JP2014134144A - Internal combustion engine fuel injection system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the air-fuel ratio of air-fuel mixture supplied into cylinders for combustion from becoming excessively high in an internal combustion engine including a cylinder injection valve and a port injection valve.SOLUTION: An injection volume of fuel from a cylinder injection valve and that of the fuel from a port injection valve are controlled so that a port injection rate that is a ratio of the injection volume of the fuel from the port injection valve to a sum of the injection volume of the fuel from the cylinder injection valve and that of the fuel from the port injection valve is equal to or lower than an air blow-by rate that is a ratio of a volume of a blow-by air during a valve overlap period to a volume of the air supplied into cylinders of an internal combustion engine.

Description

  The present invention relates to a fuel injection system for an internal combustion engine including an in-cylinder injection valve that directly injects fuel into a cylinder of the internal combustion engine and a port injection valve that injects fuel into an intake port of the internal combustion engine.

  2. Description of the Related Art Conventionally, an internal combustion engine that includes both a cylinder injection valve that directly injects fuel into a cylinder of the internal combustion engine and a port injection valve that injects fuel into an intake port of the internal combustion engine is known.

  Here, when the internal combustion engine has a supercharger, the intake pressure may be higher than the exhaust pressure. In this case, in the valve overlap period in which both the intake valve and the exhaust valve are opened in the internal combustion engine, the intake air (air) flowing into the cylinder from the intake port flows out to the exhaust port as it is. In other words, so-called “blow-through” occurs. At this time, if the fuel injected from the port injection valve exists in the vicinity of the intake valve in the intake port, the fuel also passes through the cylinder from the intake port together with air without being used for combustion in the cylinder. Blow through the exhaust port. Conventionally, various techniques have been developed in consideration of the fuel blow-through during the valve overlap period.

  In Patent Document 1, in an internal combustion engine having an in-cylinder injection valve and a port injection valve, it is determined that an unacceptable fuel blow-off occurs when the internal combustion engine is operated in a homogeneous combustion region. In this case, a technique is disclosed in which fuel injection from the port injection valve is prohibited and fuel is injected by the in-cylinder injection valve after the exhaust valve is closed.

  Patent Document 2 discloses a valve overlap period when an internal combustion engine provided with an in-cylinder injection valve and a port injection valve is operated in an operation region in which the intake pressure is higher than the exhaust pressure. A technique for injecting fuel from a port injection valve and adjusting the fuel injection amount so that the air-fuel ratio of the atmosphere around the three-way catalyst provided in the exhaust passage becomes the stoichiometric air-fuel ratio is disclosed. .

  Patent Document 3 discloses that in an internal combustion engine provided with an in-cylinder injection valve and a port injection valve, the amount of intake air and the ratio of blow-through air that does not contribute to combustion in the intake air supplied into the cylinder. The air-fuel ratio in the cylinder is calculated based on the ratio, the residual fuel amount that is the amount of fuel remaining in the cylinder among the fuel injected from the port injection valve, and the fuel injection amount from the in-cylinder injection valve. Also disclosed is a technique for controlling the air-fuel ratio in the cylinder to the target air-fuel ratio by controlling the fuel injection amount from at least one of the in-cylinder injection valve and the port injection valve.

JP 2005-133632 A JP 2008-101540 A JP 2006-177193 A JP 2007-332936 A

In an internal combustion engine equipped with an in-cylinder injection valve and a port injection valve, when air blown out during the valve overlap period, if the amount of fuel blown out with the air increases, it is used for combustion in the cylinder. The amount of fuel is reduced. For this reason, when the amount of blown-through fuel is excessively large, the air-fuel ratio of the air-fuel mixture provided for combustion in the cylinder is increased, which may cause a decrease in the output of the internal combustion engine or misfire.

  The present invention has been made in view of the above problems, and in an internal combustion engine having an in-cylinder injection valve and a port injection valve, the air-fuel ratio of the air-fuel mixture provided for combustion in the cylinder is The purpose is to suppress an excessive increase.

An internal combustion engine fuel injection system according to the present invention includes:
A fuel injection system for an internal combustion engine having a supercharger,
An in-cylinder injection valve that directly injects fuel into the cylinder of the internal combustion engine;
A port injection valve for injecting fuel into the intake port of the internal combustion engine;
An air blow-off rate calculating unit that calculates an air blow-off rate that is a ratio of the amount of air blown during the valve overlap period to the amount of air supplied into the cylinder of the internal combustion engine;
The cylinder so that the port injection rate, which is the ratio of the fuel injection amount from the port injection valve to the sum of the fuel injection amount from the cylinder injection valve and the fuel injection amount from the port injection valve, is equal to or less than the air blow-off rate. A control unit that controls an internal injection valve and a fuel injection amount from the port injection valve.

  When the port injection rate is higher than the air blow-through rate, the air-fuel ratio of the air-fuel mixture provided for combustion in the cylinder when all of the fuel injected from the port injection valve blows through the exhaust port during the valve overlap period Becomes excessively high. In the present invention, the fuel injection amount from the in-cylinder injection valve and the port injection valve is controlled by the control unit so that the port injection rate is equal to or less than the air blow-through rate. Thereby, it is possible to suppress an excessive increase in the air-fuel ratio of the air-fuel mixture provided for combustion in the cylinder.

  ADVANTAGE OF THE INVENTION According to this invention, in the internal combustion engine provided with the cylinder injection valve and the port injection valve, it can suppress that the air fuel ratio of the air-fuel mixture provided for combustion in a cylinder becomes high too much.

1 is a diagram illustrating a schematic configuration of an internal combustion engine and an intake / exhaust system thereof according to Embodiment 1. FIG. 3 is a flowchart illustrating a flow of fuel injection control according to the first embodiment. 6 is a flowchart illustrating a flow of fuel injection control according to the second embodiment.

  Hereinafter, specific embodiments of the present invention will be described with reference to the drawings. The dimensions, materials, shapes, relative arrangements, and the like of the components described in the present embodiment are not intended to limit the technical scope of the invention to those unless otherwise specified.

<Example 1>
(Outline configuration)
FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine and its intake / exhaust system according to the present embodiment. The internal combustion engine 1 is a gasoline engine for driving a vehicle having four cylinders 2.

  A piston 3 is slidably provided in the cylinder 2. An intake port 4 and an exhaust port 5 are connected to the combustion chamber in the upper part of the cylinder 2. The openings of the intake port 4 and the exhaust port 5 to the combustion chamber are opened and closed by an intake valve 6 and an exhaust valve 7, respectively.

Further, the internal combustion engine 1 is provided with a port injection valve 10, an in-cylinder injection valve 11, and a spark plug 12. The port injection valve 10 is a fuel injection valve that injects fuel into the intake port 4. The in-cylinder injection valve 11 is a fuel injection valve that directly injects fuel into the cylinder 2. The spark plug 12 ignites the air-fuel mixture in the combustion chamber in the cylinder 2.

  The intake port 4 is connected to the intake passage 8, and the exhaust port 5 is connected to the exhaust passage 9. A compressor housing 19 a of a turbocharger 19 is provided in the intake passage 8. A turbine housing 19b of a turbocharger 19 is provided in the exhaust passage 9. Instead of the turbocharger 19, a mechanical supercharger driven by the crankshaft of the internal combustion engine 1 may be used.

  An air flow meter 13 is provided in the intake passage 8 upstream of the compressor housing 19a. A throttle valve 14 is provided in the intake passage 8 downstream of the compressor housing 19a. The air flow meter 13 detects the intake air amount of the internal combustion engine 1. The throttle valve 14 adjusts the flow rate of the intake air flowing through the intake passage 8 by changing the cross-sectional area of the intake passage 8.

  An intake pressure sensor 15 is provided downstream of the throttle valve 14 in the intake passage 8. The intake pressure sensor 15 detects the pressure (intake pressure) in the intake passage 8.

  An exhaust pressure sensor 16 and an air-fuel ratio sensor 17 are provided upstream of the turbine housing 19 b in the exhaust passage 9. The exhaust pressure sensor 16 detects the pressure (exhaust pressure) in the exhaust passage 9. The air fuel ratio sensor 17 detects the air fuel ratio of the exhaust. A three-way catalyst 18 is provided as an exhaust purification catalyst downstream of the turbine housing 19b in the exhaust passage 9. In addition to the three-way catalyst 18, or in addition to the three-way catalyst 18, other catalysts appropriately selected for exhaust purification (for example, an oxidation catalyst, an occlusion reduction type NOx catalyst, a selective reduction type NOx catalyst, etc.) May be provided.

  The internal combustion engine 1 according to this embodiment is provided with an electronic control unit (ECU) 20 for controlling the internal combustion engine 1. Various sensors such as an air flow meter 13, an intake pressure sensor 15, an exhaust pressure sensor 16, an air-fuel ratio sensor 17, a crank angle sensor 21, and an accelerator opening sensor 22 are electrically connected to the ECU 20. These output signals are input to the ECU 20.

  The crank angle sensor 21 is a sensor that detects the crank angle of the internal combustion engine 1. The accelerator opening sensor 22 is a sensor that detects the accelerator opening of a vehicle on which the internal combustion engine 1 is mounted. The ECU 20 calculates the engine speed of the internal combustion engine 1 based on the detection value of the crank angle sensor 21. Further, the ECU 20 calculates the engine load of the internal combustion engine 1 based on the detection value of the accelerator opening sensor 22.

  The ECU 20 is electrically connected to a port injection valve 10, an in-cylinder injection valve 11, a spark plug 12, a throttle valve 14, and the like. These devices are controlled by the ECU 20.

[Fuel injection control]
In this embodiment, the fuel injection amount from the port injection valve 10 (hereinafter also referred to as port injection amount) and the fuel injection amount from the in-cylinder injection valve 11 (hereinafter also referred to as in-cylinder injection amount). ) And the intake air amount are controlled to be the target air-fuel ratio (for example, the theoretical air-fuel ratio), the port injection amount, the in-cylinder injection amount, and the intake air amount.

The ratio between the port injection amount and the in-cylinder injection amount is basically determined based on the operating state of the internal combustion engine 1. Specifically, a reference value of the port injection rate, which is a ratio of the port injection amount to the sum of the port injection amount and the in-cylinder injection amount, is calculated based on the operating state of the internal combustion engine 1.

  Fuel is injected from the port injection valve 10 toward the intake valve 6 in the intake port 4. When the intake valve 6 is opened, the fuel existing in the vicinity of the intake valve 6 in the intake port 4 flows into the cylinder 2 together with the intake air.

  Further, in the internal combustion engine 1, a valve overlap period that is a period in which both the intake valve 6 and the exhaust valve 7 are opened occurs. When the valve overlap period occurs when the intake pressure is higher than the exhaust pressure by being supercharged by the turbocharger 19, the intake air (air) flowing into the cylinder 2 from the intake port 4 is exhausted as it is. The air flowing out to the port 5 is blown out. At this time, if the fuel injected from the port injection valve 10 exists in the vicinity of the intake valve 6 in the intake port 4, the fuel is also supplied from the intake port 4 together with the air without being used for combustion in the cylinder 2. It passes through the cylinder 2 and blows through the exhaust port 5.

  Here, the ratio of the amount of air blown during the valve overlap period to the amount of air supplied into the cylinder 2 of the internal combustion engine 1 is defined as the air blow-off rate. Further, when all of the fuel injected from the port injection valve 10 has blown through the exhaust port 5 during the valve overlap period, the amount of blown fuel during the valve overlap period with respect to the sum of the port injection amount and the in-cylinder injection amount The ratio is the same as the port injection rate.

  Therefore, if the port injection rate is higher than the air blow-off rate, the amount of air remaining in the cylinder 2 (inside the cylinder 2) when all of the fuel injected from the port injection valve 10 blows through the exhaust port 5 during the valve overlap period. The amount of fuel in the cylinder 2 (the amount of fuel injected from the in-cylinder injection valve 11) is smaller than the total amount of air supplied to the engine (subtracting the amount of blown air during the valve overlap period). That is, the air-fuel ratio of the air-fuel mixture used for combustion in the cylinder 2 becomes excessively high. As a result, the output of the internal combustion engine 1 may be reduced or misfire may occur.

  Therefore, in this embodiment, the port injection amount and the in-cylinder injection amount are controlled so that the port injection rate is equal to or less than the air blow-through rate. Hereinafter, the flow of the fuel injection control according to the present embodiment will be described with reference to FIG. FIG. 2 is a flowchart showing a flow of fuel injection control according to the present embodiment. This flow is stored in advance in the ECU 20 and is repeatedly executed by the ECU 20.

  In this flow, first, in step S101, the air blow-through rate SCA in the valve overlap period is calculated. The air blow-through rate SCA can be calculated based on, for example, the difference between the intake pressure detected by the intake pressure sensor 15 and the exhaust pressure detected by the exhaust pressure sensor 16 and the engine speed of the internal combustion engine 1. The relationship between the difference between the intake pressure and the exhaust pressure, the engine speed of the internal combustion engine 1 and the air blow-off rate can be obtained based on experiments or the like, and is stored in advance in the ECU 20 as a map or a function.

  Further, when an exhaust flow sensor for detecting the exhaust flow rate is provided upstream of the turbine housing 19b in the exhaust passage 9, it is detected by the intake air amount detected by the air flow meter 13 and the exhaust flow sensor during the valve overlap period. The air blow-through rate SCA can also be calculated based on the flow rate of exhaust gas.

  Next, in step S102, a reference value KPFIbase of the port injection rate is calculated based on the operating state of the internal combustion engine 1. The relationship between the operating state of the internal combustion engine 1 and the reference value KPFIbase of the port injection rate is determined based on experiments or the like, and is stored in advance in the ECU 20 as a map or a function.

  Next, in step S103, it is determined whether or not the reference value KPFIbase of the port injection rate is larger than the air blow-through rate SCA. If a negative determination is made in step S103, that is, if the port injection rate reference value KPFIbase is equal to or less than the air blow-off rate SCA, then in step S105, the port injection rate KPFI is set to the reference value KPFIbase. Thus, the port injection amount and the in-cylinder injection amount are controlled so that the port injection rate becomes the reference value KPFIbase.

  On the other hand, if an affirmative determination is made in step S103, then in step S104, the port injection rate KPFI is set to the same value as the air blow-through rate SCA. Thus, the port injection amount and the in-cylinder injection amount are controlled so that the port injection rate becomes the same value as the air blow-through rate SCA.

  According to the present embodiment, the port injection amount and the in-cylinder injection amount are controlled so that the port injection rate is equal to or less than the air blow-through rate. Thereby, it can suppress that the air fuel ratio of the air-fuel mixture provided for combustion in the cylinder 2 becomes excessively high. As a result, a decrease in the output of the internal combustion engine 1 and the occurrence of misfire can be suppressed.

<Example 2>
The schematic configuration of the internal combustion engine and its intake / exhaust system according to this embodiment is the same as that of the first embodiment. Hereinafter, the fuel injection control according to the present embodiment will be described focusing on differences from the fuel injection control according to the first embodiment.

  FIG. 3 is a flowchart showing a flow of fuel injection control according to the present embodiment. This flow is stored in advance in the ECU 20 and is repeatedly executed by the ECU 20. In the present flow, steps that execute the same processing as the flow shown in FIG. 2 are denoted by the same reference numerals as those in FIG.

  Also in this flow, when a negative determination is made in step S103, that is, when the reference value KPFIbase of the port injection rate is equal to or less than the air blow-off rate SCA, the port injection rate KPFI is set to the reference value KPFIbase.

  On the other hand, if an affirmative determination is made in step S103, the process of step S204 is then executed. In step S204, the start timing of fuel injection from the port injection valve 10 is set after the closing timing of the exhaust valve 7. By making the start timing of fuel injection from the port injection valve 10 after the closing timing of the exhaust valve 7, it is possible to suppress the occurrence of blow-through of the fuel injected from the port injection valve 10.

  Next, in step S205, the end timing of fuel injection from the port injection valve 10 when the port injection rate KPFI is set to the reference value KPFIbase is calculated. The end timing of fuel injection from the port injection valve 10 in this case can be calculated based on the port injection amount when the port injection rate KPFI is set to the reference value KPFIbase. That is, as the port injection amount increases, the end timing of fuel injection from the port injection valve 10 is delayed.

  Next, in step S206, it is determined whether or not the end timing of fuel injection from the port injector 10 calculated in step S205 is before the closing timing of the intake valve 6. If the determination in step S206 is affirmative, even if the port injection rate KPFI is set to the reference value KPFIbase, before the intake valve 6 closes all of the fuel to be injected from the port injection valve 10, the port injection valve 10 Can be injected from. Therefore, in this case, in step S105, the port injection rate KPFI is set to the reference value KPFIbase.

  On the other hand, if a negative determination is made in step S206, if the port injection rate KPFI is set to the reference value KPFIbase, before the intake valve 6 closes all of the fuel to be injected from the port injector 10, the port injector 10 Can not be injected from. In this case, therefore, in step S207, the target port injection rate KPFI1 is calculated so that the port injection amount is such that the fuel injection from the port injection valve 10 ends at the closing timing of the intake valve 6. . The target port injection rate KPFI1 is smaller than the reference value KPFIbase.

  Next, in step S208, the port injection rate KPFI is set to the target port injection rate KPFI1.

  According to the present embodiment, when the reference value of the port injection rate is higher than the air blow-off rate, the execution timing of the port injection is controlled between when the exhaust valve 7 is closed and when the intake valve 6 is closed. The Therefore, the fuel injected from the port injection valve 10 is suppressed from blowing through during the valve overlap period. Also by this, it is possible to suppress an excessive increase in the air-fuel ratio of the air-fuel mixture used for combustion in the cylinder 2 as in the case where the fuel injection control according to the first embodiment is executed.

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 2 ... Cylinder 6 ... Intake valve 7 ... Exhaust valve 10 ... Port injection valve 11 ... In-cylinder injection valve 13 ... Air flow meter 14 ... Throttle valve 15 ... Atmospheric pressure sensor 19 ・ ・ Turbocharger 19a ・ Compressor housing 19b ・ Turbine housing 20 ・ ・ ECU
21 ・ ・ Crank angle sensor 22 ・ ・ Accelerator opening sensor

Claims (1)

A fuel injection system for an internal combustion engine having a supercharger,
An in-cylinder injection valve that directly injects fuel into the cylinder of the internal combustion engine;
A port injection valve for injecting fuel into the intake port of the internal combustion engine;
An air blow-off rate calculating unit that calculates an air blow-off rate that is a ratio of the amount of air blown during the valve overlap period to the amount of air supplied into the cylinder of the internal combustion engine;
The cylinder so that the port injection rate, which is the ratio of the fuel injection amount from the port injection valve to the sum of the fuel injection amount from the cylinder injection valve and the fuel injection amount from the port injection valve, is equal to or less than the air blow-off rate. A fuel injection system for an internal combustion engine, comprising: an internal injection valve; and a control unit that controls a fuel injection amount from the port injection valve.

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