JPH0571381A - Fuel supply control device for internal combustion engine - Google Patents

Abstract

(57) [Summary] [Purpose] To suppress the occurrence of a torque step when switching the set air-fuel ratio in fuel control. [Configuration] A system for controlling a fuel injection amount by switching between a normal air-fuel ratio near the stoichiometric air-fuel ratio and an air-fuel ratio significantly leaner than the stoichiometric air-fuel ratio based on operating conditions, and controlling a fuel injection valve for each cylinder. Intended for equipped systems. Here, when the set air-fuel ratio switching condition is determined, the set air-fuel ratio step is changed for each injection into each cylinder so that the set air-fuel ratio A / F can be switched stepwise by n injections. Is divided by n to change the set air-fuel ratio by a change width ΔA / F (S6) (S10), and the fuel injection amount Ti is calculated based on the set air-fuel ratio (S12).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel supply control device for an internal combustion engine, and more particularly to improvement of fuel supply control when switching the air-fuel ratio setting of an engine intake air-fuel mixture.

[0002]

2. Description of the Related Art In recent years, for the purpose of improving fuel efficiency, an air-fuel ratio (for example, 20-25) that is extremely higher than the theoretical air-fuel ratio (14.7).
A lean-burn engine is proposed which is designed to burn at. In such a lean combustion engine, for example, when operating at low rotation speed and low load, fuel efficiency is improved by burning at the lean air-fuel ratio, and torque performance is emphasized during acceleration and high load to give a theoretical air-fuel ratio. As an air-fuel ratio on the slightly rich side, both improved fuel efficiency and secured output torque are achieved.

[0003]

By the way, as described above, in an engine in which the air-fuel ratio (lean air-fuel ratio) extremely larger than the stoichiometric air-fuel ratio and the air-fuel ratio (rich air-fuel ratio) smaller than the stoichiometric air-fuel ratio can be switched. 5 when the switching setting between the air-fuel ratios is performed based on the operating conditions.
Even if the set air-fuel ratio changes significantly even under the same operating conditions, the generated torque greatly differs, so that a large torque step may occur at the time of switching the set air-fuel ratio, which may deteriorate drivability. In particular, if the lean air-fuel ratio is switched to the rich air-fuel ratio during acceleration, there is a large gap between the acceleration that is predicted from the driving sensation during lean air-fuel ratio combustion and the acceleration after switching to the rich air-fuel ratio. In addition, there was a fear that the driver would feel uncomfortable.

The present invention has been made in view of the above problems, and an object thereof is to suppress the occurrence of a torque step when switching the set air-fuel ratio and prevent the deterioration of drivability associated with the switching of the set air-fuel ratio. To do.

[0005]

Therefore, a fuel supply control device for an internal combustion engine according to the present invention is constructed as shown in FIG. In FIG. 1, the operating condition detecting means detects an engine operating condition including at least a parameter relating to the intake air amount of the engine. The fuel supply amount calculation means calculates the fuel supply amount based on the detected engine operating condition so that the air-fuel ratio of the engine intake air-fuel mixture becomes a predetermined value.

The fuel supply control means individually controls the fuel supply means provided for each cylinder based on the fuel supply quantity calculated by the fuel supply quantity calculation means. On the other hand, the air-fuel ratio switching determination means determines the engine operating condition for switching the air-fuel ratio setting of the engine intake air-fuel mixture. Then, the air-fuel ratio switching control means, when the engine operating conditions for switching the air-fuel ratio setting are determined by the air-fuel ratio switching setting means, from the air-fuel ratio before switching to the air-fuel ratio after switching for each intake stroke of each cylinder. The predetermined value of the air-fuel ratio in the fuel supply amount calculation means is changed stepwise so as to change stepwise.

Here, there is provided switching start cylinder control means for controlling so that the first cylinder whose air-fuel ratio is changed stepwise by the air-fuel ratio switching control means is different for each judgment by the air-fuel ratio switching judgment means. preferable.

[0008]

With this configuration, when the air-fuel ratio switching determination means determines the engine operating conditions for switching the air-fuel ratio setting of the engine intake air-fuel mixture, the air-fuel ratio is switched from the air-fuel ratio before switching to the air-fuel ratio after switching. -The intake stroke of each cylinder is changed from the air-fuel ratio before switching to the air-fuel ratio after switching, instead of changing the air-fuel ratio of all cylinders to the air-fuel ratio after switching from the time when switching is changed to OFF. It was changed step by step.

Further, when the air-fuel ratio is changed stepwise for each intake stroke of each cylinder, the cylinder is not started from the same cylinder as when the air-fuel ratio was switched last time.

[0010]

EXAMPLES Examples of the present invention will be described below. In FIG. 2 showing an embodiment, air is drawn into an internal combustion engine 1 from an air cleaner 2 through an intake duct 3, a throttle valve 4 and an intake manifold 5. At each branch portion of the intake manifold 5, a fuel injection valve 6 as a fuel supply means is provided for each cylinder. The fuel injection valve 6 is an electromagnetic fuel injection valve that is opened by energizing a solenoid and is opened by stopping energization, and is opened by individually controlling energization by a drive pulse signal from a control unit 12 described later. The fuel, which is pumped from a fuel pump (not shown) and adjusted to a predetermined pressure by a pressure regulator,
The injection is intermittently supplied according to the intake stroke of each cylinder.

A spark plug 7 is provided in each combustion chamber of the engine 1 to spark-ignite and ignite and burn the air-fuel mixture. Then, the exhaust gas is discharged from the engine 1 through the exhaust manifold 8, the exhaust duct 9, the catalyst 10 and the muffler 11. The control unit 12 includes a CPU, ROM, R
A microcomputer including an AM, A / D converter, an input / output interface, etc. is provided, input signals from various sensors are received, arithmetic processing is performed as described later, and the operation of the fuel injection valve 6 is controlled. To do.

As the various sensors, the intake duct 3 is used.
An air flow meter 13 is provided therein and outputs a signal according to the intake air flow rate Q of the engine 1. In addition, a crank angle sensor 14 is provided, for example, in a 4-cylinder engine that serves as a reference for fuel injection control, every 180 ° (for example, BTDC 70 °).
For each) and a unit angle signal POS for every 1 ° or 2 °. Here, the engine rotation speed Ne can be calculated by measuring the cycle of the reference angle signal REF or the number of generated unit angle signals POS within a predetermined time.

A water temperature sensor 15 for detecting the cooling water temperature Tw of the water jacket of the engine 1 is also provided.
The cylinder intake air amount can be detected based on the detection signals of the air flow meter 13 and the crank angle sensor 14, and the operating condition detecting means in the present embodiment includes the air flow meter 13, the crank angle sensor 14, and the water temperature sensor 15. Equivalent to.

Here, the CPU of the microcomputer incorporated in the control unit 12 performs arithmetic processing in accordance with the program on the ROM shown in the flowchart of FIG. 3, and the air-fuel ratio (A / F) of the engine intake air-fuel mixture is set to the empty value. Fuel injection amount Ti (fuel supply amount) to match the fuel ratio
Is calculated and the fuel injection into each cylinder of the engine 1 is individually controlled.

In the present embodiment, the functions of the fuel supply amount calculation means, the fuel supply control means, the air-fuel ratio switching determination means, the air-fuel ratio switching control means, and the switching start cylinder control means are shown in the flow chart of FIG. As described above, the control unit 12 is equipped with software. The program shown in the flow chart of FIG.
It is executed every time F is output, and fuel is injected into the cylinder that will be in the next intake stroke for each reference angle signal REF according to this program.
In the following description, the air-fuel ratio rich / lean is expressed based on the theoretical air-fuel ratio.

First, in step 1 (denoted as S1 in the drawing; the same applies hereinafter), a lean operating condition is established in which the fuel supply amount Ti is calculated based on the set air-fuel ratio which is made leaner than the stoichiometric air-fuel ratio. It is determined whether or not there is. In this embodiment, there are a lean region where combustion is performed at a lean air-fuel ratio (air-fuel ratio = 20 to 25) and a rich region where combustion is performed at a stoichiometric air-fuel ratio (= 14.7) or a slightly rich air-fuel ratio (for example, about 13). Is divided into two regions, and for example, a predetermined low load / low rotation region that is determined based on the engine speed Ne and the basic fuel injection amount Tp representing the engine load is set as the lean region, and in this lean region, the theoretical Based on the set air-fuel ratio that is made leaner than the air-fuel ratio, the fuel injection amount T
i is calculated to improve fuel efficiency. In the rich region, which is a high load / high rotation region excluding the lean region, combustion is performed at a theoretical air-fuel ratio or a slightly rich air-fuel ratio to improve torque performance. I am able to secure it.

However, in this embodiment, as will be described later, the set air-fuel ratio is finely changed depending on the operating conditions in the lean region and the rich region so that combustion can be performed at an appropriate air-fuel ratio for each operating condition. is there. When it is determined in step 1 that the lean operation condition is satisfied,
Proceeding to step 2, the lean region map (lean A / F map) in which the set air-fuel ratio in the lean region is stored in advance in association with the engine rotation speed Ne and the basic fuel injection amount Tp.
Refer to to find the lean air-fuel ratio that matches the current operating conditions.

On the other hand, when it is judged in step 1 that the lean operating condition is not satisfied, the routine proceeds to step 3,
By referring to a rich region map (normal A / F map) in which the set air-fuel ratio in the rich region is stored in advance in association with the engine rotation speed Ne and the basic fuel injection amount Tp, the rich air condition corresponding to the current operating condition is referred to. Search for the air-fuel ratio to obtain it. Next, at step 4, it is determined whether or not it is between the first switching of the lean region map and the rich region map until the injection is performed n times, in other words, the initial stage of switching between the rich air-fuel ratio and the lean air-fuel ratio. Or not.

When the rich / lean switching is not the initial stage, the routine proceeds to step 11, where the set air-fuel ratio MA / F obtained by searching from the map is set as the set air-fuel ratio A / F used in the calculation of the fuel injection amount Ti. To do. Next, the routine proceeds to step 12, where the theoretical air-fuel ratio (= 14.7) and the set air-fuel ratio A / are added to the basic fuel injection amount Tp (= Q / Ne × K; K is a constant) calculated to match the theoretical air-fuel ratio. Multiply the ratio with F,
The final fuel is corrected by correcting the basic fuel injection amount Tp corresponding to the set air-fuel ratio A / F and adding a correction amount Ts for correcting the change in the effective injection time due to the change in the battery voltage of the fuel injection valve 6. The injection amount Ti is calculated.

In addition, in calculating the fuel injection amount Ti, in addition to this, a correction coefficient based on the cooling water temperature Tw detected by the water temperature sensor 15 and an increase after the start may be taken into consideration. The calculation of is the simplest example. When the fuel injection amount Ti is calculated, in the next step 13, a drive signal having a pulse width corresponding to the fuel injection amount Ti is output to the fuel injection valve 6 of the cylinder having the next intake stroke to perform the intake Fuel is injected and supplied to the cylinder in the stroke.

On the other hand, when it is determined in step 4 that the switching of the rich / lean air-fuel ratio is in the initial stage, the process proceeds to step 5 and it is determined whether or not it is the first switching. When it is the rich / lean switching for the first time, the routine proceeds to step 6, where the set air-fuel ratio MA / F obtained by searching from the other map this time from the set air-fuel ratio A / F before switching.
To obtain the step difference of the set air-fuel ratio to be changed,
Further, by dividing the step (A / F-MA / F) of the set air-fuel ratio by the number of injections n, it is necessary to change from the air-fuel ratio before switching to the air-fuel ratio after switching at the number of injections n. Variation of set air-fuel ratio per single injection ΔA
/ F is calculated.

That is, in this embodiment, when the set air-fuel ratio is switched to rich / lean, the air-fuel ratio before switching is changed to the air-fuel ratio after switching stepwise within n injections. This is done (see FIG. 4). The width of the set air-fuel ratio that is changed for each injection in step 6 ΔA /
When F is obtained, in the next step 7, the first cylinder in which the set air-fuel ratio is changed stepwise based on the change width ΔA / F at the time of the previous change of the set air-fuel ratio, and the injection by this program execution will be performed. It is determined whether or not the same cylinder is used.

Then, when the set air-fuel ratio control based on the change width ΔA / F is about to be performed from the same cylinder as at the time of the previous switching, the routine proceeds to step 8, and the next injection is performed for the determination at the next switching. Switching control is performed after storing the cylinder as the first cylinder. Therefore,
In this case, the set air-fuel ratio M obtained by searching this time from the map
A / F is the set air-fuel ratio A used to calculate the fuel injection amount Ti
/ F will not be processed in step 11,
The fuel injection amount Ti is calculated by continuously using the set air-fuel ratio A / F before switching.

On the other hand, if it is determined in step 7 that the cylinder for the first switching last time and the cylinder for the current injection are different, the process proceeds to step 9, where the current injection cylinder is stored as the cylinder for the first time the set air-fuel ratio is switched, Then proceed to step 10. In the first switching that proceeds from step 9 to step 10, a process for changing the set air-fuel ratio stepwise by adding the change width ΔA / F calculated in step 6 to the set air-fuel ratio A / F before switching is performed. , Go to step 12.

On the other hand, if it is determined in step 5 that it is not the first time, the routine jumps to step 10 and the result obtained by further adding the change width ΔA / F to the previously set air-fuel ratio A / F is newly set. Since the processing for A / F is performed, the set air-fuel ratio A / F before switching is gradually approached to the set air-fuel ratio A / F after switching from the initial map switching to the injection n times (FIG. 4).

That is, the set air-fuel ratio A / in step 10
The stepwise change of F is performed for each injection into each cylinder. In other words, the set air-fuel ratio is switched stepwise for each intake stroke of each cylinder. As shown by the chain line, there is no large torque step like when the set air-fuel ratio is rapidly changed on and off, especially when switching from the lean set air-fuel ratio to the rich set air-fuel ratio. This will prevent sudden changes in acceleration.

Further, if the same cylinder as the first cylinder at the time of the previous switching is the injection cylinder and the process proceeds from step 7 to step 8, once the injection is performed as shown when the set air-fuel ratio decreases in FIG. Since the stepwise change of the set air-fuel ratio A / F is delayed and the stepwise change of the set air-fuel ratio A / F is started from different cylinders, the order of cylinders when the set air-fuel ratio is changed stepwise is It can be avoided that the value becomes constant, and thus a large load due to the change in the set air-fuel ratio can be prevented from being unevenly applied only to the specific cylinder.

That is, in the case of the example shown in FIG. 4, the stepwise switching from the rich air-fuel ratio to the lean air-fuel ratio is performed with the # 1 cylinder out of the four cylinders being the first, and the intake strokes in the order of # 1 → # 3 → # 4.
→ # 2 → # 1 are performed in order, but if the injection timing of the # 1 cylinder is the same when the operating condition for switching from the lean air-fuel ratio to the rich air-fuel ratio is next determined, it is stepwise. After switching the set air-fuel ratio once,
The control for gradually reducing the set air-fuel ratio from the cylinders is performed so that the set air-fuel ratio is not gradually changed from the same # 1 cylinder.

When the stepwise change of the set air-fuel ratio A / F based on the change width ΔA / F as described above is repeated n times to reach the set air-fuel ratio after the switching, steps 4 to 11 are executed. In step 12, the set air-fuel ratio A / F is continuously set with reference to the same map, and the fuel injection amount Ti is calculated based on the set air-fuel ratio A / F.

Since the number of injections n is a parameter that determines the switching speed of the set air-fuel ratio, it may be changed depending on the rich / lean change direction of the set air-fuel ratio, or the acceleration / deceleration degree of the engine. It may be changed based on the above. Further, in the present embodiment, when the rich air-fuel ratio and the lean air-fuel ratio are switched, the set air-fuel ratio is changed stepwise, but even if the same rich air-fuel ratio or lean air-fuel ratio, there is a large step. When it is necessary to change it in a stepwise manner, it may be configured to change stepwise as in the present embodiment.

[0031]

As described above, according to the present invention, when the air-fuel ratio setting is switched, the air-fuel ratio before switching is gradually changed to the air-fuel ratio after switching for each intake stroke of each cylinder. Therefore, it is possible to prevent a large torque step from occurring due to a sudden change in the set air-fuel ratio,
In particular, there is an effect that the drivability can be smoothed by avoiding a rapid change in the acceleration performance when the set air-fuel ratio is switched during acceleration.

The first cylinder when the set air-fuel ratio is changed stepwise for each intake stroke of each cylinder as described above,
Since the setting is made different every time the set air-fuel ratio is switched, there is an effect that the load due to the stepwise change of the set air-fuel ratio can be prevented from being biased to a specific cylinder.

[Brief description of drawings]

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

FIG. 2 is a system schematic diagram showing an embodiment of the present invention.

FIG. 3 is a flowchart showing air-fuel ratio control in the embodiment.

FIG. 4 is a time chart showing the characteristics of the set air-fuel ratio in the above embodiment.

FIG. 5 is a diagram for explaining the occurrence of a torque step due to switching of the set air-fuel ratio.

[Explanation of symbols]

 1 Engine 6 Fuel injection valve 12 Control unit 13 Air flow meter 14 Crank angle sensor 15 Water temperature sensor

Claims (2)

[Claims] 1. An operating condition detecting means for detecting an engine operating condition including at least a parameter relating to an intake air amount of the engine, and an empty engine intake air-fuel mixture based on the engine operating condition detected by the operating condition detecting means. Fuel supply amount calculation means for calculating the fuel supply amount so that the fuel ratio becomes a predetermined value, and fuel supply means provided for each cylinder individually based on the fuel supply amount calculated by the fuel supply amount calculation means The fuel supply control means for controlling, the air-fuel ratio switching determining means for determining the engine operating condition for switching the air-fuel ratio setting of the engine intake air-fuel mixture, and the engine operating condition for switching the air-fuel ratio setting by the air-fuel ratio switching setting means At each time, the predetermined value of the air-fuel ratio in the fuel supply amount calculation means is changed so as to change stepwise from the air-fuel ratio before switching to the air-fuel ratio after switching for each intake stroke of each cylinder. And a fuel supply control device for an internal combustion engine, comprising: 2. A switching start cylinder control means is provided for controlling so that the first cylinder whose air-fuel ratio is changed stepwise by the air-fuel ratio switching control means is different for each judgment by the air-fuel ratio switching judgment means. Claim 1 characterized by
A fuel supply control device for an internal combustion engine as described above.