JP5494571B2 - Fuel property determination device and catalyst abnormality diagnosis device provided with the same - Google Patents

Description

  The present invention relates to a fuel property determination device that determines the fuel property of fuel used in an internal combustion engine and a catalyst abnormality diagnosis device equipped with the fuel property determination device, and in particular, a fuel property determination device that can estimate the sulfur concentration of fuel used in an internal combustion engine and The present invention relates to a catalyst abnormality diagnosis apparatus provided with this.

For example, in an internal combustion engine for automobiles, 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). When the air-fuel ratio of the exhaust gas flowing into the catalyst becomes larger than the stoichiometric air-fuel ratio (stoichiometric), that is, when the engine becomes lean, the catalyst having oxygen storage capacity occludes excess oxygen present in the exhaust gas. When the fuel ratio becomes smaller than stoichiometric, that is, when it becomes rich, the stored 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, if a three-way catalyst having an oxygen storage capacity is used, the actual air-fuel ratio slightly deviates from the stoichiometric depending on the operating conditions. However, such an air-fuel ratio shift can be absorbed by the oxygen storage / release action of the three-way catalyst.

  On the other hand, when the catalyst deteriorates, the purification rate of the catalyst decreases. There is a correlation between the deterioration degree of the catalyst and the reduction degree of the oxygen storage capacity. Therefore, it is possible to detect deterioration or abnormality of the catalyst by detecting a decrease in oxygen storage capacity. In general, a method (so-called Cmax method) that performs active air-fuel ratio control that alternately switches the air-fuel ratio between rich and lean, measures the oxygen storage capacity of the catalyst, and diagnoses deterioration of the catalyst is employed.

  By the way, depending on a use area etc., sulfur (S) may be contained in fuel by comparatively high concentration. When such a high sulfur fuel is supplied, the catalyst may be sulfur poisoned (S poison) due to the influence of the sulfur component in the exhaust gas. When S poisoning occurs, the oxygen storage / release action of the catalyst is hindered, and the apparent oxygen storage capacity of the catalyst decreases. However, when the fuel with a low sulfur concentration is refueled or the catalyst is exposed to a high temperature and rich atmosphere, the poisoning state is eliminated.

  The catalyst performance degradation due to S poisoning is temporary and recoverable. Therefore, in the abnormality diagnosis of the catalyst, it is necessary not to mistakenly diagnose the temporary abnormality due to the S poisoning as an unrecoverable permanent abnormality (thermal deterioration) that should be diagnosed.

  For example, in the apparatus described in Patent Document 1, the stored oxygen amount of the catalyst is measured by the Cmax method, and when the predetermined condition is satisfied, the stored oxygen amount is measured again by delaying the timing for switching the air-fuel ratio from rich to lean. . Then, the former measurement value is corrected based on these measurement values, and the deterioration diagnosis is made after correcting the measurement value to a value corresponding to the use of the low sulfur fuel.

JP 2009-36172 A

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

  Therefore, the present invention has been made in view of such circumstances, and an object thereof is to provide a fuel property determination device that can suitably estimate the sulfur concentration of fuel, and a catalyst abnormality diagnosis device including the same. It is in.

According to a first aspect of the invention,
An upstream catalyst and a downstream catalyst respectively provided on the upstream side and the downstream side of the exhaust passage of the internal combustion engine;
Measuring means for measuring index values representing the degree of deterioration of the upstream catalyst and the downstream catalyst,
Index value estimating means for estimating the index value of the downstream catalyst based on the index value of the upstream catalyst measured by the measuring means;
A sulfur concentration estimating means for estimating the sulfur concentration of the fuel used based on the estimated index value of the downstream catalyst estimated by the index value estimating means and the measured index value of the downstream catalyst measured by the measuring means;
There is provided a fuel property determination device characterized by comprising:

  Preferably, the sulfur concentration estimating means estimates the sulfur concentration of the fuel used based on the difference between the estimated index value of the downstream catalyst and the measured index value.

  Preferably, the sulfur concentration estimation means estimates that the sulfur concentration of the fuel used is equal to or greater than a predetermined concentration when the difference is equal to or greater than a predetermined threshold.

  Preferably, the sulfur concentration estimating means variably sets the threshold value according to the value of the measurement index value of the upstream catalyst.

  Preferably, the sulfur concentration estimating means sets the threshold value to a larger value as the value of the measurement index value of the upstream catalyst is larger.

  Preferably, the index value includes an oxygen storage capacity.

  Preferably, the index value includes a catalyst temperature at a time when a predetermined time has elapsed since the cold start of the internal combustion engine.

According to a second aspect of the invention,
A catalyst abnormality diagnosis device comprising a fuel property determination device according to a first aspect and diagnosing whether at least one of the upstream catalyst and the downstream catalyst is normal or abnormal,
When the sulfur concentration estimating means estimates that the sulfur concentration of the fuel used is equal to or higher than a predetermined concentration, a diagnosis of a catalyst abnormality is provided that prohibits diagnosis.

According to a third aspect of the invention,
A catalyst abnormality diagnosis device comprising a fuel property determination device according to a first aspect and diagnosing whether at least one of the upstream catalyst and the downstream catalyst is normal or abnormal,
When the sulfur concentration estimation means estimates that the sulfur concentration of the fuel used is equal to or higher than a predetermined concentration, a temperature abnormality condition for diagnosis is changed to a higher temperature side.

  Preferably, the catalyst abnormality diagnosis device measures an index value of at least one of the upstream catalyst and the downstream catalyst by the measuring unit under the changed temperature condition, and based on the measured index value, the upstream catalyst And whether at least one of the downstream catalyst is normal or abnormal.

According to a fourth aspect of the invention,
An upstream catalyst and a downstream catalyst respectively provided on the upstream side and the downstream side of the exhaust passage of the internal combustion engine;
Measuring means for measuring an index value indicating the degree of deterioration of the upstream catalyst;
Temperature detecting means for detecting the temperature of the downstream catalyst;
Temperature estimating means for estimating the temperature of the downstream catalyst based on the index value of the upstream catalyst measured by the measuring means;
A sulfur concentration estimating means for estimating the sulfur concentration of the fuel used based on the estimated temperature of the downstream catalyst estimated by the temperature estimating means and the detected temperature of the downstream catalyst detected by the temperature detecting means;
There is provided a fuel property determination device characterized by comprising:

  Preferably, the sulfur concentration estimating means estimates the sulfur concentration of the fuel used based on the difference between the estimated temperature of the downstream catalyst and the detected temperature.

  Preferably, the sulfur concentration estimation means estimates that the sulfur concentration of the fuel used is equal to or greater than a predetermined concentration when the difference is equal to or greater than a predetermined threshold.

  Preferably, the sulfur concentration estimating means variably sets the threshold value in accordance with the index value of the upstream catalyst.

  Preferably, the sulfur concentration estimating means sets the threshold value to a larger value as the index value of the upstream catalyst is larger.

  Preferably, the index value includes an oxygen storage capacity.

  Preferably, the temperature of the downstream catalyst is a temperature at the time of measuring the index value of the upstream catalyst.

According to a fifth aspect of the present invention,
A catalyst abnormality diagnosis device comprising a fuel property determination device according to a fourth aspect and diagnosing whether at least one of the upstream catalyst and the downstream catalyst is normal or abnormal,
When the sulfur concentration estimating means estimates that the sulfur concentration of the fuel used is equal to or higher than a predetermined concentration, a diagnosis of a catalyst abnormality is provided that prohibits diagnosis.

According to a sixth aspect of the present invention,
A catalyst abnormality diagnosis device comprising a fuel property determination device according to a fourth aspect and diagnosing whether at least one of the upstream catalyst and the downstream catalyst is normal or abnormal,
When the sulfur concentration estimation means estimates that the sulfur concentration of the fuel used is equal to or higher than a predetermined concentration, a temperature abnormality condition for diagnosis is changed to a higher temperature side.

  Preferably, the catalyst abnormality diagnosis device measures an index value of at least one of the upstream catalyst and the downstream catalyst by the measuring unit under the changed temperature condition, and based on the measured index value, the upstream catalyst And whether at least one of the downstream catalyst is normal or abnormal.

  According to the present invention, it is possible to provide a fuel property determination device that can suitably estimate the sulfur concentration of fuel, and a catalyst abnormality diagnosis device that includes the fuel property determination device.

It is the schematic which shows the structure of 1st Embodiment of this invention. It is a schematic sectional drawing which shows the structure of a catalyst. It is a time chart of 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 output characteristic of a pre-catalyst sensor and a post-catalyst sensor. It is a graph which shows the relationship between the oxygen storage capacity of an upstream catalyst and a downstream catalyst. It is a map for estimating a downstream catalyst oxygen storage capacity. It is a flowchart of the catalyst abnormality diagnosis process of 1st Embodiment. It is the schematic which shows the structure of 2nd Embodiment of this invention. It is a graph which shows the relationship between the temperature of an upstream catalyst and a downstream catalyst. It is a flowchart of the catalyst abnormality diagnosis process of 2nd Embodiment. It is a flowchart of the catalyst abnormality diagnosis process of 3rd Embodiment. It is a graph which shows the relationship between upstream catalyst oxygen storage capacity and downstream catalyst temperature. It is a map for estimating downstream catalyst temperature. It is a flowchart of the catalyst abnormality diagnosis process of 3rd Embodiment.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the accompanying drawings.
[First Embodiment]
FIG. 1 is a schematic diagram showing the configuration of the first embodiment. As shown in the figure, an engine 1 that is an internal combustion engine burns a mixture of fuel and air in a combustion chamber 3 formed in a cylinder block 2 and reciprocates a piston 4 in the combustion chamber 3 to drive power. Is generated. The engine 1 of the present embodiment is a multi-cylinder engine for automobiles (only one cylinder is shown), and is a spark ignition type internal combustion engine, more specifically, a gasoline engine.

  The cylinder head of the engine 1 is provided with an intake valve Vi that opens and closes an intake port and an exhaust valve Ve that opens and closes an exhaust port 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 manifold through an intake manifold. 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. The intake pipe 13 is provided with an air flow meter 5 for detecting the amount of air flowing into the engine, that is, the amount of intake air, and an electronically controlled throttle valve 10 in order from the upstream side. An intake passage is formed by the intake port, the intake manifold, the surge tank 8 and the intake pipe 13.

  An injector for injecting fuel into an intake passage, particularly an intake port, that is, a fuel injection valve 12 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 an exhaust manifold. An exhaust passage is formed by the exhaust port, the exhaust manifold, and the exhaust pipe 6. The exhaust pipe 6 is provided with a catalyst composed of a three-way catalyst having oxygen storage capacity, that is, an upstream catalyst 11 and a downstream catalyst 19 in series on the upstream side and the downstream side. For example, the upstream catalyst 11 is disposed immediately after the exhaust manifold, and the downstream catalyst 19 is disposed under the floor of the vehicle.

An air-fuel ratio sensor that detects the air-fuel ratio of the exhaust gas based on the oxygen concentration, that is, a pre-catalyst sensor 17 and a post-catalyst sensor 18 is provided on the upstream side and the downstream side (front and rear) of the upstream catalyst 11, respectively. As shown in FIG. 5, the pre-catalyst sensor 17 is a so-called wide-range air-fuel ratio sensor, can continuously detect the 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 sensor 18 is a so-called O ₂ sensor, and has a characteristic (Z characteristic) in which the output value changes suddenly with the theoretical air-fuel ratio as a boundary.

  Further, a downstream post-catalyst sensor 23 similar to the post-catalyst sensor 18 is provided on the downstream side (rear) of the downstream catalyst 11.

  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 sensor 17, the post-catalyst sensor 18, and the downstream post-catalyst sensor 23, the ECU 20 includes a crank angle sensor 14 that detects the crank angle of the engine 1, an accelerator opening, as shown in the figure. An accelerator opening sensor 15 for detecting the degree 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 injector 12, the throttle valve 10, 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.

  When the air-fuel ratio A / F of the exhaust gas flowing into the upstream catalyst 11 and the downstream catalyst 19 is the stoichiometric air-fuel ratio (stoichiometric, for example, A / Fs = 14.6), NOx, HC and CO are simultaneously highly efficient. Purify. Therefore, in accordance with this characteristic, the ECU 20 adjusts the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber 3 (specifically, so that the air-fuel ratio of the exhaust gas flowing into the upstream catalyst 11 matches the stoichiometry during normal operation of the engine. Is feedback-controlled based on the outputs of the pre-catalyst sensor 17 and the post-catalyst sensor 18.

Here, the upstream catalyst 11 that is mainly subjected to abnormality diagnosis will be described in more detail. The downstream catalyst 19 is configured in the same manner as the upstream catalyst 11. 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 a large number of particulate catalyst components 32 are supported on the coating material 31 in a dispersed manner. 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 a role of a promoter that promotes a 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. Note that “absorption” or “adsorption” may be used in the same meaning as “occlusion”.

  For example, if the atmospheric gas in the catalyst is leaner than the stoichiometric air-fuel ratio, the oxygen storage component present around the catalyst component 32 absorbs oxygen from the atmospheric gas, and as a result, NOx is reduced and purified. On the other hand, when the atmospheric gas in the catalyst is richer than the stoichiometric air-fuel ratio, oxygen stored in the oxygen storage component is released, and the released oxygen oxidizes and purifies HC and CO.

  Due to this oxygen absorption / release action, even if the actual air-fuel ratio varies somewhat with respect to the stoichiometry during normal stoichiometric air-fuel ratio control, this variation can be absorbed.

  Incidentally, in the new catalyst 11, as described above, a large number of catalyst components 32 are evenly distributed, and the contact probability between the exhaust gas and the catalyst component 32 is maintained 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). If it becomes like this, the contact probability of exhaust gas and the catalyst component 32 will fall, and it will become the cause of reducing a purification rate. 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, there is a correlation between the degree of deterioration of the catalyst 11 and the oxygen storage capacity. Therefore, in the present embodiment, the degree of deterioration of the upstream catalyst 11 is indirectly detected by detecting the oxygen storage capacity of the upstream catalyst 11 that has a particularly large influence on the emission, thereby diagnosing whether the upstream catalyst 11 is normal or abnormal. I am going to do that. Here, the oxygen storage capacity of the catalyst 11 is represented by the size of the oxygen storage capacity (OSC; O ₂ Storage Capacity, the unit is g), which is the maximum amount of oxygen that the current catalyst 11 can store. Therefore, the oxygen storage capacity forms an index value (degradation index value) indicating the degree of deterioration of the catalyst 11.

  The catalyst abnormality diagnosis of the present embodiment is basically based on the Cmax method described above. In the abnormality diagnosis, the active air-fuel ratio control is executed by the ECU 20. That is, the ECU 20 alternates the air-fuel ratio of the exhaust gas supplied to the catalyst 11, specifically, the air-fuel ratio of the air-fuel mixture in the combustion chamber 3, in a rich and lean manner, with the stoichiometric A / Fs being the central air-fuel ratio as a boundary. And switch to active.

  The active air-fuel ratio control and diagnosis are executed only when predetermined preconditions are satisfied. This precondition will be described later.

  In this embodiment, the oxygen storage capacity of both the upstream catalyst 11 and the downstream catalyst 19 is measured, and both catalysts can be diagnosed based on these measured values. However, here, for convenience, a method (referred to as a basic method) in the case of measuring the oxygen storage capacity of only the upstream catalyst 11 alone will be described with reference to FIGS. 3 and 4.

  3A, the broken line indicates the target air-fuel ratio A / Ft, and the solid line indicates the output of the pre-catalyst sensor 17 (however, the converted value to the pre-catalyst air-fuel ratio A / Ff). In FIG. 3B, the solid line indicates the output of the post-catalyst sensor 18 (however, the output voltage Vr).

  As shown in the figure, before the time t1, lean control for switching the air-fuel ratio to lean is executed, the target air-fuel ratio A / Ft is set to lean air-fuel ratio A / Fl (for example, 15.1), and the catalyst 11 A lean gas having an air-fuel ratio equal to the target air-fuel ratio A / Ft is supplied. At this time, the catalyst 11 continues to occlude oxygen. However, when the oxygen is occluded until it is saturated, that is, full, it can no longer occlude oxygen. As a result, the lean gas passes through the catalyst 11 and flows out downstream of the catalyst 11. When this happens, the output of the post-catalyst sensor 18 changes to the lean side, and at the time t1 when the output voltage Vr reaches a predetermined lean determination value VL (for example, 0.21 V), the target air-fuel ratio A / Ft becomes the rich air-fuel ratio A / F. It is switched to Fr (for example, 14.1). Thus, rich control is started, and rich gas having an air-fuel ratio equal to the target air-fuel ratio A / Ft is supplied.

  When the rich gas is supplied, the catalyst 11 continues to release the stored oxygen. When the stored oxygen is eventually released from the catalyst 11, the catalyst 11 cannot release oxygen at that time, and the rich gas passes through the catalyst 11 and flows out downstream of the catalyst 11. When this happens, the output of the post-catalyst sensor 18 changes to the rich side, and at the time t2 when the output voltage Vr reaches a predetermined rich determination value VR (for example, 0.59 V), the target air-fuel ratio A / Ft becomes the lean air-fuel ratio A / It is switched to Fl (for example, 15.1). As a result, the lean control is started again, and a lean gas having an air-fuel ratio equal to the target air-fuel ratio A / Ft is supplied.

  When the catalyst 11 again stores oxygen until it is full and the output voltage Vr of the post-catalyst sensor 18 reaches the lean determination value VL, the target air-fuel ratio A / Ft is switched to the rich air-fuel ratio A / Fr at time t3. Rich control is started.

  In this way, every time the output of the post-catalyst sensor 18 is inverted, the lean control and the rich control are alternately and repeatedly executed.

  During execution of this active air-fuel ratio control, the oxygen storage capacity OSC of the catalyst 11 is measured by the following method.

  The larger the oxygen storage capacity of the catalyst 11, the longer the time during which oxygen can be stored or released. That is, when the catalyst has not deteriorated, the inversion period of the post-catalyst sensor output Vr (for example, the time from t1 to t2) becomes longer, and the inversion period 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 / Ff as an actual value is slightly delayed with the rich air-fuel ratio A / Ff. Switch to Fr. From the time t11 when the pre-catalyst air-fuel ratio A / Ff reaches the stoichiometric A / Fs to the time t2 when the post-catalyst sensor output Vr is next reversed, the oxygen storage capacity for each predetermined calculation cycle is obtained by the following equation (1). dOSC is sequentially calculated, and the oxygen storage capacity dOSC is sequentially accumulated from time t11 to time t2. Thus, the oxygen storage capacity OSC as the final integrated value during the rich control, that is, the amount of released oxygen indicated by OSCb in FIG. 4 is measured.

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

  Similarly, during lean control, the oxygen storage capacity, that is, the amount of stored oxygen indicated by OSCa in FIG. 4 is measured. Each time the rich control and the lean control are alternately performed, the released oxygen amount and the stored oxygen amount are alternately measured.

  As can be seen here, “oxygen storage capacity” is a generic term for “amount of released oxygen” and “amount of stored oxygen”. The “released oxygen amount” refers to the amount of oxygen released by the catalyst during rich control, and the “occluded oxygen amount” refers to the amount of oxygen stored by the catalyst during lean control.

  If a plurality of measured values of the released oxygen amount and the occluded oxygen amount are obtained in this way, whether the catalyst is normal or abnormal is determined by the following method.

  First, the ECU 20 calculates an average value of a plurality of measured values of the released oxygen amount and the stored oxygen amount. Then, the average value is compared with a predetermined abnormality determination value α1. The ECU 20 determines that the upstream catalyst 11 is normal when the average value is greater than the abnormality determination value α1, and determines that the upstream catalyst 11 is abnormal when the average value is equal to or less than the abnormality determination value α1. When it is determined that the upstream catalyst 11 is abnormal, it is preferable to activate a warning device (not shown) such as a check lamp in order to notify the user of the fact.

  As described above, in this embodiment, the oxygen storage capacities of both the upstream catalyst 11 and the downstream catalyst 19 are measured, and both catalysts can be diagnosed based on these measured values.

  In this case, the target air-fuel ratio A / Ft switching timing is different from the basic method. For example, during the rich control, in the basic method, the target air-fuel ratio A / Ft is switched to lean when the output of the post-catalyst sensor 18 reverses rich (t2). However, in this embodiment, instead of this timing, the target air-fuel ratio A / Ft is switched to lean when the output of the downstream post-catalyst sensor 23 reverses rich.

  If the stored oxygen is exhausted from the upstream catalyst 11 during the rich control, the rich gas flows out from the upstream catalyst 11, and the output of the post-catalyst sensor 18 is inverted to rich. The rich gas is supplied to the downstream catalyst 19 and releases the stored oxygen from the downstream catalyst 19. When the stored oxygen is exhausted from the downstream catalyst 19, the rich gas flows out from the downstream catalyst 19, and the output of the downstream catalyst post-sensor 23 is inverted to rich. Simultaneously with this reversal, the rich control ends, and the target air-fuel ratio A / Ft is switched to lean.

  In the period until the output of the post-catalyst sensor 18 is richly inverted, the amount of oxygen released from the upstream catalyst 11 is measured in the same manner as in the basic method. Further, the amount of oxygen released from the downstream catalyst 19 is measured during the period from when the output of the post-catalyst sensor 18 is richly inverted until the output of the downstream post-catalyst sensor 23 is richly inverted. That is, during the period, the oxygen storage capacity dOSC for each calculation cycle based on the formula (1) is sequentially accumulated.

  During the lean control, the stored oxygen amounts of the upstream catalyst 11 and the downstream catalyst 19 are measured in the same manner. In this case, the lean control ends when the output of the downstream post-catalyst sensor 23 is reversed to lean, and the target air-fuel ratio A / Ft is switched to rich.

  The method for determining whether the downstream catalyst 19 is normal or abnormal is the same as the basic method. That is, an average value of a plurality of measured values of the released oxygen amount and the stored oxygen amount of the downstream catalyst 19 is calculated, and this average value is compared with another abnormality determination value α2 for the downstream catalyst. When the average value is greater than the abnormality determination value α2, the downstream catalyst 19 is determined to be normal, and when the average value is equal to or less than the abnormality determination value α2, the downstream catalyst 19 is determined to be abnormal. Similarly to the above, it is preferable to activate the warning device at the time of abnormality determination.

  Note that the measured values of the oxygen storage capacity of the upstream catalyst 11 and the downstream catalyst 19 are not necessarily average values.

  Next, the fuel property determination in this embodiment, specifically, estimation of the sulfur concentration of the fuel will be described. Here, a fuel having a low sulfur concentration scheduled to be used in advance, that is, a fuel having a sulfur concentration lower than a predetermined concentration is referred to as a low S fuel. A fuel having a high sulfur concentration, that is, a fuel having a sulfur concentration equal to or higher than the predetermined concentration is referred to as a high S fuel.

  In general, the lower the catalyst temperature, the greater the effect of sulfur on the catalyst. That is, even if the sulfur concentration of the fuel is constant, the lower the catalyst temperature, the greater the degree of S poisoning of the catalyst, and the amount of sulfur accumulation in the catalyst increases.

  Further, when the upstream catalyst 11 and the downstream catalyst 19 are compared with each other, the downstream catalyst 19 is supplied with lower temperature exhaust gas, and therefore tends to be at a lower temperature.

  Therefore, when the sulfur concentration of the fuel is constant, there is a certain correlation between the oxygen storage capacity of the upstream catalyst 11 and the oxygen storage capacity of the downstream catalyst 19. This is illustrated in FIG.

  In FIG. 6, diamonds and solid lines are data when low S fuel is used, and squares and broken lines are data when high S fuel is used. First, regardless of the sulfur concentration of the fuel, the oxygen storage capacity OSC2 of the downstream catalyst 19 is always smaller than the oxygen storage capacity OSC1 of the upstream catalyst 11. This is because the downstream catalyst 19 has a lower temperature than the upstream catalyst 11. When the sulfur concentration of the fuel is constant, that is, when the low S fuel is used and when the high S fuel is used, the oxygen storage capacity OSC2 of the downstream catalyst 19 is proportional to the oxygen storage capacity OSC1 of the upstream catalyst 11. . The reason is that the deterioration of the upstream catalyst 11 and the downstream catalyst 19 proceeds to the same extent.

  Further, when the oxygen storage capacity OSC1 of the upstream catalyst 11 is constant, the oxygen storage capacity OSC2 of the downstream catalyst 19 when the high S fuel is used is smaller than the oxygen storage capacity OSC2 of the downstream catalyst 19 when the low S fuel is used. The reason is that the downstream catalyst 19, which is cooler than the upstream catalyst 11, is relatively strongly influenced by the sulfur of the high S fuel and the degree of S poisoning is increased.

  Therefore, in this embodiment, the ECU 20 estimates the sulfur concentration of the fuel using this characteristic. That is, the relationship between the oxygen storage capacity OSC1 of the upstream catalyst 11 and the oxygen storage capacity OSC2 of the downstream catalyst 19 when the low S fuel is used as shown in FIG. 6 is stored in advance in the ECU 20 in the form of a map (which may be a function; Keep it. FIG. 7 shows a more specific map reflecting the data of FIG. Then, the oxygen storage capacity OSC2 of the downstream catalyst 19 corresponding to the actually measured oxygen storage capacity (referred to as measured upstream oxygen storage capacity) OSC1a of the upstream catalyst 11 is estimated from the map. This estimated oxygen storage capacity (referred to as an estimated downstream oxygen storage capacity) OSC2e is a value on the solid line in FIG. Next, based on the estimated downstream oxygen storage capacity OSC2e and the actually measured oxygen storage capacity of the downstream catalyst 19 (referred to as measured downstream oxygen storage capacity) OSC2a, the sulfur concentration of the fuel used is estimated.

  Specifically, when the difference ΔOSC2 = | OSC2e−OSC2a | between the estimated downstream oxygen storage capacity OSC2e and the measured downstream oxygen storage capacity OSC2a is equal to or greater than a predetermined threshold value β1, the sulfur concentration of the fuel used is equal to or greater than the predetermined concentration. That is, it is estimated that the fuel used is high S fuel. On the other hand, when the difference ΔOSC2 is less than the predetermined threshold value β1, it is estimated that the sulfur concentration of the fuel used is less than the predetermined concentration, that is, the fuel used is low S fuel.

  If the low S fuel is used, the difference ΔOSC2 between the estimated downstream oxygen storage capacity OSC2e and the measured downstream oxygen storage capacity OSC2a on the premise of the low S fuel should be small. In this case, the used fuel can be estimated as the low S fuel. . However, when the high S fuel is used, the difference ΔOSC2 between the estimated downstream oxygen storage capacity OSC2e and the measured downstream oxygen storage capacity OSC2a on the premise of the low S fuel becomes large. Therefore, in this case, the fuel used is estimated to be high S fuel.

  This estimation method has the following advantages. First, since it is not necessary to newly install a relatively expensive sulfur concentration sensor, there is an advantage that the entire apparatus can be suppressed relatively inexpensively.

  Next, it is conceivable that the sulfur concentration of the fuel is estimated based on the oxygen storage capacity reduction amount of only one of the upstream catalyst 11 and the downstream catalyst 19, but this is a decrease due to catalyst deterioration, or the influence of sulfur. It is not possible to distinguish whether the decrease is caused by However, according to the estimation method of the present embodiment, the oxygen storage capacity measurement values or information of both the upstream catalyst 11 and the downstream catalyst 19 are used. Therefore, the cause of catalyst deterioration can be eliminated, and the sulfur concentration can be estimated based only on the cause of sulfur influence. Therefore, it is possible to estimate the sulfur concentration of the fuel by a suitable and highly accurate method.

  Here, preferably, the ECU 20 variably sets the threshold value β1 to be compared with the difference ΔOSC2 according to the measured upstream oxygen storage capacity OSC1a. Specifically, the threshold value β1 is set to a larger value as the measured upstream oxygen storage capacity OSC1a is larger. This setting can be performed using a predetermined map.

  As understood from FIG. 6, the difference ΔOSC2 between the estimated downstream oxygen storage capacity OSC2e and the measured downstream oxygen storage capacity OSC2a tends to increase as the measured upstream oxygen storage capacity OSC1a increases when the high S fuel is used. Therefore, in accordance with this tendency, the larger the value of the measured upstream oxygen storage capacity OSC1a, the larger the threshold value β1, thereby more reflecting the characteristics shown in FIG. 6 and further improving the estimation accuracy.

  In this example, the sulfur concentration is estimated in two steps of high and low, but the sulfur concentration may be estimated in a stepless manner according to the difference ΔOSC2. Instead of the difference ΔOSC2, the ratio R = OSC2e / OSC2a of the estimated downstream oxygen storage capacity OSC2e and the measured downstream oxygen storage capacity OSC2a may be used. In this case, the higher the ratio R, the higher the sulfur concentration is estimated.

  By the way, when it is estimated that the fuel to be used is a high S fuel, it is preferable to perform abnormality diagnosis of the catalyst in consideration of the influence of sulfur. Therefore, a suitable example of such an abnormality diagnosis will be shown below.

  FIG. 8 shows a routine for abnormality diagnosis processing. This routine is repeatedly executed by the ECU 20 every predetermined calculation cycle (for example, 16 msec).

  First, in step S101, it is determined whether a precondition suitable for diagnosis is satisfied. For example, (1) the engine is warmed up, (2) the upstream catalyst 11 and the downstream catalyst 19 are warmed up, and (3) the pre-catalyst sensor 17, the post-catalyst sensor 18, and the downstream post-catalyst sensor 23 are active. (4) The precondition is satisfied when the engine is in a steady operation state.

  The success or failure of the condition (1) is determined based on a detection value of a water temperature sensor (not shown). For example, if the detection value is 75 ° C. or higher, the condition is satisfied. The success or failure of the condition (2) is determined based on the temperature of each catalyst estimated or detected separately. The success or failure of the condition (3) is determined based on the detected value of the element temperature based on the element impedance of each sensor. The success or failure of the condition (4) is determined, for example, by whether or not the fluctuation range of the intake air amount Ga and the engine speed Ne within a predetermined period is within a predetermined range. The intake air amount Ga is detected by the air flow meter 5, and the engine speed Ne is calculated from the output of the crank angle sensor 14. Other examples of the precondition are possible.

  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, active air-fuel ratio control is executed. In step S103, the oxygen storage capacity OSC1 of the upstream catalyst 11 and the oxygen storage capacity OSC2 of the downstream catalyst 19 are measured during the execution of the active air-fuel ratio control.

  Next, in step S104, it is determined whether or not the measurement of the oxygen storage capacity OSC1 of the upstream catalyst 11 and the oxygen storage capacity OSC2 of the downstream catalyst 19 is completed. When a plurality of predetermined numbers of oxygen storage capacities OSC1 and OSC2 are acquired, the determination result is yes, otherwise the determination result is no and the process ends.

  When the determination result is yes, the process proceeds to step S105, and a difference ΔOSC2 = | OSC2e−OSC2a | between the estimated downstream oxygen storage capacity OSC2e and the measured downstream oxygen storage capacity OSC2a is calculated.

  In this step, first, the average values of the oxygen storage capacities OSC1 and OSC2 of the measured upstream catalyst 11 and downstream catalyst 19 are obtained, and these are the final measured values, that is, the measured upstream oxygen storage capacity OSC1a and the measured downstream oxygen storage capacity. OSC2a.

  Then, the estimated downstream oxygen storage capacity OSC2e corresponding to the measured upstream oxygen storage capacity OSC1a is calculated from the maps as shown in FIGS.

  Further, the difference ΔOSC2 is calculated according to the equation: ΔOSC2 = | OSC2e−OSC2a |. This difference ΔOSC2 becomes a high S fuel determination index value for determining whether or not the fuel used is high S fuel.

  Next, in step S106, the difference ΔOSC2 is compared with the threshold value β1.

  When the difference ΔOSC2 is less than the threshold value β1, it is estimated that the fuel used is low S fuel, and normal / abnormal determination is executed in step S109 as usual. That is, the measured upstream oxygen storage capacity OSC1a and the measured downstream oxygen storage capacity OSC2a are compared with the abnormality determination values α1 and α2, respectively, to determine whether the upstream catalyst 11 and the downstream catalyst 19 are normal or abnormal. This completes the process.

  On the other hand, when the difference ΔOSC2 is equal to or greater than the threshold value β1, it is estimated that the fuel used is high S fuel. In this case, the process proceeds to step S107, and normality / abnormality determination based on the measured upstream oxygen storage capacity OSC1a and the measured downstream oxygen storage capacity OSC2a measured this time is put on hold. This is because the upstream catalyst 11 and the downstream catalyst 19 are poisoned with S, and there is a possibility of erroneous diagnosis. In step S107, a predetermined clear process such as discarding the measured value data is performed.

  Next, in step S108, the catalyst temperature condition among the preconditions in step S101, that is, the condition (2) is changed to a higher temperature side. That is, if the condition (2) is that the upstream catalyst temperature is equal to or higher than the predetermined first temperature Ts1 and the downstream catalyst temperature is equal to or higher than the predetermined second temperature Ts2, the first temperature before the change is changed after the change in the catalyst temperature condition. Ts1 and the second temperature Ts2 are changed to higher temperature values Ts1 ′ and Ts2 ′. These changed values Ts1 'and Ts2' are preferably high enough to eliminate S poisoning of the upstream catalyst 11 and the downstream catalyst 19. When the catalyst temperature condition is changed in this way, the process is terminated.

  The re-diagnosis after the next time is executed only when a higher-temperature catalyst temperature condition is satisfied according to this routine. That is, the oxygen storage capacities OSC1 and OSC2 of the upstream catalyst 11 and the downstream catalyst 19 are measured when the precondition in step S101 is satisfied, and the difference ΔOSC2 is calculated based on these measured values. At this time, there is a high possibility that the sulfur influence of the upstream catalyst 11 and the downstream catalyst 19, that is, S poisoning is eliminated. Therefore, in this case, the difference ΔOSC2 becomes less than the threshold value β1, and normality / abnormality determination is executed as usual. In this way, it is diagnosed whether the upstream catalyst 11 and the downstream catalyst 19 are normal or abnormal based on the measured oxygen storage capacities OSC1, OSC2 under the changed catalyst temperature conditions.

  According to the above diagnosis processing, when it is estimated that the fuel used is high S fuel, the normality / abnormality determination is suspended and the diagnosis is substantially prohibited. Therefore, it is possible to prohibit the diagnosis in a state where the upstream catalyst 11 and the downstream catalyst 19 are S-poisoned, and to prevent erroneous diagnosis. In particular, it is possible to prevent a catalyst that is not normally abnormal from being erroneously diagnosed as abnormal. In addition, since the diagnosis can be performed as usual when the low S fuel is used, both the diagnosis frequency can be ensured.

  In this case, since the diagnosis is executed again under a higher temperature condition of the catalyst, the diagnosis can be executed after removing the influence of the sulfur of the upstream catalyst 11 and the downstream catalyst 19, and the diagnosis can be prevented and the diagnosis frequency can be ensured. .

  In the abnormality diagnosis process, the catalyst temperature condition was changed when normality / abnormality determination was suspended or prohibited. However, these can be done independently only one way.

  In the abnormality diagnosis process, both the upstream catalyst 11 and the downstream catalyst 19 were diagnosed. However, only one of these may be diagnosed. That is, when estimating the sulfur concentration, both the oxygen storage capacities OSC1 and OSC2 are measured, but the catalyst abnormality diagnosis can be executed only for one catalyst using only one of these measured values.

[Second Embodiment]
Next, a second embodiment of the present invention will be described. The description of the same parts as in the first embodiment will be omitted, and the differences will be mainly described below.

  The main difference between the present embodiment is that, instead of the oxygen storage capacity, the catalyst temperature, in particular, the catalyst temperature at the time when a predetermined time has elapsed from the cold start of the engine is used as the deterioration index value of the upstream catalyst 11 and the downstream catalyst 19. Is a point.

  FIG. 9 shows the configuration of the engine 1 of the present embodiment. As illustrated, the upstream catalyst 11 and the downstream catalyst 19 are provided with an upstream temperature sensor 21 and a downstream temperature sensor 22 for measuring or detecting these temperatures, respectively. The upstream temperature sensor 21 and the downstream temperature sensor 22 are electrically connected to the ECU 20 via an A / D converter or the like (not shown). The downstream post-catalyst sensor 23 provided in the first embodiment is omitted. The ECU 20 detects the temperatures of the upstream catalyst 11 and the downstream catalyst 19 at the time when a predetermined time has elapsed from when the engine is cold-started, using the upstream temperature sensor 21 and the downstream temperature sensor 22.

  The ECU 20 determines that the engine has been cold started when the engine is started when the detection value of a water temperature sensor (not shown) is within a predetermined range of room temperature. Then, the intake air amount or the fuel injection amount is sequentially integrated from the cold start, and it is determined that a predetermined time has elapsed when the integrated value reaches a predetermined value. Although the predetermined time can be arbitrarily determined, for example, it may be a time at which the normal catalyst changes from inactive to active (first time), or after the normal catalyst is activated, Then, it may be a time (second time) at a timing when diagnosis is performed.

  The greater the degree of deterioration of the catalyst, the slower the catalytic reaction, and the lower the catalyst temperature at the predetermined time point. Thus, there is a correlation between the degree of deterioration of the catalyst and the catalyst temperature. Therefore, in this embodiment, the degree of deterioration of each catalyst is indirectly detected by measuring or detecting the catalyst temperatures of the upstream catalyst 11 and the downstream catalyst 19 when a predetermined time has elapsed, thereby diagnosing whether each catalyst is normal or abnormal. To do.

  When the first time is employed, the catalyst temperatures of the upstream catalyst 11 and the downstream catalyst 19 at the time when the first time has elapsed are respectively compared with predetermined abnormality determination values. When the catalyst temperature is higher than the abnormality determination value, the catalyst is determined to be normal, and when the catalyst temperature increase is equal to or less than the abnormality determination value, the catalyst is determined to be abnormal.

  When the second time is adopted, the catalyst temperatures of the upstream catalyst 11 and the downstream catalyst 19 at the time when the second time has elapsed are respectively compared with predetermined abnormality determination values. The abnormality determination value is calculated from a predetermined map based on the integrated intake air amount or the integrated fuel injection amount. When the catalyst temperature is higher than the abnormality determination value, the catalyst is determined to be normal, and when the catalyst temperature is equal to or lower than the abnormality determination value, the catalyst is determined to be abnormal.

  Next, the fuel property determination in this embodiment, specifically, estimation of the sulfur concentration of the fuel will be described. As described above, the downstream catalyst 19 tends to be at a lower temperature than the upstream catalyst 11. Further, the lower the catalyst temperature, the greater the influence of sulfur on the catalyst, the greater the degree of S poisoning of the catalyst, and the higher the sulfur accumulation amount of the catalyst.

  Therefore, when the sulfur concentration of the fuel is constant, there is a certain correlation between the temperature of the upstream catalyst 11 and the temperature of the downstream catalyst 19. This is illustrated in FIG.

  In FIG. 10, diamonds and solid lines are data when low S fuel is used, and squares and broken lines are data when high S fuel is used. Here, the values in the warm-up state when the second time is adopted, that is, after each catalyst is activated, are shown.

  First, regardless of the sulfur concentration of the fuel, the downstream catalyst temperature T2 is always lower than the upstream catalyst temperature T1. When the fuel sulfur concentration is constant, that is, when the low S fuel is used and when the high S fuel is used, the downstream catalyst temperature T2 is proportional to the upstream catalyst temperature T1.

  Further, when the upstream catalyst temperature T1 is constant, the downstream catalyst temperature T2 when the high S fuel is used is lower than the downstream catalyst temperature T2 when the low S fuel is used. The reason is that in the downstream catalyst 19 which is lower in temperature than the upstream catalyst 11, the influence of sulfur due to the high S fuel increases, the degree of S poisoning increases, and the reaction heat of the catalyst decreases.

  Therefore, in this embodiment, the ECU 20 estimates the sulfur concentration of the fuel using this characteristic. That is, the relationship between the upstream catalyst temperature and the downstream catalyst temperature when using low S fuel as shown in the figure is stored in advance in the ECU 20 in the form of a map. Then, the downstream catalyst temperature corresponding to the actual upstream catalyst temperature (referred to as the detected upstream catalyst temperature) T1a detected by the upstream temperature sensor 21 is estimated from the map. The estimated downstream catalyst temperature (referred to as estimated downstream catalyst temperature) T2e is a value on the solid line in FIG. Next, based on the estimated downstream catalyst temperature T2e and the actual downstream catalyst temperature (referred to as the detected downstream catalyst temperature) T2a detected by the downstream temperature sensor 22, the sulfur concentration of the fuel used is estimated.

  Specifically, when the difference ΔT2 = | T2e−T2a | between the estimated downstream catalyst temperature T2e and the detected downstream catalyst temperature T2a when the second time has elapsed is equal to or greater than a predetermined threshold value β2, the sulfur concentration of the fuel used is predetermined. It is estimated that the concentration is higher than the concentration, that is, the fuel used is a high S fuel. On the other hand, when the difference ΔT2 is less than the threshold value β2, it is estimated that the sulfur concentration of the fuel used is less than a predetermined concentration, that is, the fuel used is a low S fuel.

  This estimation method has the same advantages as the first embodiment.

  Preferably, ECU 20 variably sets threshold value β2, which is a comparison target of difference ΔT2, according to detected upstream catalyst temperature T1a. Specifically, the threshold value β2 is set to a larger value as the detected upstream catalyst temperature T1a is higher. This setting can be performed using a predetermined map.

  As understood from FIG. 10, the difference ΔT2 between the estimated downstream catalyst temperature T2e and the detected downstream catalyst temperature T2a tends to increase as the upstream catalyst temperature T1 increases when the high S fuel is used. Therefore, in accordance with this tendency, the threshold value is increased as the detected upstream catalyst temperature T1a is higher, so that the characteristics shown in FIG. 10 can be reflected more and the estimation accuracy can be further improved.

  Note that the sulfur concentration may be estimated steplessly, and the ratio R = T2e / T2a may be used instead of the difference ΔT2.

  FIG. 11 shows a routine of abnormality diagnosis processing according to the present embodiment. This routine is repeatedly executed by the ECU 20 every predetermined calculation cycle (for example, 16 msec).

  Step S201 is the same as step S101. In step S202, the catalyst temperatures T1 and T2 of the upstream catalyst 11 and the downstream catalyst 19 are detected.

  In step S203, a difference ΔT2 between the estimated downstream catalyst temperature T2e and the detected downstream catalyst temperature T2a is calculated. First, the estimated downstream catalyst temperature T2e corresponding to the detected upstream catalyst temperature T1a is calculated from the map as shown in FIG. Next, the difference ΔT2 is calculated according to the equation: ΔT2 = | T2e−T2a |. This difference ΔT2 becomes a high S fuel determination index value for determining whether or not the fuel used is high S fuel.

  Next, in step S204, the difference ΔT2 is compared with the threshold value β2.

  When the difference ΔT2 is less than the threshold value β2, it is estimated that the fuel to be used is low S fuel. As usual, in step S207, the upstream catalyst 11 and the downstream catalyst 19 based on the detected upstream catalyst temperature T1a and the detected downstream catalyst temperature T2a. Normal / abnormal judgment is executed.

  On the other hand, when the difference ΔT2 is greater than or equal to the threshold value β2, it is estimated that the fuel used is high S fuel, and the normal / abnormal determination is suspended in step S205 and the catalyst temperature condition is higher in step S206 as in the above embodiment. Is changed to the side.

[Third Embodiment]
Next, a third embodiment of the present invention will be described. The description of the same parts as in the above embodiment will be omitted, and the differences will be mainly described below.

  The main difference between the present embodiment is that the temperature of the downstream catalyst is estimated based on the deterioration index value representing the degree of deterioration of the upstream catalyst, and based on the estimated temperature of the downstream catalyst and the detected temperature of the downstream catalyst separately detected. The point is to estimate the sulfur concentration of the fuel used.

  FIG. 12 shows the configuration of the engine 1 of the present embodiment. As shown in the drawing, the downstream catalyst 19 is provided with a downstream temperature sensor 22 as temperature detecting means for detecting the temperature thereof. The downstream temperature sensor 22 is electrically connected to the ECU 20 via an A / D converter or the like (not shown). The downstream post-catalyst sensor 23 provided in the first embodiment and the upstream temperature sensor 21 provided in the second embodiment are omitted.

  And oxygen storage capacity OSC1 which is a degradation index value showing the degradation degree of the upstream catalyst 11 is measured by the method similar to 1st Embodiment or its basic method. In addition, the oxygen storage capacity OSC2 of the downstream catalyst 19 may be measured.

  Based on the measured oxygen storage capacity OSC1 of the upstream catalyst 11, that is, the measured upstream oxygen storage capacity OSC1a, the temperature of the downstream catalyst 19 is estimated.

  As described above, the downstream catalyst 19 tends to be at a lower temperature than the upstream catalyst 11. In addition, the lower the catalyst temperature, the greater the influence of sulfur on the catalyst. Further, when the degree of deterioration of the upstream catalyst 11 is determined, the temperature of the downstream catalyst 19 that has deteriorated to the same extent is naturally determined.

  Therefore, when the sulfur concentration of the fuel is constant, there is a certain correlation between the oxygen storage capacity OSC1 of the upstream catalyst 11 and the temperature of the downstream catalyst 19. This is illustrated in FIG.

  As shown in FIG. 13, the downstream catalyst temperature T2 is proportional to the oxygen storage capacity OSC1 of the upstream catalyst, regardless of the sulfur concentration of the fuel. When the oxygen storage capacity OSC1 of the upstream catalyst is constant, the downstream catalyst temperature T2 when the high S fuel is used is lower than the downstream catalyst temperature T2 when the low S fuel is used. The reason is that in the downstream catalyst 19 which is lower in temperature than the upstream catalyst 11, the influence of sulfur due to the high S fuel becomes relatively large, and the reaction heat of the catalyst is reduced.

  Therefore, in this embodiment, the ECU 20 estimates the sulfur concentration of the fuel using this characteristic. That is, the relationship between the oxygen storage capacity OSC1 of the upstream catalyst 11 and the downstream catalyst temperature T2 when the low S fuel is used as shown in FIG. 13 is stored in the ECU 20 in advance in the form of a map. FIG. 14 shows a more specific map reflecting the data of FIG. Then, the actually measured oxygen storage capacity OSC1 of the upstream catalyst 11, that is, the downstream catalyst temperature T2 corresponding to the measured upstream oxygen storage capacity OSC1a is estimated from the map. The estimated downstream catalyst temperature, that is, the estimated downstream catalyst temperature T2e is a value on the solid line in FIG. Next, based on the estimated downstream catalyst temperature T2e and the downstream catalyst temperature detected by the downstream temperature sensor 22, that is, the detected downstream catalyst temperature T2a, the sulfur concentration of the fuel used is estimated.

  Specifically, when the difference ΔT2 = | T2e−T2a | between the estimated downstream catalyst temperature T2e and the detected downstream catalyst temperature T2a is equal to or greater than a predetermined threshold value β3, it is estimated that the used fuel is high S fuel. On the other hand, when the difference ΔT2 is less than the threshold value β3, it is estimated that the used fuel is low S fuel.

  This estimation method has the same advantages as those of the first and second embodiments.

  Here, preferably, the ECU 20 variably sets the threshold value β3 according to the value of the measured upstream oxygen storage capacity OSC1a. Specifically, the threshold value β3 is set to a larger value as the value of the measured upstream oxygen storage capacity OSC1a is larger. This setting can be performed using a predetermined map.

  As understood from FIG. 13, the difference ΔT2 between the estimated downstream catalyst temperature T2e and the detected downstream catalyst temperature T2a tends to increase as the measured upstream oxygen storage capacity OSC1a increases when the high S fuel is used. . Therefore, in accordance with this tendency, as the value of the measured upstream oxygen storage capacity OSC1a is larger, the threshold value β3 is increased, thereby more reflecting the characteristics of FIG. 13 and further improving the estimation accuracy.

  Note that the sulfur concentration may be estimated steplessly, and the ratio R = T2e / T2a may be used instead of the difference ΔT2.

  FIG. 15 shows a routine for abnormality diagnosis processing according to the present embodiment. This routine is repeatedly executed by the ECU 20 every predetermined calculation cycle (for example, 16 msec).

  Steps S301 and S302 are the same as steps S101 and S102. In step S303, the oxygen storage capacity OSC1 of the upstream catalyst 11 is measured during execution of the active air-fuel ratio control, and the value of the detected downstream catalyst temperature T2a is integrated. In addition, the oxygen storage capacity OSC2 of the downstream catalyst 19 may be measured.

  In step S304, it is determined whether or not the measurement of the oxygen storage capacity OSC1 of the upstream catalyst 11 is completed. If not completed, the process ends. If completed, the process proceeds to step S305. Simultaneously with this completion, the integration of the detected downstream catalyst temperature T2a is also terminated.

  In step S305, a difference Δ between the estimated downstream catalyst temperature T2e and the detected downstream catalyst temperature T2a is calculated.

  First, the average value of the measured oxygen storage capacities OSC1 of the plurality of upstream catalysts 11 is obtained, and this is used as the final measured value, that is, the measured upstream oxygen storage capacity OSC1a.

  Then, the estimated downstream catalyst temperature T2e corresponding to the measured upstream oxygen storage capacity OSC1a is calculated from the maps as shown in FIGS.

  On the other hand, the integrated value of the detected downstream catalyst temperature T2a is divided by the number of samples, and the average value of the detected downstream catalyst temperature T2a is calculated. This average value is the final detected downstream catalyst temperature T2a. That is, the detected downstream catalyst temperature T2a is a detected value of the downstream catalyst temperature T2 at the time of measurement of the oxygen storage capacity OSC1 of the upstream catalyst 11, and more specifically, detected during measurement of the oxygen storage capacity OSC1 of the upstream catalyst 11. This is the average value of the downstream catalyst temperature T2. Note that the average value is not necessarily required, and the downstream catalyst temperature T2 at an arbitrary time during the OSC1 measurement can be set as the detected downstream catalyst temperature T2a.

  Next, the difference ΔT2 is calculated according to the equation: ΔT2 = | T2e−T2a |. This difference ΔT2 becomes a high S fuel determination index value for determining whether or not the fuel used is high S fuel.

  Next, in step S306, the difference ΔT2 is compared with the threshold value β3.

  When the difference ΔT2 is less than the threshold value β3, it is estimated that the fuel used is low S fuel, and normal / abnormal determination of the upstream catalyst 11 is executed in step S309 based on the measured upstream oxygen storage capacity OSC1a as usual. When the oxygen storage capacity OSC2 of the downstream catalyst 19 is also measured, normality / abnormality determination of the downstream catalyst 19 may be executed together.

  On the other hand, when the difference ΔT2 is greater than or equal to the threshold value β3, it is estimated that the fuel used is high S fuel, and the normal / abnormal determination is suspended in step S307, and the catalyst temperature condition is higher in step S308, as in the above embodiment. Is changed to the side.

  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 automobiles, or may be a direct injection type or the like. The deterioration index values of the upstream catalyst 11 and the downstream catalyst 19 can use values other than those described above. For example, the trajectory length of the air-fuel ratio sensor output can be used. As is well known, the trajectory length of the air-fuel ratio sensor output is a value obtained by sequentially integrating the difference (differential value) between one calculation cycle of the air-fuel ratio sensor output. For example, in the case of the upstream catalyst 11, during the active air-fuel ratio control, the post-catalyst sensor output trajectory length tends to increase relative to the pre-catalyst sensor output trajectory length as the catalyst deterioration degree increases. Thus, the normality / abnormality of the upstream catalyst 11 can be diagnosed.

  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.

1 Internal combustion engine
6 Exhaust pipe 11 Upstream catalyst 12 Injector 17 Pre-catalyst sensor 18 Post-catalyst sensor 19 Downstream catalyst 20 Electronic control unit (ECU)
21 upstream temperature sensor 22 downstream temperature sensor 23 downstream downstream catalyst sensor

Claims (20)

An upstream catalyst and a downstream catalyst respectively provided on the upstream side and the downstream side of the exhaust passage of the internal combustion engine;
Measuring means for measuring index values representing the degree of deterioration of the upstream catalyst and the downstream catalyst,
Index value estimating means for estimating the index value of the downstream catalyst based on the index value of the upstream catalyst measured by the measuring means;
A sulfur concentration estimating means for estimating the sulfur concentration of the fuel used based on the estimated index value of the downstream catalyst estimated by the index value estimating means and the measured index value of the downstream catalyst measured by the measuring means;
A fuel property determining apparatus comprising: The fuel property determination device according to claim 1, wherein the sulfur concentration estimation unit estimates the sulfur concentration of the fuel used based on a difference between an estimated index value and a measured index value of the downstream catalyst. The fuel property determination device according to claim 2, wherein the sulfur concentration estimation means estimates that the sulfur concentration of the fuel used is equal to or greater than a predetermined concentration when the difference is equal to or greater than a predetermined threshold value. The fuel property determination device according to claim 3, wherein the sulfur concentration estimation unit variably sets the threshold value according to a value of a measurement index value of the upstream catalyst. The fuel property determination device according to claim 4, wherein the sulfur concentration estimation unit sets the threshold value to a larger value as the value of the measurement index value of the upstream catalyst is larger. The fuel property determination device according to any one of claims 1 to 5, wherein the index value includes an oxygen storage capacity. The fuel property determination device according to any one of claims 1 to 5, wherein the index value includes a catalyst temperature when a predetermined time has elapsed from a cold start of the internal combustion engine. A catalyst abnormality diagnosis device comprising the fuel property determination device according to any one of claims 1 to 7 and diagnosing whether at least one of the upstream catalyst and the downstream catalyst is normal or abnormal,
The catalyst abnormality diagnosis device, wherein diagnosis is prohibited when the sulfur concentration of the fuel used is estimated to be equal to or higher than a predetermined concentration by the sulfur concentration estimation means. A catalyst abnormality diagnosis device comprising the fuel property determination device according to any one of claims 1 to 7 and diagnosing whether at least one of the upstream catalyst and the downstream catalyst is normal or abnormal,
A catalyst abnormality diagnosis device characterized in that when the sulfur concentration estimation means estimates that the sulfur concentration of the fuel used is equal to or higher than a predetermined concentration, the temperature condition for diagnosis is changed to a higher temperature side.   Under the changed temperature condition, the measurement means measures at least one index value of the upstream catalyst and the downstream catalyst, and based on the measured index value, at least one of the upstream catalyst and the downstream catalyst is normal or abnormal The catalyst abnormality diagnosis device according to claim 9, wherein An upstream catalyst and a downstream catalyst respectively provided on the upstream side and the downstream side of the exhaust passage of the internal combustion engine;
Measuring means for measuring an index value indicating the degree of deterioration of the upstream catalyst;
Temperature detecting means for detecting the temperature of the downstream catalyst;
Temperature estimating means for estimating the temperature of the downstream catalyst based on the index value of the upstream catalyst measured by the measuring means;
A sulfur concentration estimating means for estimating the sulfur concentration of the fuel used based on the estimated temperature of the downstream catalyst estimated by the temperature estimating means and the detected temperature of the downstream catalyst detected by the temperature detecting means;
A fuel property determining apparatus comprising: The fuel property determination device according to claim 11, wherein the sulfur concentration estimation unit estimates a sulfur concentration of a fuel used based on a difference between an estimated temperature and a detected temperature of the downstream catalyst. The fuel property determination device according to claim 12, wherein the sulfur concentration estimation means estimates that the sulfur concentration of the fuel used is equal to or greater than a predetermined concentration when the difference is equal to or greater than a predetermined threshold value. The fuel property determination device according to claim 13, wherein the sulfur concentration estimation means variably sets the threshold value according to an index value of the upstream catalyst. The fuel property determination device according to claim 14, wherein the sulfur concentration estimation unit sets the threshold value to a larger value as the index value of the upstream catalyst is larger. The fuel property determination device according to any one of claims 11 to 15, wherein the index value includes an oxygen storage capacity. The fuel property determination device according to any one of claims 11 to 16, wherein the temperature of the downstream catalyst is a temperature at the time of measuring the index value of the upstream catalyst. A catalyst abnormality diagnosis device comprising the fuel property determination device according to any one of claims 11 to 17 and diagnosing whether at least one of the upstream catalyst and the downstream catalyst is normal or abnormal,
The catalyst abnormality diagnosis device, wherein diagnosis is prohibited when the sulfur concentration of the fuel used is estimated to be equal to or higher than a predetermined concentration by the sulfur concentration estimation means. A catalyst abnormality diagnosis device comprising the fuel property determination device according to any one of claims 11 to 17 and diagnosing whether at least one of the upstream catalyst and the downstream catalyst is normal or abnormal,
A catalyst abnormality diagnosis device characterized in that when the sulfur concentration estimation means estimates that the sulfur concentration of the fuel used is equal to or higher than a predetermined concentration, the temperature condition for diagnosis is changed to a higher temperature side.   Under the changed temperature condition, the measurement means measures at least one index value of the upstream catalyst and the downstream catalyst, and based on the measured index value, at least one of the upstream catalyst and the downstream catalyst is normal or abnormal The catalyst abnormality diagnosis device according to claim 19, wherein the abnormality of the catalyst is diagnosed.

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