JP2003090821A - System for detecting abnormality in air-fuel ratio system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a system for detecting abnormality in the air-fuel ratio system capable of detecting abnormality in the air-fuel ratio sensor with a smaller number of signal lines. SOLUTION: This system for detecting abnormality superimposes P/START information indicating abnormality on YRPVS output. Thereby, there is no need to prepare a signal line indicating the P/START information. It also prevents increasing troubles in wiring due to increasing additional signal lines and lowering reliability due to disconnection of the wire.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an abnormality detection system for an air-fuel ratio detection system. More specifically, the present invention relates to a method for protecting an abnormality detection system of an air-fuel ratio detection system, which can detect various abnormalities without increasing the number of signal lines. INDUSTRIAL APPLICATION This invention can be used for the control system of the air-fuel ratio sensor which can detect the air-fuel ratio of internal combustion engines, such as a gasoline engine, from oxygen concentration.

[0002]

2. Description of the Related Art An oxygen sensor is provided in an exhaust system in order to reduce CO, NOx, HC and the like in exhaust gas by controlling an air-fuel ratio of an air-fuel mixture supplied to an internal combustion engine such as a gasoline engine to a target value. It is known that the fuel supply amount is feedback-controlled in accordance with the oxygen concentration in the exhaust gas that has a correlation with the air-fuel ratio.

As an oxygen sensor used for such feedback control, a λ sensor whose output changes abruptly at a specific oxygen concentration (especially in the vicinity of a stoichiometric air-fuel ratio atmosphere) and an output which continuously outputs from a lean region to a rich region. Mainly used are variable range air-fuel ratio sensors. Since the full-range air-fuel ratio sensor can continuously measure the oxygen concentration in the exhaust gas as described above and can improve the speed and accuracy of feedback control, it is used when higher speed and higher accuracy control is required. Has been.

In the above-mentioned full-range air-fuel ratio sensor, two cells using an oxygen ion conductive solid electrolyte body are arranged so as to face each other, and one cell is used as a pump cell for pumping out and pumping oxygen in an interval, Further, the other cell is used as an oxygen concentration detection cell that generates a voltage due to the oxygen concentration difference between the oxygen reference chamber and the interval, and the pump cell is operated so that the output of the oxygen concentration detection cell becomes constant, and at that time, the current is supplied to the pump cell. The current is measured as a proportional value to the measured oxygen concentration. The operating principle of this full-range air-fuel ratio sensor is described in detail in Japanese Patent Application Laid-Open No. 62-148849 filed by the present applicant. On the other hand, as an abnormality detection method of the air-fuel ratio sensor for detecting whether or not such an air-fuel ratio sensor is normally operating, as a method of detecting the abnormality of the air-fuel ratio sensor disclosed in Japanese Patent Application Laid-Open No. 3-272452 of the present applicant. Various methods such as "abnormality diagnosis method" are disclosed.

[0005]

However, an ECU (Electronic Control Unit) or the like reads the result of the abnormality detection from the input signal line, but since the number of this signal line is used for other purposes, it should be avoided as much as possible. Is desired. The present invention solves such a problem, and an object of the present invention is to provide an abnormality detection system of an air-fuel ratio detection system capable of performing abnormality detection of an air-fuel ratio sensor with a smaller number of signal lines. .

[0006]

An abnormality detection system for an air-fuel ratio detection system according to the present invention includes a sensor, a control circuit connected to the sensor with a plurality of lead wires, and a control circuit for controlling the sensor and the control circuit. In the abnormality detection system of the air-fuel ratio detection system, which comprises an engine control device to which a signal from is input, the control circuit has abnormality detection means for detecting an abnormality of the sensor or the lead wire, and the abnormality detection means. Is characterized by notifying the engine control device of the abnormality by setting the voltage of the signal to a voltage outside the normal range.

The sensor is composed of a combination of an oxygen pump cell and an oxygen concentration detection cell, and the control circuit controls the oxygen pump cell so that the output voltage of the oxygen concentration detection cell becomes a predetermined value. The control circuit outputs an internal resistance signal obtained by converting the internal resistance of the oxygen concentration detection cell into a voltage to the engine control device, and the abnormality detection means normalizes the value of the internal resistance signal. By setting the value outside the time range, it is possible to notify the engine control device of the abnormality.

[Operation] The abnormality detection system of the present air-fuel ratio detection system utilizes the fact that the voltage is within a certain range when a normal signal is output to the signal line, and when an abnormality occurs, a voltage outside the range is used. It is characterized by using it to notify an abnormal state. This eliminates the need to prepare a new signal line to notify the abnormal state, reduces the number of wires between the air-fuel ratio detection system and the ECU to reduce complexity, improve reliability, and increase the signal of the corresponding signal line. Since it is possible to determine other abnormal states at the same time when confirming the adequacy of, the processing of the ECU can be reduced, which is preferable.

Further, the abnormality detection system of the present air-fuel ratio detection system is an air-fuel ratio sensor in which an oxygen pump cell and an oxygen concentration detection cell are combined, and an abnormality signal is superimposed on the internal resistance signal representing the internal resistance of the oxygen concentration detection cell. By doing so, various abnormality detections can be performed without increasing the number of signal lines with a slight circuit change. Further, when a software programmable digital circuit or element is used as the control circuit, the same effect can be obtained without changing the circuit, which is more preferable.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Since the abnormality detection system of the present air-fuel ratio detection system detects an abnormal state without increasing the number of signal lines between the air-fuel ratio detection system and the ECU, it is possible to superimpose abnormality information on existing signal lines. Is going. In addition, as a method of this superposition, it is possible to uniquely determine the voltage range of the corresponding signal line at the time of normal operation, and normally, by utilizing the fact that the voltage range on the input side of the ECU is wider than the former, This is done by setting the voltage outside the normal range. As a result, the complexity of routing the wiring due to the increase of extra signal lines does not increase, and the reliability is not deteriorated due to the disconnection of the wiring. Furthermore, since the output ranges of both the existing signal and the abnormal signal do not overlap, no problem occurs in normal use.

[0011]

Embodiments of the abnormality detection system for an air-fuel ratio detection system according to the present invention will be described in detail below with reference to FIGS. 1. Configuration of Air-Fuel Ratio Sensor A sensor element 10 used in an abnormality detection system of an air-fuel ratio detection system is shown in FIG. The sensor element 10 is arranged in an exhaust gas system of a gasoline engine, is configured by joining two cells, and is connected to a sensor control circuit 50 via three wires 41, 42, 43. For this reason, in the sensor control circuit 50, normally, the oxygen concentration in the exhaust gas and the temperature of the sensor element 10 are mainly measured. In addition, three wires connected to the two cells of the sensor element 10 are also used. It also has a function of detecting abnormalities 41, 42, and 43.

A heater 70 controlled by a heater control circuit 60 is attached to the sensor element 10 via a ceramic-based bonding agent. The heater 70 is made of ceramic such as alumina as an insulating material, and the heater wiring 72 is arranged inside the heater 70. The heater control circuit 60 functions to supply electric power to the heater 70 so as to maintain the temperature of the sensor element 10 measured by the sensor control circuit 50 at the target value and maintain the temperature of the sensor element 10 at the target value. .

The sensor element 10 includes a pump cell 14, a porous diffusion layer 18, an oxygen concentration detection cell 24 and a reinforcing plate 30.
It is configured by stacking. Pump cell 14
Is formed into a plate shape with stabilized or partially stabilized zirconia, which is an oxygen ion conductive solid electrolyte, and has porous electrodes 12 and 16 mainly formed of platinum on both surfaces thereof. Surface side porous electrode 12 exposed to measurement gas
Is referred to as an Ip + electrode because an IP + voltage is applied to flow an IP current. Also, the porous electrode 1 on the back side
Reference numeral 6 is referred to as an Ip-electrode because an Ip-voltage is applied to flow an Ip current. A wiring 43 is connected to the Ip + electrode and a wiring 42 is connected to the Ip− electrode.

Similarly, the oxygen concentration detection cell 24 is also formed of stabilized or partially stabilized zirconia, and has porous electrodes 22 and 28 mainly formed of platinum on both surfaces thereof. A gap 20 surrounded by the porous diffusion layer 18 is formed between the pump cell 14 and the oxygen concentration detection cell 24.

That is, the gap 20 is formed by the porous diffusion layer 18
Through which the measurement gas atmosphere is communicated. The porous electrode 22 arranged on the side of the gap 20 has an oxygen concentration detection cell 24.
Is referred to as a Vs- electrode because a negative voltage of electromotive force is generated, and the porous electrode 28 disposed on the reference oxygen chamber 26 side is a Vs + electrode because a positive voltage of electromotive force of the oxygen concentration detection cell 24 is generated. refer. Reference oxygen chamber 26
The reference oxygen is generated by pumping a certain amount of oxygen from the porous electrode 22 to the porous electrode 28. In addition,
A wiring 41 is connected to the Vs + electrode, and a wiring 42 is connected to the Vs− electrode. ing.

Here, oxygen according to the difference between the oxygen concentration of the measurement gas and the oxygen concentration of the gap 20 diffuses toward the gap 20 through the porous diffusion layer 18. When the atmosphere in the gap 20 is maintained at the stoichiometric air-fuel ratio, the Vs + electrode 28 and the Vs− electrode of the oxygen concentration detection cell 24 and the Vs− are due to the oxygen concentration difference between the oxygen concentration of the reference oxygen chamber 26 and the oxygen concentration of the reference oxygen chamber. Electrode 22
There is a potential difference of about 450 mV between and. Therefore, the sensor control circuit 50 changes the current Ip flowing through the pump cell 14 to the electromotive voltage Vs of the oxygen concentration detection cell 24 of 45.
By adjusting to 0 mV, the atmosphere in the gap 20 is kept at the stoichiometric air-fuel ratio, and the oxygen concentration in the measurement gas is measured based on the pump cell current amount 1P for keeping the stoichiometric air-fuel ratio.

As described above, in the sensor element 10, the sensor control circuit 50 normally adjusts the current Ip flowing through the pump cell 14 so that the electromotive voltage Vs of the oxygen concentration detection cell 24 becomes 450 mV. Therefore, by utilizing the characteristics of the current control of the Ip current of the sensor element 10 by the sensor control circuit 50, the abnormality detection of the wirings 41, 42, 43 of the sensor element 10 as described below can be performed. it can.

2. Configuration of Sensor Control Circuit Next, the configuration of the sensor control circuit 50 to which the abnormality detection method for an air-fuel ratio sensor according to an embodiment of the present invention is applied will be described with reference to FIG. As shown in FIG. 2, the sensor control circuit 5
0 is mainly the Ip driver 51, the PID control circuit 52,
It is composed of an operational amplifier 53, an Rpvs measurement circuit 54, a Vp limiter 55, a self-diagnosis circuit 58, etc. For example, in this embodiment, an integrated circuit (ASIC; Application specific application).
Specific IC). The outputs VIP, VVS, VRPVS of the sensor control circuit 50 are E
It is connected to the analog input terminal of the CU. Of these, VI
The P terminal outputs a voltage proportional to the magnitude of the current flowing between the electrodes Ip + and Ip− of the pump cell 14, and the VVS terminal outputs a voltage proportional to the voltage difference between the electrodes Vs + and Vs− of the oxygen concentration detection cell 24.

The Ip driver 51 connects the sensor element 10 with Ip.
It is an operational amplifier for flowing p current, and V is connected to the inverting input terminal.
A reference voltage of 3.6 V is connected to each of the cent terminal and the non-inverting input terminal, and an Ip + terminal is connected to the output terminal. Then, the pump cell 14 of the sensor element 10 is provided between the Vcent terminal and the Ip + terminal.
Are connected. As a result, the Ip driver 51 constitutes a negative feedback circuit, and thus the Ip current is controlled so that the potential of the Vcent terminal always maintains the reference voltage (3.6V). By controlling the voltage of the Vcent terminal so as to maintain the reference voltage of 3.6V, the pump current is controlled in cooperation with the PID control circuit so that the electromotive force Vs becomes the control target value.

The PID control circuit 52 constitutes a PID arithmetic circuit together with resistors and capacitors connected to the P1 terminal, P2 terminal and P3 terminal which are the input / output signal lines of the ASIC. This PID control circuit 52 is Vs
Oxygen concentration detection cell 24 for control target value of 450 mV
Of the deviation ΔVs of the electromotive voltage Vs of
It is output to the out terminal, and the Ip current by the Ip driver 51 is controlled by this.

That is, the electromotive voltage Vs of the oxygen concentration detection cell 24
Is higher than 450 mV, the oxygen concentration in the gap 20 is lower than the oxygen concentration in the oxygen reference chamber 26, that is, on the fuel supply excess (rich) side with respect to the stoichiometric air-fuel ratio. The deviation amount ΔVs is set to PI so that the Ip current for pumping the oxygen in the pump cell 14 flows.
The voltage calculated by D is output to the Pout terminal. On the other hand, when the electromotive voltage Vs of the oxygen concentration detection cell 24 is lower than 450 mV, the oxygen transfer rate in the gap 20 is higher than the oxygen concentration in the oxygen reference chamber 26, that is, the fuel supply is insufficient with respect to the theoretical air-fuel ratio ( Since it is on the lean side, a voltage obtained by PID-calculating the deviation amount ΔVs so that an Ip current for pumping the excess oxygen by the pump cell 14 flows is Pou.
Output to the t terminal.

A -15 μA constant current source is connected to the COM terminal to which the wiring 42 is connected, in order to prevent an error in PID calculation due to the Icp current. That is, a constant current source of +15 μA is connected to the VS + terminal, which allows the oxygen concentration detection cell 24 to have Icp.
It supplies an electric current to create an oxygen standard. For this reason,
By connecting a constant current source of −15 μA to the COM terminal and subtracting 15 μA from the current flowing into the PID calculation circuit, a calculation error due to the Icp current is prevented.

Further, the operational amplifier 53 connected between the VS + terminal and the PID control circuit 52 constitutes a voltage follower circuit. As a result, the PID control circuit 52 side looks like a high impedance from the VS + terminal, so that the supply current from the +15 μA constant current source is suppressed from flowing into the PID control circuit 52.

The Rpvs measuring circuit 54 includes the sensor element 10
The temperature of the sensor element 10 is measured from the internal resistance Rpvs of the Rpvs (which is composed of an operational amplifier, a resistor, a capacitor, etc.). By passing a current, a voltage change corresponding to the internal resistance value of the oxygen concentration detection cell 24, which has a correlation with the element temperature, is generated, and the obtained voltage change amount across the oxygen concentration detection cell is multiplied by a constant. The VRpvs voltage is calculated and amplified to change in the range of 0 to 4.5V. Further, this VRpvs voltage is superimposed on the P / START information by the OR circuit 59 and is output from the VRPVS terminal.

When the current measured by the Rpvs measurement circuit 53 is passed through the oxygen concentration detection cell 24, the PID control circuit 52 and the operational amplifier 53 are connected so that the voltage change due to the measurement current does not change the output of the PID control circuit. The switch SW interposed therebetween disconnects the connection between the two. Therefore, by this SW, the PID control circuit 5
Rp during the disconnection between the 2 and the operational amplifier 53
The measurement by the vs measurement circuit 54 is performed.

The Vp limiter 55 is a circuit for preventing so-called blackening of the pump cell 14, and operates when the voltage Vp across the pump cell 14 exceeds a certain range to shift the Vs target value. In addition,
“Blackening” refers to a phenomenon in which the surface of a pump cell is blackened due to the loss of oxygen ions.

The self-diagnosis circuit 58 is mainly composed of window comparators 58a and 58b, a comparator 58c and an OR circuit 58d, and three wirings 41, 42 and 43 connected to two cells of the sensor element 10. Abnormality detection is performed.

That is, it is determined whether or not the potential of the VS + terminal of the ASIC is within a predetermined range.
The window comparator 58b determines whether or not the potential of the COM terminal of the ASIC is within a predetermined range. In addition, VS + terminal, IP + terminal of ASIC,
The comparator 58c determines whether or not the potential of any one of the Vcent terminal, the COM terminal, and the Pout terminal has exceeded a predetermined value (predetermined voltage). Then, P indicating the state in which the logical sum of the judgment results of these three comparators can be measured by the OR circuit 58d.
/ Output as START information. This P / START
The information represents a voltage of 4.7 V or more when an abnormality occurs, and is superimposed on the VRpvs voltage by the OR circuit 59,
It is output from the VRPVS terminal.

For example, at the VS + terminal, its potential is usually a value obtained by adding the electromotive voltage Vs (450 mV) of the oxygen concentration detection cell 24 to the reference voltage of 3.6 V at the COM terminal.
It is kept at 05V. Therefore, by setting the upper limit value of the window comparator 58a to 6.35V and the lower limit value to 2.5V, the potential of the VS + terminal becomes 6.
When the voltage rises above 35V, or when the potential of the VS + terminal drops below the lower limit value of 2.5V, a signal is output indicating that an abnormality has occurred.

At the COM terminal, the potential is Ip
The driver 51 always controls the reference voltage to be 3.6V. Therefore, the window comparator 5
By setting the upper limit value of 8b to 5.5V and the lower limit value to 2.5V, when the potential of the COM terminal rises above the upper limit value of 5.5V, or when the potential of the COM terminal has the lower limit value of 2. When the voltage drops below 5 V, a signal is emitted indicating that an abnormality has occurred. It is determined that these abnormalities are due to a break in one of the terminals or a short circuit with the power supply line of the battery.

Further, in the comparator 58c, the ASIC
It is determined whether or not the respective potentials of the VS + terminal, the IP + terminal, the Vcent terminal, the COM terminal, and the Pout terminal of 8 above exceed 8V which is the drive voltage of the circuit in the ASIC.
Each of these terminals is monitored by a comparator 58c whose upper limit value is 8V, which is a value that allows for voltage fluctuations of the driving power supply, and when the potential of any of the terminals rises above 8V, that terminal is Battery power line B
It is short-circuited to ATT, and it is judged that an abnormality has occurred, and a signal is issued.

3. Effect of Abnormality Detection System of Air-Fuel Ratio Detection System As described above, in this embodiment, P / START information indicating an abnormality is superimposed on the VRPVS output. Therefore, it is not necessary to prepare a signal line representing P / START information. In addition, the complexity of routing the wiring due to the increase of extra signal lines does not increase, and the reliability is not deteriorated due to the disconnection of the wiring. Furthermore, VRPVS
The output range is 0 to 4.5 V, and the abnormal state notification by P / START is 4.7 V or more. Since both output ranges do not overlap, there is no problem in using normal VRPVS information. Also, the validity of VRPVS output (0-4.
At the same time as confirming that it is within 5V), P / ST
Since the ART information (whether it is 4.7 V or not) can be confirmed, the number required for the determination can be reduced and the processing load on the ECU can be reduced. Further, the circuit necessary for superposition only needs to be added with the OR circuit 59 and can be easily realized.

It should be noted that the present invention is not limited to the above-described embodiments, but various modifications can be made within the scope of the present invention according to the purpose and application. That is, in this embodiment, P / S
Although the TART information is superposed on the VRPVS output, the present invention is not limited to this, and it can be superposed on an arbitrary signal line such as the VVS output or the VIP output. Further, the voltage at the time of abnormality in this embodiment is
Although the voltage exceeds the normal range, the voltage may be less than the normal range. This is because the same effect as that of the embodiment can be obtained even with these measures.

Further, the target of the abnormality detection is not limited to the case where each terminal exceeds the predetermined range, and the abnormality is detected under the condition that the terminals have the same potential, such as a short circuit between lines. be able to. Also, as the sensor of the air-fuel ratio detection system, the full-range air-fuel ratio sensor that uses two cells of the oxygen ion conductive solid electrolyte is used, but it is used for the system having the oxygen sensor composed of one cell. You can also do it.

[0035]

According to the abnormality detection system of the air-fuel ratio detection system of the present invention, it is not necessary to prepare a new signal line for notifying an abnormal state, and the number of wires between the air-fuel ratio detection system and the ECU is increased. To reduce complexity and improve reliability, and at the same time, when checking the validity of the signal of the corresponding signal line, it is possible to determine other abnormal states at the same time, so the processing of the ECU is also reduced. You can
Moreover, various abnormality detections can be performed without increasing the number of signal lines with a slight circuit change.

[Brief description of drawings]

FIG. 1 is a schematic diagram for explaining the structure of an air-fuel ratio sensor to which the abnormality detection method of the present air-fuel ratio sensor is applied, and the connection configuration of a control circuit and the like thereof.

FIG. 2 is an explanatory circuit diagram showing an air-fuel ratio sensor to which an abnormality detection method of the present air-fuel ratio sensor is applied, a control circuit thereof, and the like.

[Explanation of symbols]

10; Sensor element, 12, 16, 22, 28; Porous electrode, 14; Pump cell, 18; Porous diffusion layer, 20; Gap, 24; Oxygen concentration detection cell, 26; Oxygen reference chamber, 4
1, 42, 43; wiring, 50; sensor control circuit, 58;
Self-diagnosis circuit, 58a, 58b; window comparator, 58c; converter, 70; heater.

Continued front page    F term (reference) 3G084 BA09 DA27 DA30 EA04 EA11                       EB22 FA26 FA29                 3G301 JB01 JB09 JB10 MA01 NA03                       NA04 NA05 NA08 NE17 NE19                       PD01B PD01Z PD02Z

Claims (2)

[Claims] 1. An air-fuel ratio detection system comprising a sensor, a control circuit which is connected to the sensor by a plurality of lead wires, and which controls the sensor, and an engine control device to which a signal from the control circuit is input. In the abnormality detection system, the control circuit has abnormality detection means for detecting an abnormality in the sensor or the lead wire, and the abnormality detection means sets the voltage of the signal to a voltage outside the normal range. An abnormality detection system for an air-fuel ratio detection system, wherein the abnormality is notified to the engine control device. 2. The air-fuel ratio sensor, wherein the sensor comprises a combination of an oxygen pump cell and an oxygen concentration detection cell, and the control circuit controls the oxygen pump cell so that the output voltage of the oxygen concentration detection cell becomes a predetermined value. Wherein the control circuit outputs an internal resistance signal obtained by converting the internal resistance of the oxygen concentration detection cell into a voltage to the engine control device, and the abnormality detection means normalizes the value of the internal resistance signal. The abnormality detection system for an air-fuel ratio detection system according to claim 1, wherein an abnormality is notified to the engine control device by setting the value to a value outside the time range.