JP2008025526A - Control device for internal combustion engine - Google Patents

Abstract

An output step difference at the time of switching is suppressed even when the output after switching a combustion method for each cylinder group is different.
An internal combustion engine control device includes a plurality of cylinder groups (banks) including a plurality of cylinders such as a V-type internal combustion engine, and is configured to be able to perform combustion control independently for each cylinder group. . When switching the combustion system so that each cylinder group has a different combustion system, such as switching each cylinder group from stoichiometric combustion to rich / lean control for each bank, the combustion control means first selects the combustion system. The output of each cylinder group is changed so as to be within a predetermined range with respect to the output after switching. This can be performed, for example, by changing the ignition timing or both A / F and ignition timing for each cylinder group. And a combustion control means changes A / F after that, and switches a combustion system actually.
[Selection] Figure 3

Description

  The present invention relates to control for independently changing a combustion method for each cylinder group in an internal combustion engine having a plurality of cylinder groups.

  In an internal combustion engine having a plurality of cylinder groups such as a so-called V-type internal combustion engine, a method of switching a combustion method for each cylinder group is known. In Patent Document 1, when the target air-fuel ratio is switched with a time difference for each cylinder or cylinder group, after switching the target air-fuel ratio of some cylinders, the target air-fuel ratio of other cylinders is switched after a predetermined delay. Further, it is described that during the switching, the ignition timing of the cylinder with the target air-fuel ratio rich is retarded to smooth the torque change.

  However, the above literature does not consider the case where the output after switching the combustion method differs for each cylinder group.

  Patent Document 2 discloses a technique for preventing the exhaust purification catalyst from degrading when the target air-fuel ratio of a multi-cylinder internal combustion engine is switched. Further, Patent Document 3 describes a method of gradually changing the fuel supply amount when switching the combustion mode.

JP-A-4-295151 JP-A-7-293294 Japanese Patent No. 289426

  The present invention has been made to solve the above-described problems. In an internal combustion engine capable of controlling the combustion method for each cylinder group, even if the output after switching the combustion method for each cylinder group is different, the switching is performed. It aims at suppressing the output level difference at the time.

  In one aspect of the present invention, an internal combustion engine control device including a plurality of cylinder groups includes combustion control means for controlling combustion for each cylinder group, and the combustion control means includes a combustion method in which each cylinder group is different from each other. In order to switch the combustion system of each cylinder group, the combustion system is switched after changing the output of each cylinder group to be within a predetermined range with respect to the output after switching of the combustion system.

  The control device for an internal combustion engine includes a plurality of cylinder groups (banks) including a plurality of cylinders such as a V-type internal combustion engine, and is configured to be able to perform combustion control independently for each cylinder group. Combustion control is performed mainly by changing the air-fuel ratio (A / F), ignition timing, and the like. The combustion control means can switch the combustion system so that each cylinder group has a different combustion system. For example, each cylinder group can be switched from stoichiometric combustion to bank-specific rich / lean control. Here, the rich / lean control for each bank is an example in which one cylinder group is richly burned and the other cylinder group is lean burned, and the cylinder groups have different combustion methods.

  When switching the combustion method in this way, the combustion control means first changes the output of each cylinder group so that it is within a predetermined range with respect to the output after switching the combustion method. This can be performed, for example, by changing the ignition timing or both A / F and ignition timing for each cylinder group. And a combustion control means changes A / F after that, and switches a combustion system actually.

  As a result, at the actual switching of the combustion method, the output of each cylinder group is equal to or sufficiently close to the output after the switching, so an output step occurs before and after the switching of the actual combustion method, and the driver Problems such as remembering a sense of incongruity can be prevented.

  In one aspect of the control apparatus for an internal combustion engine, when the combustion control means switches the combustion system of each cylinder group so that each cylinder group has a different combustion system, the value of the control parameter related to the combustion system Are changed independently for each cylinder group. In this aspect, when the combustion method is switched so that each cylinder group has a different combustion method, the control parameter is changed independently for each cylinder group. In a preferred example, the control parameter includes at least one of fuel injection timing, valve timing, valve lift amount, and injection ratio.

  In another aspect of the control apparatus for an internal combustion engine, the combustion control means completes the change of the value of the control parameter until the combustion method is switched. In this aspect, since each control parameter is changed before each cylinder group becomes a different combustion system, combustion of the internal combustion engine can be stabilized before and after switching of the actual combustion system.

  Preferred embodiments of the present invention will be described below with reference to the drawings.

(Device configuration)
FIG. 1 shows a schematic configuration of a control device for an internal combustion engine according to an embodiment of the present invention. In FIG. 1, solid arrows indicate the flow of intake and exhaust, and broken arrows indicate input / output of signals. In the following description, the suffix “L” or “R” is added to the reference symbol when the left and right components are distinguished, and the suffix is omitted when the left and right components are not distinguished.

  The internal combustion engine 1 is configured as a V-type six-cylinder engine in which three cylinders (cylinders) 3 are provided in each of left and right banks (cylinder group) 2. Specifically, the left bank 2L includes three cylinders 3L, and the right bank 2R includes three cylinders 3R.

  A throttle valve 11, an air flow meter 12, an air cleaner (not shown) and the like are provided in the intake passage 4 for guiding intake air to each cylinder 3. The intake passage 4 is connected to an intake manifold 5. The throttle valve 11 is controlled in throttle opening based on a control signal CS <b> 1 from the ECU 20 and controls the flow rate of intake air flowing through the intake passage 4. The air flow meter 12 detects the intake flow rate downstream of the throttle valve 11 and supplies a signal CS3 corresponding to the flow rate to the ECU 20.

  Each cylinder 3 is provided with a fuel injection valve 13. The fuel injection amount of the fuel injection valve 13 is controlled based on a control signal CS2 from the ECU 20. The fuel injection valve 13 may be a port injection type or an in-cylinder injection type.

  The exhaust manifolds 6L and 6R of the banks 2L and 2R are connected to the exhaust passages 7L and 7R, respectively. A start catalyst 15L is provided in the exhaust passage 7L, and a start catalyst 15R is provided in the exhaust passage 7R. The exhaust passages 7L and 7R join downstream of the start catalysts 15L and 15R and are connected to the common exhaust passage 8. An underfloor (UF) catalyst 16 is provided in the common exhaust passage 8. The types of the start catalyst 15 and the UF catalyst are not particularly limited, but in a preferred example, a three-way catalyst can be used as the start catalyst 15 and a NOx storage reduction catalyst can be used as the UF catalyst 16.

  The ECU 20 controls each part of the internal combustion engine 1. In particular, the ECU 20 functions as a combustion control means in the present invention, and, as will be described later, according to the combustion method (combustion mode) of the internal combustion engine 1 such as cylinder group rich / lean control, stoichiometric control, etc. Controls the fuel ratio (A / F), ignition timing, and the like. The ECU 20 outputs control signals CS1 and CS2 based on the detection signal CS3 output from the air flow meter 12, and adjusts the opening degree of the throttle valve 11, the fuel injection amount from the fuel injection valve 13, and the like. Thus, the air-fuel ratio of each bank 2 is controlled.

(Combustion system switching control)
Next, combustion system switching control according to the embodiment will be described. The combustion system (combustion mode) refers to a combustion state of the internal combustion engine such as stoichiometric combustion, rich / lean combustion by bank (hereinafter also referred to as “RL combustion by bank”). The switching of the combustion method means a change between these different combustion methods, and specifically, changes A / F, ignition timing, etc. for each bank. Specifically, in the stoichiometric combustion mode, both banks 2R and 2L burn at stoichiometric (theoretical air-fuel ratio). On the other hand, in the bank-specific RL combustion mode, one bank 2 burns in a rich state, and the other bank 2 burns in a lean state. In the bank-specific RL combustion, the air-fuel ratio of one bank 2 is set to rich, the air-fuel ratio of the other bank 2 is set to lean, and rich exhaust gas and lean exhaust gas are UF on the common exhaust passage 8. The temperature of the UF catalyst is raised by being merged by the catalyst 16, and is performed for the purpose of, for example, recovery of sulfur (S) poisoning of the NOx storage reduction catalyst in addition to warming up of the UF catalyst.

  FIG. 2 shows a timing chart of basic combustion system switching control. In this example, the internal combustion engine is switched from stoichiometric combustion to bank-specific RL combustion. The internal combustion engine 1 is initially in a stoichiometric combustion state. At time t1, the condition for switching the combustion method to the bank-specific RL combustion is satisfied, and the combustion method switching flag becomes the switching request state. The switching condition of the combustion method to the bank-specific RL combustion is satisfied, for example, when the execution condition of the sulfur poisoning recovery process of the NOx storage reduction catalyst is provided as described above. Further, in this example, after the switching of the combustion method is completed, the right bank 2R burns in a rich A / F state (hereinafter referred to as “rich combustion bank”), and the left bank 2L has a lean A / F state. (Hereinafter referred to as a “lean combustion bank”).

  Generally, in the bank-specific RL combustion state, the output of the lean combustion bank is lower than that in the stoichiometric combustion state. In addition, the rich combustion bank increases the output because the A / F becomes rich, but in reality, it is required to make the output of each bank almost the same, so the ignition timing is retarded. Reduce output. Here, since the combustion stability becomes unstable, there is a limit to the retard amount of the ignition timing of the rich combustion bank. Therefore, in the bank-specific RL combustion state, the total output is reduced as compared with the stoichiometric combustion state. Therefore, in order to compensate for this, the throttle opening is increased and the intake air amount is increased.

  Specifically, in FIG. 2, when the combustion system switching request state is reached at time t1, the ECU 20 first controls the throttle valve 11 to increase the throttle opening. Thereby, thereafter, the intake air amount gradually increases. Further, the ECU 20 gradually changes the ignition timing of the right bank 2R, which is a rich combustion bank, to the retard side, and also gradually changes the ignition timing of the left bank 2L, which is a lean combustion bank, to the retard side. Then, after time t2 when the combustion method switching flag indicates that the switching is completed, the ECU 20 changes the A / F of the right bank 2R, which is a rich combustion bank, to rich (12.0 in this example) and advances the ignition timing. Advance to the corner. Further, the A / F of the left bank 2L, which is a lean combustion bank, is changed to lean (17.0 in this example), and the ignition timing is advanced to the advance side.

  However, in this control, as shown by the broken line portions X1 and X2 in FIG. 2, at the time t2 when the switching to the bank-specific RL control is performed, the output of both the banks 2 changes instantaneously. The driver feels uncomfortable.

  Therefore, in the present invention, before switching the combustion method to RL combustion by bank, the output of each bank is brought close to the output after completion of switching. This prevents a step in the output that occurs when the combustion method is actually switched to the bank-specific RL combustion.

  FIG. 3 shows a timing chart of the combustion system switching control according to the present invention. For comparison, the ignition timing and output graph of each bank 2 in the basic combustion mode switching control shown in FIG.

  As shown in the figure, in the control of the present embodiment, the retard amount of the ignition timing of the right bank 2R, which is the rich combustion bank, is reduced at the actual switching to the bank-specific RL combustion state, that is, at the stage before time t2. At the same time, the retard amount of the ignition timing of the left bank 2L, which is a lean combustion bank, is increased. In the rich combustion bank, the retard amount is reduced, so that the ignition timing is further advanced and the output is increased. That is, before the actual switching to the bank-specific RL combustion state, the output of the rich combustion bank becomes a value close to the output after the switching. Further, in the lean combustion bank, the retard amount is increased, so the ignition timing becomes more retarded and the output becomes smaller. That is, before the actual switching to the bank-specific RL combustion state, the output of the lean combustion bank becomes a value close to the output after switching. Therefore, as indicated by broken lines X3 and X4 in FIG. 3, the output step generated in each bank at the actual switching to the bank-specific RL combustion at time t2 can be made zero or sufficiently small. The control other than the above is the same as the basic combustion mode switching control shown in FIG.

  Thus, in this embodiment, when switching the combustion system from stoichiometric combustion to bank-specific RL combustion, before actually changing the A / F and switching the combustion system to bank-specific RL combustion, the output of each bank is changed. The ignition timing is controlled to be equal to or sufficiently close to the output after switching. Then, after the output of each bank is equal to or sufficiently close to the output after switching, the A / F is changed, and the combustion method is changed to bank-specific RL combustion. Therefore, the output level difference at the time of switching to bank-specific RL combustion can be suppressed.

  In the above example, the output of each bank is adjusted by controlling the ignition timing before actually switching the combustion method to the bank-specific RL combustion. Instead, the output of each bank may be adjusted by changing A / F. In this case, however, the corresponding ignition timing must be changed as the A / F changes. That is, by controlling both the A / F and the ignition timing, the output of each bank may be adjusted to approach the output after switching the combustion method.

  Next, changes in control parameters other than the A / F and ignition timing accompanying the switching of the combustion method will be described. As described above, when switching the combustion method from stoichiometric combustion to bank-specific RL control, the value of the control parameter may differ for each bank before and after switching. Here, the control parameters include, for example, fuel injection timing, variable valve system settings such as valve timing and valve lift, and fuel injection ratio. The fuel injection ratio is the number of times fuel is injected in one cycle (for example, two times of compression stroke and intake stroke), and the location where fuel injection is performed (for example, when port injection and in-cylinder injection are performed simultaneously) 2 places).

  In such a case, in this embodiment, the value of each control parameter is changed independently for each of the left and right banks. FIG. 4 shows an example of changing the control parameter value of each bank. FIG. 4 is the same as FIG. 3 except that a graph schematically showing changes in the value of the control parameter is added. In the right bank, the value of the control parameter is gradually lowered to the value after switching. In the left bank, the value of the control parameter is gradually increased to the value after switching.

  Further, as shown in FIG. 4, it is preferable that the change of the control parameter is completed before switching to bank-specific RL combustion, that is, by time t2 when stoichiometric combustion is performed. The reason is as follows. Since the above control parameters are optimized in the steady operation state, when the fuel system is changed instantaneously (that is, at time t2), the amount of injected cylinder wall surface, the port wall temperature, the cylinder interior Until the temperature, intake air temperature, and the like are stabilized, stable operation may not always be guaranteed. For this reason, it is possible to stabilize the combustion of the internal combustion engine before and after switching the combustion mode by changing the control parameter to the value after switching the combustion mode during stoichiometric combustion with relatively high redundancy.

  From this point of view, the change of the value of the control parameter may be completed by the time of switching the combustion method, and may be gradually changed during the stoichiometric combustion as illustrated in FIG. It may be changed instantaneously at a specific timing.

  FIG. 5 shows a flowchart of the fuel system switching control according to this embodiment. This control is realized by the ECU 20 executing a program stored therein in advance.

  First, the ECU 20 determines whether or not the execution condition of the bank-specific RL control is satisfied (step S1). In the example of FIGS. 3 and 4, the execution condition of the bank-specific RL control is satisfied at time t1. When the execution condition of the bank-specific RL control is satisfied, the ECU 20 controls the throttle valve 11 to increase the throttle opening as shown in FIG. 3 (step S2). Thereby, the amount of intake air thereafter increases gradually. Further, as shown in FIG. 3, the ECU 20 changes the ignition timing of the right bank, which is a rich combustion bank, and the ignition timing of the left bank, which is a lean combustion bank, respectively to the retard side (step S3). Further, as shown in FIG. 4, the ECU 20 changes the value of the control parameter to the value after switching the combustion method (step S4). When the output of each bank becomes equal to or sufficiently close to the output after switching the combustion method, the ECU 20 changes the A / F of both banks at time t2 (step S6), and thereafter executes RL combustion by bank. .

  In step S5, the ECU 20 calculates the current and output of each bank after switching the combustion system based on the A / F, ignition timing, etc., and the current output of each bank is the output of the fuel system after switching. It can be executed by determining whether or not it is within a predetermined range. Instead, based on the A / F, ignition timing, etc., the time required for the output of each bank to be within the predetermined range of the output after switching the fuel system is calculated in advance, and the time has elapsed. Sometimes, it may be determined that the output of each bank approaches the output after switching.

1 shows a schematic configuration of a control device for an internal combustion engine according to an embodiment. It is an example of a timing chart of basic combustion system switching control. It is a timing chart of combustion system switching control by an embodiment. It is a timing chart of combustion system switching control by an embodiment. It is a flowchart of the combustion system switching control by embodiment.

Explanation of symbols

1 Internal combustion engine
2L, 2R bank (cylinder group)
3L, 3R cylinder 4 Intake passage 5 Intake manifold 6 Exhaust manifold 7L, 7R Exhaust passage 8 Common exhaust passage 15L, 15R Start catalyst 16 UF catalyst

Claims (4)

A control device for an internal combustion engine comprising a plurality of cylinder groups,
Combustion control means for controlling combustion for each cylinder group,
When switching the combustion system of each cylinder group so that each cylinder group has a different combustion system, the combustion control means is configured so that the output of each cylinder group is within a predetermined range with respect to the output after switching the combustion system. A control apparatus for an internal combustion engine, wherein the combustion system is switched after changing the output.   The combustion control means changes the control parameter value related to the combustion method independently for each cylinder group when switching the combustion method of each cylinder group so that each cylinder group has a different combustion method. The control apparatus for an internal combustion engine according to claim 1, wherein the control apparatus is an internal combustion engine.   The control device for an internal combustion engine according to claim 2, wherein the control parameter includes at least one of a fuel injection timing, a valve timing, a valve lift amount, and an injection ratio. The control apparatus for an internal combustion engine according to claim 2 or 3, wherein the combustion control means completes the change of the value of the control parameter before switching of the combustion method.

Images