JP2009091921A - Catalyst deterioration diagnosis device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the accuracy and reliability of catalyst deterioration diagnosis for an internal combustion engine where the operating angle of an intake valve is variably controlled. <P>SOLUTION: The catalyst deterioration diagnosis device measures the oxygen storage capacity of a catalyst 11, corrects the measured oxygen storage capacity in accordance with a catalyst temperature, and diagnoses the deterioration of the catalyst in accordance with the oxygen storage capacity after corrected. It comprises a means 20 for estimating the catalyst temperature, and a means 21 for variably controlling the operating angle of the intake valve Vi. It corrects the estimated catalyst temperature in accordance with the operating angle of the intake valve and corrects a measured value for the oxygen storage capacity using the corrected estimated catalyst temperature, while suppressing an error in estimating the catalyst temperature in consideration of a difference in the operating angle. Finally, an accurate measured value for the oxygen storage capacity is obtained, thus improving the accuracy and reliability of diagnosis. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an apparatus for diagnosing deterioration of a catalyst disposed in an exhaust passage of an internal combustion engine.

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 exhaust gas flowing into the catalyst to rich and lean is performed, and the oxygen storage capacity of the catalyst is measured as the active air-fuel ratio control is executed. A method (so-called Cmax method) for diagnosing deterioration of the ink is employed (see Patent Document 1, etc.).

JP 2004-176615 A

  On the other hand, in recent years, variable valve gears have been developed in which the operating angle (opening angle) of the intake valve is continuously variable according to the engine operating state. In an internal combustion engine equipped with such a variable valve device, the amount of air taken into the combustion chamber can be changed over the entire operating range by changing the operating angle of the intake valve. Therefore, the throttle opening can be opened or omitted more than usual, thereby reducing the pumping loss, the same output can be obtained with a smaller amount of air and fuel, and fuel efficiency can be improved.

  When diagnosing catalyst deterioration in an internal combustion engine equipped with such a variable valve system, it has been found that the measured value of the oxygen storage capacity changes due to the difference in the operating angle of the intake valve even if other conditions are substantially the same. . Therefore, unless such a difference in the operating angle of the intake valve is taken into consideration, not only the measured value of the oxygen storage capacity but also the accuracy and reliability of the diagnostic result itself are impaired.

  Accordingly, the present invention has been made in view of such circumstances, and an object of the present invention is to improve the accuracy and reliability of catalyst deterioration diagnosis in an internal combustion engine that variably controls the operating angle of an intake valve. An object of the present invention is to provide a catalyst deterioration diagnosis apparatus.

According to one aspect of the invention,
An apparatus for diagnosing deterioration of a catalyst disposed in an exhaust passage of an internal combustion engine,
Catalyst temperature estimating means for estimating the temperature of the catalyst;
Diagnostic means for measuring the oxygen storage capacity of the catalyst, correcting the measured oxygen storage capacity based on the catalyst temperature, and diagnosing deterioration of the catalyst based on the corrected oxygen storage capacity;
Intake valve variable control means for variably controlling the operating angle of the intake valve;
There is provided a catalyst deterioration diagnosis device for an internal combustion engine, comprising: catalyst temperature correction means for correcting the catalyst temperature estimated by the catalyst temperature estimation means based on the operating angle.

  According to the results of the study by the inventors, it has been found that the catalyst temperature changes due to the difference in the working angle. Therefore, in one embodiment of the present invention, the estimated catalyst temperature is corrected based on the operating angle. By doing so, it is possible to suppress the estimated deviation of the catalyst temperature in consideration of the difference in the operating angle. And finally, the oxygen storage capacity after correct | amending catalyst temperature exact can be obtained, and the precision and reliability of a catalyst deterioration diagnosis can be improved.

  Preferably, an intake air amount detection means for detecting an intake air amount of the internal combustion engine is provided, and the catalyst temperature estimation means estimates the catalyst temperature based on the intake air amount detected by the intake air amount detection means. .

According to another aspect of the invention,
An apparatus for diagnosing deterioration of a catalyst disposed in an exhaust passage of an internal combustion engine,
Catalyst temperature measuring means for measuring the temperature of the catalyst;
Diagnostic means for measuring the oxygen storage capacity of the catalyst, correcting the measured oxygen storage capacity based on the catalyst temperature, and diagnosing deterioration of the catalyst based on the corrected oxygen storage capacity;
Intake valve variable control means for variably controlling the operating angle of the intake valve;
Throttle valve control means for controlling the opening of a throttle valve disposed in the intake passage of the internal combustion engine;
Ignition timing control means for controlling the ignition timing of the internal combustion engine;
With
At the time of diagnosis of deterioration of the catalyst, the intake valve variable control means decreases the operating angle of the intake valve from the normal time, the throttle valve control means increases the throttle valve opening from the normal time, and the An apparatus for diagnosing catalyst deterioration in an internal combustion engine is provided in which the ignition timing control means retards the ignition timing from the normal time.

  The measured value of oxygen storage capacity varies depending on the variation of each parameter including the working angle, but if the largest possible measured value is obtained at this time, the variation effect is reduced and it is advantageous for high-precision measurement and diagnosis. . For this purpose, it is effective to perform measurement and diagnosis under as high a catalyst temperature condition as possible. By the way, when the engine output torque is constant, the catalyst temperature rises when the operating angle is reduced, the throttle opening is increased, and the ignition timing is retarded. That is, when the operating angle is reduced and the throttle opening is increased, the pumping loss is thereby reduced and the torque is increased. When the ignition timing is retarded by this torque increase, unburned components increase in the exhaust gas exhausted from the combustion chamber, which burns in the catalyst and raises the catalyst temperature. Therefore, as in other embodiments of the present invention, when diagnosing catalyst deterioration, the operating angle of the intake valve is decreased from the normal time, the throttle valve opening is increased from the normal time, and the ignition timing is set from the normal time. However, it is possible to improve the accuracy by increasing the catalyst temperature and increasing the oxygen storage capacity measurement value.

  Preferably, at the time of the deterioration diagnosis of the catalyst, the intake valve variable control means controls the operating angle so that the operating angle is equal to or greater than a predetermined lower limit value.

  In the case of an internal combustion engine having a variable intake valve working angle, the air-fuel ratio of each cylinder may deviate and the actual center air-fuel ratio deviates from the target value due to variations in the working angle of each cylinder. The smaller the is, the more likely it is to appear. In another embodiment of the present invention, since the operating angle is reduced at the time of deterioration diagnosis, such a deviation of the central air-fuel ratio, and thus a deviation of the measured value of the oxygen storage capacity, is likely to occur. Therefore, the operating angle is controlled so that the operating angle is equal to or greater than a predetermined lower limit value. By doing so, it is possible to prevent the operating angle from being reduced to such an extent that a significant shift in the center air-fuel ratio occurs, and it is possible to prevent a shift in the oxygen storage capacity measurement value caused by the shift in the center air-fuel ratio. As a result, a highly accurate and reliable diagnosis result can be obtained.

  According to the present invention, in the internal combustion engine that variably controls the working angle of the intake valve, an excellent effect that the accuracy and reliability of the catalyst deterioration diagnosis can be improved 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 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 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.

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

  A variable mechanism 21 is provided between the intake camshaft and the intake valve Vi to vary the valve operating angle α, that is, the crank angle at which the intake valve Vi is open. The operating angle α of the intake valve Vi is variably controlled through driving of the variable mechanism 21 based on a command signal from the ECU 20.

  FIG. 2 shows how the operating angle is changed by the variable mechanism 21. As can be seen from the characteristic curve shown in the figure, the operating angle α of the intake valve Vi continuously changes in synchronization with the maximum lift amount Limax. For example, the maximum lift amount Limax decreases as the operating angle α decreases. When the operating angle α decreases, the valve opening timing and the valve closing timing of the intake valve Vi approach each other, and the valve opening period of the intake valve Vi also decreases. In the present embodiment, the maximum lift amount Limax is always obtained at a certain crank angle, and the operating angle α increases or decreases around the maximum lift amount crank angle, and the opening / closing timing also changes. However, the variable characteristics of the intake valve are not limited to those described here.

  In the present embodiment, the amount of air taken into the combustion chamber 3 is adjusted by adjusting or controlling the opening (throttle opening) TH of the throttle valve 10 together with the operating angle α of the intake valve Vi. In other words, the intake air amount can be controlled only by controlling the operating angle α of the intake valve Vi, but in this embodiment, the throttle opening TH is also controlled. When trying to obtain a constant engine output torque, rather than controlling only the throttle opening as in a normal engine without the variable mechanism 21, the intake valve operating angle and the throttle opening are controlled cooperatively as in this embodiment. However, the throttle opening can be set to the wide open side. Accordingly, the pumping loss can be reduced by the amount of increase in the throttle opening, and the required air amount and fuel amount can be suppressed, and the fuel efficiency can be improved. If the variable mechanism 21 as in the present embodiment is provided, the intake air amount can be controlled over the entire area only by controlling the intake valve working angle, so that the throttle valve 10 can be omitted.

  An example of engine control including control of the intake valve working angle α and the throttle opening TH will be described. This control is executed by the ECU 20. First, based on the accelerator opening Ac detected by the accelerator opening sensor 15, the target values αtrg and THtrg of the intake valve operating angle α and the throttle opening TH are determined according to a preset map (which may be a function, the same applies hereinafter). Calculated. Then, the intake valve operating angle α and the throttle opening TH are controlled so that the actual values coincide with these target values αtrg and THtrg. The actual values of the intake valve working angle α and the throttle opening TH are detected by sensors (not shown) provided in the variable mechanism 21 and the throttle valve 10, respectively. When the intake valve operating angle α and the throttle opening TH are controlled in this way, the actual intake air amount Ga and engine rotational speed Ne become values corresponding to the intake valve operating angle α and the throttle opening TH. The actual intake air amount Ga and engine speed Ne are detected based on the outputs of the air flow meter 5 and the crank angle sensor 14, respectively. Based on the actual intake air amount Ga and the engine rotational speed Ne, the ignition timing, the fuel injection amount, and the fuel injection timing are controlled according to a preset map.

  Here, the normal engine without the variable mechanism 21 and the engine of the present embodiment with the variable mechanism 21 are compared. For example, it is assumed that the vehicle is traveling at a constant speed of 100 km / h, and at this time, the throttle opening of a value of 30 is assumed for a normal engine. At this time, in the engine of the present embodiment, the throttle opening is controlled to a larger value, for example, 40, while the intake valve operating angle α is controlled to an angle corresponding to the throttle opening of 30 or less. As described above, in the case of the engine of the present embodiment, the throttle opening is increased while the engine output torque is the same as in the case of a normal engine, thereby reducing the pumping loss and improving the fuel consumption.

  On the other hand, 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 / Fs = 14.6). In response to this, the ECU 20 normally controls 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 / Ffr, matches the stoichiometric air-fuel ratio. Specifically, the ECU 20 sets a target air-fuel ratio A / Ft equal to the theoretical air-fuel ratio, and makes the pre-catalyst air-fuel ratio A / Ffr detected by the pre-catalyst sensor 17 coincide with the target air-fuel ratio A / Ft. The fuel injection amount injected from the injector 12 and, consequently, the air-fuel ratio are feedback controlled. Control in which the pre-catalyst air-fuel ratio A / Ffr detected by the pre-catalyst sensor 17 matches the stoichiometric air-fuel ratio is referred to as main air-fuel ratio control.

  Further, the ECU 20 normally controls the air-fuel ratio so that the air-fuel ratio of the exhaust gas flowing out from the catalyst 11, that is, the post-catalyst air-fuel ratio A / Frr detected by the post-catalyst sensor 18 matches the stoichiometric air-fuel ratio. This control is called sub air-fuel ratio control. Even if the main air-fuel ratio control is being executed, the actual center air-fuel ratio may deviate from the theoretical air-fuel ratio due to product variations or deterioration of the pre-catalyst sensor 17, so the sub-air-fuel ratio control is performed for the purpose of correcting this deviation. Done at the same time. The main air-fuel ratio control is executed with a very short time period, whereas the sub air-fuel ratio control is executed with a relatively long time period. The correction amount of the sub air-fuel ratio control is updated every long time period.

Here, the catalyst 11 will be described in more detail. As shown in FIG. 3, 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 where 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 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. 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 this embodiment, the degree of deterioration of the catalyst 11 is detected by measuring or detecting the oxygen storage capacity of the catalyst 11. Here, the oxygen storage capacity of the catalyst 11 is represented by the size of the oxygen storage capacity (OSC; O ₂ Strage Capacity, the unit is g), which is the maximum amount of oxygen that the current catalyst 11 can store.

  Hereinafter, the catalyst deterioration diagnosis in the present embodiment will be described.

  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 forcibly (actively) switched alternately to the rich side and the lean side with a predetermined center air-fuel ratio A / Fc as a boundary. The air-fuel ratio when changed to the rich side is referred to as rich air-fuel ratio A / Fr, and the air-fuel ratio when changed to the lean side is referred to as lean air-fuel ratio A / Fl. When the pre-catalyst air-fuel ratio A / Ffr is changed 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.

  4A and 4B, 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, respectively. In FIG. 4A, the target air-fuel ratio A / Ft generated inside the ECU 20 is indicated by a broken line. The output values of the pre-catalyst sensor 17 and the post-catalyst sensor 18 correspond to the values of the pre-catalyst air / fuel ratio A / Ffr and the post-catalyst air / fuel ratio A / Frr, respectively.

  As shown in FIG. 4A, the target air-fuel ratio A / Ft is centered on the theoretical air-fuel ratio A / Fs as the center air-fuel ratio, and then has a predetermined amplitude (rich amplitude Ar, Ar> 0) on the rich side. ) Separated by an air-fuel ratio (rich air-fuel ratio A / Fr) and an air-fuel ratio (lean air-fuel ratio A / Fl) separated from the air-fuel ratio by a predetermined amplitude (lean amplitude Al, Al> 0) on the lean side. And alternately. Following the switching of the target air-fuel ratio A / Ft, the pre-catalyst air-fuel ratio A / Ffr as an actual value is also switched with a slight time delay with respect to the target air-fuel ratio A / Ft. From this, it will be understood that the target air-fuel ratio A / Ft and the pre-catalyst air-fuel ratio A / Ffr are equivalent except that there is a time delay.

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

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

  As shown in FIGS. 4A and 4B, 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 / 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 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 lean from the rich air-fuel ratio A / Fr. The air-fuel ratio is switched to A / Fl.

  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. 4, 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 sensor 18 reaches the lean determination value VL (t1), the target air-fuel ratio A / Ft becomes the rich air-fuel ratio A / Fr. Or reversed. In this way, the target air-fuel ratio A / Ft 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 / 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 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 when the output voltage of the post-catalyst sensor 18 reaches the rich determination value VR (t2), the target air-fuel ratio A / Ft becomes the lean air-fuel ratio A / Fl. Can be switched to.

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

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

  Basically, the oxygen storage capacity OSC measured at one time is used and compared with a predetermined deterioration judgment value OSCs. If the oxygen storage capacity OSC exceeds the deterioration judgment value OSCs, the oxygen storage capacity is normal. If the OSC is equal to or lower than the deterioration determination value OSCs, the deterioration of the catalyst can be determined such as deterioration. However, in this embodiment, in order to improve accuracy, the oxygen storage capacity (in this case, oxygen storage amount) is measured in the oxygen storage cycle in which the target air-fuel ratio A / Ft is on the lean side, and the oxygen storage capacity of these oxygen storage capacities is measured. 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. 5, 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 changed. 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. 5) in this oxygen absorption cycle is measured. The oxygen storage capacity OSC1 of the previous cycle and the oxygen storage capacity OSC2 of the current cycle should be approximately equal.

  By the way, the measured value of the oxygen storage capacity OSC changes according to the catalyst temperature Tc and tends to increase as the catalyst temperature Tc increases. Therefore, in this embodiment, the measured value of the oxygen storage capacity OSC is corrected based on the catalyst temperature Tc in order to make the catalyst temperature condition uniform. Specifically, the ECU 20 calculates a catalyst temperature correction amount from a predetermined map based on the estimated value of the catalyst temperature Tc, and multiplies or adds this catalyst temperature correction amount to the oxygen storage capacity measurement value to obtain an oxygen storage capacity. The measured value is corrected to a value corresponding to a predetermined reference temperature. That is, if the estimated catalyst temperature is higher than the reference temperature, the oxygen storage capacity measurement value is corrected to decrease to a value corresponding to the reference temperature by the correction amount based on the temperature difference. On the contrary, if the estimated catalyst temperature is lower than the reference temperature, the oxygen storage capacity measurement value is increased and corrected to a value corresponding to the reference temperature by the correction amount based on the temperature difference. As a result, the influence of the catalyst temperature change for each diagnosis is eliminated, and the diagnosis can be performed with high accuracy using a constant or uniform deterioration determination value.

  As described above, in the engine in which the operating angle α of the intake valve Vi is variably controlled as in the present embodiment, the oxygen storage capacity OSC is maintained even if other conditions are substantially the same due to the difference in the intake valve operating angle α. The measured value changes. Therefore, it is preferable to perform the deterioration diagnosis in consideration of the difference in the intake valve operating angle α in order to improve the accuracy and reliability of the measurement value and the diagnosis result.

  FIG. 6 shows test results obtained by examining the relationship between the intake air amount Ga and the exhaust gas temperature after the catalyst with respect to the intake valve operating angle α. In the drawing, squares indicate data obtained by retarding the ignition timing by a predetermined angle from the normal ignition timing obtained from the map. In the figure, diamonds indicate data obtained when the ignition timing is advanced by a predetermined angle from the normal ignition timing obtained from the map. The data shown in the figure are all data at the same engine output torque. In relation to (B), the post-catalyst exhaust temperature is the temperature of the exhaust gas detected immediately after the catalyst. This temperature is correlated with the catalyst temperature Tc, that is, the catalyst bed temperature, and can be regarded as the catalyst temperature Tc here. The data of (A) and (B) correspond to each other, for example, the data of a and c are data based on the same test result, and the data of b and d are data based on the same test result.

  The data a and b in (A) have substantially the same intake air amount, but when comparing the data c and d in (B) corresponding thereto, the data c has a slightly higher exhaust temperature after the catalyst than the data d. That is, even if the intake air amount is constant, the catalyst temperature Tc changes due to the difference in the operating angle α.

  Focusing on this point is the first aspect of the deterioration diagnosis described below. That is, in this embodiment, the measured value of the oxygen storage capacity OSC is corrected based on the catalyst temperature Tc, and the deterioration of the catalyst is diagnosed based on the corrected oxygen storage capacity measured value. Then, the catalyst temperature Tc is estimated based on the detected value of the intake air amount Ga. However, even if the detected value of the intake air amount Ga is the same, the same catalyst temperature Tc is not obtained if the operating angle α is different. Therefore, in the first aspect, the catalyst temperature Tc estimated from the intake air amount Ga is corrected based on the operating angle α. By doing so, it is possible to suppress the estimated deviation of the catalyst temperature Tc in consideration of the difference in the working angle. Finally, an accurate measurement value of the oxygen storage capacity after correcting the catalyst temperature can be obtained, and the accuracy and reliability of the catalyst deterioration diagnosis can be improved.

  FIG. 7 shows processing according to the first aspect of deterioration diagnosis. This process is executed by the ECU 20.

  First, in step S101, it is determined whether a precondition for executing 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. Note that the precondition is not limited to this example. If the precondition is not satisfied, the process is terminated. On the other hand, if the precondition is satisfied, the process proceeds to step S102.

  In step S102, measurement of the oxygen storage capacity OSC is started. As described above, the active air-fuel ratio control is started, and the oxygen storage capacity OSC of the catalyst 11 is measured with the execution of the active air-fuel ratio control.

  Next, in step S103, the measurement of the oxygen storage capacity OSC is ended. Thereby, an oxygen storage capacity measurement value OSC before the catalyst temperature correction described later is obtained.

  In the next step S104, the catalyst temperature Tc is estimated based on the detected intake air amount Ga. In step S105, the estimated catalyst temperature Tc is corrected based on the intake valve operating angle α. That is, the target value or actual value of the intake valve operating angle α is acquired, and the correction amount is calculated from a predetermined map based on this value. Then, this correction amount is multiplied or added to the estimated catalyst temperature Tc, and the corrected catalyst temperature Tc 'is calculated. Based on the test result of FIG. 6, the map is set so that the corrected catalyst temperature Tc ′ is obtained as the operating angle α is smaller.

  In the next step S106, the catalyst temperature correction amount is calculated as described above based on the corrected catalyst temperature Tc ′, and this catalyst temperature correction amount is multiplied or added to the oxygen storage capacity measurement value OSC obtained in step S103. An oxygen storage capacity measurement value OSC ′ after the catalyst temperature correction is calculated.

  Finally, in step S107, the deterioration of the catalyst is determined. That is, the measured oxygen storage capacity value OSC ′ after the catalyst temperature correction is compared with a predetermined deterioration determination value OSCs. If OSC ′> OSCs, the catalyst 11 is determined to be normal, and if OSC ′ ≦ OSCs, the catalyst 11 is determined to be deteriorated. .

  Next, a second mode of deterioration diagnosis will be described. As described above, the oxygen storage capacity measurement value OSC varies depending on the variation of each parameter including the operating angle. However, if the oxygen storage capacity measurement value OSC as large as possible is obtained at this time, the influence of the variation is reduced and the oxygen storage capacity measurement value OSC is increased. It is advantageous for accuracy measurement and diagnosis. For this purpose, it is effective to perform measurement and diagnosis under as high a catalyst temperature condition as possible.

  By the way, as can be seen by comparing the data (a, c) and (b, d) with reference to FIG. 6, when the intake air amount and the engine output torque are constant, the operating angle α is reduced and the ignition timing is set. Is retarded, the catalyst temperature Tc increases. That is, the throttle opening is opened as much as the operating angle α is reduced, thereby reducing the pumping loss and increasing the torque. When the ignition timing is retarded by this torque increase, unburned components increase in the exhaust gas exhausted from the combustion chamber, which burns in the catalyst and raises the catalyst temperature. As a result, the oxygen storage capacity measurement value OSC can be increased to improve accuracy.

  Even if the catalyst temperature condition is increased to obtain a large oxygen storage capacity measurement value, this is eventually corrected to the reference temperature by the catalyst temperature correction, and it seems that there is no effect at first glance. However, under the catalyst temperature condition on the low temperature side, the activity of the catalyst itself is poor, the measured oxygen storage capacity varies, and sometimes the oxygen storage capacity that is excessively smaller than the true value may be measured. Therefore, rather than measuring the oxygen storage capacity on the low temperature side, measuring the oxygen storage capacity on the higher temperature side is more advantageous for improving accuracy and reliability, and for this reason, the second aspect is significant. .

  FIG. 8 shows processing according to the second aspect of the deterioration diagnosis. This process is executed by the ECU 20.

  First, in step S201, as in step S101, it is determined whether a precondition for executing the diagnosis is satisfied. If the precondition is not satisfied, the process is terminated. If the precondition is satisfied, the process proceeds to step S202.

  In step S202, the intake valve operating angle α is decreased from the normal time, and the throttle opening TH is increased from the normal time. That is, the actual operating angle α is reduced by a predetermined angle with respect to the operating angle determined from the map based on the current engine operating state (specifically, the accelerator opening Ac) and the target values αtrg and THtrg of the throttle opening. In addition, the operating angle α and the throttle opening TH are controlled so that the actual throttle opening TH is increased by a predetermined opening. This reduces the pumping loss and increases the engine output torque.

  Next, in step S203, the ignition timing θig is retarded so as to cancel out the increase in torque due to the decrease in the operating angle and the increase in the throttle opening. That is, the actual ignition timing θig is delayed by a predetermined angle with respect to the target value θigtrg of the ignition timing determined from the map based on the current engine operating state (specifically, the intake air amount Ga and the rotational speed Ne). The ignition timing θig is controlled. As a result, unburned components increase in the exhaust gas discharged from the combustion chamber 3, and this burns in the catalyst, and the catalyst temperature Tc rises.

  In step S204, the measurement of the oxygen storage capacity OSC is started in the same manner as in step S102, and in step S205, the measurement of the oxygen storage capacity OSC is ended in the same manner as in step S103. In step S206, as in step S104, the catalyst temperature Tc is estimated based on the detected intake air amount Ga. At this time, the catalyst temperature Tc is estimated according to another map that defines the relationship between the intake air amount Ga and the catalyst temperature Tc created for deterioration diagnosis.

  In step S207, the catalyst temperature correction amount is calculated based on the estimated catalyst temperature Tc as described above, and this catalyst temperature correction amount is multiplied or added to the oxygen storage capacity measurement value OSC obtained in step S205 to obtain the catalyst temperature. The corrected oxygen storage capacity measurement value OSC ′ is calculated. Finally, in step S208, a catalyst deterioration determination is made in the same manner as in step S107.

  Next, a third aspect of deterioration diagnosis will be described. In an engine in which the intake valve working angle is variable as in this embodiment, due to variation in the working angle of each cylinder, the air-fuel ratio for each cylinder may shift, and the actual center air-fuel ratio may shift from the theoretical air-fuel ratio. This deviation is more likely to appear as the operating angle is smaller. The actual deviation of the center air-fuel ratio can be basically corrected by the sub air-fuel ratio control. However, for example, when the gas contact with the post-catalyst sensor 18 is not uniform, the deviation of the center air-fuel ratio is not corrected. It will remain displaced. In this case, the oxygen storage capacity measurement value OSC is shifted from the true value. When the control for reducing the operating angle is performed at the time of deterioration diagnosis as in the second aspect, problems such as a shift in the central air-fuel ratio and a shift in the oxygen storage capacity measurement value OSC due to this are likely to occur.

  FIG. 9 shows the relationship between the operating angle and the air-fuel ratio. As shown in the figure, the air-fuel ratio tends to shift to the lean side or the rich side with respect to the stoichiometry as the central air-fuel ratio as the operating angle becomes smaller.

  Therefore, in the third aspect, the operating angle α is controlled to a value equal to or greater than a predetermined lower limit value αx that does not cause a large center air-fuel ratio shift. FIG. 10 shows a control mode of the operating angle α according to the third mode. As shown in the drawing, the operating angle α is increased proportionally as the amount of intake air and thus the engine output torque increases. On the other hand, at the time of deterioration diagnosis, the lower limit value αx of the working angle is set, and the working angle α is controlled to always be a value equal to or larger than the lower limit value αx. By doing so, it is possible to prevent the operating angle from being reduced to the extent that a large center air-fuel ratio shift occurs, and to prevent the shift of the oxygen storage capacity measurement value OSC due to the center air-fuel ratio shift. As a result, a highly accurate and reliable diagnosis result can be obtained.

  FIG. 11 shows processing according to the third aspect of the deterioration diagnosis. This process is executed by the ECU 20.

  First, in step S301, as in step S101, it is determined whether a precondition for executing the diagnosis is satisfied. If the precondition is not satisfied, the process is terminated. If the precondition is satisfied, the process proceeds to step S302.

  In step S302, it is determined whether the target operating angle αtrg determined based on the engine operating state is equal to or greater than a value (αx + Δα) obtained by adding a predetermined value Δα to the lower limit αx. Here, the predetermined value Δα is a working angle reduction amount when the working angle is reduced in step S303 described later.

  If the working angle target value αtrg is equal to or greater than the value (αx + Δα), the process proceeds to step S303, and the working angle α is decreased from the normal time and the throttle opening TH is increased from the normal time, as in step S202. The That is, the operating angle α is controlled to a value obtained by subtracting the predetermined value Δα from the target operating angle value αtrg, and the throttle opening TH is controlled to a value obtained by adding the predetermined value to the target throttle opening value THtrg. In step S304, the ignition timing θig is retarded as in step S203, and the process proceeds to step S304.

  On the other hand, if the working angle target value αtrg is less than the value (αx + Δα), the process proceeds to step S305, where the working angle α is controlled to the target value αtrg or the lower limit value αx. That is, referring to FIG. 10, when the target value αtrg is within a range satisfying αx ≦ αtrg <αx + Δα, the operating angle α is controlled to the target value αtrg. When the target value αtrg is within a range satisfying αtrg <αx, the operating angle α is controlled to a lower limit value αx that is larger than the normal value. Then, steps S303 and S304 are skipped and the process proceeds to step S306. That is, when the target operating angle αtrg is less than the value (αx + Δα), the operating angle is not decreased, the throttle opening is not increased, and the ignition delay is not performed. This is because if this is done, the operating angle may fall below the lower limit αx and the center air-fuel ratio may shift.

  In steps S306 to S310, the same processes as in steps S204 to 208 are performed, respectively. As described above, in the case of other than the small working angle, the same working effect as the second mode can be exhibited. On the other hand, in the case of the small working angle, the working angle is reduced while the reduction of the working angle as in the second mode is stopped. By maintaining the lower limit value or more, it is possible to prevent a center air-fuel ratio shift, a measured value shift and a deterioration in diagnostic accuracy due to this.

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 form 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 air-fuel ratio sensor similar to the pre-catalyst sensor may be used for the post-catalyst sensor, and an O ₂ sensor similar to the post-catalyst sensor may be used for the pre-catalyst 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 one Embodiment of this invention. It is a characteristic diagram which shows the change aspect of an intake valve working angle. 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. 5 is a time chart similar to FIG. 4 for explaining a method of measuring the oxygen storage capacity. It is the test result which investigated the relationship between the amount of intake air with respect to an intake valve working angle, and the exhaust temperature after catalyst. It is a flowchart which shows the process which concerns on the 1st aspect of a deterioration diagnosis. It is a flowchart which shows the process which concerns on the 2nd aspect of a deterioration diagnosis. It is the schematic which shows the relationship between a working angle and an air fuel ratio. It is a graph which shows the control aspect of the working angle which concerns on the 3rd aspect of a deterioration diagnosis. It is a flowchart which shows the process which concerns on the 3rd aspect of a deterioration diagnosis.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 5 Air flow meter 6 Exhaust pipe 7 Ignition timing 10 Throttle valve 11 Catalyst 12 Injector 14 Crank angle sensor 15 Accelerator opening sensor 17 Pre-catalyst sensor 18 Post-catalyst sensor 20 Electronic control unit (ECU)
21 Variable mechanism OSC Oxygen storage capacity Tc Catalyst temperature α Working angle αx Lower limit of working angle Ga Intake air amount TH Throttle opening θig Ignition timing

Claims (4)

An apparatus for diagnosing deterioration of a catalyst disposed in an exhaust passage of an internal combustion engine,
Catalyst temperature estimating means for estimating the temperature of the catalyst;
Diagnostic means for measuring the oxygen storage capacity of the catalyst, correcting the measured oxygen storage capacity based on the catalyst temperature, and diagnosing deterioration of the catalyst based on the corrected oxygen storage capacity;
Intake valve variable control means for variably controlling the operating angle of the intake valve;
An apparatus for diagnosing catalyst deterioration of an internal combustion engine, comprising: catalyst temperature correcting means for correcting the catalyst temperature estimated by the catalyst temperature estimating means based on the operating angle. An intake air amount detecting means for detecting an intake air amount of the internal combustion engine;
The catalyst deterioration diagnosis apparatus for an internal combustion engine according to claim 1, wherein the catalyst temperature estimation means estimates the catalyst temperature based on the intake air amount detected by the intake air amount detection means. An apparatus for diagnosing deterioration of a catalyst disposed in an exhaust passage of an internal combustion engine,
Catalyst temperature measuring means for measuring the temperature of the catalyst;
Diagnostic means for measuring the oxygen storage capacity of the catalyst, correcting the measured oxygen storage capacity based on the catalyst temperature, and diagnosing deterioration of the catalyst based on the corrected oxygen storage capacity;
Intake valve variable control means for variably controlling the operating angle of the intake valve;
Throttle valve control means for controlling the opening of a throttle valve disposed in the intake passage of the internal combustion engine;
Ignition timing control means for controlling the ignition timing of the internal combustion engine;
With
At the time of diagnosis of deterioration of the catalyst, the intake valve variable control means decreases the operating angle of the intake valve from the normal time, the throttle valve control means increases the throttle valve opening from the normal time, and the An apparatus for diagnosing catalyst deterioration in an internal combustion engine, wherein the ignition timing control means retards the ignition timing from the normal time. The apparatus for diagnosing catalyst deterioration of an internal combustion engine according to claim 3, wherein the intake valve variable control means controls the operating angle so that the operating angle is equal to or greater than a predetermined lower limit value when the deterioration of the catalyst is diagnosed. .

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