JPH0715251B2 - Exhaust gas purification device for diesel engine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an exhaust gas purification device provided in an exhaust system of a diesel engine to collect particulates in exhaust gas.

[Conventional technology and problems]

This exhaust gas purification device has, for example, a honeycomb filter,
When the trapped amount of particulates exceeds a predetermined value, the particulates are burned to regenerate the filter. Japanese Unexamined Patent Publication (Kokai) No. 61-223215 discloses a conventional exhaust gas purification device, in which an electric heater is provided at a portion close to one end of a filter, and two bypass pipes bypassing the filter are arranged. A valve for controlling the flow of exhaust gas in these bypass pipes and filters is also provided. When collecting particulates, the exhaust gas flows through the filter and then passes through the electric heater to be discharged into the atmosphere.When the filter is regenerated, the exhaust gas flows from the electric heater side to the filter through one bypass pipe and the other. It passes through the bypass pipe and is released into the atmosphere.

However, when collecting particulates, for example, when the engine is operated under a high load and the particulates on the filter become self-combusting (hereinafter referred to as the self-combustion region), the heat from this combustion flows to the filter side along the flow of exhaust gas. However, there is a problem that the filter may be melted and damaged. On the other hand, Japanese Utility Model Laid-Open No. 60-45815 discloses a configuration in which a bypass valve is opened to reduce the amount of exhaust gas flowing into the filter when there is a possibility that the filter is melted and damaged. Since the combustion heat is transferred to the filter, it is not possible to reliably prevent the filter from being melted.

[Means for solving problems]

As shown in the configuration diagram of the invention of FIG. 1, an exhaust gas purification device according to the present invention includes a filter 15 for collecting particulates contained in exhaust gas flowing in a first direction, and an exhaust gas inside the filter 15. In the second direction opposite to the first direction in
Exhaust gas flow control means (bypass pipes 21 and 24, switching valves 31 and 32) that causes the gas to flow in the direction of air and discharge into the atmosphere, and the above filter
And a means A for judging whether or not the particulates collected in 15 are in a self-combusting engine state. When the particulates are in a self-combusting engine state, the exhaust gas flow control means (bypass pipes 21, 24) , The switching valves 31, 32) are used to cause the exhaust gas to flow in the second direction.

〔Example〕

 The present invention will be described below based on the illustrated embodiments.

2 to 4 show an embodiment of the present invention. In these figures, an enlarged diameter portion 14 is formed in the exhaust pipe 13 connected to the exhaust manifold 12 of the diesel engine 11, and in the enlarged diameter portion 14, particulates (carbon fine particles and carbon solids) in the exhaust gas are formed. A filter 15 is provided for collecting liquid HC adsorbed on the surface). Muffler 16 is
It is provided near the exhaust port on the downstream side of the expanded diameter portion 14.

The first bypass pipe 21 connects the first connecting portion 22 located between the engine 11 and the expanded diameter portion 14 and the second connecting portion 23 located between the expanded diameter portion 14 and the muffler 16. Second bypass pipe
Reference numeral 24 denotes a third connecting portion 25 located between the first connecting portion 22 and the expanded diameter portion 14, and a fourth connecting portion 23 located between the second connecting portion 23 and the muffler 16.
The connection part (26) is communicated. The first connecting portion 22 is provided with a first switching valve 31, and the fourth connecting portion 26 is provided with a second switching valve 32.

The actuator 33, which controls the opening / closing of the first switching valve 31, has a conventionally known diaphragm type structure, and is operated by the negative pressure adjusting valve 34 guiding negative pressure or atmospheric pressure. The negative pressure control valve 34 is a control circuit (ECU) 5 equipped with a microcomputer.
Controlled by 1, the negative pressure source or the atmosphere is communicated with the actuator 33. An actuator 36 for controlling the opening / closing of the second switching valve 32 also has a diaphragm type structure, and is operated by negative pressure or atmospheric pressure guided by a negative pressure adjusting valve 37 controlled by the ECU 51.

An electric heater 41 is provided on the downstream side of the filter 15, that is, on the muffler 16 side for regeneration of the filter 15, that is, combustion of particulates. The electric heater 41 is connected to the battery 43 via the relay 42. The relay 42 is controlled by the ECU 51 to open and close, and when it is determined that it is time to regenerate the filter, the heater 41 is energized to generate heat, and the particulates collected by the filter 15 are ignited and burned. . Judgment of the regeneration time of the filter 15 and regeneration control are
As is well known in the art, this is performed according to detection signals obtained from the engine speed sensor 45 and the accelerator position sensor 46, the back pressure sensor 47, and the exhaust temperature sensor 48 provided in the combustion injection pump 44.

The filter 15 is a honeycomb filter, and as shown in FIG. 5, a cordierite substrate formed by alternately arranging porous cells having plugs on the inlet side and porous cells having plugs on the outlet side. The surface of the cordierite base material is coated with γ-alumina that adsorbs malodorous components such as HC. Further, a catalyst such as copper or silver is carried on the surface of γ-alumina in order to lower the ignition temperature of the particulates during regeneration of burning the collected particulates.

First and second switching valve during normal particulate collection
As shown in FIG. 2, 31, 32 close the first and second bypass pipes 21, 24, respectively, and open the exhaust pipe 13. Therefore, the exhaust gas does not flow through the first and second bypass pipes 21 and 24, but all flows into the expanded diameter portion 14, flows in the order of the filter 15 and the electric heater 41, and is discharged into the atmosphere. During this time, the particulates contained in the exhaust gas are collected by the filter 15.

When the filter 15 is regenerated, as shown in FIG. 4, the first switching valve
31 indicates that the first bypass pipe 21 is opened and the exhaust pipe 13
The first and third connecting portions 22 and 25 of the second switching valve 3 are disconnected.
2 opens the second bypass pipe 24 and the exhaust pipe 13 at a predetermined opening. Therefore, a part of the exhaust gas passes through the first bypass pipe 21, then flows into the filter 15 from the electric heater 41 side, is discharged into the atmosphere through the second bypass pipe 24, and the remaining exhaust gas is discharged into the first exhaust gas. Muffler 16 directly from the bypass pipe 21 of
Flows to the side and is released into the atmosphere. At this time, the electric heater 41 is energized to generate heat, which causes the particulates on the filter 15 to ignite and burn.

When the particulates on the filter 15 are self-combusted even if they are not ignited by the electric heater 41, that is, in the self-combustion region, the first switching valve 31 opens the first bypass pipe 21, as shown in FIG. And the first of the exhaust pipe 13
And the third connecting portions 22 and 25 are shut off, and the second switching valve 32
Opens the second bypass pipe 24 and shuts off the second and fourth connecting portions 23 and 26 of the exhaust pipe 13, or, as shown in FIG. 4, the second bypass pipe 24 and the exhaust pipe 13 Is opened at a predetermined opening. In the case of the state shown in FIG. 3, the exhaust gas passes through the first bypass pipe 21 and flows into the filter 15 from the electric heater 41 side, and is discharged from the muffler 16 into the atmosphere through the second bypass pipe 24. In the state shown in FIG. 4, as in the case of regeneration of the filter 15, a part of the exhaust gas flows into the filter 15 from the electric heater 41 side and is released into the atmosphere, and the remaining exhaust gas passes through the filter 15. Without being released into the atmosphere.

Then, in the self-burning region, the exhaust gas passing through the filter 15 flows into the filter 15 from the electric heater 41 side. That is, the exhaust gas, as shown in FIG.
From the side to the surface 15b and flows while being in contact with the particulates P deposited on the surface 15b. Therefore, the amount of oxygen supplied to the particulate P on the filter 15 is sufficient, and the combustion heat is easily transferred to the downstream side. Therefore, most of the particulates disappear by self-combustion, which reduces the frequency of filter regeneration processing by the electric heater 41, which not only improves the durability of the electric heater 41 but also improves fuel consumption. Further, the combustion heat is less likely to be transferred from the surface 15b of the filter 15 to the back surface 15a, and the filter is reliably prevented from being melted.

Opening and closing of first and second switching valves 31, 32 and electric heater 41
Is energized by the ECU 51. ECU 51 has input port 5
2, an output port 53, a memory 54, and a central processing unit (CPU) 55, which are interconnected by a bus 56. The input port 52 is connected to the engine speed sensor 45, the accelerator position sensor 46, the back pressure sensor 47 and the exhaust temperature sensor 48, and the output port 53 is connected to the negative pressure adjusting valves 34 and 37 and the relay 42.

FIG. 6 shows a flowchart of an opening / closing control routine of the switching valves 31, 32 in the self-burning region by the ECU 51. This routine is interrupted every 100 msec.

In step 101, the engine speed is read from the engine speed sensor 45 and the accelerator opening is read from the accelerator position sensor 46. In step 102, it is determined from the engine speed and the accelerator opening degree whether or not the particulates on the filter 15 are currently in the engine state in the self-burning range. The self-combustion region is a high-load high-rotation operating region in which the engine speed is 2000 rpm or higher and the accelerator opening is 60% or higher, as indicated by reference character B in FIG. 7.

In the self-burning region, the backflow flag F is 1 in step 103.
Is set to. Backflow flag F
Is set to 1 in step 106 when the first and second bypass pipes 21 and 24 are opened and the exhaust gas flows in the direction opposite to that at the time of particulate collection (see FIGS. 3 and 4). Immediately after entering the self-burning region, the backflow flag F has not been set to 1, so the routine proceeds to step 104. Note that step 107 is also executed when F = 1 is determined in step 103.

First, at step 104, the counter C is incremented by 1. The counter C is reset to 0 in step 106, and is 0 immediately after entering the self-burning region. In step 105, it is judged whether or not the counter C exceeds a certain value, that is, whether or not 3 seconds have elapsed after entering the self-burning region. The program ends as it is before the elapse of 3 seconds, but after the elapse of 3 seconds, steps 106 and 107 are executed and the program ends.

In step 106, the first and second switching valves 31, 32 are opened, the counter C is cleared to 0, and the backflow flag F is set to 1. And exhaust gas is the third
As shown in FIG. 4 or FIG. 4, it flows into the filter 15 from the electric heater 41 side, and as shown in FIG.
Flows from the back surface 15a of 15 toward the surface 15b. The opening degree of the second switching valve 32 is determined according to the purpose. One step
At 107, the flag f is reset to 0.

When the engine state deviates from the self-combustion range, the routine proceeds from step 102 to step 111, where it is judged if the backflow flag F is set to 1. In the self-burning region, when the exhaust gas is flowing in the opposite direction to the particulate collection, the reverse flow flag F
Is set to 1, so that the routine proceeds to step 112, where it is determined whether or not the flag f is set to 1. At this time, the flag f is reset to 0 in step 107, so step 113 is executed and the timer is set and the flag f is set to 1. Step 11
At 5, it is determined whether 5 minutes have elapsed since the timer was set. Before the lapse of 5 minutes, the program ends as it is, but after 5 minutes, in step 116, the first and second switching valves 31 and 32 are set to the first and second bypass pipes 2 respectively.
1, 24 are closed, and flags F, f are reset to 0. After that, when step 111 is executed, the backflow flag F
Is reset to 0, the counter C is reset to 0 in step 114.

Then, even if the exhaust gas deviates from the self-combustion region during the reverse flow, the reverse flow is continued for 5 minutes. If the self-combustion region is reentered within the 5 minutes, that is, if the process proceeds from step 102 to step 103 before step 116 is executed again, and if the vehicle is then out of the self-combustion region, the flag f is reset to 0 in step 107. Therefore, the steps 111, 112, 113, 115 are executed in this order, and the backflow is continued for 5 minutes again.

FIG. 8 shows a flow chart of another embodiment of the opening / closing control routine of the switching valves 31, 32 in the self-burning region. This routine is interrupted every 500 msec.

When running at low speed under high load, the temperature inside the filter 15 may rise to, for example, 600 ° C. or higher, but the oxygen concentration in the exhaust gas is small at 4 to 5% or less, and the excess air ratio is too small. Particulates may not burn. In such a case, if the engine state suddenly changes to a light load state, the particulates on the filter may self-combust at once, and the filter may be melted and damaged. The control routine of FIG. 8 prevents the combustion heat of the particulates from being easily transmitted to the filter in such a case and prevents the filter from being melted.

At step 121, the exhaust gas temperature is read from the exhaust temperature sensor 48, and at step 122, it is judged if the exhaust gas temperature exceeds 550 ° C. If the exhaust gas temperature is 550 ° C. or lower, the counter T is reset to 0 in step 128 and the program ends, but if the exhaust gas temperature exceeds 550 ° C., the counter T is 0.5 in step 123.
Only added. In step 124, it is judged from the value of the counter T whether or not 5 seconds have passed since the exhaust gas temperature exceeded 550 ° C. The program ends as it is before 5 seconds have elapsed, but if 5 seconds have elapsed, the accelerator opening is read from the accelerator position sensor 46 in step 125. In step 126, it is judged whether or not the accelerator opening suddenly decreases, that is, whether or not the current accelerator opening is smaller than 1/2 of the accelerator opening one second before. If the accelerator opening does not decrease sharply, the program ends as it is, but if the accelerator opening decreases rapidly, step 127 is executed and the first and second switching valves 31, 32 are opened for 60 seconds.

Then, when the exhaust gas temperature is higher than 550 ° C. for more than 5 seconds and the accelerator opening suddenly decreases, it is determined that the particulates on the filter 15 are in the self-combustion region, The first and second bypass pipes 21 and 24 are opened. As a result, the exhaust gas flows backward and flows into the filter 15 from the electric heater 41 side, and as described above with reference to FIG. 5, combustion heat becomes difficult to transfer to the filter,
The filter is prevented from being melted.

〔The invention's effect〕

As described above, according to the present invention, when the particulates self-combust, the combustion heat of the particulates is less likely to be transmitted to the filter side, and the melting damage of the filter is reliably prevented.

[Brief description of drawings]

FIG. 1 is a block diagram of the invention, FIG. 2 is a cross-sectional view showing a particulate collection state in an embodiment apparatus of the present invention, and FIG. 3 is a cross-section showing a state in which the particulate matter is in a self-combustion area in the embodiment apparatus. 4 and 5 are sectional views showing another example of a state in which the particulates are in the self-combustion region in the self-combustion region device, FIG. 5 is an enlarged cross-sectional view of the filter, and FIG. 6 shows a switching valve opening / closing control routine. FIG. 7 is a flowchart showing a self-combustion region, and FIG. 8 is a flowchart showing another example of the switching valve opening / closing control routine. 15 ... Filter, 21, 24 ... Bypass pipe, 31, 32 ... Switching valve, 51
... control circuit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kotaro Hayashi, Inventor, Toyota Town, Toyota City, Aichi Prefecture, Toyota Motor Co., Ltd. (56) (JP, Y2) Jikkyohei 5-3695 (JP, Y2)

Claims (1)

[Claims] 1. A filter for collecting particulates contained in exhaust gas flowing in a first direction, and exhaust gas flowing in the filter in a second direction opposite to the first direction. Exhaust gas flow control means for releasing into the atmosphere, and means for determining whether or not the particulates trapped in the filter are in an engine state of self-combustion,
An exhaust emission control device for a diesel engine, wherein the exhaust gas flow control means causes the exhaust gas to flow in a second direction when the particulates are in the state of self-combustion.