JP4924396B2 - 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 an internal combustion engine provided with a catalyst having oxygen storage capacity in an exhaust passage.

  A catalyst used for purifying exhaust gas in an internal combustion engine has an oxygen storage function of storing oxygen therein. When the air-fuel ratio of the exhaust gas flowing into the catalyst is lean, oxygen is taken in and stored in the gas phase of the catalyst, and conversely, when the air-fuel ratio of the exhaust gas flowing into the catalyst is rich, the catalyst itself is stored. Oxygen is released into the gas phase. As a result, in a situation where the air-fuel ratio of the exhaust gas is lean and the NOx is relatively contained relative to HC and CO, the NOx can be reduced by the oxygen storage function of the catalyst. Conversely, in a situation where the air-fuel ratio of the exhaust gas is rich and a relatively large amount of HC and CO is contained, HC and CO can be oxidized by the oxygen releasing action of the catalyst.

  It is known that the oxygen storage capacity of such a catalyst gradually decreases due to the influence of deterioration over time. If the catalyst is continuously used in a state where the oxygen storage capacity is lowered, when the air-fuel ratio suddenly fluctuates due to disturbance or the like, there is a possibility that emissions exceeding the purification capacity of the catalyst may be discharged into the atmosphere. For this reason, many methods have conventionally been proposed for determining a decrease in the oxygen storage capacity of a catalyst.

  For example, Japanese Patent Laid-Open No. 2006-37841 proposes an internal combustion engine control device that increases at least one of the maximum lift amount and the operating angle of an intake valve when determining a decrease in the oxygen storage capacity of a catalyst. In the catalyst deterioration determination in this control device, it is necessary to continue to detect the exhaust component and the exhaust temperature until the integrated value of the intake air amount exceeds a certain value after satisfying various conditions for the determination. Is done. Therefore, at least one of the maximum lift amount and the operating angle of the intake valve is increased during such a period to shorten the period until the integrated value of the intake air amount exceeds a certain value. Thereby, since the period required for determination can be shortened, it becomes difficult to fall into a situation where the determination condition is not satisfied during determination, and the frequency of determination completion can be increased.

JP 2006-37841 A JP 2003-56387 A

  However, in the above-described conventional control device, when performing the deterioration determination of the catalyst, these are increased regardless of the current operating angle or the maximum lift amount. For this reason, when the operating angle or the maximum lift amount is already in a large state, these may be enlarged more than necessary, resulting in deterioration of fuel consumption.

  The present invention has been made to solve the above-described problems, and provides a control device for an internal combustion engine that can appropriately determine the oxygen storage capacity of a catalyst while suppressing deterioration in fuel consumption. Objective.

In order to achieve the above object, the first invention provides an internal combustion engine having a plurality of cylinders, a catalyst having an oxygen storage capacity disposed in an exhaust passage of the internal combustion engine, and a valve operating angle as a target operating angle. A control device for an internal combustion engine comprising: a variable valve mechanism for variable;
Measuring means for measuring the oxygen storage capacity of the catalyst when a predetermined execution condition is satisfied;
When executing the measuring means, if the target operating angle is smaller than the lower limit value of the operating angle at which the air-fuel ratio does not vary among the plurality of cylinders, the target operating angle is changed to the lower limit value. An angle changing means;
It is characterized by providing.

According to a second invention, in the first invention,
An actual working angle obtaining means for obtaining an actual working angle of the valve;
The measuring means starts measuring the oxygen storage capacity of the catalyst after the actual operating angle becomes equal to or greater than the lower limit value.

According to a third invention, in the first or second invention,
The internal combustion engine is mounted on a vehicle;
After the measurement by the measuring means is completed, the apparatus further comprises second target working angle changing means for changing the target working angle from the lower limit value to an appropriate value according to the driving state during a period in which the vehicle is accelerating. It is characterized by that.

  In an internal combustion engine having a plurality of cylinders, the variation in the air-fuel ratio between the cylinders is reduced as the operating angle increases. According to the first invention, when measuring the oxygen storage capacity of the catalyst, if the target operating angle is smaller than the lower limit value of the operating angle at which the air-fuel ratio variation between the cylinders does not appear, the target operating angle is the lower limit. Changed to a value. For this reason, according to the present invention, variation in the air-fuel ratio between the cylinders when measuring the oxygen storage capacity can be suppressed, so that the measurement accuracy of the oxygen storage capacity can be effectively improved. In addition, since the operating angle is increased only when the air-fuel ratio variation among the cylinders appears, it is possible to effectively avoid a situation where fuel consumption deteriorates due to the operating angle being expanded more than necessary.

  According to the second invention, the measurement of the oxygen storage capacity of the catalyst is started after the actual operating angle becomes equal to or greater than the lower limit value. For this reason, according to the present invention, the measurement of the oxygen storage capacity of the catalyst is started after completely eliminating the influence of the variation in the air-fuel ratio between the cylinders, so that the measurement accuracy can be effectively improved.

  According to the third aspect of the present invention, in the vehicle equipped with the internal combustion engine, after the measurement of the oxygen storage capacity of the catalyst is completed, the target operating angle becomes an appropriate value corresponding to the driving state during the acceleration period of the vehicle. Be changed. It is difficult to experience the deterioration of drivability during vehicle acceleration. For this reason, by changing the operating angle during this period, the operating angle can be returned to an appropriate value without causing the driver to feel uncomfortable.

  Embodiments of the present invention will be described below with reference to the drawings. The present invention is not limited to the following embodiments.

Embodiment [Configuration of Embodiment]
FIG. 1 is a diagram for explaining the configuration of the first embodiment of the present invention. As shown in FIG. 1, the internal combustion engine (engine) 10 of this embodiment is a gasoline engine that uses gasoline as fuel. The engine 10 includes a cylinder block 14 in which a piston 12 is disposed, and a cylinder head 16 assembled to the cylinder block 14. A space surrounded by the inner walls of the cylinder block 14 and the cylinder head 16 and the upper surface of the piston 12 forms a combustion chamber 18. Although only one combustion chamber 18 is shown in FIG. 1, the engine 10 is configured as a multi-cylinder engine having a plurality of combustion chambers 18.

  An intake passage 20 and an exhaust passage 22 communicate with the engine 10. An intake valve 24 for controlling a communication state between the intake passage 20 and the combustion chamber 18 is provided at a connection portion between the intake passage 20 and the combustion chamber 18. Further, an exhaust valve 26 for controlling a communication state between the exhaust passage 22 and the combustion chamber 18 is provided at a connection portion between the exhaust passage 22 and the combustion chamber 18.

  In addition, the system according to the present embodiment includes a variable valve mechanism 30. The variable valve mechanism 30 changes, for example, the amount of rocking or the rocking timing of a rocker arm (not shown) according to the rotation angle of a control shaft (not shown), thereby increasing the lift amount, working angle, and valve timing. The valve opening characteristics of the valve can be continuously changed. Note that the structure and function of the variable valve mechanism 30 in the present embodiment is not an essential part of the present invention and is a known technique, and therefore, detailed description thereof is omitted in this specification. I decided to.

In the exhaust passage 22, catalysts 32, 34 for purifying harmful components (NOx, CO, HC) in the exhaust gas are arranged in two stages. These catalysts 32 and 34 are both catalysts having oxygen storage capacity. The upstream catalyst 32 is disposed close to the exhaust manifold, and the downstream catalyst 34 is disposed under the floor of the vehicle. An A / F sensor (entire air / fuel ratio sensor) 52 is attached upstream of the catalyst 32, and an O ₂ sensor (oxygen sensor) 54 is attached downstream of the catalyst 34. The A / F sensor 52 is a sensor that outputs a linear signal with respect to the air-fuel ratio. The O ₂ sensor 54 is a sensor that outputs a signal corresponding to the oxygen concentration in the gas, and has an output characteristic that the output value is inverted with respect to the air-fuel ratio with respect to the theoretical air-fuel ratio.

The engine 10 of the present embodiment is provided with an ECU (Electronic Control Unit) 50 as a control device. The aforementioned A / F sensor 52 and O ₂ sensor 54 are connected to the ECU 50. Based on the output values of the A / F sensor 52 and the O ₂ sensor 54, the ECU 50 feedback-controls the fuel injection amount so that the air-fuel ratio of the exhaust gas flowing into the catalyst 32 becomes the stoichiometric air-fuel ratio. Hereinafter, this feedback control is referred to as “air-fuel ratio feedback control”.

The air-fuel ratio feedback control executed by the ECU 50 includes main feedback control and sub feedback control. In the main feedback control, the output value of the A / F sensor 52 is reflected in the fuel injection amount. In the sub feedback control, the output value of the O ₂ sensor 54 is reflected in the fuel injection amount. Since air-fuel ratio feedback control using the A / F sensor 52 and the O ₂ sensor 54 is a known technique, the detailed description thereof will be omitted in this specification.

[Operation in the embodiment]
Next, the operation of the system according to the present embodiment will be described with reference to the drawings.

(Catalyst deterioration judgment operation)
According to the air-fuel ratio feedback control described above, the air-fuel ratio of the exhaust gas can be maintained near the stoichiometric air-fuel ratio. However, if the oxygen storage capacity is reduced due to factors such as aging deterioration of the catalyst 32, it is assumed that harmful components cannot be purified in the catalyst 32 when the air-fuel ratio fluctuates due to disturbance or the like.

Therefore, in the system according to the present embodiment, the deterioration of the catalyst 32 is determined by measuring the oxygen storage capacity of the catalyst 32. Specifically, the oxygen storage state of the catalyst 32 can be monitored using the O ₂ sensor 54 downstream of the catalyst 32. When the catalyst 32 is saturated with oxygen, the output value of the O ₂ sensor 54 is inverted from the rich output to the lean output. On the contrary, when the catalyst 32 is depleted, the output value of the O ₂ sensor 54 is inverted from the lean output to the rich output. Therefore, the oxygen storage state of the catalyst 32 is determined based on the output value of the A / F sensor 52 or the integrated value of the intake air amount until the air-fuel ratio is richly leaned and the output value of the O ₂ sensor 54 is inverted. Can be measured.

Here, in the engine 10 of the present embodiment, the catalyst 32 is arranged close to the exhaust manifold of the engine 10. In such a structure, it is assumed that the exhaust gas discharged from each cylinder is introduced into the catalyst 32 without being reliably mixed. For this reason, when the air-fuel ratio between the cylinders varies, the oxygen storage capacity of the catalyst 32 may not be accurately measured. In other words, when rich or lean exhaust gas of some cylinders is continuously introduced into a part of the catalyst 32, the catalyst downstream even if the inside of the catalyst 32 is not completely in a rich atmosphere or lean atmosphere. These gases may be blown through and the output of the O ₂ sensor 54 may be reversed.

  Variations in the air-fuel ratio between cylinders are affected by the valve operating angle. That is, when the valve operating angle is large, the amount of air becomes large, and the variation in the air-fuel ratio between the cylinders becomes small. On the other hand, when the valve operating angle is small, the amount of air becomes small, and the variation in the air-fuel ratio between the cylinders becomes small. For this reason, when the variable valve mechanism 30 is controlled and the operating angle of the valve is varied to the small operating angle side, the variation in the air-fuel ratio between the cylinders can be suppressed by increasing the operating angle. However, since the fuel efficiency deteriorates when the operating angle is increased, it is preferable to carry out only the region where the variation in the air-fuel ratio between the cylinders is a problem.

  Therefore, in the system of the present embodiment, when the oxygen storage capacity of the catalyst 32 is measured, a lower limit value is set for the valve operating angle. Specifically, the lower limit value is set to a lower limit value (for example, about 140 °) of the operating angle at which variation in the air-fuel ratio between the cylinders does not matter. Thereby, when the target operating angle is smaller than the lower limit value, the value of the target operating angle is set to the lower limit value. On the other hand, when the target operating angle is already larger than the lower limit value, the target operating angle is maintained. Thus, since the lower limit value is specified as the minimum value within a range where the air-fuel ratio variation between the cylinders does not become a problem, the catalyst 32 is effectively avoided while the operating angle is increased unnecessarily and fuel consumption deteriorates. The measurement accuracy of the oxygen storage capacity can be maximized.

  Further, the measurement of the oxygen storage capacity of the catalyst 32 is performed after the variable operation of the operating angle is completed. For this reason, since the measurement can be started after the influence of the air-fuel ratio variation between the cylinders is completely wiped out, the measurement accuracy can be effectively improved.

  Moreover, after the measurement of the oxygen storage capacity of the catalyst 32 is completed, it is desirable to quickly return the working angle to an appropriate value according to the operating state. However, a sudden change in the working angle may cause a deterioration in drivability.

  Therefore, in this embodiment, the working angle is returned to an appropriate value while the vehicle is accelerating. It is difficult to experience the deterioration of drivability during vehicle acceleration. For this reason, by changing the operating angle during this period, the operating angle can be returned to an appropriate value without causing the driver to feel uncomfortable.

[Specific processing in the embodiment]
Next, with reference to FIG. 2 thru | or FIG. 4, the specific content of the process performed in this Embodiment is demonstrated. FIG. 2 is a flowchart of a routine that the ECU 50 executes to turn on the operating angle restriction flag. The routine shown in FIG. 2 is a routine that is repeatedly executed while the engine 10 is operating.

  In the routine shown in FIG. 2, first, it is determined whether or not the deterioration determination condition for the catalyst 32 is satisfied (step 100). Specifically, it is determined whether various conditions such as whether or not the engine 10 is in a predetermined steady operation and whether or not a predetermined period has elapsed since the completion of the previous determination are satisfied. The As a result, when it is determined that the catalyst deterioration determination condition is satisfied, it is determined that the oxygen storage amount measurement of the catalyst 32 can be performed, the process proceeds to the next step, and the operating angle limit flag is turned on. (Step 102). On the other hand, if the satisfaction of the condition is not recognized in step 100, this routine is immediately terminated.

  FIG. 3 is a flowchart of a routine in which the ECU 50 executes catalyst deterioration determination. Note that the routine shown in FIG. 3 is a routine that is repeatedly executed during operation of the engine 10, and is executed independently of the routine shown in FIG.

  In the routine shown in FIG. 3, first, the base operating angle is read (step 200). Here, specifically, the base operating angle is detected based on the rotation angle signal of the rotation angle sensor arranged on the control shaft of the variable valve mechanism 30.

  Next, it is determined whether or not the operating angle restriction flag is turned on (step 202). Here, specifically, in step 102, it is read whether or not the operating angle restriction flag is turned on. As a result, when the operating angle restriction flag is not turned on, this routine is immediately terminated.

  On the other hand, if it is determined in step 202 that the operating angle restriction flag is turned on, the process proceeds to the next step and it is determined whether or not the target operating angle is smaller than 140 ° (step). 204). Here, specifically, the current target operating angle set according to the driving state or the like is read, and the target operating angle is compared with the lower limit value (140 °). Here, the lower limit value is a value specified as the lower limit value of the operating angle at which the air-fuel ratio variation between the cylinders does not matter. As a result, when the establishment of the target operating angle <140 ° is recognized, it is determined that the target operating angle is smaller than the lower limit value, the process proceeds to the next step, and the target operating angle is the lower limit value of 140 °. (Step 206).

  After the process of step 206, or when the target operating angle <140 ° is not established in step 204, the process proceeds to the next step to determine whether the actual operating angle is 140 ° or more. (Step 208). Specifically, first, the actual working angle is read. Next, it is determined whether or not the read actual working angle is 140 ° or more which is a lower limit value of the working angle.

  In the above-mentioned step 206, when it is recognized that the actual operating angle ≧ 140 ° is established, it is determined that the variation in the air-fuel ratio between the cylinders is suppressed within the allowable range, and the process proceeds to the next step, and the catalyst A deterioration determination is executed (step 210). Here, specifically, the oxygen storage capacity of the catalyst 32 is measured to determine whether or not the catalyst 32 has deteriorated. On the other hand, if the actual operating angle ≧ 140 ° is not established in step 206, it is determined that the variation in the air-fuel ratio between the cylinders is not suppressed within the allowable range, and the catalyst deterioration determination is not executed. This routine is immediately terminated.

  FIG. 4 is a flowchart of a routine executed by the ECU 50 to turn off the operating angle restriction flag. Note that the routine shown in FIG. 4 is a routine that is repeatedly executed while the engine 10 is operating, and is a routine that is executed independently of the routines shown in FIGS. 2 and 3 described above.

  In the routine shown in FIG. 4, first, it is determined whether or not the execution of the catalyst deterioration determination has been completed (step 300). Here, specifically, it is determined whether or not catalyst deterioration determination is executed in step 210.

  Next, it is determined whether or not the operating angle restriction flag is on (step 304). Here, specifically, the same processing as in step 202 is executed. As a result, when it is determined that the operating angle restriction flag is off, this routine is immediately terminated. On the other hand, when it is determined that the operating angle restriction flag is on, the process proceeds to the next step, and it is determined whether or not the vehicle is accelerating (step 304). Here, specifically, it is determined whether or not the accelerator opening is equal to or greater than a predetermined opening. As a result, if it is determined that the vehicle is not accelerating, this routine is immediately terminated. On the other hand, if it is determined that the vehicle is accelerating, the process proceeds to the next step, and the operating angle restriction flag is turned off (step 306).

  As described above, according to the system of the present embodiment, the operating angle is guarded at the lower limit value when the oxygen storage capacity of the catalyst 32 is measured. For this reason, it is possible to effectively improve the measurement accuracy of the oxygen storage capacity by suppressing variations in the air-fuel ratio between the cylinders.

  In addition, according to the system of the present embodiment, the operating angle is returned to an appropriate value during acceleration of the vehicle, so that the operating angle can be returned to an appropriate value in a situation where it is difficult to experience a decrease in drivability.

  By the way, in the above-described embodiment, the lower limit value of the working angle is set to 140 °, but the lower limit value is not limited to this value. What is necessary is just to set the lower limit value of the working angle so that the air-fuel ratio of the exhaust gas to be introduced is not biased.

  In the above-described embodiment, the catalyst deterioration determination is executed after the actual operating angle becomes equal to or greater than the lower limit (140 °). However, the execution start timing of the catalyst deterioration determination is not limited to this. That is, when the responsiveness of the operation angle variable operation by the variable valve mechanism 30 is good, the catalyst deterioration determination may be started after changing the target operation angle to the lower limit value.

  In the above-described embodiment, the catalyst 32 corresponds to the “catalyst” in the first invention, and the ECU 50 executes the processing of steps 204 and 206 described above, whereby the first invention. The “target operating angle changing means” in FIG. 6 executes the processing of step 210 described above, thereby realizing the “measuring means” in the first invention.

  Further, in the above-described embodiment, the “actual operating angle acquisition means” in the second aspect of the present invention is realized by the ECU 50 executing the processing of step 208 described above.

  Further, in the above-described embodiment, the “second target operating angle changing means” in the third aspect of the present invention is realized by the ECU 50 executing the processing of step 306.

It is a figure for demonstrating schematic structure of the system of embodiment of this invention. It is a flowchart of a routine executed in the embodiment of the present invention. It is a flowchart of a routine executed in the embodiment of the present invention. It is a flowchart of a routine executed in the embodiment of the present invention.

Explanation of symbols

10 Internal combustion engine
12 piston 14 cylinder block 16 cylinder head 18 combustion chamber 20 intake passage 22 exhaust passage 24 intake valve 26 exhaust valve 30 variable valve mechanism 32 catalyst 34 catalyst 50 ECU (Electronic Control Unit)
52 A / F sensor 54 O ₂ sensor

Claims (3)

An internal combustion engine comprising: an internal combustion engine having a plurality of cylinders; a catalyst having an oxygen storage capability disposed in an exhaust passage of the internal combustion engine; and a variable valve mechanism for changing a valve operating angle to a target operating angle. A control device of
Measuring means for measuring the oxygen storage capacity of the catalyst when a predetermined execution condition is satisfied;
When executing the measuring means, if the target operating angle is smaller than the lower limit value of the operating angle at which the air-fuel ratio does not vary among the plurality of cylinders, the target operating angle is changed to the lower limit value. An angle changing means;
A control device for an internal combustion engine, comprising: An actual working angle obtaining means for obtaining an actual working angle of the valve;
2. The control device for an internal combustion engine according to claim 1, wherein the measuring unit starts measuring the oxygen storage capacity of the catalyst after the actual operating angle becomes equal to or greater than the lower limit value. The internal combustion engine is mounted on a vehicle;
After the measurement by the measuring means is completed, the apparatus further comprises second target working angle changing means for changing the target working angle from the lower limit value to an appropriate value according to the driving state during a period in which the vehicle is accelerating. 3. The control device for an internal combustion engine according to claim 1, wherein the control device is an internal combustion engine.

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