JP5058141B2 - Air-fuel ratio control method for internal combustion engine - Google Patents

Description

  The present invention relates to an air-fuel ratio control method for an internal combustion engine that controls an air-fuel ratio based on an output of an oxygen sensor provided in an exhaust passage.

2. Description of the Related Art Conventionally, in an internal combustion engine, particularly an engine mounted on an automobile, a catalyst is provided in an exhaust passage in order to adjust exhaust gas to an emission standard, and the amount of oxygen contained in the exhaust gas is controlled by an oxygen sensor using an oxygen sensor. , Purify the exhaust gas. For example, in Patent Document 1, the change in the air-fuel ratio is determined when the detected value at the time of the state change from the oxygen sensor is the same as the detected value after the delay period has elapsed, and based on the determination of the change in the air-fuel ratio, There is described an air-fuel ratio control device that feedback-controls an air-fuel ratio by changing a delay period according to a control gain set in advance according to an operating state.
JP-A-2-215946

  By the way, it is known that the oxygen sensor does not accurately indicate the output signal in accordance with the change of the air-fuel ratio to be detected unless the temperature of the oxygen sensor exceeds a predetermined temperature. Further, in the operating state immediately after the temperature of the oxygen sensor becomes equal to or higher than the predetermined temperature, that is, immediately after the oxygen sensor is activated, the reaction of the oxygen sensor is slow. With the configuration described above, the delay period becomes longer during warm-up operation where the control gain is small, and if the delay time is changed based on the control gain at that time immediately after activation of such an oxygen sensor, the control cycle becomes longer. Thus, the air-fuel ratio may deviate from the target air-fuel ratio. As a result, the exhaust gas purification rate in the catalyst may be reduced.

  Therefore, the present invention aims to eliminate such problems.

That is, the air-fuel ratio control method for an internal combustion engine of the present invention, a catalyst provided in an exhaust passage, in the internal combustion engine having an oxygen sensor provided on the upstream side of the catalyst, from after the oxygen sensor detects the activated An air-fuel ratio control method for an internal combustion engine that starts air-fuel ratio feedback control using an air-fuel ratio correction constant set based on an output of an oxygen sensor, wherein an elapsed time is detected after detecting that the oxygen sensor is activated. The response of the air-fuel ratio control after the determination of the air-fuel ratio is shortened by shortening the period of increase / decrease of the feedback correction coefficient until the elapsed time reaches the predetermined time until the oxygen sensor is fully activated. The air-fuel ratio correction constant is adjusted in such a direction.

  According to such a configuration, an elapsed time from immediately after activation of the oxygen sensor is detected, and it is determined that the oxygen sensor is not sufficiently activated during a period until the predetermined time is reached. Then, the air-fuel ratio correction constant is adjusted so that the response of the air-fuel ratio control after the determination of the air-fuel ratio is accelerated until the elapsed time reaches a predetermined period for the determination. Therefore, it is possible to prevent the air-fuel ratio control cycle from becoming long and the air-fuel ratio from becoming difficult to control to the target air-fuel ratio.

  The present invention is configured as described above, and the air-fuel ratio control after the determination of the air-fuel ratio is performed during a period in which the oxygen sensor is not sufficiently activated until a predetermined time elapses after the oxygen sensor is activated. By adjusting the air-fuel ratio correction coefficient in a direction that speeds up the response of the air-fuel ratio, it is possible to prevent the control period of the air-fuel ratio from becoming long and the air-fuel ratio from becoming difficult to control to the target air-fuel ratio.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

The engine 100 schematically shown in FIG. 1 is of a spark ignition type four-cycle four-cylinder for an automobile, which is representatively shown in the configuration of one cylinder. An intake system 1 of the engine 100 is provided with a throttle valve 2 that opens and closes in response to an accelerator pedal (not shown), and a surge tank 3 is provided downstream thereof. A fuel injection valve 5 is further provided in the vicinity of one end communicating with the surge tank 3, and the fuel injection valve 5 is controlled by the electronic control unit 6. The cylinder head 8 forming the combustion chamber 7 is provided with an intake valve 9 and an exhaust valve 10 and a spark plug 11 that generates a spark. Further, the exhaust system 12 is provided with a three-way catalyst 14 as a catalyst in an exhaust pipe 13 leading to a muffler (not shown), and a signal for controlling the air-fuel ratio by measuring the oxygen concentration in the exhaust gas. A main O ₂ sensor 15 as an oxygen sensor to be output is disposed at a position upstream of the three-way catalyst 14, and a sub O ₂ sensor 16 as detection means for detecting the air-fuel ratio is also downstream of the three-way catalyst 14. It is arranged. The main O ₂ sensor 15 and the sub O ₂ sensor 16 output a binary output signal h in accordance with the oxygen concentration in the exhaust gas, that is, the air-fuel ratio. The main O ₂ sensor 15 and the sub O ₂ sensor 16 of this embodiment are each provided with a heater to promote activation, and are configured to be energized to the heater at the same time as the engine 100 is started. .

The electronic control device 6 is mainly configured by a microcomputer system including a central processing unit 17, a storage device 18, an input interface 19, and an output interface 20. The input interface 19 has an intake pressure signal a output from an intake pressure sensor 21 for detecting the pressure in the surge tank 3, that is, an intake pipe pressure, and an output from a cam position sensor 22 for detecting the rotation state of the engine 100. Cylinder discrimination signal G1, crank angle reference position signal G2, engine speed signal b, vehicle speed signal c output from the vehicle speed sensor 23 for detecting the vehicle speed, idle switch for detecting the open / closed state of the throttle valve 2 IDL signal d output from 24, water temperature signal e output from water temperature sensor 25 for detecting the cooling water temperature of engine 100, output signal (voltage signal) h output from main O ₂ sensor 15 described above, sub signal An output signal (voltage signal) k or the like output from the O ₂ sensor 16 is input. On the other hand, the output interface 20 is configured to output a fuel injection signal f to the fuel injection valve 5 and an ignition pulse g to the spark plug 11.

  The electronic control device 6 has various information determined according to the operating state of the engine 100 using the intake pressure signal a output from the intake pressure sensor 21 and the rotation speed signal b output from the cam position sensor 22 as main information. The basic injection time (basic injection amount) is corrected by the correction coefficient to determine the fuel injection valve opening time, that is, the final injector energization time T, and the fuel injection valve 5 is controlled based on the determined energization time to correspond to the engine load. A program for injecting fuel into the intake system 1 is incorporated. As a correction coefficient for correcting the basic injection amount, an intake air temperature correction coefficient for increasing in accordance with the intake air temperature, a feedback correction coefficient FAF when feedback control of the air-fuel ratio is performed, and a power increase correction coefficient when output is requested and so on.

When the air-fuel ratio feedback control is executed in a state where the engine 100 is warmed up and the main O ₂ sensor 15 and the sub O ₂ sensor 16 are fully activated, the actual air-fuel ratio is almost theoretical. For example, as shown in FIG. 2, the feedback correction coefficient FAF is changed in accordance with the output signal h from the main O ₂ sensor 15 so as to be close to the air-fuel ratio.

That is, when the output signal h of the main O ₂ sensor 15 exceeds the determination value and a rich state is detected, the feedback correction coefficient FAF is gradually decreased in the direction of decreasing the fuel using a predetermined integration constant KIM. I will let you. On the other hand, when the output signal h of the main O ₂ sensor 15 is below the determination voltage and the lean state is detected, the feedback correction coefficient is obtained when the delay time TDL elapses after the output signal h reaches the determination voltage. The FAF is skipped to the side where the fuel is increased by a fixed skip value RSP, and then the feedback correction coefficient FAF is increased to the side where the fuel is increased using a predetermined integral constant KIP. Furthermore, when the main O ₂ sensor 15 detects a rich state as a result of increasing the fuel, the feedback is performed after a predetermined delay time TDR has elapsed from the time when the output signal h of the main O ₂ sensor 15 exceeds the determination voltage. The correction coefficient FAF is skipped to the side where the fuel is reduced by a fixed skip value RSM, and then the feedback correction coefficient FAF is reduced to the side where the fuel is reduced using a predetermined integration constant KIM. The actual operation of the air-fuel ratio is made closer to the stoichiometric air-fuel ratio by repeatedly executing the above operation on the feedback correction coefficient FAF.

In this embodiment, the integration constants KIM and KIP and the skip values RSP and RSM are set to constant values among the air-fuel ratio correction constants described above, but the main O ₂ sensor 15 is completely activated. Thereafter, the delay times TDR and TDL are changed in accordance with the output signal k of the sub O ₂ sensor 16.

Then, in the the air-fuel ratio control program, it controls the air-fuel ratio based on the output of the main O ₂ sensor 15 after an oxygen sensor main O ₂ sensor 15 has detected that it has activated, the main O ₂ sensor 15 measures the elapsed time from immediately after it is detected that the activated mainly O ₂ sensor 15 is of the air-fuel ratio until a sufficiently reach the elapsed time measured in a predetermined time until activated determined after The air-fuel ratio correction constant is adjusted so as to speed up the response of the air-fuel ratio control.

  The air-fuel ratio control program of this embodiment will be described with reference to FIG. This air-fuel ratio control program is executed only for a predetermined time when the engine 100 is started.

First, in step S1, it is determined whether or not the main O ₂ sensor 15 is activated. Activation of the main O ₂ sensor 15 is determined based on the state of the output signal h. When the main O ₂ sensor 15 is not activated, the output signal h exhibits a slower response than when it is activated. Specifically, for example, the activation of the main O ₂ sensor 15 is determined based on the rising or falling slope (speed) of the output signal h. The main O ₂ sensor 15 shows a slightly slower response to the output signal h as compared with the case where the main O ₂ sensor 15 is completely activated even during a predetermined time immediately after the activation determination.

If it is determined in step S1 that the main O ₂ sensor 15 has been activated, the air-fuel ratio correction constant is adjusted in step S2. In this embodiment, the delay times TDR and TDL as air-fuel ratio correction constants are adjusted to the minimum value within a controllable range. The delay times TDR and TDL may be approximately equal to the minimum value after the main O ₂ sensor 15 is fully activated, and are not set to zero. In this way, by adjusting the delay times TDR and TDL to the minimum values, the air-fuel ratio control, that is, the fuel injection amount increase / decrease control timing is advanced, so that the actual air-fuel ratio greatly deviates from the control range. Suppress.

In step S3, after determining that the main O ₂ sensor 15 is activated, it is determined whether a predetermined time has elapsed. In this case, the predetermined time is set to a time required to sufficiently activate the main O ₂ sensor 15. That is, since the main O ₂ sensor 15 functions when its temperature becomes a predetermined value or higher, the main O ₂ sensor 15 is set according to the time required for the temperature to become higher than the predetermined value due to heating by the heater.

In such a configuration, for example, starting when the engine 100 such as winter is cold, the main until the O ₂ sensor 15 is activated repeatedly executes the steps S1, main O ₂ sensor 15 since it was activated Repeats step S2 and step S3 in this order until a predetermined time elapses. Thus, the delay times TDR and TDL are set short for a predetermined time to control the air-fuel ratio. That is, even if the output signal h of the main O ₂ sensor 15 changes slowly and the output signal h is inverted from the rich state to the lean state, the delay times TDR and TDL are set to the minimum values. By doing so, the feedback correction coefficient FAF switches quickly. This shortens the period of increase / decrease of the feedback correction coefficient FAF. Even if the output signal h of the main O ₂ sensor 15 is slow, the period of the feedback correction coefficient FAF is shortened. The change period is shortened and the slow change of the output signal h is absorbed.

Accordingly, when the response of the output signal of the main O ₂ sensor 15 immediately after activation is slow, the delay times TDR, TDL, and thus the feedback correction coefficient FAF are set so as to accelerate the response of the air-fuel ratio control after the determination of the air-fuel ratio. Since it adjusts, it can suppress that the control period of an air fuel ratio becomes long.

In addition, when the engine 100 is once operated, the operation is stopped after the warm-up is completed, and then the engine 100 is started again, the temperature of the engine 100 is maintained in the state after the warm-up. The temperature of the main O ₂ sensor 15 has dropped below the activation temperature. Even in such a case, the air-fuel ratio control program is executed, and the air-fuel ratio control is performed by the main O ₂ sensor 15 immediately after the activation in which the output signal shows a slow reaction. That is, although the engine 100 itself cools while the operation is stopped, it is in a state after the warm-up, but the main O ₂ sensor 15 is lowered to a temperature that needs to be activated during the operation stop. It is determined whether or not the O ₂ sensor 15 is activated (step S1), and the air-fuel ratio correction constant is adjusted immediately after determining that the O ₂ sensor 15 is activated until a predetermined time has elapsed (steps S2 and S3). .

As described above, at the time of restart after the main O ₂ sensor 15 after the time of cold start and warm-up has cooled to a state of non-activation, fully active immediately after the activation of the main O ₂ sensor 15 By shortening the delay times TDR and TDL until the time of conversion, the air-fuel ratio is appropriately controlled to improve the exhaust gas purification rate.

  In addition, this invention is not limited to the above-mentioned embodiment.

  In the above-described embodiment, the delay times TDR and TDL as the air-fuel ratio correction constant have been described. However, skip values RSP and RSM for controlling the feedback correction coefficient FAF or integration constants KIM and KIP may be used. In this case, the skip values RSP and RSM are adjusted so as to be reduced, and the integration constants KIM and KIP are adjusted so as to reduce the rate of change thereof. As described above, by adjusting the skip values RSP, RSM or the integral constants KIM, KIP of the feedback correction coefficient FAF, the variable range, that is, the amplitude of the feedback correction coefficient FAF is reduced, and the same effect as that of the above-described embodiment can be obtained. It is.

In the above description, the engine in which the O ₂ sensors are arranged before and after the catalyst has been described. However, the engine may be applied to an engine having only the main O ₂ sensor 15 in the above-described embodiment.

In addition, the activation determination of the main O ₂ sensor 15 may be performed based on the elapsed time from the start of the engine 100.

  In addition, the specific configuration of each part is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention.

1 is a schematic configuration diagram of an embodiment of the present invention. 3 is a timing chart showing the basic air-fuel ratio control operation of the embodiment. The flowchart which shows the control procedure of the embodiment.

Explanation of symbols

6 ... electronic control device 15 ... main O ₂ sensor 16 ... sub O ₂ sensor 17 ... central processing unit 18 ... memory 19 ... input interface 20 ... Output Interface

Claims (1)

A catalyst provided in an exhaust passage, in the internal combustion engine having an oxygen sensor provided on the upstream side of the catalyst, the air-fuel ratio correction constant set on the basis of the output of the oxygen sensor from after the oxygen sensor detects the activated An air-fuel ratio control method for an internal combustion engine that starts feedback control of the used air-fuel ratio,
The time elapsed after detecting that the oxygen sensor is activated,
By shortening the period of increase / decrease of the feedback correction coefficient until the elapsed time counted for the predetermined time until the oxygen sensor is fully activated, the response of the air / fuel ratio control after the determination of the air / fuel ratio is accelerated. An air-fuel ratio control method for an internal combustion engine that adjusts an air-fuel ratio correction constant.

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