JP3564933B2 - Catalyst deterioration determination device for internal combustion engine - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a catalyst deterioration determination device that determines whether catalyst has deteriorated.
[0002]
[Prior art]
The respective output trajectory lengths of the upstream air-fuel ratio sensor disposed in the upstream exhaust passage of the catalyst disposed in the exhaust passage of the internal combustion engine and the downstream air-fuel ratio sensor disposed in the downstream exhaust passage are calculated. There is known a catalyst deterioration determination device that determines the presence or absence of catalyst deterioration based on the output trajectory length. An example of this type of catalyst deterioration determination apparatus is disclosed in Japanese Patent Application Laid-Open No. Hei 5-98948.
[0003]
The deterioration determination device of this publication calculates the output locus length of the upstream air-fuel ratio sensor and the output locus length of the downstream air-fuel ratio sensor, and determines the presence or absence of catalyst deterioration based on the ratio of these locus lengths.
[0004]
[Problems to be solved by the invention]
However, when the trajectory length of the output of the air-fuel ratio sensor on the upstream side of the catalyst is used for the catalyst deterioration determination as described above, an accurate trajectory length cannot be calculated and an error may occur in the determination.
That is, since the exhaust gas discharged from each cylinder has a different discharge timing, the exhaust gas does not uniformly mix in the exhaust pipe to form an exhaust lump for each cylinder, and reaches the upstream air-fuel ratio sensor in a state of being considerably separated from each other. For this reason, if the air-fuel ratio varies among the cylinders due to the variation in the characteristics of the fuel injection valve, the exhaust air masses having different air-fuel ratios sequentially reach the upstream air-fuel ratio sensor. For example, when the air-fuel ratio of a certain cylinder becomes a value different from the air-fuel ratio of another cylinder due to a difference in characteristics of the fuel injection valve or the like, every time exhaust from this cylinder reaches the upstream air-fuel ratio sensor. The output value of the upstream-side air-fuel ratio sensor becomes different, and there is a case where the output value greatly fluctuates every one cycle of the engine, for example, every 720 degrees of the crankshaft rotation angle in a four-stroke engine. That is, in this case, the output of the upstream air-fuel ratio sensor has a waveform in which a spike signal corresponding to the air-fuel ratio of a cylinder whose characteristic is shifted every 720 degrees is superimposed on the base air-fuel ratio (air-fuel ratio of another cylinder). When the waveform of the output of the upstream air-fuel ratio sensor includes a spike in this way, even if the air-fuel ratio of each cylinder is stable and does not change much, the trajectory length of the output of the upstream air-fuel ratio sensor becomes In some cases, the value becomes apparently large. For this reason, if the catalyst deterioration determination is performed using such an upstream air-fuel ratio sensor output trajectory length, accurate determination may not be performed. This problem is caused, for example, by arranging an upstream air-fuel ratio sensor for each exhaust passage of each cylinder bank, such as a V-type engine, so that the exhaust purification catalyst and the downstream air-fuel ratio are located on a common exhaust passage where the exhaust passages of each cylinder bank join. This is also likely to occur in engines of the type provided with a fuel ratio sensor.
[0005]
Note that the exhaust mass discharged from each cylinder is mixed with each other when passing through the catalyst, and the air-fuel ratio of the exhaust discharged to the downstream side of the catalyst becomes uniform. Therefore, the spike as described above appears in the downstream air-fuel ratio sensor output waveform. This does not occur, and the above-described problem does not occur with respect to the trajectory length of the output of the downstream air-fuel ratio sensor.
SUMMARY OF THE INVENTION It is an object of the present invention to provide a catalyst deterioration determination device capable of solving the above-described problem and performing accurate catalyst deterioration determination even when the air-fuel ratio between cylinders varies.
[0006]
[Means for Solving the Problems]
According to the first aspect of the present invention, an exhaust purification catalyst disposed in an exhaust passage of an internal combustion engine, and an upstream side disposed in an exhaust passage upstream of the exhaust purification catalyst and detecting an exhaust air-fuel ratio upstream of the catalyst. An air-fuel ratio sensor, a downstream air-fuel ratio sensor disposed in an exhaust passage downstream of the exhaust gas purification catalyst for detecting an exhaust air-fuel ratio downstream of the catalyst, and a degree of smoothing increases as the engine speed increases. Performing a smoothing calculation process to smooth variations in the output of the upstream air-fuel ratio sensor, and a smoothing calculation means for obtaining a smoothed output value of the upstream air-fuel ratio sensor; and a smoothing output value of the upstream air-fuel ratio sensor. A smoothed output value trajectory length calculating means for calculating a trajectory length of the upstream air-fuel ratio sensor smoothed output value based on the change amount, and a downstream air-fuel ratio sensor output based on the change amount of the downstream air-fuel ratio sensor output. Calculate the path length Flow-side trajectory length calculation means, degradation determination means for determining whether or not the exhaust purification catalyst has deteriorated based on the trajectory length of the upstream air-fuel ratio sensor smoothed output value and the downstream air-fuel ratio sensor output trajectory length And a catalyst deterioration determination device for an internal combustion engine, comprising:
[0007]
That is, according to the first aspect of the invention, instead of calculating the trajectory length of the output value of the upstream air-fuel ratio sensor itself, the trajectory length of the smoothed output of the upstream air-fuel ratio sensor is calculated. As a result, the spikes each time the exhaust of the cylinder in which the air-fuel ratio has shifted reaches the air-fuel ratio sensor are smoothed, and a stable output waveform close to the base air-fuel ratio can be obtained. Therefore, the trajectory length of the smoothed output waveform corresponds to the fluctuation of the base air-fuel ratio as a whole. Therefore, by performing the catalyst deterioration determination based on the trajectory length of the smoothed output and the trajectory length of the downstream air-fuel ratio sensor output, an accurate catalyst deterioration determination that eliminates the influence of the deviation of the air-fuel ratio of a specific cylinder is performed. Becomes possible.
[0008]
On the other hand, when performing such a smoothing operation process, the degree of smoothing becomes a problem. For example, if the degree of smoothing is extremely large, the follow-up of the smoothed output to the actual output of the upstream air-fuel ratio sensor will be delayed, so that even the fluctuation of the base air-fuel ratio as a whole will be smoothed, and accurate catalyst deterioration determination will be performed. May not be possible. In addition, if the degree of smoothing is small, smoothing is not performed when the frequency of exhaust from the cylinders having an air-fuel ratio deviation that has reached the upstream air-fuel ratio sensor increases, such as when the engine is running at a high speed. Because of the sufficient spike, there is a possibility that accurate catalyst deterioration determination cannot be performed.
[0009]
Therefore, in the invention of claim 1, the smoothing calculation means performs the smoothing process so that the degree of smoothing in the smoothing calculation process increases as the engine speed increases. For this reason, when the engine speed is low and the influence of the above-described spike is small, the degree of smoothing is relatively small, and the smoothed output follows the actual upstream air-fuel ratio sensor output well, and the engine speed is improved. When the number is large and the influence of spikes is large, the degree of smoothing is relatively large, and a stable smooth output value excluding the influence of spikes can be obtained.
[0010]
As the smoothing calculation process, for example, a weighted averaging process (so-called “smoothing process”) described later can be used. In this case, the weighting coefficient is set to a large value according to an increase in the engine speed. Thus, the degree of smoothing can be increased as the engine speed increases.
According to the second aspect of the present invention, the exhaust purification catalyst disposed in the exhaust passage of the internal combustion engine, and the upstream side disposed in the exhaust passage upstream of the exhaust purification catalyst and detecting the exhaust air-fuel ratio on the upstream side of the catalyst An air-fuel ratio sensor, a downstream air-fuel ratio sensor disposed in an exhaust passage downstream of the exhaust purification catalyst for detecting an exhaust air-fuel ratio downstream of the catalyst, and an output of the upstream air-fuel ratio sensor for fuel injection into the engine. Sampling means for sampling at intervals that vary in proportion to the execution interval, performing a smoothing operation on the sampled output value to obtain a smoothed output value of the upstream air-fuel ratio sensor, and the upstream air-fuel ratio sensor A smoothed output value trajectory length calculating means for calculating a trajectory length of the upstream air-fuel ratio sensor smoothed output value based on a variation amount of the smoothed output value; and a downstream side based on the variation amount of the downstream air-fuel ratio sensor output. Sky A downstream path length calculating means for calculating a path length of a ratio sensor output; a path length of the upstream side air-fuel ratio sensor smoothed output value; and a downstream path length of the exhaust purification catalyst based on the downstream side air-fuel ratio sensor output path length. A catalyst deterioration determination device for an internal combustion engine, comprising: a deterioration determination unit that determines whether or not there is deterioration.
[0011]
That is, in the invention of claim 2, the smoothing operation means samples the output of the upstream air-fuel ratio sensor at a predetermined sampling interval, and performs the smoothing operation on the output value of the sampled air-fuel ratio sensor. The sampling is performed at a sampling interval that changes in proportion to the fuel injection execution interval of the engine. Since the spike in the output waveform of the upstream air-fuel ratio sensor appears every time fuel injection is performed in a specific cylinder, sampling is performed at each fuel injection execution interval of the engine as described above to respond to execution of fuel injection in each cylinder. The output of the upstream air-fuel ratio sensor at the specified time can be sampled. Therefore, by sampling at the above intervals, the air-fuel ratio of the exhaust gas of each cylinder appears at the same frequency in the sampled sensor output value. Therefore, by performing a smoothing operation on the sampled output, the waveform of the smoothed output always becomes a waveform close to the base air-fuel ratio excluding the influence of spikes even when the degree of smoothing is fixed. Therefore, also in this case, by performing the catalyst deterioration determination based on the trajectory length of the smoothed output value and the trajectory length of the downstream air-fuel ratio sensor, accurate catalyst deterioration eliminating the influence of the deviation of the air-fuel ratio of a specific cylinder is performed. A determination can be made.
[0012]
The weighted average can be used as the smoothing operation in the second aspect of the invention. In this case, the weighting coefficient in the weighted average can be set to an appropriate constant value.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a diagram illustrating a schematic configuration of an embodiment when the present invention is applied to an internal combustion engine for a vehicle. In FIG. 1, reference numeral 1 indicates an internal combustion engine body for a vehicle. In the present embodiment, as shown in FIG. 1, the engine 1 is a V-type engine in which each cylinder is arranged in two rows in two banks (bank A and bank B) in a V-shape. In FIG. 1, reference numeral 2 denotes an intake passage of the engine 1, and reference numeral 3 denotes an air flow meter arranged in the intake passage 2. The air flow meter 3 directly measures the amount of intake air, and is, for example, a vane type air flow meter with a potentiometer that outputs an analog voltage signal proportional to the amount of intake air. The output signal of the air flow meter 3 is input to the multiplexer built-in AD converter 101 of the control circuit 10. The distributor 4 includes a crank angle sensor 5 that generates a reference position detection pulse signal each time the rotor shaft rotates 720 degrees, for example, converted to a crank angle, and a rotation angle 30 degrees, converted to a crank angle. A crank angle sensor 6 for generating a pulse signal is provided. The pulse signals of the crank angle sensors 5 and 6 are supplied to an input / output interface 102 of the control circuit 10, and the output of the crank angle sensor 6 is supplied to an interrupt terminal of the CPU 103 of the control circuit 10.
[0014]
Further, a fuel injection valve for injecting pressurized fuel from a fuel supply system is provided at an intake port of each cylinder. FIG. 1 shows only one fuel injection valve 7A, 7B of each of banks A and B among the fuel injection valves of each cylinder. Further, a water temperature sensor 9 for detecting the temperature of the engine cooling water is provided in a water jacket (not shown) of the cylinder block of the engine body 1. An analog voltage signal generated by the water temperature sensor 9 and proportional to the cooling water temperature THW is input to the AD converter 101 of the control circuit 10.
[0015]
The exhaust systems of the banks A and B of the engine 1 downstream from the exhaust manifolds 11A and 11B are provided with HC, CO, NO_XCatalytic converters 12A and 12B accommodating a three-way catalyst for purifying the three components at the same time are provided. The catalytic converters (start catalysts) 12A and 12B have a relatively small capacity so that the catalyst can be warmed up at the time of starting the engine in a short time, and are provided in the engine room.
[0016]
Further, upstream air-fuel ratio sensors 13A and 13B are provided in the exhaust pipes 11A and 11B on the upstream side of the catalytic converters 12A and 12B, respectively. In the present embodiment, the upstream air-fuel ratio sensors 13A and 13B are so-called linear air-fuel ratio sensors that output a voltage signal proportional to the air-fuel ratio in a wide air-fuel ratio range.
Furthermore, on the downstream side of the catalytic converter converters 12A and 12B, the exhaust pipes 14A and 14B of each bank join the collective exhaust pipe 15 at the collecting part 15a, and a catalytic converter containing a three-way catalyst is provided on the exhaust pipe 15. 16 are provided. The catalytic converter (main catalyst) 16 has a relatively large capacity and is disposed under the floor of the vehicle body for mainly purifying exhaust gas from the engine 1 after completion of warming up of the catalyst.
[0017]
A downstream air-fuel ratio sensor 17 is provided in the collective exhaust pipe 15 downstream of the catalytic converter 16. In the present embodiment, the downstream air-fuel ratio sensor 17 detects the oxygen concentration in the exhaust gas, and generates an output voltage having a different level depending on whether the air-fuel ratio of the exhaust gas is rich or lean with respect to the stoichiometric air-fuel ratio.₂It is a sensor. Upstream linear air-fuel ratio sensors 13A, 13B and downstream O₂The outputs of the sensors 17 are input to the AD converter 101 of the control circuit 10, respectively.
[0018]
The control circuit 10 is configured as, for example, a microcomputer, and includes an A / D converter 101, an input / output interface 102, a CPU 103, a ROM 104, a RAM 105, a backup RAM 106, a clock generation circuit 107, and the like.
The throttle valve 18 of the intake passage 2 is provided with an idle switch 19 for detecting whether or not the throttle valve is fully closed. This output signal is supplied to an input / output interface 102 of the control circuit 10.
[0019]
Reference numerals 110A and 110B in FIG. 1 denote fuel injection circuits for injecting fuel from the fuel injection valves 7A and 7B of each cylinder of the A bank and each cylinder of the B bank. The fuel injection circuits 110A and 110B inject fuel from the fuel injection valves of the respective cylinders according to a fuel injection command signal from the control circuit 10. In this embodiment, the control circuit 10 includes the upstream air-fuel ratio sensors 13A and 13B and the downstream O₂The fuel injection amount TAU from each fuel injection valve is calculated based on the output of the sensor 17 so that the engine operating air-fuel ratio becomes close to the stoichiometric air-fuel ratio. For the calculation of the fuel injection amount TAU, any known method can be used as long as the engine air-fuel ratio can be maintained in the vicinity of the stoichiometric air-fuel ratio.
[0020]
Next, the catalyst deterioration determination according to the present embodiment will be described.
In the present embodiment, as described later, the trajectory length of the outputs of the upstream air-fuel ratio sensors 13A and 13B and the downstream O₂The presence or absence of deterioration of the catalyst 16 is determined based on the ratio of the output of the sensor 17 to the trajectory length. As is known, the three-way catalyst adsorbs oxygen in the exhaust gas when the air-fuel ratio of the inflowing exhaust gas is lean, and releases oxygen adsorbed and held when the air-fuel ratio of the inflowing exhaust gas is rich.₂Performs storage action. This O₂Due to the storage action, the three-way catalyst is maintained in the stoichiometric air-fuel ratio atmosphere even when the air-fuel ratio of the exhaust gas flowing into the three-way catalyst fluctuates somewhat near the stoichiometric air-fuel ratio. Therefore, the function of the three-way catalyst is maximized.
[0021]
Also, as described above, the three-way catalyst is O₂When the storage function is sufficiently exerted, the air-fuel ratio of the exhaust gas downstream of the catalytic converter 16 is maintained substantially in the vicinity of the stoichiometric air-fuel ratio, so that the fluctuation is reduced. For this reason, the three-way catalyst₂If the storage function is fully exhibited, the downstream O₂The trajectory length LVOD of the output of the sensor 17 (FIG. 2) becomes smaller than the trajectory length LVOU of the output of the upstream air-fuel ratio sensor, and the ratio LVOD / LVOU of these trajectory lengths becomes a small value. However, when the three-way catalyst deteriorates, the catalyst O₂The storage function also decreases, and fluctuates according to the air-fuel ratio of the exhaust gas upstream of the catalytic converter 16. As a result, the downstream O₂The trajectory length LVOD of the output of the sensor 17 increases with the deterioration of the three-way catalyst, and the trajectory length ratio LVOD / LVOU gradually takes a large value. Therefore, the trajectory length of the upstream air-fuel ratio sensor output and the downstream O₂When the ratio of the sensor output to the track length becomes larger than a certain value, it can be determined that the three-way catalyst has deteriorated.
[0022]
2 (B) and 2 (C) show the downstream O due to the deterioration of the three-way catalyst.₂FIG. 3 is a diagram for explaining a change in sensor output in association with an upstream air-fuel ratio sensor output (FIG. 2A). The output of the upstream air-fuel ratio sensor in FIG. 2A is the sum of the outputs of the upstream air-fuel ratio sensors 13A and 13B in this embodiment. As shown in FIG. 2A, in this embodiment, the air-fuel ratio on the upstream side of the catalytic converter fluctuates in a relatively small range around the stoichiometric air-fuel ratio by the air-fuel ratio feedback control. Therefore, the trajectory length LVOU of the output of the upstream air-fuel ratio sensor has a relatively small value as shown in FIG.
[0023]
On the other hand, FIG. 2B shows the downstream O when no deterioration occurs in the catalytic converter.₂4 shows an output waveform of a sensor 17. As described above, when the catalytic converter has not deteriorated, the exhaust air-fuel ratio downstream of the catalytic converter is maintained near the stoichiometric air-fuel ratio.₂The sensor generates a different output voltage depending on whether the exhaust air-fuel ratio is rich or lean.₂The output of the sensor 17 fluctuates between the rich level and the lean level in a relatively long cycle. For this reason, as shown in FIG.₂The locus length LVOD of the output of the sensor 17 becomes an extremely small value, and the value of the ratio LVOD / LVOU of these locus lengths also becomes small.
[0024]
FIG. 2C shows the downstream O when the catalytic converter is deteriorated.₂4 shows an output waveform of a sensor 17. When the three-way catalyst deteriorates, the accompanying O₂Downstream O due to reduced storage action₂Since the sensor output fluctuates at substantially the same cycle as the fluctuation of the exhaust air-fuel ratio on the upstream side of the catalyst (FIG. 2A), as shown in FIG.₂The locus length LVOD of the sensor 17 increases, and the locus length ratio LVOD / LVOU takes a large value.
[0025]
FIG. 3A shows a state in which the air-fuel ratio of a specific cylinder deviates from the stoichiometric air-fuel ratio due to, for example, a deviation in the characteristics of the fuel injection valve from the state shown in FIG. 4 shows the output of the upstream air-fuel ratio sensor when the air-fuel ratio is shifted to the air-fuel ratio side). As shown in FIG. 3A, in this case, the output of the upstream air-fuel ratio sensor fluctuates greatly every time the exhaust gas from this cylinder reaches the upstream air-fuel ratio sensor, and the output of the upstream air-fuel ratio sensor changes every 720 degrees of the engine crankshaft rotation. A spike occurs in the output waveform of the side air-fuel ratio sensor. Therefore, this spike is added when calculating the output trajectory length of the upstream air-fuel ratio sensor, and although the actual air-fuel ratio fluctuation is relatively small as in FIG. In some cases, the value of the trajectory length LVOU of the output of the upstream air-fuel ratio sensor becomes extremely large. When such a state occurs, even if the catalyst actually deteriorates and the downstream-side air-fuel ratio sensor output trajectory length LVOD increases, the upstream-side air-fuel ratio sensor output trajectory length LVOU increases due to spikes. The value of the long ratio LVOD / LVOU does not increase, and the deteriorated catalyst may be erroneously determined to be normal.
[0026]
In this embodiment, the output of the upstream air-fuel ratio sensor shown in FIG. 2A is smoothed by a smoothing process (a smoothing process in this embodiment) to be described later, so that the influence of spikes as shown in FIG. To obtain a smoothed output waveform excluding. Then, the above problem is solved by using the trajectory length of the smoothed output waveform as the output trajectory length LVOU of the upstream air-fuel ratio sensor.
[0027]
Next, the smoothing operation processing according to the present embodiment will be described. In the present embodiment, the following weighted average calculation (smoothing operation) is performed as the smoothing calculation process.
VUN = VUN_n-1+ (VU-VUN_n-1) / N_n
Here, VUN is the smoothed output value (smoothed value) of the upstream air-fuel ratio sensor, VU is the output of the upstream air-fuel ratio sensor, and VUN_n-1Is the smoothed output value from the previous execution of the smoothing operation, N_nRepresents a weighting coefficient (average coefficient). That is, in the smoothing calculation process used in the present invention, the degree of the effect of the fluctuation of the upstream air-fuel ratio sensor output VU during the execution of the current routine on the value of the smoothed output VUN (the degree of smoothing) is arbitrarily set. This is a process that can be performed. When the smoothing operation is performed as the smoothing operation as described above, the smoothing coefficient N_nThe degree of smoothing changes according to the magnitude of.
[0028]
However, the annealing coefficient N_nIf you fix the value of_,When the number of spikes generated per unit time increases with an increase in the engine speed, the frequency of spike detection as the output of the upstream air-fuel ratio sensor increases, so that the smoothing coefficient N_nIf is set small, there is a problem that the output of the upstream air-fuel ratio sensor cannot be sufficiently smoothed. Also, the annealing coefficient N_nIs fixed to a large value, there arises a problem that the followability of the smoothed output value to the actual air-fuel ratio deteriorates. Therefore, in the present embodiment, the smoothing coefficient N_nBy increasing the value according to the engine speed, the degree of smoothing is increased when the engine speed is high, and sufficient smoothing is performed even when the number of spikes per unit time increases. Becomes possible. In addition, when the engine speed is low, the degree of smoothing is reduced according to the number of spikes generated per unit time, so that the smoothed output value can follow the actual air-fuel ratio even at low engine speeds. Becomes possible.
[0029]
FIG. 4 is a flowchart showing a catalyst deterioration determination operation when the above-described smoothing calculation process is used. This operation is performed by a routine executed by the control circuit 10 at regular intervals.
In FIG. 4, in step 401, the value of a determination time counter C, which will be described later, is incremented by one. In step 403, the output VU of the upstream air-fuel ratio sensors 13A and 13B is displayed together with the engine speed Ne._A, VU_BAnd downstream O₂The output VD of the sensor 17 is AD-converted and read. Then, in step 405, the aforementioned smoothing coefficient N_nIs N_n= K x Ne. Where K is a constant value_.That is, in the present embodiment, the smoothing coefficient N_nIs set so as to increase in proportion to the engine speed, and the degree of smoothing in the smoothing calculation process is set to increase in proportion to the engine speed. Note that the annealing coefficient N_nNeed not necessarily be set to a value proportional to the engine speed, but other settings are possible if they are set to increase as the engine speed increases. In practice, the smoothing factor N_nSince the relationship between the engine speed and the engine speed may change depending on the actual engine or exhaust configuration, it is preferable to determine the optimum value using the actual engine or the exhaust system. Annealing factor N_nIt has been found that setting the value to increase in proportion to the engine speed will often provide favorable results.
[0030]
Next, at step 407, the smoothing coefficient N set as described above is set._nOf the upstream air-fuel ratio sensors 13A and 13B using the value_A, VU_BEach smoothed output value VUN_A, VUN_BIs calculated by the following equation.
VUN_A= VUN_{A (n-1)}+ (VU_A-VUN_{A (n-1)}) / N_n
VUN_B= VUN_{B (n-1)}+ (VU_B-VUN_{B (n-1)}) / N_n
Where VUN_{A (n-1)}, VUN_{B (n-1)}Is the smoothed output VUN from the previous execution of this routine._A, VUN_BIs the value of
[0031]
In step 409, the smoothed output value VUN of the upstream air-fuel ratio sensors 13A and 13B calculated at the time of execution of the current routine is calculated._A, VUN_BAnd the smoothed output value VUN at the time of execution of the previous routine_{A (n-1)}, VUN_{B (n-1)}And the smoothed output value VUN_A, VUN_BTrack length LVOU_A, LVOU_BIs calculated as follows.
[0032]
LVOU_A= LVOU_A+ ｜ VUN_A-VUN_{A (n-1)}|
LVOU_B= LVOU_B+ ｜ VUN_B-VUN_{A (n-1)}|
That is, in this embodiment, the trajectory length of each smoothed output is approximately calculated by integrating the absolute value of the amount of change in the smoothed output value from the previous execution of the routine to the execution of the current routine.
[0033]
In step 411, the sum of the trajectory lengths of the respective smoothed output values obtained as described above is obtained and stored as the LVOU.
Further, in step 413, similarly to step 409, the trajectory length LVOD of the output VOD of the downstream air-fuel ratio sensor 17 is obtained by integrating the change amount of the output VOD. In step 414, VUN is prepared for the next routine execution._{A (n-1)}, VUN_{B (n-1)}, VD_n-1Are updated.
[0034]
After calculating the trajectory lengths LVOU and LVOD as described above, it is determined in step 415 whether or not the value of the determination time counter C has exceeded a predetermined value A. The counter C is a counter for counting the trajectory length integration time for catalyst deterioration determination, and the predetermined value A is equivalent to a time sufficient to calculate a significant trajectory length by eliminating the influence of a short-time disturbance or the like. This is determined in detail by experiments and the like.
[0035]
In step 415, if C ≦ A, that is, if the predetermined trajectory length integration time has not elapsed, this routine ends as it is.
If the predetermined trajectory length integration time has elapsed in step 415, that is, if C> A, the process proceeds to step 417, where it is determined whether the trajectory length ratio LVOD / LVOU is smaller than a predetermined determination value B. It is determined whether the catalyst has deteriorated. That is, when the trajectory length ratio LVOD / LVOU is smaller than the predetermined value B (when the catalyst is normal), the routine proceeds to step 419, where the value of the deterioration flag FX is set to 0, and when it is equal to or larger than the predetermined value B (catalyst). If it has deteriorated), the routine proceeds to step 421, where the value of the deterioration flag FX is set to 1. When the value of the deterioration flag FX is set to 1, a warning lamp is turned on to notify the driver of the deterioration of the catalyst by a routine separately executed by the control circuit 10. Further, the value of the deterioration flag is stored in the backup RAM 106 of the control circuit 10 and prepared for the next repair and inspection.
[0036]
After completing the above operation, the routine proceeds to step 423, where the locus length LVOU is set._A, LVOU_B, LVOD and the value of the counter C are set to 0, and the processing ends. As a result, a new trajectory length is calculated from the next execution of the routine.
Next, another embodiment of the present invention will be described.
In the embodiment of FIG. 4, the smoothing coefficient N_nIs increased as the engine speed increases, thereby eliminating the effects of spikes and ensuring that the smoothed output value follows the actual air-fuel ratio regardless of the engine speed. On the other hand, in the present embodiment, the output of the upstream air-fuel ratio sensor is smoothed by the smoothing operation process as in the embodiment of FIG._nIs fixed to a constant value regardless of the rotational speed, and the sampling of the output of the upstream air-fuel ratio sensor and the smoothing operation of the sampled output value are performed at intervals proportional to the execution interval of fuel injection to the engine. This is different from the embodiment of FIG.
[0037]
If the sampling interval of the output of the upstream air-fuel ratio sensor is fixed, if the engine speed increases and the interval between the spikes becomes short, the frequency at which the spike is detected as the output of the upstream air-fuel ratio sensor May increase, and the smoothing coefficient N_nIs constant, the output of the upstream air-fuel ratio sensor may not be sufficiently smoothed depending on the engine speed. However, as in the present embodiment, by changing the sampling interval of the output of the upstream air-fuel ratio sensor in proportion to the fuel injection execution interval, the air-fuel ratio of the exhaust gas from the cylinder having the shifted air-fuel ratio is sampled. The ratio between the number of times and the number of times the air-fuel ratio of the exhaust gas from another cylinder is sampled is always constant regardless of the engine speed. Therefore, the annealing coefficient N_nIs fixed to an appropriate constant value, regardless of the engine speed, sufficient smoothing can always be performed, and at the same time, the smoothing output value of the upstream air-fuel ratio sensor can follow the actual air-fuel ratio. Deterioration can be prevented.
[0038]
Next, the catalyst deterioration determination operation of the present embodiment will be described with reference to FIGS. FIG. 5 is a flowchart illustrating the sampling of the outputs of the upstream air-fuel ratio sensors 13A and 13B and the smoothing calculation process in the present embodiment. This routine is executed by the control circuit 10 as an interrupt routine at each fuel injection timing of the engine 1, that is, each time fuel injection is performed in any one of the cylinders of the engine 1.
[0039]
When the routine is started in FIG. 5, in step 501, the output VU of the upstream air-fuel ratio sensors 13A and 13B is determined._A, VU_BIs AD-converted and read. Next, in step 503, the output VU of the upstream air-fuel ratio sensors 13A and 13B is_A, VU_BOutput value VUN of_A, VUN_BIs calculated by the following equation.
[0040]
VUN_A= VUN_{A (n-1)}+ (VU-VUN_{A (n-1)}) / N_n
VUN_B= VUN_{B (n-1)}+ (VU-VUN_{B (n-1)}) / N_n
Here, unlike the embodiment of FIG._nIs an appropriate constant value.
By executing the routine of FIG. 5, in the present embodiment, the output VUN of the upstream air-fuel ratio sensors 13A and 13B is provided at each fuel injection timing of the engine 1._A, VUN_BIs read (sampled), and an annealing operation is performed at the same time.
[0041]
FIG. 6 is a flowchart illustrating a catalyst deterioration determination operation based on the trajectory length of the smoothed output of the upstream air-fuel ratio sensor and the output of the downstream air-fuel ratio sensor calculated as described above. In this determination operation, the smoothed output VUN calculated in the routine of FIG._A, VUN_BThe latest value of VUM_A, VUM_BAs the VUM as in the determination operation of FIG._A, VUM_BThe length of each locus is calculated (Step 607), the LVOU is obtained (Step 609), and the locus length of the output of the downstream air-fuel ratio sensor 17 read every time the routine is executed is calculated (Steps 609 and 611). Then, in steps 613 to 621, catalyst deterioration is determined, and the value of the catalyst deterioration flag FX is set according to the determination result. Also in the present embodiment, when the value of the catalyst deterioration flag FX is set to 1, a warning lamp in the driver's seat is turned on by a separately executed routine to notify the driver of catalyst deterioration. The value of FX is stored in the backup RAM 106 of the control circuit 10.
[0042]
In the present embodiment, the sampling of the output of the upstream air-fuel ratio sensor and the smoothing calculation process are performed at each fuel injection timing of the engine 1. However, the sampling and the smoothing are performed at intervals proportional to the fuel injection interval, preferably. The same effect can be obtained by executing at intervals of an integral multiple of the fuel injection interval.
In the above-described embodiment, the case where the present invention is applied to a V-type engine is described as an example. However, the present invention is not limited to the above-described embodiment, and an engine having another cylinder arrangement, for example, an in-line engine Needless to say, the present invention can be applied to a cylinder engine and the like.
[0043]
【The invention's effect】
As described above, according to the invention described in each of the claims, when the output of the air-fuel ratio sensor disposed on the upstream side of the catalyst is used for determining the deterioration of the catalyst, even when the air-fuel ratio of a specific cylinder is shifted, it is accurate. This provides an excellent effect that the deterioration of the catalyst can be determined.
[Brief description of the drawings]
FIG. 1 is a diagram showing a schematic configuration of an embodiment when the present invention is applied to a V-type engine for an automobile.
FIG. 2 is a diagram illustrating a change in output of a downstream air-fuel ratio sensor due to deterioration of a catalyst.
FIG. 3 is a diagram illustrating an output of an upstream air-fuel ratio sensor when a deviation occurs in the air-fuel ratio of a specific cylinder.
FIG. 4 is a flowchart illustrating one embodiment of a catalyst deterioration determination operation of the present invention.
FIG. 5 is a flowchart illustrating a smoothing calculation process of an output of an upstream air-fuel ratio sensor in a catalyst deterioration determination operation different from that in FIG. 4 according to the present invention.
FIG. 6 is a flowchart illustrating a catalyst deterioration determination operation using an output of an upstream air-fuel ratio sensor after the smoothing calculation process calculated in FIG. 5;
[Explanation of symbols]
1. Engine body
5, 6… Crank angle sensor
12A, 12B, 16 ... catalytic converter
13A, 13B ... upstream air-fuel ratio sensor
17 ... Downstream O₂Sensor

Claims (2)

An exhaust purification catalyst disposed in an exhaust passage of the internal combustion engine;
An upstream air-fuel ratio sensor disposed in an upstream exhaust passage of the exhaust purification catalyst and detecting an exhaust air-fuel ratio upstream of the catalyst;
A downstream air-fuel ratio sensor disposed in the exhaust passage downstream of the exhaust purification catalyst and detecting an exhaust air-fuel ratio downstream of the catalyst;
By performing a smoothing calculation process in which the degree of smoothing increases with an increase in the engine speed, the fluctuation of the output of the upstream air-fuel ratio sensor is smoothed, and the smoothing output value of the upstream air-fuel ratio sensor is obtained. Arithmetic means;
Smoothed output value trajectory length calculating means for calculating the trajectory length of the upstream air-fuel ratio sensor smoothed output value based on the amount of change in the upstream air-fuel ratio sensor smoothed output value,
Downstream locus length calculation means for calculating the locus length of the downstream air-fuel ratio sensor output based on the amount of change in the downstream air-fuel ratio sensor output,
An internal combustion engine comprising: a trajectory length of the upstream-side air-fuel ratio sensor smoothed output value; and a deterioration determination unit that determines whether the exhaust purification catalyst has deteriorated based on the downstream-side air-fuel ratio sensor output trajectory length. Catalyst deterioration determination device. An exhaust purification catalyst disposed in an exhaust passage of the internal combustion engine;
An upstream air-fuel ratio sensor disposed in an upstream exhaust passage of the exhaust purification catalyst and detecting an exhaust air-fuel ratio upstream of the catalyst;
A downstream air-fuel ratio sensor disposed in the exhaust passage downstream of the exhaust purification catalyst and detecting an exhaust air-fuel ratio downstream of the catalyst;
The output of the upstream air-fuel ratio sensor is sampled at intervals that vary in proportion to the interval of fuel injection to the engine, and a smoothing operation is performed on the sampled output value to perform a smoothing output of the upstream air-fuel ratio sensor. A smoothing operation means for obtaining a value,
Smoothed output value trajectory length calculating means for calculating the trajectory length of the upstream air-fuel ratio sensor smoothed output value based on the amount of change in the upstream air-fuel ratio sensor smoothed output value,
Downstream locus length calculation means for calculating the locus length of the downstream air-fuel ratio sensor output based on the amount of change in the downstream air-fuel ratio sensor output,
An internal combustion engine comprising: a trajectory length of the upstream-side air-fuel ratio sensor smoothed output value; and a deterioration determination unit that determines whether the exhaust purification catalyst has deteriorated based on the downstream-side air-fuel ratio sensor output trajectory length. Catalyst deterioration determination device.

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