JP2009150367A - Catalyst deterioration diagnosis device for internal combustion engine - Google Patents

Abstract

An apparatus for diagnosing catalyst deterioration in an internal combustion engine that can reduce the possibility of erroneous determination and improve the diagnostic accuracy.
An apparatus for diagnosing deterioration of a catalyst disposed in an exhaust passage of an internal combustion engine, forcing an air-fuel ratio of air and fuel supplied to the internal combustion engine based on an oxygen concentration detected downstream of the catalyst The active air-fuel ratio control means that changes between the rich side and the lean side, and the oxygen storage capacity of the catalyst during the air-fuel ratio control by the active air-fuel ratio control means are measured, and the catalyst is determined based on the measured oxygen storage capacity. An apparatus for diagnosing deterioration of an internal combustion engine having a diagnostic means for diagnosing deterioration of the internal combustion engine reduces at least a NOx component contained in an exhaust gas discharged from the internal combustion engine during lean air-fuel ratio control by the active air-fuel ratio control means NOx component reduction control means is provided.
[Selection] Figure 5

Description

  The present invention relates to a catalyst deterioration diagnosis device that diagnoses deterioration of a catalyst disposed in an exhaust passage of an internal combustion engine.

Generally, 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: OSC). 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, lean. Then, excess oxygen present in the exhaust gas is adsorbed and held, and when the air-fuel ratio of the exhaust gas flowing into the catalyst becomes smaller than stoichiometric, that is, when it 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 stoichiometric. However, when a three-way catalyst having oxygen storage capacity is used, the actual air-fuel ratio slightly deviates from stoichiometric depending on the operating conditions. Even in the case of the trapping, it is possible to absorb such an air-fuel ratio shift and maintain the purification efficiency 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 decrease in the oxygen storage capacity because they are reactions through noble metals, and it is detected that the catalyst has deteriorated by detecting that the oxygen storage capacity has decreased. can do. Therefore, active air-fuel ratio control for forcibly switching the air-fuel ratio of the exhaust gas flowing into the catalyst to the rich side and lean side is performed, and along with the execution of this active air-fuel ratio control, oxygen release of the catalyst during the rich-side control is performed. A method (so-called Cmax method) for determining the oxygen storage capacity (capacity) by averaging the capacity and the oxygen adsorption capacity at the time of lean side control and diagnosing the deterioration of the catalyst based on this oxygen storage capacity is adopted (the so-called Cmax method). For example, see Patent Document 1).

JP-A-5-133264

  By the way, in this Cmax method, the oxygen storage capacity is obtained based on the oxygen adsorption capacity for adsorbing oxygen to the catalyst during the lean side control in the active air-fuel ratio control and the oxygen release capacity for releasing oxygen from the catalyst during the rich side control. However, even though the oxygen adsorption capability remains in the catalyst during the lean side control, the oxygen sensor is lean-reversed due to the influence of NOx, and the oxygen adsorption capability obtained by measurement is the actual oxygen It became clear that it became smaller than adsorption capacity.

More specifically, while the air-fuel ratio is switched from the rich side to the lean side and the oxygen adsorption action is performed, oxygen is deprived from NOx by unburned components such as HC and CO in the exhaust gas. The reduction action is performed. However, when the oxygen adsorption capacity of the catalyst approaches saturation, unburned components such as HC and CO in the exhaust gas are oxidized and consumed by the oxygen in the exhaust gas, which is less likely to be adsorbed. It goes down and passes through the catalyst as it is. Then, since the oxygen sensor composed of a zirconia element as a base material has a characteristic of reacting not only with O ₂ but also with NOx, it reacts with NOx that has passed through the catalyst and oxygen provided downstream thereof. The sensor is lean-reversed. This becomes remarkable when the amount of NOx flowing into the catalyst is large.

  As a result, the oxygen storage capacity of the catalyst determined by calculation based on the oxygen adsorption capacity and the oxygen release capacity becomes smaller than the actual oxygen storage capacity. Since this oxygen adsorption capacity decreases as the deterioration of the catalyst progresses, the ratio of the difference between the measured oxygen storage capacity value and the actual oxygen storage capacity increases with the deterioration catalyst, making it difficult to determine whether the catalyst is normal or abnormal. As a result, there is a problem in that the possibility of erroneous determination increases.

  Accordingly, the present invention has been made in view of such circumstances, and an object of the present invention is to provide a catalyst deterioration diagnosis device for an internal combustion engine that can reduce the possibility of erroneous determination and improve diagnosis accuracy. is there.

An embodiment of a catalyst deterioration diagnosis apparatus for an internal combustion engine according to the present invention that achieves the above object is a catalyst deterioration diagnosis apparatus disposed in an exhaust passage of an internal combustion engine, wherein an oxygen concentration detected downstream of the catalyst is detected. Based on active air-fuel ratio control means for forcibly changing the air-fuel ratio of air and fuel supplied to the internal combustion engine between the rich side and the lean side, and at the time of air-fuel ratio control by the active air-fuel ratio control means In the catalyst deterioration diagnosis device for an internal combustion engine, comprising the diagnostic means for measuring the oxygen storage capacity of the catalyst and diagnosing the deterioration of the catalyst based on the measured oxygen storage capacity,
At the time of lean side control of the air-fuel ratio by the active air-fuel ratio control means, there is provided an NOx component reduction control means for reducing at least the NOx component contained in the exhaust gas discharged from the internal combustion engine.

  According to the catalyst deterioration diagnosis device for an internal combustion engine of the above aspect, at least the NOx component contained in the exhaust gas discharged from the internal combustion engine by the NOx component reduction control means during the lean side control of the air-fuel ratio by the active air-fuel ratio control means. Will be reduced. When the output gas with the reduced NOx component flows into the catalyst, almost the entire amount of NOx is reduced during the oxygen adsorption period, so that the passage of NOx through the catalyst is delayed. As a result, it is possible to prevent the oxygen sensor provided downstream of the catalyst from undergoing lean inversion in a state where oxygen cannot be completely adsorbed. Thus, since the difference between the oxygen storage capacity of the catalyst and the actual oxygen storage capacity required by calculation based on the oxygen adsorption capacity and oxygen release capacity is reduced, the possibility of erroneous determination is reduced and the diagnostic accuracy is improved. be able to.

  Here, the NOx component reduction control by the NOx component reduction control means is preferably executed when the oxygen storage capacity of the catalyst falls below a predetermined value.

  According to this aspect, since unnecessary NOx component reduction control is avoided, fuel consumption deterioration can be minimized.

  The NOx component reduction control means may delay the ignition timing from the optimum ignition timing in the operating state.

  Further, at the time of retarding the ignition timing by the NOx component decreasing control means, it is preferable that the intake air amount increasing control is executed so as to compensate for the torque decrease associated with the retarding control.

  Further, it is preferable to provide an NOx component increase control means for increasing at least the NOx component contained in the exhaust gas discharged from the internal combustion engine during the rich control of the air / fuel ratio by the active air / fuel ratio control means.

  According to this aspect, the NOx component contained in the exhaust gas discharged from the internal combustion engine is increased by the NOx component increase control means during the rich air-fuel ratio control by the active air-fuel ratio control means. When the output gas with the increased NOx component flows into the catalyst, it is promoted that NOx passes through the catalyst during the oxygen release period. As a result, the oxygen sensor provided downstream of the catalyst is prevented from being richly inverted in a state where oxygen cannot be released. Thus, the difference between the oxygen storage capacity of the catalyst and the actual oxygen storage capacity required by calculation based on the oxygen adsorption capacity and oxygen release capacity is reduced, thus reducing the possibility of misjudgment and further improving diagnostic accuracy. Can be planned.

  Further, the NOx component reduction or increase control means may increase or decrease the EGR amount when the internal combustion engine includes an exhaust gas recirculation (EGR) device. In order to increase or decrease the EGR amount, when the internal combustion engine includes a so-called variable timing mechanism that can change the opening and closing timing of the intake valve and / or the exhaust valve, the overlap of the intake and exhaust valves is increased or decreased. Accordingly, the so-called internal EGR amount may be increased or decreased.

  According to the present invention, an excellent effect of reducing the possibility of erroneous determination and improving diagnostic accuracy is exhibited.

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 a system configuration of an embodiment of a catalyst deterioration diagnosis apparatus for an internal combustion engine according to the present invention. As shown in the figure, the internal combustion engine 1 generates power by burning a fuel / air mixture in 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 multi-cylinder engine (only one cylinder is shown) mounted on a vehicle, 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.

  In this embodiment, an injector (fuel injection valve) 12 that injects fuel into an intake passage, particularly an 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 a three-way catalyst having an O ₂ storage function (oxygen storage capacity). A catalyst 11 comprising: An exhaust passage is formed by the exhaust port, the branch pipe, and the exhaust pipe 6. An air-fuel ratio sensor that detects the exhaust air-fuel ratio based on the oxygen concentration in the exhaust, that is, a pre-catalyst sensor 17 and a post-catalyst sensor 18 is installed on each of the upstream side and the downstream side of the catalyst 11. The pre-catalyst sensor 17 is a so-called wide-area air-fuel ratio sensor, can continuously detect an air-fuel ratio over a relatively wide area, and outputs a signal having a value proportional to the exhaust air-fuel ratio. On the other hand, the post-catalyst 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 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 internal combustion engine 1 and an accelerator that detects the accelerator opening, as shown in the figure. The opening 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 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 catalyst 11 simultaneously purifies NOx, HC, and CO when the air-fuel ratio (A / F) of the exhaust gas flowing into the catalyst 11 is near the stoichiometric air-fuel ratio (stoichiometric, for example, (A / F) s = 14.6). This is a so-called three-way catalyst. In response to this, during normal operation of the internal combustion engine, the ECU 20 adjusts the air-fuel ratio so that the air-fuel ratio of the exhaust gas flowing into the catalyst 11, that is, the pre-catalyst air-fuel ratio (A / F) fr, matches the stoichiometric air-fuel ratio. Control. Specifically, the ECU 20 sets a target air-fuel ratio (A / F) t equal to the theoretical air-fuel ratio, and the pre-catalyst air-fuel ratio (A / F) fr detected by the pre-catalyst sensor 17 is the target air-fuel ratio (A / F) The amount of fuel injected from the injector 12 is feedback controlled so as to match t. As a result, the air-fuel ratio of the exhaust gas flowing into the catalyst 11 is kept in the vicinity of the theoretical air-fuel ratio, and the maximum purification performance is exhibited in the catalyst 11.

Here, the catalyst 11 will be described in more detail. 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 and Pd, and serves as an active point when 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 that can adsorb and release oxygen according to the air-fuel ratio of the atmospheric gas. The oxygen storage component is made of, for example, cerium oxide 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. Conversely, if the atmosphere gas of the catalyst component 32 and the coating material 31 is leaner than the theoretical air-fuel ratio, the oxygen storage component present around the catalyst component 32 adsorbs oxygen from the atmosphere gas, and as a result, NOx is reduced and purified. The

  Even if the pre-catalyst air-fuel ratio (A / F) fr slightly varies with respect to the theoretical air-fuel ratio during the normal air-fuel ratio control, the three exhaust gases such as NOx, HC, and CO can be obtained by this oxygen absorption / release action. Ingredients can be purified simultaneously. Therefore, in normal air-fuel ratio control, it is also possible to purify exhaust gas by causing the pre-catalyst air-fuel ratio (A / F) fr to oscillate slightly around the stoichiometric air-fuel ratio and to repeatedly absorb and release 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 this embodiment, the degree of deterioration of the catalyst 11 is detected by detecting the oxygen storage capacity of the catalyst 11. Here, the oxygen storage capacity of the catalyst 11 is represented by the magnitude of the oxygen storage capacity value (OSC value or Cmax), which is the maximum amount of oxygen that can be stored by the current catalyst 11.

  Hereinafter, the catalyst deterioration diagnosis executed in the main routine in the present embodiment will be described first.

  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 pre-catalyst air-fuel ratio (A / F) fr is forcibly (actively) switched alternately to the rich side and the lean side with a predetermined center air-fuel ratio (A / F) c as a boundary. The air-fuel ratio when changed to the rich side is referred to as rich air-fuel ratio (A / F) r, and the air-fuel ratio when changed to the lean side is referred to as lean air-fuel ratio (A / F) 1. When the pre-catalyst air-fuel ratio (A / F) fr is changed to the rich side or the lean side by this active air-fuel ratio control, the oxygen storage capacity value OSC (= Cmax) of the catalyst is measured.

  The deterioration diagnosis of the catalyst 11 is executed when the internal combustion engine 1 is in a steady operation and the catalyst 11 is in the active temperature range. The temperature of the catalyst 11 (catalyst bed temperature) may be directly detected 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 determines the operation state defined by the intake air amount Ga detected by the air flow meter 5 and the engine rotational speed Ne (rpm) detected based on the output of the crank angle sensor 14, and the intake air amount Ga. Based on the accumulated value or the like, the temperature of the catalyst 11 is estimated using a map or function set through experiments or the like in advance.

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

  As shown in FIG. 3 (A), the target air-fuel ratio (A / F) t is centered on the theoretical air-fuel ratio (A / F) s as the center air-fuel ratio, and a predetermined amplitude (rich) from there to the rich side. An air-fuel ratio (rich air-fuel ratio (A / F) r) separated by an amplitude Ar, Ar> 0) and a predetermined amplitude (lean amplitude Al, Al> 0) from the stoichiometric air-fuel ratio (A / F) s to the lean side The air-fuel ratio (lean air-fuel ratio (A / F) 1) which is far away is forcibly and alternately switched. Following the switching of the target air-fuel ratio (A / F) t, the pre-catalyst air-fuel ratio (A / F) fr as an actual value is also slightly delayed from the target air-fuel ratio (A / F) t. Switch with it. From this, it will be understood that the target air-fuel ratio (A / F) t and the pre-catalyst air-fuel ratio (A / F) fr are equivalent except that there is a time delay.

  In the illustrated example, the rich amplitude Ar and the lean amplitude Al are equal. For example, theoretical air fuel ratio (A / F) s = 14.6, rich air fuel ratio (A / F) r = 14.1, lean air fuel ratio (A / F) 1 = 15.1, rich amplitude Ar = lean amplitude Al = 0.5. Compared to the normal air-fuel ratio control, the active air-fuel ratio control has a larger amplitude of the air-fuel ratio, that is, the values of the rich amplitude Ar and the lean amplitude Al are larger.

  By the way, the timing at which the target air-fuel ratio (A / F) t is switched is the timing at which the output of the post-catalyst sensor 18 switches from rich to lean, or from lean to rich. As shown in the figure, the output voltage of the post-catalyst sensor 18 changes abruptly at the theoretical air-fuel ratio (A / F) s, and the post-catalyst air-fuel ratio (A / F) rr becomes the stoichiometric air-fuel ratio (A / F). When the air-fuel ratio on the rich side is smaller than s, the output voltage becomes equal to or higher than the rich determination value VR, and the air-fuel ratio on the lean side is greater than the stoichiometric air-fuel ratio (A / F) s. In some cases, the output voltage becomes less than the lean determination value VL. Here, VR> VL, for example, VR = 0.59 (V) and VL = 0.21 (V).

  As shown in FIGS. 3A and 3B, when the output voltage of the post-catalyst sensor 18 changes from the rich value to the lean value and becomes equal to the lean determination value VL (time t1), the target sky The fuel ratio (A / F) t is switched from the lean air-fuel ratio (A / F) l to the rich air-fuel ratio (A / F) r. Thereafter, when the output voltage of the post-catalyst sensor 18 changes from the lean side value to the rich side and becomes equal to the rich judgment value VR (time t2), the target air-fuel ratio (A / F) t becomes the rich air-fuel ratio (A / F) r is switched to a lean air-fuel ratio (A / F) l.

  While performing the active air-fuel ratio control that performs such an air-fuel ratio change, the oxygen storage capacity value 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 / F) t is set to the lean air-fuel ratio (A / F) 1 before time t 1, and the lean gas flows into the catalyst 11. At this time, oxygen is continuously adsorbed by the catalyst 11, but when oxygen is fully adsorbed, oxygen can no longer be adsorbed, and the lean gas flows through the catalyst 11 and flows downstream of the catalyst 11. As a result, the post-catalyst air-fuel ratio (A / F) rr changes to the lean side, and the target air-fuel ratio (A / F) t becomes equal to the time point (t1) when the output voltage of the post-catalyst sensor 18 reaches the lean determination value VL. The rich air-fuel ratio (A / F) r is switched or reversed. In this way, the target air-fuel ratio (A / F) t is reversed using the output of the post-catalyst sensor 18 as a trigger.

  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 / F) s flows out to the downstream side of the catalyst 11 and the post-catalyst air fuel ratio (A / F) rr does not become rich, so the output of the post-catalyst sensor 18 is reversed. do not do. When oxygen is continuously released from the catalyst 11, the stored oxygen is eventually released from the catalyst 11, and at that time, no more oxygen can be released, and the rich gas flows through the catalyst 11 and flows downstream of the catalyst 11. When this happens, the post-catalyst air-fuel ratio (A / F) rr changes to the rich side, and when the output voltage of the post-catalyst sensor 18 reaches the rich determination value VR (t2), the target air-fuel ratio (A / F) t becomes It is switched to a lean air-fuel ratio (A / F) 1.

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

  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 / F) t is switched to the rich air-fuel ratio (A / F) r at time t1, the pre-catalyst air-fuel ratio (A / F) as an actual value is slightly delayed. F) fr switches to rich air-fuel ratio (A / F) r. From the time t11 when the pre-catalyst air-fuel ratio (A / F) fr reaches the theoretical air-fuel ratio (A / F) s to the time t2 when the target air-fuel ratio (A / F) t is reversed next, ) To calculate the oxygen storage capacity value dOSC (instantaneous value of the oxygen storage capacity value) for each predetermined minute time, and the oxygen storage capacity value dOSC for each minute time is integrated from time t11 to time t2. Thus, the oxygen storage capacity value, that is, the amount of released oxygen during this oxygen release period is measured.

(1) dOSC = Δ (A / F) × Q × K = {(A / F) fr− (A / F) s} × Q × K
Here, Q is a fuel injection amount, and when the air-fuel ratio difference Δ (A / 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 value OSC measured at this time is used and compared with a predetermined deterioration determination value OSCs. If the oxygen storage capacity value OSC exceeds the deterioration determination value OSCs, normal, oxygen If the storage capacity value OSC is equal to or less than the deterioration determination value OSCs, the deterioration of the catalyst 11 can be determined such as deterioration.

  However, in order to improve accuracy, the oxygen storage capacity value (in this case, the oxygen storage capacity) is also measured during the oxygen adsorption period in which the target air-fuel ratio (A / F) t is on the lean side, and these oxygen storage capacity The average value is measured as an oxygen storage capacity value of one unit related to one absorption / release cycle. Further, the absorption / release cycle is repeated a plurality of times to obtain oxygen storage capacity values of a plurality of units, and the average value is used as the final measured value of the oxygen storage capacity value, which is compared with the deterioration determination value to determine the final deterioration determination. May be performed. When it is determined that the catalyst is deteriorated, it is preferable to operate a warning device (such as a check lamp) not shown in order to notify the user (driver) of the fact.

  Regarding the measurement of the oxygen storage capacity value (oxygen storage amount) during the oxygen adsorption period, the target air-fuel ratio (A / F) t is switched to the lean air-fuel ratio (A / F) l at time t2, as shown in FIG. Thereafter, from time t21 when the pre-catalyst air-fuel ratio (A / F) fr reaches the theoretical air-fuel ratio (A / F) s, until time t3 when the target air-fuel ratio (A / F) t is reversed to the rich side next time. The oxygen storage capacity value dOSC for each minute time is calculated by the previous equation (1), and the oxygen storage capacity value dOSC for each minute time is integrated. Thus, the oxygen storage capacity value OSC, that is, the amount of stored oxygen (OSC2 in FIG. 4) during this oxygen adsorption period is measured. The oxygen storage capacity value OSC1 during the oxygen release period and the oxygen storage capacity value OSC2 during the oxygen adsorption period should be approximately equal.

  However, as described above, during the lean side control during the execution of the active air-fuel ratio control, when the oxygen adsorption capacity approaches saturation, an oxygen sensor provided downstream thereof reacts with NOx passing through the catalyst 11. Since the lean inversion occurs at an early stage, the oxygen storage capacity value OSC2 during this oxygen adsorption period tends to be smaller than the actual oxygen storage capacity.

  Therefore, in the present embodiment, the passage of NOx is delayed so that the oxygen storage capacity value OSC2 during this oxygen adsorption period accurately reflects the actual oxygen storage capacity. Hereinafter, one form of NOx component reduction control executed as a subroutine of a routine for executing the deterioration diagnosis process according to the present embodiment will be described with reference to the flowchart of FIG. This NOx component reduction control is also repeatedly executed by the ECU 20 every predetermined calculation cycle.

  First, in step S501, it is determined whether or not the active air-fuel ratio control of the deterioration diagnosis processing routine is being executed. It should be noted that the deterioration diagnosis processing routine is started when it is determined that the basic condition is satisfied. For example, 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. If the catalyst 11 and the catalyst front-rear sensors 17 and 18 reach a predetermined activation temperature, the basic condition is established. Therefore, if this basic condition is satisfied and active air-fuel ratio control is being executed, the process proceeds to step S502.

  In step S502, it is determined whether or not lean air-fuel ratio control is being performed in this active air-fuel ratio control. If it is determined in step S502 that the lean-side control is being performed, the process proceeds to step S503, where NOx component reduction control for reducing at least the NOx component contained in the exhaust gas discharged from the internal combustion engine is executed.

  On the other hand, if it is determined in step S501 that the active air-fuel ratio control of the above-described deterioration diagnosis processing routine is not being executed, or if it is determined in step S502 that the lean side control is not being executed, the process proceeds to step S504, and the above-described NOx is performed. The component reduction control is not executed or stopped.

  Here, the embodiment of the NOx component reduction control will be described in more detail. In the internal combustion engine 1 of the system shown in FIG. 1, the ECU 20 is defined by, for example, an intake air amount Ga detected by the air flow meter 5 and an engine rotational speed Ne detected based on the output of the crank angle sensor 14. By using a map or function set in advance through experiments or the like corresponding to the operating state, the ignition timing by the spark plug 7 is controlled to an optimum value so that a desired output can be obtained in the operating state. Accordingly, when the NOx component reduction control is not executed in the operating state defined by the intake air amount Ga and the engine rotational speed Ne, a predetermined angle before compression top dead center (TDC) is determined as the optimal ignition timing by the spark plug 7. It is ignited at X (for example, 40 before top dead center) ° CA (crank angle). In this case, normal combustion is performed in the combustion chamber 3, and as shown in FIG. 6, a decrease in the NOx component is hardly expected. On the other hand, when the NOx component reduction control is executed, the ignition is retarded to a predetermined angle Y before compression top dead center (for example, 5 before top dead center) ° CA. Thus, if the ignition timing is delayed from the optimum ignition timing in the operating state, the combustion in the combustion chamber 3 becomes slow, and the NOx component in the combustion gas is reduced as shown in FIG. In the present embodiment, the part that functions to delay the ignition timing by the spark plug 7 from the optimal ignition timing in the operating state constitutes the NOx component reduction control means.

  As described above, when the NOx component contained in the exhaust gas discharged from the internal combustion engine 1 is reduced by the NOx component reduction control in step S503, and the output gas with the reduced NOx component flows through the catalyst 11, the lean side control is performed. During the oxygen adsorption period, almost the entire amount of NOx is reduced, so that the passage of NOx through the catalyst 11 is delayed. As a result, the post-catalyst sensor 18 provided downstream of the catalyst 11 is prevented from lean reversal in a state where oxygen cannot be completely adsorbed. Thus, since the difference between the oxygen storage capacity value of the catalyst 11 and the actual oxygen storage capacity obtained by calculation based on the oxygen adsorption capacity and oxygen release capacity is reduced, the possibility of erroneous determination is reduced and the diagnostic accuracy is improved. Is planned.

  Next, another form of the above-described NOx component reduction control will be described with reference to the flowchart of FIG. Another form of this NOx component reduction control is also repeatedly executed by the ECU 20 at predetermined intervals. Another form of this NOx component reduction control is for minimizing deterioration in fuel consumption associated with NOx component reduction control. That is, in this other embodiment, NOx component reduction control is executed only when the deterioration diagnosis of the catalyst 11 is more accurately required, and unnecessary NOx component reduction control is avoided.

  Therefore, in step S701, as in the previous embodiment, it is determined whether the active air-fuel ratio control of the deterioration diagnosis processing routine is being executed. If it is being executed, the process proceeds to step S702. In step S702, it is determined whether or not the oxygen storage capacity value Cmax of the catalyst 11 obtained and stored in the previous trip is smaller than a predetermined value A. Specifically, the oxygen storage capacity value Cmax in the previous trip, which is obtained by measurement in the deterioration diagnosis process of the catalyst 11 performed during the previous travel and is stored in the storage device such as the nonvolatile RAM of the ECU 20, is greater than the predetermined value A. Whether it is small or not is determined. The predetermined value A can be an oxygen storage capacity value at a predetermined ratio with respect to the oxygen storage capacity of the new catalyst 11. When the oxygen storage capacity value Cmax is smaller than the predetermined value A, the process proceeds to step S703, and it is determined whether the lean side control of the air-fuel ratio is being performed in the active air-fuel ratio control, as in the previous embodiment. If it is determined in step S703 that the lean side control is being performed, the process proceeds to step S704, and NOx component reduction control for reducing at least the NOx component contained in the exhaust gas discharged from the internal combustion engine is executed as in the previous embodiment. The

  On the other hand, when it is determined in step S701 that the active air-fuel ratio control of the above-described deterioration diagnosis processing routine is not being executed, when it is determined in step S702 that the oxygen storage capacity value Cmax is not smaller than the predetermined value A, and step When it is determined in S703 that the lean-side control is not being performed, the process proceeds to step S705, and the above-described NOx component reduction control is not executed or is stopped as in the previous embodiment. Thus, in this other embodiment, NOx component reduction control is executed only when the deterioration diagnosis of the catalyst 11 is more accurately required, and unnecessary NOx component reduction control is avoided, so that deterioration of fuel consumption is minimized. It can be suppressed.

  In the NOx component reduction control described with reference to the flowchart of FIG. 5 or FIG. 7, the crank angle (X−Y) ° CA is delayed from the optimal ignition timing in the operation state. Since there is a possibility that the torque of the internal combustion engine 1 may decrease with the retard angle control, the electronically controlled throttle valve is simultaneously performed with the NOx component reduction control executed in the above-described steps S503 and S704 to compensate for such a torque decrease. It is preferable that the control for increasing the intake air amount is performed by slightly increasing the opening degree of 10 or the like.

  Further, when the internal combustion engine 1 includes an exhaust gas recirculation (EGR) device (not shown), the EGR amount is increased during the above-described lean-side control, and the portion functioning in this way is configured as a NOx component reduction control means. Also good. In order to increase the EGR amount, when the internal combustion engine 1 includes a so-called variable valve timing mechanism that can change the opening and closing timing of the intake valve Vi and / or the exhaust valve Ve, the overlap of the intake and exhaust valves is increased. It may be. This is because so-called internal EGR increases. Any of the above-described NOx component reduction control means can reduce the NOx component in the combustion gas.

  Furthermore, another embodiment of the deterioration diagnosis processing routine according to the present invention will be described with reference to the flowchart of FIG.

  In another embodiment of the deterioration diagnosis processing routine, in addition to the NOx component decrease control during the lean side control described above, the NOx component increase control during the rich side control is executed, thereby degrading whether the catalyst 11 is normal or abnormal. Diagnosis can be performed more accurately.

  Therefore, in another embodiment of this deterioration diagnosis processing routine, in step S801, as in the previous embodiment, it is determined whether or not the active air-fuel ratio control of the deterioration diagnosis processing routine is being executed. Then, the process proceeds to step S802. In step S802, it is determined whether or not the oxygen storage capacity value Cmax of the catalyst 11 obtained and stored in the previous trip is smaller than a predetermined value A. Specifically, the oxygen storage capacity value Cmax in the previous trip, which is obtained by measurement in the deterioration diagnosis process of the catalyst 11 performed during the previous travel and is stored in the storage device such as the nonvolatile RAM of the ECU 20, is greater than the predetermined value A. It is determined whether or not it is small. The predetermined value A can be an oxygen storage capacity value at a predetermined ratio with respect to the oxygen storage capacity of the new catalyst 11 as described above. When the oxygen storage capacity value Cmax is smaller than the predetermined value A, the process proceeds to step S803, and it is determined whether the lean side control or the rich side control of the air fuel ratio is being performed in the active air fuel ratio control. If it is determined in step S803 that the lean side control is being performed, the process proceeds to step S805. If it is determined that the rich side control is being performed, the process proceeds to step S806.

  Here, when it is determined in step S801 that the active air-fuel ratio control of the above-described deterioration diagnosis processing routine is not being executed, and in step S802, it is determined that the oxygen storage capacity value Cmax in the previous trip is not smaller than the predetermined value A. If so, the process proceeds to step S804, and EGR normal control is executed so that the EGR amount is suitable for the operation state. Thus, in this EGR normal control state, at least the NOx component contained in the exhaust gas discharged from the internal combustion engine 1 is an amount that can be appropriately purified by the catalyst 11 (hereinafter referred to as “NOx appropriate amount”). The amount of EGR is controlled.

  On the other hand, in step S805 that proceeds when it is determined that the lean side control is being performed in step S803 described above, NOx component reduction that reduces at least the NOx component contained in the exhaust gas discharged from the internal combustion engine 1 from the “NOx appropriate amount”. As control, EGR increase control is executed. Further, in step S806, which is performed when it is determined in step S803 that rich-side control is being performed, as NOx component increase control for increasing at least the NOx component contained in the exhaust gas discharged from the internal combustion engine 1 from the “NOx appropriate amount”. EGR reduction control is executed.

  According to this embodiment, during the lean side control of the air-fuel ratio by the active air-fuel ratio control means, the EGR increase control is executed, and in addition to the NOx component contained in the exhaust gas discharged from the internal combustion engine 1 being reduced. During the rich side control, the EGR reduction control is executed, and the NOx component contained in the exhaust gas discharged from the internal combustion engine 1 is increased. As described above, during the lean side control, when the output gas with the reduced NOx component flows into the catalyst 11, the passage of NOx through the catalyst 11 is delayed during the oxygen adsorption period. It is possible to prevent the post-catalyst sensor 18 from performing lean inversion in a state where oxygen cannot be completely adsorbed. Further, when the output gas with the increased NOx component flows into the catalyst during the rich side control, it is promoted that NOx passes through the catalyst 11 during the oxygen release period. As a result, a post-catalyst sensor provided downstream of the catalyst 11 18 is suppressed from being richly inverted in a state where oxygen cannot be released. As described above, the pre-catalyst reversal of the post-catalyst sensor 18 is suppressed in both the lean side control and the rich side control. Thus, according to the present embodiment, the difference between the oxygen storage capacity of the catalyst and the actual oxygen storage capacity obtained by calculation based on the oxygen adsorption capacity and the oxygen release capacity is smaller, so the possibility of erroneous determination is increased. It is possible to reduce and further improve the diagnostic accuracy.

  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 system configuration | structure of the catalyst deterioration diagnostic apparatus of the internal combustion engine which concerns on 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 an oxygen storage capacity value. It is a flowchart which shows one form of NOx component reduction control in embodiment of this invention. It is a graph which shows the relationship between ignition timing and the NOx component in an outgas. It is a flowchart which shows the other form of NOx component reduction control in embodiment of this invention. It is a flowchart which shows other embodiment of the deterioration diagnosis processing routine which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 6 Exhaust pipe 7 Spark plug 11 Catalyst 12 Injector 14 Crank angle sensor 17 Pre-catalyst sensor (air-fuel ratio sensor)
18 Post-catalyst sensor (oxygen (O ₂ ) sensor)
20 Electronic control unit (ECU)

Claims (5)

An apparatus for diagnosing deterioration of a catalyst disposed in an exhaust passage of an internal combustion engine, forcibly enriching an air-fuel ratio of air and fuel supplied to the internal combustion engine based on an oxygen concentration detected downstream of the catalyst Active air-fuel ratio control means for changing between the air-fuel side and the lean-side, and the oxygen storage capacity of the catalyst at the time of air-fuel ratio control by the active air-fuel ratio control means, and the catalyst based on the measured oxygen storage capacity A diagnostic means for diagnosing deterioration of the internal combustion engine, comprising:
A catalyst deterioration diagnosis for an internal combustion engine comprising NOx component reduction control means for reducing at least a NOx component contained in the exhaust gas discharged from the internal combustion engine during the lean side control of the air / fuel ratio by the active air / fuel ratio control means apparatus.   The catalyst deterioration diagnosis device for an internal combustion engine according to claim 1, wherein the NOx component reduction control by the NOx component reduction control means is executed when the oxygen storage capacity of the catalyst falls below a predetermined value.   3. The catalyst deterioration diagnosis apparatus for an internal combustion engine according to claim 1, wherein the NOx component reduction control means delays the ignition timing from the optimum ignition timing in the operating state.   4. The internal combustion engine according to claim 3, wherein during the retard control of the ignition timing by the NOx component decrease control means, intake air amount increase control is executed to compensate for a torque decrease associated with the retard control. Catalyst deterioration diagnosis device.   5. The NOx component increase control means for increasing at least the NOx component contained in the exhaust gas discharged from the internal combustion engine during the rich side control of the air / fuel ratio by the active air / fuel ratio control means. The catalyst deterioration diagnosis apparatus for an internal combustion engine according to any one of the above.

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