JP4499867B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  The present invention is NO when the excess air ratio λ is lean (λ> 1.0)._XNO contained in exhaust gas by occlusion catalyst_XNO is stored when the excess air ratio λ is near the stoichiometric air-fuel ratio (λ = 1.0)._XHC, CO and NO by making the storage catalyst function as a three-way catalyst_XNO is when the excess air ratio λ is rich (λ <1.0)._XNO stored in the storage catalyst_XThe present invention relates to an exhaust gas purification apparatus for an internal combustion engine that desorbs and reduces gas.
[0002]
[Prior art]
  NO of conventional internal combustion engines_XIn an exhaust purification system using an occlusion catalyst, NO_XThe storage catalyst is poisoned by the sulfur component contained in the exhaust gas, and NO_XWhen the storage capacity of the engine became smaller, the temperature of the engine was increased uniformly and the amount of sulfur poisoning was reduced regardless of the degree of sulfur poisoning and how the internal combustion engine was operated.
[0003]
  For example, if the excess air ratio is set in the vicinity of the theoretical air-fuel ratio (λ = 1.0), the temperature of the internal combustion engine can be raised, and NO_XThe temperature of the storage catalyst itself also rises and the sulfur component is easily desorbed. Further, by delaying the ignition timing, the temperature of the internal combustion engine rises, and the desorption of sulfur components becomes easy.
[0004]
[Problems to be solved by the invention]
  However,A conventional internal combustion engine is operated in an operating region where the storage capacity (capacity) of the catalyst is increased, and in some cases, the engine load and the engine speed are changed so that the storage capacity of the catalyst is reduced. If the catalyst loses its storage capacity, the lean operation will continue and the catalyst will _X NO can not be occluded, NO is not occluded _X May be exhausted to the atmosphere and the purification rate may deteriorate. Also, the catalyst NO corresponding to the engine load and engine speed _X Even if the storage capacity was tabulated, it took time until the map was updated to the new map after the new driving environment.
[0005]
  Therefore, in the present invention,NO catalyst _X When you can't fully occlude, you can switch lean operation to rich operation.An object of the present invention is to provide an exhaust emission control device for an internal combustion engine.
[0006]
[Means for Solving the Problems]
  In order to solve the above problems, the invention of claim 1NO in the exhaust passage _X Provided with a storage catalyst and said NO _X In an internal combustion engine provided with an oxygen sensor in the exhaust passage downstream of the storage catalyst, the engine is provided with an excess air ratio control means, a detection means for detecting the output voltage value of the oxygen sensor is provided, and the excess air ratio λ is , When the output voltage of the oxygen sensor reaches the preset air excess rate switching timing determination voltage value in the rich state of λ <1.0, the excess air rate is continuously maintained for a predetermined time. The maximum value of the output voltage is detected by the detection means, and the excess air ratio is set to the rich state of λ <1.0 next time by multiplying the maximum value by a preset coefficient, and the stored NO. _X A calculation means is provided for calculating a voltage value for determining the excess air ratio during the desorption / reduction of the air, and detecting the change timing of the excess air ratio by changing the output voltage value of the oxygen sensor due to fluctuations in the exhaust gas temperature. The accuracy was prevented from deteriorating.
[0009]
[0010]
[0011]
[0012]
[0013]
[0014]
[0015]
[0016]
[0017]
[0018]
DETAILED DESCRIPTION OF THE INVENTION
  If the excess air ratio λ is set in the vicinity of the theoretical air-fuel ratio (λ = 1.0), air and fuel are supplied without excess or deficiency, so the lean or rich state where the excess air ratio λ deviates from the theoretical air-fuel ratio. The temperature of the internal combustion engine is likely to rise as compared with the case where it is set to. When the excess air ratio is set near the stoichiometric air-fuel ratio, NO_XThe storage catalyst is HC, CO and NO in the exhaust gas._XIt acts as a three-way catalyst that simultaneously purifies. This control is called three-way control. NO_XIf the excess air ratio is set to lean, the storage catalyst will have NO in the exhaust gas._XOccluded, and if set to rich, occluded NO_XIs eliminated and reduced.
[0019]
  The above phenomenon and NO_XUsing the properties of the storage catalyst, NO in exhaust gas will be described later._XNO, without adversely affecting each part of the internal combustion engine_XEliminate sulfur poisoning of the storage catalyst.
[0020]
  FIG.Book1 is a system schematic diagram of an internal combustion engine 100 embodying the invention. In FIG. 1, air (atmosphere) taken in through an air supply pipe 21 and fuel gas sent out through a fuel supply pipe 20 are mixed in a mixer 3, and the air-fuel mixture becomes exhaust gas after combustion in an engine head 2. Gas is NO on the way_XThe exhaust gas is discharged through an exhaust pipe 22 provided with an occlusion catalyst 14 (hereinafter referred to as catalyst 14).
[0021]
  As shown in FIG. 1, an oxygen sensor 9 is provided on the upstream side of the catalyst 14, and an oxygen sensor 8 is provided on the downstream side. Further, the engine 1 is provided with an engine speed detection sensor 10 that detects the engine speed and an engine load detection sensor 12 that detects a load applied to the engine.
[0022]
  The signals detected by the oxygen sensors 8, 9, the engine speed detection sensor 10 and the engine load detection sensor 12 are sent to the controller 4 via signal lines, respectively. In order to operate λ, a control signal is sent to the stepping motor 6 via a signal line to adjust the opening degree of the excess air ratio control valve 7 (excess air ratio control means).
[0023]
  The mixer 3 is provided with a timer 11 (sulfur poisoning amount detecting means) that is reset when the excess air ratio λ changes, and the time measured by the timer 11 and the excess air ratio λ at that time are obtained via a signal line. It is sent to the controller 4.
[0024]
  (First disclosureExample)
  Figure6 is a graph showing the relationship between the fluctuation of the oxygen concentration in the exhaust gas in the exhaust pipe 22 on the downstream side of the catalyst 14 due to the fluctuation of the excess air ratio, the amount of oxygen occluded in the catalyst 14 and the output voltage of the oxygen sensor 8. It is. FIG. 7 shows the excess air ratio and the CO, HC and NO of the catalyst 14._XIt is a graph which shows the relationship of the purification rate. As can be seen from FIG. 7, the excess air ratio is NO over a certain width including λ = 1.0._X, CO and HC both show a relatively high purification rate. In FIG. 7, this width is shown by the range of a broken line, and this is called the purification | cleaning window.
[0025]
  When a large output is required, such as during acceleration or when the engine load increases, the controller 4 sends a control signal to the stepping motor 6 so that the required engine output can be obtained. 7 is set large, and the excess air ratio of the air-fuel mixture in the mixer 3 is set to the theoretical air-fuel ratio (λ = 1.0). The excess air ratio λ at this time is not limited to the stoichiometric air-fuel ratio, but may be within the purification window shown in FIG.
[0026]
  When the internal combustion engine 100 is operated in a lean state where λ> 1.0 (outside the purification window), the catalyst 14 is in NO in the exhaust gas._XHowever, when the engine load increases or the engine load increases and the engine output is increased, the excess air ratio λ slightly shifts to the rich side as before (for example, at λ = 1.5). Instead of λ = 1.4), it shifts into the purification window all at once.
[0027]
  By setting the excess air ratio λ in this way, NO in the exhaust gas_XReacts with CO and HC in the exhaust gas on the catalyst 14 to react with N₂, CO₂, H₂Changes to harmless substances such as O. At this time, the catalyst 14 is NO._XEffective as a three-way catalyst, not a storage catalyst.
[0028]
  When a large engine output is required, a larger amount of NO than before the shift can be obtained by shifting the excess air ratio to the rich side._XIs contained in the exhaust gas. Conventionally, this large amount of NO_XHowever, the remaining storage capacity of the catalyst 14 is lost in a short time. ThereIn the skyIf it is necessary to shift the excess air ratio λ to the rich side, NO_XWas not occluded in the catalyst 14, but was converted into a harmless substance on the catalyst 14 as described above, and released from the exhaust pipe 22 into the atmosphere.
[0029]
  As a result, NO_XHowever, the period until the catalyst 14 reaches the storage limit becomes longer, and the stored NO_XIt is possible to lengthen the interval at which the rich spike is executed in order to desorb and reduce the amount.
[0030]
  When the internal combustion engine 100 is operated with the excess air ratio λ in a lean state, sulfur components mixed in the exhaust gas are adsorbed on the catalyst 14 (hereinafter referred to as poisoning), and the amount of poisoning is NO._XThe storable capacity of will decrease. Therefore, if poisoning progresses, NO_XTherefore, it is necessary to remove the sulfur component from the catalyst 14 (hereinafter, this operation is called regeneration of the catalyst 14).
[0031]
  It has been found that the poisoning amount of the sulfur component to the catalyst 14 is proportional to the time during which the excess air ratio λ is operated in a lean state (outside the purification window). Therefore, the relationship between the lean operation time and the sulfur component poisoning amount is experimentally examined in advance, and a table that can estimate the poisoning amount from the degree of lean (the value of λ) and the operation time is created. The data is stored in a memory (not shown) in the controller 4. Since this table varies depending on the type of the catalyst 14, it is preferable to employ a rewritable medium such as a flash memory as the memory.
[0032]
  The controller 14 determines that the sulfur poisoning amount of the catalyst 14 has reached a predetermined value by referring to the operation time of the internal combustion engine 14, the set value of the excess air ratio λ, and the table stored in the memory in the controller 4. 4 detects. When the controller 4 detects that the sulfur poisoning amount of the catalyst 14 has reached a predetermined value, the controller 4 sends a control signal to the stepping motor 6 to set the opening degree of the excess air ratio control valve 7 large, The excess air ratio λ of the air-fuel mixture in the mixer 3 is set in the purification window.
[0033]
  In order to regenerate the catalyst 14 that has been poisoned with sulfur, it is necessary to set the temperature to be somewhat higher than the temperature at which the catalyst 14 was poisoned. In the rich and lean regions where the excess air ratio λ is far from the stoichiometric air-fuel ratio, the combustion temperature is relatively low, and therefore the temperature of the catalyst 14 is also low. However, when the excess air ratio λ is set within the purification window, the combustion temperature increases and the temperature of the catalyst 14 also increases. Therefore, if the excess air ratio λ is set within the purification window, the catalyst 14 can be easily regenerated.
[0034]
  The timer 11 provided in the mixer 3 is reset when the excess air ratio λ changes as described above, and detects a period during which the value of the excess air ratio λ is kept constant. The controller 4 knows what value (lean, rich, stoichiometric air-fuel ratio, etc.) the value of the excess air ratio λ is set to.
[0035]
  If the excess air ratio λ is set to be lean (outside the purification window) with λ> 1.0, the catalyst 14 in FIG._XAt the same time as the sulfur is occluded, the sulfur component poisons the catalyst 14. Therefore, the timer 11 measures the time when the excess air ratio λ is set to lean (λ> 1.0), and the controller 4 recognizes that the excess air ratio λ is set to lean. The increase amount of sulfur poisoning of the catalyst 14 can be estimated (increase amount estimation means).
[0036]
  Further, if the excess air ratio λ is set in the purification window, NO in the exhaust gas_XIs converted into a harmless substance, and at the same time, the exhaust gas temperature rises so that the sulfur component is easily desorbed from the catalyst 14. Therefore, the timer 11 measures the time during which the excess air ratio is set in the purification window, and the controller 4 recognizes that the excess air ratio is set in the purification window. It is possible to estimate the desorption amount of sulfur component, that is, the decrease amount of sulfur poisoning (reduction amount estimation means).
[0037]
  The time when the excess air ratio λ is operated lean is replaced by the degree of progress of sulfur poisoning, and the time when the excess air ratio λ is operated within the purification window is replaced by the degree of regeneration of the catalyst 14. . Therefore, the poisoning amount of the catalyst 14 is calculated by the equation (1).
  t_dref= C_refint∫t_LRdt-∫t_refdt (1)
  Where t_drefIs the degree of poisoning (poisoning amount) and C_refintIs a coefficient obtained in advance by experiment, and t_LRIs the operating time in lean, t_refIs the operation time at the stoichiometric air-fuel ratio or the excess air ratio in the vicinity thereof.
[0038]
  By this equation (1), the controller 4 calculates the sulfur poisoning amount of the catalyst 14, and when the sulfur poisoning amount reaches a predetermined amount set in advance, the excess air ratio λ is purified by the purification window in order to increase the temperature of the catalyst 14. Set within (theoretical air-fuel ratio or its vicinity). By doing in this way, regeneration of the catalyst 14 with advanced sulfur poisoning can be performed appropriately.
[0039]
  (FirstExample)
  NO_XThe storable capacity depends on the temperature. Therefore, when the engine load or the engine speed changes, the temperature of the engine 1 changes and the NO of the catalyst 14 changes._XThe storable capacity changes. When the engine load and the engine speed change, the NO emitted by the internal combustion engine 100_XThe amount also changes.
[0040]
  Therefore, NO that the catalyst 14 can store is NO._XA table is created by previously determining the relationship between the quantity, the engine load, and the engine speed by experiments, and stored in a memory (not shown) provided in the controller 4 (a rewritable medium similar to the above-described memory). This table also varies depending on the type of the catalyst 14.
[0041]
  From this table and the engine load detected by the engine load detection sensor 12 and the engine speed detected by the engine speed detection sensor 10, the NO in the exhaust gas is determined._XCalculate the content (NO_XAmount estimation means), the NO contained in the exhaust gas discharged by operating for a certain period of time at this engine load and engine speed_XIs calculated (discharge amount detection means).
[0042]
  This calculated NO_XThe total amount is NO storable in the catalyst 14_XNO if you do not exceed the amount_XNeed not be released into the atmosphere. FIG. 2 shows NO in exhaust gas._XIt is a flowchart of the procedure at the time of switching an excess air ratio so that it may not discharge | release to air | atmosphere.
[0043]
  When the internal combustion engine 100 (FIG. 1) is operated with the excess air ratio set to lean (for example, λ = 1.5), the catalyst 14 has NO._XIs occluded. NO in the exhaust gas discharged during time Δt_XAssuming that all is occluded in the catalyst 14, NO to the catalyst 14_XThe occlusion amount is NO before the time Δt has elapsed._XStorage amount and NO_XFlow rate (NO in exhaust gas_XContent) and the product of time Δt.
[0044]
  In this way, NO is discharged according to the ticking time._XThe amount is calculated, and it is assumed that all of this is occluded in the catalyst 14, and it is determined whether or not the storable capacity of the catalyst 14 has been reached. NO to 14_XThe amount of occlusion is calculated.
[0045]
  The catalyst 14 is no longer NO_XNO is occluded when it is determined that it is impossible to occlude_XController 4 (FIG. 1) increases the flow rate of the fuel gas by increasing the opening degree of the excess air ratio control valve 7 to shift the excess air ratio to the rich side (outside the purification window). (Λ <1.0).
[0046]
  A conventional internal combustion engine is operated in an operating region where the storage capacity (capacity) of the catalyst is large, and in some cases, the engine load and the engine speed are changed so that the storage capacity of the catalyst is reduced. If the catalyst loses its storage capacity, the lean operation will continue and the catalyst will_XNO can not be occluded, NO is not occluded_XMay be exhausted to the atmosphere and the purification rate may deteriorate. Also, the catalyst NO corresponding to the engine load and engine speed_XEven if the storage capacity was tabulated, it took time until the map was updated to the new map after the new driving environment.
[0047]
  To prevent it,First embodimentThen how much NO_XAs the catalyst flows into the catalyst 14, it is followed from moment to moment. Now, in the internal combustion engine 100 in this operating state, substantially how much NO_XIs calculated by time-integrating whether the catalyst flows into the catalyst 14. NO discharged during minute time Δt when engine load and engine speed do not fluctuate_XBy integrating the amount (time integration), the NO of the catalyst 14_XThe storage limit time can be estimated.
[0048]
  NO_XSince the storage capacity is determined by the temperature of the catalyst 14 at that time, the remaining capacity is obtained from another table. When the remaining capacity is insufficient, the excess air ratio is changed from lean to rich, and the stored NO_XIs eliminated and reduced.
[0049]
  (SecondExample)
  Second embodimentThenFirst embodimentThe oxygen sensor 8 installed in the exhaust pipe 22 on the downstream side of the catalyst 14 is used instead of the discharge amount detecting means related to the above. In summary, by determining that the output voltage of the oxygen sensor 8 has exceeded a certain threshold value, which will be described later, the timing of switching the rich air ratio λ from rich to lean is detected, and the excess air ratio λ is changed from rich to lean. Switch.
[0050]
  FIG.In the exhaust pipe 22 without the catalyst 14,It is a graph which shows the relationship between the electromotive force (output voltage) of the oxygen sensor 8 (FIG. 1), and the excess air ratio (lambda). As shown in FIG. 3, when the temperature of the oxygen sensor 8 changes, the output voltage varies even with the same excess air ratio λ.The
[0051]
  FIG. 4 shows that when the excess air ratio λ is set to a rich state where λ <1.0 (NO stored by the catalyst 14)._XIt is a graph which shows the relationship between the output voltage of the oxygen sensor 8 installed in the downstream of the catalyst 14, and time. NO on catalyst 14_XWhen oxygen is occluded (λ> 1.0), oxygen is occluded at the same time._XWhen desorbing (λ <1.0), oxygen is also desorbed at the same time.
[0052]
  In FIG. 4, when the output voltage of the oxygen sensor 8 exceeds a certain level, the NO from the catalyst 14_XHas been completed, that is, the time for setting the excess air ratio λ to rich has ended (optimum rich end time T₁) And the controller 4 determine the voltage at that time as the determination voltage V₁It is defined as
[0053]
  The oxygen sensor 8 determines the determination voltage V₁The excess air ratio λ is not changed at the time of detecting, and the operation is continued with the excess air ratio λ within a predetermined time (for example, 1 second), and then the excess air ratio λ is made lean (λ> 1.0). ). As shown in FIG. 4, when the predetermined time elapses, the output voltage is maximum, and this is the maximum rich voltage V₂Call it. This maximum rich voltage V₂Thus, it is possible to grasp how much the output voltage of the oxygen sensor 8 increases under the temperature condition.Therefore, even if the exhaust temperature changes due to fluctuations in engine load and engine speed and the temperature of the oxygen sensor 8 itself changes, NO desorbed together with oxygen _X The invention according to claim 2 enables detection of the output voltage value corresponding to the amount of discharge.
[0054]
  FIG. 5 is a flowchart for determining when to switch the excess air ratio λ from rich to lean. Judgment voltage V calculated this time₁Is the previous maximum rich voltage V₂Is multiplied by a predetermined ratio (determination voltage ratio), and the controller 4 (calculation means) calculates by the equation (2). In other words, this maximum rich voltage V₂The next judgment voltage V when switching to lean₁Is calculated.
(Judgment voltage V₁) = (Maximum rich voltage V₂) X (judgment voltage ratio) (2)
(For example, the determination voltage ratio takes a value of 0.9 to 0.95.)
  As the electromotive force of the oxygen sensor 8 changes with temperature,NO desorbed with oxygen _X Of emissionsCan be prevented from shifting.
[0055]
  (Second disclosureExample)
  When the internal combustion engine 100 is operating in a low load / low speed operation region, the amount of exhaust gas is small and the temperature of the catalyst 14 is also low, so the temperature required to regenerate the catalyst 14 is quite high. Hard to reach. However, if the ignition timing is delayed, the exhaust gas temperature becomes high. Therefore, when operating in a low load / low rotation range, the ignition timing is delayed to raise the temperature of the catalyst 14 to a reproducible temperature. As shown in FIG. 1, an exhaust temperature (catalyst temperature) is detected by a temperature sensor 13 installed in the vicinity of the catalyst 14, and the detected temperature is transmitted to the controller 4.
[0056]
  FIG. 8 is a graph showing the relationship between the engine speed of the internal combustion engine 100 and the engine load, showing the ease of regeneration of the catalyst 14. As shown in FIG. 8, the higher the engine speed Ne, the easier the regeneration, and the lower the engine speed Ne, the more difficult the regeneration. Further, the regeneration becomes easier as the engine load Pe increases, and the regeneration becomes difficult as the engine load Pe decreases.
[0057]
  Therefore, since the temperature of the catalyst 14 also varies depending on the operating state of the internal combustion engine 100, the ignition timing is retarded to such an extent that the temperature of the catalyst 14 can be raised to a temperature necessary for regeneration.
[0058]
  Here, when the internal combustion engine 100 is operating in an extremely high load / high rotation region, the amount of exhaust gas is large and the exhaust temperature is high. Therefore, it is not necessary to retard the ignition. If delayed, the catalyst 14 may be destroyed due to an excessive rise in the exhaust temperature. Accordingly, the relationship between the operation mode (the magnitude of the engine load and the magnitude of the engine speed) at which the temperature of the catalyst 14 becomes a reproducible temperature and the degree to which the ignition timing is retarded is investigated through an experiment in advance, and the table Is stored in the memory of the controller 4, and the degree of retardation of the ignition timing is determined according to this table. The temperature sensor 13, the controller 4, and a table (not shown) constitute ignition timing setting means.
[0059]
  Thus, no matter what engine load and engine speed the internal combustion engine 100 is operated at, the ignition timing is maintained so that the temperature of the catalyst 14 can be regenerated, is not deteriorated, and is not destroyed. Set.
[0060]
  (Third disclosureExample)
  First disclosureWhen it is determined by the sulfur poisoning amount detection means used in the example that the poisoning of the catalyst 14 is not progressing compared to the preset poisoning amount, regeneration is not performed and the presetting is performed. When it is determined that the poisoning is proceeding from the poisoning amount, the regeneration is performed. That is, it is determined whether or not the catalyst 14 must be regenerated until the ignition timing is delayed.
[0061]
  If the ignition timing is greatly delayed in order to regenerate the catalyst 14 and the exhaust temperature is raised too much, the components of the internal combustion engine 100 may be adversely affected by heat. Therefore, the ignition retard is performed only when both the necessity of regeneration of the catalyst 14 and the protection of the components of the internal combustion engine 100 are satisfied.
[0062]
  If possible, regeneration of the catalyst 14 is performed only during operation in a high load / high rotation range where it is not necessary to perform ignition retardation (when the catalyst 14 becomes hot). If the operation region does not reach the high load / high rotation region and the poisoning of the catalyst 14 proceeds, the boundary where regeneration is performed to the side where both the engine load and the engine speed become smaller as shown in the graph of FIG. Is moved from the boundary A to the boundary B, for example, when the operating region of the internal combustion engine 100 enters a region on the higher load side / higher rotation side than the boundary B, ignition retardation is performed, and the catalyst 14 is heated to perform regeneration. When the poisoning of the catalyst 14 progresses and the operation region of the internal combustion engine 100 is not expected to reach the boundary B region, the region is further expanded to the boundary C. When the operation region reaches the boundary C, the catalyst 14 is regenerated. Like that.
[0063]
  In this way, the catalyst 14 can be regenerated satisfactorily in the internal combustion engine 100 in which any operation is performed without raising the exhaust temperature more than necessary and impairing the durability of the internal combustion engine 100. As for the degree of ignition delay, the operating range of the internal combustion engine 100 is greatly delayed (for example, 60 degrees) in the low load / low rotation range, and is delayed (for example, 40 degrees) in the high load / high rotation range.
[0064]
  The catalyst 14 cannot be regenerated unless the temperature is higher than the temperature at the time of poisoning. For example, if it is poisoned at 600 degrees, it can be regenerated at 700 degrees, and if it is poisoned at 400 degrees, it can be reproduced at 500 degrees. Therefore, the lower the temperature, the lower the temperature during regeneration.
[0065]
  In an engine that often operates in a low load / low rotation range, the engine can be regenerated without going to a very high regeneration range. The catalyst 14 poisoned at a low temperature in the low load / low rotation region may be regenerated at a low temperature. That is, regeneration is performed at a low temperature (when the operation region is a low load / low rotation region).
[0066]
  The relationship between the engine load, the engine speed, and the degree of poisoning of the catalyst 14 when the regeneration of the catalyst 14 is executed is obtained in advance by experiments and stored in the memory of the controller 4 as a table. The controller 4 compares the pattern stored in this table with the current sulfur poisoning amount of the catalyst 14 (comparison means), and determines whether or not to execute regeneration.
[0067]
  Therefore, regeneration of the poisoned catalyst 14 in the high load / high rotation region is not performed in the low load / low rotation region, and the poisoned catalyst 14 in the low load / low rotation region does not regenerate. There is no need to perform regeneration by raising the temperature wastefully until rotation.
[0068]
  (Fourth disclosureExample)
  In general, when the excess air ratio is set to lean (λ> 1.0), the temperature of the catalyst 14 becomes low because there are few things to burn (fuel gas). Further, when the excess air ratio is set to rich (λ <1.0), the temperature of the catalyst 14 rises.
[0069]
  Assuming that the temperature of the catalyst 14 necessary for regenerating the catalyst 14 is the target regeneration temperature, when the temperature of the catalyst 14 is lower than the target regeneration temperature and is raised to reach the target regeneration temperature, the excess air ratio λ is set to Increase the frequency of setting the rich state. When the temperature of the catalyst 14 is higher than the target regeneration temperature, the frequency of setting the excess air ratio λ to be rich is reduced. Here, the target regeneration temperature is stored in the memory (storage means) of the controller 4.
[0070]
  Here, the “frequency” means that the excess air ratio λ is set by alternately repeating lean and rich, but means a relative ratio of time set to rich with respect to time set to lean. Specifically, if the rich time is 1 minute with respect to the lean time of 10 minutes, it is 1 minute with respect to 10 minutes. The above-mentioned “increasing the frequency of setting the rich state” means, for example, increasing the length of time for setting rich, such as setting the time to 1 minute to 2 minutes, or setting the time to set lean (10 minutes), for example. Shorten it to 9 minutes. This is called PWM (pulse width adjustment) control of the excess air ratio λ.
[0071]
  FIG. 9 is a flowchart for setting the temperature of the catalyst 14 to the target regeneration temperature. In FIG. 9, the controller 4 detects the excess air ratio λ by the signal transmitted from the oxygen sensor 8, detects the exhaust temperature (catalyst temperature) by the temperature sensor 13, and detects the target regeneration temperature by the controller 4 (comparing means). Compare the exhaust temperature. If there is a difference between the two, the excess air ratio λ is PID-controlled so that the exhaust temperature matches (or approaches) the target regeneration temperature, and the lean time t_LIs set (lean operation time control means).
[0072]
  By performing PWM control of the excess air ratio λ in this way, the temperature of the catalyst 14 can be raised to the target regeneration temperature and regeneration can be performed. Therefore, when the catalyst 14 is regenerated, the catalyst 14 acts as a three-way catalyst. Therefore, it is not necessary to provide the oxygen sensor 9 on the upstream side of the catalyst 14, and the apparatus can be simplified.
[0073]
  (5th disclosureExample)
  FIG. 10 is a graph showing the relationship between the oxygen storage amount of the catalyst 14 and the output voltage of the oxygen sensor 8 when the excess air ratio λ is fluctuated between the inside of the purification window and the predetermined lean value (outside the purification window). It is. In FIG. 10, three patterns D, E, and F are shown.
[0074]
  Pattern D is a case where the excess air ratio λ is appropriately controlled. Pattern E is a case where the excess air ratio λ is controlled in a state shifted to the rich side. Pattern F is a case where the excess air ratio λ is controlled in a state of being shifted to the lean side.
[0075]
  When the excess air ratio λ changes from the purification window to lean in the pattern D, the output voltage of the oxygen sensor 8 records the lowest value, which is called the determination voltage.
[0076]
  In the pattern E, the minimum value of the output voltage of the oxygen sensor 8 is higher than the determination voltage because the excess air ratio λ is shifted to the rich side. In the pattern F, the minimum value of the output voltage of the oxygen sensor 8 is lower than the determination voltage because the excess air ratio λ has shifted to the lean side.
[0077]
  Since the excess air ratio can be set in the purification window by the output voltage of the oxygen sensor 8 installed on the downstream side of the catalyst 14, three-way control is performed without providing the oxygen sensor 9 on the upstream side of the catalyst 14. Can do. Therefore, since the oxygen sensor 8 is installed on the downstream side of the catalyst 14, toxic gas is purified by the catalyst 14, and only harmless exhaust gas is discharged, so that deterioration does not easily proceed, and three-way control is performed. Compared with the case where it installs in the upstream of the catalyst 14 for performing, a lifetime is extended.
[0078]
  Conventionally, when the catalyst 14 acts as an occlusion catalyst, it is necessary to install the oxygen sensor 8 on the downstream side of the catalyst 14. In order to act as a three-way catalyst, the oxygen sensor 9 further on the upstream side of the catalyst 14. It was necessary to provideFifth disclosure exampleAccording to this, only one oxygen sensor needs to be provided on the downstream side of the catalyst 14, and the apparatus can be simplified and the cost can be reduced.
[0079]
  In FIG. 10, the excess air ratio λ is displaced from the inside of the purification window to lean (outside the purification window) by a predetermined length every predetermined time and returned to the original purification window.
[0080]
  Oxygen occlusion in the catalyst 14 reaches a limit just at the end of lean, and if the excess air ratio λ continues to be set to lean, oxygen begins to flow downstream of the catalyst 14 and the output voltage of the oxygen sensor 8 decreases. It is detected that the output voltage has dropped to a predetermined value (determination voltage), and it is detected that the oxygen storage amount of the catalyst 14 has reached the storage limit.
[0081]
  As shown in the pattern E in FIG. 10, when shifting to the rich side from the purification window, the occlusion of oxygen in the catalyst 14 does not reach the limit, so the minimum value of the output voltage of the oxygen sensor 8 becomes higher than the determination voltage. It can be detected from the difference between the output voltage value of the oxygen sensor 8 and the determination voltage that the excess air ratio λ is shifted to the rich side. Further, as shown in the pattern F, when the value deviates from the purification window toward the lean side, the output voltage value of the oxygen sensor 8 is decreased from the determination voltage, so that it is detected that the excess air ratio λ is deviated toward the lean side. be able to.
[0082]
  (Sixth disclosureExample)
  5th disclosureOnly with the configuration described in the example, it is not possible to determine how much the shift is to the rich side or the lean side. Therefore, an excess air ratio λ with respect to the engine load and the engine speed is obtained in advance by experiments, a map is created, and stored in the memory (storage means) of the controller 4.
[0083]
  FIG. 11 is a schematic diagram for setting the excess air ratio λ to a target value. When the engine load and the engine speed change, the excess air ratio λ is changed at once to the excess air ratio (load, engine speed pattern) corresponding to the changed engine load and engine speed on the map.5th disclosureMake minor corrections using the method described in the example.Sixth disclosure exampleAccording to, even if the engine load and the engine speed fluctuate,_XIt is not necessary to deteriorate the purification rate.
[0084]
  (7th disclosureExample)
  Sixth disclosureThe map described in the example has individual differences for each mass-produced internal combustion engine. Therefore, in some cases, the stored content of the map does not correspond to the internal combustion engine, and the excess air ratio λ corresponding to the engine load and the engine speed may always be shifted. In order to avoid this, the map has a learning function as shown in FIG.
[0085]
  At the beginning of operation, the excess air ratio λ is set according to the data stored in the first map (FIG. 11), and then it is determined whether or not the excess air ratio λ is within the purification window. If so, the output voltage of the oxygen sensor 8 is fed back, and the relationship of the excess air ratio λ corresponding to the engine load and engine speed inherent to the internal combustion engine 100 is overwritten on the map (correction means). FIG. 12 is a map provided with a learning function in FIG.
[0086]
  A deviation of the lowest value of the output voltage of the oxygen sensor 8 from the determination voltage is obtained, and the controller 4 performs PI control so that this deviation becomes zero, and the result is reflected in the map.
[0087]
  (8th disclosureExample)
  Assuming that the thermal efficiency does not change with the value of the excess air ratio λ, when the internal combustion engine 100 performs a certain work, the fuel supplies the same amount regardless of whether the excess air ratio is lean or rich, The amount of fuel to be burned must be constant.
[0088]
  In order to make the excess air ratio λ lean, the air (oxygen) supply amount must be increased, and in order to make it rich, it is necessary to further supply fuel that does not contribute to combustion. When the excess air ratio λ is lean, it is necessary to ensure a large ratio of combustion, that is, a large volume of air with respect to the volume of fuel gas.
[0089]
  Therefore, when the excess air ratio λ is lean, a large amount of air-fuel mixture must be supplied. In order to make the excess air ratio λ rich, a small amount of fuel may be increased. However, in order to make the lean, the lean will not be made unless a large amount of air-fuel mixture is supplied, so the throttle 5 (FIG. 1) opens rapidly. (The opening degree must be increased). On the other hand, there is almost no need to open it to make it rich. It is possible to detect λ = 1.0 depending on how the throttle opening changes.
[0090]
  FIG. 13 is a graph showing the relationship between the value of the excess air ratio λ and the throttle opening. As shown in FIG. 13, when the excess air ratio λ becomes λ = 1.0 (theoretical air / fuel ratio), the throttle opening takes the minimum value, and λ <1.0 and λ Even if it is displaced to> 1.0, the throttle opening is large.
[0091]
  FIG. 14 is a flowchart of the three-way control using the change amount of the throttle opening with respect to the change amount of the excess air ratio λ. The value of the excess air ratio λ is changed by operating the mixer 3 in FIG. 1, and the operation amount of the mixer 3 is transmitted to the controller 4 via the signal line, and when the operation amount increases, the excess air ratio λ becomes lean. Becomes rich when the operation amount is reduced.
[0092]
  In this way, λ = 1.0 can be detected by the throttle opening, so three-way control (CO, HC, NO in exhaust gas) without installing an oxygen sensor._XCan be performed at the same time. Therefore, neither of the oxygen sensors 8 and 9 in FIG. 1 is required, and the apparatus can be simplified.
[0093]
  If the engine load and the engine speed are kept at a certain value or the fluctuation is small, it becomes easy to detect the time when the excess air ratio λ becomes λ = 1.0 (theoretical air-fuel ratio) by the throttle opening.
[0094]
  (9th disclosureExample)
  8th disclosureAs explained in the example, the throttle opening takes the minimum value when the excess air ratio λ is λ = 1.0. Further, the output voltage of the oxygen sensor 9 (FIG. 1) installed on the upstream side of the catalyst 14 at λ = 1.0 becomes the determination voltage. From these, when the throttle opening takes the minimum value, the output voltage of the oxygen sensor 9 becomes the determination voltage.
[0095]
  FIG. 15 is a graph showing the relationship between the excess air ratio λ, the throttle opening, and the output voltage of the oxygen sensor 9 installed on the upstream side of the catalyst 14. In FIG. 15, the graph of A shows the change in the output voltage of the oxygen sensor 9 that has not deteriorated, and the graph of B shows the change in the output voltage of the oxygen sensor 9 that has deteriorated.
[0096]
  As can be seen from the determination voltage of G and the determination voltage of H, there is a considerable difference in the determination voltage for detecting λ = 1.0 depending on whether or not the oxygen sensor 9 is deteriorated (depending on the degree of deterioration). .
[0097]
  However, even if the oxygen sensor 9 is deteriorated, if the output voltage of the deteriorated oxygen sensor 9 when λ = 1.0 can be grasped, λ = 1.0 is detected by the output voltage of the deteriorated oxygen sensor 9. can do. Therefore, the output voltage of the oxygen sensor 9 when the throttle opening becomes the minimum value is detected.
[0098]
  In this way, λ = 1.0 can be detected by the deteriorated oxygen sensor 9 without depending on the throttle opening, so that it can be accurately performed even in an operating environment in which the engine speed and the engine load tend to fluctuate. λ = 1.0 can be detected.
[0099]
【The invention's effect】
  BookAccording to the inventionNO desorbed with oxygen even if the exhaust gas temperature changes and the output voltage of the oxygen sensor fluctuates _X The output voltage corresponding to the discharge amount of NO can be detected, NO _X Can be detected. For this reason, the catalyst is NO _X The lean operation can be switched to the rich operation when it is not possible to occlude.
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[Brief description of the drawings]
[Figure 1]Book1 is a schematic diagram of an internal combustion engine embodying the invention.
[Fig. 2] NO in exhaust gas_XIt is a flowchart of the procedure at the time of switching an excess air ratio so that it may not discharge | release to air | atmosphere.
[Fig. 3]In the exhaust pipe without catalyst,It is a graph which shows the relationship between the electromotive force of an oxygen sensor, and an excess air ratio.
[FIG. 4] When the excess air ratio λ is set to a rich state with λ <1.0 (NO stored by the catalyst)._XIt is a graph which shows the relationship between the output voltage of the oxygen sensor installed in the downstream of the catalyst, and time at the time of desorption | elimination.
FIG. 5 is a flowchart for determining when to switch the excess air ratio λ from rich to lean.
FIG. 6 is a graph showing the relationship between fluctuations in oxygen concentration in the exhaust gas in the exhaust pipe on the downstream side of the catalyst due to fluctuations in the excess air ratio, the amount of oxygen occluded in the catalyst, and the output voltage of the oxygen sensor 8;
Fig. 7 Excess air ratio and CO, HC and NO of catalysts_XIt is a graph which shows the relationship of the purification rate.
FIG. 8 is a graph showing the relationship between the engine speed of the internal combustion engine and the engine load showing the ease of regeneration of the catalyst.
FIG. 9 is a flowchart for setting the temperature of the catalyst to the target regeneration temperature.
FIG. 10 is a graph showing the relationship between the oxygen storage amount of the catalyst and the output voltage of the oxygen sensor when the excess air ratio λ is varied between the purification window and a predetermined lean value.
FIG. 11 is a schematic diagram for setting the excess air ratio λ to a target value.
FIG. 12 is a system schematic diagram in which a learning function is provided in the map in FIG.
FIG. 13 is a graph showing the relationship between the value of excess air ratio λ and the throttle opening.
FIG. 14 is a flowchart of three-way control using the amount of change in throttle opening with respect to the amount of change in excess air ratio λ.
FIG. 15 is a graph showing the relationship between the excess air ratio λ, the throttle opening, and the output voltage of the oxygen sensor installed on the upstream side of the catalyst.
[Explanation of symbols]
1 organization
2 engine head
3 Mixer
4 Controller
5 Throttle
6 Stepping motor
7 Excess air ratio control valve
8,9 Oxygen sensor
10 Engine speed detection sensor
11 Timer
12 Engine load detection sensor
13 Temperature sensor
14 NO_XStorage catalyst
100 Internal combustion engine

Claims (1)

In an internal combustion engine provided with an oxygen sensor in the exhaust passage downstream of the provided with _the NO _X storage catalyst in the exhaust passage and the _the NO _X storage catalyst,
The engine is provided with an excess air ratio control means, a detection means for detecting the output voltage value of the oxygen sensor is provided, and the output voltage of the oxygen sensor is preset in a rich state where the excess air ratio λ is λ <1.0. When the excess air ratio switching timing determination voltage value is reached, the excess air ratio is continuously maintained for a predetermined time, and the maximum value of the output voltage of the oxygen sensor is detected by the detection means, and preset to the maximum value. a calculation means for calculating an air excess ratio switching period determination voltage value at the time of desorption and reduction of NO _X which the excess air ratio was occluded by setting the rich state of the lambda <1.0 in order by multiplying the coefficient Provided,
An exhaust emission control device for an internal combustion engine, which prevents the detection accuracy of the switching timing of the excess air ratio from being deteriorated due to fluctuations in the output voltage value of the oxygen sensor due to fluctuations in exhaust gas temperature.

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