gas is extremely low) will be described. FIG. 3 is a flow chart showing the operation of the microcomputer. When power is supplied to the control circuit 11 from a power source (not shown), the microcomputer starts operating. First, in step S1, the pressure values from the first and second pressure sensors 15 and 16 are fetched and the difference between them is obtained. If the difference between the pressure values is equal to or more than the predetermined value in the next step S2, it is determined that the particulates have accumulated in the collecting hole 131 by a certain amount or more, and the filter 13
In order to reproduce the above, heating control of each heater is started in the next step S3 and subsequent steps.

When a certain amount or more of particulates are accumulated, all the first to fourth heaters are energized and heated in a trial manner in step S3 to warm the entire inside of the outer wall 12. Then, the process proceeds to the next step S4 and step S5 in order to check how the temperature rises. In step S4, based on the temperature taken in from the first temperature sensor 17, the temperature near the inlet of the filter 13, that is, near the upstream of the particulate trap 10 is a set value (about 800 °).
C) Determine whether or not the above is reached. At the beginning of heater energization, the heater itself has not been activated yet, so 800
Since it has not reached above ° C, proceed to the next step S6,
This time, based on the second temperature sensor 18, it is determined whether or not the temperature near the downstream is 800 ° C. or higher. 800 downstream
Since it has not reached above ° C, the process returns to step S3, all heaters are energized, and steps S3, S4, S
While repeating step 6, watch the upstream and downstream temperatures for a while.

Then, when the temperature rises and the upstream temperature exceeds 800 ° C., the process proceeds from step S4 to step S5, in which the energization of the second heater 142 is temporarily stopped, and the first, third, Fourth heater 141,14
Only 3 and 144 are energized. This is because the second heater 142 is not energized so that the upstream temperature does not rise too much, and the first heater 141 is energized in order to prevent the cooling effect due to exhaust gas particularly near the upstream. This is to keep the temperature on the upstream side at 800 ° C.

At this time, the temperature is usually 800 ° C. on the downstream side as well.
Since the temperature has risen above C, the process proceeds from step S6 to step S7, this time only the third heater 143 is de-energized so that the temperature on the downstream side does not rise too much and does not drop too much. Control to keep at ° C. In this manner, the second heater 142 and the third heater 143 near the center of the particulate trap are energized / de-energized to control the upstream / downstream individually, and the upstream / downstream temperature is both 800 ° C. Try to keep

Then, in the next step S8, both upstream and downstream,
When it is determined that the temperature is stable at 800 ° C or higher, in the next step S9, only the first heater 141 and the fourth heater 144, which are closest to the upstream side and the downstream side, respectively, are energized, and the upstream and downstream sides are set to 800 ° Control to keep close to C. Then, in the next step S10, the temperature on the upstream side is detected again, but at this time (during idling)
Is stable at about 800 ° C, the next step S
Proceed to 12 and check the temperature on the downstream side again. At this time, since it is stable at about 800 ° C with the upstream side,
Next, in step S14, it is determined whether the pressure difference between the upstream side and the downstream side has become equal to or less than a predetermined value, that is, whether the particulates have been burned and removed. Then, if it is not less than the predetermined value, that is, if it is not completely removed yet, the process returns to step S9, and steps S9 and S are performed until it is removed.
10. S12 and S14 are repeated. If it is removed, it is determined in step S14 that the reproduction is completed, and step S15
Then, all the heaters are de-energized and the process returns to step S1 to collect the particulates again.

Up to this point, the engine has been described when it is idling, but next, the operation and action of this example when the engine is operating at an intermediate speed and at a high speed (for example, 3000 rpm) instead of at idle speed will be described. By step S8, each heater is activated to stabilize the upstream and downstream to about 800 ° C, and the removal state of particulates is monitored in steps S9 to S14. During this monitoring, the engine rotation Even if the number rises to 3000 rpm and the upstream temperature drops to 800 ° C or lower, step S10
This temperature drop is immediately detected by. When the process proceeds to step S11 by the determination in step S10,
Only the heaters 141 and 142 on the upstream side are preferentially energized. By doing so, even if the temperature of the upstream side is lowered, only the upstream side is concentrated and heated, so that the temperature rises again to 800 ° C or higher. Further, even if the temperature on the downstream side is decreased due to the concentrated heating on the upstream side, only the heaters 143 and 144 on the downstream side are energized to raise the temperature to 800 ° C or higher again in steps S12 and S13.

In this way, even if the engine speed becomes higher than the idle speed and the flow velocity at the upstream becomes faster, both the upstream temperature and the downstream temperature are kept at least 800 ° C. or more to keep the temperature balance constant. Therefore, the outer wall 12 can be prevented from cracking. Further, even if an upstream cooling effect occurs in the heating preparation stage in steps S1 to S8, the upstream temperature can be increased by steps S6 and S7.

As in step S10, the temperature is directly detected to determine the cooling effect on the upstream side. Instead of this, the engine speed from the NE sensor is fetched,
If the engine speed is 3000 rpm or more, for example, it may be determined that the cooling effect is occurring. Further, although the number of heaters is four in this example, the number of heaters may be more than four, and if at least two heaters are provided, the upstream and downstream temperature balance can be maintained. Further, the heater may be a plate-shaped one.

[0025]

As described above, according to the present invention, the temperature difference between the upstream side and the downstream side of the particulate trap can be made equal to prevent the outer wall of the particulate trap from being damaged.

[Brief description of drawings]

FIG. 1 is a block diagram of a particulate remover showing an example of the present invention.

FIG. 2 is a sectional view taken along line AB of the particulate trap 10 in FIG.

FIG. 3 is a flowchart showing an operation of a microcomputer showing an example of the present invention.

FIG. 4 is a configuration diagram showing a conventional particulate trap.

[Explanation of symbols]

 1-Particulate removing device 11-Control circuit 13-filter

Claims (2)

[Claims] 1. A filter, which is covered by a cylindrical outer wall and collects exhaust particulates in exhaust gas, and a heating means which is provided in the filter and operates by energization to heat the exhaust particulates. An exhaust particulate matter removing device that burns and removes exhaust particulates by the heating means, wherein a rotational speed detecting means for detecting the rotational speed of an internal combustion engine and an exhaust gas temperature upstream of the filter are provided. A first temperature detecting means for detecting and a second temperature detecting means provided downstream of the filter for detecting the temperature of exhaust gas downstream thereof are provided, and the heating means is provided at least near the upstream of the filter. A first heating means and a second heating means provided at least near the downstream of the filter, and further inputs detection signals from the first temperature detecting means and the second temperature detecting means. However, the exhaust particulate removing device is characterized by being provided with control means for respectively controlling the energization of the first heating means or the second heating means based on the upstream temperature and the downstream temperature. 2. The control means inputs detection signals from the rotation speed detection means and the second temperature detection means, and determines whether the first heating means or the second heating means is based on the rotation speed and the downstream temperature of the internal combustion engine. 2. The power supply is controlled respectively.
Exhaust particulate removal device described.