JPS62162763A - Exhaust gas purifier for diesel engine - Google Patents

Abstract

PURPOSE:To permit of the perfect combustion of fuel particulates by increasing the concentration of oxygen in exhaust gas by suspending the supply of EGR when the engine load becomes less than a set load when a filter is regeneration- operated. CONSTITUTION:In an electronic control circuit 30, it is detected from the output signal of a back pressure sensor 18 if the regeneration condition for a filter 8 is established or not. When the regeneration condition is established, a bypass valve 11 is prefectly opened, and an electric heater 9 is put into electric conduction for a predetermined time. Though, except in case of the low load low revolution speed in the operation region which is represented by the stepping-in quantity of an accelerating pedal 44 which is detected by a load sensor 42 and the engine speed detected by a revolution speed sensor 40, EGR gas is supplied, the negative pressure chamber of the negative pressure diaphragm device 21 of an EGR gas control valve 22 is opened to the atmosphere in case of the low load low revolution speed in a prescribed region, and the supply of EGR gas is suspended.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to an exhaust gas purification device for a diesel engine.

[Conventional technology]

Diesel engine exhaust gas contains combustible particulates made of carbonized compounds, namely particulates.
When these particulates are released into the atmosphere, they cause air pollution. Therefore, a diesel engine is conventionally known in which a particulate collection filter is disposed in an engine exhaust passage in order to prevent particulates from being released into the atmosphere. However, in such a diesel engine, it is necessary to periodically burn and remove the particulates collected by the filter. Therefore, such diesel engines are usually equipped with an ignition device to ignite the particulates collected by the filter, and the ignition device is activated when more than a predetermined amount of particulates are collected by the filter. The filter is regenerated by igniting and burning particulates (for example, Japanese Patent Laid-Open Nos. 59-134316 and 1983-1999)
(See Publication No. 138713).

By the way, when the particulates are ignited and burned in this manner, when the combustion of the particulates becomes active, the filter is overheated, resulting in a problem that the filter is melted and damaged.

To solve this problem, the temperature of the filter is detected, and when the filter is about to overheat, the supply amount of recirculated exhaust gas (hereinafter referred to as EGR gas) is increased to reduce the oxygen concentration in the exhaust gas. A diesel engine is known in which the combustion of particulates is suppressed and the filter is prevented from overheating (Japanese Patent Laid-Open No. 59-10
(See Publication No. 1519).

[Problem that the invention seeks to solve]

However, if a large amount of EGR gas is supplied when the filter is about to overheat, the filter can be prevented from overheating, but the combustion of particulates may stop midway due to a decrease in the oxygen concentration in the exhaust gas. As a result, there are problems in that the fuel consumption rate worsens due to the increased pressure drop in the exhaust passage, or that particulates that have accumulated without being combusted continue to remain as they are without being combusted during the next regeneration operation. In particular, if a large amount of EGR gas is supplied during low-load operation, particulate combustion will stop midway because the exhaust temperature is low during low-load operation and the oxygen concentration decreases due to the supply of EGR gas. There are many cases.

[Means for solving problems]

In order to solve the above problems, the present invention includes a recirculation exhaust gas control device for controlling the amount of exhaust gas to be recirculated into the engine intake passage, and collects particulates in the engine exhaust passage. The particulate filter is equipped with an ignition device for igniting particulates collected by the filter, and when more than a predetermined amount of particulates are collected by the filter, the ignition device is activated to ignite the particulates. A diesel engine in which the filter is regenerated by combustion is equipped with a load sensor that detects the engine load, and the engine load is low load below a predetermined load during filter regeneration operation based on the output signal of the load sensor. When this happens, exhaust gas recirculation is stopped.

〔Example〕

Referring to FIG. 1, 1 indicates a diesel engine body, 2 indicates an engine-driven fuel injection pump, and 3 indicates a turbocharger. The turbocharger 3 includes an exhaust turbine 4 and an intake compressor 5, and an exhaust pipe 6 is connected to an exhaust gas outlet of the exhaust turbine 4. A filter container 7 is fixed to the exhaust pipe 6, and a filter 8 for collecting particulates is disposed within the filter container 7. Further, an electric heater 9 constituting an ignition device is arranged in the filter container 7 adjacent to the upstream end surface of the filter 8 . On the other hand, a bypass passage 10 that bypasses the filter 8 is formed in the exhaust pipe 6, and a bypass valve 11 is disposed within this bypass passage 10. This bypass valve 11 is a negative pressure diaphragm device 1
2, and its opening and closing are controlled by a negative pressure diaphragm device 12.

The negative pressure chamber 13 of the negative pressure diaphragm device 12 is connected to the electromagnetic switching valve 1
4 to either the atmosphere or a negative pressure source. Normally, that is, when the filter is not being regenerated, the negative pressure chamber 13 is open to the atmosphere, and at this time, the bypass valve 11 closes the bypass passage 10 as shown in FIG. Therefore, at this time, the exhaust gas discharged from the exhaust turbine 4 passes through the exhaust passage 15 in the exhaust pipe 6, the electric heater 9, the filter 8, and the exhaust passage 16 in the filter container 7 to the exhaust pipe 1.
It is discharged within 7 days. At this time, the electric heater 9 is not heated, and when the exhaust gas passes through the filter 8, particulates in the exhaust gas are captured by the filter 8. As the engine is used for a long period of time, the amount of particulates deposited on the filter 8 increases, and as a result, the flow resistance of the filter 8 increases.
The back pressure in the upstream exhaust passage 15 increases. As shown in FIG. 1, a back pressure sensor 18 is disposed within the exhaust passage 15, and this back pressure sensor 18 detects that the back pressure within the exhaust passage 15 has exceeded a predetermined back pressure. When this occurs, the regeneration operation of the filter 8 is started. That is, first, the electromagnetic switching valve 14 is operated, and the negative pressure chamber 13 of the negative pressure diaphragm device 12 is connected to the negative pressure source. As a result, the bypass valve 1 fully opens the bypass passage 10.

At this time, most of the exhaust gas is discharged into the exhaust pipe 17 through the bypass passage 10, and a part of the exhaust gas passes through the electric heater 9, the filter 8, and the exhaust passage 16 into the exhaust pipe 17.
discharged inside. Next, when the electric heater 9 is heated, the particulates deposited on the filter 8 closest to the electric heater 9 are first ignited, and then the flame gradually spreads downstream. Then, when all the particulates deposited on the filter 8 are burned, the regeneration operation of the filter 8 is completed.

When the regeneration operation is completed, the negative pressure chamber 13 of the negative pressure diaphragm device 12 is opened to the atmosphere again, and the bypass valve 11 closes the bypass passage IO.

As shown in FIG. 1, an exhaust manifold 19 is attached to the engine body 1, and an exhaust gas inlet of the exhaust turbine 4 is connected to an outlet portion of the exhaust manifold 19.

One end of an EGR gas supply pipe 20 is connected to the exhaust manifold 19, and the other end of the EGR gas supply pipe 20 is connected to an intake manifold (not shown). An EGR gas control valve 22 consisting of a negative pressure diaphragm device 21 is disposed within the EGR gas supply pipe 2o. The negative pressure chambers of the negative pressure diaphragm device 21 are alternately connected to the atmosphere or a negative pressure source via electromagnetic switching valves 23 at predetermined intervals. That is, if the time period during which the negative pressure chamber of the negative pressure diaphragm device 22 is connected to the negative pressure source is longer than the time period during which it is communicated with the atmosphere, the negative pressure within the negative pressure chamber increases, so that the EGR gas control valve The opening area of 22 becomes larger, thereby increasing the amount of EGR gas supplied into the intake manifold. the percentage of time that the negative pressure chamber of the negative pressure diaphragm device 22 is connected to a negative pressure source;
The duty ratio of the control pulse of the so-called electromagnetic switching valve 23 is controlled by the output signal of the electronic control unit 30. In the embodiment shown in FIG. 1, when the filter 8 is not regenerated, the supply of EGR gas is stopped during high-load engine operation, as in a normal diesel engine, and the engine load is reduced to a predetermined load. Below this, the EGR gas amount is increased as the engine load decreases.

Like the EGR gas control valve 22, the electric heater 9 and the bypass valve 11 are also controlled based on the output signal of the electronic control unit 30. As shown in FIG. 1, the electronic control unit 30 is composed of a digital computer, and includes a ROM (read only memory) 32 and a RAM (random access memory) 3 connected to each other by a bidirectional bus 31.
3, CPU (microprocessor) 34, input port 3
5 and an output boat 36. A rotation speed sensor 40 for detecting the engine rotation speed is connected to the input port 35, and a back pressure sensor 18 is further connected to the input port 35 via an AD converter 41. Further, a load sensor 42 is connected to the input port 35 via an AD converter 43.

The load sensor 42 is connected to the accelerator pedal 44, and the load sensor 42 generates a voltage proportional to the amount of depression of the accelerator pedal 44, that is, a voltage proportional to the engine load. The output boats 36 have corresponding drive circuits 45 and 4, respectively.
6 and 47 to the electromagnetic switching valve 23, electric heater 9, and electromagnetic switching valve 14.

As described above, when the particulates are ignited by the electric heater 9, the ignition flame gradually propagates downstream on the filter 8. The ease of flame propagation is related to the exhaust gas temperature and the oxygen concentration in the exhaust gas; the higher the exhaust gas temperature, the easier the flame propagation.
The higher the oxygen concentration in the exhaust gas, the easier it is to propagate.

By the way, in the low-load operating region as shown by A in Fig. 4, the exhaust temperature is low, and when a large amount of EGR gas is supplied, the oxygen concentration in the exhaust gas becomes low, causing the particulate ignition flame to ignite in the middle. It will disappear. Therefore, in the present invention, during low-load operation as shown in region A, the supply of EGR gas is stopped to increase the oxygen concentration in the exhaust gas, thereby preventing particulate combustion from stopping midway. I have to.

In addition, in FIG. 4, the vertical axis indicates the amount of depression of the accelerator pedal 44, that is, the load, and the horizontal axis NE indicates the engine speed. As shown in FIG. 4, the engine speed is approximately 3000 r.
The EGR gas supply is not stopped at low loads and high speeds such as , p, m or higher, but at such low loads and high speeds the exhaust gas temperature is high and the amount of oxygen is slightly higher than in area A, so EGR gas is not stopped. Particulates can be burned even if gas is supplied. On the other hand, when the engine speed is approximately 1000 r, p, m or less, under low load and low rotation, area A
Although the amount of oxygen is slightly higher than that in the previous example, the exhaust temperature is considerably lower, so simply stopping the supply of EGR gas may cause combustion of particulates to stop midway.

Therefore, during low-speed, low-load operation, it is preferable to increase the exhaust gas temperature by, for example, delaying the injection timing. Since the intention is to control other than EGR gas during low rotation and low load operation, the supply of EGR gas is not specifically stopped, but the supply of oil-free EGR gas can also be stopped.

Next, the regeneration control according to the present invention will be explained with reference to FIGS. 2 to 4.

FIG. 2 shows the main routine performed at every predetermined crank angle. Referring to Figure 2, first step 5
At 0, it is determined whether the reproduction condition is satisfied. As described above, this is determined from the output signal of the back pressure sensor 18, and when the back pressure becomes higher than a predetermined back pressure, it is considered that the regeneration condition is satisfied. If the reproduction conditions are met, a flag is set in step 51.

FIG. 3 shows a reproduction processing routine executed at regular intervals. Referring to FIG. 3, first, in step 60, it is determined whether a flag is set. If the flag is set, the process proceeds to step 61 where the bypass valve 11 is fully opened, and then step 62
Then, the electric heater 9 is energized for a predetermined period of time. Next, in step 63, it is determined whether or not the operating range of the engine is in the shaded area A in FIG. If it is not in region A, that is, in region B in FIG. 4, the process advances to step 64, where EGR gas supply control is performed. In other words, as mentioned above, during high engine load operation, EGR
When the gas supply is stopped and the engine load becomes lower than a predetermined constant load, the EG
The amount of R gas is increased. On the other hand, in the case of region A, the process proceeds to step 65, where the negative pressure chamber of the negative pressure diaphragm device 21 of the EGR gas control valve 22 is continuously communicated with the atmosphere, and as a result, the supply of EGR gas is stopped.

〔Effect of the invention〕

In this way, when the engine load becomes low during filter regeneration, the supply of EGR gas is stopped, so the oxygen concentration in the exhaust gas increases, and as a result, particulates can be completely combusted.

[Brief explanation of drawings]

Figure 1 is a side view of an internal combustion engine showing the engine exhaust system in cross section, Figure 2 is a flowchart showing the main routine, and Figure 3 is a flowchart showing the main routine.
The figure is a flowchart showing the regeneration processing routine, and FIG. 4 is a diagram showing the operating range in which the supply of EGR gas should be stopped. 6.17...Exhaust pipe, 8...Filter, 9.
...Electric heater, 10...Bypass passage, 1
DESCRIPTION OF SYMBOLS 1... Bypass valve, 15, 16... Exhaust passage, 22... EGR gas control valve. 6.17...Exhaust pipe 8...Filter 9...Electric heater 10...Pi/es passage 11...Bypass valve 15.16...Exhaust passage '$1 Figure 3

Claims (1)

[Claims] It is equipped with a recirculation exhaust gas control device for controlling the amount of exhaust gas to be recirculated in the engine intake passage, and a particulate collection filter is disposed in the engine exhaust passage, and the particulate matter collected by the filter is disposed in the engine exhaust passage. A diesel engine is equipped with an ignition device for igniting particulates, and when more than a predetermined amount of particulates are collected by the filter, the ignition device is activated to ignite and burn the particulates, thereby regenerating the filter. is equipped with a load sensor that detects the engine load, and stops the recirculation of exhaust gas when the engine load becomes lower than a predetermined load during filter regeneration operation based on the output signal of the load sensor. Exhaust gas purification device for diesel engine.