SE1550889A1

SE1550889A1 - A method for detecting leakage in an exhaust gas recirculation arrangement

Info

Publication number: SE1550889A1
Application number: SE1550889A
Authority: SE
Inventors: Forslund Anders
Original assignee: Scania Cv Ab
Priority date: 2015-06-26
Filing date: 2015-06-26
Publication date: 2016-12-27
Also published as: BR102016014240A8; DE102016006715A1; SE539413C2

Abstract

23 ABSTRACT The present invention relates to a method and system for detecting leakage from an exhaustgas recirculation arrangement (30) in an engine system (10) comprising an internalcombustion engine (2), an intake manifold (12) leading to the cylinders of the internalcombustion engine (2) an intake throttle (14) for adjusting the air flow into the intakemanifold (12) and an exhaust pipe (16) for the exhaust gas from the internal combustionengine (2). The exhaust gas recirculation arrangement (30) comprises an EGR pipe (32) and anEGR valve (34). The exhaust gases may be recirculated from the exhaust pipe (16) through theEGR pipe (32) and the EGR valve (34) to the intake manifold (12) downstream of the intakethrottle (14). The EGR valve (34) adjusts the EGR gas flow. The method comprises steps to: a)determine if the internal combustion engine (2) is in an idle state and the EGR valve (34) is in aclosed position, and if so; b) determine the intake manifold absolute pressure (P|M); c)determine the opening degree of the intake throttle (O); and d) determine if the EGR valve(34) is leaking based on the correlation between the intake manifold absolute pressure (P|M) and the opening degree ofthe intake throttle (O). (Fig. 2)

Description

A method for detecting leakage in an exhaust gas recirculation arrangement TECHNICAL FIELD The present invention relates to a method for detecting leakage from an exhaust gasrecirculation (EGR) valve. The invention further relates to an engine system for detectingleakage from an exhaust gas recirculation valve, a vehicle comprising the engine system, a computer program and a computer program product.

BACKGROUND AND PRIOR ART ln internal combustion engines, such as for example in diesel and Otto gas engines, exhaustgas recirculation (EGR) is often used to reduce the combustion temperature. This means thatpart of the engine's exhaust gas is recirculated back to the intake manifold of the engine. Theinert exhaust gas dilutes the oxygen in the intake air and acts as absorbent of combustion heatand thus reduces the peak temperature in the engine cylinders. With a reduced peaktemperature, the tendency of knock will be reduced. Engine systems with exhaust gasrecirculation typically comprise an EGR cooler which reduces the temperature ofthe EGR gases and thus allows higher EGR gas levels and also reduces the peak temperature further.

The EGR gas flow is normally controlled by an EGR valve, such as a butterfly valve. Thesevalves are subjected to both thermal stress and mechanical stress. The high temperatures ofthe exhaust gas that is recirculated through the EGR valve may affect the valve such that thevalve is deformed. Such deformations may affect the sealing ability when the EGR valve isclosed and EGR gas leakage may thereby occur. The EGR valve is typically closed when theengine is in an idle state. Also the mechanical wear of the EGR valve may cause leakages. lf theEGR valve is not completely sealed when closed, depending on the pressure differencebetween the exhaust gas pressure and the intake manifold pressure, EGR gases may leakthrough the EGR valve to the intake manifold of the engine. Such EGR gas leakage may stopthe combustion and thus cause misfire of the engine. lt is therefore desirable to detect EGRleakages at an early stage, such that disadvantages with leaking EGR gas can be avoided or reduced. 2 Document US2013/0133634 A1 describes a controller for an internal combustion enginecomprising a leakage determining portion detecting leakage of EGR gas when the EGR valve isfully closed. The EGR leakage is determined based on an identified EGR gas concentration inthe intake manifold. Alternatively, the EGR leakage is determined based on at least one of anintake air pressure, a gas temperature downstream of an EGR cooler and a driving torque of the EGR valve.

Despite known solutions in the field, there is still a need to develop a method for detectingleakages from an exhaust gas recirculation valve which reduces the risk of operational disruptions of the internal combustion engine.

SUMMARY OF THE INVENTION lt is an object of the present invention to provide a method for detecting leakage from anexhaust gas recirculation arrangement in an engine system comprising an internal combustionengine. By detecting the leakage it is possible to reduce the risk for operational disruptions in the internal combustion engine.

Another object of the present invention is to provide a method for detecting leakage from anexhaust gas recirculation arrangement in an engine system comprising an internal combustionengine, whereby it is possible to optimize the fuel consumption of the internal combustion engine.

A further object of the present invention is to provide an engine system with reduced risk for operational disruptions ofthe internal combustion engine.

The above mentioned objects are attained by a method according to the appended claims,relating to a method for detecting leakage from an exhaust gas recirculation (EGR)arrangement in an engine system. The engine system comprises an internal combustionengine, an intake manifold leading to the cylinders of the internal combustion engine, anintake throttle for adjusting fresh air flow into the intake manifold, and an exhaust pipe forexhaust gas flow from the internal combustion engine. The exhaust gas recirculationarrangement comprises an EGR pipe and an EGR valve. The EGR arrangement is arranged in fluid connection with the exhaust pipe and the intake manifold, such that at least part of the 3exhaust gas flow can be recirculated from the exhaust pipe through the EGR pipe and the EGRvalve to the intake manifold downstream of the intake throttle. The EGR valve is arranged toadjust the EGR gas flow being recirculated to the intake manifold. The method comprises the steps to: a) determine if the internal combustion engine is in an idle state and if the EGR valve is in a closed position, and if so; b) determine the intake manifold absolute pressure; c) determine the opening degree of the intake throttle; and d) determine if the EGR valve is leaking based on the correlation between the intake manifold absolute pressure and the opening degree of the intake throttle.

The present invention also relates to an engine system comprising an internal combustionengine, an intake manifold leading to the cylinders of the internal combustion engine, anintake throttle for adjusting fresh air flow into the intake manifold and an exhaust pipe forexhaust gas flow from the internal combustion engine and an EGR arrangement. The EGRarrangement comprises an EGR pipe and an EGR valve, wherein the EGR arrangement isarranged in fluid connection with the exhaust pipe and the intake manifold, such that at leastpart of the exhaust gas flow may be recirculated from the exhaust pipe through the EGR pipeand the EGR valve to the intake manifold downstream of the intake throttle. The EGR valve isarranged to adjust the EGR gas flow being recirculated to the intake manifold. An electroniccontrol unit is arranged to determine if the internal combustion engine is in an idle state and ifthe EGR valve is in a closed position and, if so, determining the intake manifold absolutepressure and the opening degree of the intake throttle and determining if the EGR valve isleaking based on the correlation between the intake manifold absolute pressure and the opening degree of the intake throttle.

The herein mentioned objects are also attained by an engine system, vehicle, computer program and computer program product as defined in the appended claims.

Further aspects, objects and advantages are defined in the detailed description below with reference to the appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS For the understanding of the present invention and further objects and advantages of it, thedetailed description set out below can be read together with the accompanying drawings, in which the same reference notations denote similar items in the various diagrams, and in which: Fig. 1 schematically illustrates a vehicle according to an embodiment of the invention; Fig. 2 schematically illustrates a gas flow through an engine system according to anembodiment of the invention; Fig. 3 schematically illustrates a flow chart of a method for detecting leakages from anexhaust gas recirculation arrangement in an engine system according to anembodiment of the invention; Fig. 4 illustrates a diagram of the intake manifold absolute pressure as a function of theopening degree ofthe intake throttle at idle speed according to an embodimentof the invention; and Fig. 5 schematically illustrates a control unit or computer according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION The invention is hereby described with reference to the method for detecting leakage from an exhaust gas recirculation arrangement in an engine system as generally described above.

When an internal combustion engine is in an idle state the EGR valve is typically in a closedposition. A closed position for the EGR valve means a position where normally no EGR gas isrecirculated through the EGR pipe into the intake manifold. The EGR valve is however subjectto both thermal and mechanical stress and may therefore be deformed in different ways. Thedeformation may cause leakages when the EGR valve is in its closed position. Large EGR valvesmay cause larger leakages than small EGR valves. When the internal combustion engine is inan idle state there is a pressure difference between the exhaust pipe and the intake manifold, such that a negative pressure is obtained in the intake manifold downstream of the intake 5throttle. lf the EGR valve is leaking EGR gas will be sucked into the intake manifold due to thenegative pressure and may thereby affect the combustion and thus cause misfire of theinternal combustion engine. ln an engine system with a normally functioning EGR valve,without leakages, a correlation between the opening degree of the intake throttle and theintake manifold absolute pressure exists. A certain opening degree of the intake throttle thuscorresponds to a certain intake manifold absolute pressure which is provided in order tomaintain the idle speed. The intake manifold absolute pressure may thereby be presented as afunction of the opening degree of the intake throttle at the desired idle speed of the internalcombustion engine. By determining the actual intake manifold absolute pressure and theactual opening degree of the intake throttle during the idle speed and the correlation there between, leakages from the EGR valve may be detected in a reliable and efficient way.

The desired idle speed is normally between 400-800 rpm, but can vary depending on anengine type or vehicle type. Thus the idle speed may also be lower than 400 rpm and higher than 800 rpm.

According to an aspect of the invention the intake manifold absolute pressure is determinedby means of a pressure sensing device arranged in the intake manifold. The pressure sensing device may be a manifold absolute pressure sensor (MAP sensor).

The opening degree of the intake throttle can be determined by means of a position sensorarranged in communication with the intake throttle. The intake throttle can be for example abutterfly valve comprising a disk arranged in the intake manifold. The opening degree of theintake throttle thus corresponds to an angle of the disk. The position sensor may thus identifythe angle of the disk and the opening degree of the intake throttle is thereby determined. Theopening degree is determined as a percentage where the opening degree of a completelyopen intake throttle is 100% and a completely closed intake throttle is 0%. An intake throttletypically has an opening degree between 5-20% during idle operation of the internalcombustion engine, but can vary depending on an engine type or vehicle type. Thus, the opening degree during idle operation may be lower than 5% and higher than 20%.

An electronic control unit is suitably arranged in communication with the pressure sensingdevice and the position sensor. The control unit thus receives signals from the sensing devices and determines if the EGR valve is leaking. The control unit suitably determines if the internal 6combustion engine is in an idle state and if the EGR valve is in its closed position. The controlunit suitably determines if the internal combustion engine is in an idle state by means of arevolution-counter or similar that measures the rotation speed of the internal combustionengine. Other operating condition values may also be considered, such as torque demand. Therotation speed, which is pre-determined, indicates whether the internal combustion engine isin an idle state or not. The control unit is arranged to determine if the EGR valve is in a closedposition by means of a position sensor determining the position of the EGR valve. The EGRvalve is suitably a butterfly valve comprising a disk, wherein the position sensor identifies the angle ofthe disk and thereby the position of the EGR valve.

According to an aspect of the invention the step to determine if the EGR valve is leakingincludes determining a reference value for the opening degree of the intake throttle and areference value for the intake manifold absolute pressure, and determining if the EGR valve isleaking based on a comparison between the reference values and the opening degree of theintake throttle and the intake manifold absolute pressure. The reference values are preferablypredetermined and stored in the control unit. The reference values are preferably determinedbased on the desired idle speed of the internal combustion engine. The reference values thusrepresent the intake manifold absolute pressure and the opening degree of the intake throttlethat should be provided in order to maintain the desired idle engine speed when no leakageexists. The reference values may be determined based on empirical data from functionalinternal combustion engines without leakages and the empirical data is suitable based on aspecific engine type. By comparing the actual intake manifold absolute pressure and the actualopening degree of the intake throttle with the reference values, deviations from the referencevalues may be identified. Deviations from the reference values indicate that something iswrong in the correlation between the opening degree of the intake throttle and the intakemanifold absolute pressure, and it may thereby be determined whether the EGR valve is leaking or not.

According to an aspect of the invention the reference values are determined based on at leastone of engine speed, engine friction, loads affecting the engine, a requested torque reserve,engine displacement, diameter of the throttle, altitude and/or air temperature. These factorsaffect the engine system and the internal combustion engine such that the need for outside air and thus intake manifold absolute pressure varies depending on the operating condition. 7The reference values thus depend on said factors. When the internal combustion engine is inan idle state the control unit is constantly trying to find a way to balance all of the torques inthe engine system without affecting the engine speed. For example engine friction,accessories such as generators and compressors and the transmission causes torque demandswhich constantly try to decrease the engine speed. To handle this, the combustion of air andfuel in the engine cylinder is used to generate enough torque to maintain a constant idlespeed. The engine friction, losses and loads affecting the engine may vary during the idle stateand the engine speed may thus drop below the desired idle speed or increase above thedesired idle speed. Since the control unit cannot predict the variation in torque demand atorque reserve is necessary in order to be able to handle sudden increases or decreases intorque demand during the idle state. By retarding the ignition timing in the engine cylinder atorque reserve may be built up. This way, the control unit can increase the torque output toovercome any sudden increase in torque demand. Depending on the requested size of thetorque reserve the intake manifold absolute pressure needs to be adjusted to maintain thedesired idle speed. The intake manifold absolute pressure and the opening degree of theintake throttle which are suitable for maintaining a constant idle speed, i.e. the referencevalues, thus depend on several factors, such as engine speed, engine friction, loads affectingthe engine, requested torque reserve, engine displacement, diameter of the throttle, altitudeand/or air temperature. The reference value for the intake manifold absolute pressure and theopening degree of the intake throttle are for example lower in the case where a low torque reserve is requested than in the case where a high torque reserve is requested.

According to an aspect of the invention it is determined that the EGR valve is leaking if theopening degree of the intake throttle exceeds the reference value for the opening degree ofthe intake throttle and the determined intake manifold absolute pressure exceeds thereference value for the intake manifold absolute pressure. When there is a leakage from theEGR valve inert gases can flow into the intake manifold downstream of the intake throttle. Theintake manifold absolute pressure will thereby increase. The need for fresh air is still the samebut when the intake manifold absolute pressure increases due to the leakage, the pressuredifference over the intake throttle decreases and the air flow through the intake throttle intothe intake manifold is decreased. ln order to provide enough air into the intake manifold the engine system automatically increases the opening degree of the intake throttle. Thus, an 8opening degree of the intake throttle that exceeds the reference value for the opening degree,and an intake manifold absolute pressure that exceeds the reference value for the intake manifold absolute pressure indicate that the EGR valve is leaking. ln case it is determined that the EGR valve is leaking, the intake manifold absolute pressure isincreased in order to decrease the pressure difference between the exhaust pipe and theintake manifold. By decreasing the pressure difference, less EGR gases will be drawn into theintake manifold. The intake manifold absolute pressure is suitably increased by increasing theopening degree of the intake throttle. Normally, an increase in an opening degree of theintake throttle would lead to an increased engine speed. ln order to avoid an increase inengine speed and maintain a constant idle speed, the ignition timing is retarded. The controlunit suitably controls the intake throttle such that the intake manifold absolute pressure isincreased. The control unit suitably also controls the internal combustion engine such that the ignition timing is retarded.

According to an aspect of the invention it is determined that outside air is leaking into theintake manifold if the determined intake manifold absolute pressure corresponds to thereference value for the intake manifold absolute pressure but the determined opening degreeof the intake throttle is lower than the reference value for the opening degree of the intakethrottle. Due to for example broken gaskets/seals or similar damages, fresh or outside air mayleak into the intake manifold. The need for fresh air through the intake throttle into the intakemanifold is thereby decreased and the opening degree of the intake throttle is decreased. Alower opening degree of the intake throttle but an intact intake manifold absolute pressure thus indicates that outside air is leaking into the intake manifold. ln case where it is determined that outside air is leaking into the intake manifold, downstreamof the intake throttle, the opening degree of the intake throttle is suitably decreased. ln thisway, a constant idle speed may be maintained. The control unit suitably controls the intakethrottle such that the opening degree is decreased until the air flowing through the intakethrottle together with the leaking air provides an intake manifold absolute pressure which maintains the idle speed.

According to an aspect of the invention it is determined that the EGR valve is leaking and that outside air is leaking into the intake manifold if the determined intake manifold absolute 9 pressure exceeds the reference value for the intake manifold absolute pressure but thedetermined opening degree of the intake throttle essentially corresponds to the referencevalue for the opening degree ofthe intake throttle. An EGR leakage results in an increasedintake manifold absolute pressure and an increased opening degree of the intake throttle asdescribed above. However, if there at the same time is a leakage of outside air into the intakemanifold the engine system will automatically decrease the opening degree of the intakethrottle since the need for fresh air is decreased. The result is thus an increased intakemanifold absolute pressure in relation to the reference value for the intake manifold absolute pressure, but essentially the same opening degree of the intake throttle.

The invention is now further defined with reference to the appended drawings.

Fig. l schematically shows a side view of a vehicle l compršsing an engine system 10 accordingto an embodiment of the invention. The vehicle l comprises an internal combustion engine 2connected to a gearhox 4. The internal cornbustioft engine 2 is suitably a gas engine, such asan Otto eftgine. The engine may also be a diesel eftgine. The gearbox 4 is also connected to thedriving wheels 8 of the tfehicle l through an oiltput shaft of the gearbox (hot sliowli). Thevehicle also itontprises a Chassis 9. The vehicle 1 may be a heavy vehicle, e.g. a truck or a bus.

The vehicle 1 may alternatively be a passenger car.

Fig. 2 schematically shows a gas flow through an engine system 10 according to anembodiment of the invention. The gas flow is indicated by arrows. The engine system 10comprises an internal combustion engine 2, an intake manifold 12 leading to the cylinders ofthe internal combustion engine 2, and an intake throttle 14 for adjusting the fresh air flow intothe intake manifold 12. Further, the system comprises an exhaust pipe 16 for the exhaust gasfrom the internal combustion engine 2 and an exhaust gas recirculation (EGR) arrangement30. The EGR arrangement 30 comprises an EGR pipe 32 and an EGR valve 34. The EGRarrangement 30 and the EGR pipe 32 are arranged in fluid connection with the exhaust pipe16 and the intake manifold 12, such that at least part of the exhaust gas flow can berecirculated from the exhaust pipe 16 through the EGR pipe 32 and the EGR valve 34 to theintake manifold 12, downstream of the intake throttle 14. The EGR valve 34 is arranged toadjust the amount of EGR gas flow being recirculated to the intake manifold 12. The engine system suitably comprises a turbo compressor 18 and a charge air cooler 19 arranged upstream of the intake throttle 14. An exhaust gas turbine 24 driving the turbo Compressor 18may also be arranged downstream of the internal combustion engine 2, in the exhaust pipe16. The EGR arrangement 30 may further comprise an EGR cooler 36 arranged to decrease thetemperature of the recirculated exhaust gas flow and thereby decrease the peak temperature in the engine cylinders.

An electronic control unit 20 may be arranged in communication with the turbo compressor18, the charge air cooler 19, the exhaust turbine 24, the intake throttle 14, the internalcombustion engine 2, the EGR valve 34 and the EGR cooler 36. The control unit 20 may bearranged in communication with the herein mentioned components via a controller areanetwork (CAN bus). The electronic control unit 20 is arranged to determine if the internalcombustion engine 2 is in an idle state and the EGR valve 34 is closed and, if so, determiningthe intake manifold absolute pressure P|M and the opening degree of the intake throttle O anddetermining if the EGR valve 34 is leaking based on the correlation between the intakemanifold absolute pressure P|M and the opening degree of the intake throttle O. A computer 22 may be connected to the control unit 20.

The control unit 20 is suitably adapted to determine if the internal combustion engine 2 is inan idle state by means of a revolution-counter (not shown) measuring the rotation speed ofthe internal combustion engine 2. The rotation speed indicates, possibly together with otheroperating conditions such as torque demand, whether the internal combustion engine 2 is inan idle state or not. The control unit 20 is suitably adapted to determine if the EGR valve 34 isin a closed position by means of a position sensor (not shown) determining the position of theEGR valve 34. The EGR valve 34 is suitably a butterfly valve comprising a disk, wherein theposition sensor identifies the angle of the disk and thereby the position of the EGR valve 34.The control unit 20 is suitably adapted to determine a reference value for the opening degreeof the intake throttle Oref and a reference value for the intake manifold absolute pressure Pref,and to determine if the EGR valve 34 is leaking based on a comparison between the referencevalues Oref, Pref and the opening degree of the intake throttle O and the intake manifoldabsolute pressure PM. The reference values Oref, Prefare suitably predetermined and stored in the control unit 20. 11A position sensor 40 is arranged in communication with the intake throttle 14 and the controlunit 20 for determining the opening degree of the intake throttle O. The intake throttle 14 is abutterfly valve comprising a disk (not shown) arranged in the intake manifold 12. The positionsensor 40 is thus arranged to determine the angle of the disk and thereby the opening degree of the intake throttle O.

A pressure sensing device 42 is arranged in f|uid communication with the intake manifold 12.The pressure sensing device 42 may be a manifold absolute pressure sensor (MAP sensor). Thecontrol unit 20 is arranged in communication with the pressure sensing device 42. The controlunit 20 is thus arranged to receive signals from the pressure sensing device 42 and the position sensor 40 determines if the EGR valve 34 is leaking.

Fig. 3 schematically illustrates a flow chart for a method for detecting leakages from anexhaust gas recirculation arrangement 30 in an engine system 10 according to an embodimentof the invention. The engine system 10 is configured as described in connection with Fig. 2 andcomprises the same components as the system in Fig. 2. The method comprises the steps to:a) determine if the internal combustion engine 2 is in an idle state and if the EGR valve 34 is ina closed position, and if so; b) determine the intake manifold absolute pressure P|M; c)determine the opening degree of the intake throttle O; and d) determine if the EGR valve 34 isleaking based on the correlation between the intake manifold absolute pressure P|M and the opening degree of the intake throttle O.

Returning to Fig. 2, when the internal combustion engine 2 is in an idle state the EGR valve 34is typically in a closed position. When the internal combustion engine 2 is in an idle state thereis a pressure difference between the exhaust pipe 16 and the intake manifold 12, such that anegative pressure is obtained in the intake manifold 12 downstream of the intake throttle 14.lf the EGR valve 34 is leaking the EGR gas will be sucked into the intake manifold 12 due to thenegative pressure and may thereby affect the combustion and cause misfire of the internalcombustion engine 2. ln an engine system 10 with a normally functioning EGR valve 34,without leakages, the correlation between the opening degree of the intake throttle and theintake manifold absolute pressure is essentially linear. A certain opening degree of the intakethrottle thus corresponds to a certain intake manifold absolute pressure which is provided in order to maintain a constant engine idle speed, and this is illustrated in Fig. 4 by the line R. By 12determining the actual intake manifold absolute pressure P|M and the actual opening degreeof the intake throttle O during idle speed and the correlation there between leakages from the EGR valve 34 may be detected in a reliable and efficient way.

As mentioned above, the desired idle speed may vary and could be for example from 400-800rpm. The control unit 20 suitably determines if the internal combustion engine 2 is in an idlestate and if the EGR valve 34 is in its closed position. The control unit 20 suitably determines ifthe internal combustion engine 2 is in an idle state in step a) by means of a revolution-counter(not shown) measuring the rotation speed of the internal combustion engine 2. The rotationspeed and torque demand information indicate whether the internal combustion engine 2 is inan idle state or not. The control unit 20 suitably determines if the EGR valve 34 is in a closedposition in step a) by means of a position sensor (not shown) determining the position of the EGR valve 34.

The intake manifold absolute pressure P|M is preferably determined in step b) by means of thepressure sensing device 42 arranged in fluid communication with the intake manifold 12. Thepressure sensing device 42 may be a manifold absolute pressure sensor (MAP sensor) thatmeasures the absolute pressure in the intake manifold. Other types of pressure sensingdevices may be used and it is also possible to determine absolute pressure by measuring for example an over pressure in the intake manifold.

The opening degree of the intake throttle O is preferably determined in step c) by means ofthe position sensor 40 arranged in communication with the intake throttle 14. The openingdegree is determined as a percentage where the opening degree of a completely open intakethrottle 14 is 100% and a completely closed intake throttle 14 is 0%. An intake throttle 14typically has an opening degree between 5-20% during idle operation of the internalcombustion engine 2, but the opening degree can vary depending on the type of the engine syste m The electronic control unit 20 is suitably arranged in communication with the pressure sensingdevice 42 and the position sensor 40. The control unit 20 thus receives signals from theposition sensing device 40 and the pressure sensing device 42 and determines if the EGR valve 34 is leaking. 13ln the step d), to determine if the EGR valve 34 is leaking, it is included to determine areference value for the opening degree of the intake throttle Oref and a reference value for theintake manifold absolute pressure Pref, and determining if the EGR valve 34 is leaking based ona comparison between the reference values Oref, Pref and the opening degree of the intakethrottle O and the intake manifold absolute pressure P|M. The reference values Oref, Pref arepreferably predetermined and stored in the control unit 20. The reference values Oref, Pref arepreferably determined based on the desired idle speed. The reference values Oref, Pref thusrepresent the intake manifold absolute pressure and the opening degree of the intake throttlethat is provided in order to maintain the desired idle speed when no leakage exists. Thereference values Oref, Pref may be determined based on empirical data from functional internalcombustion engines 2 without leakages. The control unit 20 thus compares the actual intakemanifold absolute pressure P|M and the actual opening degree of the intake throttle O with thereference values Oref, Pref, and identifies deviations from the reference values Oref, Pref. Thedeviations from the reference values Oref, Pref indicate that something is wrong in thecorrelation between the determined opening degree of the intake throttle O and the intakemanifold absolute pressure P|M and it may thereby be determined that the EGR valve 34 is leaking.

The reference values Oref, Pref are preferably determined based on at least one of enginespeed, engine friction, loads affecting the engine, requested torque reserve, enginedisplacement, diameter of the throttle, altitude and/or air temperature. How these factorsaffect the reference values is further described in connection with Fig. 4 and with reference to the flow chart of Fig. 2.

According to an aspect of the invention it is determined in step d) that the EGR valve 34 isleaking if the determined opening degree of the intake throttle O exceeds the reference valuefor the opening degree of the intake throttle Oref and the intake manifold absolute pressureP|M exceeds the reference value for the intake manifold absolute pressure Pref. When there is aleakage from the EGR valve 34, inert gases are flowing into the intake manifold 12downstream of the intake throttle 14. The intake manifold absolute pressure will therebyincrease. The need for fresh air is still the same but when the intake manifold absolutepressure increases due to the leakage, the pressure difference over the intake throttle 14 decreases and the air flow through the intake throttle 14 into the intake manifold 12 is 14decreased. ln order to provide enough air into the intake manifold 12 the engine system 10automatically increases the opening degree of the intake throttle 14. ln this way, an openingdegree of the intake throttle 14 exceeding the reference value for the opening degree and anintake manifold absolute pressure exceeding the reference value for the intake manifold absolute pressure thus indicates that the EGR valve 34 is leaking. ln the case when it is determined in step d) that the EGR valve 34 is leaking, the intakemanifold absolute pressure P|M is increased in order to decrease the pressure differencebetween the exhaust pipe 16 and the intake manifold 12. lf the pressure difference isdecreased, less EGR gases will be sucked into the intake manifold 12. The intake manifoldabsolute pressure P|M is suitably increased by increasing the opening degree of the intakethrottle O. Normally, an increase in an opening degree of the intake throttle would lead to anincreased engine speed. ln order to avoid an increase in engine speed and maintain thedesired idle speed the ignition timing is retarded. The control unit 20 is suitably controlling theintake throttle 14 such that the intake manifold absolute pressure is increased. The controlunit 20 is suitably controlling the internal combustion engine such that the ignition timing is retarded.

According to a further aspect of the invention it is determined in step d) that outside air isleaking into the intake manifold 12 if the determined intake manifold absolute pressure P|Mcorresponds to the reference value for the intake manifold absolute pressure Pref but thedetermined opening degree of the intake throttle O is lower than the reference value for theopening degree of the intake throttle Oref. Due to for example broken gaskets/seals or similardamages outside air may leak into the intake manifold 12. The need for fresh air through theintake throttle 14 into the intake manifold 12 is thereby decreased and the opening degree ofthe intake throttle is decreased. A lower opening degree of the intake throttle O but an intactintake manifold absolute pressure P|M thus indicates that outside air is leaking into the intake manifold 12. ln case when it is determined that outside air is leaking into the intake manifold 12,downstream the intake throttle 14, the opening degree of the intake throttle is suitablydecreased. ln this way, the desired idle speed may be maintained. The control unit 20 suitably controls the intake throttle 14 such that the opening degree is decreased until the air flowing through the intake throttle 14 together with the leaking air provides an intake manifold absolute pressure which maintains the idle speed.

According to a further aspect of the invention it is determined in step d) that the EGR valve 34is leaking and that outside air is leaking into the intake manifold 12 if the determined intakemanifold absolute pressure P|M exceeds the reference value for the intake manifold absolutepressure Pref but the determined opening degree of the intake throttle O essentiallycorresponds to the reference value for the opening degree of the intake throttle Oref. An EGRleakage results in an increased intake manifold absolute pressure and an increased openingdegree of the intake throttle as described above. However, if there at the same time is aleakage of outside air into the intake manifold 12 the engine system 10 will automaticallydecrease the opening degree of the intake throttle since the need for fresh air is decreased.The result is thus an increased intake manifold absolute pressure compared to the referencevalue for intake manifold absolute pressure, but essentially the same opening degree ofthe inta ke th rottle.

Fig. 4 illustrates a diagram of the intake manifold absolute pressure as a function of theopening degree of the intake throttle at an engine idle speed according to an embodiment ofthe invention. The idle speed may for example be around 600 rpm. The diagram relates to anengine system 10 as described in Fig. 2 and a method for detecting leakages in an EGR arrangement in an engine system as described in Fig. 3. ln an engine system 10 with a normally functioning EGR valve 34, without leakages, a linearcorrelation between the opening degree of the intake throttle and the intake manifoldabsolute pressure exists. This linear correlation is shown in the diagram as the reference lineR. A certain opening degree O of the intake throttle thus corresponds to a certain intakemanifold absolute pressure P which is provided in order to maintain the desired idle speed.The opening degree of the intake throttle and the intake manifold absolute pressure whichshould be provided in order to maintain the idle speed during certain operating conditions are the reference values Pref, Oref as described in connection with Fig. 2 and Fig. 3.

The reference values for the intake manifold absolute pressure Pref and for the opening degreeof the intake throttle Oref vary depending on several factors, such as engine speed, engine friction, loads affecting the engine, requested torque reserve, engine displacement, diameter 16of the throttle, altitude and/or air temperature. Depending for example on the requested sizeof the torque reserve the intake manifold absolute pressure P needs to be adjusted tomaintain the idle speed. The reference value for the intake manifold absolute pressure Pref ishere presented as a linear function of the opening degree of the intake throttle Oref and varieslinearly depending on the herein mentioned factors. The reference values for the intakemanifold absolute pressure and the opening degree of the intake throttle Pref, Oref thus followsthe reference line R depending on the operating condition. The reference values for the intakemanifold absolute pressure Pref and the opening degree of the intake throttle Oref are forexample lower during operating conditions where a low torque reserve is requested than in the case where a high torque reserve is requested.

Two different cases are presented in the diagram where a deviation from the reference valuesPref, Oref has been identified. ln the first case an intake manifold absolute pressure P|M1 and anopening degree of the intake pressure 01 has been determined according to the method asdescribed in Fig. 3. ln this case the determined intake manifold absolute pressure P|M1 issimilar to the reference value Pref but the opening degree of the intake throttle 01 is muchlower than the reference value for the opening degree of the intake throttle Oref. Thisindicates that outside air might be leaking into the intake manifold 12 as described in connection with Fig. 3 above. ln the second case an intake manifold absolute pressure P|M2 and an opening degree of theintake pressure OZ has been determined. ln this case the opening degree of the intake throttleOZ exceeds the reference value for the opening degree of the intake throttle Oref and theintake manifold absolute pressure P|M2 exceeds the reference value Pref. This indicates that theEGR valve 34 is leaking EGR gas into the intake manifold 12 as described in connection with Fig. 3 above.

Fig. 5 schematically illustrates a version of a device 500. The control unit 20 and/or computer22 described with reference to Fig. 2 may in a version comprise the device 500. The term”link” refers herein to a communication link which may be a physical connection such as anoptoelectronic communication line, or a non-physical connection such as a wirelessconnection, e.g. a radio link or microwave link. The device 500 comprises a non-volatile memory 520, a data processing unit 510 and a read/write memory 550. The non-volatile 17memory 520 has a first memory element 530 in which a computer program, e.g. an operatingsystem, is stored for controlling the function of the device 500. The device 500 furthercomprises a bus controller, a serial communication port, I/O means, an A/D converter, a timeand date input and transfer unit, an event counter and an interruption controller (not depicted). The non-volatile memory 520 has also a second memory element 540.

There is provided a computer program P which comprises routines for detecting leakage in anexhaust gas recirculation arrangement in an engine system 10. The computer programme Pcomprises routines for determining if the internal combustion engine is in an idle state and ifthe EGR valve is in a closed position. The computer programme P comprises routines fordetermining the intake manifold absolute pressure. The computer programme P comprisesroutines for determining the opening degree of the intake throttle. The computer programmeP comprises routines for determining ifthe EGR valve is leaking based on the correlation between the intake manifold absolute pressure and the opening degree of the intake throttle.

The program P may be stored in an executable form or in a compressed form in a memory 560 and/or in a read/write memory 550.

Where the data processing unit 510 is described as performing a certain function, it meansthat the data processing unit 510 effects a certain part of the program stored in the memory 560 or a certain part of the program stored in the read/write memory 550.

The data processing device 510 can communicate with a data port 599 via a data bus 515. Thenon-volatile memory 520 is intended for communication with the data processing unit 510 viaa data bus 512. The separate memory 560 is intended to communicate with the dataprocessing unit 510 via a data bus 511. The read/write memory 550 is adapted to communicating with the data processing unit 510 via a data bus 514.

When data are received on the data port 599, they are stored temporarily in the secondmemory element 540. When input data received have been temporarily stored, the data processing unit 510 is prepa red to effect code execution as described above. 18Parts of the methods herein described may be effected by the device 500 by means ofthe data processing unit 510 which runs the program stored in the memory 560 or the read/write memory 550. When the device 500 runs the program, methods herein described are executed.

Finally, it should be noted that the present invention is not restricted to the embodiments described above but can be varied within the protective scope of the appended claims.

Claims

19 CLAll\/IS

1. A method for detecting leakage from an exhaust gas recirculation (EGR) arrangement (30) inan engine system (10), the engine system (10) comprising an internal combustion engine (2),an intake manifold (12) leading to the cylinders of the internal combustion engine (2), anintake throttle (14) for adjusting fresh air flow into the intake manifold (12), and an exhaustpipe (16) for an exhaust gas flow from the internal combustion engine (2), wherein the EGRarrangement (30) comprises an EGR pipe (32) and an EGR valve (34), wherein the EGRarrangement (30) is arranged in fluid connection with the exhaust pipe (16) and the intakemanifold (12) such that at least part of the exhaust gas flow can be recirculated from theexhaust pipe (16) through the EGR pipe (32) and the EGR valve (34) to the intake manifold (12)downstream of the intake throttle (14), wherein the EGR valve (34) is arranged to adjust anEGR gas flow being recirculated to the intake manifold (12), characterised by the method steps to: a) determine if the internal combustion engine (2) is in an idle state and the EGR valve (34) is in a closed position, and if so; b) determine the intake manifold absolute pressure (PM), c) determine the opening degree of the intake throttle (O); and d) determine if the EGR valve (34) is leaking based on the correlation between the intake manifold absolute pressure (P|M) and the opening degree of the intake throttle (O).

2. A method according to claim 1, characterised in that the intake manifold absolute pressure(PM) is determined in step b) by means of a pressure sensing device (42) arranged in the intake manifold (12).

3. A method according to claim 1 or 2, characterised in that the opening degree of the intakethrottle (O) is determined in step c) by means of a position sensor (40) arranged in communication with the intake throttle (14).

4. A method according to any of the preceding claims, characterised in that the step d) includes determining a reference value for the opening degree of the intake throttle (Oref) and a reference value for the intake manifold absolute pressure (Pref), and determining if the EGRvalve (34) is leaking based on a comparison between the reference values (Oref, Pref) and the opening degree of the intake throttle (O) and the intake manifold absolute pressure (PMA).

5. A method according to claim 4, characterised in that the reference values (Oref, Pref) are determined based on the desired idle speed ofthe internal combustion engine (2).

6. A method according to claim 4 or 5, characterised in that the reference values (Oref, Pref) aredetermined based on at least one of engine speed, engine friction, loads affecting the engine,requested torque reserve, engine displacement, diameter of the throttle, altitude and/or air tempefatUfe.

7. A method according to any of claims 4-6, characterised in that it is determined in step d)that the EGR valve (34) is leaking if the opening degree of the intake throttle (O) exceeds thereference value for the opening degree of the intake throttle (Oref) and the intake manifold absolute pressure (PM) exceeds the reference value for the intake manifold absolute pressure (Pref)-

8. A method according to any of claims 4-7, characterised in that it is determined in step d)that outside air is leaking into the intake manifold (12) if the determined intake manifoldabsolute pressure (P|M) corresponds to the reference value for the intake manifold absolutepressure (Pref) but the determined opening degree of the intake throttle (O) is lower than the reference value for the opening degree of the intake throttle (Oref).

9. An engine system comprising an internal combustion engine (2), an intake manifold (12)leading to the cylinders of the internal combustion engine (2), an intake throttle (14) foradjusting fresh air flow into the intake manifold (12), an exhaust pipe (16) for exhaust gas flowfrom the internal combustion engine (2) and an exhaust gas recirculation (EGR) arrangement(30), wherein the EGR arrangement (30) comprises an EGR pipe (32) and an EGR valve (34),wherein the EGR arrangement (30) is arranged in fluid connection with the exhaust pipe (16)and the intake manifold (12), such that at least part of the exhaust gas flow can berecirculated from the exhaust pipe (16) through the EGR pipe (32) and the EGR valve (34) tothe intake manifold (12), downstream of the intake throttle (14), wherein the EGR valve (32) is arranged to adjust the EGR gas flow being recirculated to the intake manifold (12), 21characterised in that an electronic control unit (20) is arranged to determine if the internalcombustion engine (2) is in an idle state and the EGR valve (34) is in a closed position and, ifso, determining the intake manifold absolute pressure (PMA) and the opening degree of theintake throttle (O) and determining if the EGR valve (34) is leaking based on the correlationbetween the intake manifold absolute pressure (PMA) and the opening degree of the intake throttle (O).

10. An engine system according to claim 9, characterised in that a position sensor (40) isarranged in communication with the intake throttle (14) and the control unit (20) for determining the opening degree ofthe intake throttle (O).

11. An engine system according to claim 9 or 10, characterised in that a pressure sensingdevice (42) is arranged in communication with the intake manifold (12) and the control unit (20), for determining the intake manifold absolute pressure (PMA).

12. An engine system according to any of claims 9-11, characterised in that the control unit(20) is adapted to determine a reference value for the opening degree of the intake throttle(Oref) and a reference value for the intake manifold absolute pressure (Pref), and to determineif the EGR valve (34) is leaking based on a comparison between the reference values (Oref, Pref), the opening degree of the intake throttle (O) and the intake manifold absolute pressure (PMA).

13. An engine system according to claim 12, characterised in that the reference values (Oref, Pref) are based on the desired idle speed of the internal combustion engine (2).

14. An engine system according to any of claims 12 or 13, characterised in that the controlunit (20) is adapted to determine that the EGR valve (34) is leaking if the opening degree ofthe intake throttle (O) exceeds the reference value for the opening degree of the intakethrottle (Oref) and the intake manifold absolute pressure (PMA) exceeds the reference value for the intake manifold absolute pressure (Pref).

15. An engine system according to any of claims 12-14, characterised in that the control unit(20) is adapted to determine that outside air is leaking into the intake manifold if the intake manifold absolute pressure (PMA) corresponds with the reference value for the intake manifold 22absolute pressure (Pref) but the opening degree of the intake throttle (O) is lower than the reference value for the opening degree of the intake throttle (Oref).

16. A vehicle, characterised by an engine system (10) according to any of the claims 9-15.

17. A computer program (P), wherein said computer program comprises program code forcausing an electronic control unit (20; 500) or a computer (22; 500) connected to the electronic control unit (20; 500) to perform the steps according to any of the claims 1-8.

18. A computer program product comprising a program code stored on a computer-readablemedium for performing the method steps according to any of claims 1-8, when said computerprogram is run on an electronic control unit (20; 500) or a computer (22; 500) connected to the electronic control unit (20; 500).