JP2018173005A - Control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To further improve accuracy in estimating an oxygen storage capacity of a catalyst.SOLUTION: A control device for an internal combustion engine is configured to compare a magnitude of an output signal from an air-fuel ratio sensor which is installed at a downstream side of a catalyst in an exhaust passage of the internal combustion engine, with a lean determination value, thereby determining that an air-fuel ratio at the downstream side of the catalyst is switched from rich to lean, and to compare the magnitude of the output signal from the air-fuel ratio sensor with a rich determination value, thereby determining that the air-fuel ratio at the downstream side of the catalyst is switched from lean to rich. A period from forcibly varying an air-fuel ratio at an upstream side of the catalyst to switching the determination of the air-fuel ratio at the downstream side of the catalyst is defined as an estimation period for an oxygen storage capacity of the catalyst. In a case where a degree of reduction in responsiveness of the air-fuel ratio sensor is small, in comparison with a case where the degree of reduction in the responsiveness of the air-fuel ratio sensor is great, the lean determination value and the rich determination value are made farther from a value of the output signal of the air-fuel ratio sensor in the case where the air-fuel ratio at the downstream side of the catalyst is substantially equal to a theoretical air-fuel ratio.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a control device that controls an air-fuel ratio by adjusting a fuel injection amount in an internal combustion engine.

Generally, in the exhaust passage of an internal combustion engine, harmful substances HC contained in the exhaust gas discharged from the cylinders of the internal combustion engine, CO, three-way catalyst to harmless by oxidation / reduction of NO _x is mounted.

The oxygen storage capacity (OSC: O ₂ Storage Capacity) of the catalyst decreases due to aging. The exhaust gas purification rate by the catalyst depends on the amount of oxygen that can be adsorbed in the catalyst. As the catalyst deteriorates, the amount of harmful substances emitted increases. On the other hand, deterioration of the catalyst hardly affects the driving performance of the vehicle itself. Therefore, there is a risk that an abnormal exhaust vehicle will continue to be used unconsciously for a long time.

  In order to cope with such an event, it is also common to install a diagnosis function in the vehicle for self-diagnosis of the degree of aging of the catalyst (see, for example, the following patent document). Specifically, with the oxygen completely released from the catalyst, the air-fuel ratio of the gas flowing into the catalyst is forcibly operated to lean, and the output signal of the air-fuel ratio sensor installed upstream of the catalyst is switched to lean. The amount of oxygen occluded in the catalyst is estimated during the period until the output signal of the air-fuel ratio sensor installed downstream of the catalyst switches to lean. The oxygen storage amount at the time when the output of the air-fuel ratio sensor downstream of the catalyst is reversed to lean becomes the maximum oxygen storage capacity of the catalyst.

  Alternatively, with the oxygen stored in the catalyst to the full oxygen storage capacity, the air-fuel ratio of the gas flowing into the catalyst is forcibly made rich, and the output signal of the air-fuel ratio sensor upstream of the catalyst switches to rich. It is also possible to estimate the amount of oxygen released by the catalyst during the period until the output signal of the downstream air-fuel ratio sensor switches to rich. The amount of oxygen released when the output of the air-fuel ratio sensor downstream of the catalyst is richly inverted is the maximum oxygen releasing capacity of the catalyst, in other words, the maximum oxygen storage capacity.

  In the diagnosis of the catalyst, the estimated value of the maximum oxygen storage capacity is compared with a determination threshold value, and if the former falls below the latter, it is determined that the catalyst has deteriorated. Then, the driver is notified that the catalyst has deteriorated, and the replacement of the catalyst is urged.

JP, 2006-070105, A JP, 2006-070106, A

  The switching timing of the air-fuel ratio of the gas on the downstream side of the catalyst is obtained by comparing the output signal of the air-fuel ratio sensor downstream of the catalyst with the lean determination value and the rich determination value. That is, when the output signal of the air-fuel ratio sensor changes across the lean determination value, it is determined that the air-fuel ratio on the downstream side of the catalyst has switched from rich to lean, and the output signal of the air-fuel ratio sensor crosses the rich determination value. It is determined that the air-fuel ratio on the downstream side of the catalyst has changed from lean to rich.

  Responsiveness of the air-fuel ratio sensor (more specifically, the amount of change in the magnitude of the output signal of the air-fuel ratio sensor when the air-fuel ratio of the gas in contact with the air-fuel ratio sensor changes by a certain amount, and / or There is an individual difference in the delay in the change in the output signal of the air-fuel ratio sensor with respect to the change in the air-fuel ratio. In addition, the responsiveness of the air-fuel ratio sensor often decreases due to the influence of temperature and aging.

  If the responsiveness of the air-fuel ratio sensor downstream of the catalyst is reduced, the output signal of the air-fuel ratio sensor does not exceed the lean judgment value even though the catalyst is already filled with oxygen, or already in the catalyst It may happen that the output signal of the air-fuel ratio sensor does not exceed the rich determination value despite the lack of oxygen. As a result, the oxygen storage capacity of the catalyst cannot be estimated correctly, and the deteriorated catalyst may be overlooked. Therefore, conventionally, taking into account a decrease in the response of the air-fuel ratio sensor in advance, the lean determination value and the rich determination value are output when the air-fuel ratio sensor comes into contact with an air-fuel ratio gas substantially equal to the stoichiometric air-fuel ratio. Is set to a value close to the signal value to be used.

  However, when the responsiveness of the air-fuel ratio sensor is kept high, by setting each of the lean determination value and the rich determination value to a value close to the theoretical air-fuel ratio, the oxygen storage amount or oxygen release amount of the catalyst is reduced. The length of the counting period is unnecessarily shortened, resulting in an underestimation of the maximum oxygen storage capacity of the catalyst.

  The present invention, which was made by paying attention to the above problems for the first time, is intended to improve the accuracy of estimation of the oxygen storage capacity of a catalyst.

  In the present invention, the oxygen storage capacity of the catalyst during a period from when the air-fuel ratio on the upstream side of the exhaust gas purifying catalyst mounted in the exhaust passage of the internal combustion engine is forcibly changed until the air-fuel ratio on the downstream side fluctuates. The air-fuel ratio on the downstream side of the catalyst is switched from rich to lean by comparing the magnitude of the output signal of the air-fuel ratio sensor installed downstream of the catalyst in the exhaust passage with the lean determination value. It is determined that the air-fuel ratio on the downstream side of the catalyst has changed from lean to rich by comparing the magnitude of the output signal of the air-fuel ratio sensor with the rich judgment value, and the air-fuel ratio on the upstream side of the catalyst is forced The period until the determination of the air-fuel ratio on the downstream side of the catalyst is changed to the estimation period of the oxygen storage capacity of the catalyst, and when the degree of decrease in the responsiveness of the air-fuel ratio sensor is small, the response of the air-fuel ratio sensor The lean determination value and the rich determination value are obtained from the value of the output signal of the air-fuel ratio sensor when the air-fuel ratio on the downstream side of the catalyst is substantially equal to the stoichiometric air-fuel ratio, as compared with the case where the degree of decrease of the air is large. A control device for the internal combustion engine which is kept away is configured.

  According to the present invention, it is possible to further improve the accuracy of estimation of the oxygen storage capacity of the catalyst.

The figure which shows schematic structure of the internal combustion engine and control apparatus in one Embodiment of this invention. The timing diagram which shows transition of the fluctuation | variation of the output signal of the air fuel ratio sensor downstream of the catalyst in the fuel cut which the control apparatus of the embodiment implements. The timing diagram explaining the content of the active control for the diagnosis of the catalyst which the control apparatus of the embodiment implements.

  An embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows an outline of an internal combustion engine for a vehicle in the present embodiment. The internal combustion engine in the present embodiment is a spark ignition type 4-stroke gasoline engine, and includes a plurality of cylinders 1 (one of which is shown in FIG. 1). In the vicinity of the intake port of each cylinder 1, an injector 11 for injecting fuel is provided. A spark plug 12 is attached to the ceiling of the combustion chamber of each cylinder 1. The spark plug 12 receives spark voltage generated by the ignition coil and causes spark discharge between the center electrode and the ground electrode. The ignition coil is integrally incorporated in a coil case together with an igniter that is a semiconductor switching element.

  The intake passage 3 for supplying intake air takes in air from the outside and guides it to the intake port of each cylinder 1. On the intake passage 3, an air cleaner 31, an electronic throttle valve 32, a surge tank 33, and an intake manifold 34 are arranged in this order from the upstream.

  The exhaust passage 4 for discharging the exhaust guides the exhaust generated by burning the fuel in the cylinder 1 from the exhaust port of each cylinder 1 to the outside. An exhaust manifold 42 and an exhaust purification three-way catalyst 41 are disposed on the exhaust passage 4.

Air-fuel ratio sensors 43 and 44 for detecting the air-fuel ratio of the exhaust gas flowing through the exhaust passage are installed upstream and downstream of the catalyst 41 in the exhaust passage 4. Each of the air-fuel ratio sensors 43 and 44 may be a linear A / F sensor having an output characteristic proportional to the air-fuel ratio of the exhaust gas, or an O ₂ sensor having an output characteristic nonlinear with respect to the air-fuel ratio of the exhaust gas. It may be. In the present embodiment, linear A / F sensors are assumed as the air-fuel ratio sensor 43 upstream and the air-fuel ratio sensor 44 downstream of the catalyst 41.

  The exhaust gas recirculation device 2 realizes a so-called high pressure loop EGR, and an external EGR that communicates the upstream side of the catalyst 41 in the exhaust passage 4 and the downstream side of the throttle valve 32 in the intake passage 3. The passage 21, an EGR cooler 22 provided on the EGR passage 21, and an EGR valve 23 that opens and closes the EGR passage 21 and controls the flow rate of EGR gas flowing through the EGR passage 21 are used as elements. The inlet of the EGR passage 21 is connected to the exhaust manifold 42 in the exhaust passage 4 or a predetermined location downstream thereof. The outlet of the EGR passage 21 is connected to a predetermined location downstream of the throttle valve 32 in the intake passage 3, specifically to a surge tank 33.

  An ECU (Electronic Control Unit) 0 serving as a control device for an internal combustion engine according to the present embodiment is a microcomputer system having a processor, a memory, an input interface, an output interface, and the like.

  The input interface includes a vehicle speed signal a output from a vehicle speed sensor that detects the actual vehicle speed of the vehicle, a crank angle signal b output from a crank angle sensor (engine rotation sensor) that detects the rotation angle of the crankshaft and the engine speed. An accelerator opening signal c output from a sensor that detects the amount of depression of the accelerator pedal or the opening of the throttle valve 32 as an accelerator opening (in other words, a required engine load factor), an intake passage 3 (in particular, a surge tank 33) ), An intake air temperature / intake pressure signal d output from a temperature / pressure sensor that detects the intake air temperature and intake air pressure, a coolant temperature signal e output from a water temperature sensor that detects a coolant temperature indicating the temperature of the internal combustion engine, An air-fuel ratio signal f output from an air-fuel ratio sensor 43 that detects the air-fuel ratio of the exhaust gas upstream of the catalyst 41; The air-fuel ratio signal g outputted from the air-fuel ratio sensor 44 for detecting the air-fuel ratio of the exhaust gas on the downstream side, atmospheric pressure signal h or the like to be outputted from the atmospheric pressure sensor for detecting the atmospheric pressure is inputted.

  From the output interface, the ignition signal i for the igniter of the spark plug 12, the fuel injection signal j for the injector 11, the opening operation signal k for the throttle valve 32, and the opening operation signal l for the EGR valve 23. Etc. are output.

  The processor of the ECU 0 interprets and executes a program stored in the memory in advance, calculates operation parameters, and controls the operation of the internal combustion engine. The ECU 0 acquires various information a, b, c, d, e, f, g, h necessary for operation control of the internal combustion engine via the input interface, and requests the required fuel injection amount, fuel injection timing (for one combustion). (Including the number of times of fuel injection), fuel injection pressure, ignition timing, required EGR amount (or EGR rate), etc. are determined. The ECU 0 applies various control signals i, j, k, and l corresponding to the operation parameters via the output interface.

  The ECU 0 according to the present embodiment performs feedback control of the air-fuel ratio of the air-fuel mixture charged in the cylinder 1 and consequently the air-fuel ratio of the exhaust gas discharged from the cylinder 1 and led to the catalyst 41. The ECU 0 first calculates the amount of fresh air charged into the cylinder 1 from the intake pressure and intake temperature, the engine speed, the required EGR rate, etc., and determines the basic injection amount TP corresponding to this.

  Next, the basic injection amount TP is corrected with a feedback correction coefficient FAF determined according to the air-fuel ratio on the upstream side and / or downstream side of the catalyst 41. In general, the feedback correction coefficient FAF is adjusted according to the deviation between the air / fuel ratio of the gas actually measured via the air / fuel ratio sensors 43 and 44 and the target air / fuel ratio (normally near the theoretical air / fuel ratio 14.6), It increases when the measured air-fuel ratio is lean with respect to the target air-fuel ratio, and decreases when the measured air-fuel ratio is rich with respect to the target air-fuel ratio.

Then, the final fuel injection time (energization time for the injector 11) T is calculated in consideration of various correction factors K determined according to the state of the internal combustion engine and the invalid injection time TAUV of the injector 11. The fuel injection time T is
T = TP × FAF × K + TAUV
It becomes. Accordingly, the signal j is input to the injector 11 for the fuel injection time T, and the injector 11 is opened to inject fuel.

  The feedback control with reference to the air-fuel ratio signals f and g on the upstream side and / or downstream side of the catalyst 41 is, for example, that the cooling water temperature of the internal combustion engine is equal to or higher than a predetermined temperature, the fuel is not being cut, and the power is not being increased. This is performed when a predetermined time has elapsed since the start of the internal combustion engine, all the conditions such as the air-fuel ratio sensors 43 and 43 being active and the intake pressure being normal are all satisfied.

  On the other hand, the ECU 0 executes a fuel cut that interrupts the fuel supply to the cylinder 1 when a predetermined fuel cut condition is satisfied. The ECU 0 determines that the fuel cut condition is satisfied at least when the accelerator opening is 0 or less than a threshold value close to 0 and the engine speed is equal to or higher than the fuel cut permission speed.

  Incidentally, even if the fuel cut condition is satisfied, the fuel injection (and ignition) from the injector 11 is not always stopped immediately. If the fuel supply is cut off suddenly when the engine torque is relatively large, a torque shock that causes the engine speed and the vehicle speed to drop stepwise occurs, causing the passengers including the driver to feel the shock. In order to reduce the torque shock, the fuel injection is stopped only after the elapse of the delay time after the fuel cut condition is satisfied. During this delay time, the ignition timing is retarded and the engine torque is actively reduced.

  When a predetermined fuel cut end condition is satisfied after the start of the fuel cut, the fuel cut ends and fuel injection (and ignition) is restarted. The ECU 0 determines that the fuel cut end condition is satisfied, for example, when the accelerator opening degree exceeds the threshold value, or when the engine speed decreases until it falls below the fuel cut return speed.

  During the fuel cut, fresh air that does not contain combustion gas flows into the catalyst 41 through the cylinder 1 and the exhaust passage 4. When oxygen is stored in the catalyst 41 up to the maximum oxygen storage capacity of the catalyst 41, excess oxygen flows out downstream of the catalyst 41 in the exhaust passage 4. Utilizing this fact, the ECU 0 of the present embodiment estimates the degree of reduction in the responsiveness of the air-fuel ratio sensor 44 installed downstream of the catalyst 41 during execution of fuel cut.

  Specifically, as shown in FIG. 2, the output signal (output current or output voltage) g of the air-fuel ratio sensor 44 that fluctuates after the start of fuel cut is monitored, and a predetermined value after the magnitude starts to change. The time required ΔT until reaching the predetermined value (a value corresponding to a predetermined lean air-fuel ratio when it is assumed that the air-fuel ratio sensor 44 does not deteriorate in responsiveness) is counted. By the air-fuel ratio feedback control, the magnitude of the output signal g of the air-fuel ratio sensor 44 at the start of fuel cut is a value corresponding to the theoretical air-fuel ratio or the vicinity thereof.

  Alternatively, the value of the output signal g of the air-fuel ratio sensor 44 when a certain time has elapsed after the start of the fuel cut and the air-fuel ratio sensor 44 when the fuel cut starts or when the magnitude of the output signal g starts to change. The difference ΔI from the value of the output signal g is counted.

  Accordingly, the degree of decrease in the responsiveness of the air-fuel ratio sensor 44 downstream of the catalyst 41 is estimated based on the counted length of the required time ΔT and / or the change ΔI of the output signal g. It is considered that the degree of decrease in the responsiveness of the air-fuel ratio sensor 44 increases as ΔT increases and / or decreases as ΔI decreases.

  The ECU 0 of the present embodiment estimates the maximum oxygen storage capacity of the catalyst 41 and compares the estimated maximum oxygen storage capacity value with the deterioration determination value to determine whether the catalyst 41 is normal or abnormal. Perform diagnosis.

  The oxygen storage capacity of the catalyst 41 can be estimated by adopting any known method. Here, a typical example is shown. From the state in which the air-fuel ratio lean air-fuel mixture is supplied to the cylinder 1 of the internal combustion engine and oxygen is stored to the full capacity of the oxygen storage capacity of the catalyst 41, the air-fuel mixture supplied to the cylinder 1 is intentionally operated to be rich in the air-fuel ratio. Perform active control. Then, the output signal (output current or output voltage) f of the air-fuel ratio sensor 43 upstream of the catalyst 41 immediately shows the air-fuel ratio rich. On the other hand, the output signal g of the air-fuel ratio sensor 44 downstream of the catalyst 41 shows the rich air-fuel ratio behind the output signal f of the upstream air-fuel ratio sensor 43. The output signal g of the downstream air-fuel ratio sensor 44 is rich in the air-fuel ratio after the output signal f of the air-fuel ratio sensor 43 upstream of the catalyst 41 indicates that the air-fuel ratio is rich (or the air-fuel mixture is operated to rich air-fuel ratio). This is because the oxygen stored in the catalyst 41 is released until the shortage of oxygen is compensated.

From the output signal f of the air-fuel ratio sensor 43 upstream of the catalyst 41 indicates a rich air-fuel ratio, the time elapsed between the output signal g of the downstream air-fuel ratio sensor 44 until they show an air-fuel ratio rich T _R Distant , the total weight G _F of the fuel supplied during the T _R, if the difference between the air-fuel ratio during the stoichiometric air-fuel ratio and rich put a .DELTA.A / F _R, oxygen deficient in catalyst 41 between T _R The amount is
(Α ・ ΔA / F _R・ G _F )
It becomes. α is a weight ratio (≈0.23) of oxygen in the air.

The above equation, the catalyst 41 represents the amount of oxygen released by the time of T _R. Total weight G _F of the supplied fuel can be calculated in ECU0. That is, the fuel injection amount in one fuel injection opportunity is an amount necessary for making the air-fuel ratio a predetermined value richer than the stoichiometric air-fuel ratio (smaller than 14.6). Multiplying the number of per-expansion strokes (proportional to the engine speed) gives the fuel supply amount per unit time. Then, when multiplied by the elapsed time T _R to a fuel supply amount per unit time, the total weight G _F of the supplied fuel. In short, the output signal g of the downstream air-fuel ratio sensor 44 of the catalyst 41 based on the elapsed time T _R at the time of showing the air-fuel ratio rich, it is possible to calculate the maximum oxygen release capacity of the catalyst 41. This maximum oxygen release capacity is synonymous with the maximum oxygen storage capacity.

Strictly speaking, in the period T _R, the fuel supply amount per unit due to the accelerator operation or the like of the driver's time (or, a single injection quantity) may increase or decrease. Thus, the total weight G _F of the fuel supplied during the T _R is preferably determined supply amount g _F per unit time (t) and the time integral in the range of T _R. In this embodiment, a linear A / F sensor is arranged upstream of the catalyst 41, and the air-fuel ratio of the gas flowing into the catalyst 41 can be measured in real time. Therefore, as the difference between the measured air-fuel ratio measured .DELTA.A / F _R a (t) via a stoichiometric air-fuel ratio and the A / F sensor 43, the maximum oxygen storage capacity of the catalyst 41 is obtained as the time integral of the period T _R be able to. Ie;
α∫ {ΔA / F _R (t) · g _F (t)} dt
Alternatively, active control in which the mixture supplied to the cylinder 1 is intentionally operated to lean to the air-fuel ratio from a state in which the air-fuel ratio rich mixture is supplied to the cylinder 1 of the internal combustion engine and no oxygen is stored in the catalyst 41. Execute. Then, the output signal f of the air-fuel ratio sensor 43 upstream of the catalyst 41 immediately shows the air-fuel ratio lean. On the other hand, the output signal g of the air-fuel ratio sensor 44 downstream of the catalyst 41 shows the air-fuel ratio lean behind the output signal f of the upstream air-fuel ratio sensor 43. After the output signal f of the air-fuel ratio sensor 43 upstream of the catalyst 41 indicates the air-fuel ratio lean (or after the air-fuel mixture is operated to the air-fuel ratio lean), the output signal g of the downstream air-fuel ratio sensor 44 becomes the air-fuel ratio lean. This is because excess oxygen is adsorbed on the catalyst 41 until the time of

The time elapsed from when the output signal f of the air-fuel ratio sensor 43 upstream of the catalyst 41 indicates the air-fuel ratio lean until the output signal g of the downstream air-fuel ratio sensor 44 indicates the air-fuel ratio lean is denoted by T _L. , is the total weight of the fuel has been supplied during the T _L G _F, when the difference between the air-fuel ratio and the stoichiometric air-fuel ratio during the lean put a .DELTA.A / F _L, the excess in the catalyst 41 between T _L The amount of oxygen
(Α ・ ΔA / F _L・ G _F )
It becomes.

The above equation represents the amount of oxygen stored in the catalyst 41 at the time point T _L. Total weight G _F of the supplied fuel again, it can be calculated in ECU0. That is, the fuel injection amount in one fuel injection opportunity is an amount necessary for setting the air-fuel ratio to a predetermined value leaner than the stoichiometric air-fuel ratio (greater than 14.6). Multiply by the number of expansion strokes per unit, the fuel supply amount per unit time is obtained. Then, when multiplied by the elapsed time T _L in the fuel supply amount per unit time, the total weight G _F of the supplied fuel. In short, it is possible to calculate the maximum oxygen storage capacity of the catalyst 41 based on the elapsed time T _L when the output signal of the air-fuel ratio sensor 44 downstream of the catalyst 41 indicates the air-fuel ratio lean.

Strictly speaking, during the period of _TL , the fuel supply amount (or injection amount per time) per unit time can be increased or decreased due to the driver's accelerator operation or the like. Thus, the total weight G _F of the fuel supplied during the T _L, it is preferable to determine the supply amount g _F per unit time (t) and the time integral in the range of T _L. If ΔA / F _L (t) is the difference between the stoichiometric air-fuel ratio and the actually measured air-fuel ratio measured via the A / F sensor 43, the maximum oxygen storage capacity of the catalyst 41 is obtained as the time integral of the period of T _L. be able to. Ie;
α∫ {ΔA / F _L (t) · g _F (t)} dt
Diagnosis of the catalyst 41 is performed when a sign of deterioration of the catalyst 41 is detected. As an example of the indication, the frequency of vibration of the output signal g of the air-fuel ratio sensor 44 downstream of the catalyst 41 that fluctuates during operation of the internal combustion engine is higher than the threshold (or the period of vibration is shorter than the threshold). And the time difference between the fluctuation of the output signal f of the air-fuel ratio sensor 43 upstream of the catalyst 41 and the fluctuation of the output signal g of the downstream air-fuel ratio sensor 44 is shorter than a threshold value.

  However, the diagnosis of the catalyst 41 is performed when the cooling water temperature of the internal combustion engine is equal to or higher than a predetermined value, the load of the internal combustion engine, the intake amount charged into the cylinder 1, the engine speed, the correction coefficient FAF by the air-fuel ratio feedback control, and the catalyst 41 It is assumed that various conditions such as the temperature being within a predetermined range are all satisfied.

  Further, the diagnosis of the catalyst 41 is performed at least once every trip (a period from when the ignition switch is turned on to start the internal combustion engine until the ignition switch is turned off to stop the internal combustion engine). It is preferable to implement.

As shown in FIG. 3, in the active control, the output signal g of the air-fuel ratio sensor 44 downstream of the catalyst 41 has reached a predetermined rich determination value, that is, at the timing when the output g is switched from lean to rich. The control target air-fuel ratio is set to a predetermined lean air-fuel ratio, and the fuel injection amount is corrected so that the output signal f of the air-fuel ratio sensor 43 upstream of the catalyst 41 takes a value corresponding to the control target. As a result, the air-fuel ratio of the gas flowing into the catalyst 41 is forcibly made lean. Then, after the output signal f of the air-fuel ratio sensor 43 upstream of the catalyst 41 reaches a value corresponding to the control target, the output signal g of the downstream air-fuel ratio sensor 44 reaches a lean determination value. The elapsed time T _L , that is, the elapsed time T _L until the output g switches to lean again is measured.

In addition, at the timing when the output g of the air-fuel ratio sensor 44 downstream of the catalyst 41 switches from rich to lean, the control target air-fuel ratio is set to the predetermined air-fuel ratio on the rich side, and the air-fuel ratio sensor 43 upstream of the catalyst 41 The fuel injection amount is corrected so that the output signal f takes a value corresponding to the control target. As a result, the air-fuel ratio of the gas flowing into the catalyst 41 is forcibly enriched. Then, after the output signal f of the air-fuel ratio sensor 43 upstream of the catalyst 41 reaches a value corresponding to the control target, the output signal g of the downstream air-fuel ratio sensor 44 reaches a predetermined lean determination value. Elapsed time T _R , that is, the elapsed time T _R until the output g switches to rich again is measured.

  As already described, the ECU 0 estimates the degree of decrease in responsiveness of the air-fuel ratio sensor 44 downstream of the catalyst 41 during execution of fuel cut. In the diagnosis of the catalyst 41, as shown in FIG. 3, the lean determination value and the rich determination value are moved away from the values corresponding to the stoichiometric air-fuel ratio as the degree of decrease in the responsiveness of the air-fuel ratio sensor 44 is smaller. . Conversely, as the degree of decrease in the responsiveness of the air-fuel ratio sensor 44 is greater, the lean determination value and the rich determination value are brought closer to values corresponding to the theoretical air-fuel ratio. However, the transition of the output signals f and g of the air-fuel ratio sensors 43 and 44 and the oxygen storage amount of the catalyst 41 shown in FIG. 3 is for the case where the degree of decrease in the responsiveness of the air-fuel ratio sensor 44 is small. When the degree of decrease in the responsiveness of the air-fuel ratio sensor 44 increases, the fluctuation of the output signal g of the air-fuel ratio sensor 44 becomes slower than that depicted in FIG.

The ECU 0 determines the time T _R required for the catalyst 41 that has stored oxygen to the full oxygen storage capacity to release all of the oxygen, and the catalyst 41 that has not stored oxygen to the oxygen storage capacity to the full. the time T _L taken to storage measured more than once each, the measured T _R, the maximum oxygen storage capacity based on _{T L (α · ΔA / F} R · G F), (α · ΔA / F L Calculate G _F ) and find the average of them.

  The determination as to whether or not the catalyst 41 has deteriorated is made by comparing the maximum oxygen storage capacity of the catalyst 41 (average of a plurality of estimated values) with a determination threshold value. That is, if the maximum oxygen storage capacity is less than the determination threshold, it is diagnosed that the catalyst 41 has already deteriorated and cannot exhibit sufficient performance. The ECU 0 that has determined that the catalyst 41 has deteriorated stores and holds information indicating that the catalyst 41 is abnormal (diagnostic code) in the memory, and also indicates whether the catalyst 41 is abnormal or not. Output and alert in a manner that appeals to the auditory sense. For example, an engine check lamp in the cockpit is turned on, displayed on a display, or a warning sound is emitted to prompt inspection and replacement of the catalyst 41.

  In the present embodiment, the catalyst 41 is in a period from when the upstream air-fuel ratio of the exhaust gas purifying catalyst 41 mounted in the exhaust passage 4 of the internal combustion engine is forcibly changed until the downstream air-fuel ratio is changed. The oxygen storage capacity of the catalyst 41 is estimated by comparing the magnitude of the output signal g of the air-fuel ratio sensor 44 installed downstream of the catalyst 41 in the exhaust passage 4 with the lean determination value. It is determined that the air-fuel ratio has switched from rich to lean, and the output signal g of the air-fuel ratio sensor 44 is compared with a rich determination value to determine that the air-fuel ratio downstream of the catalyst 41 has switched from lean to rich. Then, the period from when the air-fuel ratio on the upstream side of the catalyst 41 is forcibly changed until the determination of the air-fuel ratio on the downstream side of the catalyst 41 is changed to the estimated period of the oxygen storage capacity of the catalyst 41, and the air-fuel ratio sensor 4 When the degree of decrease in the responsiveness of the air-fuel ratio sensor 44 is small, the lean determination value and the rich determination value are compared with the case where the air-fuel ratio on the downstream side of the catalyst 41 The control device 0 for the internal combustion engine is configured to be further away from the value of the output signal g of the air-fuel ratio sensor 44 when it is substantially equal to the theoretical air-fuel ratio.

  According to this embodiment, the accuracy of estimation of the oxygen storage capacity of the catalyst 41 is further improved. That is, underestimation of the maximum oxygen storage capacity of the catalyst 41 can be avoided when the degree of decrease in response of the air-fuel ratio sensor 44 downstream of the catalyst 41 is small, and the degree of decrease in response of the air-fuel ratio sensor 44 Even when is large, the maximum oxygen storage capacity of the catalyst 41 can be estimated appropriately.

  The present invention is not limited to the embodiment described in detail above. The specific configuration of each part and the specific processing procedure can be variously modified without departing from the spirit of the present invention.

  The present invention can be applied to control of an internal combustion engine mounted on a vehicle or the like.

0 ... Control unit (ECU)
DESCRIPTION OF SYMBOLS 1 ... Cylinder 11 ... Injector 4 ... Exhaust passage 41 ... Catalyst 43 ... Air-fuel ratio sensor upstream of catalyst 44 ... Air-fuel ratio sensor downstream of catalyst f ... Air-fuel ratio signal upstream of catalyst g ... Air-fuel ratio signal downstream of catalyst

Claims (1)

The oxygen storage capacity of the catalyst is estimated during a period from when the upstream air-fuel ratio of the exhaust gas purifying catalyst mounted in the exhaust passage of the internal combustion engine is forcibly changed to when the downstream air-fuel ratio is changed. And
By comparing the magnitude of the output signal of the air-fuel ratio sensor installed downstream of the catalyst in the exhaust passage with the lean determination value, it is determined that the air-fuel ratio on the downstream side of the catalyst has switched from rich to lean, and the air-fuel ratio sensor By comparing the magnitude of the output signal with the rich judgment value, it is judged that the air-fuel ratio on the downstream side of the catalyst has changed from lean to rich, the air-fuel ratio on the upstream side of the catalyst is forcibly changed, and then the downstream side of the catalyst The period until the determination of the air-fuel ratio of the catalyst is changed to the estimation period of the oxygen storage capacity of the catalyst,
When the degree of decrease in the responsiveness of the air-fuel ratio sensor is small, the lean determination value and the rich determination value are compared with those in the downstream side of the catalyst as compared with the case where the degree of decrease in responsiveness of the air-fuel ratio sensor is large. A control device for an internal combustion engine, which is further away from the value of an output signal of the air-fuel ratio sensor when the fuel ratio is substantially equal to the stoichiometric air-fuel ratio.

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