JP4346989B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

  The present invention relates to a filter provided in an exhaust system of an internal combustion engine such as a diesel engine, for collecting particulates in the exhaust, a catalyst provided on the upstream side of the filter or in the filter, and the particulates collected in the filter. The present invention relates to an exhaust gas purification apparatus for an internal combustion engine, which includes a regenerating unit that regenerates a filter by removing gas.

  Generally, when particulates (hereinafter referred to as “PM”) are clogged in this type of filter, exhaust pressure increases, leading to a decrease in output of the internal combustion engine and a deterioration in fuel consumption. Further, when the exhaust gas temperature rises from a state in which the filter is clogged, PM accumulated on the filter burns rapidly, and the filter temperature rapidly rises, resulting in cracking or breakage of the filter. For this reason, in order to prevent these problems, an exhaust emission control device that regenerates a filter is conventionally known, and is disclosed in, for example, Patent Document 1.

  In this exhaust purification device, the amount of PM deposited on the filter is calculated, and when the calculated amount of PM deposited is larger than a predetermined amount, it is added during the exhaust stroke in addition to the fuel for operating the internal combustion engine. In addition, fuel is injected into the combustion chamber, and this additional fuel injection (hereinafter referred to as “post-injection”) is continued until the accumulated amount of PM becomes a predetermined amount or less. As a result, unburnt fuel flows into the exhaust system and burns upstream of the filter, forcibly raising the exhaust temperature and burning the accumulated PM, so that PM accumulates more than necessary on the filter. I try not to.

  However, in the exhaust purification device described above, since the unburned fuel continues to flow into the exhaust system during the post injection execution period, the ratio of oxygen to the inflowed unburned fuel is reduced, and thereby the unburned fuel is discharged into the exhaust system. In this case, the temperature of the filter does not rise quickly. For this reason, the output of the internal combustion engine may be reduced and the fuel consumption may be deteriorated during the delay in the temperature rise of the filter.

  The present invention has been made to solve the above-described problems, and provides an exhaust emission control device for an internal combustion engine that can quickly regenerate a filter and reduce the amount of fuel required for regeneration. The purpose is to provide.

JP 2001-280118 A

In order to achieve the above object, the invention according to claim 1 is provided in the exhaust system 4 of the internal combustion engine 3 and is provided on the upstream side of the filter 10 or on the filter 10. The filter 10 collects particulates in the exhaust gas. Catalyst (first and second oxidation catalysts 7 and 9 in the embodiment (hereinafter the same in this section)) and regenerating means (ECU 2) for regenerating the filter 10 by removing the particulates collected by the filter 10. 2), an exhaust gas purification apparatus 1 for an internal combustion engine, which includes a regeneration determination means (ECU 2, step S2 in FIG. 2) for determining whether or not the filter 10 should be regenerated, and the regeneration determination means. When it is determined that the fuel should be regenerated, fuel supply means (in) for supplying fuel so that unburned fuel is included in the exhaust gas upstream of the filter 10. 2 and the fuel supply control means (ECU2) that repeats the supply of fuel by the fuel supply means and the interruption of the supply of fuel until the filter 10 reaches a regenerated regeneration temperature DPFREF. 2, and the fuel supply interruption time (predetermined time TPOSTSα) by the fuel supply control means is set to be shorter than the fuel supply time (predetermined time TPOSTα). It is characterized by.

According to this configuration, when it is determined that the filter should be regenerated, the fuel is supplied so that unburned fuel is included in the exhaust gas upstream of the exhaust system filter, and the supply of the fuel is performed. And the interruption is repeated until the filter reaches a regeneration temperature at which regeneration is possible. In this way, when it is necessary to regenerate the filter, the supplied fuel is included in the exhaust gas as unburned fuel, whereby the unburned fuel is burned upstream of the filter or in the filter by the catalyst. Also, by repeating the fuel supply and interruption until the filter reaches the regeneration temperature, unlike the conventional case, sufficient oxygen can be secured for the unburned fuel. As a result, unburned fuel can be sufficiently combusted upstream of the exhaust system filter or in the filter, whereby the temperature of the filter can be quickly raised to the regeneration temperature. Thereby, the filter can be quickly regenerated by quickly burning the particulates collected by the filter. Therefore, clogging of the filter can be reliably prevented, so that a decrease in the output of the internal combustion engine and a deterioration in fuel consumption can be prevented. In addition, since the fuel supply and interruption are repeated, the amount of fuel necessary for the regeneration of the filter can be reduced accordingly.
Further, according to the above-described configuration, by setting the fuel supply interruption time to be shorter than the fuel supply time, the fuel supply time is sufficiently ensured, so that the unburned fuel is sufficiently included in the exhaust gas. Can be made. Accordingly, the temperature of the filter can be raised more quickly to the regeneration temperature in combination with the securing of oxygen due to the interruption of the fuel supply.

  According to a second aspect of the present invention, in the exhaust gas purification apparatus 1 for an internal combustion engine according to the first aspect, the fuel supply means expands the internal combustion engine 3 in the combustion chamber of the internal combustion engine 3 by the fuel injection valve 3a. The fuel is supplied by injecting the fuel during the stroke or the exhaust stroke (steps S6 and S7 in FIG. 2).

  According to this configuration, since the fuel is supplied by injecting the fuel into the combustion chamber of the internal combustion engine during the expansion stroke or the exhaust stroke by the fuel injection valve, the injected fuel is combusted in the combustion chamber. Instead, it flows into the exhaust system in an unburned state and burns upstream of the filter or in the filter by the catalyst. Further, since the fuel for regeneration is supplied by using an existing fuel injection valve generally provided in the internal combustion engine, this can be performed without providing a special mechanism.

According to a third aspect of the present invention, in the exhaust gas purification apparatus 1 for an internal combustion engine according to the first or second aspect, the fuel supply control means regenerates the amount of fuel supplied by the fuel supply means. When the temperature DPFTREF is reached (step 4: YES), the temperature is controlled to a value smaller than before reaching the regeneration temperature DPFTREF (step 16) .

According to this configuration, when the filter reaches the regeneration temperature, the amount of fuel supplied by the fuel supply means is controlled to a value smaller than before reaching the regeneration temperature.

1 is a diagram schematically showing an exhaust emission control device to which the present invention is applied together with an engine. It is a flowchart which shows a post injection control process. It is a figure which shows the post injection amount determination map used by the process of FIG. It is a figure which shows the operation example obtained by the process of FIG. It is a figure which shows an example of transition, such as filter temperature at the time of performing the process of FIG. It is a figure which shows transition, such as filter temperature at the time of performing continuously without interrupting post injection as a comparative example.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. As shown in FIG. 1, an internal combustion engine (hereinafter referred to as “engine”) 3 is a diesel engine for vehicles having four cylinders # 1 to # 4, and a cylinder head (not shown) of each cylinder includes A fuel injection valve (hereinafter referred to as “injector”) 3a (fuel supply means) is attached so as to face a combustion chamber (not shown). Each injector 3a is connected to a high pressure pump (both not shown) via a common rail. The high-pressure pump boosts the fuel in a fuel tank (not shown) to a high pressure under the control of the ECU 2, which will be described later, and then sends the fuel to the injector 3a via the common rail. The injector 3a injects this fuel into the combustion chamber. The fuel injection time (fuel injection amount) and timing of the injector 3a are controlled by a drive signal from the ECU 2. This fuel injection is performed in the order of # 1 → # 3 → # 4 → # 2 in the four cylinders # 1 to # 4.

  The exhaust system 4 of the engine 3 includes an exhaust manifold 5 for guiding the exhaust discharged from the cylinders # 1 to # 4 to the downstream side, and an exhaust pipe 6 connected to the exhaust manifold 5. The exhaust pipe 6 is provided with a first oxidation catalyst 7 (catalyst), a heater-equipped catalyst 8, a second oxidation catalyst 9 (catalyst), and a filter 10 in this order from the upstream side. The first and second oxidation catalysts 7 and 9 oxidize HC and CO in the exhaust and purify the exhaust. The heater-equipped catalyst 8 includes a heater (not shown), and the exhaust gas is heated by energizing the heater. The filter 10 collects particulates such as soot in the exhaust (hereinafter referred to as “PM”), thereby reducing PM discharged into the atmosphere. The filter 10 carries a catalyst (not shown) similar to the second oxidation catalyst 9 on its surface.

  In addition, a first temperature sensor 11 is attached to the exhaust pipe 6 upstream of the heater-equipped catalyst 8, and a second temperature sensor 12 is attached between the second oxidation catalyst 9 and the filter 10. A third temperature sensor 13 is attached to the center of the upstream end of the first temperature sensor. The first temperature sensor 11 detects an exhaust gas temperature upstream of the heater-equipped catalyst 8 (hereinafter referred to as “pre-catalyst gas temperature”) EHCGT. The second temperature sensor 12 detects the exhaust gas temperature immediately upstream of the filter 10 (hereinafter referred to as “pre-filter gas temperature”) DPFGT. The third temperature sensor 13 detects the temperature of the filter 10 (hereinafter referred to as “filter temperature”) DPFT. These detection signals are output to the ECU 2.

  From the crank angle sensor 14, a CRK signal and a TDC signal that are pulse signals are output to the ECU 2, and an accelerator opening AP that is an opening of an accelerator pedal (not shown) is output from the accelerator opening sensor 15. . The CRK signal is output at every predetermined crank angle as the crankshaft (not shown) of the engine 3 rotates. The ECU 2 obtains the engine speed NE based on the CRK signal. The TDC signal is a signal indicating that the piston (not shown) of each cylinder is at a predetermined crank angle position near the TDC (top dead center) at the start of the intake stroke. In this example, the engine 3 is a four-cylinder type. , Output at every 180 ° crank angle.

  The ECU 2 (regeneration means, regeneration determination means, fuel supply means, fuel supply control means) constitutes the exhaust emission control device 1 according to the present invention together with the injector 3a and the like, and includes an I / O interface, CPU, RAM, and ROM. It consists of a microcomputer consisting of The detection signals from the various sensors 11 to 15 described above are input to the CPU after A / D conversion and shaping by the I / O interface.

  The CPU determines the operating state of the engine 3 according to these input signals, and executes post-injection control processing for regenerating the filter 10 according to the control program stored in the ROM according to the determined operating state. To do. In this post-injection control process, following the original fuel injection for operating the engine 3, fuel is additionally injected during the expansion stroke or the exhaust stroke, so that the fuel is burned in the exhaust system 4. The filter temperature DPFT is raised, PM deposited on the filter 10 is burned and removed, and the filter 10 is regenerated.

  Hereinafter, the post injection control process will be described with reference to FIG. This process is interrupted in synchronization with the input of the TDC signal. First, in step S1, the amount of PM deposited on the filter 10 (hereinafter referred to as “PM deposition amount”) DPFPMS is calculated. Specifically, according to the engine speed NE and the accelerator pedal opening AP, the PM discharge amount (not shown) is obtained from the PM discharge map (not shown), and based on the filter temperature DPFT, From the PM combustion amount table, the combustion amount of PM burned by the filter 10 is obtained. Then, the PM accumulation amount DPFPMS is calculated by subtracting the PM combustion amount from these obtained PM emission amounts. The PM emission map is obtained by an experiment to determine the amount of PM discharged from the engine 3. In this map, the PM emission increases as the engine speed NE increases and the accelerator pedal opening AP increases. It is set large. The PM combustion amount table is obtained by experimentation of the PM combustion amount burned by the filter 10, and in this map, the PM combustion amount is set larger as the filter temperature DPFT is higher.

  Next, it is determined whether or not the calculated PM deposition amount DPFPMS is larger than a predetermined determination value DFPPMREF (step S2). If this answer is NO, the post-injection interruption flag F_POSTS and the post-injection execution flag F_POST to be described later are set to “0” on the assumption that the PM accumulation amount DPFPMS is not so large and the filter 10 need not be regenerated (step S3). This process is terminated as it is. On the other hand, when the answer is YES and DPFPMS> DPFPMREF, it is determined that the PM accumulation amount DPFPMS is large and the filter 10 should be regenerated, and the filter temperature DPFT is a predetermined regeneration temperature DPFTREF ( For example, it is determined whether the temperature is higher than 600 ° C. (step S4).

  When this answer is NO, since the filter temperature DPFT is low, the PM deposited on the filter 10 is difficult to burn. Therefore, in order to regenerate the filter 10, post injection control for increasing the filter temperature DPFT is performed in the next step S5. This will be done later. In this step S5, it is determined whether or not the post-injection interruption flag F_POSTS is “1”. When the answer is NO, in step S6, the post injection amount POSTQ is obtained by searching the post injection amount determination map shown in FIG. 3 according to the engine speed NE and the required torque PMCMDREG. This post injection amount POSTQ corresponds to the amount of fuel to be injected into the combustion chamber by post injection. The required torque PMCMDREG is obtained from a required torque determination map (not shown) according to the engine speed NE and the accelerator pedal opening AP.

  In this post injection amount determination map, the post injection amount POSTQ is set to be smaller as the engine speed NE is larger and as the required torque PMCMDREG is larger. This is because the higher the engine speed NE and the larger the required torque PMCMDREG, the higher the original fuel injection amount for the operation of the engine 3, and thus the higher the exhaust temperature and the higher the filter temperature DPFT. This is because the post-injection amount POSTQ required to increase the filter temperature DPFT can be reduced accordingly.

  Next, in step S7, based on the post injection amount POSTQ obtained in step S6, a post injection start timing POSTTIM, which is a post injection start timing, is determined. The post-injection start timing POSTTIM is determined so that the end timing of the post-injection is in the exhaust stroke, with a predetermined timing in the expansion stroke (for example, 120 ° crank angle after TDC at the end of the compression stroke) as the center. As a result, the post injection start timing POSTTIM is determined to be more advanced as the post injection amount POSTQ is larger, and more retarded as the post injection amount POSTTIM is smaller. As described above, the post-injection is performed by injecting fuel into the combustion chamber during the expansion stroke or exhaust stroke of the engine 3, so that at least a part of the injected fuel is burned in the combustion chamber. Instead, it is contained in the exhaust as unburned fuel and flows into the exhaust system 4.

  Next, it is determined whether or not the post injection execution flag F_POST is “1” (step S8). When this answer is NO, the timer value TPOST of the down-count type execution timer is set to a predetermined time TPOSTα (for example, 28 sec) (supply time) (step S9), and the post-injection is being executed. In addition, the post injection execution flag F_POST is set to “1” (step S10), and the process proceeds to step S11. After executing Step S10, the answer to Step S8 is YES. In this case, Steps S9 and S10 are skipped and the process proceeds to Step S11.

  In step S11, it is determined whether or not the timer value TPOST of the execution timer set in step S9 is 0. If the answer is NO, that is, if the predetermined time TPOSTα has not elapsed after the start of post injection, the timer value TPOSTS of the down-count type interruption timer is set to a predetermined time TPOSTSα (for example, 2 seconds) shorter than the predetermined time TPOSTα (interruption) Time) (step S12), and this process is terminated.

  On the other hand, if the answer to step S11 is YES and TPOST = 0, that is, if the predetermined time TPOSTα has elapsed after the start of post injection, the post injection is interrupted by setting the post injection amount POSTQ to a value of 0 in step S13. In addition, in order to express this, the post injection interruption flag F_POSTS is set to “1”, and then the process proceeds to step S14. Further, after executing step S13, the answer to step S5 becomes YES. In this case, the steps S6 to S13 are skipped and the process proceeds to step S14.

  In step S14, it is determined whether or not the timer value TPOSTS of the interruption timer set in step S12 is 0. When this answer is NO, the present process is terminated as it is, and the post-injection is continued. On the other hand, if the answer to step S14 is YES and TPOSTS = 0, that is, if the predetermined time TPOSTSα has elapsed after the suspension of post injection, the post injection suspension flag F_POSTS and the post injection execution flag F_POST are reset to “0” (step S15), this process is terminated. After executing step S15, the answer to step S5 is NO. In this case, post-injection once suspended is resumed by executing step S6 and subsequent steps.

  On the other hand, when the answer to step S4 is YES and DPFT> DPFTREF, that is, when the filter temperature DPFT reaches the regeneration temperature DPFTREF, the maintenance post-injection is executed (step S16), and the step S3 is executed and the present process is terminated. To do. This maintenance post-injection performs post-injection with an overall smaller injection amount than post-injection after step S5 so that the filter temperature DPFT does not decrease.

  Next, an operation example obtained by the post injection control process described above will be described with reference to FIG. First, when the PM accumulation amount DPFPMS is larger than the determination value DPFPMREF (step S2: YES), it is determined that the filter 10 should be regenerated, and the condition that the filter temperature DPFT is lower than the regenerating temperature DPFREF is satisfied. (Step S4: NO), post injection is started (Steps S6, S7, time point t0). Thereafter, as long as the above condition is satisfied, post-injection is executed for a predetermined time TPOSTα (steps S6 to S11). When the predetermined time TPOSTα has elapsed (step S11: YES), the post injection is interrupted (step S13, time point t1). Thereafter, when the predetermined time TPOSTSα has elapsed (step S14: YES), the interruption of the post injection is finished and the post injection is resumed (time point t2). The execution of the post injection over the predetermined time TPOSTα and the interruption of the post injection over the predetermined time TPOSTSα are repeatedly performed.

  Next, referring to FIG. 5 and FIG. 6 respectively, an example of transition of the filter temperature DPFT and the like in the case where the post injection control process described above is executed and in the conventional case where the post injection is continuously executed without being interrupted. While explaining.

  When the post-injection control process is executed, as shown in FIG. 5, when the post-injection is started at time t0, a part of the unburned fuel that has flowed into the exhaust system 4 is caused by the first oxidation catalyst 7 thereby. By burning, the pre-catalyst gas temperature EHCGT gradually increases. The pre-filter gas temperature DPFGT, which is the temperature of the exhaust gas downstream of the pre-catalyst gas temperature EHCGT, is increased by the increase in the exhaust gas temperature due to the combustion of the unburned fuel on the upstream side and the second oxidation catalyst 9 to increase the amount of unburned gas. As the fuel burns, it rapidly rises to a temperature higher than the pre-catalyst gas temperature EHCGT, and then rises gently. The filter temperature DPTFT rapidly rises to a temperature higher than the pre-filter gas temperature DPFGT due to the increase in the pre-filter gas temperature DPFGT and further combustion of the unburned fuel by the catalyst on the surface of the filter 10, and then gradually increases. Further, the filter temperature DPFT reaches a predetermined temperature (hereinafter referred to as “combustible temperature”) TREF (for example, 600 ° C.) at which PM accumulated on the filter 10 can be combusted at time tα.

  On the other hand, in the conventional case shown in FIG. 6, after the start of post injection (after time t0), the degree of increase in the pre-catalyst gas temperature EHCGT, the pre-filter gas temperature DPFGT, and the filter temperature DPFT is determined by the post injection control process. Each is smaller than if executed. For this reason, the filter temperature DPFT reaches the combustible temperature TREF at a time point tβ that is much later than the time point tα. From the above, it was confirmed that the filter temperature DPFT can be quickly raised to the combustible temperature TREF by the post injection control process of the present embodiment.

  As described above, according to the present embodiment, when the PM accumulation amount DPFPMS is larger than the determination value DFPPMREF, it is determined that the filter 10 should be regenerated, and when the filter temperature DPFT is lower than the regeneration temperature DPFREF. The post injection for the predetermined time TPOSTα is executed and the post injection for the predetermined time TPOSTSα is repeatedly performed until the filter temperature DPFT reaches the regeneration temperature DPFTREF. By executing this post injection, unburned fuel is allowed to flow into the exhaust system 4, and by interrupting the post injection, sufficient oxygen can be secured for the unburned fuel. In the filter 10, the unburned fuel can be sufficiently burned by the second oxidation catalyst 9 or the like. As a result, the filter 10 can be quickly regenerated by rapidly increasing the filter temperature DPFT to the regeneration temperature DPFTREF. Therefore, clogging of the filter 10 can be reliably prevented, so that a decrease in the output of the engine 3 and a deterioration in fuel consumption can be prevented. Further, since the predetermined time TPOSTSα is set to be shorter than the predetermined time TPOSTα, the unburned fuel can sufficiently flow into the exhaust system 4 by sufficiently securing the execution time of the post injection. The temperature DPFT can be increased more quickly to the regeneration temperature DPFTREF.

  Furthermore, since the post-injection is interrupted for a predetermined time TPOSTSα during the post-injection execution period, the amount of fuel necessary for regeneration can be reduced accordingly. Further, since the post injection amount POSTQ is determined according to the engine speed NE and the required torque PMCMDREG, the fuel amount necessary for regeneration can be appropriately set according to the operating state of the engine 3, and this can be further reduced. it can. Further, the post injection can be performed without using a special mechanism while using the existing injector 3a.

  In addition, this invention can be implemented in various aspects, without being limited to the described embodiment. For example, in the embodiment, the supply of unburned fuel into the exhaust gas upstream of the filter is performed by post-injection into the combustion chamber using the injector 3a. Alternatively, a separate injector may be provided on the upstream side to inject fuel. In the embodiment, the predetermined time TPOSTα and the predetermined time TPOSTSα are set to predetermined fixed values. These values are set according to the operating state of the internal combustion engine, the temperature rising state of the filter, and the like. Also good. In that case, the execution / interruption of post-injection can be finely and appropriately performed according to the operating state of the internal combustion engine and the temperature rise state of the filter, so that the effects of the present invention can be obtained more effectively.

  Furthermore, in the embodiment, the filter temperature DPFT is detected by the third temperature sensor 13, but instead, it may be estimated according to the engine operating state, for example, the fuel injection amount or the engine speed. . Moreover, although embodiment described was an example which applied this invention to the diesel engine 3, this invention is not restricted to this, Various engines other than a diesel engine, for example, a gasoline engine and a crankshaft, are set to a perpendicular direction. Of course, the present invention may be applied to a marine vessel propulsion engine such as an outboard motor. In addition, it is possible to appropriately change the detailed configuration within the scope of the gist of the present invention.

Explanation of symbols

1 Exhaust gas purification device
2 ECU (regeneration means, regeneration determination means, fuel supply means, fuel supply control means)
3 Engine
3a Injector (fuel supply means)
4 Exhaust system
7 First oxidation catalyst (catalyst)
9 Second oxidation catalyst (catalyst)
10 Filter DPFTREF Regeneration temperature TPOSTSα Predetermined time (interruption time)
TPOSTα predetermined time (supply time)

Claims (3)

A filter provided in an exhaust system of an internal combustion engine for collecting particulates in the exhaust; a catalyst provided on the upstream side of the filter or in the filter; and removing the particulates collected in the filter An exhaust gas purification apparatus for an internal combustion engine comprising a regenerating means for regenerating the filter,
Reproduction determination means for determining whether or not to regenerate the filter;
Fuel supply means for supplying fuel so that unburned fuel is included in the exhaust gas upstream of the filter when the regeneration determination means determines that the filter should be regenerated;
Fuel supply by the fuel supply means, and fuel supply control means for repeating interruption of the fuel supply until the filter reaches a regenerative regeneration temperature ,
An exhaust purification device of an internal combustion engine, wherein the fuel supply control means interrupts the fuel supply in a time shorter than the fuel supply time .   The fuel supply means supplies fuel by injecting fuel into a combustion chamber of the internal combustion engine during the expansion stroke or exhaust stroke of the internal combustion engine by a fuel injection valve. 2. An exhaust gas purification apparatus for an internal combustion engine according to 1. The fuel supply control means controls the amount of fuel supplied by the fuel supply means to a value smaller than that before reaching the regeneration temperature when the filter reaches the regeneration temperature . The exhaust emission control device for an internal combustion engine according to claim 1 or 2.

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