JP4446873B2 - Air-fuel ratio control device for internal combustion engine - Google Patents

Description

  The present invention relates to an air-fuel ratio control apparatus for an internal combustion engine, and more particularly to an air-fuel ratio control apparatus in which a proportional air-fuel ratio sensor is provided in an exhaust system.

Various examples have been proposed in which a proportional air-fuel ratio sensor is provided in an exhaust system together with a three-way catalyst to perform air-fuel ratio feedback control (see, for example, Patent Document 1).
JP 11-315742 A

  In Patent Document 1, a NOx absorbent is provided downstream of a three-way catalyst in an exhaust system of an internal combustion engine, an O2 sensor is disposed therebetween, and a LAF sensor (proportional type) is arranged upstream of the three-way catalyst. A configuration in which an air-fuel ratio sensor) is disposed is disclosed.

  The feedback control according to the output of the LAF sensor is executed when the LAF feedback control condition is satisfied, and the LAF sensor is activated and the fuel supply cutoff operation or the throttle fully open operation is not executed. And so on.

When this LAF feedback control condition is satisfied, an air-fuel ratio correction coefficient is calculated based on the output of the LAF sensor, the fuel injection time is calculated by multiplying the basic fuel injection time, and the fuel injection valve is driven according to the fuel injection time. Thus, LAF feedback control is executed.
That is, when the LAF feedback control condition is satisfied, the LAF feedback control is immediately executed.

  However, the O2 sensor changes abruptly before and after the stoichiometric air-fuel ratio and outputs only two values of low level (lean) and high level (rich), whereas the LAF sensor detects oxygen concentration in the exhaust gas. Since the detection signal that is approximately proportional to the output is linearly output, if the LAF feedback control condition is satisfied when the throttle is opened and the vehicle is accelerating, the fuel tends to be rich. Change the output.

  FIG. 3 is an example showing the situation. The upper graph shows changes in the detected air-fuel ratio (indicated by a thin solid line) and the target air-fuel ratio (indicated by a thick solid line) of the LAF sensor, and the lower graph is empty. A change in the fuel ratio correction coefficient KLAF is shown.

Because it was accelerated by opening the throttle, the detected air-fuel ratio from the LAF sensor from the time T ₀ to LAF feedback control condition is satisfied is changed to increase the rich side.
Therefore, the air-fuel ratio correction coefficient KLAF is decreased to a value larger than 1.0 with respect to the change in the detected air-fuel ratio of the LAF sensor (indicated by a broken line), and the detected air-fuel ratio of the LAF sensor is brought close to the target air-fuel ratio. To change.

  A large change in the air-fuel ratio correction coefficient KLAF immediately after the establishment of the LAF feedback control condition suppresses the fuel injection amount too much, resulting in a driver feeling uncomfortable when starting the feedback control and worsening drivability.

  The present invention has been made in view of such points, and an object of the present invention is to provide an air-fuel ratio control device for an internal combustion engine that can always smoothly enter the LAF feedback control operation and maintain good drivability. There is in point to offer.

In order to achieve the above object, according to a first aspect of the present invention, a proportional air-fuel ratio sensor is provided together with a catalyst device in an exhaust system of an internal combustion engine, and the detected air-fuel ratio of the proportional air-fuel ratio sensor is fed back to perform fuel injection. In an air-fuel ratio control apparatus for an internal combustion engine that is subjected to air-fuel ratio control by being controlled in an amount, an operating state detecting means for detecting an operating state of the internal combustion engine, and a feedback control condition based on a detection result of the operating state detecting means Determination means for determining whether or not is satisfied, wherein the operating state detection means is means for detecting at least the engine speed and the throttle opening, and the determination means is configured so that at least the detected engine speed is predetermined. It is determined that the feedback control condition is satisfied when the detected throttle opening is within the predetermined opening range, and the determination means determines that the feedback control condition is satisfied. Run the feedback control for controlling the fuel injection means according to the detected air-fuel ratio of the proportional type air-fuel ratio sensor when the time it is determined that the back control condition is satisfied the predetermined time continues to feedback control condition is satisfied, the determination An air-fuel ratio control apparatus for an internal combustion engine that does not execute the feedback control when the feedback control condition is not satisfied within a predetermined time from when the means determines that the feedback control condition is satisfied .

  According to the air-fuel ratio control apparatus for an internal combustion engine according to claim 1, the fuel injection means is controlled in accordance with the air-fuel ratio detected by the proportional air-fuel ratio sensor after a predetermined time has elapsed since the determination means determined that the feedback control condition is satisfied. Therefore, a large change in the detected air-fuel ratio of the proportional air-fuel ratio sensor immediately after the feedback control condition is satisfied is ignored, and feedback control can be entered smoothly, maintaining good drivability. it can.

Hereinafter, an embodiment according to the present invention will be described with reference to FIGS. 1 and 2.
FIG. 1 is an overall configuration diagram of an air-fuel ratio control apparatus according to the present embodiment.
In the figure, an internal combustion engine 1 is operated by sucking a mixture of fuel and air from an intake pipe 2 and obtaining power by combustion. Exhaust gas after combustion is discharged to the outside through an exhaust pipe 3.

  A throttle body 4 is interposed in the middle of the intake pipe 2, a throttle valve 4a is disposed therein, a throttle valve opening sensor 10 is connected to the throttle valve 4a, and the throttle valve 4a is opened. A detection signal corresponding to the degree θTH is output.

A fuel injection valve 5 is provided for each cylinder slightly downstream of the intake valve (not shown) of the internal combustion engine 1 on the downstream side of the throttle valve 4a.
Each fuel injection valve 5 is connected to a fuel pump (not shown), and the valve opening time (fuel injection time) of the fuel injection valve 5 is controlled by an instruction signal from the ECU 20 to control the fuel injection amount.

  The operating state of the internal combustion engine 1 is detected by each load detecting means, and an intake pipe absolute pressure sensor 11 for detecting an absolute pressure PBA in the intake pipe 2 in a branch pipe immediately downstream of the throttle body 4. The engine speed NE is detected by an engine speed sensor 12 mounted around a camshaft or crankshaft (not shown) of the internal combustion engine 1, and the engine speed sensor 11 is 180 degrees of the crankshaft of the internal combustion engine 1. A signal pulse (TDC signal pulse) is output at a predetermined crank angle base for every degree rotation.

  An engine water temperature sensor 13 for detecting the cooling water temperature TW is provided on the peripheral wall of the cylinder block of the internal combustion engine 1 filled with the cooling water.

A three-way catalyst 6 is disposed in the exhaust pipe 3 to purify components such as HC, CO, NOx in the exhaust gas.
A LAF sensor 15 that is a proportional air-fuel ratio sensor is disposed upstream of the three-way catalyst 6.
The LAF sensor 15 outputs a detection signal having a level substantially proportional to the oxygen concentration in the exhaust gas.

  All the detection signals of the various sensors described above are input to the electronic control unit ECU 20. The ECU 20 includes a CPU, storage means, and an input / output interface. The CPU performs arithmetic processing based on the above information, and sends various control signals to each drive device. Output for optimal control.

As for the control of the fuel injection valve 5 that controls the air-fuel ratio, the CPU, based on the detection signals of the various sensors, provides a feedback control operation region, an open loop control operation region, etc. according to the oxygen concentration in the exhaust gas. Are determined, and the fuel injection time Tout is calculated based on the following calculation formula according to the engine operating state.
Tout = Ti × KLAF × K1 + K2

Here, Ti is a reference value of the injection time of the fuel injection valve 5, and is retrieved from a Ti map set according to the engine speed Ne and the intake pipe absolute pressure PBA.
KLAF is a LAF feedback correction coefficient and is set according to the oxygen concentration in the exhaust gas detected by the LAF sensor 15.

  K1 and K2 are other correction coefficients and correction variables that are calculated according to various engine parameter signals, and are predetermined values that can optimize various characteristics such as fuel efficiency characteristics and engine acceleration characteristics according to engine operating conditions. To be determined.

The procedure of LAF feedback control by the ECU 20 is shown in the flowchart of FIG. 2 and will be described.
First, the detected air-fuel ratio detected by the LAF sensor 15 is read (step 1). Next, the throttle opening θ by the throttle valve opening sensor 10 for detecting other operating conditions, and the engine speed by the engine speed sensor 12 are detected. The number NE is read (step 2).

In step 3, it is determined whether or not a feedback control condition is satisfied from the operating state.
The conditions for establishing feedback control are that the throttle opening θTH is in the predetermined opening range, the engine speed NE is in the predetermined speed range, and the range detected by the accelerator sensor is not in the acceleration range.

When the feedback control condition is not satisfied, the open loop control is performed without performing the feedback control.
If it is determined in step 3 that the feedback control condition is not satisfied, the process proceeds to step 4 where the timer T is restarted and in step 5 the LAF feedback correction coefficient KLAF is set to 1.

  KLAF = 1 means that the reference injection time Ti is corrected because the LAF feedback correction coefficient KLAF multiplied by the reference injection time Ti of the fuel injection valve 5 in the calculation formula of the fuel injection time Tout is 1. This means that the LAF feedback control is not performed and the open loop control is performed.

When it is determined in step 3 that the feedback control condition is satisfied, the process jumps to step 6 to determine whether or not the timer T has counted the predetermined time t1.
The timer T is restarted in the step 4 and can measure the time from when the determination is switched that the feedback control condition is satisfied in the step 3.

The predetermined time t1 is a time (for example, about 1 second) that can avoid fluctuations in the air-fuel ratio at the start of feedback control.
Until this predetermined time t1 is counted, the routine exits from step 6 and returns to step 1, and steps 1, 2, 3, and 6 are repeated. During that time, KLAF = 1 is maintained and the open loop control is continued. Yes.

When the predetermined time t1 is timed, the process proceeds from step 6 to step 7, and the target air-fuel ratio is calculated.
A search map for searching for the target air-fuel ratio from the throttle opening θTH and the engine speed NE is determined in advance and stored in the storage means. In step 7, the target air-fuel ratio is extracted and calculated from this search map.

Then, in the next step 8, the LAF feedback correction coefficient KLAF is calculated.
An appropriate LAF feedback correction coefficient KLAF for reducing the difference between the detected air-fuel ratio detected by the LAF sensor 15 and the target air-fuel ratio calculated in step 7 to bring the detected air-fuel ratio closer to the target air-fuel ratio is calculated.

  The LAF feedback correction coefficient KLAF is multiplied by the reference injection time Ti to correct the fuel injection time Tout, and feedback control is executed.

  As described above, even if the feedback control condition is satisfied, the feedback control is not performed immediately, and the feedback control is executed after the elapse of the predetermined time t1, so the air-fuel ratio correction coefficient KLAF immediately after the LAF feedback control condition is satisfied. A large change in is avoided and drivability is kept good.

If the LAF feedback control condition is satisfied while accelerating with the throttle opened, the detected air-fuel ratio of the LAF sensor is greatly rich from the time T ₀ when the LAF feedback control condition is satisfied with reference to FIG. Has changed to the side.

In the conventional case described above, when the LAF feedback control condition is satisfied, the air-fuel ratio correction coefficient KLAF immediately decreases in response to the change in the detected air-fuel ratio of the LAF sensor, and the air-fuel ratio decreases by more than 1.0 (part indicated by a broken line). Although the feedback control has been started based on the correction coefficient KLAF, in the present embodiment, the air-fuel ratio correction coefficient KLAF remains at 1.0 from the time T ₀ when the LAF feedback control condition is satisfied until the time T ₁ when a predetermined time t _{1 has} elapsed. Does not enter into the LAF feedback control.

  When entering the feedback control, the state of accelerating by opening the throttle is temporary (when the acceleration continues, it becomes the open loop control), and the predetermined time t1 is a time during which the change to the rich side of the detected air-fuel ratio subsides. It is about 1 second.

  Therefore, when the LAF feedback control condition is satisfied when the throttle is opened and the vehicle is accelerating, even if the LAF sensor reacts immediately after the LAF feedback control condition is satisfied and changes the output greatly, this is ignored and the air-fuel ratio is ignored. The correction coefficient KLAF is not affected, the fuel injection amount is not excessively suppressed, the feedback control operation can always be entered smoothly, and good drivability can be maintained.

1 is an overall configuration diagram of an air-fuel ratio control apparatus according to an embodiment of the present invention. It is a flowchart which shows the procedure of LAF feedback control. It is a figure which shows an example of the change of a target air fuel ratio, a detected air fuel ratio, and an air fuel ratio correction coefficient KLAF.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine, 2 ... Intake pipe, 3 ... Exhaust pipe, 4 ... Throttle body, 5 ... Fuel injection valve, 6 ... Three-way catalyst,
10 ... Throttle valve opening sensor, 11 ... Intake pipe absolute pressure sensor, 12 ... Engine speed sensor, 13 ... Engine water temperature sensor, 15 ... LAF sensor,
20 ... ECU.

Claims (1)

A proportional air-fuel ratio sensor is provided in the exhaust system of the internal combustion engine together with a catalyst device, and an air-fuel ratio control is performed by feeding back the detected air-fuel ratio of the proportional air-fuel ratio sensor to control the fuel injection amount. In the air-fuel ratio control device,
An operating state detecting means for detecting an operating state of the internal combustion engine;
Determination means for determining whether a feedback control condition is satisfied based on a detection result of the operating state detection means,
The operating state detecting means is means for detecting at least the engine speed and the throttle opening,
The determination means determines that the feedback control condition is satisfied when at least the detected engine speed is in a predetermined speed range and the detected throttle opening is in the predetermined opening range;
Executes feedback control for controlling the fuel injection means according to the detected air-fuel ratio of the proportional air-fuel ratio sensor when the feedback control condition is satisfied for a predetermined time after the determination means determines that the feedback control condition is satisfied. And
An air-fuel ratio control apparatus for an internal combustion engine, wherein the feedback control is not executed when the feedback control condition is not satisfied within a predetermined time from when the determination means determines that the feedback control condition is satisfied .

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