JP4699658B2 - Abnormality detection system for air-fuel ratio system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an abnormality detection system for an air-fuel ratio detection system. More particularly, the present invention relates to a method for protecting an abnormality detection system of an air-fuel ratio detection system that can perform various abnormality detections without increasing the number of signal lines. The present invention can be used in an air-fuel ratio sensor control system that can detect an air-fuel ratio of an internal combustion engine such as a gasoline engine from an oxygen concentration.
[0002]
[Prior art]
In order to control the air-fuel ratio of the air-fuel mixture supplied to an internal combustion engine such as a gasoline engine to a target value and to reduce CO, NOx, HC, etc. in the exhaust gas, an oxygen sensor is provided in the exhaust system, and the air-fuel ratio It is known that the fuel supply amount is feedback-controlled according to the oxygen concentration in the exhaust gas having a correlation with the above.
[0003]
The oxygen sensor used for such feedback control includes a λ sensor whose output changes abruptly at a specific oxygen concentration (especially in the vicinity of the theoretical air-fuel ratio atmosphere), and all sensors whose output changes continuously from the lean region to the rich region. A region air-fuel ratio sensor is mainly used. 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. Therefore, it is used when higher speed and higher accuracy control is required. It has been.
[0004]
The full-range air-fuel ratio sensor has two cells using an oxygen ion conductive solid electrolyte body facing each other, and one cell is used as a pump cell for pumping out or pumping oxygen within the interval, and the other This cell is used as an oxygen concentration detection cell that generates a voltage due to the difference in oxygen concentration 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. It is measured as a measured oxygen concentration proportional value. 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 air-fuel ratio sensor abnormality detection method for detecting whether or not such an air-fuel ratio sensor is operating normally, Japanese Patent Application Laid-Open No. 3-272252 relating to the application of the present applicant discloses Various methods such as “abnormality diagnosis method” are disclosed.
[0005]
[Problems to be solved by the invention]
However, the result of abnormality detection is read from an input signal line by an ECU (Electronic Control Unit) or the like, but since the number of signal lines is also used for other purposes, it is desired to avoid using it as much as possible.
The present invention solves such problems, and an object of the present invention is to provide an abnormality detection system for an air-fuel ratio detection system capable of detecting an abnormality of an air-fuel ratio sensor with a smaller number of signal lines. .
[0006]
[Means for Solving the Problems]
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 by a plurality of lead wires, and a control circuit for controlling the sensor, and an engine control to which a signal from the control circuit is input. In the abnormality detection system of the air-fuel ratio detection system comprising the device, the control circuit has abnormality detection means for detecting abnormality of the sensor or the lead wire, and the abnormality detection means is configured to control the engine control from the control circuit. superimposing an abnormality signal to the signal output to the device, to notify the abnormality to the engine control unit by a superposition of the abnormality signal to the value of the voltage outside the range of normal values of the voltage of the signal Features.
[0007]
The sensor is configured by a combination of an oxygen pump cell and an oxygen concentration detection cell, and the control circuit is an air-fuel ratio sensor that 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 superimposes the abnormal signal on the internal resistance signal. it can notify the abnormality to the engine control unit by a superposition of the abnormality signal to a value outside the range of the voltage value of the normal voltage of the internal resistance signal Te.
[0008]
[Action]
The abnormality detection system of this air-fuel ratio detection system uses the voltage within a certain range when a normal signal is output to the signal line, and uses an out-of-range voltage when an abnormality occurs, It is characterized by performing notification. This eliminates the need to prepare a new signal line to notify the abnormal state, reduces the complexity by reducing the number of wires between the air-fuel ratio detection system and the ECU, increases reliability, and signals on the corresponding signal line Since the other abnormal states can be determined at the same time when the validity is confirmed, the processing of the ECU can be reduced, which is preferable.
[0009]
Further, the abnormality detection system of the present air-fuel ratio detection system is an air-fuel ratio sensor that combines an oxygen pump cell and an oxygen concentration detection cell, and superimposes an abnormality signal on an internal resistance signal that represents the internal resistance of the oxygen concentration detection cell. Various abnormality detection can be performed without increasing the number of signal lines by a slight circuit change. In addition, when a digital circuit and an element that can be programmed by software are used as the control circuit, the same effect can be obtained without changing the circuit, which is more preferable.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
The abnormality detection system of the present air-fuel ratio detection system superimposes abnormality information on an existing signal line in order to detect an abnormal state without increasing the signal line between the air-fuel ratio detection system and the ECU. In addition, as a method of superimposing, the normal voltage range of the corresponding signal line can be uniquely determined. Normally, 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 by increasing the number of extra signal lines does not increase, and the reliability is not lowered by the disconnection of the wiring. Furthermore, since the output ranges of both the existing signal and the abnormal signal do not overlap, there is no problem in normal use.
[0011]
【Example】
Hereinafter, embodiments of the abnormality detection system of the air-fuel ratio detection system of the present invention will be described in detail with reference to FIGS.
1. FIG. 1 shows a sensor element 10 used in an abnormality detection system of an air-fuel ratio detection system. The sensor element 10 is disposed 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, the sensor control circuit 50 usually mainly measures the oxygen concentration in the exhaust gas and the temperature of the sensor element 10, but in addition, three wires connected to the two cells of the sensor element 10. A function for detecting abnormalities 41, 42, and 43 is also provided.
[0012]
In addition, a heater 70 controlled by the heater control circuit 60 is attached to the sensor element 10 via a ceramic-based bonding agent. The heater 70 is made of a ceramic such as alumina as an insulating material, and a heater wire 72 is disposed therein. The heater control circuit 60 functions to supply electric power to the heater 70 so as to keep the temperature of the sensor element 10 measured by the sensor control circuit 50 at the target value and to maintain the temperature of the sensor element 10 at the target value. .
[0013]
The sensor element 10 is configured by stacking a pump cell 14, a porous diffusion layer 18, an oxygen concentration detection cell 24, and a reinforcing plate 30.
The pump cell 14 is formed into a plate shape by 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. The porous electrode 12 on the surface side exposed to the measurement gas is referred to as an Ip + electrode because an IP + voltage is applied to pass an IP current. The porous electrode 16 on the back surface side is referred to as an Ip-electrode because an Ip-voltage is applied in order to pass an Ip current.
A wiring 43 is connected to the Ip + electrode, and a wiring 42 is connected to the Ip− electrode.
[0014]
Similarly, the oxygen concentration detection cell 24 is formed of stabilized or partially stabilized zirconia, and has porous electrodes 22 and 28 formed mainly 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.
[0015]
In other words, the gap 20 communicates with the measurement gas atmosphere via the porous diffusion layer 18. The porous electrode 22 disposed on the gap 20 side is referred to as a Vs-electrode because a negative voltage of the electromotive force of the oxygen concentration detection cell 24 is generated, and the porous electrode 28 disposed on the reference oxygen chamber 26 side. Is referred to as a Vs + electrode because a positive voltage of the electromotive force of the oxygen concentration detection cell 24 is generated. The reference oxygen in the reference oxygen chamber 26 is generated by pumping a certain amount of oxygen from the porous electrode 22 to the porous electrode 28.
A wiring 41 is connected to the Vs + electrode, and a wiring 42 is connected to the Vs− electrode.
[0016]
Here, oxygen corresponding to the difference between the oxygen concentration of the measurement gas and the oxygen concentration in the gap 20 diffuses to the gap 20 side 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 Vs− of the oxygen concentration detection cell 24 are caused by the difference in oxygen concentration from the reference oxygen chamber 26 in which the oxygen concentration is kept substantially constant. A potential difference of about 450 mV is generated between the electrode 22 and the electrode 22. Therefore, the sensor control circuit 50 adjusts the current Ip flowing through the pump cell 14 so that the electromotive voltage Vs of the oxygen concentration detection cell 24 is 450 mV, thereby maintaining the atmosphere in the gap 20 at the theoretical air-fuel ratio, Based on the pump cell current amount 1P for maintaining the theoretical air-fuel ratio, the oxygen concentration in the measurement gas is measured.
[0017]
In this way, the sensor element 10 adjusts the current Ip that flows through the pump cell 14 by the sensor control circuit 50 so that the electromotive voltage Vs of the oxygen concentration detection cell 24 is usually 450 mV. Therefore, by utilizing the current control characteristics of the Ip current of the sensor element 10 by the sensor control circuit 50, it is possible to detect the abnormality of the wirings 41, 42, and 43 of the sensor element 10 as described below. it can.
[0018]
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 one embodiment of the present invention is applied will be described with reference to FIG.
As shown in FIG. 2, the sensor control circuit 50 mainly includes an Ip driver 51, a PID control circuit 52, an operational amplifier 53, an Rpvs measurement circuit 54, a Vp limiter 55, a self-diagnosis circuit 58, and the like. In the embodiment, it is realized as an application specific IC (ASIC). The outputs VIP, VVS, and VRPVS of the sensor control circuit 50 are connected to an analog input terminal of the ECU. Among these, the VIP 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. To do.
[0019]
The Ip driver 51 is an operational amplifier for causing an Ip current to flow through the sensor element 10. The inverting input terminal is connected to the Vcent terminal, the non-inverting input terminal is connected to the reference voltage 3.6V, and the output terminal is connected to Ip +. The terminal is connected. The pump cell 14 of the sensor element 10 is connected between the Vcent terminal and the Ip + terminal. Thereby, since the Ip driver 51 constitutes a negative feedback circuit, the Ip current is controlled so that the potential of the Vcent terminal always maintains the reference voltage (3.6 V). By controlling the voltage at the Vcent terminal to keep the reference voltage at 3.6 V in this way, the pump current is controlled so that the electromotive force Vs becomes the control target value in cooperation with the PID control circuit.
[0020]
The PID control circuit 52 constitutes a PID arithmetic circuit together with resistors and capacitors connected to the P1 terminal, the P2 terminal and the P3 terminal which are ASIC input / output signal lines. The PID control circuit 52 outputs, to the Pout terminal, a voltage obtained by performing PID calculation on a deviation amount ΔVs of the electromotive voltage Vs of the oxygen concentration detection cell 24 with respect to 450 mV of the Vs control target value. Is controlled.
[0021]
That is, when the electromotive voltage Vs of the oxygen concentration detection cell 24 is higher than 450 mV, the fuel concentration is excessive (rich) with respect to a state where the oxygen concentration in the gap 20 is lower than the oxygen concentration in the oxygen reference chamber 26, that is, the stoichiometric air-fuel ratio. Therefore, a voltage obtained by PID calculation of the deviation amount ΔVs is output to the Pout terminal so that an Ip current for pumping the deficient oxygen by the pump cell 14 flows. On the other hand, when the electromotive voltage Vs of the oxygen concentration detection cell 24 is lower than 450 mV, the fuel supply is insufficient with respect to the stoichiometric air-fuel ratio in a state where the oxygen transfer rate in the gap 20 is higher than the oxygen concentration in the oxygen reference chamber 26 ( Since the state is on the (lean) side, a voltage obtained by PID calculation of the deviation amount ΔVs is output to the Pout terminal so that an Ip current for pumping out the excess oxygen by the pump cell 14 flows.
[0022]
Note that a constant current source of −15 μA is connected to the COM terminal to which the wiring 42 is connected, in order to prevent an error in the PID calculation due to the Icp current.
That is, a constant current source of +15 μA is connected to the VS + terminal, thereby supplying an Icp current to the oxygen concentration detection cell 24 to create an oxygen reference. For this reason, a constant current source of −15 μA is connected to the COM terminal, and the calculation error due to the Icp current is prevented by subtracting this 15 μA from the current flowing into the PID calculation circuit.
[0023]
The operational amplifier 53 connected between the VS + terminal and the PID control circuit 52 constitutes a voltage follower circuit. Thereby, since the PID control circuit 52 side looks high impedance from the VS + terminal, the supply current from the constant current source of +15 μA is prevented from flowing into the PID control circuit 52.
[0024]
The Rpvs measurement circuit 54 measures the temperature of the sensor element 10 from the internal resistance Rpvs of the sensor element 10 (consisting of an operational amplifier, a resistor, a capacitor, and the like). By causing a predetermined measurement current to flow through the oxygen concentration detection cell 24, a voltage change corresponding to the internal resistance value of the oxygen concentration detection cell 24 having a correlation with the element temperature is generated, and both ends of the oxygen concentration detection cell obtained thereby. The amount of change in voltage is computed and amplified by a constant multiple to obtain a VRpvs voltage that varies in the range of 0 to 4.5V. The VRpvs voltage is superimposed on the P / START information by the OR circuit 59 and output from the VRPVS terminal.
[0025]
When the measurement current from the Rpvs measurement circuit 53 is passed through the oxygen concentration detection cell 24, the voltage change caused by the measurement current is interposed between the PID control circuit 52 and the operational amplifier 53 so that the output of the PID control circuit does not change. The connection between the two is cut by the switch SW. Therefore, measurement by the Rpvs measurement circuit 54 is performed by the SW during the time when the PID control circuit 52 and the operational amplifier 53 are disconnected.
[0026]
The Vp limiter 55 is a circuit for preventing so-called blacking 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. “Blackening” refers to the surface blackening phenomenon of the pump cell due to the loss of oxygen ions.
[0027]
The self-diagnosis circuit 58 mainly includes window comparators 58a and 58b, a comparator 58c and an OR circuit 58d, and detects abnormality of the three wires 41, 42 and 43 connected to the two cells of the sensor element 10. Etc.
[0028]
That is, the window comparator 58a determines whether the potential of the ASIC VS + terminal is within a predetermined range, and the window comparator 58b determines whether the potential of the ASIC COM terminal is within a predetermined range. The comparator 58c determines whether the potential of any one of the ASIC's VS + terminal, IP + terminal, Vcent terminal, COM terminal, and Pout terminal exceeds a predetermined value (predetermined voltage). Then, the logical sum of the determination results by these three comparators is output as P / START information indicating a state that can be measured by the OR circuit 58d. This P / START information represents a case where an abnormality occurs with a voltage of 4.7 V or higher, is superimposed on the VRpvs voltage by the OR circuit 59, and is output from the VRPVS terminal.
[0029]
For example, at the VS + terminal, the potential is normally maintained at 4.05 V, which is a value obtained by adding the electromotive voltage Vs (450 mV) of the oxygen concentration detection cell 24 to the reference voltage 3.6 V of the COM terminal. Therefore, by setting the upper limit value of the window comparator 58a to 6.35V and the lower limit value to 2.5V, when the potential of the VS + terminal rises above the upper limit value of 6.35V, or the potential of the VS + terminal is lower limit. When the value falls below 2.5V, a signal is issued as an abnormality has occurred.
[0030]
Further, the potential at the COM terminal is controlled by the Ip driver 51 so that the reference voltage is always 3.6V. Therefore, by setting the upper limit value of the window comparator 58b 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 the potential of the COM terminal is lower than the lower limit value. When the value falls below 2.5V, a signal is issued as an abnormality has occurred.
These abnormalities are determined as one of the terminals being disconnected or being short-circuited to the battery power line.
[0031]
Further, the comparator 58c determines whether or not each potential of the ASIC's VS + terminal, IP + terminal, Vcent terminal, COM terminal, and Pout terminal exceeds 8V, which is a driving voltage of a circuit in the ASIC. Each of these terminals is monitored by a comparator 58c in which 8V, which is a value considering the voltage fluctuation of the driving power supply, is set as an upper limit value. When the potential of any terminal rises above 8V, that terminal is A short circuit is made to the battery power supply line BATT, and it is determined that an abnormality has occurred, and a signal is issued.
[0032]
3. As described above, the present embodiment superimposes P / START information representing an abnormality on the VRPVS output as described above. For this reason, it is not necessary to prepare a signal line representing P / START information. Further, the complexity of routing the wiring due to the increase of extra signal lines does not increase, and the reliability is not lowered due to the disconnection of the wiring. Furthermore, the range of VRPVS output is 0 to 4.5V, and the notification of abnormal conditions by P / START is 4.7V or higher. Since both output ranges do not overlap, there is no problem in using normal VRPVS information. .
In addition, since the validity of the VRPVS output (within 0 to 4.5V) can be confirmed, the P / START information (whether it is 4.7V) can be confirmed at the same time, so the number required for the determination can be reduced. It is possible to reduce the processing burden on the ECU. In addition, a circuit necessary for superposition only needs to add the OR circuit 59, and can be easily realized.
[0033]
In addition, in this invention, it can be set as the Example variously changed within the range of this invention not only according to the said Example but according to the objective and the use. That is, in this embodiment, the P / START information is superimposed on the VRPVS output. However, the present invention is not limited to this, and can be superimposed on an arbitrary signal line such as a VVS output or a VIP output. Moreover, although the voltage at the time of abnormality of the present embodiment is a voltage that exceeds the normal range, it can also be a voltage that is less than the normal range. This is because the same effect as in the embodiment can be obtained as a countermeasure.
[0034]
Furthermore, the object of abnormality detection is not limited to the case where each terminal exceeds a predetermined range, and an abnormality can be detected under conditions such as when the terminals are at the same potential, such as a short circuit between lines. .
Further, as the sensor of the air-fuel ratio detection system, an all-range air-fuel ratio sensor using two oxygen ion conductive solid electrolyte cells is used, but it is used for a system including an oxygen sensor composed of one cell. You can also
[0035]
【The invention's effect】
According to the abnormality detection system of the air-fuel ratio detection system according to the first aspect of the present invention, it is not necessary to prepare a new signal line in order to notify the abnormal state, and the number of wirings between the air-fuel ratio detection system and the ECU is reduced and complicated. In addition, the reliability of the signal line can be reduced, and when the validity of the signal of the corresponding signal line is confirmed, other abnormal states can be determined at the same time, so that the processing of the ECU can also be reduced.
In addition, various abnormality detections can be performed without increasing the number of signal lines by slight circuit changes.
[Brief description of the 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 its control circuit and the like.
FIG. 2 is an explanatory circuit diagram showing an air-fuel ratio sensor to which the present air-fuel ratio sensor abnormality detection method is applied, a control circuit thereof, and the like.
[Explanation of symbols]
DESCRIPTION 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, 41, 42, 43 Wiring 50; sensor control circuit 58; self-diagnostic circuit 58a, 58b; window comparator 58c; converter 70; heater.

Claims (2)

In an abnormality detection system of an air-fuel ratio detection system comprising a sensor, a control circuit that is connected to the sensor with a plurality of lead wires, and that controls the sensor, and an engine control device to which a signal from the control circuit is input ,
The control circuit includes an abnormality detection unit that detects an abnormality of the sensor or the lead wire, and the abnormality detection unit superimposes an abnormality signal on the signal output from the control circuit to the engine control device, air-fuel ratio detection system abnormality detection system and notifies the abnormality to the engine control unit by a superposition of the abnormality signal to a value outside the range of the voltage in the normal value of the voltage of the signal. The sensor is composed of a combination of an oxygen pump cell and an oxygen concentration detection cell, and the control circuit is an air-fuel ratio sensor that 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 superimposes the abnormal signal on the internal resistance signal. air-fuel ratio detection system for abnormality detection system of claim 1, wherein notifying the abnormality to the engine control unit by a superposition of the abnormality signal to the value of the voltage of the internal resistance signal and the value of the voltage outside the range of normal.

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