JP2009215924A - Fuel property determination device and catalyst deterioration diagnostic device having the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel property determination device estimating sulfur concentration of fuel, and to provide a catalyst deterioration diagnostic device having the same. <P>SOLUTION: An air-fuel ratio (a target air-fuel ratio A/Ft) of exhaust gas supplied to a catalyst is gradually changed from a rich side to a lean side, and the sulfur concentration of fuel is estimated based on values A/Ft1, A/Ft2 of the air-fuel ratio at timing t1, t2 where an output Vrr of an air-fuel ratio sensor after the catalyst is inverted to the lean side. Since the inversion timing differs depending on the sulfur concentration of fuel, the sulfur concentration of fuel is estimated by using the fact. When the estimation results in the fuel sulfur concentration of a predetermined value or more, catalyst deterioration diagnosis is suspended to prevent wrong diagnosis. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a fuel property determination device and a catalyst deterioration diagnosis device including the same, and more particularly, a fuel property determination device capable of estimating the sulfur concentration of fuel used in an internal combustion engine, and catalyst deterioration using the estimation result. The present invention relates to a catalyst deterioration diagnosis device for diagnosing the catalyst.

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

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

  For example, Patent Document 1 discloses an apparatus for determining catalyst deterioration using the Cmax method, which determines the degree of catalyst deterioration based on the measured oxygen storage capacity and the number of times the oxygen storage capacity is calculated. .

JP 2004-176611 A

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

  In order to prevent such a misdiagnosis, it is preferable to discriminate the fuel property, particularly to estimate the sulfur concentration of the fuel. This is because if such discrimination or estimation is performed, necessary measures such as deferring diagnosis when the fuel is estimated to have a high sulfur concentration can be taken, and erroneous diagnosis can be prevented in advance.

  Therefore, the present invention has been made in view of such a situation, and an object of the present invention is to prevent a misdiagnosis by using a fuel property determination device capable of estimating the sulfur concentration of fuel and an estimation result thereof. The object is to provide a catalyst deterioration diagnosis device.

According to one aspect of the invention,
A catalyst provided in the exhaust passage of the internal combustion engine;
A post-catalyst air-fuel ratio sensor provided downstream of the catalyst;
Air-fuel ratio control means for gradually changing the air-fuel ratio of the exhaust gas supplied to the catalyst from the rich side to the lean side, or vice versa;
Based on the value of the air-fuel ratio at the timing when the output of the post-catalyst air-fuel ratio sensor reverses to the lean side or the rich side when the air-fuel ratio of the exhaust gas is gradually changed by the air-fuel ratio control means, the sulfur concentration of the fuel is determined. There is provided a fuel property discriminating device comprising a sulfur concentration estimating means for estimating.

  When the air-fuel ratio of the exhaust gas supplied to the catalyst is gradually changed from the rich side to the lean side or vice versa, the timing at which the output of the post-catalyst air-fuel ratio sensor reverses to the lean side or the rich side depends on the sulfur concentration of the fuel Different. Therefore, using this correlation, the sulfur concentration of the fuel is estimated based on the value of the air-fuel ratio at the inversion timing of the post-catalyst air-fuel ratio sensor output.

  Preferably, the fuel property determination device includes a pre-catalyst air-fuel ratio sensor provided upstream of the catalyst, and the air-fuel ratio control means determines the air-fuel ratio of the exhaust gas detected by the pre-catalyst air-fuel ratio sensor. The air-fuel ratio is controlled so as to coincide with the target air-fuel ratio, and the air-fuel ratio of the exhaust gas supplied to the catalyst is gradually changed from the rich side by gradually changing the target air-fuel ratio from the rich side to the lean side or vice versa. The sulfur concentration of the fuel is determined based on the value of the target air-fuel ratio at the timing when the output of the post-catalyst air-fuel ratio sensor reverses to the lean side or the rich side. Is estimated.

  Preferably, the air-fuel ratio control means gradually changes the air-fuel ratio of the exhaust gas supplied to the catalyst from the rich side to the lean side with respect to the stoichiometry or vice versa.

  Preferably, the air-fuel ratio control unit updates the target air-fuel ratio by a predetermined value every predetermined time.

According to another aspect of the invention,
A catalyst deterioration diagnosis device comprising the fuel property determination device, wherein the catalyst deterioration diagnosis is suspended when a fuel sulfur concentration greater than a predetermined value is estimated by the sulfur concentration estimation means. A diagnostic device is provided.

  According to this, since the deterioration diagnosis of the catalyst is suspended when the fuel sulfur concentration equal to or higher than the predetermined value is estimated, a false diagnosis due to the influence of sulfur in the fuel can be prevented in advance.

  Preferably, measuring means for measuring a parameter correlated with the degree of deterioration of the catalyst is provided, and when the measured parameter is a value corresponding to the deteriorated catalyst, the air-fuel ratio is gradually changed by the air-fuel ratio control means and the sulfur The sulfur concentration is estimated by the concentration estimating means.

  According to this, the measurement of the parameter is first executed, and when the measured parameter is a value corresponding to the deteriorated catalyst, the gradual change of the air-fuel ratio and the estimation of the sulfur concentration are executed in order to examine the presence or absence of the influence of sulfur. Is done. Therefore, the gradual change of the air-fuel ratio and the estimation of the sulfur concentration can be executed with the minimum frequency.

According to yet another aspect of the invention,
A catalyst deterioration diagnosis device comprising the fuel property determination device, comprising a measuring means for measuring a parameter correlated with the degree of deterioration of the catalyst, and a fuel sulfur concentration greater than or equal to a predetermined value estimated by the sulfur concentration estimating means. A catalyst deterioration diagnosis device is provided that corrects the measured parameter and executes a catalyst deterioration diagnosis based on the corrected parameter.

  According to this, when the fuel sulfur concentration of a predetermined value or more is estimated, the measured parameter is corrected and the deterioration diagnosis of the catalyst is executed, so that erroneous diagnosis due to the influence of sulfur in the fuel is prevented in advance. be able to.

  According to the present invention, it is possible to provide a fuel property determination device that can estimate the sulfur concentration of fuel, and a catalyst deterioration diagnosis device that can prevent erroneous diagnosis by using the estimation result. Is demonstrated.

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

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

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

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

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

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

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

  The catalysts 11 and 19 simultaneously purify NOx, HC and CO when the air-fuel ratio A / F of the exhaust gas flowing into the catalysts 11 and 19 is near the stoichiometric air-fuel ratio (stoichiometric, for example, A / Fs = 14.55). In response to this, the ECU 20 normally performs feedback control of the air-fuel ratio of the exhaust gas discharged from the combustion chamber 3 and supplied to the upstream catalyst 11, that is, the pre-catalyst air-fuel ratio A / Ffr, to the stoichiometric air-fuel ratio (stoichiometric feedback). control). Specifically, the ECU 20 sets a target air-fuel ratio A / Ft equal to the theoretical air-fuel ratio, and the pre-catalyst air-fuel ratio A / Ffr detected by the pre-catalyst air-fuel ratio sensor 17 matches the target air-fuel ratio A / Ft. As described above, feedback control is performed on the fuel injection amount injected from the injector 12, and consequently the air-fuel ratio.

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

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

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

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

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

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

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

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

  In the illustrated example, the rich amplitude Ar and the lean amplitude Al are equal. For example, the center air fuel ratio = theoretical air fuel ratio A / Fs = 14.55, the rich air fuel ratio A / Fr = 14.05, the lean air fuel ratio A / Fl = 15.05, the rich amplitude Ar = the lean amplitude Al = 0.5. is there. Compared to the normal stoichiometric feedback control, the active air-fuel ratio control has a larger air-fuel ratio amplitude, that is, the values of the rich amplitude Ar and the lean amplitude Al are larger.

  By the way, the timing or timing at which the target air-fuel ratio A / Ft is switched is the timing at which the output of the post-catalyst air-fuel ratio sensor 18 switches (or reverses) from rich to lean or from lean to rich. As shown in the figure, the output voltage Vrr of the post-catalyst air-fuel ratio sensor 18 changes suddenly at the theoretical air-fuel ratio A / Fs. In order to determine the inversion timing of the output voltage Vrr, that is, whether the output voltage Vrr is inverted to the rich side or the lean side, the two inversion thresholds VR and VL relating to the output voltage Vrr are determined. It has been. Here, VR is referred to as a rich determination value, and VL is referred to as a lean determination value. VR> VL, for example, VR = 0.59 (V) and VL = 0.21 (V). When the output voltage Vrr changes to the lean side, that is, decreases and reaches the lean determination value VL, the output voltage Vrr is considered to be reversed to the lean side, and the post-catalyst air-fuel ratio A detected by the post-catalyst air-fuel ratio sensor 18 is obtained. / Frr is determined to be leaner than at least the stoichiometric air-fuel ratio. On the other hand, when the output voltage Vrr changes to the rich side, that is, increases and reaches the rich determination value VR, the output voltage Vrr is considered to be reversed to the rich side, and the post-catalyst air-fuel ratio A / Frr is at least greater than the stoichiometric air-fuel ratio. Judged to be rich.

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

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

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

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

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

  Therefore, using this fact, the oxygen storage capacity OSC is measured as follows. As shown in FIG. 4, immediately after the target air-fuel ratio A / Ft is switched to the rich air-fuel ratio A / Fr at time t1, the pre-catalyst air-fuel ratio A / Ffr as the actual value is slightly delayed with the rich air-fuel ratio A / Fr. Switch to Fr. From the time t11 when the pre-catalyst air-fuel ratio A / Ffr reaches the theoretical air-fuel ratio A / Fs to the time t2 when the target air-fuel ratio A / Ft next reverses, the following equation (1) An oxygen storage capacity dOSC (instantaneous value of the oxygen storage capacity) is calculated, and the oxygen storage capacity dOSC for each minute time is integrated from time t11 to time t2. Thus, the oxygen storage capacity, that is, the amount of released oxygen (OSC1 in FIG. 4) in this oxygen release cycle is measured.

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

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

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

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

  As described above, when fuel with a high sulfur concentration (high sulfur fuel) is supplied, the catalyst is poisoned with sulfur, and the measured value of the oxygen storage capacity decreases. And although it is a normal catalyst, there is a possibility of misdiagnosis as deterioration. In order to prevent such a misdiagnosis, it is preferable to discriminate the fuel property, particularly to estimate the sulfur concentration in the fuel. This is because if such discrimination or estimation is performed, necessary measures such as deferring diagnosis when the fuel is estimated to have a high sulfur concentration can be taken, and erroneous diagnosis can be prevented in advance.

  Therefore, in this embodiment, the determination of the fuel property, particularly the estimation of the sulfur concentration in the fuel is performed. The contents will be described below.

  In this embodiment, the air-fuel ratio of the exhaust gas supplied to the catalyst 11 is gradually changed from the rich side to the lean side, and the value of the air-fuel ratio at the timing when the output of the post-catalyst air-fuel ratio sensor 18 is reversed to the lean side at this time. Based on this, the sulfur concentration of the fuel is estimated. Hereinafter, 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 sulfur fuel or a low S fuel. A fuel having a higher sulfur concentration, that is, a fuel having a sulfur concentration higher than the predetermined value is referred to as a high sulfur fuel or a high S fuel. The low sulfur fuel is, for example, a fuel having a sulfur concentration of 30 ppm, and the high sulfur fuel is, for example, a fuel having a sulfur concentration of 300 ppm. In the following example, the stoichiometric air-fuel ratio, that is, the stoichiometric value is 14.55.

  FIG. 5 shows changes in values when such air-fuel ratio gradual change is executed. (A) is the target air-fuel ratio A / Ft, (B) is the pre-catalyst air-fuel ratio A / Ffr detected by the pre-catalyst air-fuel ratio sensor 17, and (C) is the output voltage Vrr (V) of the post-catalyst air-fuel ratio sensor 18. Indicates. The threshold value that defines the rich / lean boundary of the output voltage Vrr of the post-catalyst air-fuel ratio sensor 18 is defined as Vref. The threshold value is set to a predetermined value corresponding to the vicinity of stoichiometry, and is set to 0.5 V here.

  As shown in (A), the target air-fuel ratio A / Ft is gradually changed from a predetermined value richer than stoichiometric to a predetermined value leaner than stoichiometric. Specifically, the target air-fuel ratio A / Ft is gradually changed (swept) from a predetermined value richer than stoichiometric to a predetermined value leaner than stoichiometric at a constant speed so as to cross stoichiometric. On the other hand, since the feedback control is performed so that the pre-catalyst air-fuel ratio A / Ffr detected by the pre-catalyst air-fuel ratio sensor 17 coincides with the target air-fuel ratio A / Ft, as shown in FIG. The fuel ratio A / Ffr also changes in the same manner as the target air fuel ratio A / Ft. However, due to the characteristics of feedback control, the pre-catalyst air-fuel ratio A / Ffr changes so that the center of vibration coincides with the target air-fuel ratio A / Ft while oscillating. As a result, the air-fuel ratio of the exhaust gas supplied to the catalyst 11 also changes in the same manner as the target air-fuel ratio A / Ft.

  When such a gradual change of the air-fuel ratio is performed, as shown in (C), the output voltage Vrr of the post-catalyst air-fuel ratio sensor 18 is reversed from the rich side to the lean side at a certain timing. That is, when the target air-fuel ratio A / Ft is on the rich side from the stoichiometry at the beginning of the gradual change, the rich gas is supplied to the catalyst 11 and the rich gas that could not be reacted by the catalyst 11 is blown down downstream of the catalyst 11 The sensor output Vrr is rich. However, as the air-fuel ratio gradually changes, when the gas supplied to the catalyst 11 gradually becomes lean, the lean gas blows down downstream of the catalyst 11 at a certain timing, and the post-catalyst air-fuel ratio sensor output Vrr is reversed to the lean side. To do.

  Here, in particular, the timing at which the post-catalyst air-fuel ratio sensor output Vrr reverses to the lean side varies depending on the sulfur concentration of the fuel. That is, as shown in (C), assuming that the timing when the post-catalyst air-fuel ratio sensor output Vrr falls below the threshold value Vref is the reversal timing to the lean side, the reversal timing t2 for the high sulfur fuel is the low sulfur fuel. The reversal timing t1 is later, and the former is the timing when the target air-fuel ratio A / Ft is on the lean side than the latter. In this way, there is a correlation between the fuel sulfur concentration and the reversal timing that the reversal timing is delayed as the fuel sulfur concentration is higher. The sulfur concentration is estimated. Here, since the value of the pre-catalyst air-fuel ratio A / Ffr is accompanied by vibration, the value of the target air-fuel ratio A / Ft is used as the value of the air-fuel ratio. This makes it possible to obtain a stable air-fuel ratio value. However, the value of the pre-catalyst air-fuel ratio A / Ffr detected by the pre-catalyst air-fuel ratio sensor 17 can be used if a certain degree of fluctuation is allowed. In the illustrated example, the target air-fuel ratio corresponding to the reversal timing t2 for the high sulfur fuel is A / Ft2, and the target air-fuel ratio corresponding to the reversal timing t1 for the low sulfur fuel is A / Ft1.

  Here, the reason why the inversion timing is delayed as the fuel sulfur concentration is increased will be described together with the experimental results shown in FIG. FIG. 6 shows the relationship between the air-fuel ratio of the gas supplied to the catalyst and the purification rates (%) of CO, HC, and NOx in the catalyst. These plots are high sulfur fuel data. There is almost no difference in the HC purification rate due to the difference in fuel.

  On the other hand, paying attention to the CO purification rate, the CO purification rate increasing line when the air-fuel ratio increases to stoichiometric (14.55) is on the lean side when high sulfur fuel is used than when low sulfur fuel is used. In addition, when the air-fuel ratio is stoichiometric, the purification rate at the time of high sulfur fuel is lower than the purification rate at the time of low sulfur fuel, that is, more CO at the time of high sulfur fuel than at the time of low sulfur fuel is downstream of the catalyst. Will be discharged.

  Further, the same tendency is seen in the NOx purification rate, and the NOx purification rate descending line when the air-fuel ratio increases from stoichiometric is on the lean side when the high sulfur fuel is used than when the low sulfur fuel is used. Further, when compared at a constant air-fuel ratio (for example, 14.59) larger than stoichiometric, the purification rate at the time of high sulfur fuel is higher than the purification rate at the time of low sulfur fuel, that is, high sulfur is present downstream of the catalyst. Less NOx is emitted when fuel is used than when low sulfur fuel is used.

  From the results of these CO purification rates and NOx purification rates, if the fuel is changed from low sulfur fuel to high sulfur fuel, richer gas will be discharged to the downstream side of the catalyst even if the air-fuel ratio is the same. It can be said that the lean gas cannot be discharged downstream of the catalyst unless the gas to be made lean. From this, it is considered that the timing at which the post-catalyst air-fuel ratio sensor output Vrr is reversed to the lean side is delayed as the sulfur concentration of the fuel increases.

  Next, the fuel property determination process of the present embodiment 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). FIG. 8 shows changes in (A) the target air-fuel ratio A / Ft and (B) the post-catalyst air-fuel ratio sensor output Vrr when the fuel property determination process is executed.

  In step S101, the target air-fuel ratio A / Ft is set to a predetermined value and air-fuel ratio control is executed. The initial value of the target air-fuel ratio A / Ft is set to a predetermined value richer than the stoichiometric value.

  Next, in step S102, it is determined whether or not the post-catalyst air-fuel ratio sensor output Vrr has fallen below a threshold value Vref.

  If the post-catalyst air-fuel ratio sensor output Vrr is not lower than the threshold value Vref, the routine proceeds to step S103, where it is determined whether or not a predetermined time T has elapsed since the update of the target air-fuel ratio A / Ft. Here, in order to gradually change the target air-fuel ratio A / Ft, the target air-fuel ratio A / Ft is increased and updated by a predetermined value D every predetermined time T (see step S104). It is substantially determined whether or not the target air-fuel ratio A / Ft has been updated.

  If it is determined that the predetermined time T has not elapsed since the update of the target air-fuel ratio A / Ft, the routine is terminated. On the other hand, if it is determined that the predetermined time T has elapsed since the update of the target air-fuel ratio A / Ft, the process proceeds to step S104, where the predetermined value D is added to the current value of the target air-fuel ratio A / Ft, A / Ft is updated and the routine is terminated.

  Thus, as a result of the target air-fuel ratio A / Ft being increased and updated by the predetermined value D every predetermined time T, the air-fuel ratio of the exhaust gas supplied to the catalyst 11 is gradually changed to the lean side. When the gas discharged from the catalyst 11 becomes leaner, the post-catalyst air / fuel ratio sensor output Vrr falls below the threshold value Vref at a certain timing. Simultaneously with this lean reversal, the determination result in step S102 is yes, and the process proceeds to step S105. In step S105, the value of the target air-fuel ratio A / Ft at the time of lean inversion is acquired. In step S106, the sulfur concentration of the fuel is estimated based on the acquired target air-fuel ratio A / Ft, and the routine is terminated. Here, the fuel sulfur concentration is estimated in two stages, such as a low sulfur fuel if the acquired target air-fuel ratio A / Ft is a predetermined value B or less, and a high sulfur fuel if the value is greater than the predetermined value B. Can be estimated. Alternatively, the relationship between the target air-fuel ratio A / Ft and the fuel sulfur concentration is experimentally determined in advance by a map, function, etc., and this relationship is used to correspond to the actually acquired target air-fuel ratio A / Ft value. An estimated value of the fuel sulfur concentration may be calculated. Various other methods are possible.

  Next, the procedure of the catalyst deterioration diagnosis process using the above-described fuel property determination will be described with reference to FIG. The illustrated process is also executed by the ECU 20.

  First, in step S201, the oxygen storage capacity OSC of the catalyst 11 is measured based on the aforementioned Cmax method. In this step, it is first determined whether or not a precondition suitable for executing the deterioration diagnosis is satisfied. For example, if the engine is in a steady operation state such that the fluctuation range of the intake air amount Ga and the engine rotational speed Ne is within a predetermined range, and the catalyst 11 and the catalyst front and rear sensors 17 and 18 have reached a predetermined activation temperature. The precondition is satisfied. When the precondition is not satisfied, the standby state is entered. On the other hand, when the precondition is satisfied, measurement of the oxygen storage capacity OSC is started. That is, as described above, the active air-fuel ratio control is started, and the oxygen storage capacity OSC of the catalyst 11 is measured as the active air-fuel ratio control is executed.

  When the measurement of the oxygen storage capacity OSC is completed in this way, in step S202, the oxygen storage capacity measurement value OSC is compared with a predetermined deterioration determination value OSCs. When the oxygen storage capacity measurement value OSC is larger than the deterioration determination value OSCs, it is determined or diagnosed that the catalyst 11 is normal in step S203.

  On the other hand, when the oxygen storage capacity measurement value OSC is equal to or less than the deterioration determination value OSCs, the process proceeds to step S204. In step S204, the fuel property determination process (excluding step S106) as shown in FIG. 7 is executed, and the target air-fuel ratio A / Ft value when the post-catalyst air-fuel ratio sensor output Vrr is lean-reversed (step S204). The value acquired in S105) is acquired. As described above, the air-fuel ratio gradual change and the fuel sulfur concentration estimation are executed only when the oxygen storage capacity measurement value OSC is a value corresponding to the deterioration catalyst equal to or less than the deterioration determination value OSCs. Can be done with.

  Next, in step S205, the acquired value of the target air-fuel ratio A / Ft is compared with a predetermined value B. The predetermined value B is set to a value that defines the boundary between the low sulfur fuel and the high sulfur fuel based on the experimental results and the like. If the value of the target air-fuel ratio A / Ft is larger than the predetermined value B, it is considered that high sulfur fuel is being used, and there is a concern about misdiagnosis due to the influence of sulfur. Therefore, the process proceeds to step S206, and the catalyst 11 is normal. Neither is it determined or diagnosed as deterioration, that is, the deterioration determination or deterioration diagnosis is suspended. On the other hand, when the value of the target air-fuel ratio A / Ft is equal to or less than the predetermined value B, the low-sulfur fuel is used and there is no influence of sulfur. Therefore, the process proceeds to step S207 and the catalyst 11 is determined or diagnosed as deteriorated. .

  When the target air-fuel ratio A / Ft is larger than the predetermined value B in step S205, that is, when it is considered that high sulfur fuel is used, the value of the oxygen storage capacity OSC measured in step S201 is corrected. The corrected oxygen storage capacity OSC may be compared with the deterioration determination value OSCs to determine or diagnose whether the catalyst is normal or deteriorated. That is, when it is determined that the high sulfur fuel is being used, correction is made to compensate for the amount of decrease in the oxygen storage capacity measurement value OSC due to the influence of sulfur. By doing so, the influence of sulfur can be eliminated and misdiagnosis can be prevented. As this correction method, for example, the relationship between the target air-fuel ratio A / Ft and the correction coefficient is experimentally determined in advance by a map, function, etc., and the target air-fuel ratio A / Ft actually obtained using this relationship is used. The correction coefficient value corresponding to the value is calculated. Then, the oxygen storage capacity measurement value OSC is increased and corrected by multiplying the calculated correction coefficient by the oxygen storage capacity measurement value OSC. In addition, various correction methods are possible.

  By the way, in the above-described embodiment, the air-fuel ratio is gradually changed from the rich side to the lean side when determining the fuel property, but conversely, the air-fuel ratio may be gradually changed from the lean side to the rich side.

  FIG. 10 shows changes in values when such air-fuel ratio gradual change is executed. (A) is the target air-fuel ratio A / Ft, (B) is the pre-catalyst air-fuel ratio A / Ffr detected by the pre-catalyst air-fuel ratio sensor 17, and (C) is the output voltage Vrr (V) of the post-catalyst air-fuel ratio sensor 18. Indicates. As shown in (A), the target air-fuel ratio A / Ft is gradually changed (sweep) from a predetermined value leaner than the stoichiometric value to a predetermined value richer than the stoichiometric value at a constant speed so as to cross the stoichiometric value. ing. As shown in (B), the pre-catalyst air-fuel ratio A / Ffr also changes in the same manner as the target air-fuel ratio A / Ft. When such an air-fuel ratio gradual change is performed, as shown in (C), the output voltage Vrr of the post-catalyst air-fuel ratio sensor 18 is reversed from the lean side to the rich side.

  The timing at which the post-catalyst air-fuel ratio sensor output Vrr reverses to the rich side varies depending on the sulfur concentration of the fuel. Assuming that the timing when the post-catalyst air-fuel ratio sensor output Vrr exceeds a predetermined threshold value Vref (here, about 0.55 (V)) as the reversal timing to the rich side, the reversal timing t3 for high sulfur fuel is low. This is earlier than the reversal timing t4 for sulfur fuel, and the result is the reverse of FIG. However, the former is the timing when the target air-fuel ratio A / Ft is on the lean side than the latter, and in this respect, the same result as in FIG. 5 is obtained. Using the correlation between the fuel sulfur concentration and the reversal timing, the fuel sulfur concentration can be estimated based on the air-fuel ratio at the reversal timing, preferably the value of the target air-fuel ratio A / Ft. The target air-fuel ratios corresponding to the inversion timings t3 and t4 are indicated by A / Ft3 and A / Ft4.

  The fuel property determination process of FIG. 7 and the catalyst deterioration diagnosis process of FIG. 9 can also be used when this reverse air-fuel ratio gradual change is performed. In this case, for the fuel property determination process of FIG. 7, it is determined in step S102 whether the post-catalyst air-fuel ratio sensor output Vrr exceeds the threshold value Vref, and in step S104, the current target air-fuel ratio A / Ft is determined. A predetermined value D is subtracted from the value to update the target air-fuel ratio A / Ft. On the other hand, for the catalyst deterioration diagnosis process of FIG. 9, in step S204, the value of the target air-fuel ratio A / Ft when the post-catalyst air-fuel ratio sensor output Vrr is richly inverted is acquired.

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

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

It is the schematic which shows the structure of embodiment of this invention. It is a schematic sectional drawing which shows the structure of a catalyst. It is a time chart for demonstrating active air fuel ratio control. FIG. 4 is a time chart similar to FIG. 3 for illustrating a method for measuring the oxygen storage capacity. It is a time chart which shows the change of each value when an air fuel ratio is gradually changed to the lean side. It is a graph which shows the relationship between the air fuel ratio of the supply gas in a catalyst, and each purification rate of CO, HC, and NOx. It is a flowchart of a fuel property discrimination | determination process. It is a time chart which shows the change of each value at the time of fuel property discrimination processing execution. It is a flowchart of a catalyst deterioration diagnosis process. It is a time chart which shows the change of each value when an air fuel ratio is gradually changed to the rich side.

Explanation of symbols

1 Internal combustion engine 6 Exhaust pipe 11 Upstream catalyst 12 Injector 17 Pre-catalyst air-fuel ratio sensor 18 Post-catalyst air-fuel ratio sensor 19 Downstream catalyst 20 Electronic control unit (ECU)
OSC Oxygen storage capacity OSCs Degradation judgment value Vrr Post-catalyst air-fuel ratio sensor output Vref Threshold A / Ft Target air-fuel ratio A / Ffr Pre-catalyst air-fuel ratio

Claims (7)

A catalyst provided in the exhaust passage of the internal combustion engine;
A post-catalyst air-fuel ratio sensor provided downstream of the catalyst;
Air-fuel ratio control means for gradually changing the air-fuel ratio of the exhaust gas supplied to the catalyst from the rich side to the lean side, or vice versa;
Based on the value of the air-fuel ratio at the timing when the output of the post-catalyst air-fuel ratio sensor reverses to the lean side or the rich side when the air-fuel ratio of the exhaust gas is gradually changed by the air-fuel ratio control means, the sulfur concentration of the fuel is determined. A fuel property discrimination device comprising: a sulfur concentration estimation means for estimation. A pre-catalyst air-fuel ratio sensor provided upstream of the catalyst;
The air-fuel ratio control means controls the air-fuel ratio so that the air-fuel ratio of the exhaust gas detected by the pre-catalyst air-fuel ratio sensor matches the target air-fuel ratio, and the target air-fuel ratio is changed from the rich side to the lean side or The air-fuel ratio of the exhaust gas supplied to the catalyst is gradually changed from the rich side to the lean side or vice versa by gradually changing the reverse.
2. The sulfur concentration of the fuel is estimated based on a value of a target air-fuel ratio at a timing when the output of the post-catalyst air-fuel ratio sensor reverses to a lean side or a rich side. The fuel property discriminating apparatus described. 3. The fuel property according to claim 1, wherein the air-fuel ratio control means gradually changes the air-fuel ratio of the exhaust gas supplied to the catalyst from the rich side to the lean side with respect to the stoichiometry or vice versa. Discriminator. The fuel property determination device according to claim 2, wherein the air-fuel ratio control means updates the target air-fuel ratio by a predetermined value every predetermined time.   A catalyst deterioration diagnosis device comprising the fuel property determination device according to any one of claims 1 to 4, wherein the catalyst deterioration diagnosis is performed when a fuel sulfur concentration greater than a predetermined value is estimated by the sulfur concentration estimation means. The catalyst deterioration diagnosis device characterized by holding the battery. Measuring means for measuring a parameter correlated with the degree of deterioration of the catalyst, and when the measured parameter is a value corresponding to the deteriorated catalyst, the air-fuel ratio gradually changes by the air-fuel ratio control means and the sulfur concentration estimation means The catalyst deterioration diagnosis apparatus according to claim 5, wherein the estimation of the sulfur concentration is performed.   5. A catalyst deterioration diagnosis apparatus comprising the fuel property determination apparatus according to claim 1, further comprising a measuring unit that measures a parameter correlated with the degree of deterioration of the catalyst, and the sulfur concentration estimating unit determines a predetermined value. When the fuel sulfur concentration equal to or greater than the value is estimated, the measured parameter is corrected, and a catalyst deterioration diagnosis is performed based on the corrected parameter.

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