JPH07133736A - Fuel injection timing control device for internal combustion engine - Google Patents

Abstract

PURPOSE:To improve stability of lean combustion, and set a limit to a lean side by controlling a fuel injection timing to nearly delay side while taking an increase in an intake flow speed in consideration when lean combustion is carried out while producing forcible swirl. CONSTITUTION:A target air-fuel ratio is set to a lean side in operating condition of a normal running range, lean combustion is carried out, and swirl is taken in a cylinder by a variable swirl creating means 4. When a second injection timing memorizing means 6 is selected by an injection timing switch means 7, the injection timing of each fuel injection valve 1 is controlled so as to make it under intake stroke. The target air-fuel ratio is set to a theoretical air-fuel ratio or a rich side in operating condition of a high speed and high load range, so that creation of swirl is stopped by the variable swirl creating means 4. A first injection timing memorizing means 5 is selected by the injection timing switch means 7, and the injection timing of each fuel injection valve 1 is controlled so as to make it, for example, nearly a top dead point under exhaust stroke. It is thus possible to carry out lean combustion under prescribed operating condition.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel injection timing control device for a spark ignition type internal combustion engine which performs lean combustion under predetermined operating conditions.

[0002]

2. Description of the Related Art Heretofore, a spark which has been designed to perform lean combustion with an air-fuel ratio (A / F) of about 20 to 22 under a predetermined operating condition mainly in order to improve a fuel consumption rate. Ignition type internal combustion engines are known. For example, Japanese Patent Laid-Open No. 2-7
No. 0959 discloses that a swirl control valve gives a strong swirl to the inside of a cylinder to stabilize lean combustion, and an air-fuel ratio sensor provided in an exhaust system allows an actual air-fuel ratio along a target lean air-fuel ratio. There is shown an internal combustion engine with closed loop control. The swirl control valve is, for example, a notch provided in a part of a butterfly valve type valve body,
When the intake air flows into the cylinder in a biased manner through the notch when closed, a strong swirl can be generated and the combustion limit in a lean air-fuel mixture can be increased.

Further, in an electronically controlled fuel injection internal combustion engine in which an electromagnetic fuel injection valve is arranged for each cylinder, fuel is measured by the pulse width of the injection pulse applied to the injection valve, that is, the length of the injection period. However, in general, the injection timing is controlled so that the injection end is near the top dead center at the start of the intake stroke.

[0004]

However, as described above, in the case of performing lean combustion while giving a strong swirl by the variable swirl generating means such as the swirl control valve, when the swirl is generated, the intake air is passed from the intake port through the intake valve to the inside of the cylinder. Since the flow velocity of the intake air flowing into the engine becomes high, the stratified state of the air-fuel mixture in the combustion chamber changes, and the optimum fuel injection timing differs. That is, if the injection timing is set so that the end of injection is substantially at the top dead center as in the above-described conventional case, the injection timing will be relatively early at the time of swirl generation, and combustion stability will deteriorate. In other words, there is a problem that the limit of lean combustion is restricted accordingly.

[0005]

Therefore, according to the present invention,
The fuel injection timing is optimally controlled according to the swirl variable control. That is, the present invention, as shown in FIG. 1, includes an electromagnetic fuel injection valve 1 provided for each cylinder toward an intake port of an internal combustion engine, and an operating condition detecting means 2 for detecting an operating condition of the internal combustion engine. , An air-fuel ratio control means 3 for controlling the air-fuel ratio according to the detected operating condition so as to obtain a lean air-fuel ratio under a predetermined operating condition, and a swirl in the cylinder during lean combustion, which is controlled based on the operating condition. And a variable swirl generating means (4) for generating the first swirl generating means (4), a first injection timing storing means (5) preset with a value corresponding to the engine speed so that the injection end timing is in the exhaust stroke. The second injection timing storage means 6 in which a value corresponding to the engine speed is preset so that the injection end timing is in the intake stroke, and the first injection timing storage means 5 in the swirl stop region based on the above operating conditions. Choose or The injection timing switching means 7 for selecting the second injection timing storage means 6 in the swirl generation region and the value corresponding to the engine speed are determined from the selected injection timing storage means 5, 6 and each fuel injection valve 1 And an injection timing control means 8 for controlling the injection timing of.

The variable swirl generating means 4 is, for example,
As described in claim 2, the butterfly valve type swirl control valve has a notch formed in a part of the valve body.

Further, in the invention of claim 3, the switching boundary in the injection timing switching means 7 does not overlap with the boundaries of the swirl generation area and the swirl stop area of the variable swirl generation means 4, and is set within the swirl generation area. Has been done.

It should be noted that the exhaust stroke includes an approximately top dead center time.

[0009]

[Function] For example, under operating conditions such as a steady driving range,
The target air-fuel ratio is set to the lean side, and lean combustion is performed, but at the time of this lean combustion, the variable swirl generation means 4
Gives swirl in the cylinder. Then, the injection timing switching means 7 selects the second injection timing storage means 6. Thereby, the injection timing of each fuel injection valve 1 is
The injection end timing is controlled so as to be in the intake stroke.

On the other hand, under the operating conditions such as the high speed and high load region, the target air-fuel ratio is set to the stoichiometric air-fuel ratio or the rich side. In such a case, the swirl generation by the variable swirl generating means 4 is stopped. It Then, the first injection timing storage means 5 is selected by the injection timing switching means 7, and the injection timing of each fuel injection valve 1 is controlled so that the injection end timing is, for example, substantially top dead center during the exhaust stroke. To be done.

Further, in the third aspect of the present invention, since the switching boundary in the injection timing switching means 7 does not overlap with the boundaries between the swirl generation area and the swirl stop area of the variable swirl generation means 4, the respective switching is performed. Are not done at the same time, but at slightly different timing.
Especially when swirl generation and stop are switched,
Since the injection timing is controlled in accordance with the normal injection timing, that is, the first injection timing storage means 5, misfire at the time of switching and instability of combustion are prevented.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the drawings.

FIG. 2 is a structural explanatory view showing a mechanical structure of the injection timing control device according to the present invention, in which 11 is an internal combustion engine, 12 is an intake passage thereof, and 13 is an exhaust passage. An electromagnetic fuel injection valve 14 for supplying fuel to the intake port 12a is arranged in each of the intake passages 12 for each cylinder, and a throttle valve 15 is provided in the upstream portion which is one passage. It is equipped. This throttle valve 15
The opening degree of is detected by a throttle opening sensor 16 including a potentiometer. On the upstream side of the throttle valve 15, for example, a hot wire type air flow meter 17 for detecting the intake air amount is arranged. Further, a swirl control valve 1 including a butterfly valve as a variable swirl generating means is provided at a position near the intake port 12a of the intake passage 12.
8 is provided for each cylinder. The swirl control valve 18 is opened and closed by a diaphragm type negative pressure actuator 19. The negative pressure actuator 19 is provided for the throttle valve 1 of the intake passage 12.
5 The negative pressure on the downstream side is used as the actuation source, and it is controlled to be ON / OFF via the three-way electromagnetic system 20.

The swirl control valve 18 is
As shown in detail in FIG. 3, a butterfly valve type valve body 18
A notch 18b is formed on one side of a, and a corresponding pair of intake ports 12a is provided in each cylinder. Reference numeral 21 indicates an intake valve, and 22 indicates an exhaust valve. This swirl control valve 18
Is open, the intake air flowing from the intake passage 12 into the combustion chamber 23 flows substantially evenly through the pair of intake ports 12a, so that no swirl occurs in the combustion chamber 23. Or the swirl will be very weak.
On the other hand, when the swirl control valve 18 is closed, the intake air flow is restricted by the notch 18b of the valve body 18a so as to be biased to one side, so that as shown by an arrow S in FIG. Most of the intake air comes in. Moreover, the flow velocity of the intake air flow is increased by being restricted by the notch 18b. As a result, a strong swirl can be generated in the combustion chamber 23.

In the exhaust passage 13 of the internal combustion engine 11, for example, a catalytic converter 24 using a three-way catalyst is provided, and an air-fuel ratio sensor 25 is arranged upstream of the catalytic converter 24. . This air-fuel ratio sensor 25
Is composed of a wide area type air-fuel ratio sensor such as an oxygen pump type sensor and is adapted to obtain an output corresponding to the value of the air-fuel ratio including the lean region.

Reference numeral 26 is a water temperature sensor for detecting the cooling water temperature of the internal combustion engine 11, and 27 is a crank angle sensor for issuing a pulse signal at every predetermined crank angle so as to detect the engine speed.

The control unit 28 to which the detection signals of the various sensors described above are input uses a so-called microcomputer system, and includes a CPU 29 and a ROM.
The main components are 30, RAM 31, I / O port 32, and the like. The control unit 28 includes an intake air amount detected by the air flow meter 17 and the air-fuel ratio sensor 2
In addition to controlling the injection amount and injection timing of the fuel injection valve 14 based on the detection signal of 5 and the like, the ignition timing of the ignition plug 33 and the like are comprehensively controlled.

Explaining the basic operation of the control device having the above-mentioned structure, first, as the air-fuel ratio control, the target air-fuel ratio is sequentially set from the intake air amount and the engine speed based on a predetermined map, and the target air-fuel ratio is set accordingly. Thus, the fuel injection amount is controlled. In particular, the characteristic of the target air-fuel ratio is set so that the air-fuel ratio becomes leanest in a predetermined low and medium load region. Then, the injection pulse width applied to the fuel injection valve 14 is controlled according to the target air-fuel ratio. In addition, the air-fuel ratio sensor 2
In No. 5, the actual air-fuel ratio is detected from the exhaust gas composition, and the feedback correction coefficient calculated based on this detection signal is multiplied by the injection pulse width to maintain the actual air-fuel ratio at the target air-fuel ratio accurately. It is supposed to be. Here, the swirl control valve 18 is opened at the stoichiometric air-fuel ratio or the rich air-fuel ratio, but in the operating region in which lean combustion is performed at a predetermined air-fuel ratio or higher, the three-way solenoid valve 20
Swirl control valve 18 is closed via
A strong swirl is generated in the cylinder.

Further, the fuel injection timing is individually controlled for each cylinder so that the injection end timing becomes a target value. That is, the crank angle corresponding to the injection pulse width calculated as described above for the air-fuel ratio control is subtracted from the target crank angle to sequentially determine the injection start timing. As will be described later, the target value is set corresponding to the engine speed, and has different characteristics depending on whether the swirl control valve 18 is open or closed.

Specifically, when the swirl control valve 18 is in the open state, the injection timing table is set so that the injection end timing is substantially the top dead center (specifically, the top dead center at the start of the intake stroke). (This is referred to as the first injection timing). When the swirl control valve 18 is closed, the injection timing table is set so that the injection end timing is, for example, about 50 ° ATDC to 100 ° ATDC during the intake stroke (this is the second injection). Write it as time). The second injection timing when the swirl control valve 18 is closed is set to an optimum point in consideration of the stability of lean combustion, exhaust gas composition, fuel consumption rate and the like. As an example, FIG. 7 shows the relationship between the injection timing (injection end timing) at 2000 rpm and the engine stability, HC, NOx, and fuel consumption rate. In this case, 50 ° A
Since the combustion stability is excellent near TDC and the amount of NOx is small, this point is set as the injection end timing. It should be noted that in the vicinity of 120 ° ATDC in FIG. 3, although the combustion stability becomes higher, NOx increases, which is not preferable.

On the other hand, when the switching of the injection timing (injection end timing) table and the switching of the swirl control valve 18 between opening and closing are performed at the same time, the combustion is not performed due to factors such as differences in responsiveness. In this embodiment, the switching timings are set so that they do not overlap with each other, and the swirl control valve 1 is stabilized.
8 is switched between open and closed while the first injection timing, that is, the injection end timing is controlled so as to be substantially at the top dead center. FIG. 4 shows the boundary of the table switching at the injection end timing and the boundary of the switching of the swirl control valve 18 between open and closed, and FIG.
The respective switching timings at a constant rotation speed N1 are shown. As shown in these figures, each switching is performed with an appropriate hysteresis. The swirl control valve 18 closes on the low speed and low load side from the illustrated boundary, and gives a strong swirl as described above, but this boundary is
It is set so as to be closed in a region equal to or higher than a predetermined air-fuel ratio. Then, the injection end timing is switched so that it is in the intake stroke (second injection timing) on the low speed and low load side with respect to the illustrated boundary, and is substantially at the top dead center (first injection timing) on the high speed and high load side. . Here, the respective boundaries are set so as not to overlap each other including hysteresis, and in particular, the boundary for switching the injection end timing is set within the closed region of the swirl control valve 18.

The flow chart of FIG. 6 shows a specific processing flow of the above-mentioned injection end timing switching control.
This will be described below. The process of FIG. 6 is repeatedly executed at regular intervals, for example.

First, in step 1, the engine speed N, the load, and the cooling water temperature TW are read as engine operating conditions.
The engine load is engine speed N and intake air amount Q.
The basic fuel injection amount Tp obtained from is used. As described above, based on this engine operating condition, the air-fuel ratio is controlled according to another program (not shown), and the swirl control valve 18 is controlled to open / close according to the characteristics shown in FIG. In step 2, the air-fuel ratio at that time (target air-fuel ratio) is read, and in step 3, it is determined from the value of this air-fuel ratio whether or not it is in the lean region. In the non-lean region, that is, in the case of the stoichiometric air-fuel ratio or the rich air-fuel ratio, the routine proceeds to steps 4 and 5, where the value of the counter C serving as a timer is incremented and the value of the counter C is set to correspond to a predetermined delay period. Compare with the value C ₀ . Counter C
If the value of is greater than or equal to the set value C ₀ , the process proceeds to step 9, and the first injection timing table is selected. The first injection timing table corresponds to the open state of the swirl control valve 18, and is set so that the injection end timing is substantially at the top dead center. That is, switching to the first injection timing table is executed after a predetermined period of delay after the stoichiometric air-fuel ratio or the rich air-fuel ratio is reached.

When the air-fuel ratio is lean in step 3, the counter C is cleared (step 6) and
In steps 7 and 8, the open / closed state of the swirl control valve 18 is determined. This open / closed state is the solenoid valve 2
It is determined based on the control signal of 0 or the engine operating condition. When the swirl control valve 18 is open, the routine proceeds to step 9, where the first injection timing table is selected.

Further, when the swirl control valve 18 is in the closed state, in step 11, the load TpI which becomes the boundary of the injection timing switching at that time in accordance with the characteristics of FIG.
NJ is set as shown in FIG. 5 corresponding to the engine speed N.
4 and 5, the boundary of switching is shown as one, but in reality, there are two kinds of boundaries having slightly different characteristics when the cooling water temperature is 70 ° C. or higher and when the cooling water temperature is lower than 70 ° C. Is set, and the boundary load TpINJ is set in consideration of the water temperature.
Is set. Then, in step 12, the actual engine load Tp is compared with this boundary load TpINJ. If the boundary load TpINJ or more, the process proceeds to step 9 to select the first injection timing table, and if it is less than the boundary load TpINJ. Proceeding to step 13, the second injection timing table is selected.

Each of these injection timing tables defines the injection end timing corresponding to the engine speed N, so that the injection end timing is approximately the top dead center as described above in the first injection timing table. On the other hand, the second injection timing table is set such that the injection end timing is in the intake stroke. After selecting the injection timing table in this way, in step 10 or step 14, each injection timing table is used to determine the injection end timing corresponding to the engine speed N.

Therefore, according to the above embodiment, when the swirl control valve 18 is closed and a strong swirl is applied with the lean air-fuel ratio, the fuel injection is slightly delayed and the injection end timing is the intake time. In the process. Therefore, as shown in FIG. 7, the stability of lean combustion is improved. Also, swirl control valve 18
Since the first injection timing table is selected as the injection timing table and the injection end timing is maintained substantially at the top dead center when switching between the open and close states of No, there is no accidental misfire due to transient combustion instability.

In the above embodiment, the swirl control valve 18 is used as the variable swirl generating means. For example, a swirl is generated by fixing one of the pair of intake valves to a closed state by a variable valve mechanism. The invention can be similarly applied to an internal combustion engine using other variable swirl generating means.

[0029]

As is apparent from the above description, according to the fuel injection timing control system for an internal combustion engine of the present invention, swirl generation is performed when performing lean combustion while giving a strong swirl to the variable swirl generation means. The fuel injection timing is controlled to be slightly delayed in consideration of the fact that the intake air flow rate increases. Therefore, the stability of lean combustion can be improved, and the limit of lean combustion can be set to the lean side accordingly. Further, by setting the switching boundary in the injection timing switching means as in claim 3, it is possible to reliably avoid misfire due to transient instability of combustion.

[Brief description of drawings]

FIG. 1 is a claim correspondence diagram showing a configuration of the present invention.

FIG. 2 is a structural explanatory view showing an embodiment of an injection timing control device according to the present invention.

FIG. 3 is an explanatory diagram showing a configuration of a swirl control valve.

FIG. 4 is a characteristic diagram showing a boundary of opening / closing switching of a swirl control valve and a boundary of switching of injection timing.

FIG. 5 is a characteristic diagram showing respective boundaries at a constant engine speed.

FIG. 6 is a flowchart showing the flow of injection timing control of this embodiment.

FIG. 7 is a characteristic diagram showing a relationship between injection end timing and engine stability and the like.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Electromagnetic fuel injection valve 2 ... Operating condition detection means 3 ... Air-fuel ratio control means 4 ... Variable swirl generation means 5 ... 1st injection timing storage means 6 ... 2nd injection timing storage means 7 ... Injection timing switching means 8 ... Injection timing control means

Claims (3)

[Claims] 1. An electromagnetic fuel injection valve provided for each cylinder toward an intake port of an internal combustion engine, an operating condition detecting means for detecting an operating condition of the internal combustion engine, and a lean air-fuel ratio under predetermined operating conditions. So that the air-fuel ratio control means controls the air-fuel ratio according to the detected operating condition, and the variable swirl generating means controlled based on the operating condition to generate swirl in the cylinder during lean combustion. In this internal combustion engine, the first injection timing storage means presets a value corresponding to the engine speed so that the injection end timing is in the exhaust stroke, and the engine rotation is set so that the injection end timing is in the intake stroke. A second injection timing storage means in which a value corresponding to the number is preset, and a first injection timing storage means is selected in the swirl stop region based on the operating conditions, and a second injection timing storage is stored in the swirl generation region. An injection timing switching means for selecting a stage, and an injection timing control means for determining a value corresponding to the engine speed from the selected injection timing storage means and controlling the injection timing of each fuel injection valve. And a fuel injection timing control device for an internal combustion engine. 2. The fuel injection timing control device for an internal combustion engine according to claim 1, wherein the variable swirl generating means comprises a butterfly valve type swirl control valve in which a notch is formed in a part of a valve body. 3. The switching boundary in the injection timing switching means does not overlap with the boundaries of the swirl generation area and the swirl stop area of the variable swirl generation means, and is set within the swirl generation area. The fuel injection timing control device for an internal combustion engine according to claim 1 or 2.