JPH0475383B2 - - Google Patents

Description

Detailed Description of the Invention The present invention provides an air-fuel ratio sensor in the exhaust system of the engine, detects the air-fuel ratio based on the detection signal of the sensor, and adjusts the air-fuel mixture to be supplied to the engine based on the detected air-fuel ratio. The present invention relates to an air-fuel ratio control method for feedback-controlling the air-fuel ratio to an optimum state.

Conventionally, various engines have been developed in which the air-fuel ratio of the air-fuel mixture is detected from the oxygen concentration in the engine's exhaust gas components, and the air-fuel ratio of the air-fuel mixture supplied to the engine is controlled based on the detection signal of the air-fuel ratio sensor. In the air-fuel ratio control method, in order to appropriately control the air-fuel ratio according to various engine operating conditions (engine conditions), a readable and writable non-volatile memory is provided, and information for air-fuel ratio correction is stored in the memory. That is, data detected by the air-fuel ratio sensor during feedback control is integrated, and a value corresponding to the result of the integration is stored as information for each engine state in correspondence with the engine state at the time of the integration processing. While driving, the correction information is sequentially updated (learned), and the air-fuel ratio is controlled based on this correction information, etc., and control delays, which are problems in feedback control, are avoided, and feedback control is performed. One example is an air-fuel ratio control method that solves problems such as an increase in harmful components in exhaust gas during open-loop control, which cannot be controlled.

In these control methods, feedback control is not performed during engine conditions such as an inactive state of the air-fuel ratio sensor or a fuel cut state during deceleration that is not suitable for feedback control, and when this feedback control is stopped, the engine state is The process of storing correction information for each time is stopped to prevent control disturbances caused by storing inaccurate data.

However, simply not performing the above-mentioned memory processing during open-loop control does not allow for precise control; for example, when transitioning from open-loop control to feedback control, the air-fuel ratio may still be disturbed towards the rich side. Since correction information for each engine state is calculated and stored in memory to bring the air-fuel ratio into a lean state through feedback control, if the air-fuel ratio is subsequently controlled based on the correction information for each engine state at this point, the air-fuel ratio The fuel ratio was controlled to be excessively lean, and there was a risk that the vehicle would run sluggishly due to deterioration in emissions, making it impossible to ensure good drivability. In addition, such a state that is inappropriate for storing correction information for each engine state occurs not only immediately after the above-mentioned open-loop control shifts to feedback control, but also during a predetermined period of time after shifting from open-loop control to feedback control. It exists even during feedback control when the period has elapsed. That is, during acceleration/deceleration, etc., data such as intake air volume changes greatly and only transient and inaccurate data can be obtained, and therefore it is not appropriate to store correction information for each engine state under such conditions. .

The present invention has been made in view of the above points, and compensates for response delay in air-fuel ratio feedback control.
It is an object of the present invention to provide an air-fuel ratio control method that can always maintain an appropriate air-fuel ratio in both feedback control and open-loop control.
This purpose is performed in parallel with the feedback control in which the air-fuel ratio of the air-fuel mixture supplied to the engine is detected from the exhaust gas components of the engine by the air-fuel ratio sensor, and the air-fuel ratio of the air-fuel mixture is corrected based on the detection result. An air-fuel ratio controller that updates engine condition correction information stored in a readable and writable nonvolatile memory in response to a detection signal from an air-fuel ratio sensor, and corrects the air-fuel ratio of the air-fuel mixture based on the engine condition correction information in the memory. In the fuel ratio control method, it is determined whether the operating state of the engine is within a predetermined range suitable for updating the engine state correction information, and after the operating state of the engine falls within the predetermined range, the air-fuel ratio sensor is adjusted. It is determined whether the detection signal has reversely changed between a state representing a rich air-fuel ratio and a state representing a lean air-fuel ratio a predetermined number of times, and the engine operating state is determined to be outside the predetermined range and within the predetermined range. Achieved by an air-fuel ratio control method characterized in that updating of the engine state correction information is stopped while it is determined that the inversion change of the detection signal of the air-fuel ratio sensor is less than a predetermined number of times after the air-fuel ratio sensor is turned on. be done.

Hereinafter, examples of the present invention will be given and explained based on the drawings.

Figure 1 shows the configuration of the engine section. Engine 1
Reference numeral 1 designates a known four-stroke spark ignition six-cylinder engine installed in an automobile, in which combustion air is passed through an air cleaner 12, an intake pipe 13, and a throttle valve 14.
inhaled sequentially. Further, fuel is supplied from a fuel system (not shown) through electromagnetic fuel injection valves 15a to 15f provided corresponding to each cylinder of the engine 11. The exhaust gas after the explosion is released into the atmosphere through an exhaust pipe 17 connected to the exhaust manifold 16, a three-way catalytic converter 18, and the like.

The intake pipe 13 includes a potentiometer-type intake air amount sensor 19 that detects the amount of intake air taken into the engine 11 and outputs an analog voltage according to the amount of intake air.
A thermistor-type intake temperature sensor 20 is installed that detects the temperature of intake air and outputs an analog voltage according to the intake air temperature.

The engine 11 is also equipped with a thermistor-type water temperature sensor 21 that detects its cooling water temperature and outputs an analog voltage according to the cooling water temperature. An air-fuel ratio sensor 22 is installed to detect the fuel ratio, and the air-fuel ratio sensor 22 outputs a voltage of about 1 V (high level) when the air-fuel ratio is smaller than the stoichiometric air-fuel ratio (rich).
Outputs a voltage signal of approximately 0.1V (low level) when the air-fuel ratio is greater than the stoichiometric air-fuel ratio (lean). 23 is a rotational speed sensor that detects the rotational speed (rotational speed) of the engine; for example, it detects an ignition pulse signal from the primary terminal of an ignition coil (not shown) and detects the rotational speed with a frequency corresponding to the engine rotational speed. It can be a signal. In addition, each of the above-mentioned sensors 19~
The detection signals from 23 are sent to the control circuit 24, and the control circuit 24 calculates the fuel injection amount based on each detection signal, controls the opening time of the electromagnetic fuel injection valves 15a to 15f, and adjusts the fuel injection amount of the engine. The air-fuel ratio is controlled by controlling the

FIG. 2 shows the configuration of the control circuit 24, with 10
0 is a microprocessor (MPU) that calculates the fuel injection amount. Reference numeral 101 denotes a rotation number counter, which inputs the signal from the rotation speed sensor 23 and counts the number of pulses of this detection signal to create rotation speed data, and also issues an interrupt command to the interrupt control unit 102 in synchronization with the engine rotation. send a signal. When the interrupt control section 102 receives the interrupt command signal, it operates to output an interrupt signal to the microprocessor 100 through the common bus CB. 103 is a digital input port;
Digital signals such as an air-fuel ratio signal from the air-fuel ratio sensor 22 and a starter signal from the starter switch 25 are input and transmitted to the microprocessor 100.
104 is an analog input port consisting of an analog multiplexer and an A-D converter;
9. It has a function of converting each detection signal from the intake temperature sensor 20 and the cooling water temperature sensor 21 from analog to digital and sequentially importing the data into the microprocessor 100. 105 is a power supply circuit, which will be described later.
Power is always supplied directly to the RAM 107 from the battery 26. The battery 26 is also supplied to another power supply circuit 106 via a key switch 27, and this power supply circuit 106 supplies power to circuits and devices other than the RAM 107. Therefore, this RAM
Reference numeral 107 is a temporary storage unit that is used temporarily during program operation, but it is a non-volatile unit that is always powered on regardless of the key switch 27 and whose memory contents do not disappear even if the key switch 27 is turned off and the engine operation is stopped. Configure memory. still,
Correction amounts K ₂ and K ₃ , which will be described later, are stored in this RAM 107. A read-only memory (ROM) 108 stores programs, various constants, and the like.
Reference numeral 109 denotes a fuel injection time control counter including a register, which is composed of a down counter and receives a digital signal representing the opening time of the electromagnetic fuel injection valves 15a to 15f calculated by the microprocessor 100, that is, the fuel injection amount. , it is converted into a pulse signal with a pulse time width (duty ratio) that gives the actual opening time of the injection valve. 110 is a power amplifier that receives a valve opening pulse signal and drives the electromagnetic fuel injection valves 15a to 15f; 111 is a timer that measures elapsed time and transmits it to the microprocessor 100;

That is, the rotational speed counter 101 measures the engine rotational speed, for example, once per engine rotation based on the detection signal of the rotational speed sensor 28, and supplies an interrupt command signal to the interrupt control unit 102 at the end of the measurement. . The interrupt control unit 102 generates an interrupt signal according to the interrupt command,
The microprocessor 100 is caused to execute an interrupt processing routine for calculating the fuel injection amount.

FIG. 3 shows a schematic flowchart of a control program of the microprocessor 100 that performs air-fuel ratio control.
4. The overall operation will be explained.

First, the key switch 27 and starter switch 25 are turned on to start the engine.
A start command is generated from step 120, and the main routine arithmetic processing is started. Then, initialization is executed in step 121, and then step 122
At this point, data on the intake air temperature detected by the intake air temperature sensor 20 and data on the cooling water temperature detected by the water temperature sensor 21 are taken into the microprocessor 100 via the analog input port 104. Then, the process proceeds to step 123, and from the data of the engine intake air temperature and cooling water temperature taken in step 122, a first correction amount K ₁ is determined for controlling the increase in fuel during cold conditions and the decrease in fuel when the intake air rises.
is calculated and stored in the RAM 107. Subsequently, in step 124, the air-fuel ratio detection signal from the air-fuel ratio sensor 22 is inputted via the digital input port 103, and a second integral processing of the detection signal of the air-fuel ratio sensor 22 is performed as a function of the elapsed time by the timer 111. Calculate the correction amount K ₂ and transfer it to RAM10
Store in 7. This correction amount _K2 is determined by the air-fuel ratio sensor 22 in order to perform feedback control of the air-fuel ratio.
The calculation process is performed based on the air-fuel ratio data from the air-fuel ratio data, and is used as a correction value for the fuel injection amount during feedback control.

FIG. 4 shows a detailed flowchart of the processing step 124 in which the correction amount _K2 is increased or decreased by integral processing. First, in step 400, it is determined whether the air-fuel ratio sensor 22 is activated or not, and the feedback of the air-fuel ratio is determined in an operating state that satisfies predetermined conditions such as when fuel cut-off during deceleration is not performed. It is determined whether or not control can be performed, and if feedback control is not possible, the determination is ``YES'' and the process proceeds to step 406, where the correction amount <sub>K2</sub> is set to ``1''. On the other hand, if feedback control becomes possible based on the engine operating condition and is performed, select "NO".
Then, the process proceeds to step 401. In step 401, it is determined whether or not the elapsed time measured by the timer 111 has exceeded the unit time _Δt1 .
If it has not passed, this processing step 124 is ended without calculating the correction amount _K2 . On the other hand, if the elapsed time has exceeded _Δt1 , the determination is ``YES'' and the process proceeds to step 402, where it is determined whether the air-fuel ratio detected by the air-fuel ratio sensor 22 is rich. Here, if the detected air-fuel ratio is rich, the judgment is "YES" and the process proceeds to step 403, where ΔK ₂ is subtracted from the correction amount K ₂ calculated in the previous cycle, and the process proceeds to step 405, where a new correction is made. The quantity K ₂ is stored in RAM 107 . If the air/fuel ratio is lean in step 402, step 404
The process proceeds to step 405, where _ΔK2 is added to the correction amount _K2 , and the process proceeds to step 405, where the new correction amount _K2 is stored in the RAM. In this way, the correction amount _K2 is increased or decreased (integrated) according to the air-fuel ratio. As is well known, in addition to this integral processing, when the output of the air-fuel ratio sensor 22 is reversed, the correction amount _K2 may be increased or decreased by a predetermined value (skip) to add a proportional amount.

In the flowchart shown in Figure 3, step 125 is next.
The correction amount _K3 , which is _the correction information for each engine condition, is calculated in the step shown in FIG. Here, the correction amount _K3 is to be continuously corrected so that the calculated basic fuel injection amount matches the fuel injection amount currently requested by the engine as much as possible without performing air-fuel ratio feedback control. This improves responsiveness during engine transients when feedback control does not function adequately, satisfactorily compensates for changes in parts and characteristics over time, and also allows the air-fuel ratio to be as close to the target air-fuel ratio as possible during open-loop control. It is calculated to correct the basic injection amount.

In the calculation processing step 125 of the correction amount _K3 , first,
In step 500, it is determined whether or not to calculate the correction amount _K3 . This determination step 500 is the main part of this embodiment. The processing at step 500 will now be described in detail.

As shown in the flowchart shown in FIG. 6, it is determined whether or not the state is suitable for updating the correction amount _K3 as engine state correction information in accordance with the detected engine data. That is, first, determination step 510
, the cooling water temperature detected from the water temperature sensor 21
It is determined whether THW is within a predetermined set water temperature THW ₁ to THW ₂ (70°C to 120°C in this example),
If the water temperature THW is within the range of the set water temperature, the determination is ``YES'' and the process proceeds to step 520, and if the water temperature THW is outside the range of the set water temperature, the determination is ``NO'' and the fifth step is performed. The determination at step 500 in the figure is "NO", and the process at step 125 ends without calculating the correction amount _K3 . In step 520, it is determined whether the engine rotation speed N detected by the rotation speed sensor 23 is within the range N ₁ to _{N 2} (500 rpm to 6000 rpm in this embodiment) of the predetermined set rotation speed, and the engine rotation speed is determined. If the number N is outside the set rotational speed range, the determination is "NO" and the process of step 125 is ended without calculating the correction amount _K3 . On the other hand, if the engine speed N is within the set speed range, the determination is "YES".
Proceed to step 530. In step 530, the intake air amount Q of the engine detected by the intake air amount sensor 19 falls within a predetermined set intake air amount range Q ₁ to Q ₂ (in this embodiment, 3
m ³ /min to 100 m ³ /min), and if the intake air amount Q is outside the range of the set intake air amount, the judgment is "NO" and the correction amount K ₃ is calculated. The process of step 125 is ended without performing this step. on the other hand,
If the intake air amount Q of the engine is within the set intake air amount range, the determination is ``YES'' and step 540 is performed.
Proceed to. In this determination step 540, it is determined that the fuel injection time T calculated in the previous cycle is within a predetermined setting value range T ₁ to T ₂ (1.5 msec to 10 msec in this embodiment).
msec), and if the fuel injection time T is outside the range of set values _T1 and _T2 , the determination is "NO" and the calculation of the correction amount _K3 is performed. The process of step 125 is ended without performing this step. On the other hand, if the fuel injection time T is between the set values T ₁ and T ₂ ,
If the determination is "YES", the process proceeds to step 550. In this step 550, after it is determined that the operating state of the engine 11 is within a predetermined range by the processing in steps 510 to 540, the detection signal from the air-fuel ratio sensor 22 indicates a rich air-fuel ratio (high level). ) and the state representing lean (low level) are reversed a predetermined number of times (n). In order to delay the execution of the calculation process for updating the correction amount _K3 , for example, after the processing in steps 510 to 540, , the amount of correction caused by feedback control as shown in FIG.
It is determined whether or not the _K2 wave (in addition to the process shown in FIG. 4, the skip is increased or decreased when the output of the air-fuel ratio sensor 22 is reversed) has passed n times, and if it has not passed, the determination is "NO". Therefore, the correction amount _K3 is not calculated. However, after skipping n times, "YES"
When the determination is made, the correction amount _K3 is calculated, and the process proceeds from determination step 500 to step 501 in FIG. In addition, this number of skips n times,
In other words, the number of times the detection signal from the air-fuel ratio sensor 22 is reversed (four times in this embodiment) is determined as the time it takes to stabilize to a normal value when the correction amount deviates significantly to the increasing or decreasing side during a transient period. , and the upper and lower limits of each setting range are different depending on the vehicle type.

In this way, when the engine is operated at a predetermined range of water temperature, a predetermined engine speed range, and a predetermined intake air amount, and furthermore, when the previous fuel injection time is within a predetermined range, the engine operating state is not in a transient state and has switched to a steady state suitable for updating the correction amount K ₃ according to the output of the air-fuel ratio sensor 22, and after a predetermined delay time due to n skips has elapsed, the correction amount K ₃ The update operation is restarted. Therefore, in a transient state where the combustion state of the engine is extremely unstable, calculation processing of this correction amount _K3 is not performed, and furthermore, if a predetermined delay time has elapsed after switching from a transient state to a stable state, the correction amount K3 is not calculated. Since K ₃ update calculation processing is performed, for example, when increasing the output, an abnormally low correction amount is calculated and stored in the RAM 107, and this correction amount K ₃ is used to perform lean fuel injection control. This prevents the inconvenience of ivy.

The calculation of the correction amount _K3 is permitted in the process described above, and when the judgment step 501 shown in FIG. ₂ is
A determination is made as to whether K ₂ >1, K ₂ =1, or K ₂ <1, and if K ₂ =1, the process of this routine is ended without performing any increase/decrease correction. If K ₂ <1, the process proceeds to step 502 to make a correction toward the reduction side, where the current correction amount ΔK ₃ is subtracted, for example, from the correction amount K ₃ m corresponding to the engine speed Nm at that time;
If K ₂ >1, the process proceeds to step 503 to increase the amount of correction, and the current correction amount ΔK ₃ is added to the correction amount K ₃ m. Then, proceed to step 504,
The subtracted or added correction amount K ₃ m is RAM10
7, the calculation step 125 of the correction amount _K3 is completed, and the process returns to step 122 again.

Incidentally, the correction amount _K3 may be stored in correspondence with the value of the engine rotation speed N as described above, but
Since the amount of memory becomes large, the engine speed may be stored in blocks of 100 rpm, for example. Further, the correction amount _K3 may be stored in correspondence with the intake air amount Q, or may be stored in correspondence with both the engine speed N and the intake air amount Q, or various other parameters representing the operating state of the engine. It may also be stored in correspondence with.

As mentioned above, while steps 122 to 125 of the main routine are repeatedly executed,
From the interrupt control unit 102 to the microprocessor 1
When an interrupt signal is input to 00, an interrupt routine starting from step 130 is immediately executed, as shown in FIG. Here, first, in step 131, a signal representing the engine speed N is fetched from the rotation speed counter 101, and then the process proceeds to step 132, where the intake air amount Q is sent from the intake air amount sensor 19 via the analog input port 104. Acquire the signal representing the next step.
133, these rotation speed N and intake air amount Q data are
It is stored in a predetermined area within the RAM 107. Then, proceed to step 134, and calculate the basic fuel injection amount t from the formula t=F×Q/N (where F is a constant) using the rotational speed N and intake air amount Q stored in step 133 above. Then, in the next step 135, the three correction amounts K ₁ and K ₂ calculated in the main routine and the correction amount K ₃ corresponding to the engine condition at that time are read out from the RAM 107 and an arithmetic expression T is used to correct the basic fuel injection amount t.
The corrected fuel injection amount T is calculated from =t×K ₁ ×K ₂ ×K ₃ . The fuel injection amount T calculated in this way is set as a fuel injection time in the counter 109 in step 136, and the fuel injection time set here is sent from the counter 109 as an injection signal to each injection via the power amplifying section 110. Valve 15a-15f
is applied at a predetermined timing, and fuel injection is performed according to a controlled injection amount (time). Then, return to the main routine at step 137,
The main routine is executed again by returning to the step at which it was interrupted due to the interrupt process, and in open loop control, air-fuel ratio control is performed that matches the operating state of the engine, and in feedback control, air-fuel ratio control is performed to bring it closer to the stoichiometric air-fuel ratio.

As explained above, according to the air-fuel ratio control method of the present invention, even during feedback control, when the engine operating state is not within the predetermined range suitable for updating the engine state correction information, and when the engine operating state is within the predetermined range, Until the detection signal of the air-fuel ratio sensor changes between the rich and lean air-fuel ratio states a predetermined number of times, the process of updating the engine state correction information based on the air-fuel ratio sensor detection signal will be stopped. However, after the engine operating state falls within a predetermined range and the detection signal of the air-fuel ratio sensor changes inversely between a rich air-fuel ratio state and a lean air-fuel ratio state a predetermined number of times, the engine state correction information is updated. Therefore, the engine state correction information is not updated and stored when the air-fuel ratio is disturbed, such as during transient operation of the engine.

Therefore, as in the past, the air-fuel ratio was controlled based on correction information for each engine state based on the air-fuel ratio sensor detection signal with a disturbed transient state, and the air-fuel ratio was controlled to become excessively lean, resulting in poor emissions. Without this, the air-fuel ratio can be controlled to an appropriate air-fuel ratio with good responsiveness during both feedback control and open-loop control, and good drivability can be ensured. Furthermore, in the method of the present invention, the delay period from when the engine operating state reaches a predetermined range suitable for updating the engine state correction information to when the engine state correction information is updated is determined by the number of inversions of the air-fuel ratio detection signal. Since this setting is made, it is possible to start updating the engine's inherent correction information as soon as the air-fuel ratio becomes stable. In other words, the time it takes for the engine to enter steady operation after transient operation and for the air-fuel ratio to stabilize through feedback control varies depending on the engine operating condition, surrounding environment, etc.
In the present invention, the start timing of the update process is set based on the number of inversions of the air-fuel ratio detection signal, rather than the time, so it is possible to start the update process even though the air-fuel ratio is not stable, or vice versa. There is no case where the update process is not started even though the air-fuel ratio has stabilized, and the update process can be started at an optimal timing.

[Brief explanation of the drawing]

The figures show an embodiment of the present invention, in which Fig. 1 is a schematic configuration diagram of the engine section, Fig. 2 is a block diagram of the control circuit, Fig. 3 is a flowchart showing the overall operation of air-fuel ratio control, and Fig. 4 is a flowchart showing the overall operation of air-fuel ratio control. A flowchart showing the calculation process of the correction amount _K2 , FIG. 5 a flowchart showing the calculation process of the correction amount _K3 , and FIG. 6 a flowchart showing the process of determining whether to calculate the correction amount _K3 . FIG. 7 is an explanatory diagram showing variations in the amount of correction. 11...Engine, 22...Air-fuel ratio sensor, 2
3...Rotational speed sensor, 24...Control circuit, 100
...Microprocessor, 107...RAM (non-volatile memory).

Claims (1)

[Claims] 1. Executed in parallel with feedback control in which an air-fuel ratio sensor detects the air-fuel ratio of the air-fuel mixture supplied to the engine from engine exhaust gas components, and corrects the air-fuel ratio of the air-fuel mixture based on the detection result. and updates engine condition correction information stored in a readable/writable non-volatile memory according to the detection signal of the air-fuel ratio sensor, and corrects the air-fuel ratio of the air-fuel mixture based on the engine condition correction information in the memory. In an air-fuel ratio control method that performs It is determined whether or not the detection signal of the fuel ratio sensor has reversely changed between a state representing a rich air-fuel ratio and a state representing a lean air-fuel ratio for a predetermined number of times. An air-fuel ratio control method characterized in that updating of the engine state correction information is stopped while it is determined that the inversion change of the detection signal of the air-fuel ratio sensor is less than a predetermined number of times after entering the range.