JPH0763090A - Air-fuel ratio controller of internal combustion engine - Google Patents

Abstract

PURPOSE:To check any slippage in a feedback compensation value irrespective of the characteristic of a lean sensor detecting an air-fuel ratio by operating any delay of up to skip execution of the feedback compensation value in air-fuel ratio feedback control, on the basis of a crank angle. CONSTITUTION:An actual air-fuel ratio in a fuel mixture to be burnt in an internal combustion engine 1 is detected by a lean sensor M2. In addition, this actual air-fuel ratio detected is compared with the target air-fuel ratio, and air-fuel ratio feedback control is executed by a feedback control means M3 so as to make the actual air-fuel ratio accord with the target air-fuel ratio. In this case, rotational frequency of the engine 1 is calculated by a crank angle detecting means M4 in a crank angle unit. In succession, on the basis of a crank angle detected, any delay of up to the skip execution of a feedback compensation value is operated by a delay operational means M5. Furthermore skip executive timing is controlled according to the delay of a crank angle reference operated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an internal combustion engine which executes an air-fuel ratio feedback control for comparing the output of a lean sensor for detecting an actual air-fuel ratio with a target air-fuel ratio to match the actual air-fuel ratio with the target air-fuel ratio. Relates to the air-fuel ratio control device.

[0002]

2. Description of the Related Art Conventionally, a lean or rich determination is made by comparing an output signal of an oxygen sensor (hereinafter referred to as an O ₂ sensor) with a reference value representing a theoretical air-fuel ratio, and the air-fuel ratio is determined according to the determination result. An air-fuel ratio control device for an internal combustion engine that performs feedback control is known. Since the response speed of the O ₂ sensor in such an air-fuel ratio control device is slower when changing from rich to lean than when changing from lean to rich, the O ₂ sensor output is simply compared with the reference voltage. When the rich or lean is judged by inevitably, the air-fuel ratio becomes leaner than the stoichiometric air-fuel ratio.

On the other hand, in the air-fuel ratio control device disclosed in Japanese Patent Publication No. 61-56413, a delay is provided when the output of the O ₂ sensor exceeds or falls below the reference voltage. The delay at the time of changing from the rich to the lean is made larger than that at the time of changing from the lean to the rich so as to compensate for the difference in the response speed of the O ₂ sensor. Further, the delay value in this case was set on the basis of time, and was a fixed value of "constant time".

[0004]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
O ₂ used in the air-fuel ratio controller of No. 413
The sensor is of a type in which the output suddenly changes near the stoichiometric air-fuel ratio. However, there are other types of sensors than the O ₂ sensor. The lean sensor is a type that outputs a current signal corresponding to the air-fuel ratio of the fuel mixture used for combustion from the oxygen concentration in the exhaust gas, and linearly detects the actual air-fuel ratio. This lean sensor is characterized in that the difference in response time is larger than that of the conventional O ₂ sensor due to the difference in structure, and also greatly changes depending on the rotation speed of the engine.

Differences between the two sensors will be further described with reference to specific examples. For example, in terms of structural difference, the diffusion resistance layer thickness is generally 200 in an O ₂ sensor.
500 to 600 μm for lean sensors, while less than μm
Is. As an example of the hole diameter and the number of holes in the sensor cover, the O ₂ sensor has 32 holes with a diameter of 20 and the lean sensor has 8 holes with a diameter of 15, for example. This is mainly for protection against heat, and lean sensors must provide greater protection against heat.

The response time also differs due to such differences in the diffusion resistance layer thickness. For example, generally O ₂
The response time of the sensor is about 100 ms, whereas the response time of the lean sensor is about 500 ms to 1 s, and the lean sensor may be 10 times longer. Also,
The response time of the O ₂ sensor is almost constant regardless of the engine speed, whereas the lean sensor is about 1 s at a certain engine speed, but changes to about 500 ms as the engine speed increases. To do.

Therefore, when the lean sensor is used, if the delay is set to a constant time as in the conventional case, the deviation of the feedback (F / B) correction amount cannot be suppressed. Also, a method of making a table of "delay time" in correspondence with the number of rotations can be considered, but problems such as an increase in software capacity and complication of control arise.

In view of the above, according to the present invention, the change in the "response speed difference" due to the rotational speed appears large when time is used as a reference, but it is noted that the change is substantially constant when the crank angle is used as a reference. An object of the present invention is to solve the above problems by setting a delay based on the above.

[0009]

An air-fuel ratio control system for an internal combustion engine according to the present invention, which has been made to achieve the above object, is shown in FIG.
As illustrated in the basic configuration diagram of No. 2, the lean sensor M2 that detects information about the actual air-fuel ratio of the fuel mixture burned in the internal combustion engine M1, and the information about the actual air-fuel ratio detected by the lean sensor M2. In the air-fuel ratio control device for an internal combustion engine, comprising: feedback control means M3 for performing air-fuel ratio feedback control for matching the actual air-fuel ratio with the target air-fuel ratio. Crank angle detecting means M4 for detecting the number of revolutions of M1 in crank angle units, and delay calculating means M5 for calculating the delay until the skip of the feedback correction amount in the above feedback control are calculated based on the crank angle. Delay calculation means M
It is characterized in that the skip execution timing of the feedback correction amount is controlled in accordance with the crank angle reference delay obtained from Step 5.

[0010]

According to the air-fuel ratio control system for an internal combustion engine of the present invention having the above-mentioned structure, the lean sensor M2 detects information relating to the actual air-fuel ratio of the fuel mixture burned in the internal combustion engine M1 and performs feedback control. The means M3 compares the detected information on the actual air-fuel ratio with the information on the target air-fuel ratio and executes the air-fuel ratio feedback control for matching the actual air-fuel ratio with the target air-fuel ratio. M5 calculates the delay until the skip of the feedback correction amount in the feedback control is executed based on the crank angle detected by the crank angle detection means M4. Then, the skip execution timing of the feedback correction amount is controlled in accordance with the crank angle reference delay obtained from the delay calculation means M5.

Since the delay is set based on the crank angle as described above, the lean sensor has characteristics that the difference in response time is relatively large and that it greatly changes depending on the rotational speed of the internal combustion engine. Even if there is F /
The deviation of the B correction amount can be suppressed. This is because the difference in the response times described in the above “Column of the problem to be solved by the invention” looks large when viewed on the basis of “time”,
Focusing on the fact that the "crank angle" is a reference, the focus is on that it is almost constant. By setting the delay, which was set on the time basis, on the crank angle basis, the F / B
It is possible to suppress the deviation of the correction amount.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An air-fuel ratio control system for a vehicle internal combustion engine (hereinafter referred to as an engine) will be described below as an embodiment of the present invention. FIG. 2 shows a schematic configuration of the engine. The engine 1 is roughly divided into an intake system 3, a combustion chamber 5, and an exhaust system 7. The intake system 3 and the exhaust system 7 will be briefly described below.

The intake system 3 includes various known components such as an air cleaner (not shown), a throttle valve 9, a surge tank 11, an intake pressure sensor 13, a throttle position sensor 15, an intake temperature sensor 17 and the like. Of these, the intake pressure sensor 13 is arranged in the surge tank 11 and detects the intake pipe negative pressure. Throttle position sensor 15
Incorporates an opening sensor 15a and an idle switch 15b. The idle switch 15b is a switch that is turned on when the engine 1 is idling.

The exhaust system 7 includes a lean sensor 19, an igniter 21, a distributor 23, a rotation speed sensor 25, a cylinder discrimination sensor 27, a cooling water temperature sensor 29 and the like. The lean sensor 19 is a limiting current type sensor that outputs a current signal corresponding to the air-fuel ratio of the fuel mixture used for combustion from the oxygen concentration in the exhaust gas. , Actual air-fuel ratio). The lean sensor 19 is connected to a lean sensor drive circuit 32 described later.

Further, the rotation speed sensor 25 is one of the engine 1.
A pulse corresponding to each ° CA (crank angle) is generated. The cylinder block 1a of the engine 1 is cooled by circulating cooling water. The cooling water temperature is detected by a cooling water temperature sensor 29 provided in the cylinder block 1a.

The lean sensor 19 and the rotation speed sensor 2 described above.
The signals of the sensors such as 5 are input to the electronic control unit 30. The electronic control unit 30 is mainly composed of a microcomputer 31 having a CPU, a ROM, a RAM and the like built therein, and also has a lean sensor drive circuit 32. An input / output port (not shown) of the microcomputer 31 has an idle switch 15b, a rotation speed sensor 25, and a cylinder discrimination sensor 2
7, the igniter 21 and the like are connected. A distributor 23 is connected to the igniter 21, and a spark plug 41 is connected to the distributor 23. The fuel injection valve 39 is also driven by a command from the microcomputer via a drive circuit (not shown).

Further, analog signals of the intake pressure sensor 13, the opening sensor 15a, the intake temperature sensor 17, the cooling water temperature sensor 29, etc. are output to the input / output port of the microcomputer 31 via an A / D conversion circuit (not shown). Sensor is connected. Here, the lean sensor drive circuit 32 will be described. FIG. 3 is a circuit diagram showing an outline of the lean sensor drive circuit 32. As shown in FIG. 3, the lean sensor drive circuit 32 includes an applied voltage supply power supply (hereinafter simply referred to as a power supply).
41, a first switch 43, a resistor 45, and a second switch 47. The lean sensor 19 and the power supply 41 are connected via the first switch 43. When the first switch 43 is switched to the terminal 43a side (position shown by the solid line in FIG. 3), the voltage of the power supply 41 is not applied to the lean sensor 19, and the first switch 43 side is shown at the terminal 43b side (shown by the broken line in FIG. 3). When switched to the position, the voltage of the power supply 41 is applied to the lean sensor 19.

Further, in FIG. 3, a resistor 45 is connected in parallel between the positive and negative terminals of the power source 41 and can be opened and closed by a second switch 47. The switching of the first and second switches 43 and 47 is controlled by the microcomputer 31. Further, the output voltage V of the lean sensor 19 is determined by the microcomputer 31.
It is supposed to be detected by.

Further, the output characteristic of the lean sensor 19 will be described with reference to FIG. First switch 4 in FIG.
3 is switched to the terminal 43a side (the position shown by the solid line in FIG. 3) and the second switch 47 is opened (the position shown by the solid line in FIG. 3), the output of the lean sensor 19 is the output of the lean sensor 19. Only the electromotive force is generated, and the so-called Z characteristic is shown at the theoretical air-fuel ratio (λ = 1) as shown in FIG. The output voltage of the lean sensor 19 changes in the range of 0 to 1 V when the air-fuel ratio is about 14.7 (λ = 1). That is, the output voltage is about 1 V when rich and about 0 V when lean.

On the other hand, when the first switch 43 is switched to the terminal 43b side (the position shown by the broken line in FIG. 3) and the second switch 47 is closed (the position shown by the broken line in FIG. 3), the voltage from the power supply 41 is changed. As shown in FIG. 4B, the output of the lean sensor 19 has a linear output characteristic with respect to the air-fuel ratio on the lean side of the stoichiometric air-fuel ratio (about 14.7). In FIG. 4B, the output of the lean sensor 19 is shown by a current value.

The electronic control unit 30 detects the operating state of the engine 1 and controls the operation of the engine 1 based on the outputs of various sensors including the linear sensor 19 described above. The air-fuel ratio control will be described below. Since FIG. 5 is a flow chart showing the outline of the air-fuel ratio control, this processing is executed every 8 ms. First, it is determined whether or not the engine 1 has been warmed up (step 110; hereinafter, the step is simply referred to as S). An example of detection of the warm-up state in S110 is when the cooling water temperature of the engine 1 is 80 ° C. or higher.

When the engine warm-up is completed (S110: YES), it is determined whether the engine is in the idle state (S120), and when it is in the idle state (S120: YE).
In S) and S130, “λ = 1 control” is executed.
In the case of this λ = 1 control, in the lean sensor drive circuit 32 shown in FIG. 3, the first switch 43 is switched to the terminal 43a side (the position shown by the solid line in FIG. 3) and the second switch 47 is open. (Position shown by a solid line in FIG. 3). Therefore, the output of the lean sensor 19 is only the electromotive force of the lean sensor 19 itself, and has a so-called Z characteristic with the stoichiometric air-fuel ratio (λ = 1) as a boundary, as shown in FIG. 4 (A). The λ = 1 control is for trying to burn in a stoichiometric air-fuel ratio state where the excess air ratio λ = 1.

On the other hand, if it is determined that the idle state is not set (S
120: NO), and proceeds to S140 to execute "lean control". In the case of this lean control, in the lean sensor drive circuit 32 shown in FIG. 3, the first switch 43 is switched to the terminal 43b side (the position shown by the broken line in FIG. 3) and the second switch 47 is closed (see FIG. 3 in the position indicated by the broken line). Therefore, since the voltage is applied from the power source 41, the output of the lean sensor 19 has a linear output characteristic with respect to the air-fuel ratio, as shown in FIG. 4 (B). The lean control is for performing combustion on the lean side of the stoichiometric air-fuel ratio in order to improve exhaust performance and fuel consumption performance.

The λ = 1 control at S130 and the lean control at S140 are the same as the control processing known in the related art, and therefore will not be described in further detail. The present invention is characterized by the F / B control processing described below. In S150, it is determined whether or not a predetermined F / B condition is satisfied, and if the F / B condition is satisfied (S150: YES), the F / B condition is satisfied.
The control is executed (S160), and if the F / B condition is not satisfied (S150: NO), the open control is executed (S170).

FIG. 6 is a flow chart showing the processing relating to F / B control in the case of λ = 1 control. That is, S1
The process of 30 is executed, and is the process executed when the F / B condition is satisfied in S150. The process of FIG. 6 is executed not every predetermined time but every 5 ° CA. Further, FIG. 7 is a time chart showing the result of the F / B control.

First, in S210, the output voltage of the lean sensor 19 is set to a predetermined comparison voltage Vset (for example, Vset = 0.45).
V) to determine whether the actual air-fuel ratio is rich or lean. When the output voltage of the lean sensor 19 is equal to or higher than the comparison voltage Vset (S210: YES), it is determined that the actual air-fuel ratio is rich, and when the output voltage of the lean sensor 19 is smaller than the comparison voltage Vset (S210: NO). Determines to be lean.

When it is determined that the actual air-fuel ratio is rich, the routine proceeds to S220, where the rich delay counter TLR
Is set to a predetermined value A ° CA (for example, A = 1000). The delay here is a time (delay time) from when the output voltage of the lean sensor 19 passes the comparison voltage Vset to when the feedback correction amount is skipped. The rich delay counter TLR has a lean air-fuel ratio. Is a delay given to the response time when the signal is inverted from rich to rich.

Next, in S230, the output voltage of the lean sensor 19 is compared again with the comparison voltage Vset, and if the actual air-fuel ratio is determined to be lean, that is, S230: N.
In the case of O, the process returns to S210 and the following processes are repeated. On the other hand, when the actual air-fuel ratio is determined to be rich in S230 (S
230: YES), the process proceeds to S240, where a predetermined value α ° CA is obtained from the previous rich delay counter TLR (i).
A value obtained by subtracting (for example, α = 30) is set again in the rich delay counter TLR.

Then, in S250, it is determined whether or not the rich delay counter TLR is "0" .degree. CA, and if the TLR is not 0 (S250: NO), the process returns to S230 and the following processes are repeated. On the other hand, when TLR is 0 (S25
0: YES), it is determined that the predetermined delay has elapsed, and the process proceeds to S260. In S260, which is executed when a predetermined delay elapses, it is determined that the actual air-fuel ratio is rich, the flag XOX is set to rich, and this routine ends.

If the output voltage of the lean sensor 19 is smaller than the comparison voltage Vset as determined in S210 (S2
10: NO), it is determined to be lean, and the process proceeds to S270. In S270, the lean delay counter TR
A predetermined value B ° CA (for example, B = 2500) is set to L. The lean delay counter TRL is a delay given to the response time when the air-fuel ratio is reversed from rich to lean.

Next, in S280, the output voltage of the lean sensor 19 is again compared with the comparison voltage Vset, that is, it is determined whether or not the output voltage is larger than the comparison voltage Vset. Here, when the output voltage is equal to or lower than the comparison voltage Vset, that is, when the actual air-fuel ratio is determined to be rich (S280: NO), S21 is performed.
The processing returns to 0 and the following processing is repeated. On the other hand, when it is determined in S280 that the actual air-fuel ratio is lean (S280: YES)
In step S290, the lean delay counter TRL is set again with a value obtained by subtracting the predetermined value α ° CA from the previous lean delay counter TRL (i). In addition,
In the present embodiment, the predetermined value α in S290 is set to the above S240.
Although it is the same as the predetermined value α in, the value may be different.

Then, in S300, it is determined whether or not the lean delay counter TRL is "0" ° CA. If TRL is not 0 (S300: NO), the process returns to S280 and the following processes are repeated. On the other hand, when TRL is 0 (S30
0: YES), it is determined that the predetermined delay has elapsed, and the process proceeds to S310. In S310, it is determined that the actual air-fuel ratio is lean, the flag XOX is set to lean, and this routine ends.

The conventionally known F / B control is executed according to the state of the flag XOX set in this routine. Briefly described, a feedback correction amount for controlling the air-fuel ratio to the theoretical air-fuel ratio of 14.7 is calculated with respect to the basic injection amount T _P of the fuel injected by the fuel injection valve 39. That is, as can be seen from FIG. 7, the flag XO
When X becomes rich, the injection amount is reduced in a skip manner at that time point, and then gradually reduced by integration.
Then, when the flag XOX becomes lean, the injection amount is increased in a skip manner at that time point, and then gradually increased by integration. In this way, the feedback correction amount is calculated and reflected in the injection amount.

The response time when the air-fuel ratio A / F reverses from lean to rich and the response time when it reverses from rich to lean are usually different from each other as the characteristics of the lean sensor 19. Generally, as shown in FIG.
The response time when reversing from lean to rich is shorter than the response time when reversing from rich to lean.
Therefore, in general, the predetermined value A ° CA set in the rich delay counter TLR in S220 is S270.
Is made larger than the predetermined value B ° CA set in the lean delay counter TRL.

As described above, according to the air-fuel ratio control system for the internal combustion engine of the present embodiment, the delay is set based on the crank angle, so that the difference in the response times of the lean sensor 19 is relatively large. Even if there is a characteristic that it greatly changes depending on the rotation speed of the engine 1, F /
The deviation of the B correction amount can be suppressed. In order to make this clearer, FIG. 8 shows the control result when the engine speed changes.

Referring to FIG. 8, the reversal interval of the lean sensor output also becomes shorter as the engine speed changes. Regarding the F / B correction amount, in the conventional method indicated by the broken line, the rotation speed changes (in this case, the rotation speed rises) because the rich / lean determination delay is fixed to “constant time” based on time. Then, lean sensor 1
The response time of 9 becomes long and the F / B correction amount deviates.
However, according to the air-fuel ratio control apparatus of the present embodiment, the delay is set with the crank angle as a reference, so that there is no deviation even if the rotation speed changes, as shown by the solid line in FIG.

This is because the difference in the response time of the lean sensor 19 corresponding to the engine speed appears large when "time" is used as a reference, but it is almost constant when the "crank angle" is used as a reference. It is possible to suppress the deviation of the F / B correction amount by setting the delay set on the basis of the crank angle on the basis of the crank angle.

[0038]

As described above in detail, according to the air-fuel ratio control system for an internal combustion engine of the present invention, since the delay is set with reference to the crank angle, the difference in response time is relatively large and the internal combustion engine is Even if there is a characteristic of the lean sensor that it greatly changes depending on the rotation speed of the engine, it is possible to suppress the deviation of the F / B correction amount.

[Brief description of drawings]

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

FIG. 2 is an overall configuration diagram showing an embodiment of an air-fuel ratio control device for an internal combustion engine according to the present invention.

FIG. 3 is a circuit diagram showing an outline of a lean sensor drive circuit.

FIG. 4 is a graph showing output characteristics of a lean sensor.

FIG. 5 is a flowchart showing an outline of air-fuel ratio control.

FIG. 6 is a flowchart showing a process relating to F / B control in the case of λ = 1 control.

FIG. 7 is a time chart showing a control result in F / B control in the case of λ = 1 control.

FIG. 8 is a time chart showing a control result when the engine speed changes.

[Description of Reference Signs] M1 ... Internal combustion engine, M2 ... Lean sensor, M3 ... Feedback control means, M4 ... Crank angle detection means, M
5 ... Delay calculating means, 1 ... Engine, 15b ... Idle switch, 19 ... Lean sensor, 25 ... Rotation speed sensor, 29 ... Cooling water temperature sensor, 30 ... Electronic control device, 31 ... Microcomputer, 32 ...
Lean sensor drive circuit, 41 ... Applied voltage supply power source,
43 ... 1st switch, 47 ... 2nd switch

Claims (1)

[Claims] 1. A lean sensor for detecting information about an actual air-fuel ratio of a fuel mixture burned in an internal combustion engine, and information about an actual air-fuel ratio detected by the lean sensor is compared with information about a target air-fuel ratio. Then, in the air-fuel ratio control device for the internal combustion engine, which comprises feedback control means for executing air-fuel ratio feedback control for matching the actual air-fuel ratio with the target air-fuel ratio, the rotational speed of the internal combustion engine is detected in crank angle units. And a delay calculation unit for calculating the delay until the feedback correction amount is skipped in the feedback control based on the crank angle. The crank angle reference delay obtained by the delay calculation unit is provided. According to the above, it is possible to control the skip execution timing of the feedback correction amount. Air-fuel ratio control system for an internal combustion engine according to symptoms.