JP2010209899A - Exhaust emission control system for diesel engine and method of regenerating exhaust gas filter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control system for a diesel engine reducing the total fuel and time required for forcible regeneration. <P>SOLUTION: The exhaust emission control system for the diesel engine is provided in an exhaust passage 14 of the diesel engine, collects particulate matter in exhaust gas of the diesel engine, and uses a filter 16 carrying a catalyst for removing the collected particulate matter. An intake air supply means is provided for feeding air of an intake system of the diesel engine to a point 14B of the exhaust passage 14 further upstream of exhaust gas flow than the filter 16. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification system for a diesel engine and an exhaust gas filter regeneration method.

  Diesel engines are widely used in work machines such as construction machines, but the exhaust gas of diesel engines contains particulate matter. In order to collect the particulate matter, a filter (Diesel Particlate Filter, DPF) is used.

  This filter includes a continuous regeneration type filter. Continuously regenerating filters have both a function to collect particulate matter and a function to continuously regenerate the filter by oxidizing and removing the collected particulate matter by the action of a catalyst. An oxidation catalyst is supported on ceramics. For this reason, the particulate matter collected by the continuous regeneration type filter is continuously oxidized and removed by the action of the catalyst, and the filter is self-regenerated.

  However, this self-regeneration is not always performed satisfactorily. For example, when the engine load is small and the exhaust gas temperature does not rise sufficiently as in an idling state, the self-regeneration is insufficient, and particulate matter is contained in the filter. It will gradually accumulate. When the amount of particulate matter deposited on the filter increases, the resistance when the exhaust gas passes through the filter increases, the pressure of the exhaust system increases, and the original performance of the engine cannot be obtained. For this reason, it is necessary to perform forced regeneration to forcibly remove the particulate matter deposited on the filter.

  In forced regeneration, for example, apart from normal fuel injection timing (near the top dead center of the compression stroke), post-injection (post-injection) is performed to inject fuel into the combustion chamber in the cylinder immediately before the exhaust valve closes. Is made by The fuel supplied by post-injection (post-injection) is discharged out of the combustion chamber without being burned, supplied to the oxidation catalyst, and oxidized (combusted). The temperature of the filter rises due to the heat of oxidation reaction at this time, the particulate matter collected by the filter is burned and removed, and the filter is regenerated.

  On the other hand, if forced regeneration is performed after the amount of particulate matter trapped in the filter becomes too large, the amount of heat generated by the combustion of the particulate matter becomes excessive and the temperature of the filter rises too much. There is a problem that the durability of the catalyst is deteriorated and the oxidation catalyst supported on the filter is thermally deteriorated.

  On the other hand, Patent Document 1 discloses a technique for accurately estimating the amount of particulate matter collected by a filter. If this technique is used, particulate matter is excessively collected by the filter. Therefore, it is possible to perform forced regeneration before starting, and it is possible to prevent the temperature of the filter from excessively rising during forced regeneration.

JP 2005-90358 A

  However, the technique disclosed in Patent Document 1 is a technique for performing forced regeneration before particulate matter is excessively collected by the filter, and the total fuel and time required for forced regeneration are not reduced. For this reason, other harmful effects caused by forced regeneration, such as excessive fuel consumption and early deterioration of engine oil, have not been improved.

  The present invention has been made in view of such problems, and provides a diesel engine exhaust gas purification system and an exhaust gas filter regeneration method capable of reducing the total fuel and time required for forced regeneration. Is an issue.

  An exhaust gas purification system for a diesel engine according to the present invention is provided in an exhaust passage of the diesel engine, collects particulate matter in the exhaust gas of the diesel engine, and removes the collected particulate matter. In an exhaust gas purification system for a diesel engine using a filter carrying a catalyst for the intake air supply means for feeding air in the intake system of the diesel engine to a point of the exhaust passage upstream of the exhaust gas flow from the filter By solving this problem, the above-mentioned problems are solved.

  In the present invention, there is provided intake air supply means for supplying intake system air of the diesel engine to a point of the exhaust passage upstream of the filter from the exhaust gas flow. For this reason, oxygen can be supplied to the filter in abundance, the combustion rate of the particulate matter can be increased, and the ignition temperature of the particulate matter deposited on the filter can be lowered to reduce the particulate matter even at a lower temperature. The combustion of the substance can be promoted. For this reason, the particulate matter deposited on the filter can be efficiently oxidized and removed, and the total fuel and time required for the forced regeneration can be reduced. In some cases, post injection can be omitted or reduced in forced regeneration.

  Therefore, according to the present invention, adverse effects caused by forced regeneration (excessive fuel consumption, early deterioration of engine oil, etc.) can be improved.

  The exhaust gas purification system further includes a pressure sensor for detecting a pressure difference between both surfaces of the filter, and the intake air supply means when the detected pressure difference is a predetermined pressure difference or more. The air may be sent to the point of the exhaust passage on the upstream side.

  The exhaust gas purification system further includes a temperature sensor that detects a temperature of the exhaust gas of the diesel engine, and when the detected temperature of the exhaust gas is equal to or lower than a predetermined temperature, the intake air supply You may comprise so that the said air may be sent to the point of the said exhaust passage of the said upstream using a means.

  The exhaust gas purification system further includes a timer for detecting a cumulative operating time of the diesel engine, so that the diesel supplied from the air supply to the point or the previous post-injection by the intake air supply means can be provided. When the timer detects that the accumulated operating time of the engine has reached a predetermined time, the air may be supplied to the point by the intake air supply means.

  The intake air supply means can be configured to include a short-circuit passage with an on-off valve that short-circuits the intake passage and the exhaust passage of the diesel engine. When the diesel engine includes a turbocharger, Intake system air pressurized by the charger is sent to the exhaust passage through the short-circuit passage.

  In other words, the present invention is provided in the exhaust passage of a diesel engine to collect particulate matter in the exhaust gas of the diesel engine and to carry a catalyst for removing the collected particulate matter. In a method for regenerating an exhaust gas filter of a diesel engine using the filter, the diesel engine intake system air is sent to a point of the exhaust passage upstream of the filter in the flow of exhaust gas. It can also be regarded as a regeneration method of the exhaust gas filter.

  In the method for regenerating the exhaust gas filter, the air may be sent to the point, and post injection may be used in combination.

  According to the present invention, the total fuel and time required for forced regeneration can be reduced, and further, post injection may be omitted or reduced in forced regeneration. For this reason, adverse effects caused by the forced regeneration, for example, excessive fuel consumption and early deterioration of the engine oil can be improved.

The figure which shows the structure of the exhaust-gas purification system of the diesel engine which concerns on embodiment of this invention.

  Hereinafter, an example of a preferred embodiment of an exhaust gas purification system for a diesel engine according to the present invention will be described in detail based on the drawings.

  FIG. 1 is a diagram showing a configuration of an exhaust gas purification system for a diesel engine according to an embodiment of the present invention.

  The exhaust gas purification system 10 includes an intake passage 12, an exhaust passage 14, a filter 16, an oxidation catalyst 18, and a short-circuit passage 20 that short-circuits the intake passage 12 and the exhaust passage 14.

  The intake passage 12 is a passage through which air (air) is sent to the diesel engine 50, and the air sent to the diesel engine 50 through the intake passage 12 is pressurized by the turbocharger 24. In the middle of the intake passage 12, an intercooler 26 is provided for cooling the air that has been pressurized by the turbocharger 24 to a high temperature.

  The exhaust passage 14 is a passage for exhausting exhaust gas from the diesel engine 50. A muffler 14A is provided in the middle of the exhaust passage 14, and a filter 16 and an oxidation catalyst 18 are provided in the muffler 14A. The oxidation catalyst 18 is provided upstream of the filter 16 in the exhaust gas flow. The muffler 14A is also a part of the exhaust passage 14.

  The filter 16 is a continuous regeneration type filter, and has both a function of collecting particulate matter and a function of continuously removing the collected particulate matter by oxidation by the action of a catalyst. For example, an oxidation catalyst is supported on porous ceramics. For this reason, the particulate matter collected by the filter 16 is continuously oxidized and removed by the action of the catalyst supported on the filter 16, and the filter 16 is self-regenerated.

  The oxidation catalyst 18 has a role of increasing the temperature of the filter 16 by oxidizing (combusting) the fuel supplied by post injection (post injection) to increase the exhaust gas temperature. Thereby, the particulate matter collected by the filter 16 is burned and removed, and the filter 16 is regenerated.

  The short-circuit passage 20 is a passage branched from the intake passage 12, and short-circuits the point 12A of the intake passage 12 between the turbocharger 24 and the intercooler 26 and the point 14B upstream of the muffler 14A of the exhaust passage 14. The air that is pressurized by the turbocharger 24 is introduced into a point 14B upstream of the muffler 14A in the exhaust passage 14 to burn the particulate matter collected by the filter 16 Has a role to supply abundantly. An open / close valve 22 for controlling the communication of the short circuit passage 20 is provided at a midpoint of the short circuit passage 20, and the amount of air (oxygen amount) supplied to the exhaust passage 14 by adjusting the opening degree of the open / close valve 22. ) Can be adjusted.

  Pressure sensors 28 and 30 are provided on both sides of the filter 16 (upstream and downstream of the exhaust gas flow), respectively. The upstream pressure sensor 28 has a role of measuring the pressure of the exhaust gas flowing into the filter 16, and the downstream pressure sensor 30 has a role of measuring the pressure of the exhaust gas after passing through the filter 16. The pressure data measured by the pressure sensors 28 and 30 is sent to the controller 52 via the electric signal lines 60 and 62.

  Temperature sensors 32 and 34 are provided on both sides of the oxidation catalyst 18 (upstream and downstream of the exhaust gas flow), respectively. The upstream temperature sensor 32 has a role of measuring the temperature of the exhaust gas flowing into the oxidation catalyst 18, and the downstream temperature sensor 34 has a role of measuring the temperature of the exhaust gas flowing into the filter 16. The temperature data measured by the temperature sensors 32 and 34 is sent to the controller 52 via the electric signal lines 64 and 66.

  The controller 52 calculates the pressure difference between both surfaces of the filter 16 based on the pressure data measured by the pressure sensors 28 and 30. When the amount of particulate matter deposited on the filter 16 increases, the resistance when the exhaust gas passes through the filter 16 increases, and the pressure on the downstream side of the filter 16 becomes smaller than the pressure on the upstream side of the filter 16. Therefore, the controller 52 determines that the particulate matter is excessively deposited on the filter 16 when the pressure difference between both surfaces of the filter 16 becomes larger than the predetermined pressure difference.

  The controller 52 calculates the temperature of the exhaust gas flowing into the oxidation catalyst 18 based on the temperature data measured by the upstream temperature sensor 32, and the exhaust gas flowing into the filter 16 based on the temperature data measured by the downstream temperature sensor 34. Calculate the temperature of the gas.

  Further, the controller 52 controls the opening degree of the opening / closing valve 22 via the electric signal line 70 to adjust the degree of communication of the short-circuit passage 20, and the amount of air (oxygen) flowing into the exhaust passage 14 via the short-circuit passage 20. The amount) can be adjusted. Specifically, for example, when the pressure difference between both surfaces of the filter 16 calculated based on the pressure data measured by the pressure sensors 28 and 30 is equal to or larger than a predetermined pressure difference, the open / close valve 22 is connected via the electric signal line 70. A command is issued, the opening degree is increased, and the air of the intake system of the diesel engine 50 is sent to the point 14B of the exhaust passage 14 upstream of the filter 16 and the oxidation catalyst 18. Further, for example, when the temperature calculated based on the temperature data measured by the temperature sensor 34 (the temperature of the exhaust gas flowing into the filter 16) is equal to or lower than a predetermined temperature, a command is given to the on-off valve 22 via the electric signal line 70. The opening of the diesel engine 50 is increased and the intake system air of the diesel engine 50 is sent to the point 14B of the exhaust passage 14 upstream of the filter 16 and the oxidation catalyst 18. As a result, the amount of air (oxygen amount) flowing into the exhaust passage 14 increases, the ignition temperature of the particulate matter deposited on the filter 16 decreases, the combustion speed of the particulate matter increases, and the particulate matter is efficiently Burn.

  Further, the controller 52 can control the fuel injection device 54 via the electric signal line 68 to perform post injection. In order to burn and remove the particulate matter deposited on the filter 16, the temperature of the exhaust gas flowing into the filter 16 needs to be higher than the combustion temperature of the particulate matter. Supplying abundant oxygen to the passage 14 to lower the combustion temperature of the particulate matter deposited on the filter 16 and to further increase the temperature of the exhaust gas flowing into the filter 16 by using post injection according to the situation. Thus, the combustion of the particulate matter deposited on the filter 16 can be started smoothly. The controller 52 performs post injection if necessary according to the temperature of the exhaust gas flowing into the filter 16 (the temperature of the exhaust gas calculated based on the temperature data measured by the temperature sensor 34 on the downstream side). The temperature of the exhaust gas flowing into the filter 16 is raised above the combustion temperature of the particulate matter deposited on the filter 16.

  Here, in order for the post-injected fuel to be efficiently oxidized (combusted) in the oxidation catalyst 18, the temperature of the exhaust gas flowing into the oxidation catalyst 18 needs to be higher than the activation temperature of the oxidation catalyst 18. . Therefore, the controller 52 controls the fuel injection device 54 via the electric signal line 68 and the temperature of the exhaust gas flowing into the oxidation catalyst 18 (the exhaust gas calculated based on the temperature data measured by the upstream temperature sensor 32). Multi-injection (multi-stage injection) is performed according to the temperature), and the temperature of the exhaust gas flowing into the oxidation catalyst 18 can be raised.

  As described above, in the present embodiment, the diesel engine 50 is connected to the point 14B of the exhaust passage 14 upstream of the filter 16 by the short-circuit passage 20, the intake passage 12, and the turbocharger 24. Intake system air is supplied. Therefore, the intake air supply means for supplying the air of the intake system of the diesel engine 50 to the point 14B of the exhaust passage 14 upstream of the filter 16 by the short-circuit passage 20, the intake passage 12, and the turbocharger 24. It will be configured.

  Next, the operation of the exhaust gas purification system 10 according to this embodiment will be described.

  Air that has been pressurized by the turbocharger 24 is supplied to the diesel engine 50 through the intake passage 12 and fuel is supplied from the fuel injection device 54. Thereby, the diesel engine 50 operates. When the diesel engine 50 is operated, exhaust gas is discharged from the diesel engine 50. This exhaust gas first rotates the turbine of the turbocharger 24 at high speed. Thereby, the turbocharger 24 pressurizes the air supplied to the diesel engine 50 via the intake passage 12. The exhaust gas that has passed through the turbocharger 24 is discharged to the outside through the exhaust passage 14 and the muffler 14A. Since the oxidation catalyst 18 and the filter 16 are disposed in the muffler 14A, the exhaust gas passes through the oxidation catalyst 18 and the filter 16.

  As described above, the exhaust gas discharged from the diesel engine 50 contains particulate matter, and the particulate matter is collected by the filter 16 and deposited on the filter 16. When the amount of particulate matter deposited on the filter 16 increases, the resistance when the exhaust gas passes through the filter 16 increases, the pressure of the exhaust system increases, and the original performance of the diesel engine 50 cannot be obtained. .

  Therefore, when the pressure difference between both surfaces of the filter 16 exceeds a predetermined pressure difference, the controller 52 increases the opening degree of the opening / closing valve 22 and increases the amount of air (oxygen amount) supplied to the exhaust passage 14. The particulate matter deposited on 16 is removed by combustion. In addition, post injection is performed as necessary.

  When performing post-injection, the controller 52 first controls the fuel injection device 54 to perform multi-injection (multi-stage injection) to raise the temperature of the exhaust gas. When it is confirmed by the temperature data measured by the temperature sensor 32 that the temperature of the exhaust gas flowing into the oxidation catalyst 18 has risen above the activation temperature of the oxidation catalyst 18, the controller 52 controls the fuel injection device 54 to perform post injection. Accordingly, the exhaust gas temperature is further raised, and the degree of communication of the short-circuit passage 20 is increased by increasing the opening degree of the opening / closing valve 22 in accordance with the post injection, and the amount of air (oxygen amount) supplied to the exhaust passage 14 To lower the ignition temperature of the particulate matter. Thereby, combustion of a particulate matter starts smoothly. Moreover, since oxygen is supplied in abundance, the burning rate of the particulate matter increases.

  Thereby, the particulate matter deposited on the filter 16 is efficiently burned and removed, and the total fuel and time required for forced regeneration can be reduced. As a result, adverse effects (such as excessive fuel consumption and early deterioration of engine oil) caused by forced regeneration can be improved. The temperature of the exhaust gas flowing into the filter 16 is confirmed based on the temperature data measured by the temperature sensor 34.

  When performing post injection in forced regeneration, the amount of oxygen (amount of oxygen) supplied to the exhaust passage 14 is increased by increasing the opening of the open / close valve 22 in accordance with the post injection, and the combustion speed of the particulate matter is increased. The total fuel and time required for forced regeneration can be reduced, but the opening of the on-off valve 22 is increased from the stage before forced regeneration, and the amount of air (oxygen amount) supplied to the exhaust passage 14 To lower the ignition temperature of the particulate matter so that the combustion of the particulate matter is promoted even at a lower temperature to prevent the particulate matter from being deposited on the filter 16 in advance. . In this case, the timing of increasing the opening degree of the opening / closing valve 22 and increasing the amount of air (oxygen amount) supplied to the exhaust passage 14 is applied to the filter 16 calculated based on the temperature data measured by the temperature sensor 34, for example. The temperature of the exhaust gas flowing in can be set to be a predetermined temperature or lower.

  The amount of air (oxygen amount) supplied to the exhaust passage 14 is increased to lower the ignition temperature of the particulate matter, and the combustion of the particulate matter is promoted even at a lower temperature, thereby flowing into the filter 16. Even if the temperature of the exhaust gas is relatively low, the particulate matter deposited on the filter 16 is burned and removed, and the particulate matter is prevented from being deposited on the filter 16 beforehand. As a result, the frequency of forced regeneration can be reduced, and the total fuel and time required for forced regeneration can be reduced. Further, by promoting the combustion of the particulate matter even at a lower temperature, for example, when the exhaust gas temperature is higher than a certain level, post injection can be omitted or reduced in forced regeneration. As a result, adverse effects (such as excessive fuel consumption and early deterioration of engine oil) caused by forced regeneration can be improved.

  In the embodiment described above, the air (oxygen) pressurized by the turbocharger 24 is supplied from the intake passage 12 to the exhaust passage 14 via the short-circuit passage 20. The turbocharger 24 may not be used. However, in this case, the air in the intake system does not actively (in a pressurized state) toward the filter 16, and therefore, for example, the open / close valve 22 is always open to constantly (weak) air. It is good to set it as the control aspect which supplies.

  Further, a timer for detecting the cumulative operating time of the diesel engine 50 is further provided, and the cumulative amount of the diesel engine 50 after the opening amount of the opening / closing valve 22 is increased to increase the amount of air (oxygen amount) supplied to the exhaust passage 14. When the timer detects that the operation time or the accumulated operation time of the diesel engine 50 from the previous post-injection has reached a predetermined time, the controller 52 commands the open / close valve 22 via the electric signal line 70. Alternatively, the opening degree of the opening / closing valve 22 may be increased to increase the amount of air (oxygen amount) supplied to the exhaust passage 14. As a result, the particulate matter collected by the filter 16 is periodically promoted to be burned and removed by the catalyst supported on the filter 16, and the particulate matter is prevented from being deposited on the filter 16 beforehand. It becomes.

  For example, it can be suitably used for a construction work machine using a diesel engine.

DESCRIPTION OF SYMBOLS 10 ... Exhaust gas purification system 12 ... Intake passage 14 ... Exhaust passage 14A ... Muffler 16 ... Filter 18 ... Oxidation catalyst 20 ... Short-circuit passage 22 ... Open / close valve 24 ... Turbocharger 26 ... Intercooler 28, 30 ... Pressure sensor 32, 34 ... Temperature sensor 50 ... Diesel engine 52 ... Controller 54 ... Fuel injection device 60, 62, 64, 66, 68, 70 ... Electric signal line

Claims (8)

Diesel engine exhaust using a filter provided in an exhaust passage of a diesel engine for collecting particulate matter in the exhaust gas of the diesel engine and carrying a catalyst for removing the collected particulate matter In the gas purification system,
An exhaust gas purification system for a diesel engine, comprising intake air supply means for feeding intake system air of the diesel engine to a point of the exhaust passage upstream of the exhaust gas flow from the filter. In claim 1,
Furthermore, a pressure sensor for detecting a pressure difference between both surfaces of the filter is provided,
An exhaust gas purification system for a diesel engine, wherein when the detected pressure difference is equal to or greater than a predetermined pressure difference, the air is sent to a point in the exhaust passage on the upstream side using the intake air supply means. . In claim 1 or 2,
Furthermore, a temperature sensor for detecting the temperature of the exhaust gas of the diesel engine is provided,
When the detected temperature of the exhaust gas is equal to or lower than a predetermined temperature, exhaust air purification of a diesel engine, wherein the air is sent to a point of the upstream exhaust passage using the intake air supply means system. In any one of Claims 1-3,
Furthermore, a timer for detecting the cumulative operating time of the diesel engine is provided,
The intake air supply means when the timer detects that the air supply to the point by the intake air supply means or the cumulative operating time of the diesel engine from the previous post-injection has reached a predetermined time An exhaust gas purification system for a diesel engine, characterized in that the air is supplied to the point. In any one of Claims 1-4,
The exhaust gas purification system for a diesel engine, wherein the intake air supply means includes a short-circuit passage with an on-off valve that short-circuits the intake passage and the exhaust passage of the diesel engine. In claim 5,
The diesel engine comprises a turbocharger;
An exhaust gas purification system for a diesel engine, wherein air in an intake system pressurized by the turbocharger is sent to the exhaust passage through the short-circuit passage. Diesel engine exhaust using a filter provided in an exhaust passage of a diesel engine for collecting particulate matter in exhaust gas of the diesel engine and carrying a catalyst for removing the collected particulate matter In the regeneration method of the gas filter,
A method for regenerating an exhaust gas filter of a diesel engine, characterized in that air in an intake system of the diesel engine is sent to a point of the exhaust passage upstream of the flow of exhaust gas from the filter. In claim 7,
A method for regenerating an exhaust gas filter of a diesel engine, wherein the air is sent to the point and further post injection is used together.

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