JP5103910B2 - Diesel engine exhaust purification system - Google Patents

Description

  The present invention relates to an exhaust emission control device for a diesel engine.

  In a diesel engine, in order to prevent fine particles (particulates) in exhaust gas from being released into the atmosphere, it is common to provide a filter for collecting the fine particles in the exhaust passage. When the amount of fine particles collected by the filter exceeds a predetermined amount, it is necessary to regenerate the filter by burning the fine particles in order to prevent clogging of the filter. In order to regenerate the filter, the high temperature generated by supporting the oxidation catalyst on the filter or disposing the oxidation catalyst in the exhaust passage upstream of the filter and burning the unburned fuel supplied to the exhaust passage with the oxidation catalyst. It is also used to burn fine particles collected by a filter (see, for example, Patent Document 1). Supply of unburned fuel to the exhaust passage for filter regeneration is performed by post-injection intended for combustion with an oxidation catalyst at a time later than the injection timing of main injection intended for combustion in the engine combustion chamber. .

Patent Document 2 discloses that when the engine is decelerated, the exhaust gas during deceleration is reduced in order to prevent the oxidation catalyst from becoming too hot due to a decrease in the flow rate of the exhaust gas that cools the oxidation catalyst. Although it is disclosed that the flow rate is increased, the technique disclosed in Patent Document 1 is different from the technique of increasing the regeneration opportunity of the filter.
JP-A-8-42326 JP 2004-190668 A

  By the way, in order to regenerate the filter, it is necessary that the engine is warmed up and the oxidation catalyst, that is, the filter is heated to a certain level. Therefore, when only short-time travel (short-distance travel) is performed and long-time travel is not performed, not only the temperature of the oxidation catalyst but also the temperature of the engine itself is not sufficiently increased, and the filter is regenerated. Opportunities to perform are very limited and the problem of filter clogging becomes serious. In particular, when the engine is decelerated, both main injection and post injection are both stopped and the filter is not regenerated. That is, even when the filter is being regenerated, if the engine deceleration is detected, the regeneration of the filter is stopped.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an exhaust emission control device for a diesel engine that can increase the chance of regeneration of a filter.

In order to achieve the above object, the following solution is adopted in the present invention. That is, as described in claim 1 in the claims,
A fuel injection valve arranged to face the combustion chamber formed in the upper part of the piston;
A filter provided in an exhaust passage of the engine for collecting particulates in the exhaust gas, and an oxidation catalyst for increasing the temperature of the filter;
When the particulate matter collected by the filter reaches a predetermined amount or more, the fuel is injected from the fuel injection valve at an oxidation catalyst at a time later than the main injection for causing combustion in the engine combustion chamber. Regenerating means for performing post-injection for performing combustion in the expansion stroke;
With
The regeneration means stops the main injection when engine deceleration is detected, and continuously advances the injection timing for a predetermined period from the start of deceleration compared to when the post injection is not decelerated. Set to run,
The injection timing of the advanced post-injection is set to the advanced angle side from the vicinity of 50 degrees after compression top dead center at the crank angle of the expansion stroke with little influence on oil dilution by fuel injection in the cylinder.
It is like that. According to the above-described solution method, the regeneration is continued for a predetermined period from the start of the deceleration even when the engine that has stopped the regeneration is currently decelerating. This is preferable for preventing clogging. In particular, for a while after the start of deceleration, the temperature of the oxidation catalyst is high, the main injection is stopped, and the oxygen concentration in the exhaust gas is high. The temperature can be maintained at a high temperature by combustion with an oxidation catalyst for the purpose.

  Further, it is preferable for preventing or reducing the problem of oil dilution due to post injection. That is, the fuel injection timing by normal post-injection is considerably delayed from the main injection so as not to be involved in combustion in the combustion chamber, so the post-injected fuel (fuel spray) reaches the inner wall of the cylinder. This causes a problem of oil dilution in which the oil adhering to the cylinder inner wall is diluted with fuel, but the in-cylinder temperature is lowered by stopping the main injection at the time of deceleration. Even if the injection timing is advanced, combustion is not performed in the combustion chamber, and the post-injected fuel can be reliably supplied to the exhaust passage as unburned fuel while preventing or reducing the problem of oil dilution. It becomes possible.

  Furthermore, the injection timing of the post injection can be advanced sufficiently to prevent or reduce the problem of oil dilution more reliably.

A preferred mode based on the above solution is as described in claim 2 and the following claims. That is,
The regeneration means increases the amount of post-injection during the predetermined period as compared with the case where the post-injection is not decelerated (corresponding to claim 2). In this case, since the injection timing of the post injection is advanced, even if the injection amount of the post injection is increased, the amount of unburned fuel supplied to the exhaust passage is increased while preventing or reducing the problem of oil dilution. Thus, filter regeneration can be performed more effectively.

  The regeneration means is set to execute the post-injection during deceleration on condition that the temperature of the oxidation catalyst is equal to or higher than a predetermined temperature (corresponding to claim 3). In this case, in a situation where it is difficult for the oxidation catalyst to sufficiently burn unburned fuel at a low temperature while effectively regenerating the filter by executing post injection only when the temperature of the oxidation catalyst is high. By not performing post-injection, it is possible to prevent a situation where fuel is consumed wastefully.

  According to the present invention, the opportunity for regeneration of the filter is increased, which is preferable for preventing clogging of the filter.

  In FIG. 1, E is a multi-cylinder diesel engine (engine body), 1 is a cylinder block, 2 is a cylinder head, 3 is a piston, and 4 is a combustion chamber. An intake port 5 and an exhaust port 6 are formed in the cylinder head 2. The intake port 5 is opened and closed by an intake valve 7, and the exhaust port 6 is opened and closed by an exhaust valve 8. Further, a fuel injection valve 9 is disposed on the cylinder head 2 so as to face the combustion chamber 4.

  The intake passage 11 connected to the intake port 5 has a surge tank 12 in the middle thereof. The intake passage on the upstream side of the surge tank 12 is formed as one common intake passage 11A. The common intake passage 11A is sequentially arranged from the upstream side to the downstream side, from the air cleaner 13, the intake air amount sensor 14, and the exhaust turbo-type supercharger. A compressor wheel 15a, an intercooler 16, an intake throttle valve 17, an intake air temperature sensor 18, and an intake pressure sensor 19 of the machine 15 are disposed. The intake passage on the downstream side of the surge tank 12 is an independent intake passage 11B that is individually connected to each cylinder.

  In the exhaust passage 21 connected to the exhaust port 6 (a common exhaust passage where independent exhaust passages from each cylinder are joined), the turbine wheel 15b of the exhaust turbocharger 15 and the oxidation catalyst are sequentially arranged from the upstream side to the downstream side. 22, a pressure sensor 23, a filter 24 for collecting fine particles, a pressure sensor 25, a temperature sensor 26, and an oxygen concentration sensor 27 are provided.

  The fuel injection valve 9 performs fuel injection at a high pressure. For this reason, a common rail 32 storing high-pressure fuel from the fuel pump 31 is provided, and fuel is supplied to the common rail 32 via a fuel pipe 33. An injection valve 9 is connected. In FIG. 1, 34 is an engine speed sensor, 35 is a crank angle sensor, and 36 is an engine coolant temperature sensor.

  The intake passage 11 and the exhaust passage 21 are connected via an EGR passage 41. The connection part of the EGR passage 41 to the intake passage 11 is set between the intake pressure sensor 19 and the surge tank 12. Further, the connection portion of the EGR passage 41 to the exhaust passage 21 is set on the upstream side (exhaust port 6 side) of the turbine wheel 15b. An EGR cooler 42 and an EGR valve 43 are connected to the EGR passage 41.

  FIG. 2 is a block diagram showing a control system for performing control related to the regeneration of the filter 24, and U is a controller (control unit) configured using a microcomputer. In addition to the signals from the various sensors 23, 25, 26, and 34 to 36 described above, a signal from an accelerator opening sensor 45 that detects the accelerator opening is input to the controller U. Further, the controller U controls the fuel injection valve 9, the intake throttle valve 17, and the EGR valve 43. In FIG. 2, the input / output relations of parts not directly related to the regeneration of the filter 24 are omitted.

  The controller U determines the amount of particulates collected by the filter 24 based on the differential pressure between the pressure detected by the exhaust pressure sensor 23 and the pressure detected by the exhaust pressure sensor 25.

  The fuel injection control by the controller U is executed as follows, for example. First, when the amount of particulates collected by the filter 24 is less than a predetermined amount (for example, 70% of the maximum amount of collection), only main injection is performed to actively supply unburned fuel to the exhaust passage. Post injection is not performed. The fuel injection timing of the main injection is a timing at which the injected fuel is burned in the combustion chamber 4. The fuel injection amount in the main injection is basically determined by the accelerator opening and the engine speed, and then corrected by the cooling water temperature, the intake air temperature, etc., to obtain the final injection amount. Fuel is injected from the fuel injection valve 9 in an amount. In the embodiment, as shown in FIG. 4, a small amount of pilot injection is executed before the main injection, and the total injection amount of the pilot injection and the main injection in FIG. (When there is no pilot injection, the final injection amount is all the main injection amount).

When the amount collected by the filter 24 exceeds a predetermined amount, post injection is performed to regenerate the filter 24. As a regeneration execution condition, for example, the engine coolant temperature is equal to or higher than a predetermined temperature (for example, 60 degrees C). You can also set conditions like this. A mode of post-injection when not decelerating is shown in FIG. In the embodiment shown in FIG. 4, the post injection is executed in the expansion stroke (that is, the timing not related to the combustion in the combustion chamber 4), and divided injection divided into three times from the post injection 1 to the post injection 3 is performed. It is said that. The fuel injected by this post-injection is not burned in the combustion chamber 4 but is supplied as it is to the exhaust passage 21 and burned by the oxidation catalyst 22. The exhaust gas introduced into the filter 24 has a sufficiently high temperature due to combustion in the oxidation catalyst 22, and the particulates collected in the filter 24 are burned, and the filter 24 is regenerated. . The injection amount in the post injection may be controlled to be open based on, for example, the accelerator opening and the engine speed, or feedback controlled so that the oxygen concentration detected by the oxygen concentration sensor 27 becomes the target oxygen concentration. may be, such an open control and feedback control and may also be selectively used depending on the temperature detected by the temperature sensor 26 (temperature predetermined temperature detected by the temperature sensor 26 Select feedback control when above).

  When engine deceleration is detected during the regeneration of the filter 24 described above, the following fuel injection control is executed, but the intake throttle valve 17 and the EGR valve 43 are each fully closed. First, main injection is stopped so that combustion in the combustion chamber 4 is not performed (when pilot injection is being performed, pilot injection is also stopped). Then, post injection is continuously executed for a predetermined period from the start of deceleration. The predetermined period can be set to a predetermined time (for example, 40 seconds) set in advance from the detection of deceleration.

  Further, as a post injection execution condition at the time of deceleration, a condition is set such that the temperature detected by the temperature sensor 26 (corresponding to the temperature of the oxidation catalyst 22 and the filter 24) is equal to or higher than a predetermined temperature. More specifically, as shown in FIG. 3, when the predetermined temperature is changed using the engine speed as a parameter and the engine speed is less than a predetermined speed (in the embodiment, about 2500 rpm), a substantially constant value of about 260 is obtained. When the engine speed is equal to or greater than the predetermined rotational speed, the predetermined temperature is gradually increased as the engine rotational speed increases. When the temperature detected by the temperature sensor 26 is lower than the predetermined temperature, the post-injection is not executed even if other execution conditions are satisfied.

  As shown in FIG. 5, post-injection at the time of deceleration is divided into three divided injections as in the case other than at the time of deceleration, but each of the post-injections divided into three has an injection timing respectively. It is advanced and corrected to increase. In the embodiment, the injection timing after the advance angle is set to the advance angle side from the vicinity of 50 degrees after the compression top dead center in the crank angle. In the post-injection at the advanced timing, the amount of fuel injected from the fuel injection valve 9 (fuel spray) does not reach the inner wall of the cylinder or is very small even if it reaches the cylinder inner wall. Dilution will be prevented or reduced.

  The increase in the injection amount by the post injection is to increase the combustion temperature of the oxidation catalyst 22 and to regenerate the filter 24 more effectively. The injection amount corresponding to the increased amount can be determined, for example, using the engine speed as a parameter.

  During the regeneration of the filter 24 by post injection during engine deceleration, the post injection is stopped when the predetermined period elapses or when the temperature detected by the temperature sensor 26 is lower than the predetermined temperature shown in FIG. (A state where both the main injection and the post injection are stopped).

  FIG. 6 is a flowchart showing an example of control for regenerating the filter 24 at the time of deceleration described above. This flowchart will be described below. In the following description, S indicates a step. First, after data is input in S1, the main injection amount is determined in S2. Thereafter, in S3, the amount of particulates collected by the filter 24 is determined (estimated) based on the differential pressure between the detected values of the two pressure sensors 23 and 25.

  After S3, in S4, it is determined whether or not the amount of collected fine particles determined in S3 is less than a first predetermined amount β (set to a value close to 0 in the embodiment). If YES in S4, the regeneration flag is reset to 0 in S5, the main injection is executed in S6, and the process for stopping the post-injection is performed in S7. .

  If the determination in S4 is NO, it is determined in S8 whether or not the collection amount determined in S3 is equal to or greater than a second predetermined amount α (for example, 70% of the maximum collection amount). If the determination in S8 is YES, it is time to regenerate the filter 24. In this case, first, the regeneration flag is set to 1 in S9. Thereafter, in S11, it is determined whether or not the vehicle is decelerating. The determination in S11 is, for example, determined that the vehicle is decelerating when the accelerator opening is zero and the engine rotational speed is equal to or higher than a predetermined rotational speed (for example, a rotational speed slightly higher than the idle rotational speed).

  When the determination at S11 is NO, that is, when it is determined that the vehicle is not decelerating, fuel injection at the normal time shown in FIG. 4 is executed by the processing at S12 and S13 (both main injection and post injection). With fuel injection).

  When the determination in S11 is YES, that is, when it is determined that the vehicle is decelerating, the main injection is stopped in S14. Thereafter, in S15, it is determined whether or not it is within a predetermined period from the detection of deceleration. If YES in S15, it is determined in S16 whether the temperature detected by the temperature sensor 26, that is, the temperature of the oxidation catalyst 22 or the filter 24 is equal to or higher than a predetermined temperature γ (predetermined temperature shown in FIG. 3). Is done. If YES in S16, post-injection is executed in S17, and the injection timing is advanced and the injection amount is corrected to increase.

  When the determination at S15 is NO or when the determination at S16 is NO, the process proceeds to S7 and the post injection is stopped.

If the determination in S8 is NO, it is determined in S10 whether or not the regeneration flag is 1. If the determination in S10 is YES, the process proceeds to S11. If the determination in S10 is NO, the process proceeds to S5.

  Although the embodiment has been described above, the present invention is not limited to the embodiment, and can be appropriately changed within the scope described in the scope of claims. For example, the invention includes the following cases. . The post-injection may be performed only once, and when the divided injection is performed, the number of divisions can be appropriately changed. The predetermined period from the deceleration detection for performing post injection can be changed according to appropriate parameters such as the engine speed and the engine coolant temperature at the time of deceleration detection (for example, the higher the coolant temperature, The longer the engine speed, the longer the predetermined period). Post-injection at the time of deceleration may not be advanced, or increase correction may not be performed. The oxidation catalyst 22 may be provided integrally with the filter 24 by being carried on the filter 24 without being provided separately from the filter 24. Each step or group of steps shown in the flowchart can be expressed by adding a letter of means to a name indicating the function content. Of course, the object of the present invention is not limited to what is explicitly stated, but also implicitly includes providing what is substantially preferred or expressed as an advantage.

1 is an overall system diagram of an engine to which the present invention is applied. The block diagram which shows the example of a control system by this invention. The characteristic view which shows the temperature of the oxidation catalyst when performing post injection at the time of deceleration. The figure which shows an example of the fuel-injection aspect when performing filter reproduction | regeneration in normal time. The figure which shows an example of the fuel-injection aspect when performing filter reproduction | regeneration at the time of deceleration. The flowchart which shows the example of control of this invention.

E: Engine body U: Controller 4: Combustion chamber 9: Fuel injection valve 11: Intake passage 21: Exhaust passage 22: Oxidation catalyst 23: Exhaust pressure sensor 24: Filter 25: Exhaust pressure sensor 26: Exhaust temperature sensor

Claims (3)

A fuel injection valve arranged to face the combustion chamber formed in the upper part of the piston;
A filter provided in an exhaust passage of the engine for collecting particulates in the exhaust gas, and an oxidation catalyst for increasing the temperature of the filter;
When the particulate matter collected by the filter reaches a predetermined amount or more, the fuel is injected from the fuel injection valve at an oxidation catalyst at a time later than the main injection for causing combustion in the engine combustion chamber. Regenerating means for performing post-injection for performing combustion in the expansion stroke;
With
The regeneration means stops the main injection when engine deceleration is detected, and continuously advances the injection timing for a predetermined period from the start of deceleration compared to when the post injection is not decelerated. Set to run,
The injection timing of the advanced post-injection is set to the advanced angle side from the vicinity of 50 degrees after compression top dead center at the crank angle of the expansion stroke with little influence on oil dilution by fuel injection in the cylinder.
An exhaust emission control device for a diesel engine. In claim 1,
The exhaust gas purification apparatus for a diesel engine, wherein the regeneration means increases the injection amount of the post-injection in the predetermined period as compared to a case where the post-injection is not decelerated. In claim 1 or claim 2,
The exhaust gas purification apparatus for a diesel engine, wherein the regeneration means is set to execute the post-injection during deceleration on condition that the temperature of the oxidation catalyst is equal to or higher than a predetermined temperature.

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