JP4583402B2 - Control device for internal combustion engine - Google Patents

Description

  The present invention relates to a control device for an internal combustion engine, and more particularly to a control device for early activation of an exhaust purification catalyst.

  A three-way catalyst as an exhaust gas purification catalyst used for purifying exhaust gas from an internal combustion engine is generally activated when a temperature exceeds a certain temperature. Therefore, when the engine is cold, the catalyst temperature is low, so the catalyst is not activated, and sufficient exhaust purification performance cannot be exhibited until the catalyst reaches the activation temperature.

  By the way, as a method for early activation of the catalyst, an oxidation reaction is promoted by supplying unburned components (HC, CO) and oxygen to the catalyst, and the catalyst is activated at an early stage by increasing the temperature of the catalyst. There is known a method of increasing the amount of heat supplied to the catalyst by increasing the temperature of the exhaust gas flowing into the catalyst to promote the temperature rise of the catalyst. (For example, refer to Patent Document 1).

  As a method for promoting the former oxidation reaction, in a multi-cylinder engine, a method of providing a cylinder for setting the air-fuel ratio to lean and a cylinder for setting the air-fuel ratio to be rich, or upstream of the catalyst as in the secondary air supply system is provided. A method for supplying oxygen is known. As a method of increasing the amount of heat supplied to the latter catalyst, there is a method of increasing the amount of heat supplied to the catalyst by retarding the ignition timing within a range not exceeding the combustion stability limit and increasing the temperature of the exhaust gas. Are known.

Japanese Patent Laid-Open No. 9-79057

  Although the conventional catalyst early activation method in the control device for an internal combustion engine is configured as described above, the following problems have not been solved. That is, in the method of setting the air-fuel ratio of each cylinder to lean and rich in a multi-cylinder engine, the generated torque varies from cylinder to cylinder because the fuel supply amount to each cylinder varies (the rich cylinder has a large fuel supply amount). The torque is large and the lean cylinder has a small amount of fuel supply, so the torque is small.) In contrast, the ignition timing of the cylinder with the air-fuel ratio set to rich is retarded to reduce the generated torque and torque fluctuation There are known methods of absorbing

  In addition, by switching the cam that drives the intake valve of the cylinder whose air-fuel ratio is set to a rich one with a small valve opening period, the intake loss is reduced and the in-cylinder pressure is reduced to increase pump loss and the generated torque A method for reducing the torque difference between the lean cylinder and the lean cylinder has also been proposed. However, these methods still have the following problems.

  That is, the fuel supply amount is determined so that each cylinder has a desired air-fuel ratio by increasing the fuel in the cylinder that sets the air-fuel ratio rich and correcting the decrease in the fuel in the cylinder that sets lean. As a result, a difference in torque is generated due to a difference in fuel supply amount for each cylinder. In order to absorb this torque difference, the intake amount of the cylinder with the air-fuel ratio set to rich is reduced, but the cylinder with the air-fuel ratio set to rich has been corrected to increase the fuel supply amount. When the amount is decreased, the air-fuel ratio becomes richer and deviates from the desired air-fuel ratio.

  As a result, the amount of HC and CO supplied to the catalyst from the cylinder with the air-fuel ratio set to rich increases, and the balance with the amount of oxygen supplied to the catalyst from the cylinder with the air-fuel ratio set to lean is lost. As a result, there is a possibility that excessive HC and CO may be discharged into the atmosphere. Also, if the intake air amount is reduced to reduce the torque of the cylinder that has enriched the air-fuel ratio by increasing the fuel, the air-fuel ratio will become richer, exceeding the combustion stability limit on the rich side, and the cycle fluctuation of the engine-generated torque will be large. Therefore, there is a limit to reducing the intake air amount, and the range in which the generated torque can be reduced is limited. It can be said that it is practically difficult to obtain the desired rich air-fuel ratio and lean air-fuel ratio while making the generated torque uniform.

  In the secondary air supply system, additional parts such as an air pump and an air valve are required to send air directly into the exhaust system, and there are many disadvantageous parts such as cost. In addition, since the temperature of the exhaust gas is lowered by introducing air into the exhaust system, if a large amount of air is introduced to promote the chemical reaction, the temperature of the exhaust gas is lowered too much and the chemical reaction is suppressed. There is also a problem that it ends up. The method of increasing the exhaust gas temperature by retarding the ignition timing is not as good as other methods in terms of the effect of increasing the catalyst temperature.

  The present invention has been made in order to cope with the above-described problems, and can sufficiently suppress the output difference between the cylinders, and achieve good early activation of the catalyst while maintaining operability. It is an object of the present invention to provide a control device for an internal combustion engine capable of performing the above.

An internal combustion engine control apparatus according to the present invention is an internal combustion engine control apparatus provided with an exhaust purification catalyst that purifies the exhaust of the engine, and is detected by an operating state detecting means for detecting the operating state of the engine and the operating state detecting means. A fuel supply amount setting means for setting a fuel supply amount according to the operated state, a required intake amount setting means for setting an intake amount according to the operating state detected by the operating state detecting means, and a cylinder of the engine Among them, the air-fuel ratio of the intake mixture of a predetermined cylinder is set to a rich side with respect to the predetermined air-fuel ratio when the engine is cold, and the air-fuel ratios of other cylinders are set to the lean side with respect to the predetermined air-fuel ratio. With the air-fuel ratio setting means and the fuel supply amount setting means, the required intake air amount is adjusted so that the air-fuel ratio of each cylinder becomes a set value in a state where the fuel supply amounts of all cylinders are set to be substantially uniform. A cylinder required intake air quantity correcting means for correcting is provided for each, the air-fuel ratio setting means lean-side air-fuel ratio difference which is a difference between the target air-fuel ratio and the stoichiometric air-fuel ratio of the lean cylinders, the target air-fuel ratio enrichment cylinder which is the difference between the theoretical air-fuel ratio is set to be equal in the high temperature side of the engine coolant temperature with respect to the rich side air-fuel ratio difference, as well as set to be small at the low temperature side, the above cylinder required intake air quantity correcting means and , the total amount of intake air decreasing correction at a set cylinder to the rich side with respect to air-fuel ratio is the stoichiometric air-fuel ratio, the air-fuel ratio of the intake air amount increase correction in the cylinder that is set to the lean side with respect to a theoretical air-fuel ratio The total amount is made equal.

  Since the control device for an internal combustion engine according to the present invention is configured as described above, the exhaust gas passing through the catalyst repeats rich and lean every predetermined period, and HC, CO and oxygen are added to the catalyst. By supplying and promoting the chemical reaction and promoting the temperature rise of the catalyst, the catalyst is activated quickly, and the fuel supply amount to each cylinder, which is the biggest factor causing the fluctuation of the generated torque between the cylinders, is made almost uniform. As a result, torque fluctuations that affect driving performance can be suppressed.

Embodiment 1 FIG.
Embodiment 1 of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the overall configuration of the internal combustion engine control apparatus according to the first embodiment. Here, an example in which an in-line four-cylinder internal combustion engine (engine) is applied to an apparatus provided with a throttle valve that is independently driven in an intake pipe of each cylinder as individual intake air amount control means is shown. In addition, in FIG. 1, although the structure of only the 1st cylinder is specifically shown as a representative example, it cannot be overemphasized that it is comprised similarly about the other 2nd cylinder-4th cylinder (not shown). Yes.

  In FIG. 1, the engine 1 is provided with intake pipes 2 corresponding to a plurality of cylinders. The intake pipe 2 of each cylinder includes a throttle valve 3 for limiting the intake amount, a throttle actuator 4 for opening and closing the throttle valve 3, and a throttle opening sensor 5 for detecting the opening θ of the throttle valve 3. And a fuel injection valve 6. The throttle actuator 4 and the fuel injection valve 6 are driven by drive signals D4 and D6 from an electronic control unit (hereinafter referred to as ECU) 10, respectively.

  The ECU 10 receives a cylinder identification signal C from a cylinder identification means (crank angle detection sensor or the like) 11, a detection signal (throttle opening) θ from a throttle opening sensor 5, and other various sensors (not shown). Detection signal is input. The crank angle detection sensor 11 also generates a pulse signal indicating the engine speed Ne and inputs it to the ECU 10 together with the cylinder identification signal C described above.

  Various sensor signals include the water temperature signal from the cooling water temperature sensor (cooling water temperature Tw of the engine 1), the intake air temperature signal from the intake air temperature sensor (intake air temperature Ta), the intake air amount signal from the air flow sensor (intake air amount Qa), the accelerator There is an accelerator position signal (accelerator pedal depression amount α) from the position sensor, and the respective signals are input to the ECU 10 as shown in FIG.

Further, the engine 1 is provided with an intake valve 12 that opens and closes communication with the intake pipe 2, an exhaust valve 13 that opens and closes communication with the exhaust passage 7, and an ignition plug 14 that performs ignition control for each cylinder. Yes. The spark plug 14 is driven by an ignition signal D14 from the ECU 10.
Further, on the downstream side of the exhaust passage 7, a catalytic converter (hereinafter simply referred to as a catalyst) 15 for purifying exhaust gas discharged into the atmosphere is provided.

Here, the fuel injection amount setting, ignition timing setting, and intake air amount setting processing for each cylinder performed by the ECU 10 in the first embodiment will be described with reference to the flowchart of FIG. These processes are repeatedly executed at predetermined intervals.
First, in step S101, engine speed Ne, accelerator pedal depression amount α, cooling water temperature Tw, intake air amount Qa, charging efficiency Ec, and the like are calculated from input signals of various sensors.

  In step S102, a required torque (request Tq) corresponding to the driving force expected to be generated by the engine in the current operating state is calculated based on the various information calculated in step S101. Here, it is calculated as a function Ftq (Ne, α, Tw) having the engine speed Ne, the accelerator pedal depression amount α, and the coolant temperature Tw as arguments. Specifically, the basic required torque is calculated from the MAP using Ne and α as arguments, the water temperature correction coefficient is calculated from the MAP using Tw as an argument, and the required Tq is calculated by multiplying the required torque and the water temperature correction coefficient. A calculation method is generally used.

  In step S103, the control target value (target basic Ec) of the charging efficiency, which is the basis for controlling the intake air amount of the engine, is calculated from the request Tq. This is calculated as a function Fec (Ne, target Tq, Tw) with Ne, request Tq, Tw as arguments, for example, values read from MAP with Ne and request Tq as arguments, and read from MAP with Tw as arguments. There is a method of calculating by multiplication with a correction coefficient.

  In step S104, it is determined whether a condition for performing the catalyst temperature increase control is satisfied. Here, it is determined that the cooling water temperature Tw is between the predetermined values Tw1 and Twh shown in FIG. 3 (Tw1 ≦ Tw ≦ Twh). If YES, it is assumed that the catalyst temperature increase control execution condition is satisfied. In order to perform catalyst temperature increase control, the process proceeds to step S105 and subsequent steps. In the case of NO, it is determined that the catalyst temperature increase control execution condition is not satisfied, and the process proceeds to step S112 to perform normal control.

  In this embodiment, as described above, the engine cooling water temperature is set as the execution condition of the catalyst temperature rise control. However, the sensor is equipped with a sensor for measuring the temperature of the catalyst and a temperature sensor for detecting the exhaust gas temperature before and after the catalyst. There is also a method of using the output value of

  Steps S105 and after are the part explaining the catalyst temperature increase control process related to the present invention. In step S105, the target air-fuel ratio is set for each of the cylinder that makes the air-fuel ratio lean and the cylinder that makes rich. For example, as shown in FIG. 3, the target air-fuel ratio is set according to the engine cooling water temperature Tw. Next, in step S106, a cylinder that makes the air-fuel ratio lean and a cylinder that makes the air-fuel ratio rich are set. For example, as shown in FIG. 4, a cylinder that makes the air-fuel ratio lean and a cylinder that makes the air-fuel ratio rich are set.

  Here, the setting of the air-fuel ratio and the setting of the cylinder that makes the air-fuel ratio lean and the cylinder that makes the air-fuel ratio rich will be described in a little more detail. On the relatively high temperature side (Twm ≦ Tw ≦ Twh) among the conditions for performing the catalyst temperature increase control, as shown in FIG. 3, the target air-fuel ratio on the lean side and the target air-fuel ratio on the rich side are the respective theoretical air. The difference from the fuel ratio is set to be equal. In other words, the intake air amount for which the increase correction is performed in the cylinder having the lean air-fuel ratio is set to be equal to the intake air amount that is subjected to the decrease correction in the cylinder having the rich air-fuel ratio.

  In this case, as shown in FIG. 4B, the air-fuel ratio of each cylinder is set so that the rich cylinder and the lean cylinder are alternated, and the unburned components (HC, CO) are commensurate with it. By making oxygen (which corresponds to the theoretical air-fuel ratio) into the catalyst alternately introduced into the catalyst, the oxidation reaction is promoted, and the effect of promoting the temperature rise of the catalyst is obtained.

  On the other hand, on the low temperature side (Tw1 ≦ Tw ≦ Twm), as shown in FIG. 3, the difference between the target air-fuel ratio on the lean side and the stoichiometric air-fuel ratio is larger than the difference between the target air-fuel ratio on the rich side and the stoichiometric air-fuel ratio. It is set small (the lean side is about half of the rich side). This is because when the engine is at a low temperature, the lean side air-fuel ratio that becomes the combustion stability limit is small (close to the theoretical air-fuel ratio), and the lean degree cannot be set large.

  In this case, as shown in FIG. 4A, the air-fuel ratio of one cylinder is set to rich, and then the air-fuel ratio of two cylinders is set to lean. In this way, the amount of oxygen, which is the amount of unburned components discharged from the cylinder with the rich air-fuel ratio, and the two leaned cylinders, is set to be equivalent to the theoretical air-fuel ratio. Yes.

  In step S107, the charging efficiency (riched cylinder target Ec) at which the air-fuel ratio of the intake air-fuel mixture becomes the target air-fuel ratio RTAF is determined from the target air-fuel ratio RTAF of the cylinder that enriches the air-fuel ratio and the target basic Ec obtained in step S103. calculate. Specifically, since the target basic Ec is set assuming a theoretical air-fuel ratio, it can be calculated by calculating the ratio between the target air-fuel ratio RTAF and the theoretical air-fuel ratio and multiplying the target basic Ec.

  For example, if target basic Ec = 25%, RTAF = 12.5, theoretical air-fuel ratio = 14.7, the enriched cylinder target Ec = 25% x 12.5 ÷ 14.7 = 21.26%. As a result, the intake air amount is corrected to decrease. . In step S108, a lean cylinder target Ec which is a control target charging efficiency of the cylinder with the target air-fuel ratio made lean is calculated. This lean cylinder target Ec can be calculated by calculating the ratio of the target air-fuel ratio LTAF of the cylinder to be leaned to the stoichiometric air-fuel ratio and multiplying it by the target basic Ec, as in step S107.

  In step S109, a basic fuel supply amount is calculated as a function Fqf (target basic Ec, Ne) having target basic Ec and Ne as arguments. If it is normal control, it calculates using Ec calculated | required by step S101 like step S113 mentioned later, but here, target basic Ec is used. This is a feature of the present invention. In order to obtain a target air-fuel ratio by correcting the increase and decrease of the intake air amount for each cylinder while making the fuel supply amount to each cylinder uniform, the actual intake air amount of each cylinder is reduced. This is because it is necessary to determine the fuel supply amount according to the intake air amount before the increase / decrease correction for each cylinder, instead of determining the fuel supply amount according to the charging efficiency Ec expressed. By doing so, the fuel supply amount of each cylinder can be made substantially uniform, leading to suppression of torque fluctuation. The basic fuel supply amount is subjected to various corrections such as a water temperature correction and an air-fuel ratio feedback correction learning value to determine the final fuel supply amount. Here, the basic fuel supply amount is multiplied by a coefficient called Ctotal that is a collection of various correction coefficients.

  The ignition timing is calculated for each cylinder whose air-fuel ratio is made rich in step S110 and for each cylinder whose air-fuel ratio is made lean in step S111. First, the basic ignition timing is calculated as a function Figt (Ec, Ne, Tw) with the charging efficiency Ec, the engine speed Ne, and the engine coolant temperature Tw as arguments. Specifically, it is calculated by multiplying a value obtained by MAP search using Ec and Ne as arguments by a correction coefficient obtained by MAP search using Tw as an argument.

  The ignition timing retardation correction amount is determined for each of the cylinders in which the air-fuel ratio is rich and the cylinder in which the air-fuel ratio is lean with respect to the basic ignition timing thus determined, and the final ignition timing IGTr ( In step S110, the cylinder in which the air-fuel ratio is made rich is calculated in step S110, and IGTl (cylinder in which the air-fuel ratio is made lean) is calculated in step S111. Here, it is set so as to be retarded to the combustion stability limit of each of the rich cylinder and the lean cylinder. By doing so, the temperature of the exhaust gas is increased and the amount of heat supplied to the catalyst is increased, so that the temperature raising effect of the catalyst is further increased.

  The retardation correction amount for setting the ignition timing to the combustion stability limit is the functions Fretr (Ec, Ne, Tw) and Fretl (Ec, Ne, Tw) with Ec, Ne, and Tw as arguments. It is calculated by MAP search with three arguments. In addition to Ec, Ne, and Tw, the air-fuel ratio greatly affects the ignition timing that becomes the combustion stability limit. In the first embodiment, the air-fuel ratio of each cylinder is uniquely determined with respect to Tw in step S105. Therefore, here, if only Tw is used as an argument, it becomes possible to set the retardation correction amount in consideration of the influence of the air-fuel ratio.

  The MAP value for obtaining the retard correction amount for retarding the ignition timing to the combustion stability limit may be determined by a vehicle test at the vehicle development stage or a test with the engine alone. Specifically, the air-fuel ratio of each cylinder is set to the air-fuel ratio shown in FIGS. 3 and 4, and the ignition timing is gradually retarded from the basic ignition timing, and the engine vibration and rotational fluctuations are allowed. Check the ignition timing that exceeds. The MAP value for obtaining the retard correction amount may be set so that the ignition timing is slightly advanced (for example, about 3 degrees in crank angle) from the ignition timing at this time.

  In addition to setting the retard angle correction amount in advance as described above, a sensor for detecting ion current generated when the air-fuel mixture burns in the cylinder and a sensor for detecting pressure in the cylinder are provided. A method for detecting the combustion stability limit based on the detection value of the sensor and a method for detecting the combustion stability limit from fluctuations in the engine speed have been devised. It is also possible to configure so that the angle is gradually retarded and no further retarded when the combustion stability limit is detected.

  If it is determined in step S104 that the catalyst temperature increase control execution condition is satisfied, the target charging efficiency, the fuel supply amount of each cylinder when performing the catalyst temperature increase control by the processing in steps S105 to S111, The ignition timing is determined. Finally, the routine proceeds to step S115, where the target throttle opening (target Th) for controlling the throttle valve installed corresponding to each cylinder is set to the target Ec, which is the control target charging efficiency of each cylinder, and the engine speed. Calculation is performed as a function Fth of Ne (target Ec, Ne), and all the processes are completed. The calculation of the target Th is generally performed by a method such as MAP search using the target Ec and Ne as arguments.

  On the other hand, when it is determined in step S104 that the catalyst temperature increase control execution condition is not satisfied, normal intake air, fuel, and ignition timing control is processed in accordance with steps S112 to S114. In step S112, the target Ec of each cylinder is set. However, since the target air-fuel ratio of each cylinder is not individually set here, the target basic Ec is substituted as it is. In step S113, the fuel supply amount is calculated. Here, the charging efficiency Ec and the engine speed Ne are used as arguments, and the values calculated from the function Fqf (Ec, Ne) are added to the values calculated from the function Fqf (Ec, Ne), such as the water temperature correction, the air / fuel ratio feedback correction value, the air / fuel ratio feedback correction learning value, etc. Multiply Ctotal as various corrections to determine the final fuel supply.

  In step S114, similarly to step S110, the ignition timing IGT is calculated as a function Figt (Ec, Ne, Tw) having the charging efficiency Ec, the engine speed Ne, and the engine coolant temperature Tw as arguments. Here, since the retard angle correction is not performed, this value becomes the ignition timing as it is. Finally, the process proceeds to step S115, the target opening of the throttle valve corresponding to each cylinder is calculated, and all the processes are completed.

  The first embodiment is configured as described above. In the case where the air-fuel ratio difference is provided between the cylinders to promote the oxidation reaction of the catalyst, and the catalyst temperature is increased to accelerate the activation, each cylinder is activated. Since the air-fuel ratio difference is provided between the cylinders by increasing or decreasing the intake air amount for each cylinder while the fuel supply amount to the cylinder is almost uniform, the amount of energy input into each cylinder becomes uniform. Thus, the effect of suppressing the output step can be further enhanced as compared with the conventional device. In addition, since the exhaust gas temperature is increased by retarding the ignition timing, an effect of further increasing the temperature of the catalyst can be expected, and early activation can be further promoted.

  In the first embodiment, the configuration in which the retard control of the ignition timing is also performed has been described. However, even if only the intake air amount increase / decrease correction is performed for each cylinder, the catalyst temperature rise effect can be sufficiently obtained. Since the torque fluctuation factor caused by retarding the ignition timing of the cylinder to near the combustion stability limit is eliminated, the engine torque fluctuation can be suppressed more satisfactorily, so that only the intake air amount control may be performed.

  Further, in the first embodiment, when the ignition timing is retarded to the combustion stability limit regardless of the cylinder in which the air-fuel ratio is rich or the cylinder in which the air-fuel ratio is lean, the air-fuel ratio is set to give priority to the torque fluctuation suppression effect. One of the rich cylinder and the lean cylinder may be retarded to the combustion stability limit, and the ignition timing of the other cylinder may be set to a time at which the generated torque of each cylinder becomes equal. Specifically, the value of MAP corresponding to the functions Fretr (Ec, Ne, Tw) and Fretl (Ec, Ne, Tw) for calculating the ignition timing retardation correction amount in steps S110 and 111 in the flowchart shown in FIG. Can be easily realized by setting as follows.

  When testing the engine alone at the vehicle development stage, etc., if the air-fuel ratio is rich and the ignition timing is retarded to the combustion stability limit, the engine-generated torque and air-fuel ratio are leaned to retard the ignition timing to the combustion stability limit. Comparing the engine generated torque when the angle is set, set the MAP value for calculating the retard correction amount so that the ignition timing of the cylinder with the air-fuel ratio with the larger generated torque becomes the combustion stability limit . And if the generated torque is small when the ignition timing is retarded to the combustion stability limit, increase the generated torque by making the ignition timing more advanced than the combustion stability limit (decrease the retard amount). Then, the value of MAP for calculating the retard correction amount is set so that the ignition timing is such that the difference between the generated torques becomes smaller. By setting the MAP value that calculates the ignition timing retardation correction amount for each of the cylinders with rich air-fuel ratio and lean cylinder in this way, engine torque fluctuations can be made extremely small. In addition, the effect of suppressing torque fluctuation and the effect of early activation of the catalyst can be maximized.

  Further, in the first embodiment, the air-fuel ratio is set such that the intake air amount to be corrected for reduction in the cylinder with the rich air-fuel ratio and the intake air amount to be corrected for increase in the cylinder with the lean air-fuel ratio as a whole are equal. The air-fuel ratio on the side may be set to a value slightly close to the stoichiometric air-fuel ratio, and the air-fuel ratio may be set so that the entire exhaust gas flowing into the catalyst becomes slightly oxygen excess. Specifically, in step S105 of the flowchart of FIG. 2, the target air-fuel ratio RTAF on the rich side in FIG. 3 is slightly set (for example, about 0.6 in the air-fuel ratio) closer to the theoretical air-fuel ratio (upward in FIG. 3), In calculating the enriched cylinder target Ec in step S107, this can be realized by calculating after multiplying RTAF by a predetermined coefficient (for example, about 1.05).

  When the catalyst is in an inactive state at low temperatures, it is known that an oxygen-excess atmosphere accelerates the activation of the oxidation reaction, which causes unburned components (HC, CO) that become a problem immediately after engine cold start ) Can be expected to reduce the amount released to the atmosphere. In this case, there is a concern that the activation of the reduction reaction of NOx may be delayed, but since NOx emissions are originally low in the engine cold state, the effect on the purification of exhaust gas by prioritizing the oxidation reaction of unburned components is not effective large.

Embodiment 2. FIG.
Next, a second embodiment of the present invention will be described with reference to the drawings. The overall configuration of the internal combustion engine control device is the same as that of the first embodiment shown in the block diagram of FIG.

  In the first embodiment, the intake air amount of the cylinder in which the air-fuel ratio is set to be rich is corrected to be reduced, while the intake air amount of the cylinder in which the air-fuel ratio is set to be lean is corrected to increase the air-fuel ratio of each cylinder to a desired air-fuel ratio. In the second embodiment, the fuel supply amount is set so that the air-fuel ratio becomes rich while the fuel supply amount of each cylinder is substantially uniform. Then, in order to repeat the rich and lean exhaust gas flowing into the catalyst every predetermined period in order to promote early activation of the catalyst, the intake air amount of the cylinder having the air-fuel ratio set to lean is increased and the air-fuel ratio is increased. As a result, the air-fuel ratio becomes lean as a result of increasing the intake air amount for the cylinder with the fuel supply amount so as to be rich.

  The characteristics of the second embodiment will be described with reference to the flowchart shown in FIG. 5 regarding the fuel injection amount setting, ignition timing setting, and intake air amount setting processing for each cylinder performed by the ECU 10.

  The flowchart of FIG. 5 is a modified version of the flowchart of FIG. 2 in the first embodiment, and the steps having the same contents as those in FIG. 2 are described with the same step numbers as the step numbers in FIG. Is omitted. Steps different from FIG. 2 are steps S207 to S209. That is, in the process of setting the air-fuel ratio for each cylinder in the engine cold state, the target charging efficiency of the cylinder that enriches the air-fuel ratio (riched cylinder target Ec) and the target charging efficiency of the cylinder that makes the air-fuel ratio lean ( The step of calculating the lean cylinder target Ec) is different from the step of calculating the fuel supply amount (Qfuel) to each cylinder. Hereinafter, the process in the changed step will be described.

  First, in the same manner as in FIG. 2 of the first embodiment, the various variables indicating the operating state are calculated in steps S101 to S106. The target air-fuel ratios of both cylinders to be leaned are calculated, and the cylinders to be used as the respective target air-fuel ratios are determined. In step S207, the target charging efficiency of the cylinder that enriches the air-fuel ratio is calculated. This is the same as step S107 in FIG. 2, but the calculation method is different. In the second embodiment, the fuel supply amount of each cylinder is calculated in step S209, which will be described later, but the fuel supply amount is calculated so that the air-fuel ratio becomes richer than the target basic Ec. Therefore, in step S207, the target basic Ec may be substituted for the enriched cylinder target Ec of the cylinder that enriches the air-fuel ratio.

  Next, in step S208, a lean cylinder target Ec that is a target charging efficiency of the cylinder for leaning the air-fuel ratio is calculated. As described above, since the fuel supply amount is set so that the air-fuel ratio becomes rich, the target basic Ec is corrected to be leaner so that the air-fuel ratio is still lean considering the corresponding amount. It is necessary to calculate the cylinder target Ec. Specifically, since the fuel supply amount is determined so that the target air-fuel ratio is RTAF, which is the target air-fuel ratio of the cylinder that enriches the air-fuel ratio (described later in step S209), the target of the cylinder that leans the air-fuel ratio is determined. The ratio between LTAF and RTAF, which is the air-fuel ratio, is calculated and multiplied by the target basic Ec. For example, if target basic Ec = 25%, RTAF = 13, and LTAF = 16.5, the enriched cylinder target Ec = 25% × 16.5 ÷ 13 = 31.73%, and as a result, the intake amount is corrected to increase.

  In step S209, the amount of fuel supplied to each cylinder is calculated. This step also differs from step S109 in FIG. 2 only in the calculation method. In FIG. 2, since the fuel supply amount is set to be the stoichiometric air-fuel ratio with respect to the target basic Ec, correction calculation is performed so that the air-fuel ratio becomes rich with respect to the calculated fuel supply amount in the same manner as this. To. Specifically, the basic fuel supply amount is calculated as a function Fqf (target basic Ec, Ne) with target basic Ec and Ne as arguments, and this is multiplied by the ratio of the theoretical air-fuel ratio and the rich target air-fuel ratio RTAF. Then, it is calculated by multiplying it by various correction coefficients Ctotal.

  Thereafter, the ignition timing of each cylinder is calculated in steps S110 and S111, the target opening of the throttle corresponding to each cylinder is calculated in step S115, and the process ends. If the conditions for performing the catalyst temperature increase control are not satisfied in step S104, the same processing as in FIG. 2 is performed in steps S112 to S114.

  In general, it is known that combustion tends to become unstable when the engine is cold, and in particular, tends to become unstable when the intake air amount is small. Therefore, if the intake air amount is corrected to decrease, there is a concern that the intake air amount becomes too small and combustion becomes unstable and torque fluctuations are induced. On the other hand, if configured as in the second embodiment, the intake amount is increased only by the cylinder that makes the air-fuel ratio lean while enriching the basic air-fuel ratio by correcting the fuel supply amount uniformly. , Because it is possible to perform temperature rise promotion control to activate the catalyst early without reducing the intake air amount of the cylinder that enriches the air-fuel ratio, there is a concern that the intake air amount becomes too small and combustion becomes unstable The effect that can be wiped off is obtained.

  Further, combining the first embodiment and the second embodiment and setting the fuel supply amount so that the air-fuel ratio becomes rich, the air-fuel ratio is higher than the target air-fuel ratio of the cylinder that enriches the air-fuel ratio. The same effect can be obtained even if the intake air amount of the cylinder that enriches the air-fuel ratio is slightly reduced and corrected so that the air-fuel ratio is leaner and the intake air amount is greatly increased. I can do it.

  The above embodiments have been described on the assumption that a throttle valve is provided in the intake pipe of each cylinder. For example, the intake valve 12 is directly driven by an electromagnetic actuator to continuously adjust the valve lift amount and the valve opening period. Even when a variable mechanism is used, it is possible to provide an air-fuel ratio difference between the cylinders by increasing / decreasing the intake air amount for each cylinder. Therefore, the same effects as those of the above-described embodiments can be expected.

  Further, for example, a mechanism that continuously changes the maximum valve lift amount and the valve opening period of the intake valves of all cylinders as described in FIGS. 2 and 3 of Japanese Patent Application Laid-Open No. 2004-176644, If the target valve lift amount set for each period corresponding to the intake stroke of each cylinder is set to a value corresponding to the intake amount corrected for increase / decrease for each cylinder, the intake amount is similarly corrected for increase / decrease for each cylinder. Since an air-fuel ratio difference can be provided between them, an effect similar to that of each of the above-described embodiments can be expected.

1 is a block diagram showing an overall configuration of a control device for an internal combustion engine according to Embodiment 1 of the present invention. FIG. 3 is a flowchart for illustrating a control procedure of the internal combustion engine in the first embodiment. FIG. 2 is an explanatory diagram showing air-fuel ratio characteristics of a rich cylinder and a lean cylinder in the first embodiment. FIG. 3 is a diagram illustrating an example of air-fuel ratio setting for each cylinder in the first embodiment. 6 is a flowchart for illustrating a control procedure of the internal combustion engine in the second embodiment.

Explanation of symbols

1 engine, 2 intake pipe, 3 throttle valve,
4 throttle actuator, 5 throttle opening sensor, 6 fuel injection valve,
7 exhaust passage, 8 crankshaft, 9 air flow sensor, 10 ECU,
11 Crank angle detection sensor, 12 Intake valve, 13 Exhaust valve,
14 spark plug, 15 catalyst.

Claims (3)

In a control device for an internal combustion engine having an exhaust purification catalyst for purifying engine exhaust, an operating state detecting means for detecting an operating state of the engine, and a fuel supply amount in accordance with the operating state detected by the operating state detecting means. A fuel supply amount setting means for setting, a required intake amount setting means for setting an intake air amount in accordance with the operating state detected by the operating state detecting means, and an intake air mixture of a predetermined cylinder among the cylinders of the engine An air-fuel ratio setting means for setting the air-fuel ratio to a rich side with respect to a predetermined air-fuel ratio when the engine is cold, and an air-fuel ratio setting means for setting the air-fuel ratio of other cylinders to a lean side with respect to the predetermined air-fuel ratio, and the fuel supply amount setting Cylinder required intake air amount correcting means for correcting the required intake air amount for each cylinder so that the air-fuel ratio of each cylinder becomes a set value in a state where the fuel supply amounts of all cylinders are set to be substantially uniform by the means. The provided lean-side air-fuel ratio difference is a difference of the air-fuel ratio setting means and the target air-fuel ratio and the stoichiometric air-fuel ratio of the lean cylinders, rich side is the difference between the target air-fuel ratio and the stoichiometric air-fuel ratio enrichment cylinder set the same at a high temperature side of the engine coolant temperature with respect to the air-fuel ratio difference, the rich as well as set to be small at the low temperature side, the cylinder required intake air amount correction means, air-fuel ratio is the theoretical air-fuel ratio The total amount of intake air that is corrected to decrease in the cylinder set on the side is equal to the total amount of intake air that is corrected to increase in the cylinder whose air-fuel ratio is set on the lean side with respect to the theoretical air-fuel ratio. A control device for an internal combustion engine. Claim, characterized in that the air-fuel ratio is set in the vicinity of each of the combustion stability limit of the ignition timing to the retard side of the cylinder set in the cylinder and the lean side is set to the rich side with respect to the stoichiometric air-fuel ratio 1 The control apparatus of the internal combustion engine described in 1. Of the cylinder in which the fuel-air ratio is set cylinder and to the lean side, which is set to the rich side with respect to the stoichiometric air-fuel ratio, the ignition timing towards cylinder generated torque increases, in the vicinity of the combustion stability limit in the retard side The ignition timing of the other cylinder is set to an advance side with respect to the combustion stability limit on the retard side, and the output difference between the cylinders is suppressed. Control device for internal combustion engine.

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