Control device for internal combustion engine

Abstract

To provide a controller of an internal combustion engine comprising a device that changes a ratio of exhaust components, which can control an exhaust air-fuel ratio to a target value with accuracy.SOLUTION: A controller of an internal combustion engine comprises: an LAFS 22 that is provided in an exhaust passage 10 of an engine 2, and detects an air-fuel ratio; an engine control unit 30 that controls the air-fuel ratio of the engine so that a detected value of the LAFS 22 becomes a target air-fuel ratio; and an EGR device comprising an EGR passage 17 and an EGR valve 18. The engine control unit 30 comprises a second correction unit 37 that has a function of changing ignition timing and changes the target air-fuel ratio when a ratio of NOx and CO in exhaust gas is changed due to the operation of the EGR device or the change of the ignition timing.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a technique for detecting the exhaust air-fuel ratio of an internal combustion engine. [Background technology]

[0002] 2. Description of the Related Art An exhaust passage of an internal combustion engine is provided with a sensor for detecting the air-fuel ratio of the exhaust passage in order to control the air-fuel ratio of the internal combustion engine to improve exhaust emissions and enhance fuel economy and drivability. For example, in Patent Document 1, an air-fuel ratio sensor and an O2 sensor (oxygen concentration detection means) are provided near an exhaust purification catalyst provided in the exhaust passage, and the accuracy of the air-fuel ratio feedback control is improved by feeding back the air-fuel ratio based on the detection value of the air-fuel ratio sensor and shifting the control center of the air-fuel ratio feedback control based on the detection value of the O2 sensor. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 2790896 Summary of the Invention [Problem to be solved by the invention]

[0004] Many engines are equipped with an EGR device as one of the exhaust gas purification devices, and an ignition timing change device (function) that changes the ignition timing to prevent knocking, etc. The operation of the EGR device or ignition timing change device changes the ratio of NOx and CO in the exhaust gas. However, Patent Document 1 does not disclose changing the control center of feedback control, i.e., the target air-fuel ratio, in consideration of the ratio of NOx and CO in the exhaust gas, which is changed by the operation of an EGR device, an ignition timing change device, etc. When the ratio of NOx and CO in the exhaust gas changes, the appropriate air-fuel ratio that takes into consideration exhaust gas improvement, etc., changes.

[0005] The present invention has been made in view of the above problems, and an object of the present invention is to provide a control device for an internal combustion engine that more appropriately controls the exhaust air-fuel ratio in an internal combustion engine equipped with a device that changes the ratio of exhaust components in the exhaust, such as an EGR device or an ignition timing change device. [Means for solving the problem]

[0006] In order to achieve the above object, the control device for an internal combustion engine of the present invention comprises air-fuel ratio detecting means provided in an exhaust passage of the internal combustion engine for detecting an air-fuel ratio, air-fuel ratio control means for controlling the air-fuel ratio of the internal combustion engine so that the detected value of the air-fuel ratio detecting means becomes a target value, and In exhaust component emissions a ratio changing means for changing the ratio of nitrogen oxides and carbon monoxide in the exhaust gas by the ratio changing means; Exhaust component emissions Nitrogen oxides in and and a target value changing means for changing the target value when the ratio of carbon monoxide is changed, By changing the ratio During exhaust exhaust component emissions in against carbon monoxide Increased proportion of nitrogen oxides The more the target value is changed to the rich side, and the ratio change means Due to the change in ratio During exhaust exhaust component emissions in against nitrogen oxides Increased carbon monoxide ratio The more The target value is changed to the lean side.

[0007] As a result, even if the ratio of nitrogen oxides to carbon monoxide in the exhaust gas is changed by the ratio changing means, the target air-fuel ratio in the air-fuel ratio control means is changed, so that the air-fuel ratio of the exhaust gas can be appropriately controlled. 。

[0008] In particular, during exhaust exhaust component emissions in against carbon monoxide Increased proportion of nitrogen oxides The more The target value by the air-fuel ratio control means is changed to the rich side, and during exhaust exhaust component emissions in against nitrogen oxides Increased carbon monoxide ratio The moreBy changing the target value by the air-fuel ratio control means to the lean side, the target value of the exhaust air-fuel ratio can be changed to the central part of the appropriate range in which the emissions of nitrogen oxides and carbon monoxide (CO) are reduced. Therefore, when the exhaust air-fuel ratio fluctuates, it becomes difficult for it to deviate from the appropriate range, and exhaust performance can be improved. Preferably, the ratio change means is exhaust gas recirculation means, and the larger the amount of exhaust gas recirculated by the exhaust gas recirculation means, the more the amount of exhaust gas in the exhaust gas is reduced. exhaust component emissions in against carbon monoxide The target value change means may change the target value to the leaner side as the ratio of nitrogen oxides decreases and the amount of exhaust gas recirculated by the exhaust gas recirculation means increases.

[0009] This allows the target value of the air-fuel ratio of the exhaust gas to be changed to the central part of the appropriate range in which the emissions of nitrogen oxides and carbon monoxide are reduced. Preferably, the ratio changing means is an ignition timing changing means, and when the ignition timing is retarded by the ignition timing changing means, As nitrogen oxide and carbon monoxide emissions fall, During exhaust exhaust component emissions Nitrogen oxides in against The target value changing means may change the target value toward the richer side as the proportion of carbon monoxide decreases and the ignition timing is retarded by the ignition timing changing means.

[0010] This allows the target value of the air-fuel ratio of the exhaust gas to be changed to the central part of the appropriate range in which the emissions of nitrogen oxides and carbon monoxide are reduced. [Effects of the Invention]

[0011] According to the control device for an internal combustion engine of the present invention, the air-fuel ratio of the exhaust gas can be appropriately controlled in accordance with the ratio of the exhaust components in the exhaust gas flowing into the exhaust purification catalyst. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a schematic configuration diagram of an intake and exhaust system of an engine according to an embodiment of the present invention; [Figure 2]1 is a graph showing the purification performance of each exhaust component and the output value of an O2 sensor relative to the exhaust air-fuel ratio in a three-way catalyst. [Figure 3] 10 is an example of a map for setting a LAFS correction amount. [Figure 4] 10 is a graph showing the purification performance of each exhaust component and the output value of the O2 sensor relative to the exhaust air-fuel ratio in a three-way catalyst when the EGR amount is changed. [Figure 5] 10 is a graph showing the purification performance of each exhaust component and the output value of the O2 sensor relative to the exhaust air-fuel ratio in a three-way catalyst when the ignition timing is changed. [Figure 6] 4 is a graph showing the relationship between ignition timing and exhaust component emissions. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram of an intake and exhaust system of an engine 2 (internal combustion engine) to which an air-fuel ratio detection device according to one embodiment of the present invention is applied. The engine 2 is mounted on the vehicle as a driving source. The engine 2 is a multi-cylinder gasoline engine, and for simplicity, only one cylinder is shown in Figure 1. The engine 2 is configured so that fuel can be injected into the intake port 4 of each cylinder from a fuel injection valve 3 provided in the intake port 4 of each cylinder at any injection timing and injection amount.

[0014] An intake passage 5 of the engine 2 is provided with a throttle valve 6 for adjusting the flow rate of fresh air. On the other hand, an exhaust passage 10 of the engine 2 is provided with a three-way catalyst 12 as an exhaust purification device. The three-way catalyst 12 has the function of oxidizing HC and CO in the exhaust gas and reducing NOx at a stoichiometric air-fuel ratio, thereby removing these exhaust components from the exhaust gas.

[0015] The engine 2 is also provided with a spark plug 16 facing the combustion chamber 15 . Furthermore, the engine 2 is provided with an EGR passage 17 that connects the exhaust passage 10 upstream of the three-way catalyst 12 with the intake passage 5 and recirculates a portion of the exhaust gas back into the intake passage 5. The EGR passage 17 is provided with an EGR valve 18 that controls the amount of exhaust gas recirculation by changing the opening degree. The EGR passage 17 and the EGR valve 18 constitute an EGR device (exhaust gas recirculation device) that recirculates a portion of the exhaust gas from the engine 2 to the intake passage 5, and this EGR device corresponds to the exhaust gas recirculation means (ratio change means) of the present invention.

[0016] The exhaust passage 10 of the engine 2 is provided with an LAFS (linear air-fuel ratio sensor, air-fuel ratio detection means) 22 upstream of the three-way catalyst 12, and an O2 sensor 23 that detects the exhaust air-fuel ratio and an exhaust temperature sensor 24 that detects the exhaust temperature are provided downstream of the three-way catalyst 12. The engine control unit 30 is configured to include input / output devices, memory devices (ROM, RAM, non-volatile RAM, etc.), timers, a central processing unit (CPU), etc., and inputs detection information from various sensors such as the LAFS 22 and the O2 sensor 23, as well as other vehicle operation information such as the amount of accelerator operation of the vehicle, and based on this information, calculates the amount of fuel injection from the fuel injection valve 3, the opening of the throttle valve 6, the ignition timing by the spark plug 16, and the opening of the EGR valve 18, and controls the operation of the various devices mentioned above, thereby controlling the operation of the engine 2.

[0017] Specifically, the engine control unit 30 feedback controls the fuel injection amount so that the detected value of the LAFS 22 becomes a target air-fuel ratio (target value), for example, a value indicating the stoichiometric air-fuel ratio (air-fuel ratio control means). In addition, the engine control unit 30 has a function of retarding the ignition timing of the spark plug 16, for example, to suppress knocking, and such ignition timing change control corresponds to the ignition timing change means (ratio change means) of the present invention.

[0018] 2A and 2B are graphs showing the purification performance of each exhaust component in the three-way catalyst 12 versus the exhaust air-fuel ratio and the output value of the O2 sensor 23 when the engine 2 is operating at a predetermined rotation speed and load. In FIG. 2A, the solid line shows the output value of the LAFS 22. The dashed line shows carbon monoxide (CO) and hydrocarbons (HC), and the dashed-dotted line shows nitrogen oxides (NOx) emitted from the three-way catalyst 12. The air-fuel ratio at which carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx) emitted from the three-way catalyst 12 are reduced, i.e., the region near the stoichiometric air-fuel ratio (stoichiometric air-fuel ratio region), is set as the target air-fuel ratio, and the fuel injection amount is feedback-controlled based on the detection value of the LAFS 22. FIG. 2B shows the output value of the O2 sensor 23. 2B, the dashed line represents the output value of the O2 sensor 23 when the O2 sensor 23 is in a high temperature state, and the dashed line represents the output value of the O2 sensor 23 when the O2 sensor 23 is in a low temperature state (room temperature, i.e., a temperature equal to or higher than the activation temperature of the O2 sensor 23 but lower than the high temperature state). The output value of the O2 sensor 23 varies greatly in the stoichiometric air-fuel ratio region and varies slightly on the richer and leaner sides of the stoichiometric air-fuel ratio region. Therefore, the difference between the output value of the O2 sensor 23 at the boundary between the stoichiometric air-fuel ratio region and the rich region (rich boundary) and the output value of the O2 sensor 23 at the boundary between the stoichiometric air-fuel ratio region and the lean region (lean boundary) becomes large. For example, by setting a rich threshold and a lean threshold for the output value at the rich boundary and the lean boundary, respectively, the O2 sensor 23 can determine the state of the exhaust air-fuel ratio downstream of the three-way catalyst 12, i.e., whether the exhaust air-fuel ratio is in the stoichiometric air-fuel ratio region or in a rich or lean state, based on the output value of the O2 sensor 23.

[0019] The engine control unit 30 has a function of correcting the output value of the LAFS 22 based on the output value of the O2 sensor 23. Furthermore, the engine control unit 30 of this embodiment includes a target air-fuel ratio correction unit 1 that corrects the target air-fuel ratio in the feedback control. The target air-fuel ratio correction unit 1 includes a temperature acquisition unit 35 that acquires the temperature of the O2 sensor 23 based on the exhaust temperature detected by the exhaust temperature sensor 24, and a first correction unit 36 ​​that corrects the target air-fuel ratio based on the temperature of the O2 sensor 23.

[0020] The temperature acquisition unit 35 determines the exhaust temperature detected by the exhaust temperature sensor 24 as the temperature of the O2 sensor 23. The first correction unit 36 ​​corrects the target air-fuel ratio based on the output value of the O2 sensor 23 and the temperature of the O2 sensor 23. Specifically, using a map such as that shown in FIG. 3, the first correction unit 36 ​​sets the LAFS correction amount (the correction amount for the target air-fuel ratio) based on the output value of the O2 sensor 23 and the temperature (exhaust gas temperature) of the O2 sensor 23. As shown in FIG. 3, the absolute value of the LAFS correction amount (the correction amount for the target air-fuel ratio) is reduced as the output value of the O2 sensor 23 approaches the stoichiometric air-fuel ratio, and the absolute value of the LAFS correction amount is increased as the output value of the O2 sensor 23 becomes richer or leaner. In other words, the absolute value of the LAFS correction amount is increased as the output value of the O2 sensor 23 becomes richer or leaner, thereby significantly changing the target air-fuel ratio between rich and lean.

[0021] Furthermore, the higher the exhaust gas temperature, that is, the higher the temperature of the O2 sensor 23, the larger the absolute value of the LAFS correction amount (the correction amount of the target air-fuel ratio). By making such a correction, the target air-fuel ratio can be changed in accordance with the characteristics of the O2 sensor 23, such as the narrowing of the output value fluctuation range due to temperature rise. Therefore, using this corrected target air-fuel ratio, air-fuel ratio feedback control based on the output value of the LAFS 22 can be performed with high accuracy.

[0022] Furthermore, the target air-fuel ratio correction unit 1 has a second correction unit 37 (target value changing means) that corrects the target air-fuel ratio based on the exhaust gas recirculation amount by the EGR device and the ignition timing. The LAFS 22, the EGR passage 17, the EGR valve 18, the control function of the second correction unit 37 and the EGR valve 18, the control function of the ignition timing, and the feedback control function of the air-fuel ratio in the engine control unit 30 correspond to the control device of the present invention.

[0023] Figure 4 is a graph showing the purification performance of each exhaust component and the output value of the O2 sensor versus the exhaust air-fuel ratio in the three-way catalyst 12 when the EGR amount is changed. In Figure 4, the solid line shows the output value of the LAFS 22. The dashed line shows carbon monoxide CO, and the one-dot chain line and two-dot chain line show NOx emissions. The one-dot chain line shows the case where the EGR amount is small, and the two-dot chain line shows the case where the EGR amount is large. When the EGR amount is small, the stoichiometric air-fuel ratio region where NOx emissions and CO emissions decrease (below a predetermined amount) is indicated by a in Figure 4. In contrast, when the EGR amount is increased, NOx emissions decrease. Therefore, the stoichiometric air-fuel ratio region is indicated by b in Figure 4, which expands to the lean side.

[0024] The second correction unit 37 corrects the target air-fuel ratio to the leaner side as the EGR amount increases. Preferably, the target air-fuel ratio is set to approximately the center of the stoichiometric air-fuel ratio range expanded toward the leaner side. As shown in FIG. 4, as the EGR amount increases, the stoichiometric air-fuel ratio range expands toward the leaner side, and the center of that range also moves toward the leaner side. The correction amount for the target air-fuel ratio may be read from a map or the like based on the opening degree of the EGR valve or the throttle valve, for example, and used.

[0025] By setting the target air-fuel ratio in approximately the center of the stoichiometric air-fuel ratio range in this way, even if the air-fuel ratio fluctuates, it becomes difficult to deviate from the stoichiometric air-fuel range, and the exhaust purification performance of the three-way catalyst 12 can be improved. Fig. 5 is a graph showing the purification performance of each exhaust component and the output value of the O2 sensor versus the exhaust air-fuel ratio in the three-way catalyst 12 when the ignition timing is changed. Fig. 6 is a graph showing the relationship between the ignition timing and the amount of exhaust component emissions. In Fig. 5, the solid line shows the output value of the LAFS 22. The dashed line and the two-dot chain line show the amount of carbon monoxide (CO), and the one-dot chain line shows the amount of NOx emissions. The dashed line shows when the ignition timing is normal, and the two-dot chain line shows when the ignition timing is retarded. In Fig. 6, the one-dot chain line shows the amount of NOx emissions, and the dashed line shows the amount of CO emissions.

[0026] When the ignition timing is normal, the stoichiometric air-fuel ratio region where NOx emissions and CO emissions decrease is indicated by c in Figure 5. In contrast, when the ignition timing is retarded, CO and NOx emissions decrease, but as shown in Figure 6, CO decreases more significantly than NOx. Therefore, the stoichiometric air-fuel ratio region is indicated by d in Figure 5, and expands to the rich side. Note that in Figure 5, when the ignition timing is retarded, NOx also decreases, so the stoichiometric air-fuel ratio region also expands to the lean side. However, because the amount of decrease in NOx is smaller than the amount of decrease in CO, the amount of expansion of the stoichiometric air-fuel ratio region to the lean side is smaller than the amount to the rich side. In Figure 5, the amount of decrease in NOx and the amount of expansion of the stoichiometric air-fuel ratio region to the lean side are omitted as they are minimal.

[0027] The second corrector 37 corrects the target air-fuel ratio to the richer side as the ignition timing is retarded. Preferably, the target air-fuel ratio is set to approximately the center of the stoichiometric air-fuel ratio region expanded to the richer side. As shown in FIG. 5, retarding the ignition timing expands the stoichiometric air-fuel ratio region to the richer side, so the center portion also moves to the richer side. The correction amount of the target air-fuel ratio can be determined by reading the amount of movement of the center portion of the stoichiometric air-fuel ratio region from a map or the like based on the ignition control signal, and correcting the target air-fuel ratio.

[0028] By setting the target air-fuel ratio in approximately the center of the stoichiometric air-fuel ratio range in this way, even if the air-fuel ratio fluctuates, the air-fuel ratio is less likely to deviate from the stoichiometric air-fuel ratio range, thereby improving exhaust purification performance. In this embodiment, the second correction unit 37 determines the final correction amount of the target air-fuel ratio by adding together the correction amount of the target air-fuel ratio based on the EGR amount and the correction amount of the target air-fuel ratio based on the ignition timing. Then, the target air-fuel ratio is corrected by the correction amount determined by the second correction unit 37 and the correction amount determined by the first correction unit 36.

[0029] This concludes the description of the present invention, but the present invention is not limited to the above embodiment. For example, in the above embodiment, the target air-fuel ratio is corrected based on both the exhaust gas recirculation amount and the ignition timing, but the target air-fuel ratio may be corrected based on only one of the exhaust gas recirculation amount and the ignition timing. Furthermore, if a device for changing the ratio of nitrogen oxides to carbon monoxide in the exhaust gas of the engine 2 is provided in addition to EGR control and ignition timing control, the target air-fuel ratio may be corrected based on the operation of that device. In this case, if the target air-fuel ratio is the stoichiometric air-fuel ratio, the target air-fuel ratio may be changed toward the richer side as the ratio of NOx in the exhaust gas increases, and the target air-fuel ratio may be changed toward the leaner side as the ratio of CO in the exhaust gas increases. Furthermore, when the target air-fuel ratio is set to a value other than the stoichiometric air-fuel ratio, for example, if it is desired to increase the amount of NOx or CO emitted (the amount supplied to the catalyst) depending on the status of a three-way catalyst or other catalyst, the target air-fuel ratio may be changed toward the leaner side as the ratio of NOx in the exhaust gas increases, and the target air-fuel ratio may be changed toward the richer side as the ratio of CO in the exhaust gas increases.

[0030] Furthermore, the exhaust purification device is not limited to the three-way catalyst 12, and the target air-fuel ratio of the detected value of the LAFS 22 when feedback controlling the fuel injection amount does not have to be the stoichiometric air-fuel ratio. Furthermore, the feedback control of the fuel injection amount may be for purposes other than controlling the air-fuel ratio of the exhaust gas flowing into the exhaust purification device. The present invention can also be widely applied to internal combustion engines other than those used to drive vehicles, which are provided with an air-fuel ratio detection means in the exhaust passage and in which the air-fuel ratio is feedback-controlled based on the detection value of the air-fuel ratio detection means. [Explanation of symbols]

[0031] 1 Target air-fuel ratio correction section 2. Engine (internal combustion engine) 10 Exhaust passage 17 EGR passage (exhaust gas recirculation means, ratio change means) 18 EGR valve (exhaust gas recirculation means, ratio change means) 22 LAFS (air-fuel ratio detection means) 30 Engine control unit (air-fuel ratio control means, ignition timing change means, ratio change means) 37 Second correction unit (target value changing means)

Claims

1. an air-fuel ratio detecting means provided in an exhaust passage of the internal combustion engine and detecting an air-fuel ratio; an air-fuel ratio control means for controlling the air-fuel ratio of the internal combustion engine so that the detected value of the air-fuel ratio detection means becomes a target value; a ratio changing means for changing the ratio of nitrogen oxides and carbon monoxide in the exhaust component emissions in the exhaust gas; a target value changing means for changing the target value when the ratio of nitrogen oxides to carbon monoxide in the exhaust component emissions in the exhaust gas is changed by the ratio changing means, The target value changing means changes the target value toward the rich side as the ratio of nitrogen oxides to carbon monoxide in the exhaust component emissions in the exhaust gas increases due to the change in ratio by the ratio changing means, and changes the target value toward the lean side as the ratio of carbon monoxide to nitrogen oxides in the exhaust component emissions in the exhaust gas increases due to the change in ratio by the ratio changing means. A control device for an internal combustion engine.

2. the ratio changing means is an exhaust gas recirculation means, the greater the amount of exhaust gas recirculated by the exhaust gas recirculation means, the lower the ratio of nitrogen oxides to carbon monoxide in the exhaust component emissions in the exhaust gas; 2. The control device for an internal combustion engine according to claim 1, wherein the target value changing means changes the target value to the lean side as the amount of exhaust gas recirculated by the exhaust gas recirculation means increases.

3. the ratio changing means is an ignition timing changing means, When the ignition timing is retarded by the ignition timing changing means, the amount of nitrogen oxides and carbon monoxide emissions decreases, and the ratio of carbon monoxide to nitrogen oxides in the amount of exhaust component emissions in the exhaust gas decreases, 3. The control device for an internal combustion engine according to claim 1, wherein the target value changing means changes the target value to a richer side as the ignition timing is retarded by the ignition timing changing means.

Images