GB2416717A

GB2416717A - A method for regenerating an exhaust treatment device

Info

Publication number: GB2416717A
Application number: GB0416814A
Authority: GB
Inventors: Andrew David Sumner; Peter Graham Eastwood; Ivan Palomar; Miquel Roca; Chris Clayton; Kim Ford; Jack Carlile
Original assignee: Ford Global Technologies LLC
Current assignee: Ford Global Technologies LLC
Priority date: 2004-07-29
Filing date: 2004-07-29
Publication date: 2006-02-08
Anticipated expiration: 2024-07-29
Also published as: GB0416814D0; GB2416717A8; GB2416717B; GB2416717B8

Abstract

A method for regenerating an exhaust treatment device such as a diesel particulate filter 36 is disclosed in which an engine 12 from which exhaust gasses are produced is operated in at least two separate modes during regeneration of the exhaust treatment device 36. In one of the modes the engine 12 is operated so as to increase the temperature of the exhaust gases in a controlled and stable manner and in the other mode the engine 12 is operated so as to produce a rapid increase in the temperature of the exhaust gases entering the exhaust treatment device 36. By rapidly increasing the temperature of the exhaust gasses entering the exhaust treatment device 36, the time taken for regeneration can be reduced particularly if the engine 12 is operating under fluctuating load conditions involving a considerable amount of engine deceleration and idling.

Description

A METHOD FOR REGENERATING AN EXHAUST TREATMENT DEVICE

This invention relates to internal combustion engines and in particular to the regeneration of an exhaust treatment device arranged to receive exhaust gasses from an internal combustion engine.

It is well known to connect an exhaust treatment device such as catalytic converter, NOX trap or Diesel particulate 1C filter to the exhaust stream from an internal combustion engine so as to reduce pollution from the engine entering the atmosphere. It is further known that from time to time such exhaust treatment devices become contaminated or filled with the undesirable products of combustion and needs to be cleansed or purged of these contaminants. Such cleaning or purging is normally brought about by operating the engine in such a manner as to increase the temperature of the exhaust gasses flowing through the exhaust treatment device to permit the contaminants to be burnt off or reacted and 2r restore the exhaust treatment device to a more efficient operating state. Such a process will be referred to herein as regeneration. An example of such regeneration is given in US Patent number 6,568,173 in which the engine is operated in three modes of operation, a light-off mode used 2- to light off a catalytic converter, a regeneration mode used to regenerate the exhaust treatment device and a storage mode or normal engine operating mode in which the engine operates to provide power and the undesirable products of combustion are collected in the exhaust treatment device. 3c

It is a problem with such an arrangement is that when the engine is operating in a cyclic manner comprising of acceleration followed by deceleration and then idling such as during city driving it is difficult to achieve the 3-: exhaust gas temperature required to effectively regenerate the exhaust treatment device or the period of time required to reach such a temperature is lengthy may be as much as e, five minutes. In either case this may result in poor or no effective regeneration taking place. This is because during such transient conditions the conservative engine control strategy required to increase the temperature of the exhaust gasses without exceeding any temperature limits of the exhaust system simply does not produce sufficient heat in the exhaust gas flow to produce a rapid increase in exhaust gas temperature and so this temperature may not be reached during a short engine operating cycle or may be difficult to lo maintain.

It is an object of this invention to provide an improved method for regenerating an exhaust gas treatment device connected to an engine.

According to a first aspect of the invention there is provided a method for regenerating an exhaust treatment device connected to an internal combustion engine so as to receive exhaust gasses from the engine, the method comprising operating the engine in an operational mode during normal use of the engine, determining whether regeneration of the exhaust treatment device is required and, if regeneration is determined to be necessary, operating the engine in one of at least two separate modes of operation during regeneration dependent upon the temperature of the exhaust gases wherein, if the temperature of the exhaust gases is above a first predetermined temperature, the engine is operated in a regenerative mode of operation so as to produce a steady increase in the temperature of exhaust gasses entering the exhaust treatment device without exceeding any temperature limits for the exhaust treatment device and, if the temperature is below the first predetermined temperature, the engine is operated in a transient mode so as to produce a rapid increase in exhaust gas temperature entering the exhaust treatment device and switching to the regenerative mode of operation from the transient mode of operation when the temperature of - 3 - the exhaust gasses entering the exhaust treatment device exceeds the first predetermined temperature.

The method may further comprising switching between the regenerative and transient modes in order to maintain the exhaust gas temperature entering the exhaust treatment device sufficiently high to maintain efficient regeneration.

The method may further comprise operating the engine in l0 the transient mode when the temperature of the exhaust gases is below the first predetermined temperature but above a second predetermined temperature.

If the temperature of the exhaust gasses is below the second predetermined temperature, the engine may be operated in a light-off mode of operation.

The first predetermined temperature may be the temperature required to regenerate the exhaust treatment device.

The exhaust treatment device may be a catalytic converter and the second predetermined temperature is a light-off temperature of the catalytic converter.

Alternatively, the engine may have a catalytic converter connected thereto to receive exhaust gases from the engine and an exhaust treatment device connected downstream from the catalytic converter.

In which case, the exhaust treatment device may be one of a particulate filter and a NOX trap.

The internal combustion engine may be a diesel engine and the particulate filter may be a diesel particulate filter.

: , .:: . . . . : - 4 - The second predetermined temperature may be a light-off temperature of the catalytic converter.

The method may further comprise reverting to the operational mode when it is determined that regeneration of the exhaust treatment device is complete.

The regenerative mode may comprise a first late injection of fuel into at least one cylinder of the engine JO early in the power stroke of the engine for combustion in the respective cylinder so as to increase the temperature of the exhaust gasses leaving the respective cylinder and at least one further late injection of fuel into the respective cylinder later in the power stroke.

The transient mode may comprise a first late injection of fuel into at least one cylinder of the engine early in the power stroke of the engine for combustion in the respective cylinder so as to increase the temperature of the gasses leaving the respective cylinder and at least one further late injection of fuel into the respective cylinder later in the power stroke wherein the amount of fuel injected in the transient mode of operation is greater than the amount of fuel injected during the regenerative mode so as to produce a rapid increase in the temperature of the exhaust gases entering the exhaust treatment device.

The or each further late injection of fuel may be timed so that at least some of the fuel injected during the or each further late injection leaves the respective cylinder un-combusted.

The light-off mode may comprise a first late injection of fuel into at least one cylinder of the engine early in -35 the power stroke of the engine for combustion in the respective cylinder so as to increase the temperature of the gasses leaving the respective cylinder.

2. . . . - 5 - The engine may have a valve controlled air intake manifold and the valve may be positioned in a position to restrict the flow of air into the engine during regeneration.

According to a second aspect of the invention there is provided a system for controlling the regeneration of an exhaust treatment device connected to an internal combustion lo engine, the system comprising a controller operably connected to a temperature sensor positioned upstream from the exhaust treatment device so as to sense the temperature of the exhaust gasses entering the exhaust treatment device wherein the controller is programmed so as to control the operation of the engine so as to operate the engine in an operational mode during normal use of the engine, determine whether regeneration of the exhaust treatment device is required and, if regeneration is determined to be necessary, operate the engine in one of at least two separate modes of operation during regeneration dependent upon the temperature of the exhaust gases entering the exhaust treatment device as sensed by the temperature sensor wherein, if the temperature of the exhaust gases is above a first predetermined temperature, the engine is operated by the controller in a regenerative mode of operation so as to produce a steady increase in the temperature of exhaust gasses entering the exhaust treatment device without exceeding any temperature limits for the exhaust treatment device and, if the temperature is below the first predetermined temperature, the engine is operated by the controller in a transient mode so as to produce a rapid increase in exhaust gas temperature entering the exhaust treatment device and is further programmed to switch to the regenerative mode of operation from the transient mode of operation when the temperature of the exhaust gasses entering the exhaust treatment device as sensed by the e2. .. :2 6 - temperature sensor exceeds the first predetermined temperature.

The first predetermined temperature may be a temperature required for regeneration of the exhaust treatment device.

The engine may have a catalytic converter connected thereto and the controller may be operable to operate the engine in the transient mode only when the temperature of the exhaust gasses entering the exhaust treatment device is above the light-off temperature of the catalytic converter but below the first predetermined temperature.

The controller may be further operable to operate the engine in a lightoff mode of operation when the temperature of the exhaust gasses entering the exhaust treatment device are below the light-off temperature of the catalytic converter.

The engine may have an exhaust gas treatment device connected downstream from the catalytic converter.

The exhaust treatment device may be one of a particulate filter and a NOX trap.

The invention will now be described by way of example with reference to the accompanying drawing of which: Fig.1 is a diagrammatic representation of an engine and system according to one aspect of the invention; and Fig. 2 is a flow chart showing a method of regenerating an exhaust treatment device according to another aspect of the invention.

:. 22.

With reference to Fig.1 there is shown a diesel internal combustion engine 12 having an intake or inlet manifold 14 and an exhaust manifold to which is connected a turbocharger 13. An exhaust pipe 16 couples an outlet from the turbocharger 13 to a catalytic converter 35 and then to an exhaust treatment device in the form of a diesel particulate filter 36 (DPF). The exhaust pipe 16 has an outlet end 26 where exhaust gasses that have passed through the catalytic converter 35 and particulate filter 36 are lo exhausted into the surrounding atmosphere.

A conventional fuel supply 26 provides fuel which is injected directly into the engine 12 where it mixes with the air from the intake manifold 14 to provide a combustion l5 mixture. The injection of fuel to the engine 12 is controlled by a controller in the form of an electronic control module (ECM) 28. A throttle valve 25 is mounted in the inlet manifold 14 to control the flow of air into the engine 12. The throttle valve 25 is controlled by the ?0 electronic control unit 28 which also receives an input from an accelerator pedal (not shown) which is used to provide an indication of driver demand.

A system for controlling regeneration of the diesel particulate filter includes a controller which in this case is included as an integral part of the engine control module 28 but could be formed by one or more separate electronic controllers. The controller is arranged to receive signals from a number of sensors forming part of the system as described hereinafter and is programmed to perform certain functions in order to control the regeneration of the diesel particulate filter 36.

The term signal as meant herein is to be interpreted in its widest sense and can include but is not limited to a digital signal, data, an analogue signal, a measurement of ",','2.2''" :2'' a , i - 8 voltage or current, a measurement of frequency or variations in frequency.

The first sensor is an air sensor 22 which measures the temperature of the air entering the engine 12 through the intake manifold 14. The air sensor 22 is operable to send a signal to the electronic control module 28 indicative of the sensed temperature. The airflow through the intake manifold 14 is measured by means of a mass air flow (MAF) sensor 18 lo and a signal indicative of the mass air flow is sent to the electronic control module 28.

An engine coolant temperature sensor 30 and an engine speed (RPM) sensor 32 communicates engine temperature and engine speed information respectively to the electronic control module 28 which can be used to estimate the duty cycle of the engine 12.

The temperature of the exhaust gases entering the diesel particulate filter 36 is monitored via an upstream temperature sensor 37.

The temperature sensor 37 is located between the catalytic converter 35 and the particulate filter 36 and provides a signal to the electronic control module 28 which is indicative of the temperature of the exhaust gases within the catalytic converter 35 and also an indication of the temperature of the exhaust gases entering the diesel particulate filter 36. It will be appreciated that if required separate temperature sensors could be positioned upstream from the catalytic converter 35, within the catalytic converter 35, within or downstream from the diesel particulate filter 36 to provide additional temperature information. For example there could be a temperature 3r: sensor located upstream from the catalyst 35 to determine when the light-off temperature of the catalyst 35 has been reached and a second sensor located downstream from the 1 ' :a - 9 diesel particulate filter 36 for use in controlling the switching between different modes as will be described hereinafter.

The electronic control module 28 includes at least one microprocessor and various computer readable storage media, which may include but is not limited to a read only memory (ROM), a random access memory (RAM), and a keep-alive memory (KAM). The computer readable storage media may be implemented by any of a number of known volatile and non- volatile storage devices including but not limited to PROM, EPROM, EEPROM, flash memory, and the like, all of which are well known in the art. RAM is typically used for temporary data storage of various operating variables which are lost when the engine ignition is turned off, such as counters, timers, status flags, and the like. KAM is generally used to store learned or adaptive values which may change over time. The contents of KAM are maintained as long as some power is provided to the electronic controller 28.

Preferably, one or more ROMs within the electronic control module 28 contain control logic implemented by program instructions executed by the microprocessor along with various system parameter values and calibrations.

The electronic control module 28 receives signals from the exhaust gas temperature sensor 37, the mass air flow sensor 18 and the air sensor 22 and uses these signals co control the operation of the engine 12 and to control the regeneration of the particulate filter 36 as will be described hereinafter in greater detail.

Operation of the system is best understood with reference to the method shown in Fig.2 used to control regeneration of the diesel particulate filter 36. This method is programmed into the controller formed as part of the electronic control module 28. a.

e ' A- ea.

The method starts at step 100 which is normally when an engine on signal is received by the electronic control module 28 from an operator controlled switch.

The first step is to determine whether regeneration of the exhaust treatment device in the form of the diesel particulate filter 36 is required. This can be achieved in many ways such as, for example but without limitation, by JO analysis of the duty cycle of the engine 12, after a predetermined period of engine operation or when a pressure drop across the diesel particulate filter 36 exceeds a particular level. If regeneration is not required the method operates so as to check again whether the conditions for regeneration have been met and the electronic control module 28 will operate the engine 12 in a normal mode of operation in which torque is produced in response to actuation of the accelerator pedal.

If regeneration is determined to be required then the method advances to step 120 where a determination is made as to whether the temperature of the exhaust gases (T) as sensed by the temperature sensor 37 have exceeded a predetermined temperature T1.

That is to say the test: IS T > T1 where T is the temperature of the exhaust gases as measured by the temperature sensor 37 and T1 is a predetermined temperature threshold is performed.

In this case T1 corresponds to a light-off temperature of the catalytic converter 35 and is 300 C. Therefore if the temperature as sensed by the temperature sensor 37 is greater than 300 C the method advances to step 140 but if it is less than or equal to 300 C the method advances to step 130. This test is used to determine whether the catalytic . . . . . ee. . e a e . . - 11 - converter is lit up for if it is the temperature will exceed 300 C by some margin but if it is not lit up then it is imperative to light it up quickly in order to reduce emissions during regeneration of the diesel particulate s filter 36.

Therefore if the answer to step 120 is 'NO' the method advances to step 130 and the electronic control module 28 is operable to control the engine 12 ina first mode of operation or light-off mode indicated on Fig. 2 by the term Mode 1'.

In this mode of operation the primary aim is to increase the temperature of the exhaust gases leaving the engine 12 in order to light-off the catalytic converter 35.

In this case this is achieved by the late injection of fuel into each cylinder of the engine 12 early in its power stroke. Because the fuel is injected early in the power stroke a large proportion of the fuel will be combusted in the cylinders of the engine 12 before the exhaust stroke commences and so this will increase the temperature of the exhaust gasses leaving the cylinders of the engine 12. This high temperature gas will cause the catalytic converter 35 to be rapidly heated until at some point it will light-off and start efficiently dealing with the emissions from the engine 12.

While operating in the light-off mode the method advances to step 170 to determine whether regeneration is complete and then reverts to step 120 to recheck the temperature of the exhaust gases. The determination of whether regeneration is complete can be effected in several ways such as, for example but without limitation, by regenerating for a predetermined period of time, by monitoring the pressure drop across the diesel particulate filter or by analysis of the duty cycle of the engine during . ë e ë - 12 regeneration. If regeneration is considered to be complete, the method advances to step 200 where it ends.

When the answer to the step 120 question is 'YES' then it is known that the catalytic converter 35 is already lit up and the method advances to step 140 where a determination is made as to whether the temperature of the exhaust gasses exceed a further predetermined temperature threshold T2 If the temperature of the exhaust gasses are the same as or less than the predetermined temperature T2 then the method advances to a second mode of operation or transient mode of operation indicated on Fig.2 by the term 'Mode 2' but if the temperature of the exhaust gases are above the predetermined limit T2 then the method advances to step 160 where the engine is operated in a regenerative or third mode indicated on Fig.2 by the term 'Mode 3'.

This further predetermined temperature threshold is the temperature where efficient regeneration of the diesel particulate filter 36 will occur. In the case of a diesel particulate filter this temperature will be in the range of approximately 450 to 650 C depending upon whether a diesel particulate filter with cerium oxide fuel additive is used or a coated diesel particulate filter is used. In this case a diesel particulate filter with cerium fuel additive is used and the temperature T2 is 480 C.

In the regenerative mode the temperature of the exhaust gases must be sufficiently high to produce regeneration of the diesel particulate filter 36 which in this case requires a temperature high enough to burn the soot stored in the diesel particulate filter 36.

To achieve this high temperature the engine 12 is controlled by the electronic control module 28 to provide a first late injection of fuel into each cylinder of the . . - 13 - engine 12 early in the power stroke as previously used to create catalytic converter light-off and in addition to this, one or more further late injections of fuel into the cylinders of the engine 12 are made later in the power stroke. In the example being described only one further late injection is used but it will be appreciated that there could be two or more further late injections. As before this first late injection of fuel will tend to combust in the cylinders so as to increase thetemperature of the 0 gasses leaving the engine 12 but the further late injection of fuel is timed so that some of the fuel injected into the cylinders may remain un- combusted and is ejected from the engine 12 into the catalytic converter 35 or may not remain un-combusted but merely prolongs combustion in the chamber.

This will depend upon the operating conditions of the engine 12.

If there is un-combusted fuel then this will ignite in the catalytic converter 35 during an exothermic reaction and will further increase the temperature of the exhaust gasses exiting the catalytic converter 35 and therefore the temperature of the exhaust gases entering the diesel particulate filter 36. The control of the engine 12 during this regenerative mode is such that even under steady state conditions the increase in exhaust gas temperature will not exceed the maximum safe temperature of the turbocharger 13, catalyst 35 or diesel particulate filter 36 so that no damage will occur to these components. In addition, the Oxygen levels for the exhaust gases will be maintained within acceptable limits. However, due to the use of such a conservative strategy the rate of temperature rise is relatively slow, particularly if the engine 12 is not operating in a steady state but is subject to repeated acceleration and deceleration with periods of idling. This is because, particularly during engine deceleration, insufficient fuel is being admitted to the engine 12 to produce or maintain the desired regeneration temperature.

. . . . . - 14 During operation in the regenerative mode the electronic control module 28 is operable to continuously determine whether regeneration is complete as indicated by step 170 and to keep checking whether the temperature comparisons embodied in steps 120 and 140 remain the same or have changed. If regeneration is considered to be complete, the method advances to step 200 where it ends.

At step 140 if the temperature of the exhaust gasses as measured by the temperature sensor 37 is less than or equal to 480 C the engine 12 is operated by the electronic control module 28 in the transient mode.

The transient mode is a very aggressive mode of engine operation and if used for an extended period of time under steady state conditions may result in the maximum temperature limit of the turbocharger 13, catalyst 35 or diesel particulate filter 36 being exceeded and the minimum Oxygen levels for the exhaust may be below the limit for regeneration as used in the regeneration or third mode.

That is to say, if the transient mode were to be used for a prolonged period of time, damage to the turbocharger, catalyst 35 or the diesel particulate filter 36 may occur.

The electronic control module 28 is operable in this transient mode to operate the engine 12 so as to provide a very rapid increase in exhaust gas temperature even if the engine 12 is not operating in a steady state but is subject to repeated acceleration and deceleration with periods of idling.

In the transient mode of operation the electronic control module 28 is operable to provide a first late injection of fuel into each cylinder of the engine 12 early in the power stroke as previously used to create catalytic converter light-off and, in addition to this, a further late

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: : : : .:. . : : '

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- 15 - injection of fuel into the cylinders of the engine 12 is made later in the power stroke as with the regenerative mode. As before this further late injection of fuel is timed so that some of the fuel injected into the cylinders may remain un-combusted and is ejected from the engine 12 into the catalytic converter 35. However, unlike operation in the regenerative mode the temperature limits for the turbocharger 13, catalyst 35 or the diesel particulate filter are not considered nor are the exhaust gas Oxygen levels and the primary aim of this mode of operation is to increase the temperature of the exhaust gasses as quickly as possible. In this case this is achieved by injecting more fuel into the cylinders of the engine during the further late injection so that it is likely that more fuel is available to combust in the catalytic converter 35.

It will however be appreciated by those skilled in the art that there are various means which could be used to increase exhaust gas temperature including single or multiple late injections of fuel, variations of fuel rail pressure, variations of turbocharger boost pressure, ignition retard for spark engines plus others and that the invention is not limited to the particular method of achieving an increase in exhaust gas temperature. What is important is that, irrespective of the technique used to increase the exhaust gas temperature, in the transient mode the maximum temperature limit of the turbocharger, catalyst or diesel particulate filter and the oxygen level of the exhaust gasses are ignored whereas in the regenerative mode these limits are observed. This enables the engine 12 to be controlled in a very aggressive manner so as to produce a rapid increase in exhaust gas temperature at the entry to the diesel particulate filter 36.

During operation in the transient mode the electronic control module 28 is operable to continuously determine whether regeneration is complete as indicated by step 170 . . . - 16 - and to keep checking whether the temperature comparisons embodied in steps 120 and 140 remain the same or have changed. If regeneration is considered to be complete, the method advances to step 200 where it ends and if the temperature of the exhaust gasses exceeds the temperature T2 the electronic control module 28 will automatically switch the control of the engine 12 from the transient mode to the regenerative mode. Similarly, while operating in the regenerative mode the electronic control module 28 is lo operable to switch to the transient mode if the required regeneration temperature is not being maintained.

As a further means of assisting with regeneration the throttle valve 25 can be moved by the electronic control i5 module 28 to a position in which it restricts the flow of air into the engine 12. This has two advantages, firstly it will cause the exhaust volume from the engine to be reduced minimising the cooling effect on the diesel particulate filter 36, secondly the exhaust temperature to be higher due to the reduced air/fuel ratio than without the throttle restriction and thirdly it will impose a load on the engine 12 against which the engine 12 must work allowing more fuel to be injecting further benefiting exhaust temperatures.

2- This is particularly useful when the engine is idling or deceleratingbecause it enables more fuel to be injected into the engine 12 without increasing the output torque from the engine 12 and can be used to reduce or minimise any loss of temperature due to exhaust cooling and loss of 3c temperature in the exhaust gasses.

It will be appreciated by those skilled in the art that the use of a single temperature sensor to determine an indication of the temperature of the catalytic converter and -35 also an indication of the temperature of the exhaust gasses entering the diesel particulate filter is a very cost effective and simple method of obtaining these temperatures . . . - . . . - 17 - to a sufficient degree of accuracy to effectively control the engine 12 in accordance with this invention. However, the invention is not so limited and the use of a pre- catalyst temperature sensor to indicate catalyst light-off and a post particulate filter temperature sensor to indicate the temperature of the exhaust gasses in the particulate filter is equally suitable for use in the method shown in Fig.2 The inventors have therefore realised that significant gains can be made by ignoring normal operating constraints and using an aggressive engine control strategy which will increase the temperature of the exhaust gasses rapidly and which if allowed to continue may cause damage to the turbocharger, catalyst or the diesel particulate filter and potentially other components subject to the exhaust gasses.

By producing such a rapid increase in temperature the time needed for regeneration can be reduced which has several advantages including being able to fully regenerate the exhaust treatment device on shorter journeys than is normally possible, reducing the amount of fuel used as late injection does not need to be carried out for such an extended period of time, reducing the emissions produced due to the shorter period of time and reducing the oil dilution due to the reduction in the time in which late injection needs to be used. In addition, in situations where the engine is subject to repeated acceleration and deceleration and periods of idling, the new method will reduce the number of failed regenerations by ensuring that the required regeneration temperature is reached quickly and will maintain that temperature even if the operation of the engine is such that insufficient temperature can be produced used the more conservative regenerative mode of operation by switching in and out of the transient mode.

Although the invention has been described with respect to its use for regenerating an exhaust treatment device in :'::: .. :. :: .

8 fD - 18 - the form of a diesel particulate filter it will be appreciated it could be applied to other types of engine and to other types of exhaust treatment device. It could for example be used to regenerate a NOX trap or to purge a catalytic converter. For example, in the case of a catalytic converter, the temperature T1 would be the lightoff temperature of the catalytic converter and the temperature T2 would be the required temperature to purge sulphur from the catalytic converter.

lo It will be further appreciated by those skilled in the art that although the invention has been described by way of example with reference to a specific embodiment it is not limited to this embodiment and that various alternative embodiments or modifications to the disclosed embodiment could be made without departing from the scope of the invention. For example the invention is not limited to the precise order in which the temperature limits are checked that is to say step 140 could be carried out before step 120.

. - - 19

Claims

Claims 1. A method for regenerating an exhaust treatment device connected

to an internal combustion engine so as to receive exhaust gasses from the engine, the method comprising operating the engine in an operational mode during normal use of the engine, determining whether regeneration of the exhaust treatment device is required and, if regeneration is determined to be necessary, lo operating the engine in one of at least two separate modes of operation during regeneration dependent upon the temperature of the exhaust gases wherein, if the temperature of the exhaust gases is above a first predetermined temperature, the engine is operated in a regenerative mode of operation so as to produce a steady increase in the temperature of exhaust gasses entering the exhaust treatment device without exceeding any temperature limits for the exhaust treatment device and, if the temperature is below the first predetermined temperature, the engine is operated in a transient mode so as to produce a rapid increase in exhaust gas temperature entering the exhaust treatment device and switching to the regenerative mode of operation from the transient mode of operation when the temperature of the exhaust gasses entering the exhaust treatment device exceeds the first predetermined temperature.
2. A method as claimed in claim 1 wherein the method further comprises operating the engine in the transient mode when the temperature of the exhaust gases is below the first predetermined temperature but above a second predetermined temperature.
3. A method as claimed in claim 2 wherein, if the temperature of the exhaust gasses is below the second 3r: predetermined temperature, the engine is operated in a light-off mode of operation.

c. . . ... . . - 20
4. A method as claimed in any of claims 1 to 3 wherein the first predetermined temperature is the temperature required to regenerate the exhaust treatment device.
5. A method as claimed in claim 3 or in claim 4 when dependent upon claim 3 wherein the exhaust treatment device is a catalytic converter and the second predetermined temperature is a light-off temperature of the catalytic converter.
6. A method as claimed in any of claims 1 to 4 wherein the engine has a catalytic converter connected thereto to receive exhaust gases from the engine and an exhaust treatment device connected downstream from the catalytic converter.
7. A method as claimed in claim 6 wherein the exhaust treatment device is one of a particulate filter and a NOX trap.
8. A method as claimed in claim 7 wherein the internal combustion engine is a diesel engine and the particulate filter is a diesel particulate filter. tic
9. A method as claimed in 8 when dependent upon claim 6 or upon claim 7 wherein the second predetermined temperature is a light- off temperature of the catalytic converter.
10. A method as claimed in any of claims 1 to 9 wherein the method further comprises reverting to the operational mode when it is determined that regeneration of the exhaust treatment device is complete.
11. A method as claimed in claim 8 or in claim 9 or as claimed in claim 10 when dependent upon claim 8 or claim 9 . . . . e. .. . . - 21 in which the regenerative mode comprises a first late injection of fuel into at least one cylinder of the engine early in the power stroke of the engine for combustion in the respective cylinder so as to increase the temperature of the exhaust gasses leaving the respective cylinder and at least one further late injection of fuel into the respective cylinder later in the power stroke.
12. A method as claimed in claim 11 in which the lo transient mode comprises a first late injection of fuel into at least one cylinder of the engine early in the power stroke of the engine for combustion in the respective cylinder so as to increase the temperature of the gasses leaving the respective cylinder and at least one further late injection of fuel into the respective cylinder later in the power stroke wherein the amount of fuel injected in the transient mode of operation is greater than the amount of fuel injected during the regenerative mode so as to produce a rapid increase in the temperature of the exhaust gases entering the exhaust treatment device.
13. A method as claimed in claim 11 or in claim 12 wherein the light-off mode comprises a first late injection of fuel into at least one cylinder of the engine early in the power stroke of the engine for combustion in the respective cylinder so as to increase the temperature of the gasses leaving the respective cylinder.
14. A method as claimed in any of claims 1 to 13 wherein the engine has a valve controlled air intake manifold and the valve is positioned in a position to restrict the flow of air into the engine during regeneration.
15. A system for controlling the regeneration of an exhaust treatment device connected to an internal combustion engine, the system comprising a controller operably . . . . . . . . - 22 connected to a temperature sensor positioned upstream from the exhaust treatment device so as to sense the temperature of the exhaust gasses entering the exhaust treatment device wherein the controller is programmed so as to control the operation of the engine so as to operate the engine in an operational mode during normal use of the engine, determine whether regeneration of the exhaust treatment device is required and, if regeneration is determined to be necessary, operate the engine in one of at least two separate modes of lo operation during regeneration dependent upon the temperature of the exhaust gases entering the exhaust treatment device as sensed by the temperature sensor wherein, if the temperature of the exhaust gases is above a first predetermined temperature, the engine is operated by the :5 controller in a regenerative mode of operation so as to produce a steady increase in the temperature of exhaust gasses entering the exhaust treatment device without exceeding any temperature limits for the exhaust treatment device and, if the temperature is below the first predetermined temperature, the engine is operated by the controller in a transient mode so as to produce a rapid increase in exhaust gas temperature entering the exhaust treatment device and is further programmed to switch to the regenerative mode of operation from the transient mode of operation when the temperature of the exhaust gasses entering the exhaust treatment device as sensed by the temperature sensor exceeds the first predetermined temperature.

JO
16. A system as claimed in any of claim 15 wherein the first predetermined temperature is a temperature required for regeneration of the exhaust treatment device.
17. A system as claimed in claim 15 or in claim 16 wherein the engine has a catalytic converter connected thereto and the controller is operable to operate the engine in the transient mode only when the temperature of the - # . . ...

e. #. #

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- 23 - exhaust gasses entering the exhaust treatment device is above the light- off temperature of the catalytic converter but below the first predetermined temperature.
18. A system as claimed in claim 17 wherein the controller is further operable to operate the engine in a light-off mode of operation when the temperature of the exhaust gasses entering the exhaust treatment device are below the light-off temperature of the catalytic converter.
19. A system as claimed in any of claim 18 wherein the engine has an exhaust gas treatment device connected downstream from the catalytic converter.
20. A system as claimed in claim 19 wherein the exhaust treatment device is one of a particulate filter and a NOX trap.
21. A method substantially as described herein with reference to the accompanying drawing.
22. A system substantially as described herein with reference to the accompanying drawing. e

e e .. , * * *