JP2005155442A - Exhaust emission control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device capable of forcibly regenerating a filter even in a state where the temperature of cooling water is low. <P>SOLUTION: This exhaust emission control device comprises a particulate filter 13 and an exhaust gas throttle valve 25 incorporated in the exhaust pipe 11 of a diesel engine 1, a temperature sensor 29 detecting the water temperature of the engine, and a control device 20 performing the after-injection of fuel at a timing when the fuel is ignitable after the main injection of the fuel. The control device 20 comprises a function increasing idle rotation speed based on temperatures signals 29a from a temperature sensor 29, a function suppressing the flow of the exhaust gas 9 by an exhaust gas throttle valve 25, and a function starting an after-injection. In the control device, a temperature to start the after-injection is set higher. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an exhaust purification device.

  Diesel engine exhaust (gas oil combustion gas) contains carbonaceous soot and SOF (Soluble Organic Fraction) consisting of high-boiling hydrocarbon components as the main components, and a much smaller amount of sulfate (mist). Particulate Matter (particulate matter) with a composition to which (sulfuric acid component) is added.

  As a measure for suppressing the diffusion of particulates into the atmosphere, a filter for collecting particulates has been incorporated into the exhaust system of a diesel engine for vehicles.

  As the particulate filter, there is a filter in which a honeycomb core is formed of ceramics such as cordierite, and exhaust gas from the engine is circulated through a number of flow paths divided by a porous thin wall of the honeycomb core.

  In the above particulate filter, every other one end portion of many flow paths arranged in parallel is sealed, and exhaust is led from the engine to the unblocked one end portion of the flow path adjacent to this, and the exhaust gas from the engine is exhausted. The other end portion of the flow path into which the gas flows is sealed, and the other end portion of the flow path adjacent to the flow path is connected to a muffler or the like to open to the atmosphere.

  That is, the particulates contained in the engine exhaust are collected by the porous thin wall, and only the exhaust that permeates the porous thin wall is released into the atmosphere.

  In order to prevent the exhaust resistance from increasing, it is necessary to regenerate the particulate filter by removing the particulate deposited on the porous thin wall by combustion. However, when the diesel engine is in normal operation, the particulate filter There is little opportunity for the exhaust temperature to rise to such an extent that can spontaneously ignite.

  Therefore, a catalyst regeneration type particulate filter in which an oxidation catalyst in which a rare earth element such as cerium is added to alumina supporting platinum is supported on a particulate filter is being put to practical use. Thus, the oxidation reaction of the particulates is promoted to lower the ignition temperature, and the particulates can be burned and removed even at an exhaust temperature that does not lead to spontaneous ignition.

  The above oxidation catalyst has an active temperature range, and if the exhaust gas temperature does not reach the lower activation limit temperature (generally, a low load temperature region extends to a light load operation region), the oxidation catalyst An event occurs in which the particulates are not successfully burned off due to not being activated.

  As a countermeasure, the fuel is added to the exhaust upstream of the particulate filter and the catalyst bed temperature is increased by the reaction heat of the fuel that is oxidized on the catalyst. There has been proposed an exhaust purification device that performs an operation suitable for an oxidation reaction so as to forcibly regenerate a particulate filter (see, for example, Patent Document 1).

  In this exhaust purification system, post-injection for adding fuel to the exhaust is performed at a time when the fuel after fuel main injection in the vicinity of the compression top dead center (top dead center of the piston compression stroke) does not ignite, and the filter bed temperature is increased. The exhaust temperature is increased by performing after-injection to obtain thermal energy when the fuel after fuel main injection near the top dead center of compression is ignitable.

  Switching from the normal mode in which post-injection and after-injection are not performed to the forced regeneration mode in which the catalyst bed temperature is raised by post-injection to remove the particulates by combustion is performed at appropriate intervals for a predetermined time.

  In addition, when switching from the normal mode to the forced regeneration mode, whether or not to interpose the temperature raising mode for increasing the exhaust temperature by after injection is determined based on the exhaust temperature on the outlet side of the particulate filter, or the like. .

Further, when a flow-through type oxidation catalyst is provided in the preceding stage of the particulate filter for the purpose of supporting the oxidation reaction of the particulate filter, the exhaust gas whose temperature has been raised by the reaction heat of the added fuel oxidized by the preceding oxidation catalyst is reduced. Since it is introduced into the particulate filter, it is possible to realize the forced regeneration of the particulate filter from a lower exhaust temperature.
JP 2003-155915 A

  However, immediately after starting the engine, where the cylinder block, cooling water, etc. are close to the outside air temperature, even if after injection is performed, stable combustion cannot be obtained, and misfire may occur.

  For this reason, conventionally, after-injection and post-injection until the engine warms up to a steady state have been refrained, and filter forced regeneration cannot be performed when the coolant temperature is low.

  The present invention has been made in view of the above-described circumstances, and an object of the present invention is to provide an exhaust purification device that can perform forced filter regeneration even when the cooling water temperature is low.

  In order to achieve the above object, the present invention provides a catalyst regeneration type particulate filter incorporated in an engine exhaust system, a temperature sensor for detecting engine water temperature, an exhaust throttle means capable of restricting an exhaust flow rate, and a vicinity of top dead center. Fuel injection control means for performing fuel after-injection at a time when the fuel after the main fuel injection can be ignited, and based on the detected value of the temperature sensor, the exhaust flow rate is controlled by the exhaust throttle means. The fuel injection control means is provided with a function to suppress and a function to start after injection, and a temperature at which after injection is started is set.

  In the present invention, after the engine is started, first, the fuel injection control means increases the idle speed, and the exhaust throttle means suppresses the exhaust flow rate and actively warms the engine.

  Next, when the detected value of the temperature sensor reaches a threshold value, the fuel injection control means starts after injection to increase the catalyst bed temperature.

  (1) The engine is warmed by increasing the idling speed and suppressing the exhaust flow rate, and after injection is started to increase the catalyst bed temperature, so that forced filter regeneration can be performed even when the engine water temperature is low. Become.

  (2) The fuel delivered by after-injection stably burns and contributes to an increase in exhaust temperature, and abnormal behavior such as vibration due to misfire does not occur in the engine.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 to FIG. 4 show an example of an embodiment of an exhaust emission control device according to the present invention. 2 is supplied to the compressor 2a, and the intake air 4 pressurized by the compressor 2a flows into the intercooler 6. The intake air 4 cooled here is supplied to the intake manifold 7, and each cylinder of the diesel engine 1 is supplied. 8 (in-line 6 cylinders in FIG. 1).

  Further, the exhaust 9 discharged from the cylinder 8 of the diesel engine 1 is supplied to the turbine 2b of the turbocharger 2 through the exhaust manifold 10, and after being driven, the exhaust 9 is discharged into the atmosphere through the exhaust pipe 11. The

  A filter case 12 is incorporated in the exhaust pipe 11, and a catalyst regeneration type particulate filter 13 that integrally carries an oxidation catalyst is accommodated in a rear stage portion in the filter case 12.

  The particulate filter 13 forms a honeycomb core with ceramics, blocks every other one end portion of a large number of parallel flow paths 13a divided by the porous thin wall 13b of the honeycomb core, and is adjacent thereto. Exhaust gas 9 is guided from the diesel engine 1 to an unblocked one end portion of the flow path 13a and the other end portion of the flow path 13a is blocked (see FIG. 2).

  That is, the particulates contained in the exhaust 9 are collected by the porous thin wall 13b, and only the exhaust 9 that has permeated the porous thin wall 13b proceeds downstream and is released into the atmosphere.

  A flow-through type oxidation catalyst 14 having a honeycomb structure is accommodated in a front stage portion in the filter case 12 (see FIG. 3).

  In addition to this, a portion of the exhaust manifold 10 and the intake pipe 5 on the downstream side of the intercooler 6 is connected by an EGR pipe line 15 incorporating the EGR cooler 16 and the EGR valve 17.

  That is, the opening degree of the EGR valve 17 is adjusted to recirculate a part of the exhaust 9 from the exhaust path to the intake path, thereby reducing the combustion temperature to reduce the generation of NOx.

  Further, a temperature sensor 18 that measures the temperature of the exhaust gas 9 between the oxidation catalyst 14 and the particulate filter 13 is provided at an intermediate portion of the filter case 12 as a substitute value for the catalyst bed temperature.

  Further, the diesel engine 1 is provided with a temperature sensor 29 that measures the coolant temperature upstream of the thermostat incorporated in the coolant circulation path.

  The temperature signals 18a and 29a of the temperature sensors 18 and 29 are transmitted to a control device 20 constituting an engine control computer (ECU: Electronic Control Unit).

  An exhaust throttle valve 25 that also serves as an exhaust brake is incorporated in the exhaust pipe 11 so as to be positioned upstream of the filter case 12.

  The control device 20 is responsible for fuel injection control, and an opening signal 22a from an accelerator sensor 22 (load sensor) that detects the opening of the accelerator as a load of the diesel engine 1, and a rotation speed from the rotation sensor 23 that detects the engine rotation speed. Based on the signal 23 a and the temperature signals 18 a and 29 a from the temperature sensors 18 and 29, the injection signal 21 a is transmitted to the fuel injection device 21, and the command signals 17 a and 25 a are transmitted to the EGR valve 17 and the exhaust throttle valve 25. .

  The fuel injection device 21 has an injector or the like equipped for each cylinder 8 of the diesel engine 1, and the electromagnetic valves of these injectors open in response to the injection signal 21a, and the fuel injection timing and injection amount (valve opening time). ) To control.

The control device 20
A. In accordance with the engine load calculated from the opening signal 22a and the engine speed calculated from the rotation speed signal 23a, the normal mode injection signal 21a is transmitted to the fuel injection device 21 so that the main injection is performed near the compression top dead center. Function to
B. A function of transmitting the injection signal 21a in the forced regeneration mode to the fuel injection device 21 so that the post-injection is performed when the fuel after the main injection does not ignite when a preset time has elapsed;
C. Prior to the start of post-injection, in accordance with the catalyst bed temperature calculated from the temperature signal 18a, the fuel injection device 21 sends an injection signal 21a in the temperature raising mode so that after-injection is performed when the fuel after main injection can be ignited. The ability to send to
D. A function of transmitting an injection signal 21a to the fuel injection device 21 so that the idle speed is increased after the diesel engine 1 is started;
E. A function of transmitting a command signal 25a to the exhaust throttle valve 25 so that the exhaust flow rate is suppressed after the diesel engine 1 is started;
F. A function of transmitting an injection signal 21a to the fuel injection device 21 so that after-injection is performed according to the coolant temperature after the diesel engine 1 is started,
G. A function of transmitting an injection signal 21a to the fuel injection device 21 so that post-injection is added to after-injection in accordance with the catalyst bed temperature;
Etc.

  During normal operation of the vehicle, switching from the normal mode in which post-injection and after-injection are not performed by the functions of the A term, B term, and C term to the forced regeneration mode in which particulates are removed by combustion at appropriate intervals. Is determined for a predetermined time, and it is determined whether or not a temperature raising mode for raising the exhaust gas temperature by the after injection is interposed.

  The function of the term D is set so that when a temperature increase control request is issued after the diesel engine 1 is started, the fuel supply amount at the time of main injection increases and the idle up is turned on (see FIG. 4). ).

  Furthermore, it is desirable that the function of the D term allows idling up when all the requirements for idling stop are satisfied, and immediately returns to the normal mode when all the requirements are not satisfied. .

  The idling stop requirements include, for example, that the rotation speed signal 23a of the rotation sensor 23 is equal to or less than a predetermined value, the opening signal 22a is not transmitted from the accelerator sensor 22, the transmission is in a neutral state, and Considering that the clutch is not depressed.

  The function of the E term is set so that when the temperature increase control request is issued, the opening degree of the exhaust throttle valve 25 is narrowed so that the residual ratio of the exhaust 9 in the cylinder 8 is increased and the exhaust throttle is turned on. (See FIG. 4).

  That is, since the intake air 4 including the exhaust 9 undergoes an explosion stroke through a compression stroke, the exhaust gas temperature is further increased.

  The function of the F term is set so that after-injection is performed (turned ON) when the coolant temperature after starting the diesel engine 1 reaches T2 (threshold) (see FIG. 4). .

  Thus, since the temperature T2 at which after-injection is started is set higher than the temperature at which the idling speed is increased and the flow rate of the exhaust 9 is suppressed, the controller 20 mainly controls the diesel engine 1 until the diesel engine 1 is sufficiently warmed. Only injection is performed.

  Therefore, the exhaust temperature can be raised from any state, and abnormal behavior such as vibration due to misfire does not occur in the engine.

  It should be noted that the exhaust emission control device of the present invention is not limited to the embodiment described above, and it is needless to say that changes can be made without departing from the scope of the present invention.

  The exhaust emission control device of the present invention can be applied to various vehicle types.

It is a conceptual diagram which shows an example of embodiment of the exhaust gas purification apparatus of this invention. It is sectional drawing of the particulate filter relevant to FIG. FIG. 2 is a partially cut perspective view of an oxidation catalyst related to FIG. 1. It is a diagram showing the relationship between idle-up, exhaust throttle, after-injection, and cooling water temperature in time series.

Explanation of symbols

1 Diesel engine 11 Exhaust pipe (engine exhaust system)
13 particulate filter 20 control device (fuel injection control means)
21 Fuel injection device (fuel injection control means)
25 Exhaust throttle valve (exhaust throttle means)
29 Temperature sensor

Claims (1)

  A catalyst regeneration type particulate filter incorporated in the engine exhaust system, a temperature sensor for detecting the engine water temperature, an exhaust throttle means for limiting the exhaust flow rate, and the fuel after the main fuel injection near the top dead center can be ignited Fuel injection control means for performing fuel after-injection at the timing, and a function for increasing the idle speed based on the detection value of the temperature sensor, a function for suppressing the exhaust flow rate by the exhaust throttling means, and a function for starting after-injection An exhaust emission control device comprising a fuel injection control means and a temperature at which after injection is started is set.

Images