JPH0747942B2 - Compensation control method for sensor O 2 in air-fuel ratio control of vehicle engine - Google Patents

Description

Detailed Description of the Invention [Industrial applications]

The present invention relates to a compensation control method of the O ₂ sensor in the air-fuel ratio control of the vehicle engine to compensate for the deterioration of the O ₂ sensor.

[Prior art]

In this type of O ₂ sensor compensation control, a change in the resistance value of the O ₂ sensor is detected, it is judged as deterioration, and the slice level is changed in proportion to the resistance change in proportion to the deterioration amount. What is made to be (Japanese Patent Publication No. 58-1746), or the divided value for the upper peak of the O ₂ sensor output voltage is used as the slice level, and even if the peak value of the output voltage becomes smaller due to deterioration of the O ₂ sensor, It is known that the slice level for detecting stoichio is set (Japanese Patent Publication No. 58-1745).

[Problems to be Solved by the Invention]

However, as the O ₂ sensor deteriorates, not only the maximum output voltage decreases and the internal resistance value increases, but also the response time is affected by the deterioration. This change in response time has a large effect, and if the response time from so-called rich to lean becomes long due to deterioration of the O ₂ sensor, there arises a problem that the air-fuel ratio is lean-shifted. The present invention has been made in view of the above circumstances, and deteriorated compensation for the response of the O ₂ sensor, the O ₂ sensor in the air-fuel ratio control of the vehicle engine to allow the proper air-fuel ratio control It is an object to provide a compensation control method.

[Means for Solving the Problems]

In order to achieve the above object, the compensation control method of the O ₂ sensor in the air-fuel ratio control of the vehicle engine according to the present invention, the output value of the O ₂ sensor for detecting the oxygen concentration in the exhaust gas of the engine is compared with the slice level. Then, the air-fuel ratio is detected and the fuel supply amount is controlled based on this air-fuel ratio.
A step of detecting a response time of the O ₂ sensor, a procedure of calculating the area ratio of the O ₂ sensor output values above and below the said slice level, a procedure for setting the optimum area ratio based on the response time, the area ratio And a procedure for updating the slice level according to the deviation amount between the optimum area ratio and the optimum area ratio.

[Action]

In the present invention, the area ratio of the O ₂ sensor output values above and below the slice level is calculated, and the optimum area ratio is set based on the response time of the O ₂ sensor output values. Then, the slice level is updated according to the amount of deviation between the area ratio and the optimum area ratio. Therefore, the compensation due to the deterioration of the O ₂ sensor is reflected in the slice level, and the air-fuel ratio can be appropriately detected even if the response time changes due to the deterioration of the O ₂ sensor.

【Example】

An embodiment of the present invention will be specifically described below with reference to FIGS. 1 to 5. In FIG. 1, reference numeral 20 is an electronic control unit including a microcomputer for controlling the air-fuel ratio of the engine, and CPU1, ROM2, RAM3, input port 4, and output port 5 are connected to each other via a data bus 6. ing. The input port 4 includes an O ₂ sensor 7 for detecting the oxygen concentration in the exhaust gas of the engine, a water temperature sensor 8 for detecting the cooling water temperature representative of the engine temperature, a stoll sensor 9 for detecting the throttle opening, and an intake air. A suction pipe pressure sensor 10 for detecting pipe pressure (or an intake air amount sensor for detecting intake air amount) is connected through an A / D converter 11, and a crank angle sensor for detecting engine speed.
12 are connected. On the other hand, an injector 13 is connected to the output port 5 via a drive circuit 12. The ROM2 stores fixed data such as control programs and various tables, and the RAM3 stores data after processing output signals of the sensors and the above.
The data processed by the CPU is stored. In the CPU1, according to the control program stored in the ROM2, based on various data stored in the RAM3,
A control amount such as a fuel injection amount is set, and a corresponding signal is output to the injector 13 or the like to perform air-fuel ratio control. Further, the electronic control unit 20 constitutes a control system in which a dither variation is given to the air-fuel ratio on the intake port side and this variation is detected on the O ₂ sensor 7 side. In this system, O ₂
The output of the sensor 7 shows a fluctuation wave close to a rectangular wave if the A / F (air-fuel ratio) is swung around the stoichio (theoretical air-fuel ratio) (see FIG. 2). However, in the case of a new O ₂ sensor, it is not a perfect rectangular wave due to the response delay of the O ₂ sensor system, etc., but the waveform is distorted (lower side) as shown in the figure. . Therefore, in general, the slice level is determined so that the area ratio between the upper side and the lower side of the shaded portion is 1: 1 or a certain ratio (for example, 4: 6). In this case, if the time t from the maximum value to the minimum value of the O ₂ sensor output value is measured, the O ₂ sensor 7 deteriorates with time, and the response time t
You can see that is getting longer. For this reason, stoichio cannot be detected by the slice level determination method in which the area ratio is simply divided into a fixed ratio. Therefore, the area ratio is also changed at a constant rate along with the change of the response time t due to the deterioration of the O ₂ sensor 7.
The slice level is changed to compensate for the deterioration of the O ₂ sensor 7. Incidentally, the deterioration characteristic indicated by the response time and the area ratio due to deterioration of the O ₂ sensor 7, and the shows the output fluctuation waveform of the O ₂ sensor 7 in this case in the figure, so that the third view and Figure 4 . Here, since the response time of the O ₂ sensor 7 is significantly different depending on the engine speed and the load, the response time lookup table consisting of each rotation speed and load has a new value for the O ₂ sensor 7, The degree of deterioration of the O ₂ sensor 7 may be calculated by comparing with. In addition, the steady constant speed traveling condition, the vehicle speed, the number of revolutions, and the load are determined at only one point, and the reference value of the response time of the O ₂ sensor 7 at that time is obtained in advance (stored in ROM 2 as fixed data. ), And deterioration may be detected by measuring the response time only when the vehicle travels under the same conditions as this value. By doing so, the amount of information can be reduced. Next, the control procedure by the electronic control unit 20 will be described based on the flowchart of FIG. FIG. 5 shows a routine for reflecting the compensation for the deterioration of the O ₂ sensor 7 in the slice level. For example, in the steady state, an interrupt is executed every set time. First, A / D conversion was performed via the A / D converter 11 in step S1.
The output value VO ₂ of the O ₂ sensor 7 is read, and in step S2, the O ₂ sensor output value (VO ₂ ) _OLD read during the previous routine execution is compared with the current output value VO ₂ . And in the case of (VO _{2) OLD>} VO _2, the process proceeds to step S3, the previous O ₂ sensor output value (VO _{2) OLD} I read when running before the previous routine and the O ₂ sensor output values (VO ₂₎ Compared with _{OLD (-1)} , (VO ₂ ) _{OLD (-1)} ≤ (VO ₂ ) _OLD and the previous output value (VO ₂ ) _OLD is the current output value VO ₂ and the previous previous output value If (VO ₂ ) _{OLD (-1)} or more is judged to have indicated the maximum value of the O ₂ sensor output value during the previous routine execution, the time from the maximum value to the minimum value of the O ₂ sensor output value, That is, in order to measure the response time t, the process proceeds to step S4, the timer is started to exit the routine, and if (VO ₂ ) _{OLD (-1)} > (VO ₂ ) _OLD , the process proceeds to step S7. On the other hand, if (VO ₂ ) _OLD ≤ VO ₂ in step S2, the process proceeds to step S5, and the previous O ₂ sensor output value (VO ₂ ) _OLD and the previous O ₂ sensor output value (VO ₂ ) _OLD Compared with _(-1) , (VO ₂ ) _{OLD (-1)} > (VO ₂ ) _OLD , and the previous output value (VO ₂ ) _OLD is the current output value VO ₂ and the previous previous output value ( VO ₂ ) If it is judged that the O ₂ sensor output value at the time of the previous routine execution showed a minimum value when it was _{OLD (-1)} or less, proceed to step S6, stop the timer, and count by the timer, that is, O ₂ The response time t from the maximum value to the minimum value of the output value of the sensor is stored in the predetermined address #C of RAM3, the routine is exited, and (VO ₂ ) _{OLD (-1)} ≤ (VO ₂ ) _OLD In case of, it progresses to step S7. In step S7, the slice level V _SL ′ is calculated from the current O ₂ sensor output value VO ₂ to obtain the difference value α, and in step S8 O
₂ Compare the sensor output value VO ₂ with the slice level V _SL ′, and if VO ₂ ≦ V _SL ′, proceed to step S9, where the O ₂ sensor output value VO ₂ is below the slice level V _SL ′ Judging from the first time, in the case of the first time, the integrated value B stored in the predetermined address #B of the RAM3 in step S10 is cleared and the process proceeds to step S11. In step S11, the integral value B stored in the predetermined address #B of the RAM 3 is read, the difference value α is added to the integral value B, and the integral value B stored in the address #B is updated. , Exit the routine. That is, the integrated value B
Represents the area during which the O ₂ sensor output value VO ₂ becomes less than or equal to the slice level V _SL ′ (the area corresponding to one valley below the shaded portion in FIG. 2). On the other hand, in step S8, if VO ₂ > V _SL ′, the process proceeds to step S12, refers to the value of the flag FLG, and if the flag FLG is set (FLG = 1), the process proceeds to step S13. In the flag FLG, the O ₂ sensor output value VO ₂ crosses the slice level three times, that is, the O ₂ sensor output value VO ₂ passes the maximum value and the minimum value during this period, and VO ₂ > V _SL ′ again. It is for judging that. Then, in step S13, the difference value α calculated in step S7 is added to the integral value A stored in the predetermined address #A of the RAM 3 to update the integral value A, and step S14
Proceed to to clear the flag FLG and exit the routine. The integrated value A represents the area during which the O ₂ sensor output value VO ₂ takes a value larger than the slice level (the area corresponding to one mountain above the shaded portion in FIG. 2). Also, the flag FLG is cleared (FLG =
0), the process proceeds to step S15, the O ₂ sensor output value VO ₂ becomes a value larger than the slice level V _SL ′, and it is judged whether it is the first time or not. To step S13, and in the case of the first time, step S16
Go to. In step S16, the integrated values A and B are read from the predetermined addresses #B and #A of the RAM 3 to calculate the area ratio B / A, and step S17
Then, the response time t from the maximum value to the minimum value of the O ₂ sensor output value VO ₂ stored at the predetermined address #C of the RAM 3 is
Is read out and the optimum area ratio (B / A) _OP is obtained by a table search based on this response time t. The optimum area ratio (B / A) _OP is a target value for obtaining a slice level corresponding to Stoichio based on a change in response time t due to deterioration of the O ₂ sensor 7. For example, it is obtained in advance by experiments and stored in ROM2. It is stored as a table with the response time t as a parameter. Then, the process proceeds to step S18, the optimum area ratio (B / A) _OP is subtracted from the area ratio B / A to calculate the deviation amount X, and step S
In step 19, it is determined whether the deviation amount X is a negative value. If the deviation amount X is a negative value, the process proceeds to step S20 and the deviation amount X is added to the slice level to update this slice level. If the deviation amount X is 0 or a positive value in step S19, the process proceeds to step S21, and the deviation amount X is subtracted from the slice level to update the slice level. After updating the slice level, the process proceeds to step S22 and the integral value A stored in the predetermined address #A of the RAM 3 is stored.
Is cleared, the slice level V _SL ′ is subtracted from the O ₂ sensor output value VO ₂ in step S23 to obtain the difference value α, and step S24
Then, it is determined whether the difference value α is a positive value. If α> 0, the process proceeds to step S13. If α ≦ 0, the process proceeds to step S25 to set the flag FLG and exit the routine. . Thus, the optimum area ratio (B / A) _OP is obtained based on the response time t that fluctuates due to the deterioration of the O ₂ sensor 7, and the optimum area ratio (B / A) _OP and the O ₂ sensor above and below the slice level are obtained. so as to update the slice level by the deviation X between the area value B / a output value VO _2, since to reflect the compensation for the deterioration of the O ₂ sensor 7 in the slice level, the response due to deterioration of the O ₂ sensor 7 Even if the time changes, the air-fuel ratio can be detected appropriately, and the fuel supply amount (fuel injection pulse width) by the injector 13 set based on this air-fuel ratio becomes appropriate, and the O ₂ sensor 7 deteriorates. The lean shift of the air-fuel ratio due to is prevented. The A / F fluctuation given to the intake port to the engine at this time may be various ones such as a trapezoid having a constant inclination angle instead of a rectangular waveform. In any case, it is desirable to have a constant dither waveform, and as shown in PI control, when I minutes are changed by the number of rotations and the load, the response time is It seems that it is unsuitable for detection of deterioration because the separation calculation is not constant due to the time change of I minutes. Therefore, in the sense of accuracy, it can be said that it is better to give A / F fluctuation of the dither waveform. The output of the O ₂ sensor does not always change from peak to peak. Therefore, for example, the response time from the peak to the maximum during one minute may be used for the determination of deterioration. Alternatively, the amount of change (response speed) when the O ₂ sensor output value changes from rich to lean,
The maximum of 1 minute should be used for determining deterioration. In order to reflect this determination result on the slice level, it is preferable to prepare in advance a chart regarding the response speed of the O ₂ sensor and the area ratio above and below the slice level.

【The invention's effect】

As described in detail above, the present invention slices according to the amount of deviation between the area ratio of the O ₂ sensor output values above and below the slice level and the optimum area ratio set based on the response time of the O ₂ sensor output values. I'm trying to update the level, so O ₂
Compensation due to sensor deterioration is reflected in the slice level,
Even if the response time changes due to deterioration of the O ₂ sensor, the air-fuel ratio can be detected properly, lean shift due to deterioration of the O ₂ sensor can be prevented, and the excellent effect of improving exhaust emission can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is an A / F fluctuation at the intake port of the engine and corresponding O
₂ shows the output fluctuation waveform of the sensor, FIG. 3 is an explanatory view showing the relationship between the response time and the area ratio due to the deterioration of the O ₂ sensor, and FIG. 4 shows the output fluctuation waveform of the O ₂ sensor at that time. FIG. 5 is a flowchart showing the control procedure. 1 ... CPU, 2 ... ROM, 3 ... RAM, 4 ... input port, 5 ... output port, 6 ... data bus, 7 ... O ₂ sensor, 13 ... injector, 20 ... electronic control apparatus.

Claims (3)

[Claims] Claim: What is claimed is: 1. An air-fuel ratio is detected by comparing an output value of an O ₂ sensor for detecting an oxygen concentration in exhaust gas of an engine with a slice level, and a fuel supply amount is controlled based on the air-fuel ratio. , The procedure of detecting the response time of the O ₂ sensor, which is the repetition time when the output value of the O ₂ sensor cyclically changes to the air-fuel ratio rich state and the air-fuel ratio lean state, and the O above and below the slice level. ₂ Procedure for calculating the area ratio of sensor output values, procedure for setting the optimum area ratio based on the response time, and procedure for updating the slice level according to the deviation amount between the area ratio and the optimum area ratio. A method for compensating control of an O ₂ sensor in air-fuel ratio control of a vehicle engine, comprising: 2. The air-fuel ratio control of a vehicle engine according to claim 1, wherein the response time is a time from when the O ₂ sensor output value reaches a maximum value to a minimum value. O ₂ sensor compensation control method. 3. A method of compensating control of an O ₂ sensor in an air-fuel ratio control of a vehicle engine according to claim 1, wherein a response speed is used instead of the response time.