JP3131895B2 - Control device for multi-cylinder internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for determining whether a target air-fuel ratio is rich.
When switching to Luo lean, by decline of the amount of fuel injected from the fuel injection valve provided for each cylinder with a predetermined time difference, a control device for sequentially switching a multi-cylinder internal combustion engine air-fuel ratio of each cylinder.

[0002]

2. Description of the Related Art Such a multi-cylinder internal combustion engine is disclosed in
What is described in -295151 is publicly known.

As shown by the broken line in FIG. 3, the target air-fuel ratio is changed from rich (A / F = 14.7) to lean (A / F = 22.
0) in the continuously switched, although the output torque of the engine changes smoothly, there is a problem of emission of the NO _X from the exhaust gas purification catalyst in the intermediate air-fuel ratio abruptly increases. To avoid this, although the target air-fuel ratio can be avoided a sharp increase in the emission of instantaneously switching the NO _X from rich to lean, the shock is generated engine torque is suddenly changed, drivability The problem that worsens occurs.

Therefore, in the conventional multi-cylinder internal combustion engine, when the target air-fuel ratio is switched from rich to lean, the fuel injection amount of the fuel injection valve provided in each cylinder jumps over the intermediate air-fuel ratio where the emission deteriorates. As described above, it is sequentially reduced at predetermined intervals. As a result, a torque shock that occurs when the fuel injection amounts of all cylinders are reduced at the same time is avoided, and drivability is improved while preventing deterioration of the emission.

[0005]

However, in the above-mentioned conventional multi-cylinder internal combustion engine, a cylinder having a rich air-fuel ratio and a cylinder having a lean air-fuel ratio have the same fuel injection timing and ignition timing.
This leaves room for further improvements in fuel economy and emissions.

The present invention has been made in view of the above circumstances, and has as its object to further improve fuel efficiency and emission in the above-described multi-cylinder internal combustion engine.

[0007]

In order to achieve the above-mentioned object, the invention according to claim 1 is directed to a method for producing a rich target air-fuel ratio.
When switching from lean to lean, the air-fuel ratio of each cylinder is
The switching is performed sequentially, and the switching is started by switching the fuel injection amount from the fuel injection valve provided for each cylinder.
With a predetermined time difference made sequentially longer in accordance with the lapse of time from performed by decline, there is provided a control apparatus for a multi-cylinder internal combustion engine, when the air-fuel ratio of each cylinder is sequentially switched, the air-fuel ratio of each cylinder At the same time, the fuel injection timing and ignition timing are controlled, and the air-fuel ratio is rich.
Set the fuel injection timing of the cylinder during the exhaust stroke and
During the intake stroke, adjust the fuel injection timing of the lean fuel ratio cylinder.
Set the ignition timing of the cylinder with rich air-fuel ratio.
The ignition timing of a cylinder with a lean and air-fuel ratio
It characterized in that the advance.

[0008]

Embodiments of the present invention will be described below with reference to the drawings.

FIGS. 1 to 6 show an embodiment of the present invention. FIG. 1 is an overall configuration diagram of a control device for a multi-cylinder internal combustion engine, and FIG. 2 is a diagram for explaining a switching order of an air-fuel ratio of each cylinder. , FIG. 3 is a graph showing a change in the NO _X emission amount and the output torque accompanying the switching of the target air-fuel ratio, FIG. 4 is a graph showing the relationship between the Pmi fluctuation rate and the fuel injection timing at the time of lean operation, and FIG. FIG. 6 is a graph showing the relationship between the injection timing and the HC discharge amount, and FIG. 6 is a graph showing the relationship between the MBT and the air-fuel ratio.

[0010] As shown in FIG. 1, four cylinder internal combustion engine E (hereinafter, simply referred to as engine E) an intake passage 1 of the four-cylinder 3 ₁ to 3 ₄ # 1 to # 4 through an intake manifold 2 Connected respectively. The intake passage 1 is provided with a throttle valve 4 that is connected to an accelerator pedal (not shown) and opens and closes. A signal from a throttle opening sensor 5 that is connected to the throttle valve 4 and detects a throttle opening is electronically controlled. Input to unit U. The intake passage 1 upstream of the throttle valve 4 is provided with an intake air amount sensor 6 comprising an air flow meter for detecting an intake air amount, and a signal from the intake air amount sensor 6 is input to the electronic control unit U. . An engine speed sensor 7 for detecting an engine speed based on the rotation of a crankshaft (not shown) is provided inside the engine E, and a signal from the engine speed sensor 7 is transmitted to an electronic control unit U.
Is input to

The intake manifold 2 has four cylinders 3 ₁ to 3.
3 ₄ respectively correspond to four fuel injection valves 8 _{1-8 4} is provided. Each fuel injection valve 8 _{1-8 4} is connected to the electronic control unit U, the fuel injection amount and fuel injection timing is controlled. Four cylinders 3 respectively corresponding to _{1-3 4} 4
Number of spark plug 9 ₁ to 9 ₄ is provided. Each ignition plug 9 _to 93 ₄ are connected to the electronic control unit U, the ignition timing is controlled.

Next, the operation of the embodiment of the present invention will be described.

The electronic control unit U determines switching of the target air-fuel ratio based on the operating state of the engine E. That is,
The electronic control unit U searches the map for the target air-fuel ratio based on the throttle opening detected by the throttle opening sensor 5 and the engine speed detected by the engine speed sensor 7. The target air-fuel ratio is of two types. In the normal operation range of the engine E, the target air-fuel ratio is set to stoichiometric, that is, the stoichiometric air-fuel ratio (A / F = 14.7). The target air-fuel ratio is set to lean (for example, A / F = 22.0) in order to improve the fuel efficiency in the operating region of (1).

The switching of the target air-fuel ratio is performed by the fuel injection valve 8 ₁
It is performed by controlling the fuel injection quantity from 8 _4. When the target air-fuel ratio is the stoichiometric air-fuel ratio, the fuel injection time corresponding to the air intake amount detected by the intake air amount sensor 6 and the engine speed detected by the engine speed sensor 7 so that the stoichiometric air-fuel ratio is obtained. Is set. on the other hand,
When the target air-fuel ratio is leaner than the stoichiometric air-fuel ratio, the fuel injection time is set so that the lean target air-fuel ratio is obtained.

As shown in FIG. 2, the air-fuel ratio of each of the cylinders 3 _{1 to} 3 ₄ is not switched at the same time, but is constant with a predetermined time difference both when switching from stoichiometric to lean and when switching from lean to stoichiometric. (For example, # 1 cylinder 3 ₁ → # 3 cylinder 3 ₃ → # 4 cylinder 3 ₄ → # 2
It takes place in the cylinder 3 ₂ order).

[0016] As described above, when the target air-fuel ratio has been switched, by switching the air-fuel ratio of the four cylinders 3 ₁ to 3 ₄ are sequentially with a predetermined time difference, as shown by the solid line in FIG. 3, NO _X The torque shock of the engine E can be minimized while avoiding a sudden increase in the amount of exhaust gas.
As is apparent from the solid line in FIG.
Air-fuel ratio of _{1-3 4,} depending on the time elapsed from the start of the change over
Can be switched sequentially with a predetermined time difference
You.

[0017] Now, at the same time in the present embodiment changes the air-fuel ratio of each cylinder 3 ₁ to 3 _4, and controls the fuel injection timing and ignition timing at the same time. Hereinafter, the control of the fuel injection timing and the ignition timing will be specifically described. Fuel Injection Timing As shown in FIG. 4, the fluctuation rate of the indicated mean effective pressure Pmi of the engine with respect to the end timing of fuel injection with the air-fuel ratio being lean (hereinafter referred to as fuel injection timing) is determined during the intake stroke (after TDC). Around 100 ° crank angle)
It has a characteristic that increases before and after that. Therefore, when the air-fuel ratio is in a lean state, the fuel efficiency can be improved by setting the fuel injection timing near the crank angle of 100 ° after TDC.

On the other hand, as shown in FIG. 5, the amount of HC emission with respect to the fuel injection timing when the air-fuel ratio is in the stoichiometric state becomes maximum during the intake stroke, and during the exhaust stroke (around a crank angle of 120 ° before TDC). It has the characteristics to be minimized. Therefore, when the air-fuel ratio is in the stoichiometric state, the emission can be improved by setting the fuel injection timing to around the crank angle of 120 ° before TDC.

By setting the fuel injection timing during the intake stroke when the air-fuel ratio is lean, and setting the fuel injection timing during the exhaust stroke when the air-fuel ratio is stoichiometric, the fuel efficiency is improved. And emission can both be improved. As shown in FIG. 6, the MBT (minimum ignition advance for obtaining the maximum output torque of the engine) with respect to the air-fuel ratio is near the crank angle of 50 ° before TDC when the air-fuel ratio is lean, and When the air-fuel ratio is in the stoichiometric state, it is near the crank angle of 28 ° before TDC. Therefore, by setting the switching aforementioned MBT according to the ignition timing of each cylinder 3 ₁ to 3 ₄ air-fuel ratio, i.e., relatively ignition timing rich time along with the relatively advancing the ignition timing during lean By retarding, fuel efficiency can be improved.

As described above, when the target air-fuel ratio is switched, the air-fuel ratio of each cylinder is sequentially switched at predetermined intervals to prevent the occurrence of torque shock while preventing the deterioration of emissions, and also to prevent the occurrence of torque shock in each cylinder. Since the fuel injection timing and the ignition timing are also controlled in accordance with the switching of the fuel ratio, it is possible to achieve further improvement in emission and improvement in fuel efficiency.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments, and various design changes can be made.

For example, the specific fuel injection timing and ignition timing shown in the embodiment are merely examples, and may be appropriately changed according to the characteristics of the engine.

[0023]

As described above, according to the first aspect of the invention, when the target air-fuel ratio is switched from rich to lean, the air-fuel ratio of each cylinder is sequentially switched one by one.
The sequential switching is performed by changing the fuel injection amount from the fuel injection valve provided for each cylinder in accordance with the lapse of time from the start of switching.
Since performed by decline with a predetermined time difference becomes sequentially longer Te, the air-fuel ratio of each cylinder when changing cutting <br/> the target air-fuel ratio from rich to lean, the time elapsed from the start of the change over
It is possible to prevent the occurrence of torque shock while sequentially switched prevent deterioration of emission (surge of the NO _X emissions) sequentially become longer predetermined intervals in accordance with the
You.

[0024] When the air-fuel ratio of each cylinder is sequentially switched, by controlling the fuel injection timing and ignition timing at the same time changing the air-fuel ratio in each cylinder, according to the air-fuel ratio of each cylinder for the sequentially switched optimum Having set the timing of fuel injection and ignition timing, Ru can be improved further improved and the fuel consumption emissions. Especially when the air-fuel ratio is rich
The fuel injection timing of the cylinder is set during the exhaust stroke.
The fuel injection timing of the cylinder with a lean air-fuel ratio
By setting during the process, when the air-fuel ratio is rich,
Improved emissions (HC emissions) and lean air-fuel ratio
And improved fuel economy at the same time.
Further retard the ignition timing of cylinders with rich air-fuel ratio
At the same time, the ignition timing of the cylinder with the lean air-fuel ratio is advanced.
By doing so, the air-fuel ratio can be either rich or lean.
To improve fuel efficiency by obtaining the optimal ignition timing
Can be.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of a control device for a multi-cylinder internal combustion engine.

FIG. 2 is a diagram illustrating an air-fuel ratio switching order of each cylinder.

FIG. 3 is a graph showing changes in NO _X emissions and output torque associated with switching of a target air-fuel ratio.

FIG. 4 shows Pmi with respect to fuel injection timing during lean operation.
Graph showing the relationship between fluctuation rates

FIG. 5 is a graph showing the relationship between the fuel injection timing and the amount of HC emission during rich operation.

FIG. 6 is a graph showing the relationship between MBT and air-fuel ratio.

[Explanation of symbols]

3 ₁ to 3 _6-cylinder 8 _{1-8 4} fuel injectors U electronic control unit (control means)

────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI F02D 43/00 301 F02D 43/00 301J F02P 5/15 F02P 5 / 15B (56) References JP-A-4-295151 (JP) JP-A-6-81694 (JP, A) JP-A-5-71381 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) F02D 41/00-45/00 F02P 5/15

Claims (1)

(57) [Claims] To 1. A switching from the target air-fuel ratio rich to lean, sequentially one by one cylinder air-fuel ratio of each cylinder (3 ₁ to 3 ₄₎
The cylinders (3 ₁
To 3 ₄₎ the amount of fuel injected from the fuel injection valve provided for each (6 ₁ to 6 ₄₎ sequentially according to the time elapsed from the start of the change over
Performed by decline with a predetermined time difference becomes longer
Is, there is provided a control apparatus for a multi-cylinder internal combustion engine, when the air-fuel ratio is sequentially switched for each cylinder (3 ₁ to 3 _4), the fuel at the same time changing the air-fuel ratio of each cylinder (3 ₁ to 3 ₄₎ The injection timing and ignition timing are controlled to reduce the air-fuel ratio.
A pitch cylinder (3 ₁ to 3 ₄₎ the fuel injection timing of the exhaust line of
Cylinder that has a lean air-fuel ratio
The fuel injection timing of the (3 ₁ to 3 ₄₎ is set in the intake stroke,
The ignition of the air-fuel ratio is rich cylinder (3 ₁ to 3 ₄₎
Cylinder with a lean air-fuel ratio (3
Characterized by advancing the ignition timing of the _{1-3 4),} the control equipment for a multi-cylinder internal combustion engine.