JP2012219803A - Fuel property determining device and catalyst abnormality diagnostic device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel property determining device capable of suitably estimating a sulfur concentration in fuel, and to provide a catalyst abnormality diagnostic device equipped with the same.SOLUTION: An upstream temperature sensor and a downstream temperature sensor detect temperatures of an upstream catalyst and a downstream catalyst provided to an exhaust path of an internal combustion engine, respectively. The temperature of the downstream catalyst is estimated based upon the detected temperature of the upstream catalyst, and the sulfur concentration of the fuel in use is estimated based upon the estimated temperature and the detected temperature of the downstream catalyst. The catalyst abnormality diagnostic device executes active air-fuel ratio control in which an air-fuel ratio is controlled to be alternately lean and rich, and measures amounts of oxygen that the upstream catalyst absorbs and emits during lean control and rich control. Then it is determined whether the upstream catalyst is normal or abnormal based upon a plurality of measured amounts of oxygen. When it is estimated when the sulfur concentration of the fuel in use is equal to or larger than a predetermined value, control change to reduce influence of sulfur on the upstream catalyst is made.

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 stoichiometry. 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, air-fuel ratio control (active control) is performed in which the air-fuel ratio is changed between a rich state and a lean state, and the oxygen of the catalyst is determined based on changes in the air-fuel ratio or oxygen concentration in the exhaust passage. Calculate the storage capacity. Then, based on the calculated oxygen storage capacity, it is determined whether or not a phenomenon in which the oxygen storage capacity temporarily decreases occurs.

JP 2007-56723 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;
An upstream temperature sensor and a downstream temperature sensor for detecting the temperatures of the upstream catalyst and the downstream catalyst, respectively;
Temperature estimation means for estimating the temperature of the downstream catalyst based on the detected temperature of the upstream catalyst detected by the upstream temperature sensor;
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 downstream temperature sensor;
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 a difference between the estimated temperature and the detected temperature of the downstream catalyst at a predetermined time or an integrated value of the difference within a predetermined period.

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

  Preferably, the sulfur concentration estimating means variably sets the predetermined value in accordance with a value at the predetermined time of the detected temperature of the upstream catalyst, or an average value or an integrated value within the predetermined period.

  Preferably, the sulfur concentration estimating means sets the predetermined value to a larger value as the value of the detected temperature of the upstream catalyst at the predetermined time, or the average value or integrated value within the predetermined period is higher.

According to a second aspect of the invention,
A catalyst abnormality diagnosis device comprising the fuel property determination device of the first aspect and diagnosing whether the upstream catalyst is normal or abnormal,
Active air-fuel ratio control means for performing active air-fuel ratio control for alternately controlling the air-fuel ratio on the upstream side of the upstream catalyst in a lean and rich manner;
Measuring means for measuring the amount of oxygen absorbed and released by the upstream catalyst during lean control and rich control of the air-fuel ratio;
Determining means for determining whether the upstream catalyst is normal or abnormal based on a plurality of oxygen amounts measured by the measuring means;
Control change means for executing a control change for reducing the influence of sulfur on the upstream catalyst when the sulfur concentration of the used fuel is estimated to be a predetermined value or more by the sulfur concentration estimation means;
There is provided a catalyst abnormality diagnosis device characterized by comprising:

Preferably, in the active air-fuel ratio control, the lean control or the rich control for a predetermined number of times from the start thereof is invalid times, and the invalidating times may not be measured or measured by the measuring unit. The determination means is not used as a basis for determination by the determination means,
The control change includes increasing the number of invalid times, increasing the amplitude of the rich control in the invalid times, and the invalid time in comparison with a case where the sulfur concentration of the fuel used is less than a predetermined value. It comprises at least one of delaying the switching timing from the rich control to the lean control.

According to a third aspect of the invention,
A catalyst abnormality diagnosis device comprising the fuel property determination device of the first aspect and diagnosing whether the upstream catalyst is normal or abnormal,
Active air-fuel ratio control means for performing active air-fuel ratio control for alternately controlling the air-fuel ratio on the upstream side of the upstream catalyst in a lean and rich manner;
Measuring means for measuring the amount of oxygen absorbed and released by the upstream catalyst during lean control and rich control of the air-fuel ratio;
Determining means for determining whether the upstream catalyst is normal or abnormal based on a plurality of oxygen amounts measured by the measuring means;
When the sulfur concentration estimation unit estimates that the sulfur concentration of the fuel used is equal to or higher than a predetermined value, temperature increase control is performed to increase the temperature of the upstream catalyst at least before measurement by the measurement unit. Temperature rise control means,
There is provided a catalyst abnormality diagnosis device characterized by comprising:

  Preferably, the temperature increase control includes at least one of retard control for retarding the ignition timing of the internal combustion engine and imbalance control for forcibly varying the air-fuel ratio of each cylinder of the internal combustion engine.

According to a fourth aspect of the invention,
A catalyst abnormality diagnosis device comprising the fuel property determination device of the first aspect and diagnosing whether the upstream 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 value, a diagnosis of a catalyst abnormality is provided, which prohibits diagnosis.

  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 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 upstream catalyst temperature and downstream catalyst temperature. It is a flowchart of a fuel property determination process. It is a flowchart which concerns on 1st Example of a catalyst abnormality diagnosis process. It is a flowchart which concerns on 2nd Example of a catalyst abnormality diagnosis process. It is a time chart which concerns on the 1st example of control change. It is a time chart concerning the 2nd example of control change. It is a time chart concerning the 3rd example of control change. It is a flowchart which concerns on 3rd Example of a catalyst abnormality diagnosis process.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the accompanying drawings.

  FIG. 1 is a schematic diagram showing the configuration of the present 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.

On the upstream side and downstream side of the upstream catalyst 11, air-fuel ratio sensors that detect the air-fuel ratio of the exhaust gas based on the oxygen concentration, that is, the pre-catalyst sensor 17 and the post-catalyst sensor 18, are provided. 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.

  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, and the post-catalyst sensor 18, the ECU 20 includes a crank angle sensor 14 that detects the crank angle of the engine 1, and an accelerator opening that detects the accelerator opening, as shown in the figure. The degree sensor 15 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.

  Further, an upstream temperature sensor 21 and a downstream temperature sensor 22 for detecting the temperatures of the upstream catalyst 11 and the downstream catalyst 19 are electrically connected to the ECU 20 via an A / D converter or the like (not shown).

  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 to be 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 degree of decrease in the oxygen storage capacity of the catalyst 11. 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, and the abnormality of the upstream catalyst 11 is diagnosed. 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.

  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.

  Hereinafter, a method for measuring the oxygen storage capacity of the upstream catalyst 11 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 11 during rich control, and the “occluded oxygen amount” refers to the amount of oxygen stored by the catalyst 11 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 OSCav of the measured values of the released oxygen amount and the stored oxygen amount. The average value OSCav is compared with a predetermined abnormality determination value α. The ECU 20 determines that the catalyst 11 is normal when the average value OSCav is greater than the abnormality determination value α, and determines that the catalyst 11 is abnormal when the average value OSCav is less than or equal to the abnormality determination value α. When it is determined that the catalyst 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.

  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 less than a predetermined value 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 value 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 fuel sulfur concentration 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. 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 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. This is because in the downstream catalyst 19 which is lower in temperature than the upstream catalyst 11, the influence of sulfur by the high S fuel is increased, the degree of S poisoning is increased, 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 upstream catalyst temperature and the downstream catalyst temperature when using the low S fuel as shown in the figure is stored in advance in the ECU 20 in the form of a map (which may be a function, the same applies hereinafter). Then, the downstream catalyst temperature corresponding to the actual upstream catalyst temperature (referred to as upstream catalyst detection temperature) T1a detected by the upstream temperature sensor 21 is estimated from the map. This estimated value of downstream catalyst temperature (referred to as downstream catalyst estimated temperature) T2b is a value on the solid line in FIG. Next, based on the downstream catalyst estimated temperature T2b and the actual downstream catalyst temperature (referred to as downstream catalyst detection temperature) T2a detected by the downstream temperature sensor 22, the sulfur concentration of the fuel used is estimated.

  Specifically, the difference ΔT2 = | T2b−T2a | between the estimated downstream catalyst temperature T2b and the detected downstream catalyst temperature T2a at a predetermined time or a predetermined calculation time, or the integrated value ΣΔT2 within the predetermined period or a plurality of calculation periods When it is equal to or higher than the predetermined value, it is estimated that the sulfur concentration of the fuel used is higher than the predetermined value, that is, the fuel used is a high S fuel. On the other hand, when the difference ΔT2 or its integrated value ΣΔT2 is less than a predetermined value, it is estimated that the sulfur concentration of the fuel used is less than the predetermined value, that is, the fuel used is low S fuel.

  When the low S fuel is used, the difference ΔT2 between the downstream catalyst estimated temperature T2b and the downstream catalyst detection temperature T2a on the premise of the low S fuel should be small, and in this case, the used fuel can be estimated as the low S fuel. However, when high S fuel is used, the difference ΔT2 between the downstream catalyst estimated temperature T2b and the downstream catalyst detection temperature T2a on the premise of low S fuel increases. Therefore, in this case, the fuel used is estimated to be high S fuel.

  This estimation method has the following advantages. First, compared with the case where the sulfur concentration of the fuel used is detected by the sulfur concentration sensor, the two temperature sensors 21 and 22 are relatively inexpensive, so that there is an advantage that the apparatus configuration can be suppressed relatively inexpensively.

  Next, it is conceivable to estimate the sulfur concentration of the fuel based on the detected temperature decrease amount of only one of the upstream catalyst 11 and the downstream catalyst 19, but this may be a temperature decrease due to catalyst deterioration or the influence of sulfur. It is impossible to distinguish whether the temperature drop is caused by. However, according to the estimation method of the present embodiment, the detected temperature or information of both the upstream catalyst 11 and the downstream catalyst 19 is used. In particular, the difference ΔT2 between the downstream catalyst estimated temperature T2b and the downstream catalyst detected temperature T2a estimated based on the upstream catalyst detected temperature T1 is used. Thus, 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 determines a predetermined value to be compared with the difference ΔT2 or the integrated value ΣΔT2 according to the upstream catalyst detection temperature T1 at a predetermined time or the average value or integrated value of the upstream catalyst detection temperature T1 within a predetermined period. Variable setting. Specifically, the predetermined value is set to a larger value as the average value or integrated value of the upstream catalyst detection temperature T1 at a predetermined time or the upstream catalyst detection temperature T1 within a predetermined period is higher. This setting can be performed using a predetermined map.

  As understood from FIG. 6, the difference ΔT2 between the estimated downstream catalyst temperature T2b 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, as the average value or integrated value of the upstream catalyst detection temperature T1 at a predetermined time or the upstream catalyst detection temperature T1 within a predetermined period is higher, the predetermined value is increased to reflect the characteristics of FIG. Thus, the estimation accuracy can be further improved.

  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 ΔT2 or the integrated value ΣΔT2. Instead of the difference ΔT2, the ratio R = T2b / T2a between the estimated downstream catalyst temperature T2b and the detected downstream catalyst temperature T2a 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.

  First, FIG. 7 shows a routine of the fuel property determination process performed as a premise of the abnormality diagnosis process. 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 or not the ignition switch (IG) has been turned on from off, that is, whether or not this time is the IG on timing.
If it is IG on timing, a high S fuel flag (described in detail later) is turned on in step S102, and the process proceeds to step S103. On the other hand, if it is not IG ON timing, step S102 is skipped and the process proceeds to step S103. That is, the high S fuel flag is turned on only for the first time when the IG is turned on.

  In step S103, it is determined whether a precondition suitable for performing the fuel property determination process is satisfied. For example, (1) the engine is in a warm-up state, (2) the upstream catalyst 11 and the downstream catalyst 19 are in a warm-up state, (3) the fuel cut is not being executed, and (4) after returning from the fuel cut If a predetermined time (for example, 5 seconds) has elapsed, the precondition is satisfied. The success or failure of the condition (1) is determined based on the detection value of a water temperature sensor (not shown). For example, the condition is satisfied when the detection value is 75 ° C. or higher. The success or failure of the condition (2) is determined based on the upstream catalyst detection temperature T1a and the downstream catalyst detection temperature T2a. 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 S104.

  In step S104, the difference ΔT2 between the current estimated downstream catalyst temperature T2b and the detected downstream catalyst temperature T2a is calculated, and the difference ΔT2 is integrated.

  Next, in step S105, it is determined whether or not the number of integrations is equal to or greater than a predetermined value N, that is, whether or not the number of integrations has reached a predetermined value N. The predetermined value N is a relatively large positive value. If the integration count has not reached the predetermined value N, the process is terminated. On the other hand, if the integration count has reached the predetermined value N, the process proceeds to step S106.

  In step S106, the integrated value ΣΔT2 of the difference ΔT2 is compared with a predetermined value, that is, a predetermined high S determination value β.

  If the integrated value ΣΔT2 is smaller than the high S determination value β, the process proceeds to step S107, the high S fuel flag is turned off, the integrated value ΣΔT2 is cleared, and the process is terminated.

  On the other hand, if the integrated value ΣΔT2 is greater than or equal to the high S determination value β, the process proceeds to step S108, the high S fuel flag is turned on, the integrated value ΣΔT2 is cleared, and the process ends.

  As can be seen, the high S fuel flag is turned on when it is estimated that the fuel used is high S fuel, and is turned off when it is estimated that the fuel used is not high S fuel (low S fuel). Flag. In step S102, for the sake of convenience, the high S fuel flag is turned on when the IG is turned on. The reason for this is to prevent the abnormality diagnosis from being normally executed on the premise of the low S fuel when it is unknown whether the used fuel is the high S fuel or the low S fuel.

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

  First, in step S201, it is determined whether or not a precondition suitable for performing the catalyst abnormality diagnosis process is satisfied. For example, (1) the engine is in a warm-up state, (2) the upstream catalyst 11 and the downstream catalyst 19 are in a warm-up state, (3) the pre-catalyst sensor 17 and the post-catalyst sensor 18 are in an active state, (4 ) If the engine is in steady operation and (5) the high S fuel flag is off, the precondition is met. 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 the pre-catalyst sensor 17 and the post-catalyst sensor 18. 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. Condition (5) is based on the result of the fuel property determination process of FIG. Other examples of the precondition are possible.

  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 and the value of the oxygen storage capacity OSC is measured. That is, rich control and lean control are alternately performed a plurality of times, and the value of the released oxygen amount is measured during the rich control, and the value of the stored oxygen amount is measured during the lean control.

  In step S203, it is determined whether or not the measurement of the oxygen storage capacity OSC is completed. That is, in this embodiment, a plurality of values of the predetermined number of oxygen storage capacities OSC are measured, and the measurement is completed when the values of the predetermined number of oxygen storage capacities OSC have been measured.

  In step S204, an average value OSCav of a predetermined number of oxygen storage capacity measurement values is calculated, and this average value OSCav is compared with a predetermined abnormality determination value α.

  When the average value OSCav is larger than the abnormality determination value α, the process proceeds to step S205, where the upstream catalyst 11 is determined to be normal, and the process is terminated.

  On the other hand, if the average value OSCav is less than or equal to the abnormality determination value α, the process proceeds to step S206, where it is determined that the upstream catalyst 11 is abnormal, and the process ends.

  By the way, in the first embodiment, the precondition of step S201 includes (5) the condition that the high S fuel flag is off. That is, only when it is estimated that the used fuel is low S fuel, the substantial diagnostic processing after step S202 is executed. When the used fuel is estimated to be high S fuel, the processing is immediately terminated, and after step S202. The substantial diagnosis process is not executed.

  In other words, if the fuel used is estimated to be high S fuel, diagnosis is prohibited. Accordingly, it is possible to prevent an erroneous diagnosis result from being obtained when the high S fuel is used, and to prevent erroneous diagnosis in advance. 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.

  Next, a second embodiment of the catalyst abnormality diagnosis process will be described with reference to FIG. The illustrated routine is also repeatedly executed by the ECU 20 every predetermined calculation cycle (for example, 16 msec).

  The main feature of the second embodiment is that a control change for reducing the influence of sulfur on the upstream catalyst 11 is executed when the fuel used is estimated to be high S fuel.

  First, in step S301, as in step S201, it is determined whether a precondition suitable for performing the catalyst abnormality diagnosis process is satisfied. However, the preconditions here are different from the preconditions in step S201, except for the precondition in step S201 excluding the condition that (5) the high S fuel flag is off.

  If the precondition is not satisfied, the process is terminated. If the precondition is satisfied, the process proceeds to step S302.

  In step S302, it is determined whether the high S fuel flag is on. If it is on, the process proceeds to step S303 to execute the control change, and then proceeds to step S304. On the other hand, if it is off, step S303 is skipped and the process proceeds to step S304.

  Steps S304 to S308 are the same as steps S202 to S206.

  Here, some examples regarding the control change are shown. First, a first example will be described with reference to FIG.

  FIG. 10 shows the target air-fuel ratio A / Ft, the pre-catalyst sensor output (however, converted to the pre-catalyst air-fuel ratio A / Ff), and the oxygen storage capacity measurement as shown in FIG. The value OSCi (i = 1, 2, 3,...) Is indicated. Time t1 is the start of active air-fuel ratio control.

  In the present embodiment, the lean control or rich control for a predetermined number of times from the start of the active air-fuel ratio control is invalid (so-called abandonment). For the invalid times, the oxygen storage capacity is not measured, or the measured value is not used as a basis for determining whether the catalyst is normal or abnormal. In other words, in the invalid time, the active air-fuel ratio control is only substantially executed.

  In the illustrated example, lean control is executed for the first time corresponding to OSC1, and rich control is executed for the second time corresponding to OSC2 (the same applies hereinafter). In this embodiment, for example, lean control and rich control for two times from the beginning (that is, up to the second rich control) are invalid times. In the illustrated example, these invalid oxygen storage capacities OSC1, OSC2 are measured, but these may not be measured. The measurement of the oxygen storage capacity is started from the third lean control corresponding to OSC3. This measurement is terminated when, for example, the OSC 10 finishes measuring in the tenth rich control (at the same time, the active air-fuel ratio control is terminated). The oxygen storage capacity average value OSCav is calculated based on the remaining eight oxygen storage capacity measurement values OSC3 to OSC10 (up to OSC8 shown) excluding the invalid batch. In this example, a total of ten lean controls and rich controls are executed, of which the first two times are invalid times and the remaining eight times are valid times.

  Thus, the reference value of invalid times is 2, which is referred to as reference invalid times. The reason for providing such invalid times is to reduce the variation in the catalyst state due to the difference in the engine operation state before the start of the active air-fuel ratio control, and to stabilize the catalyst state. Of course, the number of reference invalid times can be arbitrarily determined.

  The number of reference invalid times is set on the premise of low S fuel as the base fuel. On the other hand, when the high S fuel flag is on, that is, when the used fuel is estimated to be high S fuel, the number of invalid times is increased from the number of reference invalid times, for example, four. This increased invalid number of times is referred to as an increased invalid number of times. Of course, the number of invalid increases can be arbitrarily determined. In this case, the oxygen storage capacity average value OSCav is calculated based on the remaining oxygen storage capacity measurement values OSC5 to OSC10.

  In general, sulfur poisoning of a catalyst tends to be eliminated as the temperature of the catalyst is higher and the atmosphere of the catalyst is richer. According to the first example, since the number of invalid times is increased when the fuel used is estimated to be high S fuel, the number of lean control and rich control before measurement can be increased compared to when low S fuel is used. it can. In particular, by increasing the number of rich controls, the sulfur poisoning of the catalyst can be eliminated during the invalidation, and the measurement can be started after that.

  Therefore, as a result, it is possible to reduce the influence of sulfur on the catalyst, obtain a measurement value with less error, and execute a highly accurate diagnosis. Further, it is possible to prevent an erroneous diagnosis in which a catalyst that is not normally abnormal is erroneously diagnosed as abnormal. When using low S fuel, diagnosis can be performed as usual using the reference invalid times.

  In this first example, the number of measurements may be increased by the increment of invalid times to ensure the same number of measurement values as when using low S fuel. For example, if the number of invalid times is increased by 2, the number of times of measurement is also increased by 2, and the same eight measurement values as when using low S fuel are secured.

  Next, a second example of control change will be described with reference to FIG.

  FIG. 11 is a view similar to FIG. In this second example, the number of reference invalid times is 4, and a total of 10 lean controls and rich controls are executed, and the oxygen storage capacity measurement values used as the basis of determination are OSC5 to OSC10 (shown up to OSC8). Of 6 times.

  In this second example, when the fuel used is estimated to be high S fuel, the number of invalid times is not increased, but instead the amplitude of the rich control at invalid times is increased. That is, as shown in FIG. 11, when the fuel used is estimated to be high S fuel, the amplitude of the rich control is increased by a predetermined value ΔAr from the reference value Ar assuming low S fuel, and Ar ′ It is said. Ar is referred to as a reference amplitude, Ar ′ is referred to as an increase amplitude, and ΔAr is referred to as an amplitude increase amount.

  For example, Ar = 0.5, Ar ′ = 0.8, and ΔAr = 0.3. When the stoichiometric A / Fs is set to 14.6, the rich air-fuel ratio A / Fr at the time of reference assuming low S fuel is 14.1, and the rich air-fuel ratio A / Fr ′ when the amplitude is increased is 13.8. . However, these values can be determined arbitrarily. There is no change in lean control.

  As described above, the sulfur poisoning of the catalyst tends to be eliminated as the temperature of the catalyst is higher and the catalyst atmosphere is richer. According to the second example, when the use fuel is estimated to be high S fuel, the amplitude of the rich control in the invalid time is increased, so that sulfur poisoning of the catalyst is eliminated during the invalid time, Measurement can be started with.

  Therefore, as a result, it is possible to reduce the influence of sulfur on the catalyst, obtain a measurement value with less error, and execute a highly accurate diagnosis. Further, it is possible to prevent an erroneous diagnosis in which a catalyst that is not normally abnormal is erroneously diagnosed as abnormal. When using low S fuel, diagnosis can be performed as usual using the reference amplitude Ar even in invalid times.

  Next, a third example of control change will be described with reference to FIG.

  FIG. 12 is also similar to FIG. Also in this third example, the number of reference invalid times is 4, and a total of 10 lean controls and rich controls are executed, and the oxygen storage capacity measurement values used as the basis of the determination are OSC5 to OSC10 (shown from OSC8 to OSC8). ) 6 times.

  In this third example, when the fuel used is estimated to be high S fuel, the switching timing from the rich control to the lean control in the invalid time is delayed. That is, when the low S fuel is used or when it is estimated that the used fuel is the low S fuel, as shown in FIGS. 3 and 4, the rich catalyst value Vr reaches the rich determination value VR as shown in FIGS. Switching from control to lean control is performed. However, as shown in FIG. 12, when the high S fuel is used or when it is estimated that the used fuel is the high S fuel, the catalyst output Vr after the catalyst reaches a predetermined value than the timings t2 and t3 when the rich determination value VR is reached. The rich control is switched to the lean control at timings t2 ′ and t3 ′ delayed by the delay time Δtd. The delay time Δtd is, for example, several seconds. There is no change in lean control.

  As described above, the sulfur poisoning of the catalyst tends to be eliminated as the temperature of the catalyst is higher and the catalyst atmosphere is richer. According to the third example, when the fuel used is estimated to be high S fuel, the switching timing from the rich control to the lean control in the invalid time is delayed. Therefore, rich control can be performed for a longer time in the invalid time, and sulfur poisoning of the catalyst can be eliminated during the invalid time, and measurement can be started after that.

  Therefore, as a result, it is possible to reduce the influence of sulfur on the catalyst, obtain a measurement value with less error, and execute a highly accurate diagnosis. Further, it is possible to prevent an erroneous diagnosis in which a catalyst that is not normally abnormal is erroneously diagnosed as abnormal. When low S fuel is used, the switching timing in the invalid time is normal, and diagnosis can be performed as usual.

  In the illustrated example, the measurement of the oxygen storage capacities OSC2 and OSC4 is terminated at a normal timing when the post-catalyst sensor output Vr reaches the rich determination value VR during the rich control in the invalid time. However, since the measurement value at the invalid time is not used as a basis for determining the normal / abnormality, the measurement may be terminated at timings t2 'and t3' after the delay time has elapsed. As already described, it is not necessary to perform measurement at invalid times.

  The above first to third examples can be appropriately combined.

  Next, a third embodiment of the catalyst abnormality diagnosis process will be described with reference to FIG. The illustrated routine is also repeatedly executed by the ECU 20 every predetermined calculation cycle (for example, 16 msec).

  The main feature of the third embodiment is that, when the fuel used is estimated to be high S fuel, temperature increase control for increasing the temperature of the upstream catalyst 11 is executed at least before measuring the oxygen storage capacity. .

  In step S401, as in step S201, it is determined whether a precondition suitable for performing the catalyst abnormality diagnosis process is satisfied. However, the preconditions here are different from the preconditions in step S201, except for the precondition in step S201 excluding the condition that (5) the high S fuel flag is off.

  If the precondition is not satisfied, the process is terminated. If the precondition is satisfied, the process proceeds to step S402.

  In step S402, it is determined whether the high S fuel flag is on. If it is on, the routine proceeds to step S403, where the temperature raising control is executed, and then it is judged at step S404 whether the temperature raising control has ended. If completed, the process proceeds to step S405. If not completed, the process ends. On the other hand, if the high S fuel flag is off in step S402, steps S403 and S404 are skipped and the process proceeds to step S405.

  Steps S405 to S409 are the same as steps S202 to S206.

  Here, some examples relating to the temperature rise control will be shown. First, the first example is retard angle control that retards the ignition timing of the engine 1. By this retard control, the ignition timing of the engine 1 is retarded by a predetermined crank angle from the reference ignition timing on the premise of low S fuel.

  As described above, the sulfur poisoning of the catalyst tends to be eliminated as the temperature of the catalyst is higher and the catalyst atmosphere is richer. According to this first example, the ignition timing is retarded from the reference ignition timing when the fuel used is estimated to be high S fuel. Then, the combustion in the combustion chamber 3 becomes slow, and the exhaust gas discharged from the combustion chamber 3 contains more unburned components such as HC and CO. Since the unburned component is oxidized and burned in the upstream catalyst 11, the upstream catalyst 11 is heated. Thereby, the sulfur poisoning of the upstream catalyst 11 can be eliminated, and the measurement can be started after that.

  Therefore, as a result, it is possible to reduce the influence of sulfur on the catalyst, obtain a measurement value with less error, and execute a highly accurate diagnosis. Further, it is possible to prevent an erroneous diagnosis in which a catalyst that is not normally abnormal is erroneously diagnosed as abnormal. In addition, when using low S fuel, diagnosis can be performed as usual without performing the retard control.

  Next, a second example of temperature rise control will be described. This second example is imbalance control in which the air-fuel ratio of each cylinder of the engine 1 is forcibly varied. Usually, the air-fuel ratio of each cylinder is controlled so as to coincide with a target air-fuel ratio (for example, stoichiometric A / Fs), and the fuel injection amount of each cylinder is controlled so as to be so. On the other hand, when the imbalance control is executed, only the air-fuel ratio of a predetermined partial cylinder (for example, one cylinder) among all the cylinders is controlled to a predetermined air-fuel ratio that deviates from the target air-fuel ratio, and each cylinder is set so as to do so. The fuel injection amount is controlled. As a result, the air-fuel ratio of each cylinder is forcibly varied.

  As described above, the sulfur poisoning of the catalyst tends to be eliminated as the temperature of the catalyst is higher and the catalyst atmosphere is richer. According to this second example, the air-fuel ratio of each cylinder is forcibly varied when the fuel used is estimated to be high S fuel. Then, since the air-fuel ratio of the exhaust gas supplied to the upstream catalyst 11 changes to the lean side and the rich side during one engine cycle, the oxidation-reduction reaction is performed each time, the upstream catalyst 11 is activated, and the upstream catalyst 11 Rises in temperature. Thereby, the sulfur poisoning of the upstream catalyst 11 can be eliminated, and the measurement can be started after that.

  Therefore, as a result, it is possible to reduce the influence of sulfur on the catalyst, obtain a measurement value with less error, and execute a highly accurate diagnosis. Further, it is possible to prevent an erroneous diagnosis in which a catalyst that is not normally abnormal is erroneously diagnosed as abnormal. When using low S fuel, diagnosis can be performed as usual without performing such imbalance control.

  In this embodiment, as shown in FIG. 13, when the high S fuel is estimated, the temperature increase control is performed for a predetermined time before the start of the active air-fuel ratio control. Then, after the active air-fuel ratio control is started, after the reference number is invalidated, the measurement of the oxygen storage capacity is substantially started. However, the temperature raising control may be performed during the invalid times after the start of the active air-fuel ratio control. In short, it is sufficient that the temperature increase control is executed before the substantial measurement of the oxygen storage capacity is started.

  The first example and the second example can be combined. It is also possible to combine the third embodiment with the second embodiment. Specifically, at least one of the first example and the second example of the third embodiment can be combined with at least one of the first to third examples of the second embodiment.

  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 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 19 Downstream catalyst 12 Injector 17 Pre-catalyst sensor 18 Post-catalyst sensor 20 Electronic control unit (ECU)
21 upstream temperature sensor 22 downstream temperature sensor

Claims (10)

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;
An upstream temperature sensor and a downstream temperature sensor for detecting the temperatures of the upstream catalyst and the downstream catalyst, respectively;
Temperature estimation means for estimating the temperature of the downstream catalyst based on the detected temperature of the upstream catalyst detected by the upstream temperature sensor;
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 downstream temperature sensor;
A fuel property determining apparatus comprising: The sulfur concentration estimating means estimates the sulfur concentration of the fuel used based on a difference between an estimated temperature of the downstream catalyst at a predetermined time and a detected temperature, or an integrated value of the difference within a predetermined period. Item 2. The fuel property determination device according to Item 1. The fuel property determination device according to claim 2, wherein the sulfur concentration estimation unit estimates that the sulfur concentration of the fuel used is equal to or greater than a predetermined value when the difference or the integrated value is equal to or greater than a predetermined value. 4. The sulfur concentration estimating means variably sets the predetermined value according to a value at the predetermined time of the detected temperature of the upstream catalyst, or an average value or an integrated value within the predetermined period. Fuel property judgment device. The sulfur concentration estimating means sets the predetermined value to a larger value as the value of the detected temperature of the upstream catalyst at the predetermined time or the average value or integrated value within the predetermined period is higher. 4. The fuel property determining apparatus according to 4. A catalyst abnormality diagnosis device comprising the fuel property determination device according to any one of claims 1 to 5 and diagnosing whether the upstream catalyst is normal or abnormal,
Active air-fuel ratio control means for performing active air-fuel ratio control for alternately controlling the air-fuel ratio on the upstream side of the upstream catalyst in a lean and rich manner;
Measuring means for measuring the amount of oxygen absorbed and released by the upstream catalyst during lean control and rich control of the air-fuel ratio;
Determining means for determining whether the upstream catalyst is normal or abnormal based on a plurality of oxygen amounts measured by the measuring means;
Control change means for executing a control change for reducing the influence of sulfur on the upstream catalyst when the sulfur concentration of the used fuel is estimated to be a predetermined value or more by the sulfur concentration estimation means;
A catalyst abnormality diagnosis device comprising: Among the active air-fuel ratio control, the lean control or the rich control for a predetermined number of times from the start thereof is an invalid time, and the invalid value is not measured by the measuring unit or the measured value is measured. Is not used as the basis for the determination by the determination means,
The control change includes increasing the number of invalid times, increasing the amplitude of the rich control in the invalid times, and the invalid time in comparison with a case where the sulfur concentration of the fuel used is less than a predetermined value. The catalyst abnormality diagnosis device according to claim 6, comprising at least one of delaying a switching timing from the rich control to the lean control. A catalyst abnormality diagnosis device comprising the fuel property determination device according to any one of claims 1 to 5 and diagnosing whether the upstream catalyst is normal or abnormal,
Active air-fuel ratio control means for performing active air-fuel ratio control for alternately controlling the air-fuel ratio on the upstream side of the upstream catalyst in a lean and rich manner;
Measuring means for measuring the amount of oxygen absorbed and released by the upstream catalyst during lean control and rich control of the air-fuel ratio;
Determining means for determining whether the upstream catalyst is normal or abnormal based on a plurality of oxygen amounts measured by the measuring means;
When the sulfur concentration estimation unit estimates that the sulfur concentration of the fuel used is equal to or higher than a predetermined value, temperature increase control is performed to increase the temperature of the upstream catalyst at least before measurement by the measurement unit. Temperature rise control means,
A catalyst abnormality diagnosis device comprising: The temperature increase control includes at least one of a retard angle control that retards the ignition timing of the internal combustion engine and an imbalance control that forcibly varies the air-fuel ratio of each cylinder of the internal combustion engine. The catalyst abnormality diagnosis device according to claim 8. A catalyst abnormality diagnosis device comprising the fuel property determination device according to any one of claims 1 to 5 and diagnosing whether the upstream catalyst is normal or abnormal,
A catalyst abnormality diagnosis device characterized by prohibiting diagnosis when the sulfur concentration estimating means estimates that the sulfur concentration of the fuel used is equal to or higher than a predetermined value.

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