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US20020029562A1 - Engine exhaust purifying apparatus - Google Patents

Engine exhaust purifying apparatus Download PDF

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Publication number
US20020029562A1
US20020029562A1 US09/950,604 US95060401A US2002029562A1 US 20020029562 A1 US20020029562 A1 US 20020029562A1 US 95060401 A US95060401 A US 95060401A US 2002029562 A1 US2002029562 A1 US 2002029562A1
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United States
Prior art keywords
nox
trap
air
exhaust
fuel ratio
Prior art date
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Abandoned
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US09/950,604
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English (en)
Inventor
Toshio Ishii
Yutaka Takaku
Shigeru Kawamoto
Shinji Nakagawa
Minoru Ohsuga
Yoshihisa Fujii
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Hitachi Ltd
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Hitachi Ltd
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Priority to US09/950,604 priority Critical patent/US20020029562A1/en
Publication of US20020029562A1 publication Critical patent/US20020029562A1/en
Priority to US10/195,558 priority patent/US20020184877A1/en
Abandoned legal-status Critical Current

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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL-COMBUSTION ENGINES
    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/0807—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents
    • F01N3/0828—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents characterised by the absorbed or adsorbed substances
    • F01N3/0842—Nitrogen oxides
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL-COMBUSTION ENGINES
    • F01N11/00—Monitoring or diagnostic devices for exhaust-gas treatment apparatus
    • F01N11/007—Monitoring or diagnostic devices for exhaust-gas treatment apparatus the diagnostic devices measuring oxygen or air concentration downstream of the exhaust apparatus
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL-COMBUSTION ENGINES
    • F01N2550/00—Monitoring or diagnosing the deterioration of exhaust systems
    • F01N2550/03—Monitoring or diagnosing the deterioration of exhaust systems of sorbing activity of adsorbents or absorbents
    • 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

Definitions

  • the present invention relates to an engine exhaust purifying apparatus.
  • Japanese Patent No. 2692380 (WO94/17291) has been proposed.
  • the air/fuel ratio detected by an air/fuel ratio sensor mounted at the downstream of a NOx trap is changed from lean to rich after the air/fuel ratio has been switched from lean to the stoichiomtry or rich, the completion of the release of NOx is to be judged.
  • Japanese Patent Laid-Open No. 10-128058 (corresponds to U.S. Pat. No. 5,743,084) discloses the technology in which the quantity of NOx is estimated, which is trapped by a time difference until the air/fuel ratio detected by the air/fuel ratio sensor mounted at the downstream of the NOx trap is switched from lean to rich after the air/fuel ratio has been switched from lean to the stoichiometry or rich, thereby monitoring the performance of the NOx trap.
  • NOx trap an output waveform of the air/fuel ratio sensor mounted at the downstream of a NOx trap or a trapping device (hereinafter referred to as “NOx trap”) is affected by the oxygen storage capacity even if the quantity of NOx trapped in the NOx trap is the same. This, however, has not been taken into consideration in the aforementioned prior art.
  • the present invention has its object to judge the establishment of conditions influencing on the evaluation of performance of a NOx catalyst, whereby when being established, the evaluation of performance of a NOx catalyst is stopped to thereby prevent the performance of a NOx catalyst from being erroneously judged.
  • an engine exhaust purifying apparatus comprising an exhaust component trap which is provided in an exhaust passage of an engine and having a trapping function to adsorb or absorb an exhaust component and means for evaluating the performance of said exhaust component trap, wherein when at least one of an operating state of an engine system, the operating state of said exhaust component trap, and said means for evaluating the performance of said exhaust component trap is judged to be beyond a predetermined operating range, the performance evaluation of said exhaust component trap is inhibited or stopped.
  • an engine exhaust purifying apparatus comprising a NOx trap which is provided in an exhaust passage of an engine to trap NOx in exhaust gases by adsorption or absorption when the air/fuel ratio of a mixture gas is lean, and to release or reduce NOx when the air/fuel ratio is rich, and NOx trapping quantity judging means for evaluating the exhaust purifying performance including the NOx trapping quantity of said NOx trap, wherein the operating state of said NOx trap is measured directly or indirectly, and when said measured operating state is judged to be beyond a predetermined range, the purifying performance evaluation of said NOx trap is inhibited or stopped.
  • the present invention it is possible to provide an engine exhaust purifying apparatus in which since the release of oxygen stored and the release timing of NOx trapped are separately detected from an output of the air/fuel ratio sensor at the downstream of the NOx trap for trapping the exhaust gas component, for example, NOx, the NOx trapping quantity and the oxygen storage capacity can be separately detected with high accuracy. Under the circumstances that said detection accuracy cannot be secured, the detecting operation is inhibited or stopped to thereby enable prevention of erroneous detection.
  • FIG. 1 shows a schematic view of an engine exhaust purifying apparatus according to the present invention
  • FIG. 2 is a characteristic view of an air/fuel ratio sensor
  • FIG. 3 is a constitutional view of ECU
  • FIG. 4 is a map of a target equivalent ratio every operating region
  • FIG. 5 is a view for explaining a relationship between an output waveform of an air/fuel ratio at the downstream of a NOx trap when a NOx purge is controlled and a difference in NOx trap;
  • FIG. 6 is a view for explaining a judging method for an oxygen storage quantity and a NOx trapping quantity based on an output waveform of an air/fuel ratio at the downstream of a NOx trap when a NOx purge is controlled;
  • FIG. 7 is a view showing a relationship between T 2 and the NOx trapping quantity
  • FIG. 8 is a view showing a relationship between T 1 and the oxygen storage quantity
  • FIG. 9 is a view for explaining a judging method for an oxygen storage quantity and a NOx trapping quantity based on an output waveform of an air/fuel ratio at the downstream of a NOx trap when a NOx purge is controlled, in prior art;
  • FIG. 10 is a view showing a relationship between Tx and the NOx trapping quantity, in prior art
  • FIG. 11 is a view for explaining the NOx purge control, the deterioration judging timing, and so on;
  • FIG. 12 is a flow chart for explaining a fuel control process
  • FIG. 13 is a flow chart for explaining a NOx purge control process
  • FIG. 14 is a flow chart for explaining a deterioration judging process
  • FIG. 15 is a flow chart for inhibiting a NOx catalyst (trap) diagnosis.
  • FIG. 16 is a flow chart for judging the abnormality of an engine system.
  • the quantity of NOx trap absorbed in the NOx trap and the trapping performance are estimated by the air/fuel ratio sensor, a great error possibly results.
  • the oxygen storage quantity is great, when the air/fuel ratio is temporarily switched changed from lean to the stochiometric air/fuel ratio or rich, the time when the output of the air/fuel ratio sensor mounted at the downstream of the NOx trap indicates lean becomes longer. Because of this, the NOx quantity is erroneously judged to be great.
  • the oxygen storage quantity is small
  • the air/fuel ratio is temporarily switched changed from lean to the stochiometric air/fuel ratio or rich
  • the output of the air/fuel ratio sensor mounted at the downstream of the NOx trap indicates rich early. Because of this, the NOx trap quantity is erroneously judged to be small.
  • the oxygen storage quantity reaches oxygen storage capacity in a short time, but since the oxygen storage capacity itself becomes uneven due to the deterioration or the like, the erroneous judgment as described above possibly occurs.
  • the NOx trap having oxygen storage capacity or the catalyst and so on having oxygen storage capacity arranged at the upstream and downstream close to the NOx trap are subjected to oxidizing reaction of unburnt HC, CO based on the oxygen storage capacity. Accordingly, if the oxygen storage capacity lowers, the oxidizing and reducing reactions thereof become weaken so that Nox trap and the catalyst having the oxygen storage capacity arranged at the upstream and downstream close to the NOx trap becomes deteriorated, and it is therefore desired that the oxygen storage capacity be detected independently. Also in this case, separation from the quantity of NOx trap is necessary as described above. The performance of the NOx trap is greatly affected by the state of the NOx trap itself.
  • the temperature of NOx trap For example, they are the temperature of NOx trap, the O 2 storage quantity, the performance of a three-way catalytic converter and so on.
  • the engine exhaust component construction ratio of components
  • the exhaust quantity the exhaust temperature
  • the performance of sensing means for evaluating the performance of the NOx trap is deteriorated, it exerts influence on the result of evaluation for the performance of the NOx trap.
  • FIG. 1 is a constitutional view of an air/fuel ratio control device of the engine according to one embodiment of the present invention.
  • An intake system 23 of an engine 1 comprises an air cleaner 2 , an air flow sensor 3 for detecting the quantity of intake air, a throttle valve 4 for regulating the quantity of intake air, a throttle valve driving means 5 , a throttle opening-degree sensor 5 a, a swirl control valve 6 , a swirl control valve driving means 7 , and an intake valve 8 .
  • the swirl control valves 6 are provided directly before the intake valve 8 with respect to each cylinder and constituted for integral operation.
  • a combustion chamber 9 of the engine 1 comprises a fuel injection valve 10 for injecting fuel into the combustion chamber 9 directly, an ignition plug 11 , and a cylinder pressure sensor 12 .
  • An exhaust system 24 of the engine 1 comprises an exhaust valve 13 , a first air/fuel ratio sensor 14 , a NOx trap 15 , and a second air/fuel ratio sensor 25 .
  • the air/fuel ratio control device further comprises a sensing plate 16 mounted on a crank shaft of the engine 1 , a crank angle sensor 17 for detecting a projecting portion thereof to thereby detect a rotational speed and a crank angle, and an accelerator sensor 19 for detecting an angle of an accelerator pedal.
  • ECU 20 The detected values of the respective sensors are input into an electronic control unit (hereinafter referred to as ECU) 20 , which ECU 20 detects or computes an angle of an accelerator, an intake air quantity, an engine speed (rotational speed), a crank angle, a cylinder pressure, a throttle opening-degree, etc.
  • ECU 20 detects or computes an angle of an accelerator, an intake air quantity, an engine speed (rotational speed), a crank angle, a cylinder pressure, a throttle opening-degree, etc.
  • the quantity of fuel supplied to the engine 1 and the timing are computed to output a driving pulse to the fuel injection valve 10
  • the opening degree of the throttle valve 4 is computed to output a control signal to the throttle valve driving means 5
  • the ignition timing or the like is computed to output an ignition signal to the ignition plug 11 .
  • a signal is output to an alarm lamp 26 for giving warning to an operator.
  • Fuel is fed under pressure by a fuel pump from a fuel tank not shown, and is maintained at predetermined pressure (approximately 5 to 15 MPa) by means of a fuel pressure regulator and supplied to the fuel injection valve 10 .
  • a predetermined quantity of fuel is directly injected to the combustion chamber 9 in response to a driving pulse output by the ECU 20 .
  • Operating modes of the engine 1 include a stoichiometric operation, a homogenous lean operation, a stratified operation and so on.
  • fuel is injected in the intake stroke to mix with air and burn a homogenous mixture.
  • fuel is injected in the compression stroke to distribute fuel in stratified form into the mixture, and fuel is gathered near the ignition plug 11 (to provide a rich mixture).
  • the swirl strength is controlled by the swirl control valve 6 .
  • the swirl control valve 6 Normally, it is set so that in the stratified operation and in the homogenous lean operation, the swirl strength is high, and in other operations, the swirl strength is low.
  • fuel is not spread over the whole combustion chamber 9 but gathered near the ignition plug 11 due to the aforementioned fuel injection timing, the air flow caused by the swirl, and the shape of a cavity 22 provided in the upper surface of the piston 21 .
  • a mixture of fuel and intake air is ignited by the ignition plug 9 and burns. Exhaust gases after combustion are discharged to the exhaust system 24 through the exhaust valve 13 . The exhaust gases flow into the NOx trap 15 arranged in the exhaust system 24 .
  • the first air/fuel ratio sensor 14 outputs a signal corresponding to concentration of oxygen in the exhaust gases at the upstream of the NOx trap 15 to enable detection of the actual air/fuel ratio from the output. On the basis of the actual air/fuel ratio detected by the first air/fuel ratio sensor 14 , the air/fuel ratio of the mixture supplied so as to have a target air/fuel ratio is feedback-controlled.
  • the second air/fuel ratio sensor 25 outputs a signal corresponding to concentration of oxygen in the exhaust gases at the downstream of the NOx trap 15 to enable detection of the actual air/fuel ratio from the output.
  • the quantity of NOx trapped by the NOx trap 15 is judged on The basis of the actual air/fuel ratio detected by the second air/fuel ratio sensor 25 .
  • the second air/fuel ratio sensor 25 a so-called O 2 sensor is used, in which as shown in FIG. 2, the air/fuel ratio is changed suddenly in the vicinity of stoichiometry to output a binary value
  • the sensor is not limited thereto.
  • a so-called wide air/fuel ratio sensor may be employed in which a substantially linear output is generated according to the air/fuel ratio on the basis of concentration of oxygen in the exhaust gases.
  • a passage and an EGR valve not shown are provided from the exhaust system 24 to the intake system 23 .
  • a large quantity of EGR is introduced in order to suppress the generation of NOx and in order to suppress the combustion speed.
  • FIG. 3 shows the construction of an ECU 20 .
  • Signals 3 s, 5 s, 12 s, 14 s, 25 s, 17 s, and 19 s of the aforementioned air flow sensor 3 , the throttle valve opening-degree sensor 5 a, the cylinder pressure sensor 12 , the first air/fuel ratio sensor 14 , the second air/fuel ratio sensor 25 , the crank angle sensor 17 and the accelerator sensor 19 , and a signal of a cylinder discrimination sensor 27 not shown are input into an input circuit 31 .
  • a CPU 30 reads, on the basis of a program and a constant stored in a ROM 37 , the input signals through an input/output port 32 to carry out arithmetic processing.
  • the ignition timing, the injector driving pulse width and timing, the throttle valve opening-degree instructions, and the swirl control valve opening-degree instructions are output from the CPU 30 to an ignition output circuit 33 , a fuel injection valve driving circuit 34 , a throttle valve driving circuit 35 , and a swirl control valve driving circuit 36 through the input/output port 32 to execute the ignition, the fuel injection, the throttle valve opening-degree control, and the swirl control valve opening-degree control.
  • an alarm lamp 26 is turned on by an alarm lamp driving circuit 37 .
  • a RAM 38 is used to store values of input signal, results of operation and so on.
  • the fuel injection time Ti is calculated, for example, by the following equation, and fuel is injected from the fuel injection valve 10 and supplied to the engine 1 .
  • K is the coefficient based on the characteristic of the fuel injection valve 10 or the like
  • Qa is the quantity of intake air
  • Ne is the engine speed
  • TGFBA is the target equivalent ratio of a mixture to be supplied to the engine 1
  • ALPHA is the feedback correcting coefficient.
  • Kr is the air/fuel ratio correcting coefficient in the air/fuel ratio changing control (hereinafter referred to as NOx purge control) for temporarily changing the air/fuel ratio of exhaust gas from lean to the stoichiometric air/fuel ratio or rich at a predetermined period.
  • the target equivalent ratio TGFBA is stored in the ROM 37 in advance, for example, as shown in FIG. 4, as a map of the engine speed Ne and a load (for example, a target torque calculated on the basis of a signal of the accelerator sensor 19 for detecting an angle of the accelerator pedal 18 ).
  • the feedback control is made so that the air/fuel ratio is correctly stoichiometric on the basis of the actual air/fuel ratio detected by the first air/fuel ratio sensor 14 , and the feedback correcting coefficient ALPHA is calculated to be reflected on the fuel injection time Ti.
  • ALPHA reduces when the actual air/fuel ratio is rich and increases when the actual air/fuel ratio is lean, and normally moves up and down about 1.0.
  • ALPHA is fixed to a predetermined value or a learning value in the operations other than the stoichiometric operation.
  • the throttle valve 6 is mainly operated in the closing direction by the throttle valve driving means 5 to reduce the quantity of intake air and to control the quantity of fuel supplied, thereby changing the air/fuel ratio, it is to be noted that it is not limited to such a method as described above.
  • the NOx trap 15 is constituted so as to have both the so-called three-way catalyst performance in order to secure the NOx trapping at the time of lean and the exhaust purifying performance at the time of stoichiometry.
  • alumina is made to serve as a carrier, and alkaline metal and alkaline earth such as sodium Na, barium Ba or the like, and noble metal such as platinum Pt and rhodium Rh are carried.
  • cerium Ce having the oxygen storage capacity in order to enhance the so-called three-way performance at stoichiometry is sometimes carried.
  • the NOx trap 15 adsorbs or absorbs the NOx for trapping when the air/fuel ratio of exhaust gases flown in is lean, and the Nox having been adsorbed reacts with HC or NOx in the exhaust gases and is reduced when the concentration of oxygen in the exhaust gases lowers (for example, at stoichiometric or rich).
  • the NOx having been absorbed reacts with HC or CO in the exhaust gases, for example, by the catalyst action of platinum Pt after the NOx has been released and is reduced. In this manner, the quantity of NOx released into the atmosphere can be reduced.
  • HC and Co in the exhaust gases are oxidized, for example, by the catalyst action of platinum Pt, and NOx is reduced, thus enabling the reduction of the exhaust gas components.
  • Some Nox traps have the effect of reducing a part of NOx by HC or CO in the exhaust gases even if the air/fuel ratio of the mixture flown in is lean, depending on the kind of the NOx trap.
  • NOx trapping capacity of the NOx trap there is a limit in the NOx trapping capacity of the NOx trap. If the NOx trap traps Nox until the trapping capacity becomes saturated, NOx can not be absorbed any longer, and NOx passes through the Nox trap and is released to the atmosphere. Therefore, it is necessary to release NOx from the NOx trap 15 before the NOx trapping capacity of the NOx trap 15 becomes saturated. So, it is necessary to estimate how much NOx is trapped in the NOx trap 15 . Next, a method for estimating the quantity of trapping NOx of the NOx trap 15 will be explained below.
  • the quantity of NOx (per unit time) in the exhaust gases discharged from the engine 1 increases, the quantity of NOx (per unit time) trapped by adsorption or absorption in the NOx trap 15 also increases. Since the quantity of NOx (per unit time) in the exhaust gases discharged from the engine 1 is substantially determined based on the engine speed of the engine 1 and the load, the quantity of NOx (per unit time) trapped in the NOx trap 15 is a function of the engine speed of the engine 1 and the load. Accordingly, the quantity of NOx (per unit time) NOAS trapped in the NOx trap 15 is measured in advance as a function of the engine speed of the engine 1 and the load and stored in advance in the ROM 37 in the form of a map.
  • the quantity TNOA of NOx estimated to be trapped in the NOx tap 15 can be obtained by accumulating NOAS every predetermined time as in the following equation during continuation of lean operation.
  • TNOA (new) TNOA (old)+ NOAS
  • the air/fuel ratio of the mixture is temporarily made stoichiometric or rich so that NOx is released or reduced from the NOx trap 15 .
  • the quantity of NOx (per unit time) NOAS trapped in the NOx trap 15 is affected where the ignition timing and the fuel injection time are changed, it is therefore preferable that the quantity thereof be corrected by these parameters. Further, the quantity of NOx (per unit time) trapped in the NOx trap 15 is affected also by the quantity of NOx already trapped in the NOx trap 15 . Accordingly, with the quantity of NOx (per unit time) trapped in the NOx trap 15 in the state that the NOx trapping quantity of the NOx trap 15 is rarely present being NOAS, the quantity TNOA of NOx estimated to be trapped in the NOx trap 15 may be obtained, for example, by the following equation.
  • TNOA (new) TNOA (old)+(1 ⁇ TNOA (old)/ TNOAMX ) ⁇ NOAS
  • the quantity of NOx (per unit time) trapped in the NOx trap 15 is substantially proportional to the value obtained by subtracting the quantity already trapped from the saturated trapping quantity.
  • Curves a and b show output waveforms of the second air/fuel ratio sensor 25 when the NOx traps 15 different in oxygen storage quantity (oxygen storage capacity) are used to make the NOx trapping quantity same, the curve a and the curve b showing that the oxygen storage capacity is small and large, respectively. If the lean operation is carried out, oxygen is stored fully to the oxygen storage capacity in a short period of time, in which case, therefore, it may be considered that the oxygen storage quantity and the oxygen storage capacity are the same.
  • Curves b and c show output waveforms of the second air/fuel ratio sensor 25 when one NOx trap 15 is used to change the NOx trapping quantity, the curves b and c showing that the NOx trapping quantity is small and large, respectively. In this case the oxygen storage quantity (oxygen storage capacity) is the same.
  • threshold VS 1 showing lean and threshold VS 2 showing rich are set, T 1 indicating the time between the time when an output of the second air/fuel ratio sensor 25 crosses VS 1 and the start of the NOx purge control, T 2 indicating that the time between the time when an output of the second air/fuel ratio sensor 25 crosses VS 2 and the start of the NOx purge control.
  • FIGS. 7 and 8 show relationships between the NOx trapping quantity and T 2 and between the oxygen storage quantity and T 1 , respectively, at the time of the same operating condition. As will be apparent from the drawings, a substantially linear relationship is considered between T 2 and the NOx trapping quantity and between T 1 and the oxygen storage quantity.
  • the voltage values of VS 1 and VS 2 become changed. Therefore, it is preferable, for example, that the voltage values of VS 1 and VS 2 be corrected according to the output at the lean operation and the output at the rich operation.
  • FIG. 9 shows a method for detecting the NOx trapping quantity according to prior art.
  • Threshold VSx approximately 0.5V showing the vicinity of stoichiometry is set to measure the time Tx between the time when the output crosses VSx and the start of the NOx purge control.
  • a relationship between the NOx trapping quantity and Tx is as shown in FIG. 10. If the oxygen storage quantity is constant, the NOx trapping quantity can be detected from Tx, but if the oxygen storage quantity is different, the NOx trapping quantity can not be detected accurately from Tx.
  • k1 designates proportional constant
  • others designates those explained in the equation of Ti. Since the quantity NODS of NOx released or reduced from the NOx trap 15 per unit time is proportional to Qfex, if the proportional constant is k2, NODS is expressed by the following equation.
  • Kr at the normal NOx purge control is sometimes set to a somewhat large value (for example, Kr>1.1) in order to quicken the release or reduction of NOx. Because of this, with respect to Kr at the NOx purge control when the NOx trapping quantity is obtained, a value (for example, 1 ⁇ Kr ⁇ 1.1) different from that of the normal NOx purge control is preferable.
  • Kr is often a fixed value (for example, a plurality of fixed values are set in advance every operating mode). Accordingly, the total sum TNOD of NODS during the period of T 2 is proportional to the total sum of Qa during the period of T 2 . From this, TNOD may be obtained by the following equation.
  • k′ designates a proportional constant
  • Qave designates an average value of Qa during T 2 .
  • the quantity TNOA trapped in the NOx trap 15 at the NOx purge control should be the NOx saturated trapping quantity.
  • the normal NOx purge control is executed when the NOx quantity TNOA estimated to be absorbed in the NOx trap 15 is the value TNOAP smaller than the NOx saturated trapping quantity TNOAMX. For this reason, as shown in FIG.
  • the NOx purge control is executed, and only when the NOx saturated trapping quantity TNOAMX is detected and when TNOA is somewhat larger in value than the NOx saturated trapping quantity TNOAMX, the NOx purge control is executed. Then, the NOx trapping quantity detected value TNOD is obtained by the aforementioned method, the NOx saturated trapping quantity TNOAMX is updated according to TNOD, and further, the threshold TNOAP for starting the normal NOx purge control is also updated.
  • the NOx saturated trapping quantity TNOAMX of the NOx trap 15 is detected by the method as described above. Where the detected NOx saturated trapping quantity TNOAMX is smaller than a predetermined value, for example, SOx poisoning regeneration control for recovering damages caused by SOx is carried out, and where thereafter, also, the detected NOx saturated trapping quantity TNOAMX is smaller than a predetermined value, judgment is made that the NOx trap 15 is deteriorated, and the storage of a code representative of deterioration of the NOx catalyst, and/or the warning by way of lighting of an alarm lamp to an operator is executed.
  • a predetermined value for example, SOx poisoning regeneration control for recovering damages caused by SOx is carried out
  • the SOx poisoning regeneration control is achieved by elevating the temperature of the NOx trap 15 up to a preset temperature, for example, not less than 600° C., and making the air/fuel ratio rich to continue the operation for a predetermined period of time.
  • the estimated NOx trapping quantity TNOA includes an error since it is a estimated value to the end.
  • the error results, for example, from a deviation between a map value in which the NOx quantity (released or reduced from the engine) trapped in the aforementioned NOx trap is preset and the actual value, or a deterioration in the NOx absorbing performance of the NOx trap 15 . Accordingly, for example, it is preferable to use the estimated NOx trapping quantity TNOA by amending (correcting) it as follows.
  • the NOx trapping quantity detected value TNOD detected for the normal NOx purge control is compared with the threshold TNOAP for the estimated NOx trapping quantity TNOA for staring the NOx purge control so that the estimated NOx trapping quantity is corrected so as to be the NOx trapping quantity detected value TNOD.
  • the aforementioned detection of the NOx saturated trapping quantity TNOAMX and the judgment of deterioration of the NOx trap 15 are executed only when the fixed conditions are established, for example, when the temperature of the NOx trap 15 and the operating conditions are in the fixed range, or after passage of the fixed time, or when the deterioration is judged by kc as described above. The reasons will be explained below.
  • the condition relating to the temperature of the NOx trap 15 is set.
  • the NOx trap 15 lowers in NOx trapping quantity even if the temperature is too low or too high.
  • the temperature may be measured directly or estimated from the operating condition.
  • the operating conditions are set, for example, for improving the estimated accuracy of the estimated NOx trapping quantity TNOA. Since the lean operation is continued until the estimated NOx trapping quantity TNOA assumes the NOx saturated trapping quantity TNOAMX or more, when the estimated NOx trapping quantity is estimated to be smaller than the actual value, the quantity of NOx passing through the NOx trap 15 increased as a consequence. Further, when the estimated NOx trapping quantity TNOA is estimated to be larger than the actual value, the NOx purge control starts before the NOx trapping quantity assumes the NOx saturated trapping quantity TNOAMX, possibly resulting in judgment that the NOx saturated trapping quantity TNOAMX is smaller than the actual value. For this reason, the operating area in which combustion is stable is set as the condition.
  • the NOx saturated trapping quantity TNOAMX is compared with the predetermined value for judgment of execution of the SOx poisoning regeneration control or judgment of deterioration of the NOx trap 15 .
  • the threshold TNOAP for starting the NOx purge control is increased at a predetermined timing, for example by a predetermined value to provide TNOAPC.
  • the respective NOx trapping quantity detected values TNOD when the threshold is TNOAP and TNOAPC, respectively, are obtained, a difference between which is calculated.
  • TNOAP is reduced by the predetermined value.
  • the updated TNOAP is not larger than a predetermined value, judgment is made that the NOx trap 15 is deteriorated.
  • the thereafter processes are similar to those in the aforementioned embodiment.
  • utilization is made of the fact that if the NOx trapping quantity is within the NOx saturated trapping quantity TNOAMX, the NOx trapping quantity also changes in reponse to the Nox quantity flowing in the NOx trap 15 .
  • the NOx trapping quantity reaches the NOx saturated trapping quantity TNOAMX the NOx trapping quantity in the NOx trap 15 will not increase even if any quantity of NOx flows in later.
  • the essence of this invention lies in that a change in the NOx trapping quantity detected value TNOD when the estimated NOx trapping quantity TNOA is changed is examined to judge if it reaches the NOx saturated trapping quantity TNOAMX, thus not limiting other processes.
  • FIG. 12 is a flow chart showing the air/fuel ratio control process according to the embodiment. This control is started every predetermined time (for example 20 ms) from a main routine not shown.
  • Step 100 if an area is a lean operating area is examined.
  • the procedure proceeds to Step 113 , where 1 is set to TGFBA, and 1 is set to Kr also. That is, the stoichiometric operation is carried out.
  • Step 114 the feedback control of the air/fuel ratio is executed on the basis of an output of the first air/fuel ratio sensor 14 .
  • Step 100 judgment is made that the area is a lean operating area
  • the procedure proceeds to Step 101 , where the subject value ( ⁇ 1) is retrieved from the map of the speed and load of the engine 1 shown in FIG. 4 and set to the target equivalent ratio TGFBA.
  • next Step 106 the estimated NOx trapping quantity TNOA is accumulated, during continuation of the lean operation, and obtained by the following equation.
  • NOAS is calculated from the map or the like preset according to the operating condition of the engine 1 .
  • kc designates the estimated error correcting coefficient.
  • Step 107 if the counter CNOP for the number of times of the normal NOx purge control is not less than the judgment value KNOP is examined. In case of not less than KNOP, judgment is made that judgment of deterioration of the NOx trap 15 is necessary, and the procedure proceeds to Step 110 .
  • the estimated NOx trapping quantity TNOA exceeds saturated NOx trapping quantity TNOAMX+a
  • Step 107 CNOP is less than judgment value KNOP
  • the procedure proceeds to Step 108 to examine the starting condition of the normal NOx purge control.
  • FIG. 13 is a flow chart showing the normal NOx purge control process according to the embodiment.
  • NOx purge control request flag is set from the control flow shown in FIG. 12, it is started as a sub-routine.
  • the operating mode before the NOx purge control is started is the stratified operating mode (the extremely lean combustion operating mode whose air/fuel ratio is approximately 40 to 50 with a stratified mixture formed)
  • the homogenous operating mode the operating mode for homogenously supplying fuel.
  • the control of an opening degree of the swirl control valve 6 the control of the EGR quantity, and the control of changing the fuel injection timing and reducing the intake air quantity are executed.
  • Step 201 the fuel injection time Ti is calculated by the following equation.
  • next Step 202 if output Vo of the second air/fuel ratio sensor 25 exceeds VS 2 is examined. If not exceeding, if Vo exceeds VS 1 is examined in next Step 202 . If not exceeding VS 1 , release or reduction of NOx is not started (stored oxygen is released or reduced), and therefore, this control flow is terminated. In case of exceeding VS 1 , NOx is being released or reduced, and therefore, in next Step 204 , T 2 is added ⁇ T (control start period) (may be added 1 by 1). Next, in Step 205 , an accumulated value SQa of an air flow rate Qa and an accumulated times counter CQa are respectively updated.
  • Step 202 Where in Step 202 , Vo exceeds VS 2 , the release or reduction of NOx is terminated, and therefore, the procedure proceeds to Step 206 for termination process.
  • T 2 is the value obtained by measuring the time from VS 1 to VS 2 .
  • Step 208 the NOx trapping quantity detected value TNOD is calculated by the following equation.
  • Step 209 the estimated error correcting coefficient kc is calculated by the following equation.
  • Step 210 TNOD, TNOA, T 2 , SQa and CQa are initialized, and this control flow is terminated.
  • the operating mode before starting the NOx purge control is the stratified operating mode
  • the control for switching the operating mode from the homogenous operating mode to the stratified operation is also executed, after which this control flow is terminated.
  • FIG. 14 is a flow chart showing the deterioration judging process according to the embodiment.
  • a deterioration judgment request flag is set from the control flow shown in FIG. 12, there is started as a sub-routine.
  • the operating mode prior to starting of the NOx purge control is a stratified operating mode (the extremely lean combustion operating mode at about air/fuel ratio of 40 to 50 with a stratified miture formed)
  • controlling of switching the operating mode to a homogenous operating mode the operating mode for homogenously supplying fuel. For this reason, controlling such as the control of an opening degree of the swirl control valve 6 , the control of EGR quantity, the change in fuel injection timing, the reduction in intake air quantity and so on is also executed.
  • Step 301 the fuel injection time Ti is calculated by the following equation.
  • next Step 302 if output Vo of the second air/fuel ratio sensor 25 exceeds VS 2 is examined. If not exceeding, if Vo exceeds VS 1 is examined in next Step 302 . If not exceeding VS 1 , release or reduction of NOx is not started (stored oxygen is released or reduced), and therefore, this control flow is terminated. In case of exceeding VS 1 , NOx is being released or reduced, and therefore, in next Step 304 , T 2 is added ⁇ T (control start period) (may be added 1 by 1). Next, in Step 305 , an accumulated value SQa of an air flow rate Qa and an accumulated times counter CQa are respectively updated.
  • Step 306 is the value obtained by measuring the time from VS 1 to VS 2 .
  • Step 308 the NOx trapping quantity detected value TNOD is calculated by the following equation.
  • Step 309 the NOx saturated trapping quantity TNOAMX is updated according to TNOD, and the threshold TNOAP for starting the normal NOx purge control is also updated. Specifically, the following equation is used.
  • Kp is a constant, which is a value of 0.6 to 0.8.
  • Step 310 TNOD, TNOA, T 2 , SQa, and CQa are initialized.
  • the operating mode before starting of the NOx purge control is a stratified operating mode
  • the control for switching the operating mode from the homogenous operating mode to the stratified operation is executed, after which this control flow is terminated.
  • a code representative of a deterioration of the NOx trap 15 is stored by control not shown, and the warning to an operator such as turning on of an alarm lamp is executed.
  • FIG. 15 shows the conditions for executing diagnosis of the trap material.
  • the judgment of the engine system is carried out to judge if the state is a state of exhaust gas input in the trap material to be diagnosed, for example, a state in which the air/fuel ratio, the exhaust gas quantity, the exhaust gas component or the like are suited for diagnosis. That is, where the state of exhaust input in the trap material is changed, there is the possibility of exerting bad influence on the diagnostic result to result in erroneous diagnosis.
  • Step 1501 contemplated include abnormalities of the air flow sensor 3 , the throttle valve opening-degree sensor 25 , the cylinder pressure sensor 12 , the first air/fuel ratio sensor 14 , the crank angle sensor 17 , the accelerator sensor 19 , etc., and in addition, abnormalities of the fuel pressure, the ignition timing, the supplied fuel quantity (for example, mistake in the air/fuel ratio every cylinder), the combustion pressure, the exhaust temperature, the EGR system, and the performance of a catalyst installed at the upstream of the trap material. Further, if the number of engine speed, the engine load and so on are states suited for diagnosis are also judged.
  • FIG. 16 shows an example of a flow chart for judging if the state of the engine system is a state suited for the diagnosis of the NOx trap.
  • Step 1502 in FIG. 15 judgment is made that the engine system is abnormal as described above, the evaluation of performance of the trap material in Step 1507 is bypassed. Further, in Step 1503 , judgment is made if the trap material itself is a state suited for the evaluation of performance.
  • the element thereof there is, for example, the temperature of the trap material, but as the actual applied example, the temperature of exhaust gas at the upstream or downstream of the trap material is measured indirectly, or the temperature of the inside of the trap material is measured directly to judge the state of the trap material.
  • the temperature of the tap material measured directly or indirectly is not within the fixed range (300° C. to 400° C. in the present embodiment, though being different depending on the quality of the trap material)
  • Step 1507 is bypassed.
  • the another performance of the trap material (for example, such as the conversion efficiency of exhaust component different from that to be trapped) is taken into consideration.
  • Step 1507 is bypassed.
  • the form of the present invention taking an example of the cylinder injection type gasoline engine, the form is not limited thereto. Even the port injection type gasoline engine, or even the Diesel engine, the judgment method for the NOx trap by means of an air/fuel ratio sensor at the downstream of the NOx trap which comprises the essential pat of the present invention can be applied. Further, while in the present invention, the performance evaluation of the trap material under the circumstances not suited for the performance evaluation of the trap material is inhibited or stopped, the result of the performance evaluation can be corrected depending on the circumstances.
  • the NOx trap is mainly referred to, it is to be noted that the procedure of the present application can be also applied, for the purpose of enhancing the diagnostic accuracy, to the HC trap for adsorbing or absorbing HC of the exhaust gas component.
  • the present invention since the release of oxygen stored and the timing of the release of NOx trapped are detected separately by the output of the air/fuel ratio sensor at the downstream of the NO trap for trapping NOx, it is possible to provide an engine exhaust purifying apparatus capable of detecting the NOx trap quantity and the oxygen storage capacity separately with good accuracy. Under the circumstances that the aforesaid detection accuracy cannot be secured, it is possible to prevent an erroneous detection by inhibiting or stopping the detecting operation.

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Exhaust Gas After Treatment (AREA)
  • Electrical Control Of Air Or Fuel Supplied To Internal-Combustion Engine (AREA)
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US6839637B2 (en) * 2001-05-18 2005-01-04 Honda Giken Kogyo Kabushiki Kaisha Exhaust emission control system for internal combustion engine
US20050022516A1 (en) * 2003-07-31 2005-02-03 Nissan Motor Co., Ltd. Engine exhaust gas cleaning apparatus
US20050144933A1 (en) * 2002-03-29 2005-07-07 Kazuhiro Enoki Method of deciding on catalyst deterioration and means for deciding on catalyst deterioration in Nox purging system
US20050222748A1 (en) * 2004-03-30 2005-10-06 Naik Sanjeev M Control strategy for lean NOx trap regeneration
US20080173009A1 (en) * 2006-12-22 2008-07-24 Kocher Lyle E System for controlling regeneration of an adsorber
FR2916017A1 (fr) * 2007-05-11 2008-11-14 Renault Sas Procede de surveillance de l'efficacite d'un convertisseur catalytique stockant les nox implante dans une ligne d'echappement d'un moteur a combustion interne et moteur comportant un dispositif mettant en oeuvre ledit procede
US20120131992A1 (en) * 2010-11-25 2012-05-31 Toyota Jidosha Kabushiki Kaisha Catalyst deterioration diagnostic device and diagnostic method
US20120324869A1 (en) * 2010-03-09 2012-12-27 Toyota Jidosha Kabushiki Kaisha Catalyst degradation detection apparatus
US20170058805A1 (en) * 2015-08-24 2017-03-02 Ford Global Technologies, Llc Method of operating an engine
US9828899B2 (en) * 2013-09-30 2017-11-28 Isuzu Motors Limited Exhaust gas purification system and exhaust gas purification method

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JP2002309928A (ja) * 2001-04-13 2002-10-23 Yanmar Diesel Engine Co Ltd 内燃機関の排気浄化装置
DE10122636A1 (de) * 2001-05-10 2002-11-21 Bosch Gmbh Robert Verfahren zum Betreiben einer Brennkraftmaschine, insbesondere eines Kraftfahrzeugs
JP3828425B2 (ja) 2002-01-08 2006-10-04 三菱電機株式会社 内燃機関の排気ガス浄化方法
US7155331B1 (en) 2003-12-15 2006-12-26 Donaldson Company, Inc. Method of prediction of NOx mass flow in exhaust
FR2866925B1 (fr) * 2004-02-27 2006-10-13 Peugeot Citroen Automobiles Sa Procede de controle du traitement des gaz d'echappement d'un moteur thermique et vehicule a moteur thermique mettant en oeuvre ce procede
FR2866926B1 (fr) * 2004-02-27 2008-02-22 Peugeot Citroen Automobiles Sa Procede de diagnostic pour un catalyseur de gaz d'echappement d'un moteur thermique et vehicule mettant en oeuvre ce procede
DE102006041479B4 (de) * 2006-09-05 2023-03-30 Robert Bosch Gmbh Verfahren zur Bestimmung der Sauerstoff-Speicherfähigkeit einer Abgasreinigungsanlage
JP4447002B2 (ja) * 2006-12-22 2010-04-07 本田技研工業株式会社 内燃機関
US8146345B2 (en) * 2007-03-20 2012-04-03 GM Global Technology Operations LLC Normalizing oxygen storage capacity(OSC) for catalyst monitoring
JP4615558B2 (ja) * 2007-11-13 2011-01-19 本田技研工業株式会社 内燃機関の排気浄化装置
FR2929652B1 (fr) * 2008-04-04 2012-07-20 Renault Sas Systeme et procede de controle de l'air frais et des gaz brules introduits dans un moteur a combustion interne lors des transitions entre la purge d'un piege a oxydes d'azote et la regeneration d'un filtre a particules
CN102667460B (zh) * 2009-12-09 2014-09-03 丰田自动车株式会社 硫磺成分检测装置
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US6839637B2 (en) * 2001-05-18 2005-01-04 Honda Giken Kogyo Kabushiki Kaisha Exhaust emission control system for internal combustion engine
US20050144933A1 (en) * 2002-03-29 2005-07-07 Kazuhiro Enoki Method of deciding on catalyst deterioration and means for deciding on catalyst deterioration in Nox purging system
US7247190B2 (en) * 2003-07-31 2007-07-24 Nissan Motor Co., Ltd. Engine exhaust gas cleaning apparatus
US20050022516A1 (en) * 2003-07-31 2005-02-03 Nissan Motor Co., Ltd. Engine exhaust gas cleaning apparatus
US7797923B2 (en) 2004-03-30 2010-09-21 Gm Global Technology Operations, Inc. Control strategy for lean NOx trap regeneration
US20050222748A1 (en) * 2004-03-30 2005-10-06 Naik Sanjeev M Control strategy for lean NOx trap regeneration
US20080229729A1 (en) * 2004-03-30 2008-09-25 General Motors Corporation CONTROL STRATEGY FOR LEAN NOx TRAP REGENERATION
US7401462B2 (en) * 2004-03-30 2008-07-22 General Motors Corporation Control strategy for lean NOx trap regeneration
US20080173009A1 (en) * 2006-12-22 2008-07-24 Kocher Lyle E System for controlling regeneration of an adsorber
US8474243B2 (en) 2006-12-22 2013-07-02 Cummins, Inc. System for controlling regeneration of an adsorber
WO2008142342A3 (fr) * 2007-05-11 2009-02-12 Renault Sa Procede de surveillance de l'efficacite d'un convertisseur catalytique stockant les nox implante dans une ligne d'echappement d'un moteur a combustion interne et moteur comportant un dispositif mettant en oeuvre ledit procede
FR2916017A1 (fr) * 2007-05-11 2008-11-14 Renault Sas Procede de surveillance de l'efficacite d'un convertisseur catalytique stockant les nox implante dans une ligne d'echappement d'un moteur a combustion interne et moteur comportant un dispositif mettant en oeuvre ledit procede
US20120324869A1 (en) * 2010-03-09 2012-12-27 Toyota Jidosha Kabushiki Kaisha Catalyst degradation detection apparatus
US8938947B2 (en) * 2010-03-09 2015-01-27 Toyota Jidosha Kabushiki Kaisha Catalyst degradation detection apparatus
US20120131992A1 (en) * 2010-11-25 2012-05-31 Toyota Jidosha Kabushiki Kaisha Catalyst deterioration diagnostic device and diagnostic method
US8573044B2 (en) * 2010-11-25 2013-11-05 Toyota Jidosha Kabushiki Kaisha Catalyst deterioration diagnostic device and diagnostic method
US9027396B2 (en) 2010-11-25 2015-05-12 Toyota Jidosha Kabushiki Kaisha Catalyst deterioration diagnostic device and diagnostic method
US9828899B2 (en) * 2013-09-30 2017-11-28 Isuzu Motors Limited Exhaust gas purification system and exhaust gas purification method
US20170058805A1 (en) * 2015-08-24 2017-03-02 Ford Global Technologies, Llc Method of operating an engine
CN106481466A (zh) * 2015-08-24 2017-03-08 福特环球技术公司 操作发动机的方法
US10280857B2 (en) * 2015-08-24 2019-05-07 Ford Global Technologies, Llc Method of operating an engine

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US20020184877A1 (en) 2002-12-12
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