JP4236896B2 - Exhaust purification equipment - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust emission control device.
[0002]
[Prior art]
Particulate matter (particulate matter) discharged from a diesel engine is mainly composed of soot composed of carbonaceous matter and SOF content (Soluble Organic Fraction) composed of high-boiling hydrocarbon components. The composition contains a small amount of sulfate (mist-like sulfuric acid component). As a measure to reduce this type of particulates, a particulate filter is installed in the middle of the exhaust pipe through which the exhaust gas flows. It has been done conventionally.
[0003]
This type of particulate filter has a porous honeycomb structure made of ceramics such as cordierite, and the inlets of the respective flow paths partitioned in a lattice shape are alternately sealed, and the inlets are not sealed. About the flow path, the exit is sealed, and only the exhaust gas which permeate | transmitted the porous thin wall which divides each flow path is discharged | emitted downstream.
[0004]
Then, the particulates in the exhaust gas are collected and deposited on the inner surface of the porous thin wall, so that the particulates are appropriately burned and removed before the exhaust resistance increases due to clogging. It is necessary to regenerate, but in normal diesel engine operating conditions, there are few opportunities to obtain exhaust temperatures that are high enough for the particulates to self-combust. For example, an appropriate amount for alumina loaded with platinum A catalyst regeneration type particulate filter in which an oxidation catalyst formed by adding rare earth elements such as cerium is integrally supported is being put to practical use.
[0005]
That is, if such a catalyst regeneration type particulate filter is employed, the oxidation reaction of the collected particulates is promoted to lower the ignition temperature, and the particulates can be burned and removed even at an exhaust temperature lower than the conventional one. It becomes possible.
[0006]
However, even when such a catalyst regeneration type particulate filter is adopted, in the operation region where the exhaust gas temperature is low, the trapping amount will exceed the processing amount of particulates. If the exhaust filter continues to operate at a low exhaust temperature, there is still a possibility that the particulate filter will not regenerate well and clogging may still occur. It has been studied to forcibly regenerate the particulate filter by adding fuel to the exhaust gas upstream of the filter.
[0007]
In other words, if fuel is added upstream from the particulate filter, the added fuel undergoes an oxidation reaction on the oxidation catalyst of the particulate filter, and the heat of the reaction raises the catalyst bed temperature to burn out the particulate. Thus, regeneration of the particulate filter is achieved (for example, see Patent Document 1 and Patent Document 2).
[0008]
[Patent Document 1]
JP-A-8-42326 [Patent Document 2]
Japanese Patent Laid-Open No. 2002-30919
[Problems to be solved by the invention]
However, when performing the regeneration control as described above, for example, if the regeneration control is started when the engine is in a low-speed operation state where the exhaust temperature is low such that intermittent slow driving is repeated on a congested road or the like, the particulates In order to increase the temperature to a catalyst bed temperature at which the fuel can be efficiently removed by combustion, a large amount of fuel is required, which may cause a significant deterioration in fuel consumption.
[0010]
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 capable of significantly suppressing the amount of fuel added for regeneration control of a particulate filter as compared with the prior art.
[0011]
[Means for Solving the Problems]
The present invention is equipped with a catalyst regeneration type particulate filter in the middle of an exhaust pipe through which exhaust gas from an internal combustion engine circulates, and fuel addition means for adding fuel to the exhaust gas upstream of the particulate filter; A vehicle speed is detected in an exhaust emission control device including a control device that outputs a fuel addition command to the fuel addition means when it is necessary to regenerate the particulate filter by burning and removing the collected particulates. A vehicle speed sensor for outputting a vehicle speed signal to the control device, the control device calculates an average vehicle speed per predetermined time based on the vehicle speed signal of the vehicle speed sensor, and the average vehicle speed is equal to or less than a set value. The control device is configured not to output a new fuel addition command under the conditions.
[0012]
Thus, in this way, based on the vehicle speed measured by the vehicle speed sensor, the control device always monitors whether or not the average vehicle speed per predetermined time is equal to or less than the set value, and intermittently on a congested road or the like. When the engine is in a low-speed operation state where the exhaust temperature is low, such as repeating slow driving, a new fuel addition command may be output from the control device because the average vehicle speed is below the set value. As a result, there is an increased opportunity for the fuel addition command to be output from the control device in a suitable steady operation state where the vehicle continuously travels at a high exhaust temperature for a certain time, and the fuel required for regeneration control of the particulate filter The amount of addition will be less than before.
[0013]
Further, in concrete implementation of the present invention, a fuel injection device that injects fuel into each cylinder of the internal combustion engine is used as a fuel addition means, and the fuel injection into the cylinder is controlled by the control device so that it is not in the exhaust gas. It is good to comprise so that fuel addition may be performed by leaving much fuel fuel content.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[0015]
FIG. 1 and FIG. 2 show an example of an embodiment for carrying out the present invention. In FIG. 1, reference numeral 1 denotes a diesel engine equipped with a turbocharger 2, and intake air 4 guided from an air cleaner 3 is an intake pipe 5. And the intake air 4 pressurized by the compressor 2a is sent to the intercooler 6 to be cooled, and the intake air 4 further flows from the intercooler 6 to the intake manifold 7. It is guided and distributed to each cylinder 8 of the diesel engine 1 (the case of in-line 6 cylinders is illustrated in FIG. 1).
[0016]
Further, the exhaust gas 9 discharged from each cylinder 8 of the diesel engine 1 is sent to the turbine 2b of the turbocharger 2 through the exhaust manifold 10, and the exhaust gas 9 that has driven the turbine 2b passes through the exhaust pipe 11. It is designed to be discharged outside the vehicle.
[0017]
Further, in the middle of the exhaust pipe 11, a catalyst regeneration type particulate filter 12 integrally carrying an oxidation catalyst is mounted and mounted on a filter case 13, and is shown in an enlarged view in FIG. As described above, the particulate filter 12 has a porous honeycomb structure made of ceramic, and the inlets of the respective channels 12a partitioned in a lattice pattern are alternately sealed, and the channels are not sealed. About 12a, the exit is sealed, and only the exhaust gas 9 which permeate | transmitted the porous thin wall 12b which divides each flow path 12a is discharged | emitted downstream.
[0018]
A temperature sensor 14 that measures the temperature of the exhaust gas 9 that has passed through the particulate filter 12 as a substitute value for the catalyst bed temperature is provided at the outlet of the filter case 13, and a temperature signal 14 a of the temperature sensor 14 is provided. Is input to a control device 15 constituting an engine control computer (ECU: Electronic Control Unit).
[0019]
Since this control device 15 also serves as an engine control computer, it is also responsible for control related to fuel injection. More specifically, the control device 15 detects an accelerator opening as a load of the diesel engine 1 ( A fuel injection device that injects fuel into each cylinder 8 of the diesel engine 1 based on an accelerator opening signal 16a from the load sensor) and a rotation speed signal 17a from the rotation sensor 17 that detects the engine rotation speed of the diesel engine 1. The fuel injection signal 18a is output toward the engine 18, and the operation state of the diesel engine 1 is always grasped by the control device 15 when the fuel injection signal 18a is output.
[0020]
Here, the fuel injection device 18 is composed of a plurality of injectors 19 provided for each cylinder 8, and the electromagnetic valves of these injectors 19 are appropriately controlled to open by the fuel injection signal 18a. The injection timing (valve opening timing) and the injection amount (valve opening time) are appropriately controlled.
[0021]
On the other hand, in the control device 15, the fuel injection signal 18a in the normal mode is determined on the basis of the accelerator opening signal 16a and the rotation speed signal 17a. On the other hand, it is necessary to perform regeneration control of the particulate filter 12. In this case, the normal mode is switched to the regeneration mode, and the post-injection is performed at the non-ignition timing later than the compression top dead center following the main injection of fuel performed near the compression top dead center (crank angle 0 °). A fuel injection signal 18a is determined.
[0022]
That is, when post-injection is performed at a non-ignition timing later than the compression top dead center following main injection, unburned fuel (mainly HC: hydrocarbon) is added to the exhaust gas 9 by this post-injection. As a result, the unburned fuel undergoes an oxidation reaction on the oxidation catalyst on the surface of the particulate filter 12, the catalyst bed temperature rises due to the reaction heat, and the particulates in the particulate filter 12 are burned and removed. It will be.
[0023]
Further, the control device 15 extracts the rotational speed of the diesel engine 1 based on the rotational speed signal 17a from the rotational sensor 17, and at the time of determining the fuel injection signal 18a based on the accelerator opening signal 16a from the accelerator sensor 16. The known fuel injection amount is extracted, and the basic generation amount of the particulates based on the current operation state of the diesel engine 1 is estimated from the particulate generation map based on the rotation speed and the injection amount. Multiply the basic generation amount by a correction coefficient considering various conditions related to the generation of particulates, and subtract the particulate processing amount in the current operating state to obtain the final generation amount. The amount of particulates accumulated is estimated from time to time to estimate the amount of particulates deposited.
[0024]
Note that there are various ways of estimating the amount of particulate deposition, and it is of course possible to estimate the amount of particulate deposition using a method other than the estimation method exemplified here.
[0025]
Further, after the control device 15 estimates that the amount of accumulated particulates has reached a predetermined target value, the outlet exhaust temperature of the particulate filter 12 is equal to or higher than the predetermined temperature based on the temperature signal 14a from the temperature sensor 14. After waiting for the condition, the combustion injection control is switched from the normal mode to the regeneration mode, and fuel is added to the exhaust gas 9 on the upstream side of the particulate filter 12.
[0026]
In the present embodiment, a vehicle speed sensor that is generally installed in a vehicle is related to an exhaust gas purification device that can add fuel to the exhaust gas 9 upstream of the particulate filter 12 as described above. 20 vehicle speed signals 20a are guided to the control device 15, and the control device 15 calculates the average vehicle speed per predetermined time and does not output a new fuel addition command under the condition that the average vehicle speed is less than or equal to the set value. More specifically, the combustion injection control in the control device 15 is not switched from the normal mode to the regeneration mode under the condition that the average vehicle speed is equal to or lower than the set value. is there.
[0027]
However, if the regeneration mode has already been entered before the average vehicle speed falls below the set value, the regeneration mode is continued as it is even if the average vehicle speed falls below the set value, and regeneration control of the particulate filter 12 is performed. It is supposed to be completed.
[0028]
Thus, if the exhaust emission control device is configured in this way, it is estimated that the amount of accumulated particulate has reached a predetermined target value in the control device 15 under the condition that the average vehicle speed is not lower than the set value. Then, based on the temperature signal 14a from the temperature sensor 14, the combustion injection control is switched from the normal mode to the regeneration mode after the outlet exhaust temperature of the particulate filter 12 becomes a condition equal to or higher than the predetermined temperature, and the main injection is continued. The fuel added unburned in the exhaust gas 9 by the post injection causes an oxidation reaction on the oxidation catalyst of the particulate filter 12 to generate heat of reaction, and the heat of reaction greatly increases the catalyst bed temperature. Is burned and removed satisfactorily, and the particulate filter 12 is regenerated.
[0029]
Here, whether or not the average vehicle speed is less than or equal to the set value is constantly monitored by the control device 15 based on the vehicle speed measured by the vehicle speed sensor 20, and intermittent slow driving is repeated on a congested road or the like. When the engine is in a low-speed operation state where the exhaust temperature is low and the average vehicle speed is below the set value, a new fuel addition command is not output from the control device 15 and combustion injection is performed. Since the control does not switch from the normal mode to the regeneration mode, as a result, the opportunity for the fuel addition command to be output from the control device 15 in a preferable steady operation state where the vehicle continuously travels at a high exhaust temperature for a certain period of time is increased. Therefore, the amount of fuel added for the regeneration control of the particulate filter can be reduced as compared with the prior art.
[0030]
Therefore, according to the above embodiment, the fuel is added to the exhaust gas 9 on the upstream side of the particulate filter 12, the fuel is oxidized on the oxidation catalyst of the particulate filter 12, and the heat of reaction causes the catalyst bed temperature. In order to carry out regeneration control that actively burns and removes the particulates that have been collected, the regeneration is newly performed when the engine is in a low-speed operation state where the exhaust temperature is low, such as intermittent slow driving on a congested road. The situation in which the control is started can be avoided in advance, and the amount of fuel added for the regeneration control of the particulate filter 12 can be significantly reduced as compared with the conventional case. Therefore, this type of regeneration control can be performed. The fuel consumption in the possible exhaust purification device can be remarkably improved.
[0031]
The exhaust emission control device of the present invention is not limited to the above-described embodiment. In the above embodiment, the fuel injection device is used as the fuel addition means, and the fuel is performed near the compression top dead center. Fuel is added to the exhaust gas by performing post-injection at a timing of non-ignition later than the compression top dead center following the main injection of the engine, but the timing of main injection into the cylinder is delayed from normal The fuel may be added to the exhaust gas, and only the means for adding fuel by controlling the fuel injection into the cylinder and leaving a large amount of unburned fuel in the exhaust gas. In addition, an injector may be provided as a fuel addition means at an appropriate position of the exhaust pipe (or an exhaust manifold is acceptable), and fuel may be directly injected into the exhaust gas by this injector, It is of course that various changes and modifications may be made without departing from the scope and spirit of the present invention.
[0032]
【The invention's effect】
According to the above-described exhaust gas purification apparatus of the present invention, fuel is added to the exhaust gas upstream of the particulate filter, the fuel is oxidized on the oxidation catalyst of the particulate filter, and the heat of reaction causes the catalyst bed temperature. In order to carry out regeneration control that actively burns and removes the particulates that have been collected, the regeneration is newly performed when the engine is in a low-speed operation state where the exhaust temperature is low, such as intermittent slow driving on a congested road. The situation where the control is started can be avoided in advance, and the amount of fuel added for the regeneration control of the particulate filter can be greatly suppressed compared to the conventional case, so this type of regeneration control can be performed. It is possible to achieve an excellent effect that the fuel consumption in a simple exhaust purification device can be remarkably improved.
[Brief description of the drawings]
FIG. 1 is a schematic view showing an example of an embodiment for carrying out the present invention.
FIG. 2 is a cross-sectional view showing details of the particulate filter of FIG.
[Explanation of symbols]
1 Diesel engine (internal combustion engine)
8 cylinder 9 exhaust gas 11 exhaust pipe 12 particulate filter 15 control device 18 fuel injection device (fuel addition means)
18a Fuel injection signal 20 Vehicle speed sensor 20a Vehicle speed signal

Claims (2)

A catalyst regeneration type particulate filter is provided in the middle of an exhaust pipe through which exhaust gas from the internal combustion engine circulates, and fuel addition means for adding fuel to the exhaust gas upstream of the particulate filter; An exhaust emission control apparatus comprising: a control device that outputs a fuel addition command to the fuel addition means when it is necessary to regenerate the particulate filter by burning and removing the curate. A vehicle speed sensor that outputs a vehicle speed signal toward the vehicle, and the control device calculates an average vehicle speed per predetermined time based on the vehicle speed signal of the vehicle speed sensor and the average vehicle speed is less than a set value. An exhaust emission control device configured not to output a new fuel addition command to a control device. A fuel injection device that injects fuel into each cylinder of the internal combustion engine is adopted as a fuel addition means, and fuel addition is performed by controlling fuel injection into the cylinder by the control device and leaving a large amount of unburned fuel in the exhaust gas. The exhaust emission control device according to claim 1, wherein the exhaust purification device is configured to be executed.

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