JP2018131949A - Control device for internal combustion engine - Google Patents

Abstract

A fuel injection timing is appropriately controlled when the ignition timing is retarded to suppress the occurrence of knocking during the stratified combustion mode operation. When knocking is detected during operation in a stratified combustion mode in which fuel is injected from an in-cylinder injection valve in a compression stroke and a stratified mixture is formed in the vicinity of a spark plug to perform stratified combustion. The ignition timing is retarded until knocking is no longer detected. If knocking is not detected, the fuel injection timing is retarded during a period in which the combustion speed in the current cycle is higher than the combustion speed in the previous cycle under the ignition timing when knocking is no longer detected. [Selection] Figure 1

Description

  The present invention relates to a control device for an internal combustion engine. More specifically, the present invention relates to a control device for a spark ignition direct injection engine capable of selecting a stratified combustion mode in which fuel injection is performed in a compression stroke and stratified combustion is performed.

  There is known a spark ignition direct injection engine capable of operating in a stratified combustion mode in which fuel is injected into a cylinder in a compression stroke to generate and burn a stratified mixture. For example, Patent Document 1 discloses that when knocking is detected during operation in the stratified combustion mode, the ignition timing is retarded and the fuel injection timing is retarded according to the ignition timing retard amount. Has been.

JP 2004-003429 A Japanese Patent Laying-Open No. 2005-030293 Japanese Patent Laid-Open No. 11-030177 Japanese Patent Laid-Open No. 04-183951

  In the stratified combustion mode, the optimal combustion fuel injection timing with respect to the ignition timing, that is, the optimal interval between the ignition timing and the fuel injection timing varies depending on the engine speed, the combustion injection amount, the valve timing, and the like. Therefore, when the fuel injection timing is determined only by the ignition timing retard amount, it is difficult to optimally control the fuel injection timing, and the fuel property may be deteriorated by the retard. In this regard, there is room for improvement in the fuel injection timing control of Patent Document 1.

  In order to solve the above-described problems, the present invention improves the internal combustion engine so that the fuel injection timing can be appropriately controlled when the ignition timing is retarded in order to suppress the occurrence of knocking during the stratified combustion mode operation. An object of the present invention is to provide an engine control device.

  In order to achieve the above object, the control device for an internal combustion engine according to the present invention performs a compression stroke injection, which is a fuel injection from a cylinder injection valve in a compression stroke, and forms a stratified mixture in the vicinity of a spark plug to stratify combustion The control device is applied to an internal combustion engine capable of selecting a stratified combustion mode for performing the above, and has the following configuration. If knocking is detected during operation of the internal combustion engine in the stratified combustion mode, the ignition timing is retarded until knocking is no longer detected. If knocking is not detected, the fuel injection timing is retarded during a period in which the combustion speed in the current cycle is higher than the combustion speed in the previous cycle under the ignition timing when knocking is no longer detected.

  According to the control of the present invention, it is possible to retard the fuel injection timing to the timing at which the combustion speed becomes the fastest while suppressing the occurrence of knocking by the ignition timing retarding, minimizing deterioration in combustibility and torque reduction. To the limit. Further, since a large amount of map for complicated control and control execution is not required, the occurrence of control delay can be suppressed. Furthermore, since the fuel injection timing is determined during operation in the actual machine, it is possible to control the fuel injection timing at an appropriate timing while suppressing the influence of aging of the in-cylinder injection valve, manufacturing variations, and the like.

4 is a timing chart for explaining control of fuel injection timing and ignition timing in the embodiment. It is a figure for demonstrating the change of the unsteady tumble ratio in a cylinder. It is a flowchart for demonstrating the routine of control which a control apparatus performs in embodiment.

  An internal combustion engine (hereinafter simply referred to as an engine) to which a control device according to an embodiment of the present invention is applied is a spark ignition direct injection engine. Each cylinder of the engine is provided with an in-cylinder injection valve that injects fuel into the combustion chamber so that the tip of the cylinder faces the combustion chamber. A spark plug is installed near the top of the combustion chamber. This engine can be operated in the stratified combustion mode in which fuel is injected from the in-cylinder injection valve in the compression stroke, and a stratified mixture is formed in the vicinity of the spark plug to perform stratified combustion.

  Various sensors and actuators of the engine are electrically connected to the control device. The control device is an ECU (Electronic Control Unit). The control device controls the entire engine system, and is mainly composed of a computer including at least one CPU, ROM, and RAM. The ROM stores various control routines including control routines for ignition timing and fuel injection timing, which will be described later. The control device controls the engine by operating each actuator based on a signal from each sensor.

  Specifically, the control device of the present embodiment has a function of detecting knocking, detecting engine rotation speed, and detecting torque or combustion speed based on signals from the sensors. In addition, when knocking is detected during operation in the stratified combustion mode, the control device determines and controls the fuel injection timing and the ignition timing by the following control.

  Hereinafter, the control of the fuel injection timing and the ignition timing will be specifically described. FIG. 1 is a timing chart for explaining control of fuel injection timing and ignition timing in the present embodiment. Since this control is control in the stratified combustion mode, fuel injection is executed from the in-cylinder injection valve in the compression stroke, and ignition is performed at a predetermined timing when a stratified mixture is formed in the vicinity of the spark plug.

  In the example of FIG. 1, when the occurrence of knocking is detected at time t1 in a certain combustion cycle operating in the stratified combustion mode, the ignition timing is retarded from time t2 in the next combustion cycle, Until the time t3 at which knocking is not detected, the retardation is retarded by the repetitive retardation amount dθs.

  When knocking is not detected at time t3, the delay of the fuel injection timing is started at time t4 in the next combustion cycle. The fuel injection timing is repeatedly retarded by the delay amount dθi until knocking is detected again or until a decrease in combustion speed is detected due to the delay of the fuel injection timing. In the example of FIG. 1, the delay of the fuel injection timing is repeated until time t5 when knocking is detected again. During this time, the ignition timing is maintained at the ignition timing set immediately before time t3 when knocking is not detected.

  When knocking is detected at time t5, the ignition timing is retarded again from time t6 in the next cycle. On the other hand, the retardation of the fuel injection timing is stopped. Therefore, the fuel injection timing is maintained at the fuel injection timing set immediately before the time t5 when knocking is detected again.

  When knocking is no longer detected at time t7, the delay of the fuel injection timing is resumed at time t8 in the next combustion cycle. The retard of the ignition timing is stopped and maintained at the ignition timing set immediately before time t7 when knocking is not detected.

  Thereafter, when it is detected at time t9 that the combustion speed in the current cycle is slower than the previous cycle, the fuel injection timing in the next cycle is set immediately before time t8 when the combustion speed becomes slower. The fuel injection timing is restored. In other words, assuming that knocking has not occurred, the delay of the fuel injection timing is the period during which the combustion speed in the current combustion cycle is higher than the combustion speed in the previous combustion cycle, that is, the combustion period is While continuing the shortening, the delay of the fuel injection period is repeated.

  In the above control, the retard amount dθs of the ignition timing and the retard amount dθi of the fuel injection timing are not necessarily the same, and need not be constant. FIG. 2 is a diagram for explaining the change in the unsteady tumble ratio in the cylinder as a result of the CFD analysis. 2 that the tumble ratio becomes weaker as the fuel injection timing is retarded. If the tumble ratio decreases, it is expected that the timing at which the fuel reaches the vicinity of the spark plug will be delayed. Therefore, it is desirable that the fuel injection timing retard amount be smaller than the ignition timing retard amount. Further, the retard amounts dθs and dθi can be calculated according to a map.

  FIG. 3 is a diagram for explaining a control routine executed by the control device in the embodiment. In the routine of FIG. 3, it is first determined whether or not knocking has occurred in step S2. The presence or absence of knocking can be determined according to the output of a knocking sensor or the like. If it is determined in step S2 that knocking has not occurred, the current process is temporarily terminated.

  On the other hand, if it is determined in step S2 that knocking has occurred, then in step S4, the ignition timing is retarded by the retard amount dθs. Next, in step S6, it is determined whether knocking has occurred under the retarded ignition timing.

  If it is determined in step S6 that knocking has occurred, the process returns to step S4, and the ignition timing is retarded again by the retard amount dθs from the current ignition timing. The process of determining whether the ignition timing is retarded in step S4 and whether knocking has occurred in step S6 is repeated until it is determined in step S6 that knocking has not occurred.

  If it is determined in step S6 that knocking has not occurred, then in S8, the fuel injection timing is retarded by the retard amount dθi from the current fuel injection timing. Next, in step S10, it is determined whether or not knocking has occurred under the conditions of the retarded ignition timing and fuel injection timing. If it is determined that knocking has occurred, the process returns to step S4, and the above-described processes are sequentially performed from the retarded ignition timing.

  On the other hand, if it is determined in step S10 that knocking has not occurred, then in step S11, the combustion period t1 under the current ignition timing and fuel injection timing is calculated and stored. The combustion period can be calculated according to a known arithmetic expression using, for example, the output of the in-cylinder pressure sensor.

  Next, in step S12, the fuel injection timing is retarded by the retard amount dθi. Next, in step S14, it is determined whether knocking has occurred under the conditions of the set ignition timing and fuel injection timing. If it is determined in step S14 that knocking has occurred, the process returns to S4 again, and the above-described processes are sequentially performed from the retarded ignition timing.

  On the other hand, if it is determined in step S14 that knocking has not occurred, then in step S16, the combustion period t2 under the current ignition timing and fuel injection timing is calculated. Next, in step S18, it is determined whether or not the combustion period t2 calculated in step S16 is shorter than the combustion period t1 in the previous combustion cycle, that is, whether or not the combustion period is shortened.

  If it is determined in step S18 that the combustion period has been shortened, the process proceeds to step S20, and the combustion period t2 calculated in step S16 is stored as the combustion period t1. Thereafter, the process returns to step S12, and the fuel injection timing is retarded again by the retard amount dθi.

  The retardation of the fuel injection timing is repeated until it is determined in step S18 that the combustion period is not shortened. However, if the occurrence of knocking is detected in step S14 while the processes in steps S12 to S18 are repeated, the process returns to step S4, and the above-described processes are sequentially performed from the retarded ignition timing. The

  If it is determined in step S18 that the combustion period is not shortened, that is, if a decrease in combustion speed is confirmed, then in step S22, the current fuel injection timing is advanced by the retard amount dθi. Save the advanced fuel injection timing. That is, the fuel injection timing is returned to the fuel injection timing set immediately before the combustion speed decreases. Thereafter, the current process is temporarily terminated.

  As described above, according to the control of the present embodiment, the fuel injection timing is gradually retarded while avoiding knocking by the retard of the ignition timing, and finally the fuel whose combustion period is the shortest. Set to injection timing. Therefore, it is possible to control the optimum fuel injection timing for each cylinder for each operating condition in the actual machine without performing complicated control using a large amount of maps. Also, if knocking is avoided by retarding only the ignition timing, torque will be reduced, but the ignition timing is retarded because the fuel injection timing is retarded while the ignition timing is retarded to avoid knocking. It becomes possible to minimize the influence of torque reduction due to corners.

  The retard amount dθs of the ignition timing and the retard amount dθi of the fuel injection timing are not limited to being constant values. That is, the retard amount dθs of the ignition timing and the fuel injection timing dθi may be values that change according to the operating conditions. For example, a two-dimensional map that defines the relationship between the engine speed or the injection amount and each retard amount. Or it is good also as a structure calculated according to the three-dimensional map which defined the relationship between engine rotational speed, injection amount, and each retard amount.

  In the above embodiment, when referring to the number of each element, quantity, quantity, range, etc., the reference is made unless otherwise specified or the number is clearly specified in principle. The invention is not limited to the numbers. Further, the structure and the like described in this embodiment are not necessarily essential to the present invention unless otherwise specified or clearly specified in principle.

Claims (1)

A control device for an internal combustion engine capable of selecting a stratified combustion mode in which a stratified combustion is performed by performing a compression stroke injection that is a fuel injection from an in-cylinder injection valve in a compression stroke and forming a stratified mixture in the vicinity of an ignition plug,
During operation in the stratified combustion mode,
If knocking is detected, retard the ignition timing until knocking is no longer detected,
If knocking is not detected, the fuel injection timing is retarded during the period in which the combustion speed in the current combustion cycle is higher than the combustion speed in the previous combustion cycle under the ignition timing when knocking is no longer detected.
A control device for an internal combustion engine configured as described above.

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