EP1669580A1

EP1669580A1 - A process for controlling regeneration of a particulate filter

Info

Publication number: EP1669580A1
Application number: EP04257637A
Authority: EP
Inventors: Peter J. Calnan
Original assignee: Delphi Technologies Inc
Current assignee: Delphi Technologies Inc
Priority date: 2004-12-08
Filing date: 2004-12-08
Publication date: 2006-06-14
Anticipated expiration: 2024-12-08
Also published as: ATE391843T1; DE602004013026T2; EP1669580B1; DE602004013026D1

Abstract

A process for controlling regeneration of a particulate filter of an internal combustion engine comprising determining the efficiency of a catalytic device provided in the exhaust upstream of the particulate filter and adjusting at least one operating parameter of the engine in order to increase the exhaust gas temperature upstream of the catalytic device to compensate for a reduction in efficiency of the catalytic device due to ageing.

Description

The present invention relates to a process for controlling regeneration of a particulate filter of an internal combustion engine of a vehicle, in particular to compensate for ageing of a catalytic device provided in the exhaust system of the internal combustion engine upstream of the particulate filter.
Diesel engines are frequently fitted with particulate filters in the exhaust system thereof due to the demands of emission legislation. Such filters are usually mounted in the exhaust system downstream of a catalytic device such as an oxidation catalyst and other exhaust components, such as a turbocharger.
In order to avoid blockage of the particulate filter by accumulated soot, leading to an increase in exhaust backpressure, and ultimately a breakdown of the filter, particulate filters require periodic regeneration. During regeneration the temperature of the filter is increased so that the accumulated soot is burnt off, thereby ensuring both acceptable back pressure levels and the avoidance of filter overload.
This periodic regeneration process requires the temperature of the particulate filter to be greatly elevated. The temperature of the particulate filter must be raised to around 600°C in order to burn off the soot, compared to a normal exhaust operating temperature of 150°C. In a known regeneration process extra fuel is injected late in the injection cycle such that unburnt fuel combusts in a catalytic device in the exhaust upstream of the particulate filter in order to achieve the required elevated temperature of the particulate filter.
It is known to utilise a closed loop feedback control system whereby the temperature at the outlet of the catalytic device is monitored and the amount of extra fuel injected is controlled to achieve the required temperature increase.
As the catalytic device ages, its conversion efficiency decreases for a given inlet temperature and this eventually reaches a point where increasing excess fuelling does not provide the required temperature increase. It is then necessary to increase the temperature of the exhaust gases from the engine (and thus further increase the temperature of the catalytic device). In order to avoid this failure to reach the required regeneration temperature when the catalytic device has aged, it is presently necessary to calibrate the engine exhaust gas temperature (by adjusting the base calibration setting of the main fuel injection timing) to a level higher than that required when the catalytic device is new, reducing the efficiency of the regeneration process and increasing the likelihood of component failure (for example contamination of the lubrication system with fuel or excessive turbocharger temperature).
The present invention overcomes this problem by providing progressive compensation for this ageing process of the catalytic device, maximising regeneration efficiency whilst reducing the potential impact of the regeneration conditions on the engine and exhaust components over the lifetime of the vehicle.
According to the present invention there is provided a process for controlling regeneration of a particulate filter of an internal combustion engine comprising determining the efficiency of a catalytic device provided in the exhaust upstream of the particulate filter and adjusting at least one operating parameter of the engine in order to increase the exhaust gas temperature upstream of the catalytic device to compensate for a reduction in efficiency of the catalytic device due to ageing.
Preferably the efficiency of the catalytic device is determined by determining the exhaust gas temperature downstream of the catalytic device and comparing said exhaust gas temperature with a target temperature to obtain a measure of the temperature increase lost due to reduced catalytic effectiveness, the at least one operating parameter of the engine being adjusted to reduce the error between the actual exhaust temperature downstream of the catalytic device and a target temperature.
Preferably the step of determining the exhaust gas temperature downstream of the catalytic device comprises recording the exhaust gas temperature at intervals over a complete regeneration cycle and determining the mean exhaust gas temperature as an average of the measured temperature over a plurality of selected intervals during said complete regeneration cycle, the step of adjusting at least one operating parameter of the engine occurring over one or more subsequent regeneration cycles.
In an alternative embodiment, the averaging of the temperature difference might be replaced by a form of integral measure of the temperature difference over the regeneration event.
In one embodiment the step of determining the exhaust gas temperature downstream of the catalytic device comprises filtering the recorded temperature values used to determine the average exhaust gas temperature and using only those recorded values where the first order differential of the temperature difference between successive recorded values falls below a predetermined value, or is zero in order to minimise transient effects. Additionally, the averaging process is only based upon those values corresponding to those operating points where the target temperature can be reached with fully functioning catalytic activity.
In an alternative embodiment, measurements of engine load and engine speed are recorded along with exhaust gas temperature and the recorded values are filtered such that those recorded temperatures associated with engine load/speed conditions known not to be able to achieve the temperature target are not utilised in the determination of the average exhaust gas temperature (or, alternatively, are taken into account with a lower temperature target when calculating the temperature differential). The matching of specific engine load/speed conditions to sensor output requires the implementation of a lag filter in order to take into account thermal inertia and a signal delay in order to take into account system transport delays.
Should a more refined compensation approach be required, the above technique of engine load/speed temperature matching can be used to construct a rolling average of temperature differential on an engine load/speed specific basis that produces a temperature matrix which could be used to refine the adjustment of engine operating parameter on a load/speed basis.
Preferably the operating parameters of the engine that are adjusted comprise main fuel injection timing and throttle position. However, it is envisaged that other engine operating parameters may also, or alternatively, be adjusted. Preferably the main fuel injection timing comprises a primary engine operating parameter which is adjusted.
Preferably the adjustment of the operating parameter(s) of the engine is proportional to the difference between the determined mean exhaust gas temperature and the target temperature. This may be made on a load/speed specific basis if a correspondent temperature matrix is available. The relationship between the temperature difference and the engine operating parameter adjustment may not necessarily be linear. For example, a temperature difference of 200°C may result in an additional main fuel injection timing retard of 8°, whereas a temperature difference of 100°C may result in an additional main fuel injection timing retard of 3°.
Preferably the magnitude of engine operating parameter adjustment for each operating parameter of the engine to be varied is limited to a maximum adjustment value (e.g. 8° retard for main fuel injection timing). The adjustment of an engine operating parameter may be phased in over two or more consecutive regeneration cycles.
The reduction in temperature difference (or other measure of catalyst efficiency) through adjustment of engine operating parameter should not be allowed to reverse the above mentioned adjustment of engine operating parameter and thereby result in reversal of the ageing compensation. This may preferably be achieved by only allowing reversal of the parameter adjustment when the polarity of the temperature difference(or other measure of catalyst efficiency) is seen to have been reversed.
The priority and scheduling of adjustment of each engine operating parameter to be adjusted may be predetermined by means of a temperature compensation algorithm, preferably as a function of the degree of temperature difference between the determined mean exhaust gas temperature over a regeneration cycle and the target temperature.
In an alternative embodiment the efficiency of the catalytic device may be determined by determining the level of hydrocarbons and/or oxygen in the exhaust gas downstream of the catalytic device and comparing said level to a target level (based on that achieved by a fully effective catalytic device). The abovementioned averaging processes may be applied equally to such alternative embodiment, processing the measured values of hydrocarbon or oxygen content in the exhaust gas in place of exhaust gas temperature.
An embodiment of the present invention will now be described with reference to the accompanying drawings, in which:-

Figure 1 is a schematic illustration of a regeneration process according to a first embodiment of the present invention;
Figure 2 is a schematic view of the catalyst performance monitoring device of the regeneration process of Fig. 1; and
Figure 3 is a schematic view of the engine parameter modifier device of the regeneration process of Fig. 1.

The position, within the overall regeneration control structure, of an engine parameter change algorithm used to effect actual compensation of the temperature increase loss due to catalytic ageing is shown in fig.1. The base regeneration strategy device 1 is shown in Fig. 1 is conventional in the prior art, whereas the catalyst performance monitoring device 2 and the engine parameter modifier device 3 represent the additional devices performing the process of the present invention.
The catalyst performance monitoring device 2 determines the efficiency of the catalytic device and the engine parameter modifier device 3 determines the necessary changes to the engine parameters used to realise the progressive compensation for catalytic device ageing.
The outputs of the engine parameter modifier device 3 comprise the engine parameter modifications required to compensate for catalytic device ageing and such outputs are combined with the base engine parameter modifications determined by the known regeneration strategy device 1 to provide an output signal for the controlling the amount of fuel injected, the main fuel injection timing and the throttle position required to achieve the exhaust gas temperature necessary for regeneration of the particulate filter.
Device 2 is shown in further detail in figure.2.
The preferred inputs to device 2 are engine load 1 engine speed 2 and catalyst outlet temperature 3.
The catalyst performance monitoring device 2 monitors these inputs over a complete regeneration cycle and compares the mean catalytic device (DOC) outlet temperature with a predetermined target temperature to provide an output of the temperature difference between the measured DOC outlet temperature and the target temperature as a measure of the DOC efficiency. This measure is recorded over a plurality of selected intervals during said complete regeneration cycle.
Figure 2 shows the use of a target temperature limitation table to provide load and speed dependent criteria for selecting recorded measurements to be used in the averaging calculation in order to restrict the average to those recorded measurements where the target temperature can actually be reached. The load and speed inputs to this table are filtered and delayed in order to match load and speed values to the corresponding measured temperature.
An additional measurement selection criteria based upon the first order differential of the temperature difference is used to reduce the influence of temperature transients.
The base regeneration strategy device 1 provides a full regeneration active flag to the catalytic performance monitoring device 2 so that the sampling and averaging only occurs during the particulate filter regeneration process. The catalyst performance monitoring device 2 also provides filtered engine load and speed readings for use by the engine parameter modifier device 3.
The engine parameter modifier device 3 is shown in further detail in figure 3. The averaged temperature difference and filtered engine load and speed values from the Catalyst performance monitoring device 2 are fed to the engine parameter modifier device 3. This device 3 provides a calibration or control parameter modification signal which is used to control at least one operating parameter of the engine, such as main fuel injection timing, to increase the DOC inlet temperature (i.e. engine exhaust gas temperature) by the amount required to compensate for the determined loss in efficiency of the oxidation catalyst to ensure the oxidation catalyst outlet temperature reaches the target temperature required for particulate filter regeneration during the next and subsequent regeneration cycles.
Fig.3 shows two actuator blocks 8, 9 for adjusting a selected engine operating parameter for which the primary input is the averaged temperature difference (defining a measure of the catalytic efficiency). It is this primary input that essentially defines the output of the actuator blocks, being the magnitude of actuator setting adjustment. Actuator setting adjustment would only be reversed if the temperature difference were seen to reverse polarity.
The output may also determined a function of engine load and speed. Temperature difference threshold tables 10, 11 for each engine operating parameter actuator 8,9, provide an output linked to the available temperature increase for a given associated engine operating adjustment as a function of load and speed and required temperature increase, and enable the scheduling, prioritising or sequencing of more than one actuator to be achieved. In this embodiment the selection of which engine operating parameter to adjust is made on the basis of a comparison between the averaged temperature difference and the contents of the look-up tables 10,11.
Each engine operating parameter actuator 8,9 is associated with a determining unit 12,13 that utilises engine speed and load inputs to define the absolute limit of the available engine operating adjustment (as a function of load and speed) and the maximum amount of adjustment that may change over each update event.

Claims

A process for controlling regeneration of a particulate filter of an internal combustion engine comprising determining the efficiency of a catalytic device provided in the exhaust upstream of the particulate filter and adjusting at least one operating parameter of the engine in order to increase the exhaust gas temperature upstream of the catalytic device to compensate for a reduction in efficiency of the catalytic device due to ageing.
A process as claimed in claim 1, wherein the efficiency of the catalytic device is determined by determining the exhaust gas temperature downstream of the catalytic device and comparing said exhaust gas temperature with a target temperature to obtain a measure of the temperature increase lost due to reduced catalytic effectiveness, the at least one operating parameter of the engine being adjusted to reduce the error between the actual exhaust temperature downstream of the catalytic device and a target temperature.
A process as claimed in claim 2, wherein the efficiency of the catalytic device may be determined through an integration of the difference between exhaust gas temperature and the target temperature over one or more regeneration cycles.
A process as claimed in claim 2 or claim 3, wherein the step of determining the exhaust gas temperature downstream of the catalytic device comprises recording the exhaust gas temperature at intervals over a complete regeneration cycle and determining the mean exhaust gas temperature as an average of the measured temperature over a plurality of selected intervals during said complete regeneration cycle, the step of adjusting at least one operating parameter of the engine occurring over one or more subsequent regeneration cycles.
A process as claimed in any of claims 2 to 4, wherein the step of determining the exhaust gas temperature downstream of the catalytic device comprises filtering the recorded temperature values used to determine the average exhaust gas temperature and using only those recorded values where the first order differential of the temperature difference between successive recorded values falls below a predetermined value, or is zero in order to minimise transient effects.
A process as claimed in claim 4 or claim 5, the averaging process is only based upon those values corresponding to those operating points where the target temperature can be reached with fully functioning catalytic activity.
A process as claimed in any of claims 3 to 6, wherein measurements of engine load and engine speed are recorded along with exhaust gas temperature and the recorded values are filtered such that those recorded temperatures associated with engine load/speed conditions known not to be able to achieve the temperature target are not utilised in the determination of the average exhaust gas temperature (or, alternatively, are taken into account with a lower temperature target when calculating the temperature differential).
A process as claimed in claim 7, wherein a lag filter is used to filter the measurements of engine load and speed in order to take into account thermal inertia.
A process as claimed in claim 7 or claim 8, wherein a signal delay is used in the measurement of engine speed and load in order to take into account system transport delays.
A process as claimed in any preceding claim, wherein the operating parameters of the engine that are adjusted comprise main fuel injection timing and throttle position.
A process as claimed in claim 10, wherein the main fuel injection timing comprises a primary engine operating parameter which is adjusted.
A process as claimed in any preceding claim, wherein the adjustment of the operating parameter(s) of the engine is proportional to the difference between the determined mean exhaust gas temperature and the target temperature.
A process as claimed in any preceding claim, wherein the magnitude of engine operating parameter adjustment for each operating parameter of the engine to be varied is limited to a maximum adjustment value.
A process as claimed in any preceding claim, wherein the adjustment of an engine operating parameter is phased in over two or more consecutive regeneration cycles.
A process as claimed in any preceding claim, wherein the priority and scheduling of adjustment of each engine operating parameter to be adjusted may be predetermined by means of a temperature compensation algorithm, preferably as a function of the degree of temperature difference between the determined mean exhaust gas temperature over a regeneration cycle and the target temperature.
A process as claimed in claim 1, wherein the efficiency of the catalytic device may be determined by determining the level of hydrocarbons and/or oxygen in the exhaust gas downstream of the catalytic device and comparing said level to a target level based on that achieved by a fully effective catalytic device.