Signal control function of a heated broadband probe with temperature adjustment during operating voltage changes to reduce blackening.

Abstract

A signal control function for reducing the occurrence of blackening of a heated oxygen sensor element, e.g. a broadband lambda probe (UEGO 200), when operating with variable constant voltage in at least two voltage stages for an internal combustion engine reduces the operating temperature of the oxygen sensor element from a first temperature (T1) to a second temperature (T2) before a transition from a lower operating voltage (V1, Vp1, Vn1) to a higher operating voltage (Vh, Vp2, Vn2), where the second temperature (T2) is increased when the first temperature (T1) increases; and is reduced when the difference between the higher operating voltage (Vh, Vp2, Vn2) and a threshold voltage (503) of a lower limit of an overpotential range becomes larger, where a ramp rate from the lower operating voltage (V1, Vp1, Vn1) to the higher operating voltage (Vh, Vp2, Vn2) is reduced when the second temperature (T2) is increased.

Description

Area

[0001] The present invention relates to a signal control function for reducing the occurrence of blackening of a heated oxygen sensor element, e.g. in the form of a broadband lambda probe, during operation with variable constant voltage in at least two voltage levels, for an internal combustion engine, and to a signal evaluation function using such a signal control function. Background / Brief description

[0002] Intake and / or exhaust gas sensors can be used to provide information on various intake and exhaust gas components. For example, the output from a wideband oxygen sensor (UEGO sensor) can be used to determine the air-fuel ratio (AFR) of the exhaust gas. Information on the oxygen content of the intake and exhaust gases can be used to adjust various engine operating parameters, such as fuel supply. As such, the measurement accuracy of an oxygen sensor can be significantly affected by a malfunction of a component within the sensor, such as blackening of a sensor element. Blackening of an oxygen sensor element is a form of malfunction that can occur when the sensor operates at a voltage that is above the potential range of a sensor element, when an electrical current exceeding a threshold is generated.

[0003] Several approaches have been used to reduce blackening of oxygen sensor elements. In one exemplary approach, presented by Tsukada et al. in US 2012 / 0001641A1, the pump voltage used in the oxygen sensor's pump cell can be limited to a threshold voltage. This threshold voltage can correspond to the limit of the cell's overpotential range. During variable-voltage operation of the sensor, where the sensor's operation alternates between a higher and a lower voltage, neither the lower nor the higher operating voltage should exceed the threshold voltage.

[0004] Further gas and oxygen sensors are known, among others, from German patent DE 10 2015 117 147 A1, which describes methods and systems for adjusting the rate of change of a reference voltage of an oxygen sensor when the voltage changes from a lower to a higher voltage, where the rate of change depends on engine operating conditions, as well as from German patent DE 10 2007 057 707 A1 and US 5 228 375 A. A more comprehensive study of amperometric oxygen sensors using zirconium dioxide can be found in the publication by Jeffrey Allen Blanchard: Specific gas sensing using zirconia amperometric oxygen sensors. Ann Arbor, MI: UMI, 1998. 152 pp. - Also: Graduate College, Arz., Univ., Master's thesis, 1998.

[0005] However, the inventors of the present disclosure have recognized potential disadvantages in the aforementioned approaches. For example, the accuracy of the oxygen content measurement by the sensor may be reduced if the pump voltage is limited to a threshold. The desired pump voltage can change based on factors such as gas concentration, and a fixed upper voltage threshold can impair sensor operation. The possibility of blackening can also change based on the sensor's operating temperature, and at higher operating temperatures, blackening of the sensor element may occur even when operating within a threshold voltage. The inventors have also recognized that operating the sensor in variable voltage mode can lead to blackening because the cell exceeds the target pump voltage during the transition to the higher voltage.The excessive voltage can cause the sensor to enter the overpotential range (i.e., a range where the higher voltage can cause the electrolyte in the sensor to partially electrolyze due to a removal of oxygen from the sensor).

[0006] An alternative approach to controlling the blackening of oxygen sensor elements involves using a lower ramp rate to achieve a desired higher voltage in the UEGO sensor cells, thus reducing the likelihood of voltage overshoot into the overpotential range. However, the inventors have also identified potential problems with this approach. For example, using a lower ramp rate to increase the operating voltage can be time-consuming and lead to delays in the sensor's measurements, thereby impacting sensor operation.

[0007] To mitigate the described problem, the present invention proposes a signal control function according to claim 1 and a signal evaluation function according to claim 12, using the aforementioned signal control function according to claim 1. Preferred embodiments of the invention are the subject of the dependent claims.

[0008] The inventors of this disclosure recognized that the voltage threshold for entering the overpotential region increases when the sensor's operating temperature is reduced. Thus, by reducing the sensor's operating temperature, the voltage required to blacken the sensor can be increased, allowing the sensor to operate over a wider voltage range before blackening occurs. In an example, the problems described above can be addressed by a method for an engine that includes: during operation of a variable-voltage oxygen sensor, reducing the occurrence of blackening of an oxygen sensor element by decreasing the oxygen sensor's operating temperature from a first temperature to a second temperature before transitioning from a lower to a higher operating voltage.In this way, by adjusting the temperature of the UEGO sensor during operation of the UEGO sensor with variable voltage, the movement of the UEGO cells due to being in the overpotential range can be reduced, which reduces the possibility of the sensor blackening.

[0009] As an example, the temperature of the UEGO sensor can be reduced during conditions when a UEGO exhaust gas sensor is operating in a variable-voltage mode, such as for estimating the oxygen content of the exhaust gas, at least before the UEGO sensor voltage is increased from a lower, nominal voltage to a higher voltage. Lowering the sensor temperature shifts the overpotential limit towards a higher absolute voltage. The extent of the UEGO temperature reduction can be determined based on parameters such as the sensor's current temperature and the difference between the desired higher voltage and the temperature-modified overpotential limit. The UEGO temperature reduction can also be achieved by adjusting the settings of a heating element coupled to the UEGO sensor so that the heating device generates less heat.If it is determined that the overpotential limit cannot be shifted to a desired level simply by lowering the UEGO temperature (for example, due to higher ambient temperatures or other temperature constraints), the upper voltage can be limited to a threshold voltage at or below the overpotential limit. A lower voltage ramp rate can then be used to achieve the higher voltage within the threshold range, thus reducing voltage overshoot.

[0010] By first lowering the UEGO temperature and then transitioning the UEGO sensor from a lower to a higher voltage, the overpotential limit can be shifted to a higher voltage value. During operation at the higher voltage, this reduces the risk of the UEGO sensor elements blackening. Allowing for a higher voltage during variable-voltage UEGO operation results in greater accuracy in UEGO sensor measurements. This, in turn, increases the operating voltage range of the UEGO sensor. The technical benefit of shifting the overpotential limit to a higher voltage is that a faster ramp rate can be used to reach the higher voltage without the risk of voltage overshoot into the overpotential range.Additionally, the risk of voltage overshoot into the overpotential range during voltage transitions can be reduced. By using a faster ramp rate, the higher voltage can be reached within a shorter time, which can increase measurement accuracy. Overall, the risk of oxygen sensor malfunction due to blackening of the UEGO element can be reduced, and the accuracy of the oxygen sensor operation is maintained, thus enabling efficient engine performance. Brief description of the drawings Fig. Figure 1 shows an exemplary engine system with intake and exhaust oxygen sensors. Fig. Figure 2 shows a schematic representation of an example UEGO sensor. Fig. Figure 3 shows a flowchart illustrating a procedure that can be implemented to reduce the occurrence of blackening in oxygen sensors. Fig. Figure 4 shows an example diagram of the change in the threshold of the overpotential area with temperature. Fig. Figure 5 shows an exemplary operation of the UEGO cells to reduce the occurrence of blackening. Detailed description

[0011] Oxygen sensors can be located in an intake air duct or an exhaust duct, such as in the engine system of the Fig. 1 shown, arranged. Fig. Figure 2 shows a schematic view of an oxygen sensor that could be affected by blackening. An engine control unit may be configured to run a routine, such as the example routine from Fig. 3, to perform in order to reduce the occurrence of blackening in each of the pump cell and Nernst cell of the UEGO sensor. Fig. Figure 4 shows the shift of the lower threshold of the overpotential range based on the sensor's operating temperature. An example of operating the UEGO sensor to reduce blackening is shown in Fig. 5 shown.

[0012] Fig. Figure 1 is a schematic diagram showing a cylinder of a multi-cylinder engine 10 in an engine system 100. The engine 10 can be controlled, at least partially, by a control system including a controller 12 and by input from a driver 132 via an input device 130. In this example, the input device 130 includes an accelerator pedal and a pedal position sensor 134 for generating a pedal position proportional signal PP. A combustion chamber (cylinder) 30 of the engine 10 can include combustion chamber walls 32 with a piston 36 arranged therein. The piston 36 can be coupled to a crankshaft 40, so that a reciprocating motion of the piston is translated into a rotational motion of the crankshaft. The crankshaft 40 can be coupled to at least one drive wheel of a vehicle via an intermediate transmission system.Furthermore, a starter can be coupled to the crankshaft 40 via a flywheel in order to start the operation of the engine 10.

[0013] The combustion chamber 30 can draw in intake air from an intake manifold 44 via an intake port 42 and discharge combustion gases via the exhaust port 48. The intake manifold 44 and the exhaust port 48 can be selectively connected to the combustion chamber 30 via a respective intake valve 52 and exhaust valve 54. In some embodiments, the combustion chamber 30 can include two or more intake valves and / or two or more exhaust valves.

[0014] In this example, the inlet valve 52 and the exhaust valve 54 can be controlled by cam actuation via respective cam actuation systems 51 and 53. The cam actuation systems 51 and 53 can each include one or more cams and use one or more of the following systems: cam profile adjustment (CPS), variable cam actuation (VCT), variable valve actuation (VVT), and / or variable valve lift (VVL) systems, which can be operated by the controller 12 to vary the valve operation. The position of the inlet valve 52 and the exhaust valve 54 can each be determined by position sensors 55 and 57, respectively. In alternative embodiments, the inlet valve 52 and / or the exhaust valve 54 can be controlled by an electric valve actuator.For example, combustion chamber 30 can alternatively include an inlet valve controlled by an electric valve actuation and an exhaust valve controlled by cam actuation systems, including CPS and / or VCT systems.

[0015] A fuel injection unit 66 is shown to be directly coupled to the combustion chamber 30 for injecting fuel directly into it, proportional to the pulse width of the FPW signal received by the control device 12 via an electronic driver 68. In this way, the fuel injection unit 66 provides what is known as direct fuel injection into the combustion chamber 30. The fuel injection unit can be mounted, for example, in the side of the combustion chamber or in the top of the combustion chamber (as shown). Fuel can be supplied to the fuel injection unit 66 via a fuel system (not shown) that includes a fuel tank, a fuel pump, and a fuel line.In some embodiments, the combustion chamber 30 may alternatively or additionally have a fuel injection system arranged in the intake manifold 44 in a configuration that provides what is known as intake manifold injection of fuel into the intake port upstream of the combustion chamber 30.

[0016] The intake duct 42 can include a throttle 62 with a throttle valve 64. In this particular example, the position of the throttle valve 64 can be changed by the controller 12 via a signal provided to an electric motor or actuator integrated into the throttle 62, a configuration generally referred to as electronic throttle control (ETC). In this way, the throttle 62 can be operated to vary the intake air supplied to the combustion chamber 30, among other engine cylinders. The position of the throttle valve 64 can be provided to the controller 12 by a throttle position signal TP. The air intake duct 42 can include the intake air temperature (IAT) sensor 125 and the barometric pressure (BP) sensor 128. The IAT sensor 125 estimates the temperature of the intake air to be used during engine operation and provides a signal to the controller 12.Similarly, the BP sensor 128 estimates the ambient pressure for engine operation and provides a signal to the control unit 12. The intake duct 42 can also include an air mass flow sensor 120 and a manifold air pressure sensor 122 to provide the respective MAF and MAP signals to the control unit 12.

[0017] An exhaust gas sensor 126 is shown coupled to the exhaust gas channel 48 upstream of an emission control device 70. The sensor 126 can be any suitable sensor for providing an indication of an exhaust air-fuel ratio (AFR), such as a linear oxygen sensor (lambda probe) or UEGO (universal or wide-range exhaust gas oxygen), a dual-state oxygen sensor (or dual-state lambda probe) or EGO, a HEGO (heated EGO), a NOx, HC, or CO sensor. A detailed embodiment of the oxygen sensor (UEGO sensor) is described with reference to Fig. 2. An oxygen sensor can be used to estimate the AFR for both intake and exhaust gases. Based on the AFR estimate, engine operating parameters, such as fuel supply, can be regulated. Additionally, using the AFR estimate in the exhaust gas can improve the operating performance of an emissions control device.

[0018] To improve engine operation, it is desirable to minimize the occurrence of any functional impairment in the oxygen sensor. For example, operating the oxygen sensor at higher voltages (such as in the sensor's overpotential range) can generate electrical currents above a threshold. These currents can partially electrolyze the white zirconium oxide present in the sensor cells to form a darker material, zirconium oxide, thus causing sensor dysfunction. This phenomenon can be described as blackening of the UEGO cells. To reduce the occurrence of blackening when a UEGO exhaust gas sensor is operating in variable-voltage mode, the temperature of the UEGO sensor can be lowered before increasing the UEGO sensor voltage from a lower to a higher voltage.By reducing the sensor temperature, the limit of the overpotential range can be shifted towards a higher absolute voltage. A detailed procedure for reducing the occurrence of impaired exhaust gas sensor function due to blackening of a component is described with reference to [reference to be added]. Fig. 3 - 5 explained.

[0019] The emission control device 70 is shown arranged along the exhaust gas channel 48 downstream of the exhaust gas sensor 126. The device 70 can be a three-way catalytic converter (TWC), a NOx trap, various other emission control devices, or combinations thereof. In some embodiments, the emission control device 70 can be periodically reset during operation of the engine 10 by operating at least one cylinder of the engine with a specific air / fuel ratio.

[0020] Furthermore, an exhaust gas recirculation (EGR) system 140 can direct a desired proportion of the exhaust gas from the exhaust duct 48 into the intake manifold 44 via an EGR channel 142. The amount of EGR supplied to the intake manifold 44 can be varied by the control unit 12 via an EGR valve 144. An EGR sensor 146 can also be located within the EGR channel 142 and can provide a reading of one or more parameters, including pressure, temperature, and concentration of exhaust gas components. A linear oxygen sensor 172 can be located on the intake duct, downstream of the intake throttle, to facilitate EGR control. Under certain conditions, the EGR system 140 can also be used to regulate the temperature of the air-fuel mixture in the combustion chamber, thus providing a method for controlling the ignition timing in some combustion modes.Furthermore, under certain conditions, some of the combustion gases can be retained or captured in the combustion chamber by controlling the actuation of the exhaust valve, such as by controlling a variable valve actuation mechanism.

[0021] Control 12 is in Fig. 1 shown as a microcomputer, comprising a microprocessor unit 102, input / output ports 104, an electronic storage medium for executable programs and calibration values, shown as a read-only memory chip 106 in this particular example, a random-access memory 108, a life support memory 110 and a data bus.The control unit 12 can receive various signals from sensors connected to the engine 10, in addition to the signals discussed previously, including measurements of one or more air-fuel ratio and humidity from oxygen sensors 126 and 172; mass airflow (MAF) from the mass airflow sensor 120; engine coolant temperature (ECT) from a temperature sensor 112 coupled to a cooling sleeve 114; ignition profile recording (PIP) signal from a Hall effect sensor 118 (or other type) coupled to the crankshaft 40; throttle position (TP) from a throttle position sensor; and absolute manifold pressure (MAP) signal from sensor 122. An engine speed (RPM) signal can be generated by the control unit 12 from the PIP signal. The manifold pressure (MAP) signal from a manifold pressure sensor can be used to provide an indication of vacuum or pressure in the intake manifold.It should be noted that various combinations of the above sensors can be used, such as a MAF sensor without a MAP sensor, or vice versa. During stoichiometric operation, the MAP sensor can provide an indication of engine torque. Furthermore, this sensor, together with the detected engine speed, can provide an estimate of the charge (including air) being fed into the cylinder. In one example, sensor 118, which is also used as an engine speed sensor, can generate a predetermined number of evenly spaced pulses with each revolution of the crankshaft.

[0022] The read-only memory 106 can be programmed with computer-readable data representing non-volatile instructions that can be executed by the processor 102 to perform the procedures described above, as well as other conceivable but not explicitly listed variations. As described above, Fig. 1. One cylinder of a multi-cylinder engine, and each cylinder can equally include its own set of inlet / outlet valves, fuel injections, spark plugs, etc.

[0023] The controller 12 receives signals from the various sensors of the Fig. 1 and uses the various actuators of the Fig. 1. To adjust the motor operation based on the received signals and instructions stored in a memory of the controller 12. In one example, the controller 12 can receive inputs from the oxygen sensors 126 and 172 regarding the operating temperature and voltage of the sensors. During a transition from a lower to a higher operating voltage of the oxygen sensor, the controller 12 can send a signal to a heating device (heating element) coupled to the oxygen sensor to reduce the heat generated by the heating device, thereby lowering the operating temperature of the oxygen sensor. For example, an output of the sensor heating device (e.g., voltage or current output of the heating device) can be reduced.

[0024] Fig. Figure 2 shows a schematic view of an embodiment of an exhaust gas oxygen sensor, such as the UEGO sensor 200, configured to measure the concentration of oxygen (O2) in an exhaust gas stream during fuel supply. In one example, the UEGO sensor 200 is an embodiment of the UEGO sensor 126 of the Fig. 1. However, it will be understood that the sensor of Fig. 2 alternatively, it can represent an intake oxygen sensor, such as sensor 172 of the Fig. 1.

[0025] The sensor 200 comprises a multitude of layers of one or more ceramic materials arranged in a stacked configuration. In the embodiment of the Fig. Figure 2 shows five ceramic layers (elements) designated as layers 201, 202, 203, 204, and 205. These layers comprise one or more layers of a solid electrolyte capable of conducting ionic oxygen. In some embodiments, such as those shown in Figure 2, the ceramic layers are also represented as layers 201, 202, 203, 204, and 205. Fig. As shown in Figure 2, a heating device 207 can also be arranged in thermal contact with the layers. The temperature setting of the heating device can be adjusted to change the operating temperature of the sensor. While the UEGO sensor 200 shown is formed from five ceramic layers, it will be understood that the UEGO sensor can include a different suitable number of ceramic layers.

[0026] Examples of suitable solid electrolytes include materials based on zirconium oxide (also known as zirconia, ZrO2). ZrO2 is typically white. When used at higher voltages (in the overpotential range), the two oxygen atoms can be removed from the ZrO2, transforming the white ZrO2 into dark-colored metallic zirconium (Zr), resulting in a blackening of the element. Other reasons for this blackening can include high operating temperatures and low atmospheric and oxygen conditions. The newly formed Zr exhibits not only ionic conductivity but also electronic conductivity. This electronic conductivity can increase proportionally to the degree of blackening, affecting the accuracy of sensor measurements.

[0027] Layer 202 contains a porous material or materials that create a diffusion path 210. The diffusion path 210 is configured to introduce exhaust gases by diffusion into a first inner cavity (also referred to as a gas collection cavity) 222. The diffusion path 210 can be configured to allow one or more components of the exhaust gas, including, among others, a desired analyte (e.g., O2), to diffuse into the inner cavity 222 at a more restricted rate than that at which the analyte can be pumped in and out by pump electrode pairs 212 and 214. In this way, a stoichiometric level of O2 can be maintained in the first inner cavity 222.

[0028] The sensor 200 further includes a second inner cavity 224 within layer 204 and separated from the first inner cavity 222 by layer 203. The second inner cavity 224 is configured to maintain a constant oxygen partial pressure, equivalent to a stoichiometric condition; for example, the oxygen level present in the second inner cavity 224 is equal to that which the exhaust gas would have if the air-fuel ratio were stoichiometric. The oxygen concentration in the second inner cavity 224 is controlled by the pump voltage V. cp kept constant. The second inner cavity 224 can be referred to as a reference cell.

[0029] A pair of measuring electrodes 216 and 218 is arranged in conjunction with the first inner cavity 222 and the reference cell 224. The measuring electrode pair 216 and 218 detects a concentration gradient that can develop between the first inner cavity 222 and the reference cell 224 due to an oxygen concentration in the exhaust gas that is higher or lower than the stoichiometric level. A high oxygen concentration can be caused by a lean intake air or exhaust gas mixture, while a low oxygen concentration can be caused by a rich mixture.

[0030] The pair of pump electrodes 212 and 214 is arranged in conjunction with the inner cavity 222 and is configured to electrochemically pump a selected gas component (e.g., O2) from the inner cavity 222 through the layer 201 and out of the sensor 200. Alternatively, the pair of pump electrodes 212 and 214 can be configured to electrochemically pump a selected gas through the layer 201 and into the inner cavity 222. In this case, the electrolyte layer 201 together with the pump electrode pair 212 and 214 can be referred to as an O2 pump cell. Furthermore, the electrolyte layer 203 together with the electrode pair 216 and 218 can be referred to as a Nernst cell (also known as a measuring cell). The electrodes 212, 214, 216, and 218 can be made of various suitable materials.In some embodiments, the electrodes 212, 214, 216 and 218 can be made at least partially of a material that catalyzes the splitting of molecular oxygen. Examples of such materials include, among others, electrodes containing platinum and / or gold.

[0031] The measuring cell (Nernst cell) can passively measure the oxygen concentration in the first inner cavity (gas collection cavity) 222. The pump cell can adjust the oxygen concentration in cavity 222 based on feedback from the measuring cell. An external comparator circuit can compare the voltage generated by the measuring cell with a reference voltage V. p compare. In one example, the reference voltage V can be pUnder normal operating conditions, the voltage at the pump cell can be 450 mV. The voltage to the pump cell can be proportional to the voltage at the Nernst cell. Thus, the voltage generated by the Nernst cell can be approximately 450 mV at this time, with one electrode exposed to air (with ~20% oxygen concentration) and the other electrode exposed to a low oxygen concentration (~10 ppm oxygen). This oxygen concentration (~10 ppm) can correspond to stoichiometry. If the oxygen concentration in cavity 222 is lower than the stoichiometry concentration (~10 ppm) due to reducing agents such as carbon monoxide or hydrogen, the comparator circuit can send a signal to the pump cell to pump oxygen from the outlet into cavity 222.The oxygen reacts with the reducing agents, causing the oxygen concentration to rise until it reaches the level corresponding to stoichiometry (~10 ppm), as measured by the measuring cell (Nernst cell). The amount of reducing agent in the cavity determines how much oxygen must be pumped into the cavity by the pump cell to complete the reaction. The pump current I. p The pumped oxygen flow rate is directly proportional to the oxygen concentration in the pump cell. The amount of oxygen pumped is just sufficient to react completely with all the reducing agents. The sensor can employ various techniques to determine the concentration of reducing agents. For example, the pump current, which is proportional to the oxygen concentration in the pump cell, can be used to estimate the reducing agent concentration.

[0032] If the oxygen concentration in the cavity is higher than the oxygen concentration corresponding to stoichiometry (~10 ppm), a reverse procedure can take place. The measuring cell can apply a voltage below the reference voltage V. p (450 mV) measure and the comparator circuit can send a signal to the pump cell to pump oxygen out of the cavity by means of a pump current I p is applied in the opposite direction. The pump current I pis directly proportional to the amount of oxygen pumped out of the cell, which in turn is directly proportional to the amount of oxygen diffusing into cavity 222. This amount of oxygen can be directly proportional to the oxygen concentration in the exhaust gas. Under selected conditions, the oxygen sensor, when included as an exhaust gas oxygen sensor, can be operated at variable voltage, such as for detecting the alcohol content of the fuel burned in the engine, for moisture estimation, water detection, component and sensor aging correction, exhaust pressure detection, etc.As another example, when included as an intake air oxygen sensor, the sensor can be operated in a variable voltage mode under selected conditions to measure intake air humidity, measure the amount of water injected by a water injection system, determine the composition of the washer fluid injection and air-fuel ratio, and for torque control based on the amount of hydrocarbons, moisture, oxygen and EGR entering the engine.

[0033] During variable-voltage operation of the sensor, a higher voltage at the Nernst cell may be desired. Accordingly, the pump cell voltage can be increased from a lower operating voltage to a higher voltage to achieve the higher Nernst cell voltage. For example, the lower operating voltage V1 used during variable-voltage operation might be 450 mV, and the higher operating voltage Vh available during variable-voltage operation might be 1 V. Thus, there is a direct relationship between the Nernst cell voltage and the pump cell voltage; they are proportional to each other. The pump cell voltage is the voltage applied across the pump cell to achieve a desired measured Nernst cell voltage.Therefore, if there is an instruction that the voltage of the Nernst cell should change from a low voltage (Vs) to a high voltage during variable voltage operation, the pump cell voltage will also change from the lower to the higher voltage to achieve this. Thus, if the Nernst cell is operated at 450 mV, the pump cell will also have approximately 450 mV, and if the desired voltage of the Nernst cell is, for example, approximately 1 V, then the pump cell voltage will also be approximately 1 V.

[0034] During variable voltage operation, an electric current higher than the threshold can be generated when the higher voltage is applied, provided the applied voltage is in the overpotential range. This over-threshold electric current can lead to the conversion of the zirconium oxide present in each of the pump cells and the Nernst cell to metallic zirconium, which can accumulate on the electrodes of the pump cells and the Nernst cell. Such accumulation of metallic zirconium can cause blackening of the sensor cells, which can impair the sensor's performance.

[0035] To reduce the occurrence of such blackening during the operation of a variable-voltage oxygen sensor, a controller can lower the sensor's operating temperature (e.g., from a first / current temperature to a second, lower temperature) before transitioning from a lower to a higher operating voltage. The inventors of this disclosure recognized that the voltage at which the Nernst cell or pump cell enters the overpotential region increases when the sensor's operating temperature is reduced. In other words, a wider range of operating voltages is available for operating the variable-voltage oxygen sensor at lower operating temperatures (before problems with sensor blackening occur). Thus, by reducing the sensor's operating temperature, the upper voltage beyond which the sensor can blacken can be increased.This increases sensor accuracy and reliability and reduces sensor degradation. For example, the operating temperature can be lowered by reducing the output of a sensor heating element. Alternatively, the operating temperature can be lowered by reducing the temperature of the exhaust gas reaching the sensor.

[0036] It will be understood that the oxygen sensor described herein is merely one embodiment of a UEGO sensor and that other embodiments of intake or exhaust oxygen sensors may have additional and / or alternative features and / or designs.

[0037] In this way, the system enables Fig. 1 and Fig. 2 an engine system comprising: an engine with an exhaust; a fuel injection system for supplying fuel to an engine cylinder; an oxygen sensor coupled to the exhaust, the oxygen sensor comprising a heating device, a pump cell and a Nernst cell; and a control system.The control system can be configured with computer-readable instructions stored on non-volatile memory to: apply an initial lower voltage to the pump cell; after application, set a temperature setting of the heating device to lower the temperature of each of the pump cell and the Nernst cell; after setting, increase a pump cell voltage from the initial voltage to a second voltage; based on a change in the pump cell current at the second voltage relative to the initial voltage, estimate an oxygen content of the exhaust gas; and adjust the engine fuel supply in response to the estimated oxygen content.The system may further include a temperature sensor for estimating an ambient temperature, with the controller also including instructions to: lower the temperature of each of the pump cells and the Nernst cell based on the ambient temperature, whereby the temperature setting of the heating device is adjusted to a higher temperature of each of the pump cells and the Nernst cell as the ambient temperature increases. Additionally or optionally, the controller may also include instructions to: increase the pump cell voltage from the first voltage to the second voltage with a higher ramp rate when the second voltage is higher, and with a lower ramp rate when the second voltage is lower.

[0038] Fig. Figure 3 illustrates an exemplary method 300 for reducing the occurrence of blackening in elements of the broadband oxygen probe (UEGO sensor) by adjusting the operating temperature of the sensor cells during variable voltage operation. Instructions for executing method 300 and the other methods contained herein can be executed by a controller based on instructions stored in a memory of the controller and in conjunction with signals received from sensors of the engine system, such as those previously described in relation to Fig. The sensors described in Section 1. The control unit can use engine actuators of the engine system to adjust engine operation according to the procedures described below. The oxygen sensor can be an intake oxygen sensor coupled to an intake port downstream of an intake throttle (and upstream of an EGR valve), or an exhaust oxygen sensor coupled to an exhaust port upstream of an exhaust catalyst. The procedure reduces the occurrence of blackening of an oxygen sensor element, particularly during operation of a variable-voltage oxygen sensor, by lowering the operating temperature of the oxygen sensor from a first temperature to a second temperature before transitioning from a lower to a higher operating voltage.Instructions for performing the procedure 300 can be executed by a controller based on instructions stored in a memory of the controller and in conjunction with signals received from sensors of the motor system, such as those previously mentioned in relation to . Fig. 1 and Fig. The two sensors described below. The control system can use motor actuators of the motor system to adjust the motor operation according to the procedures described below.

[0039] At 302, a first lower (nominal) voltage (Vi) can be applied across the pump cell. In one example, the lower voltage could be 450 mV. Accordingly, the voltage at the Nernst cell can reach this first lower voltage value. In another example, the first lower voltage could be a standard voltage applied to the sensor whenever the sensor is operated for oxygen content estimation.

[0040] In step 304, the routine involves determining whether an increase in voltage (to a higher operating voltage) at the Nernst cell is desired. For example, an increase in voltage might be desired in response to a request to operate the sensor in a variable-voltage mode, such as for fuel alcohol content estimation. Furthermore, the request to operate the oxygen sensor in variable voltage might be a response to a request for one or more estimations of the alcohol content of the fuel burned in the engine, the ambient humidity of an intake air charge, or the oxygen content of the intake air charge or exhaust gas.As further examples, an exhaust gas oxygen sensor can be operated in variable voltage mode to detect the alcohol content of the fuel burned in the engine, estimate moisture content, detect water, correct for component and sensor aging, and detect exhaust pressure. Meanwhile, an intake gas oxygen sensor can be operated in variable voltage mode to measure the humidity of the intake air, measure the amount of water injected by a water injection system, determine a detergent injection composition, calculate an air-fuel ratio, and control torque based on the amount of hydrocarbons, moisture, oxygen, and EGR entering the engine. If, as determined in section 306, an increase in the Nernst cell voltage is undesirable, the pump cell voltage can be maintained at a lower voltage level (Vi).Consequently, the voltage of the Nernst cell can also remain at the lower value.

[0041] If it is determined at 308 that a higher operating voltage at the Nernst cell is desired, the controller can determine the desired voltage (Vh) at the Nernst cell based on the engine operating conditions and exhaust oxygen levels. In one example, the desired voltage is 1 V. Additionally, the current operating temperature of the sensor (of each of the pump cell and the Nernst cell) can be determined. In one example, the operating temperature of the sensor can be determined from the settings of a sensor heating element (such as the heating device 207 in Fig. 2) and environmental conditions. In another example, the operating temperature of the sensor can be determined based on the temperature of the exhaust gas flowing through the sensor.

[0042] At step 310, the routine involves determining whether the desired higher voltage (Vh) is higher than a threshold voltage. The threshold voltage can correspond to a lower limit of an overpotential range. Specifically, the threshold voltage can be a voltage at which the rate of increase of the pump cell current for a given change in pump cell voltage is higher than a threshold value. If the UEGO cells are operated at a voltage within the overpotential range, an electric current higher than a threshold value can be generated, which can lead to electrolysis of the zirconium oxide present in the cells, causing blackening of the sensor. Thus, the operating voltage at each of the UEGO cells can be kept below the overpotential range to reduce the occurrence of blackening in a UEGO sensor.During a transition to the higher voltage, however, the actual voltage can overshoot and unintentionally enter the overpotential range. As such, the limit of the overpotential range can depend on the sensor's operating temperature. At lower operating temperatures, the overpotential range limit may be at a higher absolute voltage, thus increasing the range of available operating voltages for the sensor before blackening can occur.

[0043] If it is determined that the desired higher voltage (Vh) is higher than the threshold voltage (for the current operating conditions, including the current operating temperature), it can be concluded that increasing the pump cell voltage to Vh may cause each of the pump cells and the Nernst cell to operate within the overpotential range, with a higher risk of blackening. To shift the overpotential limit at 312 to a higher absolute voltage, the operating temperature of the UEGO sensor can be lowered. Lowering the sensor's operating temperature involves lowering the operating temperature of each of the pump cells and the Nernst cell of the oxygen sensor.The extent of the reduction in UEGO temperature can be determined based on parameters such as the current temperature of the sensor and a difference between the desired higher voltage and the temperature-modified limit of the overpotential voltage.

[0044] In one example, the temperature can be decreased from a first temperature to a second temperature. The second temperature is set based on the first temperature and the difference between the higher operating voltage and a threshold voltage. Specifically, the second temperature can be decreased as the difference between the higher operating voltage and the threshold voltage increases. Furthermore, the second temperature can be increased as the first temperature increases. The second temperature can also be set based on the ambient temperature, with the second temperature increasing towards the first temperature as the ambient temperature rises. As outlined here, a ramp rate from the lower to the higher operating voltage can be increased as the second temperature is increased.

[0045] Reducing the UEGO temperature can be achieved by adjusting the settings of the heating element coupled to the UEGO sensor, thus reducing the amount of heat generated by the heating device. For example, lowering the operating temperature might involve adjusting the output of a heating element on the oxygen sensor to limit the heat produced during sensor operation. This output could include a current and voltage from the heating element. In one example, the controller could send a signal to the heating element's thermostat to change its temperature settings. In another example, the controller could send a signal to the heating element to decrease its output (current or voltage).

[0046] For example, the controller can determine that a control signal is sent to the actuator of the sensor element, such as the pulse width of the signal, which is determined based on a calculation of the difference between the desired higher voltage and the temperature-modified limit of the overpotential voltage. The desired higher voltage can be based on the type of sensing requested by the sensor, while the temperature-modified limit can be based on a map or model, as referenced in the map of the Fig. 4 is elaborated. The controller can determine the pulse width by a determination that takes into account the predicted or modeled change in the upper voltage, such as increasing the pulse width when the predicted difference becomes larger. Alternatively, the controller can determine the pulse width based on a calculation using a lookup table, where the input is the desired upper voltage or the desired change in the upper voltage (for operating the sensor with variable voltage) and the output is the pulse width.

[0047] Once the operating temperature of the UEGO sensor has been reduced at step 314, the routine can include determining whether the desired higher operating voltage (Vh) lies outside the temperature-modified limit of the overpotential range. If, at step 316, it is confirmed that the modified limit for the overpotential range is higher than Vh, the desired higher voltage (Vh) can be applied to the pump cell, and accordingly, the voltage of the Nernst cell can also increase to Vh. Alternatively, the routine can proceed directly to step 316 if, at step 310, it is determined that the desired voltage Vh is lower than the limit of the overpotential range (without requiring a temperature change), in which case the operating voltage of the pump cell can be directly increased to Vh without changing the operating temperature.Since the desired higher voltage is lower than the limit of the overpotential range, a higher ramp rate can be used to achieve Vh without an increased risk of voltage overshoot into the overpotential range during the transition. Specifically, the routine after reducing the operating temperature of the oxygen sensor (e.g., from the first to the second temperature) involves a transition of the sensor from the lower voltage to the higher voltage at a ramp rate, where the ramp rate is determined as a function of the second temperature relative to the first temperature. For example, the ramp rate can be reduced as the difference between the first and second temperatures decreases (i.e., a slower rate for a smaller voltage change from the lower voltage to the higher voltage and a faster rate for a larger voltage change from the lower voltage to the higher voltage).By using a higher ramp rate, Vh can be reached within a shorter time, which can increase the accuracy of the UEGO sensor's operation.

[0048] However, if it is determined at 314 that the desired higher voltage (Vh) remains within the overpotential range even after lowering the sensor temperature, it can be concluded that the desired shift in the overpotential range boundary cannot be achieved simply by lowering the temperature. This can occur if the temperature reduction is limited due to higher ambient temperatures or other temperature constraints. For example, if the ambient temperature is higher, the sensor operating temperature may adjust to the (higher) ambient temperature even if the sensor output is reduced, causing the sensor's higher voltage to approach the overpotential range.To prevent the UEGO cells from operating in the overpotential range, the temperature setting at 318 is limited based on the ambient temperature, and the upper voltage is limited to a threshold voltage at or below the upper potential range by the limited temperature setting. A lower ramp rate can also be used to reach the threshold voltage to reduce the possibility of voltage overshoot into the overpotential range.

[0049] After the transition to the higher voltage at terminals 316 and 318, the control unit can generate a reading of the exhaust oxygen content or fuel alcohol content (as determined based on the start-up for the variable voltage operating mode), the reading being based on a change in the oxygen sensor's pump current during variable voltage operation. Furthermore, the control unit can adjust an engine operating parameter, including cylinder fuel supply, based on this reading.

[0050] The map 400 of the Fig. Figure 4 shows an example of the change in the lower limit of an oxygen sensor's overpotential range as the operating temperature changes. The map shows the pump cell pumping current along the Y-axis (Ip) and the pump cell pumping voltage along the X-axis (Vp). Exemplary curves of the voltage change with a current change for a temperature range T1 to T6 (here varying from 950° to 580° as an example) are shown by curves 402-412, which have lines with different patterns (solid, dashed, etc.).

[0051] The overpotential region is defined as the region where the current begins to increase rapidly when a given voltage is applied. Referring to curve 402 (calibrated for a first temperature T1, such as 950 °C), the overpotential region begins, for example, at or above V1. Before V1, the current is linear for a given Vp, but after V1, the current increases exponentially. Therefore, during operation with a variable voltage at T1 (e.g., 950 °C), the highest voltage that can be applied to the sensor is limited to V1 (or just below).

[0052] In comparison, referring to curve 412 (calibrated for a second temperature T2, lower than T1, such as 580°C), the overpotential area begins at or above V2, which is higher than V1. Before V2, the current is linear for a given Vp, but after V2, the current increases exponentially. Therefore, during operation with variable voltage at T2 (e.g., 580°C), the highest upper voltage that can be applied to the sensor is limited to V2 (or just below).

[0053] Lowering the temperature from T1 to T2 thus increases the voltage range available for variable voltage operation by ΔV, defined here as V2 - V1. As such, the change in temperature cannot be linear with the change in voltage range across all temperatures. For example, the relationship may be linear at some temperatures and non-linear at others. A relationship between the change in the sensor's operating temperature and the change in voltage range (or the highest possible voltage before overpotential is reached) can be learned during a calibration routine and stored in the controller's memory as a lookup table as a function of temperature. The controller can access this map during the calibration routine. Fig. 3, as with 310 and 312.

[0054] Returning to Fig.Figure 5 shows an example chart 500 for adjusting the operation of an oxygen sensor to reduce malfunction and blackening due to deviations into the overpotential range. In this example, the sensor is an exhaust gas oxygen sensor. In alternative examples, the sensor could be an intake air oxygen sensor. Chart 500 shows changes in the sensor's pump cell voltage (curve 502), changes in the sensor's Nernst cell voltage (curve 504), the sensor operating temperature (curve 504), and the ambient temperature (curve 508). Changes in the lower limit of the pump cell's overpotential range are shown as a dashed line (503), and corresponding changes in the lower limit of the Nernst cell's overpotential range are shown as a dashed line (505). All curves are plotted against time along the x-axis.

[0055] Before t1, the sensor operates in a fixed-voltage mode for oxygen content estimation. The Nernst cell is initially set to a lower voltage, Vn1, which causes a corresponding change in the pump cell voltage to a lower voltage, Vp1. This voltage is maintained until t1, and the current output from the pump cell after Vp1 is applied is used to estimate the oxygen content of the exhaust gas. The sensor is not operated between t1 and t1.

[0056] At t2, the sensor switches to a variable voltage mode for fuel alcohol content estimation. At this time, the sensor temperature is higher (at T1) and the ambient temperature is lower. Between t2 and t3, the first voltage Vn1 is applied to the Nernst cell, resulting in a corresponding change in the pump cell voltage relative to the first voltage Vp1. Between t2 and t3, the change in current output by the pump cell after the application of Vp1 is learned (as delta Ip1).

[0057] During operation with variable voltage, it may be desirable to apply a second, higher voltage Vp2 to the pump cell. However, under the current sensor temperature conditions, this would cause the pump cell to operate very close to or within the overpotential range, as indicated by the lower limit of the overpotential range at dashed line 503. Similarly, operating the pump cell at this voltage would require the Nernst cell to also operate very close to or within the overpotential range, as indicated by the lower limit of the overpotential range at dashed line 505. To improve the boundary to the overpotential range at t3, the output of a sensor heater is set below the sensor operating temperature.In particular, the sensor operating temperature can be reduced due to the lower ambient temperature and based on the difference between Vp1 and Vp2 from T1 to T2. As a result of this reduction, the threshold range to the overpotential region is increased, so that when Vp2 is applied to the pump cell, the risk of a transition into the overpotential region is reduced. Furthermore, due to the larger threshold range, the Nernst cell and the pump cell transition to the higher voltage (Vp2 and Vn2) at a faster ramp rate at t4.

[0058] Between t4 and t5, the second voltage Vn2 is applied to the Nernst cell, resulting in a corresponding change in the pump cell's voltage relative to the first voltage Vp2. Between t4 and t5, a change in the pump cell's current output after applying Vp2 is learned (as delta Ip2). Based on the difference between delta Ip1 and delta Ip2, the oxygen content of the fuel burned in the engine is determined.

[0059] At t5, a further operating mode with variable voltage is requested for estimating the exhaust gas oxygen content. Accordingly, at t5, the sensor switches to a variable voltage mode by reducing the voltage of the Nernst cell and pump cell to the first lower voltage (Vn1 and Vp1). Additionally, the sensor output is adjusted to increase the sensor operating temperature to T1. The ambient temperature may have increased in the meantime.

[0060] Between t5 and t6, the first voltage Vn1 is applied to the Nernst cell, which leads to a corresponding change in the voltage of the pump cell to the first voltage Vp1.

[0061] Between t5 and t6, a change in the current output by the pump cell after the application of Vp1 is learned (as delta Ip3).

[0062] During operation with variable voltage, it may be desirable to apply a second, higher voltage Vp2 to the pump cell. However, under the current sensor temperature conditions, this would cause the pump cell to operate very close to or within the overpotential range, as indicated by the lower limit of the overpotential range at dashed line 503. Similarly, operating the pump cell at this voltage would require the Nernst cell to also operate very close to or within the overpotential range, as indicated by the lower limit of the overpotential range at dashed line 505. To improve the boundary to the overpotential range at t6, the output of a sensor heater is set below the sensor operating temperature.Due to the higher ambient temperature and based on the difference between Vp1 and Vp2, the sensor operating temperature can only be reduced from T1 to T3 and cannot be reduced to T2. As a result of this reduction, the threshold for the overpotential region is increased, but the increase is not as large as it would have been if the temperature had been reduced to T2 (at t3-t4). Therefore, when Vp2 is applied to the pump cell, the risk of transitioning into the overpotential region is reduced, but not as much as desired. To compensate for the larger threshold, the Nernst cell and the pump cell transition to the higher voltage (Vp2 and Vn2) at t7 with a slower ramp rate to avoid entering the overpotential region.

[0063] Between t7 and t8, the second voltage Vn2 is applied to the Nernst cell, resulting in a corresponding change in the pump cell voltage relative to the first voltage Vp2. Between t7 and t8, a change in the current output by the pump cell after the application of Vp2 is learned (as delta Ip4). Based on the difference between delta Ip3 and delta Ip4, an oxygen content of the exhaust gas is learned and used for air-fuel correction. For example, if the learned oxygen content indicates that the exhaust gas is richer than stoichiometric, the fuel supply can be reduced to restore the air-fuel ratio to stoichiometric. Conversely, if the learned oxygen content indicates that the exhaust gas is leaner than stoichiometric, the fuel supply can be increased to restore the air-fuel ratio to stoichiometric.

[0064] It will be understood that in another example, if the ambient temperature is the same and a larger voltage change is desired during variable voltage operation (such as to Vp2', where Vp2'-Vp1 is greater than Vp2-Vp1), and all other things being equal, a greater drop in the sensor's operating temperature would be required to provide the same threshold range to the overpotential region. Additionally, due to the larger voltage difference, the voltage can transition from the lower to the upper voltage at a higher ramp rate.

[0065] In this way, a controller, in response to a request to operate a variable-voltage oxygen sensor, received while the sensor is at a first temperature and voltage, can set an output from an oxygen sensor element to lower the oxygen sensor to a second temperature; and after lowering, raise the oxygen sensor from the first voltage to a second voltage that is higher than the first voltage, with a ramp rate set depending on the second temperature. Additionally or optionally, the second temperature can be set to limit the second voltage to below a threshold voltage in an overpotential range of the oxygen sensor. Furthermore, the ramp rate can be reduced as the second temperature approaches the first temperature.The requirement for variable-voltage operation of the oxygen sensor can be a response to a requirement for one or more of the following: estimating the alcohol content of the fuel burned in the engine, estimating the ambient humidity of an intake air charge, and estimating the oxygen content of the intake air charge or exhaust gas. The oxygen sensor can be an intake oxygen sensor coupled to an intake port downstream of an intake throttle, or an exhaust oxygen sensor coupled to an exhaust port upstream of a catalytic converter.

[0066] By reducing the temperature of an oxygen sensor during variable voltage operation, the voltage range for variable voltage operation can be increased. This allows the sensor to operate with higher accuracy and reliability. Additionally, extending the range reduces unintended deviations of the pump cell voltage into an overpotential range. Furthermore, by extending the range and allowing the sensor to operate with a larger difference between the lower and higher voltages applied during variable voltage operation, a faster voltage ramp rate is achieved, enabling faster measurement and thus increasing sensor accuracy.By reducing the probability of the oxygen sensor operating in the overpotential range, the sensor's functionality is reduced due to blackening of the sensor element. This, in addition to increasing sensor performance, also extends the sensor's lifespan.

[0067] An exemplary method for an engine comprises: during operation of a variable-voltage oxygen sensor, reducing the occurrence of blackening of an oxygen sensor element by decreasing the operating temperature of the oxygen sensor from a first temperature to a second temperature before a transition from a lower to a higher operating voltage. In the foregoing example, the second temperature is additionally or optionally set as a function of the first temperature and a difference between the higher operating voltage and a threshold voltage. In any or all of the foregoing examples, the second temperature is additionally or optionally decreased as the difference between the higher operating voltage and the threshold voltage increases, and increased as the first temperature increases.In each or all of the foregoing examples, the second temperature is further adjusted based on the ambient temperature, with the second temperature increasing towards the first temperature as the ambient temperature increases. In each or all of the foregoing examples, the method further comprises, furthermore or optionally, reducing a ramp rate from the lower operating temperature to the higher operating temperature as the second temperature increases. In each or all of the foregoing examples, furthermore or optionally, the threshold voltage is a voltage at which the rate of increase of the pump cell current for a given change in the pump cell voltage is higher than a threshold value.In each or all of the foregoing examples, additionally or optionally, reducing the operating temperature of the sensor includes reducing the operating temperature of each of the pump cells and Nernst cells of the oxygen sensor. In each or all of the foregoing examples, additionally or optionally, reducing the operating temperature includes adjusting the output of a heating element of the oxygen sensor to limit the heat generated during sensor operation, wherein the output includes a heating element current and a heating element voltage.In each or all of the preceding examples, additionally or optionally, the method further comprises, after reducing the operating temperature of the oxygen sensor from the first to the second temperature, a transition of the sensor from the lower voltage to the higher voltage at a ramp rate, the ramp rate being determined as a function of the second temperature relative to the first temperature. In each or all of the preceding examples, additionally or optionally, the ramp rate is reduced as the difference between the first and second temperatures decreases. In each or all of the preceding examples, additionally or optionally, the variable-voltage operation of the oxygen sensor is a response to a requirement for an estimation of the exhaust gas oxygen concentration.In each or all of the foregoing examples, additionally or optionally, the method further comprises generating a fuel alcohol content reading based on a change in the oxygen sensor's pump current during variable voltage operation; and adjusting an engine operating parameter, including cylinder fuel supply, based on the reading.

[0068] Another exemplary procedure for an engine comprises: in response to a request to operate a variable-voltage oxygen sensor, received while the sensor is at a first temperature and voltage, setting an output of an oxygen sensor element to lower the oxygen sensor to a second temperature; and after lowering, ramping the oxygen sensor from the first voltage to a second voltage higher than the first voltage, with a ramp rate set depending on the second temperature. In the preceding example, additionally or optionally, the second temperature is set to limit the second voltage to below a threshold voltage in an overpotential range of the oxygen sensor.In each or all of the foregoing examples, additionally or optionally, the ramp rate is reduced as the second temperature approaches the first. In each or all of the foregoing examples, additionally or optionally, the requirement for variable-voltage operation of the oxygen sensor is a response to a requirement for one or more: an estimate of the alcohol content of the fuel burned in the engine; an estimate of the ambient humidity of an intake air charge; and an estimate of the oxygen content of the intake air charge or exhaust gas. In each or all of the foregoing examples, additionally or optionally, the oxygen sensor is one consisting of an intake oxygen sensor coupled to an intake port downstream of an intake throttle and an exhaust oxygen sensor coupled to an exhaust port upstream of an exhaust catalyst.

[0069] Another exemplary engine system comprises: an engine with one exhaust; a fuel injection system for supplying fuel to one engine cylinder; an oxygen sensor coupled to the exhaust, the oxygen sensor comprising a heater, a pump cell, and a Nernst cell; and a controller with computer-readable instructions stored in non-volatile memory for: applying an initial lower voltage to the pump cell; after application, setting a temperature setting for the heater to lower the temperature of each of the pump cell and the Nernst cell; after setting, increasing a pump cell voltage from the initial voltage to a second voltage; and, based on a change in the pump cell current at the second voltage relative to the initial voltage, estimating the oxygen content of the exhaust gas.and adjusting the engine fuel supply in response to the estimated oxygen content. In the foregoing example, additionally or optionally, the system further comprises a temperature sensor for estimating an ambient temperature, wherein the control further includes instructions to: lower the temperature of each of the pump cell and the Nernst cell based on the ambient temperature, wherein the temperature setting of the heating device is adjusted to a higher temperature of each of the pump cell and the Nernst cell as the ambient temperature increases. In each or all of the foregoing examples, the control further includes, additionally or optionally, instructions to: increase the pump cell voltage from the first voltage to the second voltage at a higher ramp rate when the second voltage is higher, and at a lower ramp rate when the second voltage is lower.

[0070] In another representation, during a first condition where an oxygen sensor is at a first operating temperature, the voltage is increased to a second voltage with a first, lower ramp rate after an initial, lower voltage is applied to a pump cell of the oxygen sensor. Furthermore, during a second condition where the oxygen sensor is at a second operating temperature, which is lower than the first operating temperature, the voltage is increased to a third voltage with a second, higher ramp rate after the first voltage is applied to the pump cell of the oxygen sensor. In this case, the third voltage is higher than the second voltage.Furthermore, during the first condition, the temperature of the oxygen sensor is reduced to the first temperature by adjusting a sensor heating device, and during the second condition, the temperature of the oxygen sensor is reduced to the second temperature by adjusting the sensor heating device. Additionally, the ambient temperature is higher during the first condition and lower during the second condition.

Claims

[1] A signal control function for reducing the occurrence of blackening of a heated oxygen sensor element, e.g. a broadband lambda probe (UEGO 200), when operating with variable constant voltage in at least two voltage levels for an internal combustion engine reduces the operating temperature of the oxygen sensor element from a first temperature (T1) to a second temperature (T2) before a transition from a lower operating voltage (V1, Vp1, Vn1) to a higher operating voltage (Vh, Vp2, Vn2), where the second temperature (T2) is increased when the first temperature (T1) increases; and is reduced when the difference between the higher operating voltage (Vh, Vp2, Vn2) and a threshold voltage (503) of a lower limit of an overpotential range becomes larger, where a ramp rate from the lower operating voltage (V1, Vp1, Vn1) to the higher operating voltage (Vh, Vp2, Vn2) is reduced when the second temperature (T2) is increased. [2] Signal control function according to claim 1, wherein the second temperature (T2) is increased in the direction of the first temperature (T1) when the ambient temperature increases. [3] Signal control function according to claim 1, wherein the threshold voltage is a limit voltage from which the pump cell current (Ip) begins to increase rapidly with increasing pump cell voltage (Vp). [4] Signal control function according to claim 1, wherein the ramp rate is reduced when the difference between the first temperature (T1) and the second temperature (T2) becomes smaller. [5] Signal evaluation function using the signal control function according to claim 1, comprising generating a fuel alcohol content indication based on a change in the pump current (Ip) of the oxygen sensor element after the transition from the lower voltage (Vl, Vp1) to the higher voltage (Vh, Vp2) based on the difference between the change in current output (ΔIp1) after applying the lower voltage (Vl, Vp1) in conjunction with the change in current output (ΔIp2) after applying the higher voltage (Vh, Vp2) for setting an internal combustion engine operating parameter, including a cylinder fuel supply, based on the indication.

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