JP2012189058A - Fuel injection control device for multiple cylinder internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel injection control device that can improve an exhaust emission control performance when variations among rich side cylinders occur even in a multiple cylinder internal combustion engine in which a lift amount of an intake valve is changed.SOLUTION: An engine 10 includes a lift amount variable mechanism 42 for changing the lift amount of the intake valve 30. An electronic control device 50 detects the variations among the cylinders which are the variations of air-fuel ratio among the cylinders and performs increase correction of a fuel injection quantity when the variations among the cylinders are biased to the rich side. An increase correction quantity of the fuel injection quantity is increased as the lift amount of the intake valve 30 becomes smaller.

Description

  The present invention relates to a fuel injection control device for a multi-cylinder internal combustion engine.

  In an internal combustion engine, air-fuel ratio control is performed to correct the fuel injection amount so that the actual air-fuel ratio becomes the target air-fuel ratio. In addition, as described in Patent Document 1, a variation among cylinders, which is a variation in air-fuel ratio among cylinders of a multi-cylinder internal combustion engine, is also performed.

  For example, when the air-fuel ratio of a specific cylinder is shifted to the rich side and the air-fuel ratios of the other cylinders are maintained near the theoretical air-fuel ratio, the inter-cylinder variation is reduced to the rich side. When it is biased, the fuel injection amount is reduced through the air-fuel ratio control. As a result, the air-fuel ratio of the specific cylinder approaches the stoichiometric air-fuel ratio, but the air-fuel ratios of other cylinders that have been maintained near the stoichiometric air-fuel ratio until then become lean. As a result, the atmosphere of the catalyst provided in the exhaust passage also becomes lean, and the exhaust purification performance may be deteriorated.

  Therefore, when the variation between the cylinders is biased toward the rich side (hereinafter, this state is referred to as the variation between the rich side cylinders), the fuel injection amount is corrected to be increased to suppress the leanness of the catalyst atmosphere. The above-described decrease in exhaust purification performance can be suppressed.

JP 2009-074388

  By the way, in a multi-cylinder internal combustion engine having a variable lift amount mechanism that changes the lift amount of the intake valve, the exhaust purification performance will not be improved unless the fuel increase correction is optimized according to the lift amount when the above-mentioned rich side cylinder variation occurs. May decrease.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to purify exhaust when there is variation between rich-side cylinders even in a multi-cylinder internal combustion engine in which the lift amount of the intake valve is changed. An object of the present invention is to provide a fuel injection control device for a multi-cylinder internal combustion engine capable of improving performance.

In the following, means for achieving the above object and its effects are described.
The invention according to claim 1 is applied to a multi-cylinder internal combustion engine having a lift amount variable mechanism for changing the lift amount of the intake valve, and detects variation among cylinders which is variation in air-fuel ratio among the cylinders. A fuel injection control device that corrects an increase in fuel injection amount when the variation between cylinders is biased to the rich side, wherein the increase correction amount of the fuel injection amount is variably set based on the lift amount. And

  In a multi-cylinder internal combustion engine having a variable lift amount mechanism, the lift amount in each cylinder varies due to a mechanical error or the like. The variation in the intake air amount to each cylinder due to the variation in the lift amount becomes larger as the lift amount is smaller. Therefore, the deviation amount of the actual air-fuel ratio from the theoretical air-fuel ratio becomes larger as the lift amount is smaller. Therefore, when the fuel injection amount increase correction is performed in order to suppress the leanness of the catalyst atmosphere when the variation between the rich side cylinders occurs, the increase correction amount should be increased as the lift amount is smaller. Thus, the leanness of the catalyst atmosphere can be appropriately suppressed, and the exhaust purification performance can be improved. Based on this knowledge, in this configuration, the fuel injection amount increase correction amount is variably set based on the intake valve lift amount, which is made variable, thereby increasing the fuel increase when rich-side cylinder-to-cylinder variations occur. The correction can be optimized according to the lift amount. Therefore, even in a multi-cylinder internal combustion engine in which the lift amount of the intake valve is changed, it is possible to improve the exhaust purification performance when the rich side cylinder variation occurs.

  When the fuel injection amount increase correction amount is variably set based on the lift amount, a configuration is adopted in which, as the lift amount is smaller, the increase correction amount is increased as the lift amount is smaller. By doing so, the variable setting of the increase correction amount can be optimized.

  On the other hand, the variation in the intake air amount to each cylinder due to the variation in the lift amount of the intake valve becomes smaller as the lift amount becomes larger, so the deviation amount of the actual air-fuel ratio from the theoretical air-fuel ratio becomes smaller as the lift amount becomes larger. . Therefore, as described in claim 3, when the lift amount is larger than a predetermined value, the variable correction amount is increased by adopting a configuration in which variable setting of the increase correction amount by the lift amount is stopped. The variable setting can be simplified.

1 is a schematic diagram showing the structure of an engine to which the fuel injection control device for a multi-cylinder internal combustion engine according to the present invention is embodied, to which the fuel injection control device is applied. The graph which shows the change aspect of the lift amount of an intake valve based on the action | operation of a lift amount variable mechanism. 1 is a schematic diagram showing the positions of air-fuel ratio sensors and oxygen sensors in an exhaust passage. The flowchart which shows the procedure about calculation processing of the injection correction amount. The graph which shows the relationship between the lift amount of an intake valve, the deviation | shift amount of an actual air fuel ratio, and a richening correction coefficient.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment embodying a fuel injection control device for an internal combustion engine according to the present invention will be described below with reference to FIGS.
As shown in FIG. 1, a throttle valve 14 is provided in the intake passage 12 of the internal combustion engine 10. A throttle motor 16 is connected to the throttle valve 14. Then, the opening degree of the throttle valve 14 (throttle opening degree TA) is adjusted through the drive control of the throttle motor 16, and thereby the amount of air taken into the combustion chamber 18 through the intake passage 12 is adjusted. The intake passage 12 is provided with a fuel injection valve 20. The fuel injection valve 20 injects fuel into the intake passage 12. Further, an exhaust purification catalyst 34 is provided in the exhaust passage 28 of the internal combustion engine 10.

  In the combustion chamber 18 of the internal combustion engine 10, ignition by the spark plug 22 is performed on the air-fuel mixture composed of intake air and injected fuel. By this ignition operation, the air-fuel mixture burns, the piston 24 reciprocates, and the crankshaft 26 rotates. The combusted air-fuel mixture is sent as exhaust gas from the combustion chamber 18 to the exhaust passage 28, purified through the exhaust purification catalyst 34, and then discharged outside the exhaust passage 28.

  In the internal combustion engine 10, the intake passage 12 and the combustion chamber 18 are communicated and blocked by the opening / closing operation of the intake valve 30. The intake valve 30 opens and closes with the rotation of the intake camshaft 32 to which the rotation of the crankshaft 26 is transmitted. Further, a variable lift amount mechanism 42 is provided between the intake valve 30 and the intake camshaft 32. The variable lift amount mechanism 42 changes the lift amount VL (specifically, the maximum lift amount) of the intake valve 30 according to engine operating conditions, and operates through drive control of an actuator 44 such as an electric motor. As shown in FIG. 2, the lift amount VL of the intake valve 30 changes in synchronization with the valve opening period (lift operation angle) by the operation of the lift amount variable mechanism 42. For example, the lift amount VL decreases as the lift operation angle decreases. Becomes smaller.

  Various sensors for detecting the operating state of the internal combustion engine 10 are provided. Examples of the various sensors include a crank sensor 52 for detecting the rotational speed of the crankshaft 26 (engine rotational speed NE), and an intake air amount for detecting the amount of air passing through the intake passage 12 (intake air amount GA). The sensor 54 and the accelerator sensor 56 for detecting the depression amount AC of the accelerator pedal 36 are provided. Further, a throttle sensor 58 for detecting the throttle opening degree TA and a lift amount sensor 60 for detecting the lift amount VL of the intake valve 30 (more precisely, the operation amount of the lift amount variable mechanism 42) are provided. Yes. In addition, an air-fuel ratio sensor 62 that is provided in a portion upstream of the exhaust purification catalyst 34 in the exhaust passage 28 (specifically, an exhaust manifold) and outputs a signal corresponding to the oxygen concentration of the exhaust, or the above-mentioned in the exhaust passage 28. An oxygen sensor 64 and the like that are provided on the downstream side of the exhaust purification catalyst 34 and output a signal corresponding to the oxygen concentration of the exhaust are also provided.

  As shown in FIG. 3, the internal combustion engine 10 has four cylinders # 1, # 2, # 3, and # 4. The air-fuel ratio sensor 62 is an exhaust passage 28 extending from each cylinder # 1 to # 4. A portion common to all the cylinders is provided at a portion where the two are joined (specifically, an exhaust manifold).

  The air-fuel ratio sensor 62 is a known limiting current oxygen sensor. This limiting current type oxygen sensor is a sensor that provides an output current according to the oxygen concentration in the exhaust gas by providing a ceramic layer called a diffusion rate limiting layer in the detection part of the concentration cell type oxygen sensor, and the oxygen concentration in the exhaust gas When the air-fuel ratio of the air-fuel mixture that is closely related to the stoichiometric air-fuel ratio is the stoichiometric air-fuel ratio, the output current is “0”. Further, as the air-fuel ratio of the air-fuel mixture becomes richer, the output current increases in the negative direction, and as the air-fuel ratio becomes leaner, the output current increases in the positive direction. Therefore, based on the output signal of the air-fuel ratio sensor 62, the lean degree or rich degree of the air-fuel ratio of the air-fuel mixture can be detected.

  The oxygen sensor 64 is a well-known concentration cell type oxygen sensor. When the oxygen concentration of the exhaust gas is the concentration when the air-fuel ratio of the air-fuel mixture is richer than the stoichiometric air-fuel ratio, an output voltage of about 1 volt is obtained from this concentration cell type oxygen sensor. An output voltage of about 0 volts can be obtained when the concentration is a concentration when the fuel ratio is leaner than the stoichiometric air-fuel ratio. The output voltage of the concentration cell type oxygen sensor greatly changes when the oxygen concentration of the exhaust gas is the concentration when the air-fuel ratio of the air-fuel mixture is close to the stoichiometric air-fuel ratio. Therefore, based on the output signal of the oxygen sensor 64, it is possible to detect whether the exhaust gas downstream of the exhaust purification catalyst 34 has a property corresponding to lean or a property corresponding to rich.

  The oxygen sensor 64 is provided on the downstream side of the exhaust purification catalyst 34 in order to monitor the state of the exhaust purification action of the exhaust purification catalyst 34. That is, when the reduction action at the exhaust purification catalyst 34 is promoted and oxygen is released into the exhaust, the output signal of the oxygen sensor 64 has a value corresponding to lean. On the other hand, when the oxidation action in the exhaust purification catalyst 34 is promoted and oxygen in the exhaust is consumed, the output signal of the oxygen sensor 64 becomes a value corresponding to rich. Based on the detection result of the oxygen sensor 64, the state of the exhaust gas purification action is monitored.

  The electronic control device 50 having a microcomputer takes in detection signals from various sensors and performs various calculations, and based on the calculation results, the drive control of the throttle motor 16 (throttle control) and the drive control of the fuel injection valve 20 (fuel injection). Control), drive control of the actuator 44 (lift amount change control) and the like.

  In the present embodiment, the intake air amount GA taken into the combustion chamber 18 is adjusted as follows through throttle control and lift amount change control. That is, a control target value (target intake air amount GAp) for the intake air amount GA is calculated based on the depression amount AC of the accelerator pedal 36 and the engine speed NE, and the target intake air amount GAp and the actual intake air amount GA are calculated. The throttle control and the lift amount change control are executed so as to match. When performing the throttle control and the lift amount changing control, when the warm-up is not completed (for example, cooling water temperature <predetermined temperature), the lift amount VL is fixed at the large lift operating angle, while the throttle opening degree TA is changed. Thus, the intake air amount GA is adjusted. On the other hand, when the warm-up is completed (for example, cooling water temperature ≧ predetermined temperature), the throttle opening degree TA is almost fully opened, and the intake air amount GA is adjusted by changing the lift amount VL. At this time, basically, the lift amount VL of the intake valve 30 is set to be larger as the target intake air amount GAp suitable for the operating state of the internal combustion engine 10 is larger.

  In the present embodiment, the fuel injection amount is adjusted according to the intake air amount GA adjusted through throttle control and lift amount change control. Specifically, the fuel amount at which the air-fuel ratio of the air-fuel mixture becomes the stoichiometric air-fuel ratio with respect to the intake air amount GA is calculated as the fuel injection amount command value (target injection amount Tq). Then, the fuel injection valve 20 is driven so that an amount of fuel equal to the target injection amount Tq is injected. Thereby, the air-fuel ratio of the air-fuel mixture burned in the combustion chamber 18 can be brought close to the stoichiometric air-fuel ratio to some extent.

  Here, the exhaust purification catalyst 34 has an action of purifying exhaust by oxidizing HC and CO in the exhaust and reducing NOx in the exhaust in a state where combustion near the stoichiometric air-fuel ratio is performed, In particular, all of the main harmful components (HC, CO, NOx) in the exhaust gas are efficiently purified within a narrow range (window) where the air-fuel ratio of the air-fuel mixture becomes a ratio in the vicinity of the stoichiometric air-fuel ratio. Therefore, in order for the exhaust purification catalyst 34 to function effectively, it is necessary to strictly adjust the air-fuel ratio so that the air-fuel ratio of the air-fuel mixture matches the center of the window.

Hereinafter, an outline of such air-fuel ratio control will be described.
First, the actual air-fuel ratio of the air-fuel mixture is detected by the air-fuel ratio sensor 62, and the feedback correction amount MFB is calculated based on the degree of deviation between the actual air-fuel ratio and the target air-fuel ratio (here, the theoretical air-fuel ratio). At the same time, the target injection amount Tq is corrected based on the feedback correction amount MFB. Through the feedback control based on the feedback correction amount MFB, the fuel injection amount is adjusted so that the actual air-fuel ratio matches the target air-fuel ratio.

  Further, it is estimated from the detection result of the oxygen sensor 64 whether the exhaust purification catalyst 34 is in an oxygen storage state or an oxygen release state, and further correction is made to the target injection amount Tq based on the estimation result. Done. Specifically, a sub feedback correction amount SFBa for increasing or decreasing the target injection amount Tq is set. When the output signal of the oxygen sensor 64 is a value indicating richness, the sub feedback correction amount SFBa is decreased by a fixed amount α for each calculation cycle so that the fuel injection amount is gradually decreased. On the other hand, when the output signal of the oxygen sensor 64 is a value indicating lean, the sub feedback correction amount SFBa is increased by a fixed amount α for each calculation cycle so that the fuel injection amount is gradually increased. Through the sub feedback control (sub air-fuel ratio control) based on the sub feedback correction amount SFBa, the fuel injection amount is adjusted in accordance with the actual purification state of the exhaust purification catalyst 34, and the purification action of the exhaust purification catalyst 34 is accurately performed. Demonstrated.

  On the other hand, the electronic control unit 50 monitors whether the air-fuel ratio varies among the cylinders (# 1, # 2, # 3, # 4). For example, in the present embodiment, the magnitude of the inclination of the output signal variation of the air-fuel ratio sensor 62 is calculated, and it is determined that the cylinder-to-cylinder variation occurs when the calculated magnitude of the inclination exceeds a predetermined value. I have to. Further, based on the fluctuation pattern of the output signal of the air-fuel ratio sensor 62, it is determined whether the variation between the cylinders is biased to the rich side or the lean side. It should be noted that the variation between cylinders can also be detected by another known method (for example, the method described in JP-A-2003-13862).

  And, when the variation between cylinders is biased to the rich side, that is, when the air-fuel ratio of a specific cylinder is shifted to the rich side compared to the air-fuel ratio of other cylinders, and the rich-side cylinder variation occurs The fuel injection amount is reduced through the air-fuel ratio control. As a result, the air-fuel ratio of the specific cylinder approaches the stoichiometric air-fuel ratio, but the air-fuel ratios of other cylinders that have been maintained near the stoichiometric air-fuel ratio until then become lean. As a result, the atmosphere of the exhaust purification catalyst 34 also becomes lean, and the exhaust purification performance may be deteriorated.

  Therefore, in addition to correcting the fuel injection amount by air-fuel ratio control, the electronic control unit 50 further increases the fuel injection amount to make the air-fuel ratio rich by correcting the fuel injection amount to increase the amount of catalyst atmosphere. Leaning is suppressed, thereby preventing a decrease in exhaust purification performance. The calculation of the injection correction amount H used for increasing the fuel injection amount is performed as follows.

FIG. 4 shows a processing procedure for calculating the injection correction amount H. This process is repeatedly executed by the electronic control unit 50 at predetermined intervals.
When this process is started, it is first determined whether or not there is a variation between rich cylinders (S100). If there is a variation between the rich side cylinders, the enrichment correction coefficient RK is calculated based on the current lift amount VL, the engine speed NE, and the engine load KL (S110).

  The enrichment correction coefficient RK is calculated when the maximum correction amount allowed as the fuel injection amount increase correction value when the variation between the rich side cylinders occurs is “inter-cylinder variation reflection amount M”. This value is multiplied by the inter-period variation reflection amount M, and is variably set in the range of “0 or more and 1 or less”. The enrichment correction coefficient RK based on the lift amount VL is calculated for the following reason.

  That is, in the engine 10 having the lift amount variable mechanism 42, the lift amount VL in each cylinder varies due to individual differences, deterioration with time, or mechanical errors such as assembly errors. The variation in the intake air amount to each cylinder due to the variation in the lift amount VL becomes larger as the lift amount VL is smaller. As shown in FIG. 5, the deviation amount of the actual air-fuel ratio from the theoretical air-fuel ratio is the lift amount VL. The smaller the is, the larger it becomes. Therefore, when the fuel injection amount increase correction is performed in order to suppress the leanness of the catalyst atmosphere when the rich side cylinder variation occurs, the increase correction amount is increased as the lift amount VL is smaller. As a result, the leanness of the catalyst atmosphere can be appropriately suppressed, and the exhaust purification performance can be improved. Therefore, in the present embodiment, as shown in FIG. 5, the richening correction coefficient RK increases as the lift amount VL decreases.

  Further, the enrichment correction coefficient RK based on the engine speed NE and the engine load KL is calculated for the following reason. That is, if the intake air amount distributed to the combustion chamber 18 of each cylinder, that is, the intake distribution amount to each cylinder, is different, this also causes the same phenomenon as the variation in the intake air amount to each cylinder due to the variation in the lift amount VL. Become. That is, the larger the variation in the intake air distribution amount, the larger the deviation amount of the actual air-fuel ratio from the stoichiometric air-fuel ratio, and it is desirable to increase the fuel injection amount increase correction amount. Therefore, in the present embodiment, the relationship between the engine rotational speed NE and the engine load KL and the intake air distribution amount to each cylinder is obtained in advance through experiments or the like, and the richening correction coefficient RK increases as the variation in the intake air distribution amount increases. Is trying to grow.

  When the enrichment correction coefficient RK is calculated based on the lift amount VL, the engine speed NE, and the engine load KL, in step S120, the injection correction amount H for increasing the fuel injection amount is calculated. The injection correction amount H is calculated by multiplying the cylinder variation reflection amount M by the richening correction coefficient RK. And this process is once complete | finished.

As described above, according to the present embodiment, the following effects can be obtained.
(1) When the inter-cylinder variation is biased to the rich side, the fuel injection amount is corrected to increase, and this increase correction amount (injection correction amount H) is variably set based on the lift amount VL of the intake valve. Like to do. More specifically, the enrichment correction coefficient RK is changed according to the lift amount VL so that the increase correction amount (injection correction amount H) is increased as the lift amount VL is smaller. Therefore, it is possible to appropriately suppress the leaning of the catalyst atmosphere when the variation between the rich side cylinders occurs, and the exhaust purification performance can be improved.
(2) When the enrichment correction coefficient RK is variably set, the intake distribution amount to each cylinder is taken into account in addition to the lift amount VL. Therefore, the leanness of the catalyst atmosphere due to the variation in the amount of air taken into each cylinder can be more appropriately suppressed.

In addition, the said embodiment can also be changed and implemented as follows.
The variation in intake air amount to each cylinder due to the variation in intake valve lift amount VL becomes smaller as the lift amount VL is larger. Therefore, the deviation amount of the actual air-fuel ratio from the theoretical air-fuel ratio also increases as the lift amount VL increases. Get smaller. Therefore, when the lift amount VL is larger than a predetermined value and the effect of the lift amount VL on the deviation amount of the actual air-fuel ratio is sufficiently low, the fuel injection amount increase correction amount (injection correction amount H) is variably set by the lift amount VL. May be canceled. That is, when the lift amount VL is larger than a predetermined value, the enrichment correction coefficient RK may be set to a predetermined constant value. In this case, variable setting of the increase correction amount can be simplified.

In addition, the technical idea that can be grasped from the above embodiment will be described below together with the effects thereof.
(A) In the fuel injection control device for a multi-cylinder internal combustion engine according to any one of claims 1 to 3, the increase correction amount is changed in accordance with an intake distribution amount to each cylinder. A fuel injection control device for a multi-cylinder internal combustion engine.

According to this apparatus, when calculating the amount of increase correction, the intake distribution amount to each cylinder is taken into account in addition to the lift amount VL. Therefore, the leanness of the catalyst atmosphere due to the variation in the amount of air taken into each cylinder can be more appropriately suppressed.
(B) In the fuel injection control device for a multi-cylinder internal combustion engine described in (a) above, the increase correction amount corresponding to the intake air distribution amount is calculated based on an engine speed and an engine load. A fuel injection control device for a multi-cylinder internal combustion engine.

  According to this apparatus, it is possible to variably set the increase correction amount according to the intake distribution amount without separately providing a sensor or the like for detecting the intake distribution amount.

  DESCRIPTION OF SYMBOLS 10 ... Internal combustion engine, 12 ... Intake passage, 14 ... Throttle valve, 16 ... Throttle motor, 18 ... Combustion chamber, 20 ... Fuel injection valve, 22 ... Spark plug, 24 ... Piston, 26 ... Crankshaft, 28 ... Exhaust passage, DESCRIPTION OF SYMBOLS 30 ... Intake valve, 32 ... Intake camshaft, 34 ... Exhaust purification catalyst, 36 ... Accelerator pedal, 42 ... Lift amount variable mechanism, 44 ... Actuator, 50 ... Electronic control unit, 52 ... Crank sensor, 54 ... Intake amount sensor, 56 ... accelerator sensor, 58 ... throttle sensor, 60 ... lift amount sensor, 62 ... air-fuel ratio sensor, 64 ... oxygen sensor.

Claims (3)

This is applied to a multi-cylinder internal combustion engine having a lift variable mechanism that changes the lift amount of the intake valve, and detects variation among cylinders, which is variation in air-fuel ratio among the cylinders, and the variation between cylinders is biased to the rich side. A fuel injection control device that corrects the fuel injection amount when the fuel injection amount is increased,
A fuel injection control device for a multi-cylinder internal combustion engine, wherein an increase correction amount for the fuel injection amount is variably set based on the lift amount. The fuel injection control device for a multi-cylinder internal combustion engine according to claim 1, wherein the increase correction amount is increased as the lift amount is smaller. The fuel injection control device for a multi-cylinder internal combustion engine according to claim 1 or 2, wherein when the lift amount is larger than a predetermined value, the variable setting of the increase correction amount by the lift amount is stopped.

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