Exhaust Gas Purifier

Abstract

Provided is an exhaust emission control device which makes it possible to arbitrarily effect forcible regeneration of a particulate filter by a driver's will. A catalytic regenerative particulate filter 6 is incorporated in an exhaust pipe 4 through which exhaust gas 3 flows. Provided are control and fuel injection devices 12 and 13 for forcibly burning off particulates captured by the particulate filter to regenerate the particulate filter 6 as well as a regeneration button 17 in a driver's cabin for arbitrarily actuating the devices.

Description

TECHNICAL FIELD

The present invention relates to an exhaust emission control device.

BACKGROUND ART

Particulates or particulate matter from a diesel engine is mainly constituted by carbonic soot and a soluble organic fraction (SOF) of high-boiling hydrocarbon and contains a trace of sulfate (misty sulfuric acid fraction). In order to suppress such kind of particulates from being discharged to atmosphere, conventionally a particulate filter is incorporated in an exhaust pipe through which exhaust gas flows.

This kind of particulate filter is constituted by a porous honeycomb structure made of ceramics such as cordierite and having lattice-like compartmentalized passages; alternate ones of the passages have plugged inlets and the remaining passages with unplugged open inlets are plugged at their outlets. Thus, only the exhaust gas passing through thin porous walls compartmentalizing the respective passages is discharged downstream.

The particulates, which are captured by and accumulated on inner surfaces of the walls, require to be burned off so as to regenerate the particulate filter before exhaust resistance increases considerably due to clogging. However, the exhaust gas from the diesel engine in a normal operating status rarely has a chance to reach a temperature level at which the particulates spontaneously ignite. Thus, a catalytic regenerative particulate filter integrally carrying oxidation catalyst has been developed for practical use, said oxidation catalyst being for example platinum-alumina catalyst added with an appropriate amount of rare-earth element such as cerium.

Adoption of such catalytic regenerative particulate filter accelerates oxidation reaction of the captured particulates to lower their ignition temperature, so that the particulates can be burned off at an exhaust temperature lower than ever before.

However, even if such catalytic regenerative particulate filter is adopted, there does exist a temperature range for activation of the oxidation catalyst carried by the particulate filter; so, when an operation continues with temperature lower than a lower limit of such activation temperature range, there may occur deficiency that the particulates are not satisfactorily burned off due to inactive oxidation catalyst. In order to overcome this, it has been suggested that fuel addition means is employed to add fuel to the exhaust gas upstream of the particulate filter to thereby conduct forcible regeneration of the particulate filter through positive heating.

In this case, the fuel added upstream of the particulate filter is oxidized on the oxidation catalyst of the particulate filter and resultant reaction heat elevates catalytic floor temperature, so that the particulates in the particulate filter are burned off.

SUMMARY OF THE INVENTION

Problems to be Solved by the Invention

However, conventionally prevailing is a design concept for automatic forcible regeneration of a particulate filter during running of an automobile. The automatic forcible regeneration is conducted on the basis of determination of excessive capturing, for example, through detection of pressure difference by pressure sensors arranged oppositely to each other with the particulate filter between, or through conjecture in terms of travel distance, operating hours and the like. Thus, there has been a fear that forcible regeneration of a particulate filter cannot be instantly conducted at a driver's will when particulates come to be accumulated in large quantity in the particulate filter for any reason.

The invention was made in view of the above and has its object to provide an exhaust emission control device which makes it possible to arbitrarily conduct forcible regeneration of a particulate filter at a driver's will.

MEANS OR MEASURES FOR SOLVING THE PROBLEMS

The invention is directed to an exhaust emission control device with a catalytic regenerative particulate filter incorporated in an exhaust pipe through which exhaust gas flows, comprising forcible regeneration means for forcibly burning off particulates captured by the particulate filter to regenerate the particulate filter and operating means arranged in a driver's cabin for arbitrarily activating the forcible regeneration means.

Thus, when forcible regeneration of the particulate filter is promptly needed due to excessive capturing or when forcible regeneration of a particulate filter is desired on a regular basis at a driver's will, the driver can operate the operating means to activate the forcible regeneration means, whereby the forcible regeneration of the particulate filter can be arbitrarily conducted at the driver's will.

EFFECTS OF THE INVENTION

An exhaust emission control device of the invention can exhibit an excellent effect or advantage such that a particulate filter can be arbitrarily forcibly regenerated at a driver's will by activating operating means in a driver's cabin, so that when the particulates come to be accumulated in large quantity in the particulate filter for any reason, forcible regeneration means can be instantly activated to regenerate the particulate filter or forcible regeneration can be conducted on a regular basis by the driver's will so as to keep excessive capturing from occurring.

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of the invention will be described in conjunction with drawings.

FIGS. 1-3 show the embodiment of the invention. In the exhaust emission control device of the invention, as exemplarily shown in FIG. 1, exhaust gas 3 discharged from an automobile's diesel engine (internal combustion engine) 1 via an exhaust manifold 2 flows through an exhaust pipe 4 with a muffler 5 which receives therein a catalytic regenerative particulate filter 6 integrally carrying oxidation catalyst. The particulate filter 6 is encased by a filter casing 7 which constitutes an outer cylinder of the muffler 5.

More specifically, the particulate filter 6 as shown in FIG. 2 in enlarged scale is received in the filter casing 7 with inlet and outlet pipes 8 and 9. The particulate filter 6 is in the form of a porous honeycomb structure made of ceramics and has lattice-like compartmentalized passages 6a; alternate ones of the passages 6a are plugged at their inlets and the remaining passages 6a with unplugged open inlets are plugged at their outlets. Only the exhaust gas 3 passing through porous thin walls 6b compartmentalizing the respective passages 6a is discharged downstream.

The pipes 8 and 9 of the filter casing 7 are provided with pressure sensors 10 and 11 for measuring inlet and outlet gas pressures of the exhaust gas 3, respectively, detection signals 10a and 11a from the sensors 10 and 11 being inputted into a control device 12 which constitutes an electronic control unit (ECU) or engine controlling computer. In the control device 12, whether pressure difference between inlet and outlet pressures of the particulate filter 6 is within a normal range or not is determined on the basis of the detection signals 10a and 11a from the pressure sensors 10 and 11; when the pressure difference is beyond the normal range, the particulate filter 6 is determined to be in a state of excessively capturing the particulates.

In the control device 12, a fuel injection signal 13a for commanding fuel injection timing and amount to be injected is outputted to a fuel injection device 13 which injects fuel to the respective cylinders of the diesel engine 1.

The fuel injection device 13 is constituted by a plurality of injectors (not shown) each fitted to each cylinder, an electromagnetic valve for each of the injectors being appropriately controlled in opening to appropriately control the fuel injection timing (starting and ending of the injection) and amount to be injected (time period of the valve being opened).

An accelerator pedal (not shown) in the driver's cabin is provided with a load or accelerator sensor 14 which detects a stepped degree of the accelerator pedal as load for the diesel engine 1, and the diesel engine 1 is provided with a revolution sensor 15 for detecting revolving speed thereof. Accelerator-pedal stepped-in degree signal 14a and revolving speed signal 15a from the sensors 14 and 15 are also inputted into the control device 12.

Further arranged for example on an instrument panel in the driver's cabin are a caution-advisory indicator 16 which is lit by receipt of a warning signal 16a from the control device 12 when the particulate filter 6 is determined in the control device 12 to be in the excessive capturing state as well as a regeneration button 17 which constitutes operating means for arbitrarily activating forcible regeneration means to be detailed hereinafter.

In the control device 12, the fuel injection signal 13a for the normal mode is determined on the basis of the accelerator pedal stepped-in degree signal 14a and revolving speed signal 15a. Meanwhile, the driver's operation or pushing of the button 17 to input a regeneration command signal 17a to the control device causes changeover from the normal mode to the forcible regeneration mode to thereby determine the fuel injection signal 13a such that main fuel injection conducted near the compression upper dead center (crank angle being 0°) is followed by post injection conducted at non-ignition timing after the compression upper dead center.

More specifically, in the embodiment, forcible regeneration means for the particulate filter 6 is constituted by the control device 12 and the fuel injection device 13. When the main injection is followed, as mentioned above, by post injection at non-ignition timing after the compression upper dead center, such post injection causes unburned fuel (consisting mainly of HC: carbon hydride) to be added to the exhaust gas 3. The unburned fuel is oxidized on the oxidation catalyst of the surface of the particulate filter 6. A resultant reaction heat elevates the catalytic floor temperature and the particulates in the particulate filter 6 are burned off.

Thus, when the particulate filter 6 is determined in the control device to be in an excessive capturing state on the basis of the detection signals 10a and 11a from the pressure sensors 10 and 11 and the caution-advisory indicator 16 is lit by receipt of the warning signal 16a from the control device 12, the driver, who sees the indicator being lit, pushes the button 17 so that the control of the fuel injection device 13 by the control device 12 is changed over from the normal mode to the forcible regeneration mode. As a result, the main injection is followed by post injection at non-ignition timing after the compression upper dead center, resulting in addition of unburned fuel to the exhaust gas 3. The added fuel is oxidized on the oxidation catalyst of the surface of the particulate filter 6 and a resultant reaction heat elevates the catalytic floor temperature and the particulates in the particulate filter 6 are burned off.

However, to conduct forcible regeneration under the condition that the filter is already in an excessive capturing state may have a fear that a great amount of particulates are suddenly burned at higher temperature to cause the particulate filter to be melted. Thus, it is preferable to divide the changeover to the forcible regeneration mode through pushing of the regeneration button 17 into several batches; in order to prevent sudden burning at higher temperature from occurring, in initial ones among the batches, fuel post injection is suppressed to an extent that the particulates are moderately oxidized and decomposed on the oxidation catalyst into carbon dioxide and water, and in the remaining batches thereafter, full-scale post injection is carried out.

When the operation is conducted at an operation area with low exhaust temperature insufficient for oxidization of the fuel added by post injection on the oxidation catalyst of the particulate filter 6, after-injection to be detailed hereinafter may be employed at the same time.

More specifically, with respect to the forcible regeneration mode by the control device 12, the fuel injection signal 13a is determined such that after-injection is carried out at combustible timing just after fuel main injection and is followed by post injection at non-ignition timing after the compression upper dead center.

When such after-injection is carried out at combustible timing just after the main injection, the fuel added by the after-injection is burned at timing hardly convertible into output to thereby lower the thermal efficiency of the diesel engine 1, resulting in increase of heat amount part not utilized for motive energy among the heat amount from the fuel and thus elevation of the exhaust temperature. This ensures the temperature necessary for oxidation of fuel added by the succeeding post injection on the oxidation catalyst of the particulate filter 6.

Thus, according to the above-mentioned embodiment, by operating the regeneration button 17 in the driver's cabin, forcible regeneration of the particulate filter 6 can be conducted at the driver's will, so that when a great amount of particulates come to be accumulated in the particulate filter 6 for any reason, the forcible regeneration means can be instantly activated to regenerate the particulate filter 6, or forcible regeneration of the particulate filter 6 on a regular basis by the driver can preliminarily prevent the filter from excessively capturing the particulates.

Timing for pushing the regeneration button 17 may be two alternatives, i.e., during running and upon idling stop. In a case where forcible regeneration is carried out during idling stop, the temperature and flow rate of the exhaust gas 3 tend to be too low and hardly enough for burn-off of the particulates; therefore, when the regeneration button 17 is pushed upon idling stop, there is a necessity that the revolutionary speed of the diesel engine 1 is automatically enhanced up to a medium revolutionary speed by the control device 12.

However, to automatically increase the revolutionary speed of the diesel engine 1 upon idling stop may cause a problem that the driver erroneously shifts the gear to a position other than neutral to thereby make unintended acceleration of the vehicle. To overcome this, it is preferable that control logic for emergency release to be detailed hereinafter is incorporated in the control device 12.

More specifically, as shown in FIG. 3, the normal mode at step S1 proceeds to pushing- or switching-on of the regeneration button 17 at step S2. Then, at step S3, checking is made whether idling stop requirements are satisfied or not. The control logic is such that only when all the requirements are satisfied at step S3, the operation proceeds to step S4 where the forcible regeneration mode is continued for a predetermined time period T before returning to the normal mode; even if only one of the idling stop requirements is not satisfied at step S3, the operation is instantly returned to the normal mode.

The idling stop requirements in step S3 may be, for example, as follows:

1) The revolutionary speed of the engine is below a predetermined revolutionary speed.

2) The accelerator pedal is not activated.

3) The gear is on a neutral position.

4) The clutch is not activated.

Any further requirements may be added.

In the embodiment mentioned above, the description has been made on changeover of the injection pattern of the fuel injection device 13 by the control device 12 as forcible regeneration means for the particulate filter 6. Alternatively, the forcible regeneration means may be in the form of an additional injector for addition of fuel incorporated in an exhaust passage from the exhaust manifold 2 to the exhaust pipe 4, whereby fuel is added to the exhaust gas 3 by this injector. Alternatively, heating means such as electric heater may be arranged for the particulate filter 6.

INDUSTRIAL APPLICABILITY

It is to be understood that an exhaust emission control device according to the invention is not limited to the above-mentioned embodiment and that various changes and modifications may be made without departing from the spirit of the invention. For example, the operating means may be of switch type other than the regeneration button.

BRIEF DESCRIPTION OF THE DRAWINGS

[FIG. 1] A schematic view showing an embodiment of the invention.

[FIG. 2] A sectional view showing details of the particulate filter shown in FIG. 1.

[FIG. 3] A flow sheet showing an example of control logic for emergency release of the forcible regeneration.

EXPLANATION OF THE REFERENCE NUMERALS

• 3 exhaust gas
• 4 exhaust pipe
• 6 particulate filter
• 12 control device (forcible regeneration means)
• 13 fuel injection device (forcible regeneration means)
• 17 regeneration button (operating means)

Claims

1. An exhaust emission control device comprising a catalytic regenerative particulate filter incorporated in an exhaust pipe through which exhaust gas flows, forcible regeneration means for forcibly burning off particulates captured by the particulate filter to regenerate the particulate filter and operating means in a driver's cabin for arbitrarily actuating said forcible regeneration means.