JP2000186597A - Direct injection type internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a direct injection type internal combustion engine which can suppress the occurrence of difference between a target air-fuel ratio and an actual air-fuel ratio caused by adherence of fuel to a cylinder wall face or the like. SOLUTION: In this direct injection type internal combustion engine, injection finish timing of an injection valve is corrected on a retard angle side (for example, up to about 250 deg. BTDC) by an injection timing correction means when a temperature of an engine detected by a temperature detection means is low. Accordingly, a fuel adherence ratio to an upper face of a piston and a cylinder wall is lowered, and a fuel injection amount is corrected by an amount according to the fuel adherence ratio.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a direct injection internal combustion engine, and more particularly, to a fuel injection control technique for performing an intake stroke injection in a direct injection internal combustion engine.

[0002]

2. Related Background Art In recent years, in order to further improve fuel efficiency, fuel is directly injected into a combustion chamber, and switching between stratified combustion (compression stroke injection) and uniform combustion (intake stroke injection) is performed according to the engine load state. In-cylinder injection type internal combustion engines have been put to practical use. In this type of internal combustion engine, for example, Japanese Patent Laid-Open No. 10-1
As disclosed in Japanese Patent No. 76564, the amount of fuel injected from the injection valve is determined according to a sensor output for detecting an operating state.

[0003]

However, in general, the fuel injected from the injection valve of this type of internal combustion engine is set at a high pressure even when performing the intake stroke injection, and the fuel is directly combusted. When the fuel is injected into the chamber, the fuel adheres to the upper surface of the piston or the wall surface of the cylinder depending on the injection timing and mixes into, for example, oil, a carbon layer on the surface, or clevis. Therefore, there is no particular problem if the engine temperature is already high and the mixed fuel is immediately vaporized.For example, at the time of a cold start, the mixed fuel contributes to combustion with a first-order delay. There is a problem that a difference occurs between the target air-fuel ratio and the actual air-fuel ratio due to the loss or the loss.

[0004] When the difference between the target air-fuel ratio and the actual air-fuel ratio is generated, for example, exhaust gas characteristics are degraded during idling operation immediately after a cold start, and sufficient acceleration performance is obtained at the start immediately after the start. This is not preferable because of problems such as not being able to be performed. The present invention has been made to solve such a problem, and an object thereof is to provide a cylinder capable of suppressing the occurrence of a difference between a target air-fuel ratio and an actual air-fuel ratio due to fuel adhesion to a cylinder wall or the like. An internal injection type internal combustion engine is provided.

[0005]

In order to achieve the above object, according to the first aspect of the present invention, in an in-cylinder injection type internal combustion engine, an engine temperature detected by a temperature detection means by an injection timing correction means is low. At this time, the injection end timing of the injection valve is retarded. For example, when the target air-fuel ratio is switched to the rich air-fuel ratio when the engine temperature is low, or when the intake air amount is increased and the injection amount is increased, the injection end timing is appropriately delayed on the retard side. And it becomes difficult for fuel to adhere to the piston upper surface and the cylinder wall surface.
The first-order lag of combustion due to the attached fuel is suitably suppressed, and the air-fuel ratio control is optimized. As a result, deterioration of exhaust gas characteristics at the time of a cold start and poor acceleration at the time of starting immediately after the start are prevented.

[0006] Since an appropriate injection end timing varies depending on the fuel property, that is, volatility (heavy or light), it is preferable to change the correction amount of the injection end timing according to the fuel property. According to the second aspect of the present invention, in addition to the retard correction of the injection end timing, the injection amount correction means is configured to increase and correct the fuel injection amount from the injection valve when the engine temperature is low.

As a result, the amount of fuel is increased by the amount of the adhering fuel, the first-order lag of combustion by the adhering fuel is more suitably suppressed, and the exhaust gas characteristics at the time of a cold start are deteriorated, Acceleration failure at the time of starting is reliably prevented.

[0008]

Embodiments of the present invention will be described below with reference to the accompanying drawings. Referring to FIG. 1, there is shown a schematic configuration diagram of a direct injection internal combustion engine of the present invention mounted on a vehicle, and the configuration of the direct injection internal combustion engine of the present invention will be described below with reference to FIG. .

Engine body (hereinafter simply referred to as engine) 1
Performs, for example, fuel injection in the intake stroke (intake stroke injection mode) in which uniform combustion is performed by switching the fuel injection mode (operation mode) or fuel injection in the compression stroke (compression stroke injection mode) in which stratified combustion is performed. It is a possible in-cylinder injection spark ignition in-line four-cylinder gasoline engine. The in-cylinder injection type engine 1 can be easily operated at a stoichiometric air-fuel ratio (stoichiometric ratio), at a rich air-fuel ratio (rich air-fuel ratio operation), or at a lean air-fuel ratio (lean air-fuel ratio). In particular, in the compression stroke injection mode, it is possible to operate at a super lean air-fuel ratio.

As shown in FIG. 1, an electromagnetic fuel injection valve 6 is attached to a cylinder head 2 of an engine 1 together with a spark plug 4 for each cylinder, whereby fuel is injected into a combustion chamber 8. Direct injection is possible. A fuel supply device (both not shown) having a fuel tank is connected to the fuel injection valve 6 via a fuel pipe. More specifically, the fuel supply device is provided with a low-pressure fuel pump and a high-pressure fuel pump, whereby the fuel in the fuel tank is supplied to the fuel injection valve 6 at a low fuel pressure or a high fuel pressure. From the fuel injection valve 6 into the combustion chamber at a desired fuel pressure. At this time, the fuel injection amount depends on the fuel discharge pressure of the high-pressure fuel pump and the valve opening time of the fuel injection valve 6,
That is, it is determined from the fuel injection time.

An intake port is formed in the cylinder head 2 in a substantially upright direction for each cylinder, and one end of an intake manifold 10 is connected to communicate with each intake port. A throttle valve 11 is connected to the other end of the intake manifold 10. The throttle valve 11 is provided with a throttle sensor 11a for detecting a throttle opening θth.

An exhaust port is formed in the cylinder head 2 in a substantially horizontal direction for each cylinder, and one end of an exhaust manifold 12 is connected to communicate with each exhaust port. A piston 7 is slidably fitted in the cylinder portion of the cylinder block 3 of the engine 1, and the piston 7 is connected to a crankshaft (not shown) via a connecting rod.

That is, a combustion chamber 8 is formed surrounded by the lower surface 2a of the cylinder head 2, the upper surface 7a of the piston 7, and the cylinder wall 3a. In the figure, reference numeral 20 denotes a crank angle sensor for detecting a crank angle, and the crank angle sensor 20 is also capable of detecting the engine rotation speed Ne. Reference numeral 22 denotes a coolant temperature sensor (temperature detecting means) for detecting the coolant temperature of the engine 1, that is, the engine temperature. Further, reference numeral 24 denotes a knock sensor that detects knocking by detecting abnormal vibration of the engine 1, and the fuel property (heavy or light) is determined based on the detection information of the knock sensor 24.

The in-cylinder injection type engine 1 is already known, and the detailed description of its configuration is omitted here. The exhaust pipe 12 is provided in the exhaust manifold 12.
The exhaust pipe 14 is connected to a muffler (not shown) through an exhaust purification catalyst device (three-way catalyst or the like) 30.
Is connected.

The exhaust manifold 12 is provided with a linear O ₂ sensor 26. Linear O ₂ sensor 2
Numeral 6 detects the amount of oxygen as a value correlating with the concentration of NOx in the exhaust gas, which makes it possible to detect the actual air-fuel ratio (actual A / F) satisfactorily. further,
I / O device, storage device (ROM, RAM, nonvolatile RA
M), an electronic control unit (ECU) 40 including a central processing unit (CPU), a timer counter, and the like. The ECU 40 is used to control the direct injection type internal combustion engine including the engine 1 according to the present invention. Comprehensive control is performed. On the input side of the ECU 40, the above-described throttle sensor 11a, crank angle sensor 20, water temperature sensor 2
2, various sensors such as a knock sensor 24 and a linear O ₂ sensor 26 are connected, and detection information from these sensors is input.

On the other hand, the output side of the ECU 40 is connected to the above-described ignition plug 4, the fuel injection valve 6, and the like via an ignition coil. Optimum values such as the fuel injection amount, the fuel injection timing, and the ignition timing calculated based on the detection information are output. As a result, an appropriate amount of fuel is injected from the fuel injection valve 6 at an appropriate timing, and ignition is performed by the spark plug 4 at an appropriate timing.

Actually, the ECU 40 calculates the target average effective pressure Pe corresponding to the engine load based on the throttle opening information θth from the throttle sensor 11a and the engine rotation speed information Ne from the crank angle sensor 9. And a map (not shown) corresponding to the target average effective pressure Pe and the engine speed information Ne.
The fuel injection mode is set more. For example, when the target average effective pressure Pe and the engine rotation speed Ne are both small, the fuel injection mode is set to the compression stroke injection mode, and the fuel is injected in the compression stroke to perform stratified combustion, while the target average effective pressure Pe is decreased. When the engine speed increases or the engine speed Ne increases, the fuel injection mode is set to the intake stroke injection mode, and the fuel is injected during the intake stroke to perform uniform combustion. The intake stroke injection mode includes an intake lean mode that is a lean air-fuel ratio, a stoichiometric feedback mode that is a stoichiometric air-fuel ratio (stoichio), and
There is an open loop mode with a rich air-fuel ratio.

Then, a target air-fuel ratio (target A / A) is set as a control target based on the target average effective pressure Pe and the engine speed Ne.
F) is set, and the appropriate amount of fuel injection is set to the target A /
It is determined based on F (injection amount control means). When the target average effective pressure Pe and the engine rotation speed Ne are set, the fuel injection end timing is set accordingly. When the fuel injection amount and the injection end time are set as described above,
First, based on the set fuel injection amount, the fuel injection pressure is determined from the fuel discharge pressure of the high-pressure fuel pump and the relationship between the fuel injection time and the fuel injection amount, and the set injection end timing and the fuel injection time are determined. Injection time and fuel injection timing,
That is, the injection start timing is determined (injection timing control means).

When the target average effective pressure Pe and the engine speed Ne are determined, usually, the fuel injection end timing, that is, the fuel injection timing is uniquely set. However, in the intake stroke injection mode, actually, the fuel injected from the fuel injection valve 6 adheres to the upper surface 7a of the piston 7 or the wall surface of the cylinder wall 3a depending on the injection timing and mixes with, for example, lubricating oil. As described above, the attached fuel has a first-order lag response and contributes to combustion. When the first-order lag response occurs, the target air-fuel ratio is shifted and the combustion becomes unstable, which is not preferable.

In particular, during idling immediately after a cold start, the intake stroke injection mode is selected in order to stabilize the combustion. However, in practice, the first-order lag response of the attached fuel becomes remarkable and the target air-fuel ratio , And combustion becomes unstable. When the first-order lag response becomes remarkable and the target air-fuel ratio largely shifts in this way, the exhaust purification catalyst device 30 is not sufficiently activated immediately after the cold start.
The deviation of the air-fuel ratio adversely affects the exhaust gas characteristics, which is not preferable.

Therefore, in the present invention, the first-order lag response due to the attached fuel is suppressed. Hereinafter, the operation of the in-cylinder injection type internal combustion engine of the present invention, that is, the primary fuel in the intake stroke injection mode, will be described. A method for suppressing the delay response will be described. Referring to FIG. 2, immediately after a cold start with a low engine temperature, an idling operation state (for example, the engine rotation speed N
e is about 1500 rpm), the fuel injection mode is switched from the stoichiometric feedback mode to the open loop mode, for example, and the target A / F is set to the value A.
When the fuel injection amount is increased by switching from F1 (for example, stoichiometric air-fuel ratio 14.7) to value AF2 (for example, rich air-fuel ratio 11) and the actual air-fuel ratio (actual A / F The change of the actual A / F when the actual A / F is switched with good response to the switching of the target A / F without a combustion delay is shown in FIG. As shown by the broken line, the fuel is
Or when it adheres to the wall surface of the cylinder wall 3a,
The combustion responds with a first-order delay with a combustion delay ΔB.

However, as a result of a recent experiment, it has been found that in such a first-order lag response, the amount of fuel adhering to the upper surface 7a of the piston 7 and the wall surface of the cylinder wall 3a is greatly influenced by the degree of the lag. Have been. Further, referring to FIG. 3, when the engine temperature is low, the target A / F
The relationship (experimental data) between the fuel injection end timing and the fuel adhesion rate in the first cycle immediately after the switching of the fuel is shown by fuel properties (heavy fuel “●” and light fuel “▲”). For reference, the case where the engine temperature is high is indicated by a circle and a triangle, respectively.
It has been found that when the engine temperature is low, the fuel adhesion rate (the amount of adhesion) greatly depends on the fuel injection end timing.

That is, there is an injection end timing at which the fuel adhesion rate (adhesion amount) becomes the minimum on the retard side from a preset reference injection timing (for example, 320 ° BTDC). This is probably because the lower the piston 7 moves away from the fuel injection valve 6, the smaller the amount of fuel adhering to the upper surface 7 a. Note that the fuel adhesion rate increases again on the more retarded side than the injection end timing at which the fuel adhesion rate becomes minimum, but this is due to the cylinder wall 3a exposed to fuel when the piston 7 descends. It is considered that the area increases, and the fuel easily adheres to the cylinder wall 3a.

It can also be seen from the figure that the lowest injection end timing is affected by the fuel properties. this is,
The less volatile heavy fuel “●”, the more piston 7
Is likely to adhere to the upper surface 7a and the cylinder wall 3a. Therefore, in the present invention, the water temperature sensor 2
When the fuel injection amount increases in a case where the engine temperature detected by step 2 is low, first, based on the data in FIG. 3, the fuel injection end timing is determined according to the fuel property by the fuel adhesion rate (adhesion amount). The retard correction is performed at the minimum injection end timing (injection timing correction means).

That is, based on the information from the knock sensor 24, when the fuel is light “▲”, the injection end timing is set to the injection at which the fuel adhesion rate becomes the minimum from the reference injection timing (for example, 320 ° BTDC). End time (for example, 250 ° BTDC
), And when the fuel is heavy “●”, the injection end timing is also retarded to the injection end timing (for example, about 280 ° BTDC) at which the fuel adhesion rate becomes minimum. To do. FIG. 3 shows exemplary data, and the injection end timing at which the fuel adhesion rate becomes the minimum is actually obtained by interpolation processing based on the exemplary data in accordance with the engine temperature and the fuel property.

However, in practice, even if the injection end timing is retarded in this way, the fuel adhesion rate does not completely become 0% as shown in FIG. A first-order lag response will occur. Therefore, in the present invention, in addition to the retard of the injection end timing, a first-order lag correction is further performed. Specifically, the fuel injection amount is corrected for the first-order lag in each calculation cycle of the fuel injection amount based on the following equation (1) (injection amount correction means).

Q = Qbase + ΔQ / K (1) where Q is the fuel injection amount after the primary delay correction, and Qba
se is the fuel injection amount set based on the intake air amount and the target A / F, ΔQ is the adhesion amount, and K is the combustion rate {1- (fuel adhesion rate)}. Note that the fuel adhesion rate is obtained from FIG. 3 described above, and the adhesion amount ΔQ is easily calculated by the product of the fuel adhesion rate and Qbase. However, the adhesion amount ΔQ gradually decreases as the combustion is promoted with the lapse of time. Therefore, after the start of the first-order lag response (first cycle), the following equation is obtained.
It is calculated from (2).

ΔQ (n) = C · ΔQ (n−1) + (1−C) (1−K) Qbase (2) where C is a degree of decrease, that is, a time constant indicating a time required for decrease. It is. It is known that, as a phenomenon, the time constant C increases as the cooling water temperature, that is, the engine temperature decreases. Therefore, the time constant C is appropriately read from the map showing the relationship between the cooling water temperature and the time constant C shown in FIG.

That is, FIG. 4 shows a conceptual diagram of the first-order lag correction. As described above, in the first-order lag correction, the fuel injection amount Qbase set based on the target A / F is shown.
Is added to the correction amount ΔQ / K calculated for each calculation cycle. When such correction is performed, (Qbase + Δ
When only Q / K) of fuel is injected, the fuel amount (combustion amount) actually contributing to combustion always coincides with the fuel injection amount Qbase, thereby suppressing the first-order lag. . That is, by the primary delay correction, the combustion delay ΔB as shown in FIG. 2 is eliminated, the linear O ₂ sensor 26
As shown by the broken line in the figure, the actual A / F detected by
The response changes in response to the switching of the target A / F.

[0030] Thus, acceleration running from idling operation under low engine temperature conditions can be smoothly performed without insufficient output, and the occupant of the vehicle is preferably prevented from feeling uncomfortable. Further, since the first-order lag correction is executed at the time of idling immediately after the cold start, deterioration of the exhaust gas characteristics is suitably prevented. By the way, in the above embodiment,
When the target A / F is switched to the rich air-fuel ratio side when the engine temperature is low and the engine speed Ne is low, first, the injection end timing is delayed until the injection end timing at which the fuel adhesion rate becomes the minimum. The angle correction is performed, and then the first-order lag correction is further performed. However, in the case where the injection end time cannot be retarded to the injection end time when the fuel adhesion rate becomes the minimum due to factors such as the operating condition of the engine 1. Even so,
Alternatively, even in the case where the fuel injection rate is retarded beyond the injection end timing at which the fuel adhesion rate becomes the minimum, the primary delay correction can be easily performed based on FIG. That is, FIG.
Since the fuel adhesion rate corresponding to the injection end timing can be read based on the fuel adhesion rate, the above equation (1) is calculated based on the fuel adhesion rate.
Thus, the fuel injection amount after the first-order lag correction can be easily obtained.

In other words, even when the above-described retardation correction of the injection end timing is not always appropriate, the first-order lag correction can be surely performed, whereby the acceleration from the idling operation under the condition where the engine temperature is low can be performed. The traveling can be smoothly performed at all times with good response, and the occupant of the vehicle can be reliably prevented from feeling uncomfortable.

In the above embodiment, when the engine temperature is low and the engine speed Ne is low, the target A
Although the case where / F is switched to the rich air-fuel ratio side to increase the amount of fuel has been described, when the target A / F is switched from the rich air-fuel ratio side to the stoichiometric or lean air-fuel ratio side to reduce the fuel, Regardless of the decrease, the fuel adhering to the upper surface 7a of the piston 7 and the cylinder wall 3a is continuously burned by the first-order lag response, so that the first-order lag correction can be performed in the same manner as described above. In this case, the fuel injection amount after the first-order lag correction is calculated by the following equation (3) in which the sign on the right side of the above equation (1) is changed.

Q = Qbase−ΔQ / K (3) As a result, during deceleration running under a low engine temperature, the primary delay of combustion is suppressed, and the vehicle is inadvertently propelled. Therefore, the occupant of the vehicle can be prevented from feeling uncomfortable. In the above embodiment, the case where the target A / F is switched to the rich air-fuel ratio side to increase the fuel injection amount has been described as an example. However, even if the target A / F is constant, the intake air amount increases. Therefore, the correction (first-order lag correction) of the present invention may be applied when the fuel injection amount increases with such an increase in the intake air amount.

In the above embodiment, the cooling water temperature from the water temperature sensor 22 is used as the engine temperature. However, the temperature detecting means of the present invention is not particularly limited to the water temperature sensor 22, It is only necessary to detect or estimate the surface temperature of the intake / exhaust valve 7a and the cylinder wall 3a. For example, the temperature of the intake / exhaust valve close to these temperatures and capable of detecting the temperature is detected (temperature detecting means). It may be used as the engine temperature.

[0035]

As described above in detail, according to the in-cylinder injection type internal combustion engine of the first aspect of the present invention, when the engine temperature is low, the injection end timing can be appropriately retarded. By correcting the end time, fuel adhesion to the piston upper surface and cylinder wall surface is suppressed, and accurate air-fuel ratio control is realized.
Deterioration of exhaust gas characteristics during cold start and poor acceleration at start immediately after start can be prevented.

Further, according to the in-cylinder injection type internal combustion engine of the present invention, in addition to the retard correction of the injection end timing, the amount of fuel is increased by the amount of the attached fuel, thereby achieving more accurate air-fuel ratio control. It is possible to surely prevent deterioration of exhaust gas characteristics at the time of cold start and poor acceleration at the time of starting immediately after the start.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a direct injection internal combustion engine of the present invention.

FIG. 2 shows that an acceleration operation is performed from an idle operation state immediately after a cold start with a low engine temperature, and a target A / F is set to a value AF1.
FIG. 7 is a diagram showing a change timing of a fuel injection amount and a change of an actual air-fuel ratio (actual A / F) when the value is switched from a stoichiometric air-fuel ratio (eg, 14.7) to a value AF2 (eg, a rich air-fuel ratio of 11). is there.

FIG. 3 is a diagram showing a relationship (experimental data) between the fuel injection end timing and the fuel adhesion rate in the first cycle immediately after the target A / F is switched when the engine temperature is low.

FIG. 4 is a conceptual diagram of first-order lag correction.

FIG. 5 is a map showing a relationship between a cooling water temperature and a time constant C.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Engine (in-cylinder injection internal combustion engine) 2 Cylinder head 3 Cylinder block 3a Cylinder wall 4 Spark plug 6 Fuel injection valve 7 Piston 7a Upper surface 8 Combustion chamber 20 Crank angle sensor 22 Water temperature sensor (temperature detecting means) 24 Knock sensor 26 Linear O ₂ sensor 40 Electronic control unit (ECU)

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) F02D 45/00 312 F02D 45/00 312Q (72) Inventor Jun Takemura 5-33-8 Shiba 5-chome, Minato-ku, Tokyo Mitsubishi Motors Inside Industrial Co., Ltd. (72) Inventor Jun Aoki 5-33-8 Shiba, Minato-ku, Tokyo Mitsubishi Motors Corporation (72) Inventor Kazuchika Tajima 5-33-8 Shiba, Minato-ku, Tokyo Mitsubishi Motors In-house F-term (reference) 3G084 AA04 BA13 BA15 DA04 DA12 EC02 EC03 FA20 FA38 3G301 HA01 HA04 HA16 JA03 JA12 KA01 KA05 KA07 KA12 LB04 MA01 MA11 MA19 MA20 NA06 NA08 NB06 NE01 NE12 NE13 NE14 NE15 NE22 PA01Z PA11ZZZPZPZPZPZPZP02Z PE03Z PE08Z

Claims (2)

[Claims] 1. An injection valve for injecting fuel directly into a combustion chamber formed by a lower surface of a cylinder head, a wall surface of a cylinder, and an upper surface of a piston inserted into a cylinder, and an injection timing of the injection valve according to an operation state of the internal combustion engine. Injection timing control means for controlling, temperature detection means for detecting the temperature of the internal combustion engine, and injection timing correction means for retarding the injection end timing of the injection valve when the engine temperature detected by the temperature detection means is low. An in-cylinder injection type internal combustion engine, comprising: 2. An injection amount control means for controlling a fuel injection amount from the injector according to an operation state of the internal combustion engine, and an injection amount for increasing and correcting the fuel injection amount from the injector when the engine temperature is low. 2. The direct injection internal combustion engine according to claim 1, further comprising a correction unit.