GB2505650A - Method of controlling an engine including an exhaust gas recirculation system with a bypass circuit. - Google Patents

Method of controlling an engine including an exhaust gas recirculation system with a bypass circuit. Download PDF

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Publication number
GB2505650A
GB2505650A GB1215826.7A GB201215826A GB2505650A GB 2505650 A GB2505650 A GB 2505650A GB 201215826 A GB201215826 A GB 201215826A GB 2505650 A GB2505650 A GB 2505650A
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United Kingdom
Prior art keywords
egr
temperature
before compressor
relative humidity
compressor
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
GB1215826.7A
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GB201215826D0 (en
Inventor
Federico Luigi Guglielmone
Alberto Vassallo
Hans H Drangel
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GM Global Technology Operations LLC
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GM Global Technology Operations LLC
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Priority to GB1215826.7A priority Critical patent/GB2505650A/en
Publication of GB201215826D0 publication Critical patent/GB201215826D0/en
Publication of GB2505650A publication Critical patent/GB2505650A/en
Withdrawn legal-status Critical Current

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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/0002—Controlling intake air
    • F02D41/0007—Controlling intake air for control of turbo-charged or super-charged engines
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/0025—Controlling engines characterised by use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures
    • F02D41/0047—Controlling exhaust gas recirculation [EGR]
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/0025—Controlling engines characterised by use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures
    • F02D41/0047—Controlling exhaust gas recirculation [EGR]
    • F02D41/0065—Specific aspects of external EGR control
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/0025—Controlling engines characterised by use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures
    • F02D41/0047—Controlling exhaust gas recirculation [EGR]
    • F02D41/0065—Specific aspects of external EGR control
    • F02D2041/0067—Determining the EGR temperature
    • F02D2041/007—Determining the EGR temperature by estimation
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/02—Circuit arrangements for generating control signals
    • F02D41/14—Introducing closed-loop corrections
    • F02D41/1438—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor
    • F02D41/1444—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases
    • F02D2041/1472—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases the characteristics being a humidity or water content of the exhaust gases
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D2200/00—Input parameters for engine control
    • F02D2200/02—Input parameters for engine control the parameters being related to the engine
    • F02D2200/04—Engine intake system parameters
    • F02D2200/0414—Air temperature
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/02—Circuit arrangements for generating control signals
    • F02D41/14—Introducing closed-loop corrections
    • F02D41/1438—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor
    • F02D41/1444—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases
    • F02D41/1445—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases the characteristics being related to the exhaust flow
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/02—Circuit arrangements for generating control signals
    • F02D41/14—Introducing closed-loop corrections
    • F02D41/1438—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor
    • F02D41/1444—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases
    • F02D41/1446—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases the characteristics being exhaust temperatures
    • F02D41/1447—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases the characteristics being exhaust temperatures with determination means using an estimation
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/02—Circuit arrangements for generating control signals
    • F02D41/18—Circuit arrangements for generating control signals by measuring intake air flow
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02M—SUPPLYING COMBUSTION ENGINES IN GENERAL WITH COMBUSTIBLE MIXTURES OR CONSTITUENTS THEREOF
    • F02M26/00—Engine-pertinent apparatus for adding exhaust gases to combustion-air, main fuel or fuel-air mixture, e.g. by exhaust gas recirculation [EGR] systems
    • F02M26/02—EGR systems specially adapted for supercharged engines
    • F02M26/04—EGR systems specially adapted for supercharged engines with a single turbocharger
    • F02M26/06—Low pressure loops, i.e. wherein recirculated exhaust gas is taken out from the exhaust downstream of the turbocharger turbine and reintroduced into the intake system upstream of the compressor
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02M—SUPPLYING COMBUSTION ENGINES IN GENERAL WITH COMBUSTIBLE MIXTURES OR CONSTITUENTS THEREOF
    • F02M26/00—Engine-pertinent apparatus for adding exhaust gases to combustion-air, main fuel or fuel-air mixture, e.g. by exhaust gas recirculation [EGR] systems
    • F02M26/13—Arrangement or layout of EGR passages, e.g. in relation to specific engine parts or for incorporation of accessories
    • F02M26/22—Arrangement or layout of EGR passages, e.g. in relation to specific engine parts or for incorporation of accessories with coolers in the recirculation passage
    • F02M26/23—Layout, e.g. schematics
    • F02M26/25—Layout, e.g. schematics with coolers having bypasses
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/10—Internal combustion engine [ICE] based vehicles
    • Y02T10/12—Improving ICE efficiencies
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/10—Internal combustion engine [ICE] based vehicles
    • Y02T10/40—Engine management systems

Landscapes

  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Exhaust-Gas Circulating Devices (AREA)
  • Output Control And Ontrol Of Special Type Engine (AREA)

Abstract

The engine comprises a turbocharger 230 and a low pressure EGR system 300 with an EGR valve 320, a cooler 310, a bypass circuit and a control valve. The method cyclically estimates a relative humidity before compressor 240 and compares it to a calibratable threshold, using the difference to operate the control valve, thus controlling the temperature of the exhaust gases. The relative humidity may be calculated as a function of H2O fraction, temperature and pressure before compressor. The temperature may be estimated as a function of ambient temperature, air-flow rate, exhaust gas flow rate and temperature at exit of the EGR cooler. The calibratable threshold may be the saturation condition and the control valve may be a continuous valve. An electronic control unit ECU, a data carrier and a computer program may be used to implement the method.

Description

METHOD OF CONTROLLING A LOWPRESSURE EGR SYSTEM
OF AN INTERNAL COMBUSTION ENGINE
TECHNICAL FIELD
The present disclosure relates to a method of controlling a low pressure EGR system (LP-EGR)of an internal combustion engines.
BACKGROUND
An internal combustion engine, particularly a highly efficient diesel engine is normally provided with an exhaust gas after-treatment system, for degrading and/or removing the pollutants from the exhaust gas emitted by the Diesel engine, before discharging it in the environment, The after-treatment system generally comprises an exhaust line for leading the exhaust gas from the Diesel engine to the environment, a Diesel Oxidation Catalyst (DOC) located in the exhaust line, for oxidizing hydrocarbon (HC) and carbon monoxides (CO) into carbon dioxide (C02) and water (H20), and a Diesel Particulate Filter (DPF) located in the exhaust line downstream the DOCI for removing diesel particulate matter or soot from the exhaust gas.
Another well-known exhaust gas after-treatment system of a Diesel engine is the Lean NO Trap (LNT), which is provided for trapping nitrogen oxides NO contained in the exhaust gas and is located in the exhaust line. A LNT is a catalytic device containing catalysts, such as Rhodium, Platinum and Palladium, and adsorbents, such as barium based elements, which provide active sites suitable for binding the nitrogen oxides (NOr) contained in the exhaust gas, in order to trap them within the device itself. Lean NO Traps (LNT) are subjected to periodic regeneration processes, whereby such regeneration processes are generally provided to release and reduce the trapped nitrogen oxides (NO,) from the LNT.
To further reduce the emissions content, in particular NOx emissions, normally Diesel engines include an exhaust gas recirculation (EGR) system coupled between the exhaust manifold and the intake manifold. This embodiment is also called as high pressure exhaust gas recirculation (HP-EGR). As known, the EGR works by recirculating a portion of an engine's exhaust gas back to the engine cylinders. In a diesel engine, the exhaust gas replaces some of the excess oxygen in the pre-combustion mixture.
Because NOx forms primarily when a mixture of nitrogen and oxygen is subjected to high temperature, the lower combustion chamber temperatures caused by EGR reduces the amount of NOx the combustion generates. More recent embodiments also include a low pressure EGR system (LP-EGR) characterized by a long route" of the exhaust gases. In this case the additional EGR valve will recirculate the exhaust gases downstream the aftertreatment devices towards the compressor inlet. The operating principle of the LP-EGR is the same of the HP-EGR, with the further advantage that the LP-EGR recirculates exhaust gases at still lower temperature.
Although the combination of HP-EGR and LP-EGR, together with the mentioned after-treatment systems, seems very promising for controlling exhaust emissions, the use of LP-EGR could imply an important issue. In fact, as mentioned, LP-EGR systems recirculate EGR gases before compressor. The high amount of recirculated water (present into the exhaust gases in form of vapour) could be transformed in condensed water before compressor if the temperature at the same place is too low. In this case, there is a serious risk of damaging the compressor. In particular, as experienced in preliminary tests, for ambient temperature c 10°C, current LP-EGR systems can suffer this phenomenon. Current way of protecting the compressor is to limit the LP-EGR recirculation rate in such ambient conditions, by calibration of the split between HP-EGR and LP-EGR. Drawback of this is a direct negative impact on EGR system capability to lower NOX engine out. Above all in view of future emission regulations this could be impacting in the overall emissions system capability.
Therefore a need exists for a method of minimizing the loss of LP EGR System under cold ambient conditions.
An object of this invention is to provide a method which minimizes the loss of EGR system capability, by differently controlling the water condensation before compressor in cold conditions, by acting on the temperature of the recirculating gases instead of their flow-rate.
Another object is to provide an apparatus which allows to perform the above method.
These objects are achieved by a method, by an apparatus, by an engine, by a computer program and computer program product, and by an electromagnetic signal having the features recited in the independent claims.
The dependent claims delineate preferred and/or especially advantageous aspects.
SUMMARY
An embodiment of the disclosure provides a method of coAtrolling an internal combustion engine comprising a turbocharger and a low pressure EGR system, wherein the low pressure EGR system comprises at least an EGR valve, an EGR cooler and a bypass circuit with a control valve, wherein the method cyclically -estimating a relative humidity before compressor and comparing said relative humidity before compressor with a calibratable threshold, -using the difference from the above comparison to control the opening of said control valve of the by-pass circuit, thus controlling a temperature of the exhaust gases at the exit of the EGR cooler.
Consequently, an apparatus is disclosed for controlling a low pressure EGR system of an internal combustion engine, the apparatus comprising -means for estimating a relative humidity before compressor and comparing said relative humidity before compressor with a calibratable threshold, -means for using the difference from the above comparison to control the opening of said control valve of the by-pass circuit, thus controlling a temperature of the exhaust gases at the exit of the EGR cooler.
An advantage of this embodiment is that it provides a method which avoids water condensation before compressor, maintaining a good level of the EGR system capability, for future emission standards, like Real Drive Emissions Compliance Factors and improving the capability for Cold Emissions Test.
According to another embodiment of the invention, said relative humidity before compressor is calculated as function of H20 fraction, temperature and pressure before compressor.
An advantage of this embodiment is that it provides further parameters influencing the relative humidity before compressor, other than the exhaust gas flow-rate, thus avoiding the reduction of the LP-EGR flow-rate and consequently the benefits of the LP-EGR system.
According to a further embodiment of the invention said temperature before compressor is estimated as function of ambient temperature, air flow-rate, LP-EGR flow-rate and temperature at the exit of the LP-EGR cooler.
An advantage of this embodiment is that the method detects the temperature at the exit of the LP-EGR cooler as one parameter influencing the water condensation before compressor and which can be regulated for this purpose instead of the LP-EGR flow-rate.
According to a still further embodiment, said calibratable threshold of the relative humidity before compressor corresponds to the saturation condition.
An advantage of this embodiment is that the method only applies if there is a real risk of water condensation, thus limiting the bypass of the LP-EGR cooler and avoiding high temperature at the inlet of the LP-EGR valve or at the outlet of the compressor.
According to another embodiment, the invention provides an internal combustion engine of an automotive system, the engine comprising a low pressure EGR valve, a low pressure EGR cooler, an EGR cooler by-pass circuit and a control valve, the automotive system being configured for carrying out the above method.
According to a still further embodiment said control valve of the LP-EGR cooler by-pass circuit is a continuous valve.
The method according to one of its aspects can be carried out with the help of a computer program comprising a program-code for carrying out all the steps of the method described above, and in the form of computer program product comprising the computer program.
The computer program product can be embodied as a control apparatus for an internal combustion engine, comprising an Electronic Control Unit (ECU), a data carrier associated to the ECU, and the computer program stored in a data carrier, so that the control apparatus defines the embodiments described in the same way as the method. In this case! when the control apparatus executes the computer program all the steps of the method described above are carried out.
The method according to a further aspect can be also embodied as an electromagnetic signal, said signal being modulated to carry a sequence of data bits which represents a computer program to carry out all steps of the method.
A still further aspect of the disclosure provides an internal combustion engine specially arranged for carrying out the method claimed.
BRIEF DESCRIPTION OF THE DRAWINGS
The various embodiments will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 shows an automotive system.
Figure 2 is a section of an internal combustion engine belonging to the automotive system of figure 1.
Figure 3 is a scheme of an internal combustion engine cornprising an EGR cooler by-pass according to an embodiment of the invention.
Figure 4 is a psychometric chart depicting the working areas of the LP-EGR, as function of the ambient temperature.
Figure 5 is a flowchart of an estimation method of the relative humidity before compressor.
Figure 6 is a flowchart of the method according to an ernbodirnent of the invention.
DETAILED DESCRIPTION OF THE DRAWINGS
Some embodiments may include an automotive system 100, as shown in Figures 1 and 2, that includes an internal combustion engine (ICE) 110 having an engine block 120 defining at least one cylinder 125 having a piston 140 coupled to rotate a crankshaft 145.
A cylinder head 130 cooperates with the piston 140 to define a combustion chamber 150.
A fuel and air mixture (not shown) is disposed in the combustion chamber 150 and ignited, resulting in hot expanding exhaust gasses causing reciprocal movement of the piston 140. The fuel is provided by at least one fuel injector 160 and the air through at least one intake port 210. The fuel is provided at high pressure to the fuel injector 160 from a fuel rail 170 in fluid communication with a high pressure fuel pump 180 that increase the pressure of the fuel received a fuel source 190. Each of the cylinders 125 has at least two valves 215, actuated by a camshaft 135 rotating in time with the crankshaft 145. The valves 215 selectively allow air into the combustion chamber 150 from the port 210 and alternately allow exhaust gases to exit through a port 220. In some examples, a cam phaser 155 may selectively vary the timing between the camshaft 135 and the crankshaft 145.
The air may be distributed to the air intake port(s) 210 through an intake manifold 200.
An air intake duct 205 may provide air from the ambient environment to the intake manifold 200. In other embodiments, a throttle body 330 may be provided to regulate the flow of air into the manifold 200. In still other embodiments, a forced air system such as a turbocharger 230, having a compressor 240 rotationally coupled to a turbine 250, may be provided. Rotation of the compressor 240 increases the pressure and temperature of the air in the duct 205 and manifold 200. An intercooler 260 disposed in the duct 205 may * 25 reduce the temperature of the air. The turbine 250 rotates by receiving exhaust gases
B
from an exhaust manifold 225 that directs exhaust gases from the exhaust pods 220 and through a series of vanes prior to expansion through the turbine 250. The exhaust gases exit the turbine 250 and are directed into an exhaust system 210. This example shows a variable geometry turbine (VGT) 250 with a VGT actuator 290 arranged to move the vanes to alter the flow of the exhaust gases through the turbine 250. In other embodiments the turbocharger 230 may be fixed geometry and/or include a waste gate.
The exhaust system 270 may include an exhaust pipe 275 having one or more exhaust aftertreatment devices 280. The aftertreatment devices may be any device configured to change the composition of the exhaust gases. Some examples of aftertreatment devices 280 include, but are not limited to, catalytic converters (two and three way), oxidation catalysts 281, lean NOx traps, hydrocarbon adsorbers, selective catalytic reduction (SCR) systems, particulate filters (DPF) 282 or a combination of the last two devices, i.e. selective catalytic reduction system comprising a particulate filter (SCRF). Some embodiments include an exhaust gas recirculation (EGR) system 300 coupled between the exhaust manifold 225 and the intake manifold 200. The EGR system 300 may include an EGR cooler 310 to reduce the temperature of the exhaust gases in the EGS system 300. An EGR valve 320 regulates a flow of exhaust gases in the EGR system 300. Still other embodiments (Fig. 3) may include a low pressure EGR system (LP-EGR) characterized by a "long route" of the exhaust gases. In this case an additional low pressure EGR valve 325 will recirculate the exhaust gases downstream the aftertreatment devices towards the compressor 240 inlet. Moreover, a low pressure EGR-cooler 326 can be provided, together with a cooler by-pass circuit 327 and a control valve 328. 9.
The automotive system 100 may further include an electronic control unit (ECU) 450 in communication with one or more sensors and/cr devices associated with the ICE 110 and equipped with a data carrier 40. The ECU 450 may receive input signals from various sensors configured to generate the signals in proportion to various physical parameters associated with the ICE 110. The sensors include, but are not limited to, a mass airflow and temperature sensor 340, a manifold pressure and temperature sensor 350, a combustion pressure sensor 360, coolant and oil temperature and level sensors 380, a fuel rail pressure sensor 400, a cam position sensor 410, a crank position sensor 420, exhaust pressure and temperature sensors 430, an EGR temperature sensor 440, and an accelerator pedal position sensor 445. Furthermore the ECU 450 may generate output signals to various control devices that are arranged to control the operation of the ICE 110, including, but not limited to, the fuel injectors 160, the throttle body 330, the EGR Valve 320, the VGT actuator 290, and the cam phaser 155. Note, dashed lines are used to indicate communication between the ECU 450 and the various sensors and devices, but some are omitted for clarity.
Turning now to the ECU 450, this apparatus may include a digital central processing unit (CPU) in communication with a memory system and an interface bus. The CPU is configured to execute instructions stored as a program in the memory system, and send and receive signals to/from the interface bus. The memory system may include various storage types including optical storage, magnetic storage, solid state storage, and other non-volatile memory. The interface bus may be configured to send, receive, and modulate analog and/or digital signals to/from the various sensors and control devices.
The program may embody the methods disclosed herein, allowing the CPU to carryout out the steps of such methods and control the ICE 110.
The method according to the invention is related to the control of the water condensation before the compressor 240 of the internal combustion engine, adopting the LP-EGR system. A low pressure EGR system, also called "long route" EGR system, is the one showed in Fig. 3. The term low pressure, as known, means that the exhaust gases are also recirculated downstream the aftertreatment devices through a low pressure EGR valve 325 to the inlet system, upstream the compressor 240. The LP-EGR system is normally provided with an EGR cooler 326.
The proposed method aims to avoid water condensation before the compressor 240, because of serious risks of compressor damage. A good index of possible condensation, is the relative humidity, which, to avoid condensation, shall stay under a threshold, for example, should be C 100%.
Figure 4 is a qualitative graph depicting the working areas of the LP-EGR, as function of the ambient temperature. The graph is a psychometric chart in which several curves at different relative humidity (RH, growing according to the arrow) are represented as function of the temperature at compressor inlet and the absolute humidity. Rectangle 500 represents the LP-EGR working area for ambient temperature Tamb > 20°C, while rectangle 510 is the LP-EGR working area for Tamb c 20°C. As can be observed, decreasing ambient temperature, the LP-EGR working area moves towards lower inlet compressor temperature.
Therefore the problem is that for lower ambient temperatures, there is more risk of having relative humidity close to the saturation conditions, that leads to water ti condensation and consequent damage of the compressor. Nowadays the current way of protecting the compressor in engines adopting LP-EGR systems is to continuous calculate the relative humidity before compressor by means of an estimation model algorithm. In case RH exceeds a predetermined threshold, the recovery action is to reduce the LP-EGR rate, through a splitting factor with the HP-EGR rate, until the previous algorithm reaches a safe LP-EGR rate.
Figure 5 shows the mentioned estimation model. At first, the fraction of H20 which is present in the exhaust gases is calculated 20 as function of the air/fuel ratio sensor signal: [H2Oj=f(X) (1) Where: [H2OJe, is the water fraction in the exhaust gases X is the air/fuel ratio Then, the calculation 21 of the ambient specific humidity is performed, by using a map like the one in Fig. 4 and considering a RH = 100% and the ambient temperature Tamb.
Further, the estimation 22 of the H20 fraction before compressor is realized as function of the air flow-rate (signal coming from the mass air flow sensor, MAF), the air humidity (derived from the ambient specific humidity and the H20 fraction at the exhaust) and the LP-EGR flow-rate: [H2O]BTc = f(thair,XQIPPthLpE) (2) where: [H201s10 is the water fraction before compressor th air is the airflow rate Xair is the air humidity th is the LP-EGR flow-rate Then, by using the thermodynamic principle of the enthalpy balance 23 the temperature before compressor TbethIeTC is estimated as function of ambient temperature, air flow-rate, LP-EGR flow-rate and temperature at the exit of the LP-EGR cooler TLP.EGR Ier As known according to the first law of the thermodynamics, the enthalpy of the mixture air and low pressure EGR before compressor is equal to the sum of the single enthalpies of the fresh air and the exhaust gas. Finally, by using the values of the H20 fraction, the temperature and the pressure before compressor PIIOTC, the relative humidity before compressor is calculated 24 by the following equation: HbeforeTC = f ([H2O]RTC, Poejore,rc Tbe!ore,rc) (3) where: H before, IC relative humidity before compressor [H2OJc water fraction before compressor P before,TC is the pressure before compressor T before,TC is the temperature before compressor When the relative humidity before compressor reaches the saturation condition (100%), then 25 a recovery action is put in place.
According to a known method, since the relative humidity before compressor depends on the H20 fraction and the temperature before compressor, reducing the LP-EGR rate is a possible way to reduce the relative humidity before compressor: lower LP-EGR rate means lower H20 fraction before compressor. This solution is obtained by calibration of the split between HP-EGR and LP-EGR. In fact, the humidity estimation before compressor is compared with a threshold (e.g. defined by a calibration parameter, for example, 100%) and the recovery action acts in the direction of reducing the split between HP-EGR and LP-EGR in order to reduce the humidity upstream the compressor. But, higher HP-EGR rate jeopardizes the capability of lowering the NJOx, since too hot EGR flows at the engine intake manifold. Therefore, the known solution has a negative impact on EGR system capability to lower NOx engine out, and in view of future emission regulations, this could be impacting in the overall emissions system capability.
Therefore the invention is proposing a system and an algorithm, additional to a classical LP-EGR system, capable to avoid the water condensation before compressor in cold conditions, and minimizing the loss of EGR system capability. The proposed technique involves the employment of a specific component to be added to the conventional LP-EGH currently known: it is LP-EGR cooler by-pass 327, provided with a control valve 328. Preferably this control valve should be a continuous valve.
The method applies the previous estimation model but starts from a different consideration: as said, the relative humidity before compressor depends on H20 fraction and on the temperature before compressor. This temperature is the result of the air temperature (at ambient temperature) and the LP-EGR temperature (which is the temperature at the exit of the LP-EGR cooler 326, TLPEGR cooler). Considering that the higher is TLpEGR cooler, the higher is TbehreTC, the LP-EGR cooler bypass 327 is a way to have higher temperature before compressor and consequently lower risk of having relative humidity very close to saturation conditions.
The new method therefore is proposing (see Fia 6) the following recovery action: the relative humidity before compressor is filtered 26 by means of a low pass band filter, in order to acquire a clean signal, then is compared 27 with a threshold (e.g. defined by a calibration parameter, for example, 100%). The difference between the relative humidity before compressor and the threshold acts as input for a controller 28 (e.g. the electronic control unit of the engine). Therefore, the recovery action 25 acts in the direction of incrementing the temperature at the exit of the LP-EGR cooler 326, through a continuous bypass valve 328, whose position is automatically set by the above method. Of course the method and the estimation model have to work in closed loop mode.
Effect of this protection is to avoid water condensation before compressor, through temperature increase, and no longer through a. strong LP-EGR rate reduction, thus minimizing the impact on overall EGR system capability in NOx engine out reduction at low temperature conditions. Maintaining a good level of the EGR system capability is a "must" for future emission standards, like Real Drive Emissions Compliance Factors and for improving the Cold Emissions Test capability.
While at least one exemplary embodiment has been presented in the foregoing summary and detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration in any way. Rather, the foregoing summary and detailed description will provide those skilled in the art with a convenient road map for implementing at least one exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope as set forth in the appended claims and their legal equivalents.
REFERENCE NUMBERS block
21 block 22 block 23 block 24 block block 26 block 27 block 28 block data carrier automotive system internal combustion engine engine block 125 cylinder cylinder head camshaft piston crankshaft 150 combustion chamber cam phaser fuel injector fuel rail fuel pump 190 fuel source intake manifold 205 air intake pipe 210 intake port 215 valves 220 port 225 exhaust manifold 230 turbocharger 240 compressor 245 turbocharger shaft 250 Variable geometry turbine (VGT) 260 intercooler 270 exhaust system 275 exhaust pipe 280 aftertreatment devices 281 oxidation catalyst (DOC) 282 particulate filter (DPF) 290 VGT actuator 300 exhaust gas recirculation system 310 EGR cooler 320 EGR valve 324 low pressure EGR system 325 low pressure EGR valve 326 low pressure EGR cooler 327 LP-EGR cooler by-pass circuit 328 control valve of the LP-EGR cooler by-pass circuit 330 throttle body 340 mass airflow (MAF) and temperature sensor 350 manifold pressure and temperature sensor 360 combustion pressure sensor 360 coolant temperature and level sensors 385 lubricating oil temperature and level sensor 390 metal temperature sensor 400 fuel rail pressure sensor 410 cam position sensor 420 crank position sensor 430 exhaust pressure and temperature sensors 440 EGR temperature sensor 445 accelerator position sensor 446 accelerator pedal 450 ECU 500 LP-EGR working area, Tarnb> 20°C 510 LP-EGR working area, Tamb < 20°C Tamb Ambient temperature RH relative humidity rh1 LP-EGR flow-rate P beroreTC pressure before compressor T before,TC temperature before compressor I LP-EGR cooler temperature at the exit of the LP-EGR cooler [H2O]e,d, water fraction in the exhaust gases X air/fuel ratio [H20]BTc water fraction before compressor II before.TC humidity before compressor th air airflow rate Xair air humidity

Claims (10)

  1. CLAIMS1. Method of controlling an internal combustion engine (110) comprising a turbocharger (230) and a low pressure EGR system (324), wherein the low pressure EGR system (324) comprises at least an EGR valve (325) an EGR cooler (326) and a bypass circuit (327) with a control valve (328), wherein the method cyclically -estimating (24) a relative humidity before compressor and comparing (27) said relative humidity before compressor with a calibratable threshold, -using the difference from the above comparison to control (28) the opening of said control valve (328) of the by-pass circuit (327), thus controlling a temperature of the exhaust gases at the exit of the EGR cooler (326).
  2. 2. Method according to claim 1, wherein said relative humidity before compressor is calculated as function of H20 fraction before compressor, temperature before compressor and pressure before compressor.
  3. 3. Method according to claim 2, wherein said temperature before compressor is estimated (23) as function of ambient temperature, air flow-rate, LP-EGR flow-rate and temperature at the exit of the LP-EGR cooler.
  4. 4. Method according to one of the previous claims, wherein said calibratable threshold of the relative humidity before compressor corresponds to the saturation condition.
  5. 5. Internal combustion engine (110) of an automotive system (100), the engine comprising a turbocharger (230), a low pressure EGR valve (325), a low pressure EGR cooler (326), an EGR cooler by-pass circuit (327) and a control valve (328), the automotive system (100) being configured for carrying out the method according to claim 1 or4.
  6. 6. Internal combustion engine according to claim 5, wherein said control valve (328) of the LP-EGR cooler by-pass circuit (327) is a continuous valve.
  7. 7. A computer program comprising a computer-code suitable for performing the method according to any of the claims 1-4.
  8. 8. Computer program product on which the computer program according to claim 7 is stored.
  9. 9. Control apparatus for an internal combustion engine, comprising an Electronic Control Unit (450), a data carrier (40) associated to the Electronic Control Unit (450) and a computer program according to claim 7 stored in the data carrier (40).
  10. 10. An electromagnetic signal modulated as a carrier for a sequence of data bits representing the computer program according to claim 7.
GB1215826.7A 2012-09-05 2012-09-05 Method of controlling an engine including an exhaust gas recirculation system with a bypass circuit. Withdrawn GB2505650A (en)

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN105089831A (en) * 2014-05-23 2015-11-25 福特环球技术公司 System and method for estimating ambient humidity
CN112682189A (en) * 2020-12-25 2021-04-20 潍柴动力股份有限公司 EGR valve control method and device and electronic equipment

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US20070144501A1 (en) * 2005-12-09 2007-06-28 Volker Joergl Exhaust gas recirculation cooler bypass
US20080059049A1 (en) * 2006-09-05 2008-03-06 Totten Lynn A Humidity based control system for an internal combustion engine
US20120012088A1 (en) * 2010-07-16 2012-01-19 Kia Motors Corporation Apparatus and method for control low pressure exhaust gas recirculation system

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20070144501A1 (en) * 2005-12-09 2007-06-28 Volker Joergl Exhaust gas recirculation cooler bypass
US20080059049A1 (en) * 2006-09-05 2008-03-06 Totten Lynn A Humidity based control system for an internal combustion engine
US20120012088A1 (en) * 2010-07-16 2012-01-19 Kia Motors Corporation Apparatus and method for control low pressure exhaust gas recirculation system

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN105089831A (en) * 2014-05-23 2015-11-25 福特环球技术公司 System and method for estimating ambient humidity
CN112682189A (en) * 2020-12-25 2021-04-20 潍柴动力股份有限公司 EGR valve control method and device and electronic equipment

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