JPH0599043A - Method for judging failure of air fuel ratio sensing system - Google Patents

Abstract

PURPOSE:To surely detect failures such as disconnection, short circuit and the like by judging an output signal value of an air fuel ratio sensing system on the basis of upper and lower limit judging values never obtained in the normal running of an engine. CONSTITUTION:An electronic controller 40 compares an air fuel ratio signal outputted from a linear A/F sensor amplifier 45 with a desired air fuel ratio by the use of a linear air fuel ratio sensor S to judge which controls the air fuel raio either stoichiometric A/F feed-back or lean A/F feed-back. When the output signal value from the air fuel ratio sensing system is larger than a predetermined upper limit judging value continuously for a predetermined time in either one of the control conditions or when an engine is not under the predetermined acceleration or deceleration running condition and the output signal value from the air fuel ratio sensing system is smaller than the predetermined lower limit judging value continuously for the predetermined time, the air fuel sensing system is judged to be failured.

Description

Detailed Description of the Invention

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is called a so-called linear air-fuel ratio sensor and is used for feedback control of the air-fuel ratio to a target air-fuel ratio near the stoichiometric air-fuel ratio or on the fuel lean side of the stoichiometric air-fuel ratio according to the engine operating condition. The present invention relates to a failure determination method for an air-fuel ratio sensing system including an air-fuel ratio sensor used in the.

2. Description of the Related Art Conventionally, the characteristics of zirconia such as oxygen concentration cell action and oxygen ion pumping action have been utilized to make the air-fuel ratio of the air-fuel mixture supplied to the engine from the oxygen concentration in the exhaust gas more fuel-rich than the theoretical air-fuel ratio. There is known a so-called linear air-fuel ratio sensor capable of detecting not only the value on the fuel-lean side or the fuel-lean side, but also the value of the value. When a linear air-fuel ratio sensor is used, it works in cooperation with an air-fuel ratio sensor amplifier, an electronic control unit, a fuel injection valve, and various sensors that detect the operating state of the engine, and it is a relatively large engine, for example, during acceleration or starting. In the engine operating state where the output is required, the air-fuel ratio can be feedback-controlled near the stoichiometric air-fuel ratio, and during other steady running, the air-fuel ratio can be feedback-controlled to the target air-fuel ratio on the fuel lean side of about 22. In this way, accurately controlling the air-fuel ratio to the target value will improve engine performance by improving fuel efficiency, improving engine output, stabilizing idle rotation, improving exhaust gas characteristics, improving drivability, etc. Is extremely important. The linear air-fuel ratio sensor is a sensor cell that outputs an electric signal according to the oxygen concentration in the exhaust gas, a pump cell that moves oxygen ions according to the supplied pump current, a heater that heats the sensor cell and the pump cell to an active temperature, etc. Is equipped with. The air-fuel ratio sensor amplifier is a control circuit that outputs a pump current to the pump cell so that the output from the sensor cell becomes a set value, and an air-fuel ratio detection that outputs an air-fuel ratio signal according to the pump current exchanged between the control circuit and the pump cell. It is equipped with circuits.

However, in the air-fuel ratio sensing system including the linear air-fuel ratio sensor, the wiring between the sensor and the amplifier, the air-fuel ratio sensor amplifier, the wiring between the amplifier and the electronic control unit, a disconnection or a short circuit occurs. In this case, the air-fuel ratio control in the electronic control unit becomes impossible, which not only adversely affects the exhaust gas characteristics and the stabilization of the idle rotation, but also causes the engine to malfunction and, in the worst case, to stop the engine. The present invention has been made to solve such an inconvenience, and an object thereof is to provide a failure determination method of an air-fuel ratio sensing system capable of reliably detecting a failure of the air-fuel ratio sensing system such as disconnection or short circuit. And

In order to achieve the above object, in the present invention, a signal value corresponding to the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine is detected by detecting the oxygen concentration in the exhaust gas. According to the output signal value, the air-fuel ratio is feedback-controlled to one of the first target air-fuel ratio near the stoichiometric air-fuel ratio and the second target air-fuel ratio on the fuel lean side of the first target air-fuel ratio. In a method of determining a failure of an air-fuel ratio sensing system, the output signal value from the air-fuel ratio sensing system is a predetermined upper limit determination value when the air-fuel ratio is feedback-controlled to either one of the first and second target air-fuel ratios. A larger state continues for a first predetermined time, or the internal combustion engine is not in a predetermined acceleration or deceleration operation state, and the output signal value from the air-fuel ratio sensing system is below a predetermined value. When than determination value small state has continued over a second predetermined time, and judging that the air-fuel ratio sensing system is faulty, the fault determination method of the air-fuel ratio sensing system is provided.

The malfunction of the air-fuel ratio sensing system can be determined by whether or not the output signal value deviates from the upper and lower limit determination values that cannot occur during normal operation of the engine. In this case, when the air-fuel ratio sensing system is operating normally, the output signal value from the air-fuel ratio sensing system is a value equal to or higher than the predetermined lower limit determination value, except when the internal combustion engine is in a predetermined acceleration or deceleration operation state. Indicates. When detecting that the output signal value from the air-fuel ratio sensing system is smaller than this predetermined lower limit judgment value and making a failure judgment of the air-fuel ratio sensing system, the above-mentioned internal combustion engine fails in a predetermined acceleration or deceleration operation state. By prohibiting the determination, it is possible to reliably detect the failure of the air-fuel ratio sensing system.

An embodiment of the present invention will be described below with reference to the accompanying drawings. FIG. 1 shows a schematic configuration of an air-fuel ratio control device to which a failure determination method for an air-fuel ratio sensing system of the present invention is applied. The engine E is, for example, a 4-cylinder gasoline engine, and is designed so that the air-fuel mixture supplied to the cylinders can burn not only at the theoretical air-fuel ratio but also at a lean air-fuel ratio of about 22. There is. A fuel injection valve 2 is provided at each intake port of each cylinder of the engine E. The fuel injection valve 2 is electrically connected to the output side of an electronic control unit 40, which will be described later, and opens by a valve opening drive signal from the electronic control unit 40 to inject a required amount of fuel into the engine E. Supply. On the other hand, in the middle of the exhaust passage 3, a linear air-fuel ratio sensor S that detects the oxygen concentration in the exhaust gas is provided, and the linear A / F sensor amplifier 45 is provided.
It is connected to the electronic control unit 40 via. FIG. 2 shows the linear air-fuel ratio sensor S and the linear A / F sensor amplifier 4.
5 shows an internal configuration of No. 5. The linear air-fuel ratio sensor S has a sensor cell 2 whose base is a stabilized zirconia element.
0 and the pump cell 21 are connected via an insulating layer 22. Diffusion port 2 through which exhaust gas passes in both cells
3, 24 are formed, and diffusion holes 23, 2 are formed in the insulating layer 22.
A detection chamber 25 for accommodating the exhaust gas from 4 is formed, and these constitute a diffusion rate controlling body. A reference chamber 25a is formed in the insulating layer 22 and is configured to guide the reference gas atmosphere to the reference chamber 25a. Further, platinum electrodes 26 to 29 are provided in both cells as a catalyst,
These electrodes have a large number of micropores. Reference numeral 3 in the figure
Reference numeral 0 denotes an electric heater, and the electric heater 30 is current-controlled by a heater driving circuit 32 to heat the entire cell to a predetermined temperature and operate each cell in an activated state. The sensor cell 20 has a property of generating an electromotive force when there is a difference in oxygen concentration between the electrodes 26 and 27 according to the same principle as that of the conventional oxygen sensor, and the pump cell 21 conversely forces the pump current Ip between the electrodes 28 and 29. It has the property of pumping oxygen from the negative electrode side to the positive electrode side when flowing. Therefore, the linear A / F sensor amplifier 45 is used for the sensor cell 20.
Of the electromotive force Vs of the detection chamber 25 is detected and the electromotive force Vs is kept constant, that is, in the detection chamber 25 or the diffusion holes 23, 24.
The pump current Ip is feedback-controlled so that the inside is maintained at the oxygen concentration corresponding to the theoretical air-fuel ratio. Since the pump current Ip at this time continuously changes according to the air-fuel ratio,
The air-fuel ratio can be calculated from the pump current Ip. In the comparison circuit 10, the control unit 31 of the linear A / F sensor amplifier 45 compares the electromotive force Vs of the sensor cell 20 with a reference voltage Vref (for example, 0.4V) corresponding to the stoichiometric air-fuel ratio, and outputs the output from the integration amplifier. The positive or negative control output integrated by 12 is applied between the electrodes 28 and 29 of the pump cell 21, and as described above, the pump current Ip is applied to the pump cell 21 so that the electromotive force Vs of the sensor cell 20 becomes equal to the reference power Vref. Shed. A resistor 15 for current detection is provided in the circuit of the pump current Ip, and the pump current Ip is detected by the current detection circuit 13 from the voltage drop of the resistor 15. Further, the output of the circuit 13 is input to the adding circuit 14,
An air-fuel ratio signal Vout corresponding to the air-fuel ratio (A / F) as shown in FIG.
0 is being supplied. Vout = G · Ip + Vst Here, G is a current / voltage conversion gain, and Vst is a step-up voltage (for example, 2.5V). Sensor cell 20
A detection circuit 38 for detecting the sensor cell electromotive force Vs is connected between the control unit 31 of the linear A / F sensor amplifier 45 and the detection signal Vs is supplied to the electronic control unit 40. A pump cut circuit 39 that receives a pump cut signal (high level signal) from the electronic control unit 40 and cuts the pump current Ip is connected between the comparison circuit 10 and the integration amplifier 12. The input terminal (base terminal) 39a side of the pump cut circuit 39 is connected to a predetermined voltage power source + Vcc via a resistor 39b. Electronic control unit 4
0 is an electromotive force Vs detected by the sensor cell electromotive force detection circuit 38 described above, and although not shown, a heater temperature detection circuit (this circuit detects applied voltage and supply current of the heater 30 to detect heater temperature and abnormality). To monitor)
When the linear air-fuel ratio sensor S is not sufficiently heated by the heater 30, the above-mentioned pump cut signal is detected. The output signal is output to the pump cut circuit 39. When the pump cut signal is output to the pump cut circuit 39, the output side voltage level of the comparison circuit 10 becomes 0, and as a result, the detection chamber 25 is kept at the stoichiometric air-fuel ratio as the air-fuel ratio signal Vout. The pseudo signal Vst (see FIG. 3) will be output. If the pump cut signal line between the pump cut circuit 39 and the electronic control unit 40 is broken for some reason, the input terminal (base terminal) 39a side of the pump cut circuit 39 is pulled up by a predetermined voltage (for example, 5V). Therefore, a high level is input to the pump cut circuit 39,
Even when the signal line is broken, the pump current Ip can be set to 0 and blackening of the linear air-fuel ratio sensor S can be prevented. In the present specification, the air-fuel ratio sensing system including the linear air-fuel ratio sensor S, the linear A / F sensor amplifier 45, the wiring between the sensor S and the amplifier 45, and the wiring between the amplifier 45 and the electronic control unit 40 described above. Will be defined. The electronic control unit 40 has a function of constantly monitoring a failure of the air-fuel ratio sensing system as described later and controlling the amount of fuel supplied to the engine E, that is, the air-fuel ratio. The electronic control unit 40 is a central processing unit (CPU) that executes programs for failure monitoring of the air-fuel ratio sensing system and air-fuel ratio control.
40a, a storage device 40b for storing the above-mentioned programs and calculation results by the CPU, various program variable values, etc., inputting signal values from various sensors, outputting a valve opening drive signal for driving the fuel injection valve 2, etc. It is composed of an input / output circuit (not shown) and the like. On the input side of the electronic control unit 40, various sensors that detect the operating state of the engine E, for example, an air flow sensor 41 that is arranged in the intake passage and detects the intake air amount from the generation cycle of Karman vortices, the engine A rotation speed sensor 42 for detecting a rotation speed, an ignition key switch sensor 43 for detecting an on / off state of an ignition key switch (SW), a water temperature sensor 44 for detecting a cooling water temperature of the engine E, etc. are connected to the electronic control unit 40. Engine operating state signals detected by these sensors are input. When the electronic control unit 40 executes the air-fuel ratio feedback control, the target air-fuel ratio corresponding to the engine operating state from the various sensors described above is set. For example, it has been detected that the engine E is in an operating state in which a relatively large engine output is required, that is, in an operating state in which the air-fuel ratio should be feedback-controlled to the stoichiometric air-fuel ratio, such as during rapid acceleration operation and start acceleration operation. In this case, the target air-fuel ratio is set to the theoretical air-fuel ratio (14.7). On the other hand, in the operating states other than the above, the target air-fuel ratio is set to a predetermined value (for example, 22) on the fuel lean side of the theoretical air-fuel ratio or a value according to the operating state. Then, the electronic control unit 40 compares the air-fuel ratio signal Vout output from the linear A / F sensor amplifier 45 with the target air-fuel ratio and calculates a feedback correction coefficient so that the air-fuel ratio becomes the target air-fuel ratio, The fuel supply amount is calculated by multiplying the basic fuel amount calculated by the load and the engine speed by the above feedback correction coefficient, the correction coefficient according to the cooling water temperature, and the like. Then, a valve opening drive signal corresponding to the calculated fuel supply amount is supplied to the fuel injection valve 2 to provide a required amount of fuel to the engine E.
To be injected and supplied. On the other hand, when the electronic control unit 40 performs the open-loop control of the air-fuel ratio, the basic fuel amount calculated by the engine load (for example, volumetric efficiency Ev) and the engine speed is provided with a correction coefficient or the like according to the cooling water temperature. The fuel supply amount is calculated by multiplication. In the present invention, the air-fuel ratio control method by feedback control or open loop control is not particularly limited, and various conventionally known methods can be adopted. Next, the failure determination method of the air-fuel ratio sensing system according to the present invention will be described with reference to the flowcharts shown in FIGS. The electronic control unit 40 firstly performs step S10.
In S12 and S12, the linear air-fuel ratio sensor S is used to determine whether the air-fuel ratio is feedback-controlled. In step S10, it is determined whether or not the air-fuel ratio is feedback-controlled (Stoichio A / F feedback control) with the stoichiometric air-fuel ratio as a target value.
At 12, it is determined whether the air-fuel ratio is under feedback control (lean A / F feedback control) with the air-fuel ratio on the fuel lean side of the stoichiometric air-fuel ratio as the target value. If any of these determinations is negative (No), steps S10 and S12 are repeatedly executed. That is,
When the air-fuel ratio feedback control is not executed, the failure determination of the air-fuel ratio sensing system is not performed. If the determination result of either step S10 or S12 is affirmative (Yes), the process proceeds to step S14,
It is determined whether or not the air-fuel ratio signal Vout is larger than the predetermined upper limit determination value _VHF . As shown in FIG. 3, the upper limit determination value V _HF is an upper limit value V _H detected by the air-fuel ratio sensing system during normal operation of the engine E (for example, the air-fuel ratio 28
Value slightly larger than 4.4V corresponding to
4.5V). If the air-fuel ratio signal Vout is less than or equal to the upper limit determination value _VHF , that is, if the determination result of step S14 is negative, the process proceeds to step S18 of FIG. In step S14, if it the air-fuel ratio signal Vout is greater than the upper limit determination value V _HF is detected, the state the air-fuel ratio signal Vout is greater than the upper limit determination value V _HF is in a predetermined t
It is determined whether or not the operation has continued for 1 hour (for example, 10 seconds) (step S16). This determination prevents the electronic control unit 40 from immediately determining that the air-fuel ratio sensing system is abnormal due to an abnormal value that temporarily occurs due to noise or the like. If the state in which the air-fuel ratio signal Vout is larger than the upper limit determination value V _HF does not continue for a predetermined time, the process proceeds to step S18, but if it continues, step S2.
In step 4, it is determined that the air-fuel ratio sensing system is out of order, and this is stored. At this time, for example, a warning light may be lit on the instrument panel or the like to warn the driver that the air-fuel ratio sensing system is out of order. In step S18 of FIG. 5, it is determined whether the engine E is in a predetermined acceleration operation state or a predetermined deceleration operation state. Such a determination can be made, for example, by detecting the valve opening position and valve opening speed of a throttle valve (not shown). When the engine E is in a predetermined acceleration operation state or a predetermined deceleration operation state, the air-fuel ratio sensing system is operating normally such that the air-fuel ratio detected from the exhaust gas shows a very small value (rich signal). In some cases, however, a peculiar air-fuel ratio signal may be output. In such a case, the failure determination cannot be made, so the process returns to step S10 described above. If the determination result in step S18 is negative, that is, if it is determined that the vehicle is not traveling in the predetermined acceleration or deceleration, the process proceeds to step S20, and the air-fuel ratio signal Vout is smaller than the predetermined lower limit determination value V _LF . Determine whether or not. As shown in FIG. 3, the lower limit determination value V _LF is smaller than the lower limit _VL (for example, 0.6 V corresponding to the air-fuel ratio 10) detected by the air-fuel ratio sensing system during normal operation of the engine E. A small value (for example, 0.5
V) is set. If the air-fuel ratio signal Vout is greater than or equal to this lower limit determination value _VLF , that is, if the determination result of step S20 is negative, there is no abnormality in the air-fuel ratio sensing system, and the process returns to step S10 of FIG. On the other hand, in step S20, the air-fuel ratio when the signal Vout is detected to be smaller than the lower limit determination value V _LF, the air-fuel ratio signal Vout is lower determination value V _LF from a small state a predetermined time t2 (e.g., It is determined whether it has continued for 10 seconds (step S22). This determination prevents the electronic control unit 40 from immediately determining that the air-fuel ratio sensing system is abnormal due to an abnormal value that instantaneously occurs due to noise or the like. If the state in which the air-fuel ratio signal Vout is smaller than the lower limit determination value V _LF does not continue for a predetermined time, there is no abnormality in the air-fuel ratio sensing system, and in this case also, the process returns to step S10 in FIG. When it is determined in step S22 that the air-fuel ratio signal Vout is smaller than the lower limit determination value V _LF for a predetermined time, the process proceeds to step S24 described above, and the air-fuel ratio (A / F) It is determined that the sensing system is out of order, and this is stored. When a failure of the air-fuel ratio sensing system is determined,
The electronic control unit 40 stops the feedback control of the air-fuel ratio and executes the open loop air-fuel ratio (A / F) control described above. In this case, since the air-fuel ratio information from the malfunctioning air-fuel ratio sensing system is not used, the situation in which the air-fuel ratio control cannot be prevented is prevented and the air-fuel ratio is properly maintained. Then, it is determined whether or not the ignition key switch (SW) 43 is off (step S
28), the determination result is negative, that is, as long as the engine E is operating, step S26 is repeatedly executed,
The open loop A / F control is continued. On the other hand, turn off the ignition key switch (SW) and set the engine E
Is stopped, the failure determination of the air-fuel ratio (A / F) sensing system stored in the storage device 40b is canceled (step S30), and the execution of the program ends. Therefore, when the engine E is restarted, the failure determination of the air-fuel ratio sensing system is restarted from the beginning.

As is apparent from the above description, according to the device of the present invention, when the air-fuel ratio is feedback-controlled to the target air-fuel ratio, the output signal value from the air-fuel ratio sensing system is higher than the predetermined upper limit judgment value. The large state continues for the first predetermined time, or the internal combustion engine is not in the predetermined acceleration or deceleration operation state, and the output signal value from the air-fuel ratio sensing system is smaller than the predetermined lower limit determination value. When the air-fuel ratio sensing system is determined to be out of order when it continues for the second predetermined time, it is possible to reliably detect the failure of the air-fuel ratio sensing system, and to detect an abnormality in the air-fuel ratio sensing system. Also, if the air-fuel ratio is immediately subjected to open loop control, exhaust gas characteristics will deteriorate, drability will decrease, idle rotation will become unstable, etc. To prevent harm, or can be kept to a minimum.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of an air-fuel ratio control device to which a failure determination method for an air-fuel ratio sensing system of the present invention is applied.

2 is a circuit diagram showing the internal configuration of a linear air-fuel ratio sensor S and a linear A / F sensor amplifier 45 shown in FIG.

FIG. 3 is a graph showing the relationship between the air-fuel ratio signal Vout output from the linear A / F sensor amplifier 45 shown in FIG. 1 and the air-fuel ratio.

FIG. 4 is a part of a flowchart showing a procedure of a failure determination of the air-fuel ratio sensing system executed by the electronic control unit 40 shown in FIG.

5 is a flowchart of the remaining part following the procedure of the failure determination of the air-fuel ratio sensing system of FIG.

[Explanation of symbols]

 E Internal combustion engine S Linear air-fuel ratio sensor 2 Fuel injection valve 10 Comparison circuit 12 Integration circuit 13 Current detection circuit 14 Addition circuit 20 Sensor cell 21 Pump cell 30 Heater 31 Control circuit 38 Sensor cell electromotive force detection circuit 39 Pump cut circuit 40 Electronic control device 45 Linear A / F sensor amplifier

Claims (1)

[Claims] 1. A signal value corresponding to the air-fuel ratio of an air-fuel mixture supplied to an internal combustion engine is output by detecting the oxygen concentration in the exhaust gas, and the air-fuel ratio is set in the vicinity of the theoretical air-fuel ratio in accordance with the output signal value. In the failure determination method of the air-fuel ratio sensing system, which performs feedback control to either one of the first target air-fuel ratio and the second target air-fuel ratio on the fuel lean side of the first target air-fuel ratio, the air-fuel ratio is set to the first When performing feedback control to either one of the second target air-fuel ratio and the second target air-fuel ratio, a state in which the output signal value from the air-fuel ratio sensing system is larger than a predetermined upper limit determination value continues for a first predetermined time, or The internal combustion engine is not in the prescribed acceleration or deceleration operation state,
And, when the state where the output signal value from the air-fuel ratio sensing system is smaller than the predetermined lower limit determination value continues for the second predetermined time, it is determined that the air-fuel ratio sensing system is in failure. Failure determination method for air-fuel ratio sensing system.