Method for Operating an Oxygen Sensor, Computer Program Product and Oxygen Sensor

Abstract

A method and apparatus for compensates for oxygen sensor aging determines a correction of by measuring oxygen content above a specified threshold value and measuring current flowing through the sensor over time.

Claims

1. A method for operating an oxygen sensor having a sensor element for an intake tract of an internal combustion engine, wherein sensor element aging is compensated for as a function of sensor element operating time, the method comprising; measuring a pumping current required to pump oxygen through a zirconium membrane of the sensor; determining oxygen content by evaluating the equation:
O.sub.2=r*(a+b*I.sub.pump+c*I.sub.pump.sup.2), wherein I.sub.pump is the measured pumping current, a, b and c are factors for quadratic factory calibration, and r is the recalibration factor for aging compensation; and changing the value of r responsive to the operating time of the sensor element.

2. The method of claim 1, wherein the aging compensation is performed responsive to determining a contamination of the sensor element.

3. The method of claim 1, wherein the aging compensation is performed at fixed operating time intervals, the fixed operating time intervals being determined responsive to the operating time of the sensor element.

4. The method of claim 1, wherein oxygen content of ambient air is used as a threshold value.

5. The method of claim 1, wherein correction of the aging compensation is performed when the oxygen sensor delivers, over a specified time period, at least a specified number of measured values of oxygen content above the specified threshold value.

6. A computer having a computer-readable medium and program code stored in the computer-readable medium, which, when executed causes the computer to execute a method as claimed in claim 1.

7. An apparatus comprising: an oxygen sensor comprising yttrium-stabilized zirconium oxide ceramic; a computer, operatively coupled to the oxygen sensor; a memory device operatively coupled to the computer and storing program instructions, which when executed cause the computer to: compensate for aging of the oxygen sensor as a function of an operating time of the oxygen sensor; the compensation comprising: measuring a pumping current required to pump oxygen through a zirconium membrane of the sensor; determining oxygen content by evaluating the equation:
O.sub.2=r*(a+b*I.sub.pump+c*I.sub.pump.sup.2), wherein I.sub.pump is the measured pumping current, a, b and c are factors for quadratic factory calibration, and r is the recalibration factor for aging compensation; and changing the value of r responsive to the operating time of the sensor element.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0023] Hereinafter, the invention is described in greater detail by means of exemplary embodiments with reference to the appended drawings, in which:

[0024] FIG. 1 is a schematic diagram of an internal combustion engine having an intake tract and an oxygen sensor arranged therein according to an embodiment of the invention; and

[0025] FIG. 2 is a schematic diagram of a flow diagram of a method for operating the oxygen sensor according to FIG. 1.

DETAILED DESCRIPTION

[0026] FIG. 1 shows an internal combustion engine 1, which can be implemented, for example, as a gasoline or diesel engine of a vehicle. The internal combustion engine 1 is assigned an intake tract 2, through which combustion air is fed to the internal combustion engine 1. Furthermore, the internal combustion engine 1 is assigned an exhaust tract 3, through which exhaust gases of the internal combustion engine 1 can be discharged.

[0027] The internal combustion engine 1 has a system for exhaust gas recirculation, in which exhaust gases from the exhaust tract 3 are recirculated via an exhaust gas recirculation pipe 4 into the intake tract 2. In this way, knocking combustion, in particular, can be avoided in an economical and environmentally friendly fashion. The exhaust gas recirculation rate 4 is regulated using a system that is not shown in the schematic representation according to FIG. 1. To regulate the exhaust gas recirculation rate this system requires, in particular, measurement values from an oxygen sensor 5, arranged in the intake tract between the junction of the exhaust gas recirculation pipe 4 and the internal combustion engine 1.

[0028] The oxygen sensor 5 has a sensor element composed of an yttrium-stabilized zirconium oxide ceramic. The sensor 5 is assigned a control device 6, which is connected to the oxygen sensor 5 via a signal cable 7 and which receives the measured values from the oxygen sensor 5 and controls the sensor 5. The control device 6 can be the engine control device of the internal combustion engine 1, however, it can also be a separate sensor control device.

[0029] The control device 6 has a computer-readable medium 8, which can be implemented, in particular, as a non-volatile memory and on which program code is stored, which, when executed on the control device 6, instructs the control device 6 to execute the following method:

[0030] The control unit 6 records the operating time of the sensor element of the oxygen sensor 5 and compensates for aging of the sensor element by initially performing a computational overcompensation of the aging and subsequently a correction of the aging compensation in cases where the oxygen sensor measures an oxygen content above a specified threshold value. The threshold value employed is the oxygen content of the ambient air of approximately 21% by volume.

[0031] In the process, the oxygen content is measured, for example, by measuring the pumping current required to pump oxygen through the zirconium membrane of the sensor. From this, the oxygen content is determined, for example, on the basis of the formula

O.sub.2=r*(a+b*I.sub.pump+c*I.sub.pump.sup.2),

[0032] wherein I.sub.pump is the measured pumping current, a, b and c are factors for quadratic factory calibration, and r is the recalibration factor for aging compensation. During factory calibration r is set to 1 and is later used to compensate for aging-related loss of sensitivity of the sensor.

[0033] Due to the initial overcompensation of the aging, the control device 6 initially typically determines slightly too high values of the oxygen content in the intake air. However, if this deviation is too large, oxygen content values above the specified threshold value occur and correction of the aging compensation is triggered.

[0034] This results in a periodic self-calibration of the oxygen sensor 5. Although at first, slightly increased oxygen content values are typically determined, the correction of the aging compensation ensures, nevertheless, that this systematic overestimation of the oxygen content does not exceed a specified level.

[0035] FIG. 2 illustrates the sequence of a method for operating the oxygen sensor 5 according to FIG. 1. In a step 100 the method is started. For example, the oxygen sensor 5 is put into operation when the internal combustion engine 1 is started.

[0036] In a step 200 an aging compensation is performed by mathematically correcting the oxygen concentrations determined by the sensor 5, as a function of the operating time t of the sensor 5 using a compensation factor.

[0037] In a step 300 the aging-compensated results thus determined are checked to ascertain whether they represent oxygen content values in the intake tract 2 that are higher than a specified threshold value. If this is not the case, the method is continued.

[0038] If oxygen levels above the threshold value are output, then a correction of the aging compensation is made in a step 400, after which the method is continued.