JP2010255508A - Fuel injection control device for spark ignition internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress the deterioration in combustion stability and exhaust performance when fuel supplied to a cylinder direct injection injector is not sufficiently boosted, in a spark ignition internal combustion engine including the cylinder direct injection injector and a port injection injector. <P>SOLUTION: In this fuel injection control device for the spark ignition internal combustion engine, injection control in starting is performed in starting so that compression stroke injection is performed by the cylinder direct injection injector after the fuel supplied to the cylinder direct injection injector is boosted to a reference pressure or more by a fuel booster, and injection control after starting is performed so that two fuel injections, that is, fuel injection by the port injection injector and compression stroke injection by the cylinder direct injection injector are performed after the operating condition of the internal combustion engine satisfies a predetermined condition. When a fuel pressure after lapse of a predetermined period from starting of pressure rising by the fuel booster in the injection control in starting does not reach the reference pressure, it is determined that pressure rising by the fuel booster is failure, and control is switched from the injection control in starting to the injection control after starting without depending on whether the operating condition of the internal combustion engine satisfies or not the predetermined condition. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a fuel injection control device for a spark ignition type internal combustion engine.

  As a technique related to fuel injection control of an internal combustion engine having an in-cylinder direct injection injector that injects fuel into a cylinder, Patent Document 1 discloses a fuel injection by an in-cylinder direct injection injector after the fuel pressure rises to a predetermined level or more at start-up. In the case where the fuel pressure increase is poor, it is described that only one bank cylinder or the number of cylinders is reduced and injection is performed by an in-cylinder direct injection injector.

  As a technique related to fuel injection control of an internal combustion engine provided with two injectors, an in-cylinder direct injection injector and a port injection injector that injects fuel into an intake passage, Patent Document 2 discloses that a predetermined time elapses immediately after a cold start of the engine. Describes that the compression stroke injection is performed only by the in-cylinder direct injection injector, and after the elapse of a predetermined time, both the intake passage injection by the port injection injector and the compression stroke injection by the in-cylinder direct injection injector are performed.

JP 2006-336593 A JP 2006-274949 A

  If the fuel supplied to the in-cylinder direct injection injector cannot be sufficiently boosted, the fuel spray injected into the high-pressure cylinder in the latter half of the compression stroke will not reach the vicinity of the spark plug. Leaning may result in deterioration of combustion stability and exhaust performance.

  The present invention has been made in view of such circumstances, and in a spark ignition type internal combustion engine having an in-cylinder direct injection injector and a port injection injector, the fuel supplied to the in-cylinder direct injection injector cannot be sufficiently boosted. The purpose is to suppress the deterioration of combustion stability and exhaust performance.

In order to solve the above problems, a fuel injection control device for a spark ignition type internal combustion engine according to the present invention includes:
A port injection injector for injecting fuel into the intake passage of the internal combustion engine;
An in-cylinder direct injection injector for injecting fuel into a cylinder of the internal combustion engine;
A fuel booster for boosting the fuel supplied to the in-cylinder direct injection injector;
When the internal combustion engine is started, the fuel pressure booster boosts the fuel to a predetermined reference pressure or higher, and then performs fuel injection in the compression stroke by the in-cylinder direct injection injector, and starts the operation state of the internal combustion engine. Control means for performing post-startup injection control for performing two fuel injections, fuel injection by the port injection injector and fuel injection in a compression stroke by the in-cylinder direct injection injector, after satisfying a predetermined condition;
With
The control means determines that the boosting by the fuel boosting device is defective when the fuel pressure after a predetermined period of time has not reached the reference pressure after the boosting by the fuel boosting device is started in the start-up injection control. Then, regardless of whether or not the operating state of the internal combustion engine satisfies the predetermined condition, the start-time injection control is switched to the post-start-up injection control.

  As a result, when the pressure of the fuel supplied to the in-cylinder direct injection injector is poor, the fuel injection is performed immediately by both the in-cylinder direct injection injector and the port injection injector regardless of the operating state of the internal combustion engine. Therefore, it is possible to avoid a situation in which fuel injection is performed only by the in-cylinder direct injection injector with insufficient pressure increase, and it is possible to suppress deterioration in combustion stability and exhaust performance.

  In addition, the injection timing which can supply a fuel in a cylinder by the fuel injection by a port injection injector is limited. In other words, the fuel injection into the intake passage by the port injector must be performed at the latest before the intake stroke ends (a period during which the intake valve is opened or a period before the intake valve is opened). is there. For example, the timing of the first half of the exhaust stroke, the timing of the second half of the intake stroke, the arbitrary timing of the intake stroke, and the like can be set as the fuel injection timing by the port injector.

  Therefore, in the above description, “when the fuel boost to the in-cylinder direct injection injector is faulty, immediately switch from the start-time injection control to the post-start-up injection control” means that the boost by the fuel booster is faulty. This means that the cylinder at a crank angle at which fuel injection by the port injection injector can be performed at the time of determination is immediately switched from start-time injection control to post-start-up injection control, and the boosting by the fuel booster is poor. For the cylinders that have already passed the time when the fuel injection by the port injection injector is possible (the cylinders that are in the compression stroke) at the time of the determination, the injection control at the time of starting that performs only the compression stroke injection by the in-cylinder direct injection injector I do. And it switches to the after-start injection control from the next cycle.

  In the present invention, the “reference pressure” is a fuel pressure threshold value for determining whether or not the fuel injection by the in-cylinder direct injection injector in the start-up injection control is feasible. The reference pressure can be determined based on the lower limit value of the pressure at which the fuel spray can reach the vicinity of the spark plug when fuel injection is performed by the in-cylinder direct injection injector during the compression stroke.

  The “predetermined condition” of the operation state for switching from the start-time injection control to the post-start-time injection control is, for example, when the rotation speed exceeds a predetermined threshold or when the elapsed time since the start-time injection control is started is predetermined. It is satisfied when the threshold value is exceeded.

  The “predetermined period” is a threshold value for a boosting period for determining whether or not the fuel boosting by the fuel booster is defective. The predetermined period can be determined based on the maximum value of the period required for boosting the fuel pressure to the reference pressure when the boosting by the fuel booster is normal. Based on the same concept, it may be determined whether or not the fuel pressure has reached the reference pressure when the number of times of boosting by the fuel boosting device has become a predetermined number or more.

  According to the present invention, in a spark ignition internal combustion engine having an in-cylinder direct injection injector and a port injection injector, deterioration in combustion stability and exhaust performance when the fuel supplied to the in-cylinder direct injection injector cannot be sufficiently boosted. It becomes possible to suppress.

It is a figure which shows schematic structure of the spark ignition type internal combustion engine which concerns on an Example. (A) Engine speed, (B) Fuel pressure of in-cylinder direct injection injector, (C) Fuel injection amount of in-cylinder direct injection, (D) Port injection when fuel injection control according to the embodiment is performed It is a time chart showing the time change of the fuel injection quantity of an injector. It is a flowchart of the fuel injection control which concerns on an Example.

  Hereinafter, embodiments of the present invention will be described in detail. The dimensions, materials, shapes, relative arrangements, and the like of the component parts described in the present embodiment are not intended to limit the technical scope of the invention only to those unless otherwise specified.

  FIG. 1 is a conceptual diagram schematically showing a schematic configuration of the internal combustion engine and its intake system and exhaust system according to the present embodiment. The engine 1 of FIG. 1 is a spark ignition type internal combustion engine, and a spark plug 12 is provided at the top of the cylinder 2. A piston 3 is slidably inserted into the cylinder 2. A combustion chamber 18 formed by the inner wall of the cylinder 2 and the top surface of the piston 3 communicates with the intake passage 4 through the intake port 9 and also communicates with the exhaust passage 5 through the exhaust port 10. The engine 1 is provided with an intake valve 6 that opens and closes an intake port 9 and an exhaust valve 7 that opens and closes an exhaust port 10.

  The engine 1 is provided with two fuel injection injectors, that is, an in-cylinder direct injection injector 11 that injects fuel into the cylinder 2 and a port injection injector 8 that injects fuel into the intake port 9. The in-cylinder direct injection injector 11 is configured to inject fuel toward a cavity 13 formed on the top surface of the piston 3 when the piston 3 is in a predetermined timing of the compression stroke. The fuel in the fuel tank 15 is supplied to the in-cylinder direct injection injector 11 through the fuel supply path 17. The fuel supplied to the in-cylinder direct injection injector 11 is boosted by the booster pump 16. The booster pump 16 is driven by a rotational driving force of a crankshaft (not shown). The engine 1 is naturally provided with a fuel supply system to the port injector 8 but is not shown for simplicity. The booster pump 16 corresponds to the fuel booster in the present invention.

  The engine 1 is provided with an ECU 20 that is a computer that controls the operating state of the engine 1. Measurement data from various sensors (not shown) is input to the ECU 20, and the operating state of the engine 1 and the driver's request are acquired based on the input data, and based on the in-cylinder direct injection injector 11 and the port injection injector 8. Signals for controlling fuel injection, ignition operation by the spark plug 12, and the like are output.

  Here, the fuel injection control of the engine 1 will be described.

  When the engine 1 is started, fuel is injected by the in-cylinder direct injection injector 11. This is referred to as “startup injection control”. After the start-up injection control is started, when the rotational speed of the engine 1 exceeds a predetermined threshold value Ne1, the routine proceeds to “post-startup injection control” in which fuel injection is performed by both the in-cylinder direct injection injector 11 and the port injection injector 8. .

  In the starting injection control, first, the fuel pressure supplied to the in-cylinder direct injection injector 11 is increased by the booster pump 16, and the fuel by the in-cylinder direct injection injector 11 is increased when the fuel pressure is increased to a predetermined reference value PR1. Injection is permitted.

  When the fuel injection by the in-cylinder direct injection injector 11 is permitted, the fuel injection by the in-cylinder direct injection injector 11 is performed while controlling the fuel pressure so that the fuel pressure becomes the predetermined target value PRreq1.

Fuel injection by the in-cylinder direct injection injector 11 is performed at a predetermined time Ainjd1 in the latter half of the compression stroke. The fuel injection timing Ainjd1 by the in-cylinder direct injection injector 11 is formed on the top surface of the piston 3 as the fuel spray injected from the in-cylinder direct injection injector 11 flies toward the piston 3 rising in the cylinder 2. The flight path along the lip portion 14 of the cavity 13 is changed to the direction of the spark plug 12 and is adapted to reach the spark plug 12.

  By injecting fuel in the latter half of the compression stroke by the in-cylinder direct injection injector 11, an air-fuel mixture having a high fuel concentration can be localized in the vicinity of the spark plug 12, and combustion by ignition by the spark plug 12 has good ignitability. Can be performed. Such a combustion mode is referred to as “stratified combustion”.

  In the post-startup injection control, the required injection amount calculated in accordance with conditions such as the intake air amount is divided into fuel injection by the port injection injector 8 and fuel injection by the in-cylinder direct injection injector 11 for injection. The ratio of the injection amount by the port injection injector 8 to the injection amount by the in-cylinder direct injection injector 11 in the required injection amount is determined according to the operating conditions of the engine 1 and the like.

  First, fuel is injected into the intake port 9 by the port injector 8, whereby an air-fuel mixture is formed in the intake port 9. This air-fuel mixture is sucked into the combustion chamber 18 as the intake valve 6 is opened.

  Next, fuel injection is performed in the combustion chamber 18 by the in-cylinder direct injection injector 11 at a predetermined time Ainjd1 in the latter half of the compression stroke. As in the case of the start-time injection control, fuel injection by the in-cylinder direct injection injector 11 is performed while controlling the fuel pressure so that the fuel pressure becomes a predetermined target value PRreq1. In the case of post-startup injection control, unlike in the case of start-up injection control, fuel injection by the in-cylinder direct injection injector 11 is performed in the air-fuel mixture atmosphere by the fuel injected by the port injector 8.

  Here, when some trouble occurs in the booster pump 16 and the fuel supplied to the in-cylinder direct injection injector 11 cannot be sufficiently boosted, the in-cylinder direct injection injector 11 uses a fuel pressure that does not satisfy the reference value PR1. The fuel injection from the in-cylinder direct injection injector 11 is performed at a fuel pressure less than the target value PRreq1. In this case, the fuel spray injected from the in-cylinder direct injection injector 11 is unlikely to reach the spark plug 12, so that a state in which an air-fuel mixture that can be ignited is localized in the vicinity of the spark plug 12 in the start-up injection control. It cannot be produced, and the start by stratified combustion cannot be performed well. For this reason, the startability may be deteriorated, and the combustion stability and exhaust performance may be deteriorated.

  With respect to this problem, in the system of the present embodiment, when it is determined that the boosting of the fuel by the booster pump 16 is poor in the start-up injection control, it is determined whether or not the rotational speed of the engine 1 exceeds the threshold value Ne1. Regardless, it was decided to switch from the starting injection control to the post-starting injection control.

  As a result, when the fuel pressure increase by the pressure boosting pump 16 is poor, fuel injection is immediately performed by both the in-cylinder direct injection injector 11 and the port injection injector 8, and therefore the in-cylinder direct injection with insufficient pressure increase is performed. A situation in which fuel injection is performed only by the injector 11 can be avoided, and deterioration of combustion stability and exhaust performance can be suppressed.

FIG. 2 shows (A) engine speed, (B) fuel pressure of in-cylinder direct injection injector 11, and (C) fuel injection of in-cylinder direct injection injector 11 when fuel injection control according to the present embodiment is performed. It is a time chart showing an example of the time change of quantity, and the fuel injection quantity of (D) port injection injector. In FIG. 2, PFI means fuel injection by the port injection injector 8, and DI means fuel injection by the in-cylinder direct injection injector 11. A solid line represents a case where the fuel pressure increase by the booster pump 16 is poor, and a broken line represents a normal case.

  When start-up injection control is started at time t0, the rotational speed is gradually increased by cranking, and the boost pump 16 is started to start boosting the fuel supplied to the in-cylinder direct injection injector 11. When the booster pump 16 is normal, the fuel pressure is increased to a pressure equal to or higher than the reference value PR1 at a time t1 when a predetermined time has elapsed after the start of boosting by the booster pump 16, as indicated by a broken line in FIG. In this case, as shown in FIG. 2 (C), the engine speed is raised to the threshold value Ne only by the compression stroke injection by the in-cylinder direct injection injector 11 (time t2), and thereafter shown in FIGS. 2 (C) and (D). Thus, the port injection by the port injection injector 8 and the compression stroke in-cylinder injection by the in-cylinder direct injection injector 11 are shifted to twice divided injection.

  On the other hand, as shown by the solid line in FIG. 2B, if the fuel pressure does not reach the reference value PR1 even at a time t1 when a predetermined time has elapsed after the start of boosting by the boosting pump 16, the boosting by the boosting pump 16 is poor. Judge that there is. In this case, for the cylinder 2 in which the position of the piston 3 is after the intake stroke at this time (time t1), the start-up injection control is performed, and only the compression stroke injection by the in-cylinder direct injection injector 11 is executed. And it shifts to the post-startup injection control from the next cycle, and the split injection by the port injector 8 and the in-cylinder direct injection injector 11 is performed twice. Further, for the cylinder 2 in which the position of the piston 3 is before the intake stroke at the time t1, the control immediately shifts to the post-startup injection control, and the split injection by the port injection injector 8 and the in-cylinder direct injection injector 11 is performed twice. Do.

  As shown in FIG. 2 (A), when it is determined that the boosting by the boosting pump 16 is poor, at the timing t2 ′ when the control is shifted to the post-startup injection control for all the cylinders 2, the engine speed is set to the threshold value Ne1. Although not reached, nevertheless, switching from the starting injection control to the post-starting injection control is executed. As a result, it is possible to avoid a situation in which fuel injection is performed only by the in-cylinder direct injection injector 11 in a state where the fuel pressure is insufficient, and it is possible to suitably suppress deterioration of startability, combustion stability, and exhaust performance. It becomes.

  FIG. 3 is a flowchart of the fuel injection control according to the present embodiment. The processing represented by this flowchart is repeatedly executed by the ECU 20 during operation of the engine 1.

  In step S101, the ECU 20 determines whether or not the engine 1 is being started. When it is determined that the engine is at the time of starting (Yes), the ECU 20 proceeds to the subsequent step S102 and starts boosting the fuel by the booster pump 16. When it is determined that it is not at the time of starting (No), the ECU 20 once exits the processing of this flowchart.

  In step S <b> 103, the ECU 20 determines whether or not a predetermined time or more has elapsed since the boosting by the booster pump 16 was started. Here, the predetermined time or more is determined based on the maximum value of the period during which the fuel pressure can be increased to a pressure equal to or higher than the reference value PR1 if the fuel pressure increase by the booster pump 16 is normal. If it is determined in step S103 that the predetermined time or more has not elapsed (No), the ECU 20 exits the processing of this flowchart. If it is determined in step S103 that a predetermined time or more has elapsed (Yes), the ECU 20 proceeds to the process of step S104.

In step S104, the ECU 20 determines whether or not the fuel pressure is greater than or equal to the reference value PR1. When the fuel pressure is greater than or equal to the reference value PR1 (Yes), the ECU 20 determines that the fuel pressure increase by the pressure increasing pump 16 is normal, proceeds to the process of step S105, and executes normal stratification start control. As described above, the normal stratified start-up control performs the start-up injection control until the engine speed reaches the threshold value Ne1, and performs only the compression stroke injection by the in-cylinder direct injection injector 11, and the engine speed is set to the threshold value Ne1. After reaching the above, after-starting injection control is performed, and switching is performed such that the port injection injector 8 and the in-cylinder direct injection injector 11 perform two injections.

  In step S104, when the fuel pressure is lower than the reference value PR1 (No), the ECU 20 determines that the fuel pressure increase by the booster pump 16 is poor, and proceeds to the early execution process of post-startup injection control after step S106.

  Specifically, in step S106, the ECU 20 determines whether or not the position of the piston 3 of each cylinder 2 is a crank angle after the intake stroke. For the cylinder 2 determined to be after the intake stroke, the process of step S107 is executed, and the single injection of only the in-cylinder direct injection injector 11 is executed (that is, start-up injection control is performed). This is because, as described above, in the cylinder 2 after the intake stroke, fuel cannot be supplied into the combustion chamber 18 by fuel injection by the port injector 8.

  On the other hand, for the cylinder 2 determined to be before the intake stroke, the process of step S108 is executed, and the two injections by the port injection injector 8 and the in-cylinder direct injection injector 11 are executed (that is, the post-start injection) Control).

  In the above embodiment, when it is determined that the boosting of the fuel by the booster pump 16 is poor, if the crank angle is after the intake stroke, only the in-cylinder direct injection injector 11 is injected once. However, when the crank angle is after the first half of the exhaust stroke, only the in-cylinder direct injection injector 11 may perform a single injection, or when the crank angle is after the second half of the intake stroke, The single injection of only the injector 11 may be performed, or when the crank angle is after the compression stroke, the single injection of only the in-cylinder direct injection injector 11 may be performed. These are determined based on the timing at which the air-fuel mixture can be preferably sucked into the combustion chamber 18 by performing the port injection by the port injection injector 8 before.

  Further, in step S103, instead of determining whether or not the boosting period by the booster pump 16 is greater than or equal to a predetermined value, it may be determined whether or not the number of times of boosting by the booster pump 16 is greater than or equal to a predetermined value. In this case, the determination reference value can also be determined based on the same concept as the determination reference value for the boost time.

  In the above-described embodiment, when it is determined that the boosting of the fuel by the booster pump 16 is poor in the start-up injection control, one injection by the in-cylinder direct injection injector 11 is performed by skipping one cylinder. good. In the case of an engine having two banks, only one cylinder in one bank performs a single injection by the in-cylinder direct injection injector 11, and the cylinder injection in the other bank stops the fuel injection by the in-cylinder direct injection injector 11. May be. In this way, by reducing the number of cylinders in which the direct injection by the in-cylinder direct injection injector 11 is performed in the start-up injection control, the burden of fuel injection by the in-cylinder direct injection injector 11 can be reduced, so the pressure increase is poor. In this case, the deterioration of combustion stability can be reduced.

DESCRIPTION OF SYMBOLS 1 Engine 2 Cylinder 3 Piston 4 Intake passage 5 Exhaust passage 6 Intake valve 7 Exhaust valve 8 Port injection injector 9 Intake port 10 Exhaust port 11 In-cylinder direct injection injector 12 Spark plug 13 Cavity 14 Lip part 15 Fuel tank 16 Booster pump 17 Fuel Supply path 18 Combustion chamber 20 ECU

Claims (1)

A port injection injector for injecting fuel into the intake passage of the internal combustion engine;
An in-cylinder direct injection injector for injecting fuel into a cylinder of the internal combustion engine;
A fuel booster for boosting the fuel supplied to the in-cylinder direct injection injector;
When the internal combustion engine is started, the fuel pressure booster boosts the fuel to a predetermined reference pressure or higher, and then performs fuel injection in the compression stroke by the in-cylinder direct injection injector, and starts the operation state of the internal combustion engine. Control means for performing post-startup injection control for performing two fuel injections, fuel injection by the port injection injector and fuel injection in a compression stroke by the in-cylinder direct injection injector, after satisfying a predetermined condition;
With
The control means determines that the boosting by the fuel boosting device is defective when the fuel pressure after a predetermined period of time has not reached the reference pressure after the boosting by the fuel boosting device is started in the start-up injection control. A fuel injection control device for a spark ignition type internal combustion engine, wherein the fuel injection control device is switched from the start-time injection control to the post-start-up injection control regardless of whether or not the operating state of the internal combustion engine satisfies the predetermined condition. .

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