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
  • F02D41/02—Circuit arrangements for generating control signals
• • 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
  • F02D41/021—Introducing corrections for particular conditions exterior to the engine
  • F02D41/0235—Introducing corrections for particular conditions exterior to the engine in relation with the state of the exhaust gas treating apparatus
  • F02D41/0295—Control according to the amount of oxygen that is stored on the exhaust gas treating apparatus
• • 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
  • F02D41/04—Introducing corrections for particular operating conditions
  • F02D41/12—Introducing corrections for particular operating conditions for deceleration
• • 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
  • F02D41/04—Introducing corrections for particular operating conditions
  • F02D41/12—Introducing corrections for particular operating conditions for deceleration
  • F02D41/123—Introducing corrections for particular operating conditions for deceleration the fuel injection being cut-off
  • F02D41/126—Introducing corrections for particular operating conditions for deceleration the fuel injection being cut-off transitional corrections at the end of the cut-off period
• • 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
• • 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
  • F02D41/1439—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the position of the sensor
• • 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
  • F02D2200/08—Exhaust gas treatment apparatus parameters
  • F02D2200/0814—Oxygen storage amount
• • 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
  • F02D2200/08—Exhaust gas treatment apparatus parameters
  • F02D2200/0816—Oxygen storage capacity
• • 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
  • F02D41/1473—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the regulation method
  • F02D41/1475—Regulating the air fuel ratio at a value other than stoichiometry

Definitions

• the present invention relates to a method for purifying the exhaust gases of an internal combustion engine having a catalytic converter which comprises oxygen storage components.
• the invention is concerned particularly with the restoration of the optimum filling degree of the oxygen storage components for regulated (lambda controlled) stoichiometric operation of the engine after it has been operated under lean conditions.
• the air ratio lambda ( ⁇ ) is often used to describe the composition of the air/fuel mixture supplied to the engine. Said air ratio is the air/fuel ratio normalized in relation to stoichiometric conditions. The air/fuel ratio describes how many kilograms of air are supplied to the internal combustion engine per kilogram of fuel. The air/fuel ratio for a stoichiometric combustion is 14.7 for common engine fuels. At this point, the air ratio lambda is 1. Air/fuel ratios below 14.7, or air ratios below 1, are referred to as rich and air/fuel ratios above 14.7, or air ratios above 1, are referred to as lean.
• the air ratio of the exhaust gas corresponds to the air ratio of the air/fuel mixture supplied to the engine.
• OSC oxygen storage components
• Compounds which permit a change in their oxidation state are suitable as oxygen storage components in a catalytic converter.
• Use is preferably made of cerium oxide, which may be present both as Ce 2 O 3 and also CeO 2 . To stabilize the cerium oxide, it is used for example as a mixed oxide with zirconium oxide.
• the storage capacity of the oxygen storage components is to be understood to mean the mass of oxygen which can be absorbed by the oxygen storage component per gram. Accordingly, the filling degree refers to the ratio of the actually stored mass of oxygen to the storage capacity.
• the storage capacity may be determined experimentally using various methods known to a person skilled in the art.
• the aim of the regulation of the air ratio is to prevent a complete filling or a substantial emptying of the oxygen storage.
• a breakthrough of lean exhaust gas occurs and therefore nitrogen oxides are emitted.
• nitrogen oxides are emitted.
• rich breakthroughs occur, that is to say carbon monoxide and hydrocarbons are emitted.
• the signal of an oxygen probe (lambda probe) which is arranged upstream of the catalytic converter (pre-cat probe) in the flow direction of the exhaust gas is used for regulating the air ratio.
• the air/fuel mixture supplied to the engine is regulated such that the exhaust gas is of stoichiometric composition before entering the catalytic converter.
• said regulation is referred to as lambda regulation.
• An oxygen probe is usually incorporated in the drive train downstream of the catalytic converter in addition to the pre-cat probe.
• the target stoichiometry of the lambda regulation can be re-adjusted by means of said post-cat probe. This is referred to as post-cat regulation.
• Post-cat regulation serves in particular for monitoring and adjusting the filling degree of the oxygen storage of the catalytic converter.
• the probes generate an electrical voltage as a function of the oxygen content of the exhaust gas.
• two-point lambda probes which are also referred to as step change lambda probes.
• said lambda probes have a volt- age of approximately 0.2 V, which jumps from 0.2 V to over 0.7 V in a very narrow lambda interval at the transition to rich exhaust gas.
• the post- cat regulation is configured so as to yield a probe voltage of approximately 0.65 V. This point lies on the steepest branch of the probe characteristic curve and corresponds to an optimum filling degree of the oxygen storage of approximately 50%. In this way, upward or downward deviations from the stoichiometry of the exhaust gas can be easily detected and corrected.
• a spark-ignition engine is operated predominantly with air/fuel mixtures of stoichiometric composition. However, if the engine is to no longer output power, the fuel supply is conventionally cut off. In the event of this so-called overrun fuel cutoff, only air is supplied to the engine, such that the exhaust-gas composition corresponds to the ambient air.
• the oxygen storage components of the catalytic converter are completely saturated, or filled, with oxygen.
• post-cat regulation is not possible.
• a complete filling of the oxygen storage may also occur in other driving situations, for example on account of regulating errors of the lambda regulation.
• DE 10 2004 038 482 B3 is concerned with setting the filling degree of the oxygen storage after a transient operating state of the engine, such as for example an overrun fuel cutoff.
• the oxygen storage should be quickly emptied to an optimum value of approximately 50% of its filling degree.
• a rich air/fuel ratio ⁇ ⁇ 1 is set and then adjusted back toward 1 with optimum speed.
• DE 10 2004 019 831 Al prevents an undesired oxygen loading of the exhaust-gas catalytic converter during an overrun fuel cutoff phase by virtue of a catalytic converter mass flow with a defined, predetermined lambda value being supplied to the catalytic converter.
• DE 10 2006 044 458 Al is likewise concerned with the fuel injection after an overrun fuel cutoff.
• the fuel pulse width is set such that a fuel supply quantity is significantly increased in relation to an inlet air quantity, and the ignition time is set to a first retarded ignition time.
• a fuel pulse width is set which has a smaller increase width of the fuel, and the ignition time is set to a second retarded ignition time which is retarded to a lesser extent than the first retarded ignition time.
• the inventors have observed that, in the known methods, the rich pulse after an overrun fuel cutoff leads to a temporary emission of carbon monox- ide and hydrogen. Said emissions last for approximately 100 seconds and, at a maximum, have a concentration of 10 to 500 ppm carbon monoxide, as a result of which the post-cat regulation after the overrun fuel cutoff is disrupted and delayed. It is therefore an object of the invention to specify a method by means of which the transition from the overrun fuel cutoff to regulated stoichiometric operation can be accelerated.
• the method relates to the purification of the exhaust gases of an internal combustion engine having a catalytic converter which comprises an oxygen storage composed of oxygen storage components, with the engine being equipped with an electronic engine controller and being operated with a regulated, stoichiometric air/fuel mixture over the greater part of the operating duration thereof, with temporary lean operating phases also occurring as a function of the driving situations.
• the method is characterized in that, after a temporary lean operating phase of the engine with a lean air/fuel mixture, which is associated with a sub- stantial filling of the oxygen store, and before the resumption of regulated engine operation, the filling degree of the oxygen storage is returned to an optimum level for stoichiometric operation by virtue of the engine being supplied with a rich pulse followed by a lean pulse, with the quantity of oxidative components supplied to the catalytic converter by means of the lean pulse being lower than would be required for fully compensating the quantity of rich exhaust-gas components supplied by means of the rich pulse.
• the invention is based on the observation that, after an overrun fuel cutoff, the optimum filling degree of the oxygen storage for the stoichiometric regulation of the air/fuel ratio can be restored very quickly if a short rich pulse after the overrun fuel cutoff is followed by a short lean pulse.
• the rich pulse and lean pulse are generated by means of corresponding control of the air/fuel ratio supplied to the engine. This preferably occurs by virtue of the pre-cat lambda probe predefining a corresponding chronologi- cal lambda profile.
• an equilibrium state of the oxygen storage is always set with the reducing and oxidizing components of the exhaust gas, that is to say in the equilibrium state, the reduction of the oxygen storage by means of carbon monoxide, hydrogen or hydrocarbons is compensated exactly by means of a corresponding oxidation with carbon dioxide and water.
• a further consequence of the equilibrium behavior is that a completely emp- tied oxygen storage is also partially oxidized again by moderately rich exhaust gas until a new equilibrium state is set with the moderately rich exhaust gas.
• the oxygen store by means of reaction with water or carbon dioxide, forms the components of carbon monoxide and hydrogen. Said situation arises if, according to the prior art, after an overrun fuel cutoff, the oxygen storage is emptied again only with a rich pulse. By means of said single rich pulse, the oxygen storage is significantly reduced (thoroughly emptied). If said thoroughly emptied oxygen storage is acted on with stoichiometric or slightly rich exhaust gas after the rich pulse, it generates carbon monoxide and hydrogen for a time period of 10 to several hundred seconds.
• Typical concentrations of said carbon monoxide and hydrogen release are approximately 10 ppm to 500 ppm. Said pollutant release may be reduced slightly if the rich pulse is not ended abruptly but rather is returned slowly to the stoichiometric value. However, this increases the time period between the end of the overrun fuel cutoff and the resumption of regulated operation, with the risk of further pollutant emissions.
• the carbon monoxide released from the front part of the catalytic converter and the hydrogen can empty the rear part of the catalytic converter to the desired extent.
• the above-described carbon monoxide and hydrogen emissions in a vehicle operated according to the prior art have an adverse effect on the stability of the resuming post-cat regulation.
• For the post-cat regulation use is made of a probe arranged downstream of the catalytic converter.
• the post-cat regulation is misled by the overall rich exhaust gas.
• the post-cat regulation attempts to compensate the rich offset by setting the air/fuel mixture supplied to the engine to be leaner.
• the oxygen storage is filled with oxygen again, contrary to the actual purpose of the regulation. In the filled state, a breakthrough of nitrogen oxide occurs in the event of the slightest lean deviation of the exhaust gas.
• Said enrichment has a similar effect as the rich pulse after an overrun fuel cutoff: the oxygen storage is firstly emptied very thoroughly. Said thorough emptying results in the above-described carbon monoxide and hydrogen emissions.
• the post- cat regulation reacts to this with a leaning of the air/fuel mixture supplied to the engine, which can lead to a renewed lean breakthrough with a fall in the post-cat probe voltage.
• the fall in the post-cat probe voltage starts the described process of carbon monoxide and hydrogen emissions, leaning and lean breakthrough from the beginning.
• a periodic oscillation of the exhaust- gas stoichiometry with periodic lean breakthroughs and corresponding nitrogen oxide emissions thus occurs. Said oscillating behavior is well known to a control engineer.
• the response time of the regulation must be increased by adjusting the regulating parameters. Said solution is of course not optimal because, as a result of the reduced speed of the regulation, the lambda deviations which inevitably occur in driving operation can be compensated only with an unnecessarily lengthened response time.
• the stated problems of the conventional method are reduced or even completely eliminated in that, after the end of the lean operating phase, the filling degree of the oxygen storage is returned to the optimum level for the subsequent post-cat regulation by means of at least one rich pulse and one lean pulse.
• the quantity of rich exhaust-gas components prefferably be greater than that required for setting the optimum filling degree for stoichiometric operation but smaller than the quantity of rich exhaust-gas components which would be required for completely emptying the storage capacity of the oxygen store.
• a rich pulse is used which is capable of emptying the catalytic converter over the entire length thereof.
• the front part of the store is thoroughly emptied.
• Said thorough emptying in the front part is ended by means of a relatively small lean pulse.
• the lean pulse will inevitably fill a small zone at the inlet of the catalytic converter beyond the optimum filling degree again. This may be compensated by means of a further rich pulse which is selected such that the quantity of rich components provided by it is smaller than that required for completely compensating the preceding lean pulse.
• the reducing agent quantity in the first rich pulse must be greater than the equivalent quantity of oxygen which must be extracted from the catalytic converter at the transition from the fully oxidized state into the stoichiometric operating state.
• the catalytic converter is thus firstly thoroughly emp- tied.
• the reducing agent quantity in the first rich pulse is however preferably selected to be smaller than the equivalent oxygen quantity which can be extracted from the catalytic converter by means of a steady-state rich operating mode.
• the pulse sequence is preferably configured, as a function of the operating state of the engine and the aging state of the catalytic converter, such that, after the end of the pulse sequence, the store loading distribution corre- sponds to the distribution which would also be set during regulated operation of the catalytic converter at said operating point.
• An optimum pulse sequence may be identified in that, after the end of the pulse sequence, the voltage of the post-cat probe assumes, in a stable manner, the setpoint value of the post-cat regulation.
• the amplitude and/or the duration of the rich pulse and lean pulse are available as influential variables for said optimization.
• the amplitude and/or duration may be optimized as a function of the temperature and spatial velocity of the exhaust gas and/or an aging state of the catalytic converter.
• the engine may be supplied with further rich and lean pulses after the first rich pulse and lean pulse, with the quantity of rich components supplied with the respective rich pulse being greater than that which can be compensated with the oxidative components of the subsequent lean pulse.
• the optimum number of successive lean/rich pulses may be determined in preliminary tests as a function of the operating conditions after an overrun fuel cutoff.
• the method is preferably used for the exhaust-gas purification of stoichiometrically operated internal combustion engines in which overrun fuel cutoffs occur if engine power is no longer required.
• the overrun fuel cutoffs form the temporary lean operating phases.
• Temporary lean operating phases may however also be caused by undesired regulation fluctuations of the stoichiometric operation.
• a further field of use of the invention is the exhaust-gas purification of a lean-operated internal combustion engine which is operated partially stoichiometrically and partially lean.
• the engine is operated lean in order to save fuel. If higher levels of power are demanded, the engine must be switched to stoichiometric operation. It is thus the case here that the oxygen storage in the catalytic converter is completely filled in the lean operating mode, in exactly the same way as in the event of an overrun fuel cutoff.
• the switch to stoichiometric operation leads to the same problems as those encountered after an overrun fuel cutoff.
• Undesired temporary lean operating phases as a result of a regulating error are preferably detected in that the post-cat probe indicates lean exhaust gas.
• a step change probe If the signal voltage thereof falls below a predefined threshold value, then a temporary lean operating phase according to this invention is present.
• the threshold value may be selected as a function of the temperature and the spatial velocity of the exhaust gas, as a function of the exhaust-gas stoichiometry and as a function of the aging state of the catalytic converter. Said threshold values are preferably stored in a table of the engine controller.
• the oxygen storage components of the exhaust-gas purification catalytic converter continuously lose storage capacity as a result of thermal aging.
• the method makes it possible to determine the storage capacity still re- maining.
• the output signal of the oxygen probe arranged downstream of the catalytic converter in the exhaust section may be used for this purpose. If the signal voltage lies below the expected voltage after the step from the temporary lean operating phase into regulated stoichiometric operation, then the remaining oxygen storage capacity of the catalytic converter is lower than assumed. In this way, it is thus possible to determine the remaining oxygen storage capacity from the signal voltage in the stoichiometric operating mode after an overrun fuel cutoff. If the remaining oxygen storage capacity falls below a predefined value, then a corresponding warning signal can be activated.
• the determination of the remaining oxygen storage capacity makes it possible to adapt the quantity of rich and lean components supplied to the catalytic converter by means of the rich and lean pulses to the remaining oxygen storage capacity, and to thereby optimize the transition from the overrun fuel cutoff to regulated stoichiometric operation. This preferably takes place by virtue of the amplitudes of the rich and lean pulses being reduced by a factor corresponding to the remaining oxygen storage capac- ity.
• the factor may be stored in a table of the engine controller as a function of the remaining oxygen storage capacity.
• figure 1 shows the release of carbon monoxide/hydrogen in the stoichiometric operating mode following a rich pulse.
• figure 2 shows a conventional lambda profile after an overrun fuel cutoff and the resulting profile of the voltage of the lambda probe downstream of the catalytic converter for two different rich pulses after an overrun fuel cutoff
• figure 3 shows a lambda profile according to the invention after an overrun fuel cutoff and the resulting profile of the voltage of the lambda probe downstream of the catalytic converter
• Figure 1 shows the emissions of carbon monoxide and hydrogen after an overrun fuel cutoff and a return to stoichiometric operation by means of a single rich pulse.
• a conventional three-way catalytic converter was tested in a model gas system.
• the upper diagram shows the profile of the air ratio lambda as a function of the time (lambda profile).
• an overrun fuel cutoff with a lambda value of 1.1 was simulated.
• the two lower diagrams show in each case the measured profile of the hydrogen and carbon monoxide concentrations downstream of the catalytic converter. After a time delay after the rich pulse, hydrogen and carbon monoxide are released by the catalytic converter. The emissions of said two pollutants last for a period of longer than 40 seconds.
• Figure 2 shows the result of simulation calculations for the case of a con- ventional lambda profile after an overrun fuel cutoff with complete filling of the oxygen store. The calculations were carried out for two rich pulses of different length with a lambda value of 0.9. The lambda profiles upstream of the catalytic converter are shown in the upper diagram. The lower diagram shows the calculated signal voltages of the post-cat probe.
• the signal voltage of the post-cat probe starts at approximately 0.1 V and indicates a very lean exhaust gas (lean operating phase) with a high oxygen component.
• the oxygen storage has virtually a 100% filling degree.
• the exhaust gas is briefly enriched upstream of the catalytic converter.
• Figure 3 shows the result of simulation calculations for the case of a lambda profile according to the invention.
• the exhaust gas upstream of the catalytic converter has two pairs of rich and lean pulses with an overall duration of approximately 20 seconds.
• the diagram with the signal voltage of the post-cat probe reaches the desired 0.65 V, and remains at this voltage level, already after approximately 4 seconds.
• the oxygen storage has thus reached an optimum filling level, averaged over its entire length, already after said short time with only one rich/lean pulse pair. Nevertheless, on account of the above-described axial distribution of the filling level, a further rich/lean pulse pair is required to optimally set the filling degree over the entire length of the catalytic converter.
• the post-cat regulation remains deactivated after the end of the preceding lean operating phase at the time zero until the end of the final rich/lean pulse pair at approximately 20 seconds. Only thereafter is the post-cat regulation resumed.

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Combustion & Propulsion (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Exhaust Gas After Treatment (AREA)
• Electrical Control Of Air Or Fuel Supplied To Internal-Combustion Engine (AREA)

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• 2009
  • 2009-05-22 AT AT09160947T patent/ATE517245T1/de active
  • 2009-05-22 EP EP09160947A patent/EP2253821B1/de active Active
• 2010
  • 2010-05-20 WO PCT/EP2010/003111 patent/WO2010133370A1/en active Application Filing
  • 2010-05-20 US US13/321,769 patent/US20120067030A1/en not_active Abandoned
  • 2010-05-20 KR KR1020117027516A patent/KR20120024617A/ko not_active Application Discontinuation
  • 2010-05-20 CN CN2010800222327A patent/CN102439278A/zh active Pending
  • 2010-05-20 BR BRPI1012807A patent/BRPI1012807A2/pt not_active IP Right Cessation
  • 2010-05-20 RU RU2011152239/06A patent/RU2011152239A/ru not_active Application Discontinuation
  • 2010-05-20 JP JP2012511196A patent/JP2012527560A/ja active Pending

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