JP2009191787A - Fuel property determining device and catalyst deterioration diagnosing device equipped with it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel property determining device of high precision and reliability and a catalyst deterioration diagnosing device equipped with it. <P>SOLUTION: The fuel property determining device actively changes and controls an air-fuel ratio to a rich side or a lean side whenever the air-fuel ratio detected by a post-catalyst air-fuel sensor on a catalyst downstream side turns around to the lean side or the rich side and estimates a sulfur concentration of fuel based on a rich time TR and a lean time TL at that time. The fuel property determining device corrects a measured value of an oxygen storage capacity based on the rich time TR and the lean time TL and diagnoses catalyst deterioration while eliminating sulfur affection. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a fuel property determination device for determining the fuel property of fuel used in an internal combustion engine and a catalyst deterioration diagnosis device equipped with the fuel property determination device, and more particularly to a fuel property determination device capable of estimating the sulfur concentration of fuel used in an internal combustion engine and The present invention relates to a catalyst deterioration diagnosis apparatus provided with this.

For example, in an internal combustion engine for a vehicle, a catalyst for purifying exhaust gas is installed in the exhaust system. Some of these catalysts have an oxygen storage capacity (O ₂ storage capacity). This is because when the air-fuel ratio of the exhaust gas flowing into the catalyst becomes larger than the stoichiometric air-fuel ratio (stoichiometric), that is, the exhaust gas becomes lean. Excess oxygen present in the gas is adsorbed and held, and when the air-fuel ratio of the catalyst inflow exhaust gas becomes smaller than the stoichiometric, that is, becomes rich, the adsorbed and held oxygen is released. For example, in a gasoline engine, air-fuel ratio control is performed so that the exhaust gas flowing into the catalyst is in the vicinity of the stoichiometric. However, such an air-fuel ratio shift can be absorbed by the oxygen storage / release action of the three-way catalyst.

  By the way, when the catalyst deteriorates, the purification efficiency of the catalyst decreases. On the other hand, there is a correlation between the degree of deterioration of the catalyst and the degree of reduction of the oxygen storage capacity because they are reactions through noble metals. Therefore, it is possible to detect that the catalyst has deteriorated by detecting that the oxygen storage capacity has decreased. In general, active air-fuel ratio control for forcibly switching the air-fuel ratio of the air-fuel mixture in the combustion chamber and thus the exhaust gas flowing into the catalyst to rich or lean is performed, and the oxygen storage of the catalyst is performed as the active air-fuel ratio control is executed. A method of measuring the capacity and diagnosing catalyst deterioration (so-called Cmax method) is employed.

JP 2003-83145 A

  On the other hand, sulfur (S) may be contained in the fuel at a relatively high concentration depending on the region of use. When such fuel is supplied, poisoning (S poisoning) occurs in which sulfur components accumulate in the catalyst and the performance of the catalyst decreases. When S poisoning occurs, the oxygen storage / release reaction of the catalyst is hindered, and the apparent oxygen storage capacity of the catalyst decreases. However, if the fuel with a low sulfur concentration is refueled, the poisoning state will eventually be resolved. The performance degradation of the catalyst due to S poisoning is temporary. Therefore, in the deterioration diagnosis of the catalyst, it is necessary not to mistakenly diagnose the temporary deterioration due to the S poisoning as permanent deterioration that should be diagnosed. In particular, it is necessary to prevent a catalyst that is still normal while being in the vicinity of the boundary between normality and deterioration (criteria) from being erroneously diagnosed as deterioration.

  In order to prevent such a misdiagnosis, it is preferable to estimate or determine the fuel properties, particularly the sulfur concentration in the fuel. This is because if such estimation or determination is performed, necessary measures such as stopping the catalyst deterioration diagnosis can be taken when it is determined that the fuel has a high sulfur concentration, and erroneous diagnosis can be prevented in advance.

  Regarding such fuel property determination, Patent Document 1 discloses that the three-way catalyst is poisoned with sulfur when the maximum output value (rich side output maximum value) of the O2 sensor installed on the downstream side of the three-way catalyst is equal to or less than a predetermined value. A technique for determining that the image is present is disclosed. This utilizes the property that the maximum output value of the downstream O2 sensor is smaller as the sulfur content in gasoline as fuel is larger.

  However, if the method focuses only on the maximum output value of the downstream O2 sensor, there is a possibility that accurate fuel property determination cannot be performed due to manufacturing variations of the downstream O2 sensor, and there remains room for improvement in terms of accuracy and reliability. .

  Therefore, the present invention has been made in view of such circumstances, and an object thereof is to provide a highly accurate and reliable fuel property determination device and a catalyst deterioration diagnosis device including the same.

According to one aspect of the invention,
A catalyst provided in the exhaust passage of the internal combustion engine;
A post-catalyst air-fuel ratio sensor provided downstream of the catalyst;
Active air-fuel ratio control means for actively switching the air-fuel ratio to the rich side or the lean side every time the air-fuel ratio detected by the post-catalyst air-fuel ratio sensor is reversed to the lean side or the rich side;
Based on the rich time when the air-fuel ratio is switched to the rich side by the active air-fuel ratio control means and the lean time when the air-fuel ratio is switched to the lean side by the active air-fuel ratio control means, There is provided a fuel property judgment device comprising a sulfur concentration estimation means for estimating a sulfur concentration.

  According to this, the sulfur concentration of the fuel is estimated based on the rich time when the air-fuel ratio is switched to the rich side and the lean time when the air-fuel ratio is switched to the lean side. The sulfur concentration of the fuel can be estimated without relying only on the output absolute value of the post-catalyst air-fuel ratio sensor. Therefore, it becomes difficult to be influenced by manufacturing variation of the post-catalyst air-fuel ratio sensor, and the fuel property determination with high accuracy and reliability can be performed.

  Preferably, the sulfur concentration estimating means estimates the sulfur concentration of the fuel based on a ratio between the rich time and the lean time. Since the ratio is a value that correlates with the sulfur concentration of the fuel, it is preferable to estimate the sulfur concentration of the fuel based on the ratio.

According to another aspect of the invention,
A catalyst deterioration diagnosis device comprising the fuel property determination device,
Measuring means for measuring the oxygen storage capacity of the catalyst in accordance with air-fuel ratio switching control by the active air-fuel ratio control means;
There is provided a catalyst deterioration diagnosis device comprising: a correction unit that corrects the value of the oxygen storage capacity measured by the measurement unit based on the rich time and the lean time.

  Thereby, the catalyst deterioration diagnosis can be executed after correcting the measured value of the oxygen storage capacity to a value obtained when the sulfur concentration of the fuel is low, and the influence of sulfur can be eliminated to prevent erroneous diagnosis.

  Preferably, the correction means obtains the oxygen storage capacity measurement value when the sulfur concentration estimated by the sulfur concentration estimation means is greater than a predetermined value, and a value obtained when the sulfur concentration is less than or equal to the predetermined value. To correct.

  Preferably, the correction unit performs the correction by multiplying or adding the correction amount corresponding to the ratio of the rich time and the lean time to the oxygen storage capacity measurement value.

  According to the present invention, it is possible to provide an excellent effect that a highly accurate and reliable fuel property determination device and a catalyst deterioration diagnosis device including the same can be provided.

  The best mode for carrying out the present invention will be described below with reference to the accompanying drawings.

  FIG. 1 is a schematic diagram showing the configuration of the present embodiment. As shown in the figure, the internal combustion engine 1 generates power by burning a mixture of fuel and air inside a combustion chamber 3 formed in a cylinder block 2 and reciprocating a piston 4 in the combustion chamber 3. To do. The internal combustion engine 1 is a vehicular multi-cylinder engine (only one cylinder is shown), and is a spark ignition type internal combustion engine, more specifically, a gasoline engine.

  In the cylinder head of the internal combustion engine 1, an intake valve Vi for opening and closing the intake port and an exhaust valve Ve for opening and closing the exhaust port are provided for each cylinder. Each intake valve Vi and each exhaust valve Ve are opened and closed by a camshaft (not shown). A spark plug 7 for igniting the air-fuel mixture in the combustion chamber 3 is attached to the top of the cylinder head for each cylinder.

  The intake port of each cylinder is connected to a surge tank 8 serving as an intake air collecting chamber via a branch pipe for each cylinder. An intake pipe 13 that forms an intake manifold passage is connected to the upstream side of the surge tank 8, and an air cleaner 9 is provided at the upstream end of the intake pipe 13. An air flow meter 5 for detecting the intake air amount and an electronically controlled throttle valve 10 are incorporated in the intake pipe 13 in order from the upstream side. An intake passage is formed by the intake port, the surge tank 8 and the intake pipe 13.

  An injector (fuel injection valve) 12 that injects fuel into the intake passage, particularly into the intake port, is provided for each cylinder. The fuel injected from the injector 12 is mixed with intake air to form an air-fuel mixture. The air-fuel mixture is sucked into the combustion chamber 3 when the intake valve Vi is opened, compressed by the piston 4, and ignited and burned by the spark plug 7. It is done.

On the other hand, the exhaust port of each cylinder is connected to an exhaust pipe 6 forming an exhaust collecting passage through a branch pipe for each cylinder, and the exhaust pipe 6 has catalysts 11, 19 made of a three-way catalyst having an oxygen storage capacity. Are attached in series. An exhaust passage is formed by the exhaust port, the branch pipe, and the exhaust pipe 6. Air-fuel ratio sensors for detecting the air-fuel ratio of exhaust gas, that is, a pre-catalyst air-fuel ratio sensor 17 and a post-catalyst air-fuel ratio sensor 18 are installed on the upstream side and the downstream side of the upstream catalyst 11, respectively. The pre-catalyst air-fuel ratio sensor 17 is a so-called wide-area air-fuel ratio sensor, can continuously detect an air-fuel ratio over a relatively wide range, and outputs a signal having a value proportional to the air-fuel ratio. On the other hand, the post-catalyst air-fuel ratio sensor 18 is a so-called O ₂ sensor and has a characteristic that the output value changes suddenly at the theoretical air-fuel ratio. The post-catalyst air-fuel ratio sensor 18 is installed between the upstream catalyst 11 and the downstream catalyst 19.

  The spark plug 7, the throttle valve 10, the injector 12, and the like described above are electrically connected to an electronic control unit (hereinafter referred to as ECU) 20 as control means. The ECU 20 includes a CPU, a ROM, a RAM, an input / output port, a storage device, and the like, all not shown. In addition to the air flow meter 5, the pre-catalyst air-fuel ratio sensor 17, and the post-catalyst air-fuel ratio sensor 18, the ECU 20 includes a crank angle sensor 14 that detects the crank angle of the internal combustion engine 1, an accelerator opening, as shown in the figure. The accelerator opening sensor 15 for detecting the above and other various sensors are electrically connected via an A / D converter or the like (not shown). The ECU 20 controls the ignition plug 7, the throttle valve 10, the injector 12, etc. so as to obtain a desired output based on the detection values of various sensors, etc., and the ignition timing, fuel injection amount, fuel injection timing, throttle opening. Control the degree etc.

  The catalysts 11 and 19 simultaneously purify NOx, HC and CO with high efficiency when the air-fuel ratio A / F of the exhaust gas flowing into the catalysts 11 and 19 is the stoichiometric air-fuel ratio (stoichiometric, for example, A / Fs = 14.6). Correspondingly, during normal operation of the internal combustion engine, the ECU 20 sets the air-fuel ratio (pre-catalyst air-fuel ratio) A / Ffr of the air-fuel mixture in the combustion chamber 3 and the exhaust gas flowing into the upstream catalyst 11 to the stoichiometric air-fuel ratio. The air-fuel ratio is controlled so as to match. Specifically, the ECU 20 sets a target air-fuel ratio A / Ft equal to the theoretical air-fuel ratio, and the pre-catalyst air-fuel ratio A / Ffr detected by the pre-catalyst air-fuel ratio sensor 17 matches the target air-fuel ratio A / Ft. As described above, the amount of fuel injected from the injector 12 is feedback-controlled. As a result, the air-fuel ratio of the exhaust gas flowing into the catalyst 11 is kept in the vicinity of the theoretical air-fuel ratio, and the maximum purification performance is exhibited in the catalyst 11.

Here, the upstream catalyst 11 will be described in more detail. The following description applies to the downstream catalyst 19 as well. As shown in FIG. 2, in the catalyst 11, a coating material 31 is coated on the surface of a carrier base material (not shown), and the coating material 31 is held in a state in which a large number of particulate catalyst components 32 are dispersedly arranged. The catalyst 11 is exposed inside. The catalyst component 32 is mainly composed of a noble metal such as Pt or Pd, and serves as an active point for reacting exhaust gas components such as NOx, HC and CO. On the other hand, the coating material 31 plays the role of a promoter that promotes the reaction at the interface between the exhaust gas and the catalyst component 32 and includes an oxygen storage component capable of absorbing and releasing oxygen according to the air-fuel ratio of the atmospheric gas. The oxygen storage component is made of, for example, cerium dioxide CeO ₂ or zirconia. For example, if the atmosphere gas of the catalyst component 32 and the coating material 31 is richer than the stoichiometric air-fuel ratio, the oxygen stored in the oxygen storage component present around the catalyst component 32 is released, and as a result, the released oxygen As a result, unburned components such as HC and CO are oxidized and purified. On the contrary, when the atmosphere gas of the catalyst component 32 and the coating material 31 is leaner than the stoichiometric air-fuel ratio, the oxygen storage component present around the catalyst component 32 absorbs oxygen from the atmosphere gas, and as a result, NOx is reduced and purified. The

  By such an oxygen absorption / release action, even if the pre-catalyst air-fuel ratio A / Ffr slightly varies from the stoichiometric air-fuel ratio during normal air-fuel ratio control, three exhaust gas components such as NOx, HC and CO are simultaneously purified. can do. Therefore, in normal air-fuel ratio control, it is also possible to purify the exhaust gas by making the pre-catalyst air-fuel ratio A / Ffr oscillate minutely around the theoretical air-fuel ratio and repeating the absorption and release of oxygen.

  By the way, in the catalyst 11 in the new state, as described above, a large number of fine particulate catalyst components 32 are uniformly distributed, and the contact probability between the exhaust gas and the catalyst component 32 is kept high. However, when the catalyst 11 deteriorates, some of the catalyst components 32 are lost, and some of the catalyst components 32 are baked and solidified by exhaust heat (see broken lines in the figure). In this case, the contact probability between the exhaust gas and the catalyst component 32 is lowered, and the purification rate is lowered. In addition to this, the amount of the coating material 31 existing around the catalyst component 32, that is, the amount of the oxygen storage component decreases, and the oxygen storage capacity itself decreases.

Thus, the degree of deterioration of the catalyst 11 and the degree of decrease in the oxygen storage capacity of the catalyst 11 are in a correlation. Therefore, in the present embodiment, the deterioration degree of the upstream catalyst 11 is detected by detecting the oxygen storage capacity of the upstream catalyst 11 that has a particularly large influence on the emission. Here, the oxygen storage capacity of the catalyst 11 is represented by the size of the oxygen storage capacity (OSC; O ₂ Strage Capacity, the unit is g), which is the maximum amount of oxygen that the current catalyst 11 can store.

  The catalyst deterioration diagnosis of the present embodiment is basically based on the Cmax method described above. When the deterioration diagnosis of the catalyst 11 is performed, the active air-fuel ratio control is executed by the ECU 20. In the active air-fuel ratio control, the air-fuel ratio of the air-fuel mixture, and thus the pre-catalyst air-fuel ratio A / Ffr, is switched alternately (forcedly) to the rich side and the lean side at a predetermined center air-fuel ratio A / Fc. The air-fuel ratio when switched to the rich side is referred to as rich air-fuel ratio A / Fr, and the air-fuel ratio when switched to the lean side is referred to as lean air-fuel ratio A / Fl. While the pre-catalyst air-fuel ratio A / Ffr is switched to the rich side or the lean side by this active air-fuel ratio control, the oxygen storage capacity OSC of the catalyst is measured.

  The deterioration diagnosis of the catalyst 11 is executed during steady operation of the internal combustion engine 1 and when the catalyst 11 is in the active temperature range. Measurement of the temperature of the catalyst 11 (catalyst bed temperature) may be detected directly using a temperature sensor, but in the present embodiment, it is estimated from the operating state of the internal combustion engine. For example, the ECU 20 estimates the temperature Tc of the catalyst 11 using a preset map based on the intake air amount Ga detected by the air flow meter 5. It should be noted that parameters other than the intake air amount Ga, for example, the engine rotational speed Ne (rpm) may be included in the parameters used for the catalyst temperature estimation.

  3A and 3B, the outputs of the pre-catalyst air-fuel ratio sensor 17 and the post-catalyst air-fuel ratio sensor 18 when the active air-fuel ratio control is executed are indicated by solid lines. In FIG. 3A, the target air-fuel ratio A / Ft generated inside the ECU 20 is indicated by a broken line. The output values of the pre-catalyst air-fuel ratio sensor 17 and the post-catalyst air-fuel ratio sensor 18 correspond to the values of the pre-catalyst air-fuel ratio A / Ffr and the post-catalyst air-fuel ratio A / Frr, respectively.

  As shown in FIG. 3A, the target air-fuel ratio A / Ft is centered on the stoichiometric air-fuel ratio (stoichiometric) A / Fs as the center air-fuel ratio, and a predetermined amplitude (rich amplitude Ar, An air-fuel ratio (rich air-fuel ratio A / Fr) separated by Ar> 0), and an air-fuel ratio (lean air-fuel ratio A / Fl) separated from it by a predetermined amplitude (lean amplitude Al, Al> 0) Forcibly and alternately. Following the switching of the target air-fuel ratio A / Ft, the pre-catalyst air-fuel ratio A / Ffr as an actual value is also switched with a slight time delay with respect to the target air-fuel ratio A / Ft. From this, it will be understood that the target air-fuel ratio A / Ft and the pre-catalyst air-fuel ratio A / Ffr are equivalent except that there is a time delay.

  In the illustrated example, the rich amplitude Ar and the lean amplitude Al are equal. For example, theoretical air fuel ratio A / Fs = 14.6, rich air fuel ratio A / Fr = 14.1, lean air fuel ratio A / Fl = 15.1, rich amplitude Ar = lean amplitude Al = 0.5. Compared with the normal air-fuel ratio control, the active air-fuel ratio control has a larger amplitude of the air-fuel ratio, that is, the values of the rich amplitude Ar and the lean amplitude Al are larger.

  By the way, the timing at which the target air-fuel ratio A / Ft is switched is the timing at which the output of the post-catalyst air-fuel ratio sensor 18 is switched from rich to lean, or from lean to rich. As shown in the drawing, the output voltage of the post-catalyst air-fuel ratio sensor 18 changes suddenly at the stoichiometric air-fuel ratio A / Fs, and the rich-side air-fuel ratio is smaller than the stoichiometric air-fuel ratio A / Fs. The output voltage becomes greater than or equal to the rich determination value VR. When the post-catalyst air-fuel ratio A / Frr is the lean air-fuel ratio greater than the theoretical air-fuel ratio A / Fs, the output voltage becomes less than the lean determination value VL. Here, VR> VL, for example, VR = 0.59 (V) and VL = 0.21 (V).

  As shown in FIGS. 3A and 3B, when the output voltage of the post-catalyst air-fuel ratio sensor 18 changes from the rich side value to the lean side and becomes equal to the lean determination value VL (time t1), The target air-fuel ratio A / Ft is switched from the lean air-fuel ratio A / Fl to the rich air-fuel ratio A / Fr. Thereafter, when the output voltage of the post-catalyst air-fuel ratio sensor 18 changes from the lean value to the rich side and becomes equal to the rich determination value VR (time t2), the target air-fuel ratio A / Ft becomes the rich air-fuel ratio A / Fr. To a lean air-fuel ratio A / Fl. In this way, every time the post-catalyst air-fuel ratio A / Frr detected by the post-catalyst air-fuel ratio sensor 18 is reversed to the lean side or the rich side, the air-fuel ratio is actively switched to the rich side or the lean side.

  While performing the active air-fuel ratio control that performs such an air-fuel ratio change, the oxygen storage capacity OSC of the catalyst 11 is measured as follows, and the deterioration of the catalyst 11 is determined.

  Referring to FIG. 3, the target air-fuel ratio A / Ft is set to the lean air-fuel ratio A / Fl before time t1, and the lean gas flows into the catalyst 11. At this time, the catalyst 11 continues to absorb oxygen, but when it fully absorbs oxygen, it can no longer absorb oxygen, and the lean gas flows through the catalyst 11 and flows downstream of the catalyst 11. When this happens, the post-catalyst air-fuel ratio A / Frr changes to the lean side, and when the output voltage of the post-catalyst air-fuel ratio sensor 18 reaches the lean determination value VL (t1), the target air-fuel ratio A / Ft becomes the rich air-fuel ratio A. Switched to / Fr or inverted.

  This time, rich gas flows into the catalyst 11. At this time, the oxygen stored in the catalyst 11 continues to be released from the catalyst 11. Therefore, the exhaust gas of the theoretical air-fuel ratio A / Fs flows out to the downstream side of the catalyst 11 and the post-catalyst air-fuel ratio A / Frr does not become rich, so the output of the post-catalyst air-fuel ratio sensor 18 is not reversed. When oxygen is continuously released from the catalyst 11, all the stored oxygen is eventually released from the catalyst 11, and at that time, oxygen can no longer be released, and rich gas flows through the catalyst 11 and flows downstream of the catalyst 11. When this happens, the post-catalyst air-fuel ratio A / Frr changes to the rich side, and the target air-fuel ratio A / Ft becomes the lean air-fuel ratio A when the output voltage of the post-catalyst air-fuel ratio sensor 18 reaches the rich determination value VR (t2). / Fl.

  The larger the oxygen storage capacity OSC, the longer the time during which oxygen can be absorbed or released. That is, when the catalyst is not deteriorated, the inversion cycle of the target air-fuel ratio A / Ft (for example, the time from t1 to t2) becomes longer, and the inversion cycle of the target air-fuel ratio A / Ft becomes shorter as the deterioration of the catalyst proceeds. .

  Therefore, using this fact, the oxygen storage capacity OSC is measured as follows. As shown in FIG. 4, immediately after the target air-fuel ratio A / Ft is switched to the rich air-fuel ratio A / Fr at time t1, the pre-catalyst air-fuel ratio A / Ffr as the actual value is slightly delayed with the rich air-fuel ratio A / Fr. Switch to Fr. From the time t11 when the pre-catalyst air-fuel ratio A / Ffr reaches the theoretical air-fuel ratio A / Fs to the time t2 when the target air-fuel ratio A / Ft next reverses, the following equation (1) An oxygen storage capacity dOSC (instantaneous value of the oxygen storage capacity) is calculated, and the oxygen storage capacity dOSC for each minute time is integrated from time t11 to time t2. Thus, the oxygen storage capacity, that is, the amount of released oxygen in this oxygen release cycle is measured.

  Here, Q is a fuel injection amount. When the air-fuel ratio difference ΔA / F is multiplied by the fuel injection amount Q, an air amount that is insufficient or excessive with respect to the stoichiometry can be calculated. K is a constant representing the proportion of oxygen contained in air (about 0.23).

  Basically, the oxygen storage capacity OSC measured at one time is used and compared with a predetermined deterioration judgment value OSCs. If the oxygen storage capacity OSC exceeds the deterioration judgment value OSCs, the oxygen storage capacity is normal. If the OSC is equal to or lower than the deterioration determination value OSCs, the deterioration of the catalyst can be determined such as deterioration. However, in this embodiment, in order to improve the accuracy, the oxygen storage capacity (the stored oxygen amount in this case) is also measured in the oxygen storage cycle in which the target air-fuel ratio A / Ft is on the lean side. The average value is measured as an oxygen storage capacity of one unit related to one absorption / release cycle. Further, the absorption / release cycle is repeated a plurality of times to obtain a value of oxygen storage capacity of a plurality of units, and the average value is used as the final oxygen storage capacity measurement value.

  Regarding the measurement of the oxygen storage capacity (oxygen storage amount) in the oxygen storage cycle, as shown in FIG. 4, after the target air-fuel ratio A / Ft is switched to the lean air-fuel ratio A / Fl at time t2, the pre-catalyst air-fuel ratio is measured. From time t21 when A / Ffr reaches the theoretical air-fuel ratio A / Fs to time t3 when the target air-fuel ratio A / Ft reverses to the rich side next, the oxygen storage capacity dOSC for each minute time is calculated from the previous equation (1). The calculated oxygen storage capacity dOSC for each minute time is integrated. Thus, the oxygen storage capacity OSC, that is, the amount of stored oxygen (OSC2 in FIG. 4) in this oxygen storage cycle is measured. Ideally, the oxygen storage capacity OSC1 of the oxygen release cycle and the oxygen storage capacity OSC2 of the oxygen storage cycle are substantially equal to each other.

  Next, the deterioration of the catalyst is determined using the measured oxygen storage capacity. That is, the oxygen storage capacity measurement value OSC is compared with the predetermined deterioration determination value OSCs. If the oxygen storage capacity measurement value OSC is larger than the deterioration determination value OSCs, the catalyst is normal, and if the oxygen storage capacity measurement value OSC is less than or equal to the deterioration determination value OSCs. The catalyst is judged to be deteriorated. When it is determined that the catalyst is deteriorated, it is preferable to activate a warning device such as a check lamp in order to notify the user of the fact. The above is the basic content of the catalyst deterioration diagnosis.

  Next, the fuel property determination in this embodiment, particularly the estimation of the sulfur concentration of the fuel will be described.

  The present inventors investigated how the output changes of the pre-catalyst air-fuel ratio sensor 17 and the post-catalyst air-fuel ratio sensor 18 during active air-fuel ratio control change depending on the sulfur concentration of the fuel. Here, a fuel having a low sulfur concentration scheduled to be used in advance, that is, a fuel having a sulfur concentration equal to or lower than a predetermined value is referred to as a normal fuel. A fuel having a sulfur concentration higher than the predetermined value is referred to as a high sulfur fuel.

  The time when the air-fuel ratio is switched to the richer side than the stoichiometric air-fuel ratio, specifically, the time when the target air-fuel ratio A / Ft is set to the rich air-fuel ratio A / Fr is referred to as a rich time TR. The rich time TR corresponds to the period from t1 to t2 shown in FIG. Further, the time when the air-fuel ratio is switched to the lean side from the stoichiometric air-fuel ratio, specifically, the time when the target air-fuel ratio A / Ft is set to the lean air-fuel ratio A / Fl is referred to as a lean time TL. . This lean time TL corresponds to the period from t2 to t3 shown in FIG. The ratio between the rich time TR and the lean time TL is referred to as a time ratio H, which is defined as H = TR / TL.

  According to the test results, as shown in FIG. 3, the lean time TL for the normal fuel and the lean time TL ′ for the high sulfur fuel are not so different, but the rich time TR and the high sulfur for the normal fuel are not. It was found that there is a difference between the rich time TR ′ in the case of fuel and the rich time TR ′ in the case of high sulfur fuel tends to be significantly shorter than the rich time TR in the case of normal fuel. Therefore, the time ratio H is smaller in the case of high sulfur fuel than in the case of normal fuel. Since the time ratio H is a value that correlates with the sulfur concentration of the fuel in this way, the sulfur concentration of the fuel can be estimated by using the rich time TR and the lean time TL as a parameter representing the sulfur concentration, and hence the time ratio H. It is.

  FIG. 5 shows the relationship between the fuel sulfur concentration and the time ratio H. As indicated by white circles in the figure, the time ratio H tends to decrease as the sulfur concentration of the fuel increases. Therefore, a predetermined threshold value Hs relating to the time ratio H is set, and when the time ratio H falls below the threshold value Hs, it can be determined that the fuel is a high sulfur fuel. At the time of such determination, by taking necessary measures such as canceling the catalyst deterioration diagnosis, it is possible to prevent erroneous diagnosis in the catalyst deterioration diagnosis.

  The reason why the rich time TR and the lean time TL are affected by the fuel sulfur concentration as described above is considered as follows. First, when the air-fuel ratio is lean and oxygen is stored in the catalyst, this is simply a mechanism in which oxygen in the lean gas is adsorbed by the oxygen storage component of the catalyst. On the other hand, in the case of high-sulfur fuel, the sulfur component is adsorbed on the oxygen storage component of the catalyst, the amount of oxygen adsorption decreases accordingly, and the lean time TL becomes slightly shorter than that of normal fuel. However, the reaction rate in the catalyst, that is, the oxygen adsorption rate is not reduced so much by the influence of sulfur. Therefore, the reduction amount of the lean time TL when changing from the normal fuel to the high sulfur fuel is not so large. Therefore, the value of the oxygen storage capacity OSC measured in the oxygen storage cycle does not decrease so much.

  However, when the air-fuel ratio is rich and oxygen is released from the catalyst, the oxygen adsorbed by the oxygen storage component of the catalyst is extracted by the rich gas via the catalyst component 32 made of noble metal and reacts with the rich gas. . On the other hand, in the case of a high sulfur fuel, the catalyst component 32 and the oxygen storage component are poisoned by the sulfur compound, the reaction rate and the oxygen release rate through the catalyst component 32 are remarkably reduced, and the rich gas not consumed in the reaction is fast. The catalyst will slip through the timing. Therefore, when the normal fuel is changed to the high sulfur fuel, the reduction time of the rich time TR is large, and the value of the oxygen storage capacity OSC measured in the oxygen release cycle is also greatly reduced.

  Hereinafter, the content of the fuel property determination process in the present embodiment will be described with reference to FIG. The illustrated routine is repeatedly executed by the ECU 20 at a predetermined cycle (for example, every 16 msec).

  First, in step S101, it is determined whether or not a precondition suitable for performing the fuel property determination process is satisfied. For example, the fluctuation range of the intake air amount Ga and the engine rotation speed Ne is within a predetermined range, and the engine is in a steady operation state, and the catalyst 11 and the catalyst front-rear air-fuel ratio sensors 17 and 18 have reached a predetermined activation temperature. If so, the precondition is satisfied. Note that the precondition is not limited to this example. If the precondition is not satisfied, the process is terminated. On the other hand, if the precondition is satisfied, the process proceeds to step S102.

  In step S102, the active air-fuel ratio control as described above is executed, and the rich time TR and the lean time TL during the active air-fuel ratio control are measured and acquired, respectively. In this case, it is preferable that the rich time TR and the lean time TL are measured plural times by repeatedly performing the rich control and the lean control, and the average value of the rich time TR and the lean time TL is set as the final value.

  Next, in step S103, a time ratio H = TR / TL, which is a ratio of the rich time TR and the lean time TL, is calculated, and the time ratio H is compared with a predetermined threshold value Hs.

  When the time ratio H is equal to or greater than the threshold value Hs, it is determined in step S104 that normal fuel having a sulfur concentration equal to or less than a predetermined value is used, and the process is terminated. On the other hand, when the time ratio H is smaller than the threshold value Hs, it is determined in step S105 that a high sulfur fuel having a sulfur concentration larger than a predetermined value is used, and the process is terminated.

  In this example, the fuel is classified into two steps according to whether the sulfur concentration is low or high. However, the fuel may be distinguished steplessly according to the time ratio H. The ratio of the rich time TR and the lean time TL may be TL / TR which is the reciprocal of the time ratio H. In this case, the smaller the TL / TR, the higher the sulfur concentration of the fuel. These modifications can also be applied to catalyst deterioration diagnosis described later.

  Next, the content of the catalyst deterioration diagnosis process in the present embodiment will be described with reference to FIG. The illustrated routine is repeatedly executed by the ECU 20 at a predetermined cycle (for example, every 16 msec).

  First, in step S201, whether or not the precondition is satisfied is determined as in step S101. If the precondition is not satisfied, the process is terminated. If the precondition is satisfied, the process proceeds to step S202.

  In step S202, active air-fuel ratio control is executed as in step S102, and the rich time TR and lean time TL are measured. At the same time, the value of the oxygen storage capacity OSC is measured. That is, the measurement of the rich time TR and the lean time TL and the measurement of the oxygen storage capacity OSC are performed simultaneously.

  In step S203, the time ratio H = TR / TL is calculated as in step S103, and the time ratio H is compared with a predetermined threshold value Hs. When the time ratio H is equal to or greater than the threshold value Hs, it is determined in step S204 that normal fuel having a sulfur concentration equal to or less than a predetermined value is being used.

  On the other hand, when the time ratio H is smaller than the threshold value Hs, it is determined in step S205 that a high sulfur fuel having a sulfur concentration larger than a predetermined value is being used. In step S206, the oxygen storage capacity measurement value OSC is corrected based on the time ratio H (referred to as fuel correction). That is, when it is determined that the sulfur concentration of the fuel is high, the catalyst deterioration diagnosis is not stopped, but the oxygen storage capacity measurement value OSC is corrected to a value that can be obtained when the fuel is normal (the broken line in FIG. 5). (Refer to circle) Diagnosis of catalyst deterioration is performed. In this way, more diagnostic frequency can be secured, and the influence of sulfur can be eliminated to prevent misdiagnosis.

  Since the time ratio H and the sulfur concentration of the fuel are correlated with each other, the sulfur concentration of the fuel may be calculated based on the time ratio H, and the oxygen storage capacity measurement value OSC may be corrected based on the sulfur concentration. In this case, the correction is still performed based on the rich time TR and the lean time TL.

  The correction method includes, for example, a method of multiplying the oxygen storage capacity measurement value OSC by the correction coefficient B and a method of adding the correction addition value D to the oxygen storage capacity measurement value OSC. The correction coefficient B and the correction addition value D are collectively referred to as a correction amount. When the former method is adopted, for example, a map (function may be used. The same applies hereinafter) that defines the relationship between the time ratio H and the correction coefficient B as shown in FIG. Keep it. Then, the correction coefficient B is calculated from the actually obtained time ratio H, and the corrected oxygen storage capacity OSC is obtained by multiplying the correction coefficient B by the oxygen storage capacity measurement value OSC. When the map shown in FIG. 8 is used, when H ≧ Hs, B = 1.0 is not substantially corrected, and when H <Hs, a constant correction coefficient B = B1 (> 1.0) is an oxygen storage capacity. Correction is performed by multiplying the measured value OSC.

  Instead of this map, a map as shown in FIG. 9 may be used. In this case, the point that B = 1.0 is the same when H ≧ Hs. On the other hand, when H <Hs, the correction coefficient B increases as the time ratio H decreases (that is, the fuel sulfur concentration increases). Used.

  On the other hand, when the latter method of adding the correction addition value D is employed, the correction addition value D can be calculated using, for example, a map as shown in FIG. Here, when H ≧ Hs, D = 0 is not substantially corrected, and when H <Hs, a constant correction addition value D = D1 (> 0) is added to the oxygen storage capacity measurement value OSC to perform correction. Is called.

  Instead of this map, a map as shown in FIG. 11 may be used. In this case, the point that D = 0 is the same when H ≧ Hs. On the other hand, when H <Hs, the corrected addition value D is used which increases as the time ratio H decreases (that is, as the fuel sulfur concentration increases). It is done.

  Now, referring back to FIG. 7, after step S204 or S206, the process proceeds to step S207, where the oxygen storage capacity measurement value OSC (or the corrected value after step S206) is compared with a predetermined deterioration determination value OSCs.

  If OSC> OSCs, the catalyst 11 is determined to be normal in step S208, and if OSC ≦ OSCs, the catalyst 11 is determined to be degraded. When it is determined that the catalyst has deteriorated, a warning device such as a check lamp is activated to prompt the user to replace the catalyst, and at the same time, a diagnostic code corresponding to the catalyst deterioration is stored in the ECU 20.

  Preferably, regardless of whether the catalyst is normal or deteriorated, a warning device such as a check lamp is also activated when it is determined in step S205 that the high sulfur fuel is being used. This is for urging the user to replace the fuel or to regenerate the catalyst with sulfur poisoning. The ECU 20 stores a diagnostic code corresponding to the use of high sulfur fuel. For example, when a warning is given due to the use of high sulfur fuel when the catalyst is normal, when the user transports the vehicle to the dealer, the dealer can confirm the fact based on the diagnostic code. Then, without replacing the catalyst, however, the engine and the catalyst can be returned to their original normal state by performing fuel replacement and sulfur poisoning regeneration of the catalyst (or instructing the user to perform these).

  As described above, according to the present embodiment, the sulfur concentration of the fuel is estimated based on the rich time TR when the air-fuel ratio is switched to the rich side and the lean time TL when the air-fuel ratio is switched to the lean side. Therefore, the sulfur concentration of the fuel can be estimated without relying only on the output absolute value of the post-catalyst air-fuel ratio sensor 18 on the downstream side of the catalyst. Therefore, it becomes difficult to be influenced by manufacturing variations of the post-catalyst air-fuel ratio sensor 18 and the like, and it is possible to accurately estimate the sulfur concentration and perform highly accurate and reliable fuel property determination. Further, since it is not necessary to measure the oxygen storage capacity of the catalyst when estimating the sulfur concentration of the fuel, the fuel property can be determined by a simple method. Further, the oxygen storage capacity measurement value is corrected based on the rich time TR and the lean time TL, or the sulfur concentration of the fuel estimated based on these, and the catalyst deterioration diagnosis is performed based on the corrected oxygen storage capacity measurement value. Since it performs, a catalyst deterioration diagnosis can be performed based on the value of the oxygen storage capacity without the influence of sulfur. Therefore, misdiagnosis can be prevented in advance, and more diagnosis frequency can be secured as compared with the case where the diagnosis is stopped.

Although the embodiment of the present invention has been described in detail above, various other embodiments of the present invention are conceivable. For example, the use and type of the internal combustion engine are arbitrary, and may be other than for vehicles, for example, a direct injection type or the like. A wide-area air-fuel ratio sensor similar to the pre-catalyst air-fuel ratio sensor may be used as the post-catalyst air-fuel ratio sensor, or an O ₂ sensor similar to the post-catalyst air-fuel ratio sensor may be used as the pre-catalyst air-fuel ratio sensor. A wide range of sensors that detect the exhaust air-fuel ratio, including these wide-range air-fuel ratio sensors and O ₂ sensors, are referred to as air-fuel ratio sensors.

  The present invention includes all modifications, applications, and equivalents included in the spirit of the present invention defined by the claims. Therefore, the present invention should not be construed as being limited, and can be applied to any other technique belonging to the scope of the idea of the present invention.

It is the schematic which shows the structure of embodiment of this invention. It is a schematic sectional drawing which shows the structure of a catalyst. It is a time chart for demonstrating active air fuel ratio control. FIG. 4 is a time chart similar to FIG. 3 for illustrating a method for measuring the oxygen storage capacity. It is a graph which shows the relationship between the sulfur concentration of fuel, and time ratio. It is a flowchart of a fuel property determination process. It is a flowchart of a catalyst deterioration diagnosis process. An example of a correction coefficient calculation map is shown. The other example of a correction coefficient calculation map is shown. An example of a correction addition value calculation map is shown. The other example of a correction addition value calculation map is shown.

Explanation of symbols

1 Internal combustion engine 6 Exhaust pipe 11 Upstream catalyst 12 Injector 17 Pre-catalyst air-fuel ratio sensor 18 Post-catalyst air-fuel ratio sensor 19 Downstream catalyst 20 Electronic control unit (ECU)
TR Rich time TL Lean time H Time ratio OSC Oxygen storage capacity B Correction coefficient D Correction addition value

Claims (5)

A catalyst provided in the exhaust passage of the internal combustion engine;
A post-catalyst air-fuel ratio sensor provided downstream of the catalyst;
Active air-fuel ratio control means for actively switching the air-fuel ratio to the rich side or the lean side every time the air-fuel ratio detected by the post-catalyst air-fuel ratio sensor is reversed to the lean side or the rich side;
Based on the rich time when the air-fuel ratio is switched to the rich side by the active air-fuel ratio control means and the lean time when the air-fuel ratio is switched to the lean side by the active air-fuel ratio control means, A fuel property judging device comprising: a sulfur concentration estimating means for estimating a sulfur concentration. The fuel property determination device according to claim 1, wherein the sulfur concentration estimation unit estimates a sulfur concentration of the fuel based on a ratio between the rich time and the lean time. A catalyst deterioration diagnosis device comprising the fuel property determination device according to claim 1,
Measuring means for measuring the oxygen storage capacity of the catalyst in accordance with air-fuel ratio switching control by the active air-fuel ratio control means;
A catalyst deterioration diagnosis apparatus comprising: a correction unit that corrects the value of the oxygen storage capacity measured by the measurement unit based on the rich time and the lean time. The correction means corrects the measured oxygen storage capacity to a value obtained when the sulfur concentration is less than or equal to the predetermined value when the sulfur concentration estimated by the sulfur concentration estimation means is greater than a predetermined value. The catalyst deterioration diagnosis device according to claim 3. 5. The catalyst according to claim 3, wherein the correction unit performs correction by multiplying or adding the correction amount according to a ratio of the rich time and the lean time to the oxygen storage capacity measurement value. Deterioration diagnostic device.

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