CN101512130A

CN101512130A - Catalyst monitoring system and monitoring method

Info

Publication number: CN101512130A
Application number: CNA2007800321744A
Authority: CN
Inventors: 泽田裕; 堀恒元
Original assignee: Denso Corp; Toyota Motor Corp
Current assignee: Toyota Motor Corp
Priority date: 2006-08-30
Filing date: 2007-08-28
Publication date: 2009-08-19
Also published as: JP4737010B2; JP2008057404A; WO2008029236A1; US20090199543A1; EP2057366A1

Abstract

A catalyst monitoring system diagnoses deterioration of an NOx catalyst (18) which is arranged in an exhaust passage (12) of an internal combustion engine (10). An NOx sensor (25) is arranged downstream of the NOx catalyst (18). An output integrated value of the NOx sensor (25) is calculated by integrating an output from the NOx sensor (25) is calclated by integrating an outputfrom the NOx sensor (25) during at least a period near the end of rich spike control. Deterioration of the NOx catalyst (18) is diagnosed based on the output integrated value of the NOx sensor (25), as there is a correlation between the amount of ammonia NH3 which flows downstream of the NOx catalyst and the NOx sensor output integrated value near the line when the rich spike control ends.

Description

Catalyst monitoring system and monitoring method

Technical field

The present invention relates to a kind of catalyst monitoring system and monitoring method.

Background technique

See the current emission regulation of implementing control from the amount of the harmful matter of vehicle discharge from the viewpoint of environmental protection.In addition, also implementing so-called " On-Board Diagnostics (OBD) (OBD) regulation ", it requires vehicle to be equipped with Exhaust gas purifying device is diagnosed automatically with the fault of inspection Exhaust gas purifying device or the OBD system of deterioration.

Three-way catalyst can not fully purify NOx when the air fuel ratio of the exhaust that flows into is rarer than chemically correct fuel.Therefore, the lean-combustion engine that for example can turn round under rarer air fuel ratio rarer than chemically correct fuel is equipped with the NOx catalyzer in exhaust passageway.This NOx catalyzer can store NOx when the air-fuel ratio of exhaust.

Japan Patent No.3316066 has described a kind of diagnostic system of Exhaust gas purifying device that is used for as a kind of OBD system that is used for lean-combustion engine.This diagnostic system be provided with in NOx catalyzer downstream the NOx sensor and based on by the NOx sensor to actual NOx concentration at predetermined amount of time the discharge amount of NOx is quadratured.Diagnostic system checks the NOx catalyzer whether fault is arranged based on integral value then.

In lean-combustion engine,, carry out the what is called " dense peak control (rich spike control) " that the air fuel ratio of exhaust is temporarily switched to dense air fuel ratio or chemically correct fuel from rare air fuel ratio periodically in order to reduce and to purify the NOx that is stored in the NOx catalyzer.Therefore, the NOx that enters the atmosphere from lean-combustion engine can be divided into two classes, promptly flows through the NOx of NOx catalyzer and the NOx that discharges from the NOx catalyzer at dense peak control period during lean-burn operation.The preceding a kind of NOx that flows through the NOx catalyzer during lean-burn operation discharges and flows through the NOx catalyzer and not by the NOx of NOx catalyst traps from motor.The back a kind of NOx that discharges from the NOx catalyzer at dense peak control period is stored in the NOx catalyzer but discharges and the NOx that do not reduced fully from the NOx catalyzer at dense peak control period subsequently.

The restriction current type NOx sensor of Shi Yonging is to NH in recent years ₃And NOx responds.When the air fuel ratio of exhaust is dense, the nitrogen reaction in reducing agent (for example unburned fuel) and the catalyzer, thus produce NH ₃Therefore, when the air fuel ratio of exhaust is dense (for example at dense peak control period), the NOx sensor can not only detect the concentration of NOx, because the NOx sensor is also to the NH in the exhaust ₃Respond.Therefore, the NOx sensor can not detect in the amount of dense peak control period from the NOx of NOx catalyzer discharge.Because this problem, the OBD system (being included in the diagnostic system of describing among the Japan Patent No.3316066) that is provided with the NOx sensor is designed to only not comprise NH in exhaust ₃The time lean-burn operation during with NOx sensor NOx concentration.

But, under recent strict regulations, exist to be difficult to by only detect the situation that the NOx that flows through detects the deterioration of NOx catalyzer during lean-burn operation.This will be described hereinafter.

Figure 12 and 13 illustrates NOx emission regulation value and the OBD specified value according to the STEP IV in Europe and the SULEV of the U.S. (the super low emission vehicle of crossing).As shown in figure 13, SULEV not only has strict NOx emission regulation value, and has extremely strict OBD specified value, for example is 1.75 times of NOx emission regulation value.That is to say that the degradation scope is minimum, the feasible deterioration that need diagnose the NOx catalyzer with high precision.

Figure 14 A and 14B are all at the transverse axis express time and the longitudinal axis is represented shown in the plotted curve of NOx discharge amount the laboratory data about the NOx that discharges from lean-burn engine systems.Figure 14 A illustrates the NOx catalyzer of situation use to(for) the STEP IV in Europe, and Figure 14 B illustrates the NOx catalyzer of situation use to(for) the SULEV of the U.S..In Figure 14 A and 14B, the solid line in the plotted curve represents to use the i.e. data that catalyzer obtained of deterioration not of the catalyzer corresponding with NOx emission regulation value.On the other hand, the dotted line in the plotted curve represents to use the catalyzer corresponding with the OBD specified value promptly to corrupt to the data that catalyzer obtained that must stipulate to detect the level of NOx catalyst degradation according to OBD.That is to say,, when the NOx discharge amount has increased to the level of dotted line among Figure 14 A, must detect the deterioration of NOx catalyzer in order to satisfy the OBD regulation of in the STEP in Europe IV emission standard, setting.Simultaneously, in order to satisfy the OBD regulation of in the SULEV of U.S. emission standard, setting, when having increased to the level of dotted line among Figure 14 B, the NOx discharge amount must detect the deterioration of NOx catalyzer.

As from Figure 14 A as seen, for the STEP IV emission standard in Europe, in the amount of the NOx that flows through the NOx catalyzer corresponding during the lean-burn operation with flowing through during the lean-burn operation between the amount with the NOx of the corresponding NOx catalyzer of OBD specified value and have bigger difference with the emission regulation value.Therefore, stipulate for the OBD in the STEP IV emission standard in Europe, the NOx sensor flows through the amount of the NOx of NOx catalyzer during lean-burn operation, and can be by detected NOx value and the decision content of being scheduled to are compared the deterioration of judging the NOx catalyzer.

On the other hand, as from Figure 14 B as seen, for stricter U.S. SULEV emission standard, during lean-burn operation, almost do not have NOx to flow through NOx catalyzer corresponding or the NOx catalyzer corresponding, thereby small difference is only arranged between two kinds of NOx catalyzer with the OBD specified value with the emission regulation value.Therefore, for the SULEV emission standard of the U.S.,, also be difficult to judge the deterioration of NOx catalyzer even the NOx sensor flows through the amount of the NOx of NOx catalyzer during lean-burn operation.On the other hand, between the amount of the NOx that discharges with the corresponding NOx catalyzer of OBD specified value, there is bigger difference in the amount of the NOx that dense peak control period is discharged from the NOx catalyzer corresponding with the emission regulation value with at dense peak control period.But, as mentioned above, when the air fuel ratio of exhaust is dense, be difficult to only accurately detect the concentration of NOx, because the NOx sensor is also to NH in the exhaust with the NOx sensor ₃Respond.Therefore, also be difficult to be used in dense peak control period is judged the NOx catalyzer from the difference of the NOx amount of NOx catalyzer discharge deterioration.

Like this, the feasible deterioration that is difficult to judge the NOx catalyzer of the OBD of increasingly stringent regulation by the method for using NOx concentration in the exhaust of NOx sensor.

Summary of the invention

The invention provides the catalyst monitoring system and the monitoring method of the deterioration of the NOx catalyzer in the exhaust passageway that a kind of accurate diagnosis is configured in internal-combustion engine thus.

Catalyst monitoring system according to first aspect present invention comprises: the NOx catalyzer, and described NOx catalyzer is configured in the exhaust passageway of internal-combustion engine; NOx sensor, described NOx sensor configuration are in the downstream of described NOx catalyzer and detect the concentration of NOx; Air-fuel ratio control device, described air-fuel ratio control device are used for the exhaust air-fuel ratio during the described internal combustion engine operation is temporarily switched to dense air fuel ratio or chemically correct fuel from rare air fuel ratio; Computing device, described computing device be used for by near the period at least when air fuel ratio control finishes to assign to calculate the output integral value of described NOx sensor from the output quadrature of described NOx sensor; And diagnosis apparatus, described diagnosis apparatus is used for diagnosing based on the output integral value of described NOx sensor the deterioration of described NOx catalyzer.

In addition, described NOx sensor can detect the concentration of NH3 and the concentration of NOx.

In addition, described NOx sensor can be a restriction current type NOx sensor.

Near when in addition, described air fuel ratio control finishes the described period can be from the temporary transient period that increases suddenly of the output of described NOx sensor.

In addition, described catalyst monitoring system also can comprise the reducing agent device for calculating, and described reducing agent device for calculating is used for calculating the amount that has flowed into the reducing agent of described NOx catalyzer at described air fuel ratio control period.When described reduction dosage reached prearranging quatity, described air-fuel ratio control device can stop described air fuel ratio control.

In addition, the described diagnosis apparatus deterioration that can diagnose described NOx catalyzer based on the output integral value and the described reduction dosage of described NOx sensor.

In addition, described catalyst monitoring system also can comprise the recovery time measuring device, and described recovery time measuring device is used for controlling according to described air fuel ratio the recovery time of measuring N Ox.The deterioration that described diagnosis apparatus can be diagnosed described NOx catalyzer based on the output integral value of described NOx sensor and described recovery time.

In addition, when the amount of the NOx in flowing into described NOx catalyzer reached predetermined value, described air-fuel ratio control device can begin described air fuel ratio control.

In addition, described catalyst monitoring system also can comprise O ₂Sensor, described O ₂Sensor configuration is at the downstream and the detection O of described NOx catalyzer ₂Concentration.When the control of described air fuel ratio is carried out from described O ₂When the output of sensor became described dense air fuel ratio, described air-fuel ratio control device can stop described air fuel ratio control.

In addition, when the predetermined executive condition that is used to judge deterioration satisfied, described diagnosis apparatus can begin to diagnose the deterioration of described NOx catalyzer.Described being used to judges that the predetermined executive condition of deterioration can comprise: the i) condition that described internal-combustion engine turns round with the intended operation condition when described air fuel ratio control is carried out; Ii) the temperature of described NOx catalyzer is in condition in the predetermined temperature range when the control of described air fuel ratio is carried out.

In addition, described intended operation condition can comprise that in the air inflow of the throttle opening of the speed of described internal-combustion engine, described internal-combustion engine and described internal-combustion engine at least one is in the condition in the prespecified range.

The near when control of described air fuel ratio finishes the described period can comprise from the output of described NOx sensor because the NH that discharges from described NOx catalyzer ₃And the temporary transient period that increases suddenly.

Described computing device can by to the air inflow physical quantity corresponding and the described output integral value of assigning to calculate described NOx sensor from the product quadrature of the output of described NOx sensor that flow in the described NOx catalyzer.

When the control of described air fuel ratio is carried out from the output current of described NOx sensor during corresponding to described dense air fuel ratio, described air-fuel ratio control device can stop described air fuel ratio control.

Catalyst monitoring method according to second aspect present invention may further comprise the steps: carry out air fuel ratio control, described air fuel ratio control temporarily switches to dense air fuel ratio or chemically correct fuel with the exhaust air-fuel ratio during the internal combustion engine operation from rare air fuel ratio; By near the period at least when the control of described air fuel ratio finishes to assign to calculate the output integral value of described NOx sensor from the output quadrature of NOx sensor, described NOx sensor configuration is in the downstream of the NOx of the exhaust passageway that is arranged in described internal-combustion engine catalyzer; With the deterioration of diagnosing described NOx catalyzer based on the output integral value of described NOx sensor.

Description of drawings

From seeing that to knowing embodiment's the explanation above and other objects of the present invention, feature and advantage, similar in the accompanying drawings reference character are used to represent similar element and wherein with reference to the accompanying drawings:

Fig. 1 is the schematic representation according to the system configuration of first embodiment of the invention;

Fig. 2 is provided in a side of the sectional view of the structure of the NOx sensor in the system shown in Figure 1;

Fig. 3 is a sequential chart, and wherein Fig. 3 A illustrates the output from the A/F sensor, and Fig. 3 B illustrates the NOx concentration in NOx catalyzer downstream, and Fig. 3 C illustrates the output from the NOx sensor;

Fig. 4 is the flow chart that is illustrated in the program of carrying out in the first embodiment of the invention;

Fig. 5 is the sequential chart that the various operations of first embodiment of the invention are shown, and wherein Fig. 5 A illustrates the integration amount that flows into the NOx in the NOx catalyzer, and Fig. 5 B illustrates air fuel ratio control and carries out mark, and Fig. 5 C illustrates the O from the downstream ₂The output of sensor, Fig. 5 D illustrates the output from the A/F sensor, and Fig. 5 E illustrates reduction dosage integral value, and Fig. 5 F illustrates the output from the NOx sensor, and Fig. 5 G illustrates NOx sensor output integral value;

Fig. 6 is the chart that the benchmark decision content in the first embodiment of the invention is shown;

Fig. 7 is the sequential chart that the method that is used to calculate reduction dosage integral value is shown;

Fig. 8 is the chart that the benchmark decision content in the second embodiment of the invention is shown;

Fig. 9 is the chart that the benchmark decision content in the third embodiment of the invention is shown;

Figure 10 is the schematic representation according to the system configuration of the modified example of first embodiment of the invention;

Figure 11 illustrates the sequential chart that is used for obtaining in modified example reduction dosage integral value and the method for recovery time;

Figure 12 illustrates according to the NOx emission regulation value of the SULEV emission standard of the STEP IV emission standard in Europe and the U.S. and the chart of OBD specified value;

Figure 13 illustrates according to the NOx emission regulation value of the SULEV emission standard of the STEP IV emission standard in Europe and the U.S. and the plotted curve of OBD specified value;

Figure 14 A is the plotted curve of the laboratory data of the NOx amount of discharging from lean-burn engine systems when being illustrated in use at the NOx catalyzer of the STEP IV emission standard in Europe; With

Figure 14 B is the plotted curve of the laboratory data of the NOx amount of discharging from lean-burn engine systems when being illustrated in use at the NOx catalyzer of the SULEV emission standard of the U.S..

Embodiment

Fig. 1 is the schematic representation according to the system configuration of first embodiment of the invention.System shown in Figure 1 has internal-combustion engine 10.Internal-combustion engine 10 shown in the figure is the in-line four cylinder type internal-combustion engines with four cylinders " #1 " to " #4 ".But, the invention is not restricted to this, promptly the quantity of cylinder and layout are not limited thereto.

Internal-combustion engine 10 can be by turning round with the air fuel ratio rarer than chemically correct fuel (that is, hereinafter, this air fuel ratio will be known as " rare air fuel ratio ") combustion fuel.Internal-combustion engine 10 can be the fuel tuned port injection type internal-combustion engine that sprayed into suction port, fuel by in the inner cylinder direct injection type internal-combustion engine of direct cylinder injection any, or adopts the combination of these two types of internal-combustion engines of tuned port injection and inner cylinder direct injection.

In addition, in first embodiment, internal-combustion engine 10 is spark-ignited internal combustion engines, but the present invention also can be applicable to the catalyst monitoring system of compression ignition internal combustion engine.

In the way of the exhaust passageway 12 of internal-combustion engine 10, be provided with 14 and 16 and NOx catalyzer of two start catalysts (upstream catalyst) (NSR) 18.Exhaust from #1 and #4 cylinder flows into start catalysts 14, and flows into start catalysts 16 from the exhaust of #2 and #3 cylinder.Flow through the exhaust of start catalysts 14 and assembled, and they flow into NOx catalyzer 18 together with the exhaust of flowing through start catalysts 16.

Start

catalysts

14 and 16 is as the three-way catalyst that can purify HC, CO and NOx and storage and release oxygen in the air fuel ratio of the exhaust that flows into during near chemically correct fuel simultaneously.Should be appreciated that " storage " used herein is meant with absorption, adhesion, absorption, capture, occlusion and at least a form in other keeps material (solid, liquid, gas molecule).

NOx catalytic converter 18 is as the NOx storage-reduction catalyzer that stores NOx when the air-fuel ratio of the exhaust that flows into and the stored NOx of reduction purifies NOx (after this NOx is released) thus when the air fuel ratio of the exhaust that flows into is dense.This NOx storage-reduction catalyzer 18 also has the ability that stores oxygen and can be used as three-way catalyst when internal-combustion engine 10 turns round with chemically correct fuel.

NOx catalyzer 18 according to first embodiment is the high-performance NOx catalyzer that can satisfy strict exhaust regulation.

In exhaust passageway 12, dispose A/F sensor 20 in start catalysts 14 upstreams, dispose A/F sensor 22 in start catalysts 16 upstreams, dispose A/F sensor 24, and dispose NOx sensor 25 and O in NOx catalyzer 18 downstreams in NOx catalyzer 18 upstreams ₂Sensor 26.

A/

F sensor

20,22 and 24 is the air-fuel ratio sensors that produce the linear output signal of expression exhaust air-fuel ratio.In addition, O ₂Sensor 26 is that producing according to exhaust air-fuel ratio is than the richer or the lambda sensor of the output signal of and unexpected variation rarer than chemically correct fuel.

NOx sensor 25 not only detects the NOx concentration in the exhaust, and detects the NH in the exhaust ₃(ammonia) concentration.This NOx sensor 25 will describe in detail in the back.

In NOx catalyzer 18, dispose the temperature transducer 28 of temperature (bed temperature) TCAT that detects NOx catalyzer 18.Incidentally, can directly not detect the temperature T CAT of NOx catalyzer 18, that is, and can be from infer the temperature T CAT of (estimation) NOx catalyzer 18 by the detected delivery temperature of exhaust gas temperature sensor that is located at NOx catalyzer 18 upstreams or downstream.Perhaps, can infer the temperature T CAT of NOx catalyzer 18 based on the operating condition of internal-combustion engine 10.

In addition, on internal-combustion engine 10, be connected with and suck air and the unshowned gas handling system of air distribution to each cylinder.

System according to first embodiment comprises ECU (electronic control unit) 30.This ECU 30 also is electrically connected to the various sensors of detection of engine speed NE, suction pressure PM, air inflow GA and throttle opening TH etc. except that the sensor.ECU 30 also is electrically connected to various actuators, for example fuel injector, spark plug and closure.

According to first embodiment's internal-combustion engine 10 by in the intended operation scope with rare air fuel ratio burning turn round (this running will be known as " lean-burn operation " hereinafter).During lean-burn operation, NOx is difficult to be cleaned in

start catalysts

14 and 16, thereby it temporarily is stored in the NOx catalyzer 18.When NOx gathered in NOx catalyzer 18, ECU 30 carried out the air fuel ratio that will flow into the exhaust in the NOx catalyzer 18 temporarily switches to dense air fuel ratio or chemically correct fuel from rare air fuel ratio dense peak control.As a result, the NOx that has been stored in the NOx catalyzer 18 can and be reduced (that is, being cleaned) thus from 18 releases of NOx catalyzer.

The method that the air fuel ratio that is used for flowing into the exhaust of NOx catalyzer 18 temporarily switches to dense air fuel ratio or chemically correct fuel from rare air fuel ratio can be any the following method: promptly, the air-fuel ratio of internal-combustion engine 10 is switched to the method for dense air fuel ratio or chemically correct fuel from rare air fuel ratio, at expansion stroke back during half or the method for during exhaust stroke, spraying additional fuel, or fuel is sprayed into method in the exhaust passageway 12 of NOx catalyzer 18 upstreams from cylinder fuel injection device.In this first embodiment, by the air-fuel ratio of internal-combustion engine 10 is switched to dense air fuel ratio or chemically correct fuel is carried out the control of dense peak from rare air fuel ratio.

Fig. 2 is provided in a side of the sectional view of structure of the sensor part of the NOx sensor 25 in the system shown in Figure 1.As described below, the NOx sensor 25 among this first embodiment is restriction current type NOx sensors.As shown in Figure 2, the sensor part of NOx sensor 25 is made by six oxygen ionic conductive solid dielectric substrates such as oxidized zirconium oxide stacked together.These six solid electrolyte layers will be known as first layer L by from top to bottom order hereinafter ₁, second layer L ₂, the 3rd layer of L ₃, the 4th layer of L ₄, layer 5 L ₅With layer 6 L ₆

At first layer L ₁With the 3rd layer of L ₃Between for example dispose first diffusion control parts 50 of porous and the second diffusion control parts 51 of porous.Between these

diffusion control parts

50 and 51, be formed with first chamber 52, at the second diffusion control parts 51 and second layer L ₂Between be formed with second chamber 53.In addition, at the 3rd layer of L ₃With layer 5 L ₅Between be formed with the atmospheric chamber 54 that is communicated with ambient air.Simultaneously, the exterior edge face of the first diffusion control parts 50 contacts with exhaust.Therefore, exhaust flows in first chamber 52 through the first diffusion control parts 50, makes the chamber 52 of winning be full of exhaust.

Simultaneously, at first layer L ₁On the inner peripheral surface of first chamber 52, be formed with cathode side first pump electrode 55, at first layer L ₁Outer circumferential face on be formed with anode-side first pump electrode 56.The first pump voltage source 57 is on-load voltage between these first pump electrodes 55 and 56.When voltage was carried between

first pump electrode

55 and 56, the oxygen in the exhaust in first chamber 52 contacted with cathode side first pump electrode 55 and becomes oxonium ion.These oxonium ions are at first layer L ₁Interior mobile towards anode-side first pump electrode 56.Therefore, the oxygen in the exhaust in first chamber 52 is at first layer L ₁In move and be sucked into the outside.The amount that is sucked into outside oxygen this moment raises along with the voltage in the first pump voltage source 57 and increases.

Simultaneously, at the 3rd layer of L ₃On the inner peripheral surface of atmospheric chamber 54, be formed with reference electrode 58.When the oxygen concentration on the side of the solid electrolyte layer in the oxygen ionic conductive solid electrolyte there are differences with respect to the oxygen concentration on the opposite side, oxonium ion in solid electrolyte layer from the high side of oxygen concentration towards the low side shifting of oxygen concentration.In example shown in Figure 2, the oxygen concentration in the atmospheric chamber 54 is higher than the oxygen concentration in first chamber 52, thereby the oxygen in the atmospheric chamber 54 receives electric charge by contacting with reference electrode 58, and the result becomes oxonium ion.These oxonium ions are at the 3rd layer of L ₃, second layer L ₂With first layer L ₁Interior moving, and in cathode side first pump electrode 55, discharge electric charge.As a result, between reference electrode 58 and cathode side first pump electrode 55, produce the voltage V that represents with reference character 59 ₀This voltage V ₀And the difference between the oxygen concentration in the oxygen concentration in the atmospheric chamber 54 and first chamber 52 is proportional.

In example shown in Figure 2, the voltage in the first pump voltage source 57 is fed control, makes this voltage V ₀The voltage that becomes and produce when equaling oxygen concentration in first chamber 52 for 1ppm.That is to say that the oxygen in first chamber 52 is through first layer L ₁Be sucked out, make the oxygen concentration in the chamber 52 of winning become 1ppm.This makes the oxygen concentration in the chamber 52 of winning can maintain 1ppm.

Cathode side first pump electrode 55 by the NOx reducing capacity a little less than the material of (reducibility is low) such as the alloy of golden Au and platinum Pt make.Therefore, in first chamber 52, almost do not have the NOx in the exhaust to be reduced, thereby NOx flow in second chamber 53 through the second diffusion control parts 51.Simultaneously, at first layer L ₁On the inner peripheral surface of second chamber 53, be formed with cathode side second pump electrode 60.The second pump voltage source 61 is on-load voltage between cathode side second pump electrode 60 and anode-side first pump electrode 56.When voltage was carried between these

pump electrodes

60 and 56, the oxygen in the exhaust in second chamber 53 contacted with cathode side second pump electrode 60 and becomes oxonium ion.These oxonium ions are at first layer L ₁Interior mobile towards anode-side first pump electrode 56.Therefore, the oxygen in the exhaust in second chamber 53 is at first layer L ₁In move and be sucked into the outside.The amount that is sucked into outside oxygen this moment raises along with the voltage in the second pump voltage source 61 and increases.

Simultaneously, as mentioned above, when the oxygen concentration on the side of the solid electrolyte layer in the oxygen ionic conductive solid electrolyte there are differences with respect to the oxygen concentration on the opposite side, oxonium ion in solid electrolyte layer from the high side of oxygen concentration towards the low side shifting of oxygen concentration.In example shown in Figure 2, the oxygen concentration in the atmospheric chamber 54 is higher than the oxygen concentration in second chamber 53, thereby the oxygen in the atmospheric chamber 54 receives electric charge by contacting with reference electrode 58, and the result becomes oxonium ion.These oxonium ions are at the 3rd layer of L ₃, second layer L ₂With first layer L ₁Interior moving, and in cathode side second pump electrode 60, discharge electric charge.As a result, between reference electrode 58 and cathode side second pump electrode 60, produce the voltage V that represents with reference character 62 ₁This voltage V ₁And the difference between the oxygen concentration in the oxygen concentration in the atmospheric chamber 54 and second chamber 53 is proportional.

In example shown in Figure 2, the voltage in the second pump voltage source 61 is fed control, makes this voltage V ₁The voltage that becomes and produce when equaling oxygen concentration in second chamber 53 for 0.01ppm.That is to say that the oxygen in second chamber 53 is through first layer L ₁Be sucked out, make that the oxygen concentration in second chamber 53 becomes 0.01ppm.This makes the oxygen concentration in second chamber 53 can maintain 0.01ppm.

Cathode side second pump electrode 60 a little less than by the NOx reducing capacity material such as the alloy of golden Au and platinum Pt make.Therefore, even NOx contacts with cathode side second pump electrode 60, almost there is not NOx to be reduced in the exhaust yet.Simultaneously, at the 3rd layer of L ₃On the inner peripheral surface of second chamber 53, be formed with the cathode side pump electrode 63 that is used to detect NOx.This cathode side pump electrode 63 is made by the strong material of NOx reducing capacity such as rhodium Rh or platinum Pt.Therefore, the most NO that promptly in fact constitutes among the NOx of the NOx in second chamber 53 is separated into N on cathode side pump electrode 63 ₂And O ₂Between this cathode side pump electrode 63 and reference electrode 58, be loaded with constant voltage 64, the O that the result produces on cathode side pump electrode 63 ₂Become at the 3rd layer of L ₃The interior oxonium ion that moves towards reference electrode 58.At this moment, with the proportional electric current I of representing with reference character 65 of the amount of these oxonium ions ₁Between cathode side pump electrode 63 and reference electrode 58, flow.

As mentioned above, in first chamber 52, almost do not have NOx to be reduced, and in second chamber 53, have oxygen hardly.Therefore, electric current I ₁Proportional with the NOx concentration in the exhaust, thus the NOx concentration in the exhaust is from electric current I ₁Be detected.

Simultaneously, the ammonia NH in the exhaust ₃In first chamber 52, be separated into NO and H ₂O (4NH ₃+ 5O ₂-4NO+6H ₂O), and the NO that is produced flow in second chamber 53 through the second diffusion control parts 51.This NO is separated into N on cathode side pump electrode 63 ₂And O ₂, and the O that is produced ₂Become at the 3rd layer of L ₃The interior oxonium ion that moves towards reference electrode 58.In addition at this moment, electric current I ₁With the NH in the exhaust ₃Concentration is proportional, thus the NH in the exhaust ₃Concentration is from electric current I ₁Be detected.

Like this, on principle, detect NOx and NH in the exhaust simultaneously according to first embodiment's NOx sensor 25 ₃Therefore, in exhaust, there is NH ₃The time, the electric current I of NOx sensor 25 ₁(this electric current I hereinafter ₁To be called " output of NOx sensor 25 " for short) be according to the output of NOx with according to NH ₃The combined value of output.

On the other hand, the promptly rarer air fuel ratio of higher oxygen concentration in the exhaust causes more oxygen to be sucked out to the outside from first chamber 52, and the electric current I of representing with reference character 66 thus ₂Increase.Therefore, the air fuel ratio of exhaust can be from this electric current I ₂Be detected.

Incidentally, at layer 5 L ₅With layer 6 L ₆Between be provided with the electric heater 67 of the sensor part that is used to heat NOx sensor 25.This electric heater 67 is heated to the sensor part of NOx sensor 25 between 700 ℃ and 800 ℃.

Next, with reference to Fig. 3 ammonia NH in the exhaust is described ₃Concentration.Fig. 3 is a sequential chart, and wherein Fig. 3 A illustrates the output from A/F sensor 24, and Fig. 3 B illustrates the NOx concentration in NOx catalyzer 18 downstreams, and Fig. 3 C illustrates the output from NOx sensor 25.

In Fig. 3, internal-combustion engine 10 turns round with rare air fuel ratio before moment t1, promptly is in the lean-burn operation.When air-fuel ratio, promptly when atmosphere is oxygenant, almost there is not ammonia NH ₃Produce.In addition, as mentioned above, the amount of the NOx that during lean-burn operation, flows through minimum (seeing Fig. 3 B) in NOx catalyzer 18 downstreams.Therefore, during lean-burn operation, be zero substantially from the output of NOx sensor 25, because almost do not have NOx and ammonia NH ₃Downstream at NOx catalyzer 18 is flow through.

Simultaneously, when the air fuel ratio of exhaust switches to when dense from rare, promptly when exhaust changes reducing atmosphere into, by carrying out the control of dense peak, the nitrogen N in the exhaust ₂In

start catalysts

14 and 16, reduced, produce ammonia NH thus by hydrocarbon HC ₃But when the air-fuel ratio of exhaust, the NOx that is stored in the NOx catalyzer 18 is released.The ammonia NH that is produced ₃Be used to reduce this NOx.Therefore,, or more properly, be used at ammonia NH3 and discharge and during reducing NOx, almost do not have ammonia NH just when NOx catalyzer 18 is released at NOx ₃Discharge from NOx catalyzer 18.Therefore, shown in Fig. 3 C, even in control beginning the back, dense peak (that is, constantly behind the t1), also temporarily keeping from the output of NOx sensor 25 is zero substantially.

Relative with it, when air fuel ratio has finished after NOx catalyzer 18 discharges still when dense ammonia NH at NOx ₃No longer be consumed reducing NOx, thus this moment ammonia NH ₃Discharge from NOx catalyzer 18.

Incidentally, even similar phenomenon can not take place yet when start

catalysts

14 and 16 is arranged on NOx catalyzer 18 upstreams.That is to say that NOx catalyzer 18 also is provided with catalyzer such as the platinum Pt with restoring function, thereby when air-fuel ratio, ammonia NH ₃Can in NOx catalyzer 18, produce.But, even ammonia NH3 produces under dense air fuel ratio, ammonia NH ₃Also be used to reduce the NOx that discharges from NOx catalyzer 18, thereby almost do not have ammonia NH ₃Discharge from NOx catalyzer 18.But, when air fuel ratio has finished after NOx catalyzer 18 discharges still when dense ammonia NH at NOx ₃No longer be consumed reducing NOx, thus this moment ammonia NH ₃Discharge from NOx catalyzer 18.

Therefore, near the moment ammonia NH (t2 constantly) when the control of dense peak finishes ₃Flow to the downstream side of NOx catalyzer 18.Since the delay of exhaust campaign, this ammonia NH ₃Detect slightly behindhand by NOx sensor 25.Therefore, shown in Fig. 3 C, temporarily increase suddenly near the moment the output of NOx sensor 25 is when the control of dense peak finishes.Shown in Fig. 3 B, because the influence of the NOx that is discharged from as mentioned above, near the moment of NOx concentration also when the control of dense peak finishes increases.But, to compare with rising from the output of NOx sensor 25, this moment, NOx concentration only raise a little.Promptly we can say, near the moment when the control of dense peak finishes from the whole output of NOx sensor 25 because the percentage of the output of NOx (NOx that is discharged from) is little, and be because ammonia NH from the major part in the output of NOx sensor 25 ₃

As mentioned above, under the OBD of strictness regulation, minimum in amount that flows through as yet the NOx of the NOx catalyzer 18 of deterioration not during the lean-burn operation and the difference that flows through between the amount of NOx of NOx catalyzer 18 (abbreviating " the NOx catalyzer 18 of deterioration " hereinafter as) of the deterioration corresponding with the OBD specified value.Therefore, detect by NOx sensor 25, also be difficult to detect the deterioration of NOx catalyzer 18 even flow through the NOx of NOx catalyzer 18.Therefore, the deterioration of NOx catalyzer 18 need be from detecting in the difference of dense peak control period from the amount of the NOx of NOx catalyzer 18 discharges.But, as mentioned above, ammonia NH ₃Flow out in the downstream of NOx catalyzer 18 in control back, dense peak, thereby be not easy to only obtain the discharge capacity of NOx from the output of NOx sensor 25.

Therefore, the present inventor finds that the deterioration of NOx catalyzer 18 can accurately be diagnosed based on the value (this value will be known as " NOx sensor output integral value NOxSCNT " hereinafter) that near the integration in the moment expression NOx sensor 25 is when the control of dense peak finishes is exported.

The discharge capacity of NOx increases along with the deterioration of NOx catalyzer 18, but this is because the reduction of reduction efficiency.As mentioned above, as long as the ammonia NH that produces in the exhaust ₃Be consumed and reduce the NOx that discharges from NOx catalyzer 18, ammonia NH ₃Just can be in NOx catalyzer 18 downstream flow.In other words, along with reduction efficiency reduces, ammonia NH ₃Become and be difficult to be consumed reducing NOx.As a result, more ammonia NH ₃Become in NOx catalyzer 18 downstream flow.Therefore, we can say that the discharge capacity of NOx is along with the ammonia NH in NOx catalyzer 18 downstream flow ₃Amount increase and increase.As mentioned above, near the major part of the moment when the control of dense peak finishes from the output of NOx sensor 25 is because ammonia NH ₃, thereby at the ammonia NH of NOx catalyzer 18 downstream flow ₃Amount and near the NOx sensor output integral value NOxSCNT in the dense peak control moment when finishing between have dependency relation.Therefore, the discharge capacity that can infer NOx increases along with near the increase in the moment NOx sensor output integral value NOxSCNT is when the control of dense peak finishes.

Like this, according to first embodiment, the deterioration of NOx catalyzer 18 can be diagnosed based on the NOx sensor output integral value NOxSCNT relevant greatly with the discharge capacity of dense peak control period NOx, and this can diagnose deterioration more accurately.

Fig. 4 is by the flow chart of ECU 30 execution with the program of the deterioration of diagnosis NOx catalyzer 18 in first embodiment.This program repeats at interval with preset time.Fig. 5 A to 5G is the sequential chart that first embodiment's various operations are shown.Comprising the described operation of the dense peak of carrying out three times in being controlled at shown in Fig. 5 A to 5G.

According to program shown in Figure 4, at first, read the value (step 100) of the NOxIN of the integration amount of representing the NOx in the inflow NOx catalyzer 18.Fig. 5 A illustrates this NoxIN.In first embodiment, the relation between the amount of the NOx that the load of internal-combustion engine 10 and speed and time per unit produce is checked by experiment in advance.This relation is stored among the ECU 30 in advance.ECU 30 counts the NOx amount that time per unit produces under the actual load of combustion machine 10 and the speed based on described relation then, and the integral value of calculating the NOx amount that time per unit produces is as NOxIN.

Fig. 5 B illustrates the control of dense peak and carries out flag F R.When the control of dense peak was carried out, FR equaled 1.When the control of dense peak was not carried out, FR equaled 0.After NOx in being stored in NOx catalyzer 18 discharged by execution dense peak control, NOxIN was reset.That is to say that NOxIN is illustrated in after the control end of dense peak and has flowed into the presumed value of the amount of the NOx in the NOx catalyzer 18 between before the control end of dense next time peak.

Incidentally, the method that is used to calculate NOxIN is not limited to infer from the operating condition of internal-combustion engine 10 method of NOxIN.That is to say, can detect the NOx sensor of NOx concentration in the configuration of the upstream of NOx catalyzer 18, and can be based on calculating NOxIN from the output of this NOx sensor.

In first embodiment, when the amount that has promptly flowed into the NOx in the NOx catalyzer 18 as NOxIN reaches predetermined value, the control beginning of dense peak.Therefore, when in step 100, reading NOxIN, judge whether NOxIN is equal to or greater than predetermined value (step 102).If NOxIN does not reach predetermined value as yet in step 102, then by detected output NOxS quadrature from NOx sensor 25 in this circulation of program is assigned to upgrade NOx sensor output integral value NOxSCNT (step 104).Then, this loop ends of program.

Fig. 5 F illustrates the output NoxS from NOx sensor 25, and Fig. 5 G illustrates NOx sensor output integral value NOxSCNT.Shown in Fig. 5 G, in this first embodiment, by from the control beginning of dense peak the time be carved into the control beginning of dense next time peak the moment to NOx sensor output NOxS quadrature assign to calculate NOx sensor output integral value NOxSCNT.Therefore, when in step 102, being judged to be NOxIN when having reached predetermined value, to the end (step 106) of quadraturing of a last NOxS.

In addition, shown in Fig. 5 G, in this first embodiment, NOx sensor output integral value NOxSCNT is separated into NOxSCNT _RAnd NOxSCNT _LNOxSCNT _RThe value that expression was quadratured to NOx sensor output NOxS at such period, the major part of NOx sensor output NOxS is the ammonia NH that produces owing at dense peak control period in the described period ₃On the other hand, NOxSCNT _LThe value that expression was quadratured to NOx sensor output NOxS at such period, the major part of NOx sensor output NOxS is owing to flow through the NOx of NOx catalyzer 18 during lean-burn operation in the described period.In step 106, also execution is used to calculate NOxSCNT _RProcessing.More specifically, shown in Fig. 5 G, decidable is because ammonia NH for the major part of NOx sensor output NOxS in the temporary transient period that increases suddenly of NOx sensor output NOxS ₃Therefore, the integral value of NOx sensor output NOxS can be used as NOxSCNT in this period _R, and the integral value of NOx sensor output NOxS can be used as NOxSCNT in other period except that this period _L

When NOxIN reaches predetermined value,, begin then at this circulation NOx sensor output NoxS quadrature (step 110) in the dense peak control beginning of this circuit of step 106 back (step 108).

Fig. 5 C illustrates the O from NOx catalyzer 18 downstreams ₂The output O of sensor ₂S.In this first embodiment, when from O ₂The output O of sensor 26 ₂When S became dense output, the control of dense peak finished.Therefore, when carrying out the control of dense peak, judge from O ₂Whether the output O2S of sensor 26 has become dense output (step 112).When being judged to be from O ₂The output O of sensor 26 ₂When S had become dense output, the control of dense peak finished (step 114) at this circuit.

When the control of dense peak finishes, just judge whether satisfy the condition (step 116) that is used to judge NOx catalyzer 18 deteriorations.This deterioration judging condition more specifically comprises two conditions.These conditions are: (1) operating condition (for example engine speed NE, throttle opening TH or air inflow GA) when carrying out the control of dense peak is in the prespecified range; (2) the temperature T CAT of NOx catalyzer 18 is in the predetermined temperature range when carrying out the control of dense peak.

Above-mentioned condition (1) is such condition, its be configured to have only when dense peak be controlled at do not have to quicken suddenly or the intended operation condition of deceleration etc. under the data that obtained when carrying out just be used as the basis that catalyst degradation judges so that prevent owing to the error of calculations of NOxIN etc. etc. causes misinterpretation.Above-mentioned condition (2) is to prevent that Temperature Influence owing to NOx catalyzer 18 from causing the condition of misinterpretation.That is to say that the storage-reduction ability of NOx catalyzer 18 changes according to its temperature.The data that obtained when therefore, above-mentioned condition (2) is configured to have only the storage-reduction ability that is controlled at NOx catalyzer 18 when dense peak to be counted as carrying out in the stationary temperature scope just are used as the basis that catalyst degradation is judged.

Do not satisfy the deterioration judging condition if be judged to be in step 116, then decidable is judged for not carrying out catalyst degradation.Therefore, in this case, this circuit program directly finishes.On the other hand, satisfy the deterioration judging condition if be judged to be in step 116, then catalyst degradation judges that execution is as follows.At first, the NOxSCNT that will in step 116, calculate _RCompare (step 118) with predetermined benchmark decision content β.As mentioned above, decidable is to be illustrated in the NOxSCNT that near the NOx sensor that the is integrated output NOxS in the moment when finishing is controlled at dense peak _RBig more, the ammonia NH that flows out in NOx catalyzer 18 downstreams then ₃Many more.In addition, decidable is the ammonia NH that flows out in NOx catalyzer 18 downstreams ₃Many more, then the NOx amount of discharging at dense peak control period is big more.Therefore, as NOxSCNT in step 118 _RWhen being equal to or greater than benchmark decision content β, be judged to be NOx catalyzer 18 deteriorations (step 120).On the other hand, work as NOxSCNT _RDuring less than benchmark decision content β, be judged to be NOx catalyzer 18 normal (promptly not deterioration) (step 122).

Next benchmark decision content β will be described.Fig. 6 is illustrated in that transverse axis is represented the temperature T ACT of NOx catalyzer 18 and the longitudinal axis is represented NOx sensor output integral value NOxSCNT _RSystem of coordinates on the chart of a plurality of laboratory datas of drawing out.In Fig. 6, black box is represented the laboratory data with the discharge capacity level of the NOx NOx catalyzer 18 corresponding with the emission regulation value (this catalyzer will be known as " normal catalytic agent (X) " hereinafter) acquisition.Relative with it, black diamond block is represented the laboratory data with the discharge capacity level of the NOx NOx catalyzer 18 corresponding with the OBD specified value (this catalyzer will be known as " deterioration catalyzer (Y) " hereinafter) acquisition.As seen from Figure 6, can for the value shown in the straight line among Fig. 6 normal catalytic agent (X) and deterioration catalyzer (Y) be made a distinction reliably by benchmark decision content β being set for for example.

Like this, according to this first embodiment, can be by exporting integral value NOxSCNT based on the NOx sensor relevant with the NOx amount of discharging at dense peak control period _RThe deterioration of diagnosis NOx catalyzer 18 obtains high diagnostic accuracy.

Incidentally, in the example depicted in fig. 6, benchmark decision content β is constant and irrelevant with the temperature T CAT of NOx catalyzer 18.But perhaps, benchmark decision content β also can change according to TACT.In addition, benchmark decision content β can change according to other operating condition of internal-combustion engine 10.

In addition, in program shown in Figure 4, NOx sensor output integral value NOxSCNT is separated into NOxSCNT _RAnd NOxSCNT _LAnd based on NOxSCNT _RCarrying out the catalyst degradation of NOx catalyzer 18 judges.But, the invention is not restricted to this decision method.Perhaps, can be separated into NOxSCNT based on NOx sensor output integral value NOxSCNT _RAnd NOxSCNT _LNOxSCNT before carries out catalyst degradation and judges, because and NOxSCNT _RValue compare NOxSCNT _LValue little and have slight influence thus.In addition, also can just only calculate NOxSCNT from beginning _RValue.That is to say, in the present invention, judge that as catalyst degradation the integration period of the NOx sensor output NOxS on basis only need be included near the output of the moment NOx sensor 25 of dense peak control when finishing because ammonia NH ₃And the temporary transient period that increases suddenly.

In addition, in above-mentioned first embodiment, assign to calculate NOx sensor output integral value NOxSCNT by the NOx sensor being exported the NOxS quadrature.But the method that is used to calculate NOx sensor output integral value NOxSCNT is not limited thereto.Perhaps, for example, also can by to flow into NOx catalyzer 18 in the physical quantity of air quantity corresponding (promptly corresponding to air inflow) assign to calculate the NOx sensor with the product quadrature of NOx sensor output NOxS and export integral value NOxSCNT.Incidentally, flow into air quantity (also being known as " air inflow " hereinafter) in the NOx catalyzer 18 can be for example based on calculating by the detected air inflow GA of Air flow meter, fuel injection amount or from the output of A/F sensor 24.

In addition, in first embodiment, as O from NOx catalyzer 18 downstreams ₂When the output of sensor 26 became dense output, the control of dense peak finished.Perhaps, dense peak control can be used the O of NOx sensor 25 ₂Sensor function or A/F sensor function finish.For example, utilize the NOx sensor 25 among first embodiment, as described in reference Fig. 2, the air fuel ratio of exhaust can be from the electric current I of NOx sensor 25 ₂Be detected.Therefore, dense peak control can be in this electric current I ₂Finish during corresponding to dense air fuel ratio.In this case, no longer need to provide the O in NOx catalyzer 18 downstreams ₂Sensor 26, thus can reduce cost.

Next will first embodiment's modified example be described.In above-mentioned program shown in Figure 4, as O from NOx catalyzer 18 downstreams ₂When the output of sensor 26 became dense output, the control of dense peak finished.Perhaps, in this modified example, when the amount that has flowed into the reducing agent in the NOx catalyzer 18 after the control beginning of dense peak reached predetermined value gamma, the control of dense peak finished.

The method that is used for calculating the reduction dosage that has flowed into NOx catalyzer 18 is not particularly limited.For example, can use following method.Fig. 7 is the sequential chart that the method that is used to calculate reduction dosage integral value FRCNT is shown.More specifically, among Fig. 7 by the last variation that illustrates reduction dosage integral value FRCNT, and among Fig. 7 by under illustrate output AFS_2 from A/F sensor 24, promptly flow into the air fuel ratio AFS_2 of the exhaust in the NOx catalyzer 18.

Reduction dosage integral value RFCNT is a value of representing to flow into owing to the control of dense peak the amount of the reducing agent in the NOx catalyzer 18, and calculates according to following formula.

RFCNT=∑ (that is, the reduction dosage of time per unit multiply by the computing cycle of ECU) ... (1)

Among dense peak control period had flowed into fuel in the NOx catalyzer 18, the fuel (that is excess of fuel) that surpasses realization theory air fuel ratio (being 14.6 in this case) aequum was as reducing agent.Therefore, the reduction dosage of time per unit can calculate according to following formula.

Reduction dosage=(flow into fuel quantity in the NOx catalyzer and deduct the air quantity that flows in the NOx catalyzer)=(1/AFS_2-1/14.6) * the flow into air quantity in the NOx catalyzer ... (2) divided by 14.6

When carrying out the control of dense peak, reduction dosage integral value RFCNT can be calculated based on above-mentioned formula (1) and (2) continuously by ECU 30.In this modified example, when the reduction dosage integral value RFCNT that calculates as described above reached predetermined value gamma, the control of dense peak finished.Therefore, the total amount of the reducing agent of supplying with at dense peak control period can be all constant at every turn.

Simultaneously, be controlled at O when dense peak from NOx catalyzer 18 downstreams ₂When finishing when the output of sensor 26 becomes dense output, the amount of reducing agent can change according to the deterioration level of NOx catalyzer 18.For example, when high and NOx storage volume was minimum when the deterioration level of NOx catalyzer 18, all NOx that are stored just were reduced soon, thereby from O ₂The output of sensor 26 just becomes dense output soon.As a result, constipation bundle is soon controlled at dense peak, and is minimum thereby the quantitative change of reducing agent gets.When the amount of reducing agent hour, the ammonia NH that is produced ₃Amount also little.In these cases, whether NOx sensor output integral value NOxSCNT is calculated little and high irrelevant with the deterioration level of NOx catalyzer 18, thereby exists NOx catalyzer 18 to be decided to be normal possibility by erroneous judgement.

Relative with it, according to this modified example, can make the amount of reducing agent of dense peak control period constant, thereby also can make the ammonia NH that is produced ₃Amount constant.As ammonia NH ₃Amount when constant, the ammonia NH that flows out in NOx catalyzer 18 downstreams ₃Amount be that NOx sensor output integral value NOxSCNT can be promptly relevant more accurately with reduction efficiency with the discharge capacity of NOx.Therefore, according to this modified example, can prevent for example above-mentioned misinterpretation more reliably, this can diagnose the deterioration of NOx catalyzer 18 more accurately.

In addition, in first embodiment, " air-fuel ratio control device " of the present invention can be realized by the ECU 30 of execution in

step

108 and 114, " computing device " of the present invention can be realized by the ECU 30 of execution in step 104,106 and 110, and " diagnosis apparatus " of the present invention can be realized by the ECU 30 of execution in

step

118 and 120 and 122.

In addition, in first embodiment's modified example, reduction dosage integral value RFCNT can be counted as " reduction dosage " of the present invention.In addition, " reducing agent device for calculating " of the present invention can be realized by the ECU 30 based on above-mentioned formula (1) and (2) calculating reduction dosage integral value RFCNT.In addition, " air-fuel ratio control device " of the present invention also can be realized by the ECU 30 that stops the control of dense peak when reduction dosage integral value RFCNT reaches predetermined value gamma.

Next with reference to Fig. 8 the second embodiment of the present invention is described.But below explanation will concentrate on those points different with above-mentioned first embodiment.To simplify or omit with similar explanation in above-mentioned first embodiment.

In above-mentioned first embodiment, by the NOx sensor is exported integral value NOxSCNT _RCompare the deterioration judging (step 118 of program among Fig. 4) of carrying out NOx catalyzer 18 with benchmark decision content β.Relative with it, in this second embodiment, by the NOx sensor is exported integral value NOxSCNT _RThe merchant NOxSCNT that obtains divided by the amount that flows into the reducing agent in the NOx catalyzer 18 (that is, reduction dosage integral value RFCNT) _R/ RFCNT and benchmark decision content compare the deterioration judging of carrying out NOx catalyzer 18.

Fig. 8 represents the temperature T CAT of NOx catalyzer 18 and the longitudinal axis is represented NOxSCNT at transverse axis _RDraw out on the merchant's of/RFCNT the system of coordinates use with Fig. 6 in the chart of laboratory data of identical catalyzer.That is to say that in Fig. 8, black box is represented the laboratory data of normal catalytic agent (X), and black diamond block is represented the laboratory data of deterioration catalyzer (Y).Incidentally, dense peak control termination condition is set so that the O from NOx catalyzer 18 downstreams ₂Sensor 26 is output as dense output.As seen, in this second embodiment, can normal catalytic agent (X) and deterioration catalyzer (Y) be made a distinction reliably by the benchmark decision content of setting shown in the angled straight lines among Fig. 8 from Fig. 8.

NOxSCNT _RThe merchant of/RFCNT represents to flow through NOx catalyzer 18 and is not consumed and reduces the reducing agent of the NOx that discharges from NOx catalyzer 18 and account for the percentage that flows into the reducing agent total amount the NOx catalyzer 18.Therefore, we can say NOxSCNT _RThe merchant of/RFCNT is a value of representing the reduction efficiency of NOx catalyzer 18 more accurately.Therefore, according to this second embodiment, by with NOxSCNT _RThe merchant of/RFCNT and benchmark decision content compare the deterioration of diagnosing NOx catalyzer 18 can obtain higher diagnostic accuracy.

Incidentally, in Fig. 8, the benchmark decision content diminishes along with the rising of the temperature T CAT of dense peak control period NOx catalyzer 18.It is believed that this is the temperature T CAT height owing to NOx catalyzer 18 when internal-combustion engine 10 turns round under high load.When internal-combustion engine 10 turned round under high load, air inflow GA was big, thereby even flow through the ammonia NH of NOx catalyzer 18 ₃Amount identical, the concentration of ammonia NH3 also reduces.As a result, NOxS is littler for the output of NOx sensor, thus NOx sensor output integral value NOxSCNT _RAlso littler.Therefore, the benchmark decision content is considered to along with the rising of the temperature T CAT of NOx catalyzer 18 and diminishes.

But when this trend was not detected in experimental result, the benchmark decision content can be a steady state value and irrelevant with the temperature T CAT of NOx catalyzer 18.

The concrete processing of second exemplary embodiment is as follows.Basis was calculated reduction dosage integral value RFCNT one by one with used identical method in first embodiment's modified example when ECU 30 carried out in the control of dense peak.With reference to the step 118 of program among Fig. 4, by exporting integral value NOxSCNT with the NOx sensor _RReduction dosage integral value RFCNT when finishing divided by the control of dense peak calculates NOxSCNT _RThe merchant of/RFCNT.Next, the temperature T CAT based on NOx catalyzer 18 obtains the benchmark decision content according to relation shown in Figure 8.Then with this benchmark decision content and NOxSCNT _RThe merchant of/RFCNT compares.If NOxSCNT _RThe merchant of/RFCNT is equal to or greater than the benchmark decision content, then is judged to be NOx catalyzer 18 deteriorations (step 120).Simultaneously, if NOxSCNT _RThe merchant of/RFCNT then is judged to be NOx catalyzer 18 normal (step 122) less than the benchmark decision content.

In all others, second embodiment and first embodiment are similar, thereby omit further instruction.In a second embodiment, reduction dosage integral value RFCNT can be counted as " reduction dosage " of the present invention.In addition, " reducing agent device for calculating " of the present invention also can be realized by the ECU 30 that calculates reduction dosage integral value RFCNT, and " diagnosis apparatus " of the present invention also can be by with NOxSCNT _RThe merchant of/RFCNT and benchmark decision content compare and diagnose the ECU of the deterioration of NOx catalyzer 18 to realize.

Next with reference to Fig. 9 the third embodiment of the present invention is described.But below explanation will concentrate on those points different with above-mentioned first embodiment.To simplify or omit with similar explanation in above-mentioned first embodiment.

In the 3rd embodiment, by the NOx sensor is exported integral value NOxSCNT _RDivided by recovery time T according to the control of dense peak _RSThe merchant who obtains is NOxSCNT _R/ T _RSMerchant and benchmark decision content compare the deterioration judging of carrying out NOx catalyzer 18.

In the 3rd embodiment, shown in Fig. 5 B, recovery time T _RSBe the time that the control of dense peak continues, but recovery time T _RSBe not limited thereto.For example, recovery time T _RSIt also can be the time that is maintained dense output from the output of the A/F sensor 24 of NOx catalyzer 18 upstreams.

Fig. 9 represents the temperature T CAT of NOx catalyzer 18 and the longitudinal axis is represented NOxSCNT at transverse axis _R/ T _RSMerchant's system of coordinates on draw out use with Fig. 6 in the chart of laboratory data of identical catalyzer.That is to say that in Fig. 9, black box is represented the laboratory data with normal catalytic agent (X) acquisition, and black diamond block is represented the laboratory data with deterioration catalyzer (Y) acquisition.Incidentally, dense peak control termination condition is set so that the O from NOx catalyzer 18 downstreams ₂Sensor 26 is output as dense output.As seen, in the 3rd embodiment, can normal catalytic agent (X) and deterioration catalyzer (Y) be made a distinction reliably by the benchmark decision content of setting shown in the angled straight lines among Fig. 9 from Fig. 9.

Usually, we can say that the amount (that is reduction dosage integral value RFCNT) of the reducing agent in the inflow NOx catalyzer 18 is along with recovery time T _RSProlongation and increase.Therefore, NOxSCNT _R/ T _RSThe merchant can be used as with second embodiment in NOxSCNT _RThe similar index of the merchant of/RFCNT.Therefore, with the same in a second embodiment, also can obtain higher diagnostic accuracy according to the 3rd embodiment.

The 3rd embodiment's concrete processing is as follows.ECU 30 measures recovery time T when the control of dense peak is carried out _RSWith reference to the step 118 of program among Fig. 4, by exporting integral value NOxSCNT with the NOx sensor _RDivided by recovery time T _RSCalculate NOxSCNT _R/ T _RSThe merchant.Next, the temperature T CAT based on NOx catalyzer 18 obtains the benchmark decision content according to relation shown in Figure 9.Then with this benchmark decision content and NOxSCNT _R/ T _RSThe merchant compare.If NOxSCNT _R/ T _RSThe merchant be equal to or greater than the benchmark decision content, then be judged to be NOx catalyzer 18 deteriorations (step 120).Simultaneously, if NOxSCNT _R/ T _RSThe merchant less than the benchmark decision content, then be judged to be NOx catalyzer 18 normal (step 122).

In all others, the 3rd embodiment and first embodiment are similar, thereby omit further instruction.In the 3rd embodiment, " recovery time computing device " of the present invention can be by measuring recovery time T _RSECU 30 realize.In addition, " diagnosis apparatus " of the present invention also can be by with NOxSCNT _R/ T _RSMerchant and benchmark decision content compare and diagnose the ECU of the deterioration of NOx catalyzer 18 to realize.

In above-mentioned each embodiment, such system has been described, wherein A/F sensor 24 is configured in the upstream of NOx catalyzer 18 and O ₂Sensor 26 is configured in the downstream of NOx catalyzer 18.But system configuration of the present invention is not limited thereto.For example, its also modification as described below.

Figure 10 is the system configuration according to the modified example of first embodiment of the invention.In system shown in Figure 10, when becoming richer than or be leaner than chemically correct fuel, the air fuel ratio of exhaust produces the O of the output signal that changes suddenly ₂ Sensor 27 replaces the upstream that A/F sensor 24 is configured in NOx sensor 18.In all others, system shown in Figure 10 and system class shown in Figure 1 are seemingly.Hereinafter, for the purpose of simplifying the description, be configured in the O of NOx catalyzer 18 upstreams ₂Sensor 27 will be known as " upstream O ₂Sensor 27 " and be configured in the O in NOx catalyzer 18 downstreams ₂Sensor 26 will be known as " downstream O ₂Sensor 26 ".

Figure 11 illustrates to be used for obtaining reduction dosage integral value RFCNT and recovery time T in this modified example _RSThe sequential chart of method.More specifically, lean on last illustrating among Figure 11 from downstream O ₂The output of sensor 26, placed in the middle illustrating among Figure 11 from downstream O ₂The output of sensor 27, and among Figure 11 by under illustrate output from one of the A/F sensor 20 that is configured in

start catalysts

14 and 16 upstreams or 22, or as from A/

F sensor

20 and 22 both outputs (being known as " output of A/F sensor " hereinafter) of mean value of output.

As shown in figure 11, when the control beginning of dense peak and exhaust with dense air fuel ratio begin when internal-combustion engine 10 is discharged, the output of A/F sensor switches to dense (t1 constantly) from rare.Then, the institute's aerobic in being stored in

start catalysts

14 and 16 is flowed into reducing agent in

start catalysts

14 and 16 when using up, and the exhaust with dense air fuel ratio begins to flow through the downstream side to start catalysts 14 and 16.As a result, upstream O ₂The output of sensor 27 becomes dense (constantly t2) from rare.

From moment t2, reducing agent begins to flow in the NOx catalyzer 18.When all oxygen in being stored in NOx catalyzer 18 and NOx were reduced agent and use up then, the exhaust with dense air fuel ratio began to flow through the downstream side to NOx catalyzer 18.As a result, downstream O ₂The output of sensor 26 becomes dense (constantly t3) from rare.

In this modified example, the amount (that is reduction dosage integral value RFCNT) that has flowed into the reducing agent in the NOx catalyzer 18 can be exported based on the A/F sensor from moment t2 to moment t3 and calculate (dash area Figure 11).In addition, recovery time T _RSCan obtain by the time of measuring from moment t2 to moment t3.

As another modified example of first embodiment of the invention, the amount that is stored in oxygen in the NOx catalyzer 18 and NOx can be calculated from reduction dosage integral value RFCNT.In the present invention, also can combine with the deterioration judging result who uses above-mentioned NOx sensor 25 to obtain and with high precision execution deterioration judging by the deterioration judging result who makes the NOx catalyzer 18 that obtains based on the amount that is stored in oxygen in the NOx catalyzer 18 and NOx.

Although with reference to embodiment the present invention has been described, be to be understood that to the invention is not restricted to described embodiment or structure.On the contrary, the invention is intended to contain various modification and equivalent arrangements.In addition, be various combinations and configuration although embodiment's various elements are depicted as, comprise more, still less or only other combination and the configuration of single-element also are in the spirit and scope of the present invention.

Claims

1. catalyst monitoring system comprises:

The NOx catalyzer, described NOx catalyzer is configured in the exhaust passageway of internal-combustion engine;

NOx sensor, described NOx sensor configuration are in the downstream of described NOx catalyzer and detect the concentration of NOx;

Air-fuel ratio control device, described air-fuel ratio control device are used for the exhaust air-fuel ratio during the described internal combustion engine operation is temporarily switched to dense air fuel ratio or chemically correct fuel from rare air fuel ratio;

Computing device, described computing device be used for by near the period at least when air fuel ratio control finishes to assign to calculate the output integral value of described NOx sensor from the output quadrature of described NOx sensor; With

Diagnosis apparatus, described diagnosis apparatus is used for diagnosing based on the output integral value of described NOx sensor the deterioration of described NOx catalyzer.

2. catalyst monitoring system according to claim 1, wherein

Described NOx sensor can detect NH ₃Concentration and the concentration of NOx.

3. catalyst monitoring system according to claim 1 and 2, wherein

Described NOx sensor is a restriction current type NOx sensor.

4. according to each described catalyst monitoring system in the claim 1 to 3, wherein

Near when described air fuel ratio control finishes the described period is from the temporary transient period that increases suddenly of the output of described NOx sensor.

5. according to each described catalyst monitoring system in the claim 1 to 4, also comprise

Reducing agent device for calculating, described reducing agent device for calculating are used for calculating the amount that has flowed into the reducing agent of described NOx catalyzer at described air fuel ratio control period,

Wherein when described reduction dosage reached prearranging quatity, described air-fuel ratio control device stopped described air fuel ratio control.

6. according to each described catalyst monitoring system in the claim 1 to 4, also comprise

The deterioration that wherein said diagnosis apparatus is diagnosed described NOx catalyzer based on the output integral value and the described reduction dosage of described NOx sensor.

7. according to each described catalyst monitoring system in the claim 1 to 4, also comprise

Recovery time measuring device, described recovery time measuring device are used for controlling according to described air fuel ratio the recovery time of measuring N Ox,

The deterioration that wherein said diagnosis apparatus is diagnosed described NOx catalyzer based on the output integral value of described NOx sensor and described recovery time.

8. according to each described catalyst monitoring system in the claim 1 to 7, wherein

When the amount of the NOx in flowing into described NOx catalyzer reached predetermined value, described air-fuel ratio control device began described air fuel ratio control.

9. according to each described catalyst monitoring system in the claim 1 to 4, also comprise

O ₂Sensor, described O ₂Sensor configuration is at the downstream and the detection O of described NOx catalyzer ₂Concentration,

Wherein when when the control of described air fuel ratio is carried out from described O ₂When the output of sensor became described dense air fuel ratio, described air-fuel ratio control device stopped described air fuel ratio control.

10. according to each described catalyst monitoring system in the claim 1 to 9, wherein

When the predetermined executive condition that is used to judge deterioration satisfied, described diagnosis apparatus began to diagnose the deterioration of described NOx catalyzer, and

Described being used to judges that the predetermined executive condition of deterioration comprises: the i) condition that described internal-combustion engine turns round with the intended operation condition when described air fuel ratio control is carried out; Ii) the temperature of described NOx catalyzer is in condition in the predetermined temperature range when the control of described air fuel ratio is carried out.

11. catalyst monitoring system according to claim 10, wherein

Described intended operation condition comprises that in the air inflow of the throttle opening of the speed of described internal-combustion engine, described internal-combustion engine and described internal-combustion engine at least one is in the condition in the prespecified range.

12. catalyst monitoring system according to claim 4, wherein

The near when control of described air fuel ratio finishes the described period comprises from the output of described NOx sensor because the NH3 that discharges from described NOx catalyzer and the temporary transient period that increases suddenly.

13. according to each described catalyst monitoring system in the claim 1 to 12, wherein

Described computing device by to the air inflow physical quantity corresponding and the described output integral value of assigning to calculate described NOx sensor from the product quadrature of the output of described NOx sensor that flow in the described NOx catalyzer.

14. according to each described catalyst monitoring system in the claim 1 to 4, wherein

When the control of described air fuel ratio is carried out from the output current of described NOx sensor during corresponding to described dense air fuel ratio, described air-fuel ratio control device stops described air fuel ratio control.

15. a catalyst monitoring method comprises:

The control of execution air fuel ratio, described air fuel ratio control temporarily switches to dense air fuel ratio or chemically correct fuel with the exhaust air-fuel ratio during the internal combustion engine operation from rare air fuel ratio;

By near the period at least when the control of described air fuel ratio finishes to assign to calculate the output integral value of described NOx sensor from the output quadrature of NOx sensor, described NOx sensor configuration is in the downstream of the NOx of the exhaust passageway that is arranged in described internal-combustion engine catalyzer; With

Diagnose the deterioration of described NOx catalyzer based on the output integral value of described NOx sensor.

16. a catalyst monitoring system comprises:

Air fuel ratio control device, the described air fuel ratio control device exhaust air-fuel ratio during with described internal combustion engine operation temporarily switches to dense air fuel ratio or chemically correct fuel from rare air fuel ratio;

Calculating part, described calculating part by near the period at least when the control of described air fuel ratio finishes to assign to calculate the output integral value of described NOx sensor from the output quadrature of described NOx sensor; With

Diagnosis portion, described diagnosis portion diagnoses the deterioration of described NOx catalyzer based on the output integral value of described NOx sensor.