Method for heating an exhaust gas sensor - Patents.com

Abstract

A method is proposed for heating an exhaust gas sensor including at least one heating element, comprising the steps of: a) providing an energy model of the exhaust gas sensor, the energy model describing an energy input via an effective heater voltage of the heating element and a heater resistance of the heating element, b) determining an energy threshold, c) continuously calculating the energy input using the energy model, thereby obtaining a calculated energy input, and d) heating the exhaust gas sensor using the heating element until the calculated energy input reaches the energy threshold.

Description

[Technical Field]

[0001] To comply with current exhaust gas regulations, it is fundamentally necessary to use different exhaust gas sensors for exhaust gas aftertreatment on modern internal combustion engines. x ) sensors, particle sensors, wideband lambda probes, and binary jump probes are used, the latter of which are basically only used in gasoline or gas engines. The lambda signal of the wideband lambda probe is used, for example, to meter the fuel amount, improve exhaust gas aftertreatment, and monitor the efficiency of three-way catalysts. Based on the nitrogen oxide sensor, it is basically possible to determine the nitrogen oxide and / or oxygen concentration in the exhaust gas. If an SCR catalyst is used, it is also possible to determine the ammonia concentration. In the case of a nitrogen oxide storage catalyst, this basically allows the detection of storage or the end of storage potential, while in the case of an SCR catalyst, it basically allows the precise metering of a urea-water solution. [Background technology]

[0002] The above-mentioned exhaust gas sensors are basically provided with a heating element to ensure their respective functions. The heating element of the particle sensor is basically used to regenerate the sensor element of the particle sensor, in which case the heating is used to burn off the soot. The heating element here is basically only operated transiently. The further sensor basically only functions when the operating temperature of the sensor ceramic is sufficiently high, and therefore is basically heated continuously to the specified target temperature.

[0003] The heating phase of the sensor is essentially determined by a heating profile in the form of a voltage transition, which is defined in the technical customer documentation. Since it is typically not possible to control the voltage supply itself in a closed loop, which corresponds to the vehicle electrical system, the desired effective voltage is essentially ensured by the heater output stage using the duty cycle.

[0004] To ensure overheating protection of the sensor, a maximum heating time is defined. If a valid temperature signal is not available, the probe heater must be switched off after this time or must enter a safe operating mode with a significantly reduced effective heater voltage. The above-mentioned maximum time is typically designed for battery voltages above 12 V, taking into account manufacturing variations in the heater resistor at the specified heating gradient and critical ambient conditions. However, the actual required sensor heating time can deviate significantly from this maximum time, for example, due to low ambient temperatures, long propulsion phases, and reduced battery voltages. For example, the sensor installation location, residual moisture, and water in the exhaust gas pipe can be further influencing factors.

[0005] It is basically known how to adapt the heating method in the event of a drop in battery voltage. In this case, the heating time is set as a function of the battery voltage, and this heating time t~U 2 varies approximately proportionally to the square of the voltage. Further influence on the actual sensor temperature is essentially negligible during the heating phase.

[0006] Some diagnostics of heated exhaust gas sensors can be performed robustly only when the probe is very hot or extremely hot. To make this possible, diagnostics based on energy models are typically performed intermittently. Summary of the Invention [Problem to be solved by the invention]

[0007] Disclosure of the Invention Therefore, a method for heating an exhaust gas sensor, a system including at least one exhaust gas sensor and at least one control device, a computer program, and a data carrier are proposed, which at least largely avoid the drawbacks of the known devices and methods described above. In particular, there is a need to enable faster heating of the exhaust gas sensor under variable boundary and environmental conditions and taking into account component protection.

[0008] An "exhaust gas sensor" in the sense of the present invention is to be understood as essentially any device configured to detect at least one measurand of exhaust gases, for example a physical and / or chemical measurand, in particular an optical and / or electrical measurand. For example, the exhaust gases may be exhaust gases of an internal combustion engine, in particular in the automotive field. The exhaust gas sensor can be configured in particular to generate at least one sensor signal, in particular at least one electrical sensor signal, for example an analog and / or digital sensor signal.

[0009] The exhaust gas sensor can in particular be selected from the group consisting of nitrogen oxide sensors, particle sensors, lambda probes, in particular wideband lambda probes, binary jump probes. In principle, other embodiments are also conceivable.

[0010] The exhaust gas sensor may in particular include at least one heating element, which may in particular be configured to heat at least one component of the exhaust gas sensor.

[0011] In particular, the exhaust gas sensor may be a particle sensor, and the heating element may be configured to regenerate the exhaust gas sensor, in which case the particles, in particular soot, are burned off by a heating process. In this case, the heating element may be particularly operable in a non-stationary manner. The particle sensor may have an integrated temperature measuring element, in particular with a measuring range of -40°C to 950°C, in order to enable precise control of the regeneration.

[0012] The further exhaust gas sensor basically only functions if the operating temperature of the ceramic element of the exhaust gas sensor is sufficiently high and is therefore essentially continuously heated up to the specified target temperature.

[0013] In contrast, in the case of nitrogen oxide sensors and lambda probes, the temperature of the ceramic element is determined essentially via the internal resistance of the ceramic element, which essentially becomes measurable only after a certain high temperature has been exceeded, depending on the respective ceramic element and the evaluation logic used, in particular an analog circuit or ASIC. [Means for solving the problem]

[0014] In a first aspect of the present invention, a method for heating an exhaust gas sensor is proposed.

[0015] The method comprises the steps listed below. The method may comprise further steps not listed. These steps may be carried out at least partially repeatedly, in particular in tandem.

[0016] The method comprises the following steps: a) providing an energy model of the exhaust gas sensor, the energy model describing energy input via an effective heater voltage of a heating element and a heater resistance of the heating element; b) determining an energy threshold; c) continuously calculating the energy input using the energy model, thereby obtaining a calculated energy input; d) heating the exhaust gas sensor with a heating element until the calculated energy input reaches an energy threshold; Includes.

[0017] The method may in particular be a computer-implemented method. The term "computer-implemented" may in particular refer to a process which is fully or partly implemented using data processing means, in particular using at least one processor.

[0018] As mentioned above, in step a) an energy model is provided. The energy model may describe the heating state of the exhaust gas sensor. The energy model may be based on an energy balance of the exhaust gas sensor.

[0019] The energy model can be used to determine the energy input via the effective heater voltage of the heating element and the heater resistance of the heating element. The effective heater voltage can be, in particular, the battery voltage of the battery of the heating element or can include the battery voltage. The effective heater voltage can be varied using the duty ratio. Within the scope of the present invention, the duty ratio should be understood as the ratio of the pulse duration to the pulse period. The duty ratio is expressed as a dimensionless ratio having a value between 0 and 1 or between 0% and 100%. By varying the duty ratio, for example, the arithmetic mean value of the effective heater voltage can be varied. The effective heater voltage can be calculated, in particular, from the product of the heater voltage and the duty ratio.

[0020] The energy model can further consider at least one parameter selected from the group consisting of convective energy exchange between the exhaust gas and the ceramic element of the exhaust gas sensor and / or the housing of the exhaust gas sensor, conductive energy exchange between the ceramic element of the exhaust gas sensor and the housing of the exhaust gas sensor, conductive energy exchange between the housing of the exhaust gas sensor and the environment outside the exhaust gas sensor, thermal radiation between the ceramic element of the exhaust gas sensor and the housing of the exhaust gas sensor, and thermal radiation between the ceramic element of the exhaust gas sensor and the protective tube of the exhaust gas sensor. Basically, other parameters are also conceivable. During the heating phase, convective energy exchange, conductive energy exchange, and thermal radiation typically act in the form of heat losses in the probe ceramic, which can possibly be considered as total power losses. The energy losses used for the energy balance can be set as a function of the modeled energy or as a constant value.

[0021] As described above, in step b), an energy threshold is determined based on the energy model. The term "energy threshold" basically refers to the energy that must be supplied to a physical system to initiate a specific reaction. The energy threshold can be determined using the WPA model in real-world operation of the exhaust gas sensor, especially under adverse ambient conditions. In particular, the energy threshold can be determined using the WPA model during cold start-up. Furthermore, the energy threshold can be determined using the WPA model in cold ambient conditions. Furthermore, the energy threshold can be determined using the BP model. The BP model (Best Performance Model) is essentially an error-free system. An error-free system may have a specified minimum heater resistance, especially depending on manufacturing tolerances.

[0022] The energy threshold can be selected to achieve a temperature-target corridor, specifically by the energy threshold. The temperature-target corridor can be determined by probing boundary locations. The WPA model can be used to determine the lower temperature, and the BP model can be used to determine the upper temperature.

[0023] The term cold start basically refers to starting a vehicle without preheating. In particular, all components of the vehicle, in particular all components, may have the same temperature level during start-up. In particular, all temperature sensors of the vehicle, in particular all temperature sensors, may have the same temperature level. In particular, the lambda probe may have a temperature of less than 50°C during cold start-up.

[0024] The WPA model (Worst Case Acceptable Model) may be a particularly aged, error-free system, i.e., the system is still barely able to maintain the exhaust gas limit values. This system may be particularly a vehicle at the end of its life. All verification measurements required for the error system to obtain approval from the authorities are also basically carried out on the aged system. The WPA model can take into account particularly critically high heater resistances of the heating elements.

[0025] As mentioned above, in step c) the energy input is continuously calculated via the effective heater voltage of the heating element and the heater resistance of the heating element. Within the scope of the present invention, the term "continuously calculated" should be understood to mean that the energy input is calculated as soon as the control unit (English: electronic control unit, ECU) is ready for operation and the software is running. Additional special switch-on conditions and / or boundary conditions can be omitted. Therefore, there are no special switch-on conditions and / or boundary conditions.

[0026] Method steps a) to d) can be performed by a computer program when executed on a computer or computer network, and step c) can be initiated as soon as the computer program is running, i.e., as soon as the computer program is executed. Furthermore, step c) can be performed within a time period during which operation of the heating element would be possible. However, the heating element may not be operating.

[0027] As mentioned above, in step d) the exhaust gas sensor is heated using the heating element until the energy input reaches the energy threshold. This results in a variable heating time. The term heating time basically means the time period required to heat the element to the target temperature. An exemplary calculation is given below:

[0028] Effective heater voltage U h,eff (unit: volts) is the heater voltage U h It is calculated by multiplying the duty cycle DC by the voltage (unit: volts). U h,eff =DC·U h (1)

[0029] Heater current I h (unit: ampere) is the heater voltage U h (unit: volts) and heater resistance R h (unit: ohm) and I h =U h / R h (2)

[0030] The heating power P is Effective heater voltage U h,eff (unit: volts) and Heater current I h It is calculated by multiplying it by the current (unit: ampere).

number

[0031] The energy E of the exhaust gas sensor (unit: joules) is calculated from the time integral: h corresponds to the heating power (unit: watt), and P hloss corresponds to the total power loss (unit: watts).

number

[0032] Typical values ​​at target temperatures are: U h =12V R h =5 ohms DC=0.2 P hloss =P h =5.76W It could be.

[0033] P hloss and P h The equation with is performed assuming an energy balance.

[0034] In a further aspect of the present invention, a system is proposed comprising at least one exhaust gas sensor and at least one control device, the control device comprising at least one processor, the control device being configured to perform the method steps according to the method as described above or as further described below.

[0035] In a further aspect of the invention, a computer program is proposed which, when executed on a computer or on a computer network, is arranged to carry out a method as described above or further below.

[0036] In a further aspect of the invention, a computer program is proposed comprising program code means, the computer program being arranged to perform a method as set out above or as further described below when the computer program is executed on a computer or on a computer network.

[0037] In a further aspect of the invention, a data carrier is proposed on which a data structure is stored, the data structure being configured for carrying out a method as described above or as further described below after being loaded into the working memory and / or main memory of a computer or computer network.

[0038] In a further aspect of the present invention, a computer program product is proposed comprising program code means stored on a machine-readable carrier for performing a method as set out above or as further described below when executed on a computer or on a computer network.

[0039] In this case, a computer program product is understood to mean a program that is available as a commercial product. A computer program product may essentially be in any form, for example on paper or on a computer-readable data carrier, and may in particular be distributed via a data transmission network. In particular, the program code means may be stored on a computer-readable data carrier and / or on a computer-readable memory medium. The terms "computer-readable data carrier" and "computer-readable memory medium" as used herein may in particular relate to non-transitory data memories, for example hardware data memory media on which computer-executable instructions are stored. A computer-readable data carrier or a computer-readable memory medium may in particular be or include a memory medium such as a random access memory (RAM) and / or a read-only memory (ROM).

[0040] In a further aspect of the present invention, a modulated data signal is proposed comprising instructions executable by a computer system or computer network for carrying out a method as set out above or as further described below.

[0041] The method according to the invention and the device according to the invention have a number of advantages over known methods and devices, in particular they can allow for faster heating of the probe under variable boundary and environmental conditions and taking into account component protection.

[0042] The basis is essentially an energy model of the exhaust gas sensor, which describes the heating state and can be used to trigger diagnostics. While known heating methods essentially only take into account the battery voltage, energy modeling is based primarily on the energy balance of the sensor element. By appropriately defining energy or temperature thresholds in the energy model, the permissible heating time can be flexibly adapted to environmental conditions, enabling a reliable transition to closed-loop controlled operation.

[0043] In addition to the advantages mentioned above, the present invention also substantially reduces application costs. Furthermore, fewer parameters are required, which essentially reduces the memory requirements of the software. According to the model-based approach, the heating duration is essentially described as a function of multiple influence parameters, which, according to the current prior art, would essentially not be reproducible if directly considered for each application due to the multidimensionality of the solution space.

[0044] The heating state of the heated exhaust gas sensor can be determined via an energy balance. Depending on the selected state variable (energy or temperature), the following influence variables can be taken into account, in particular (but not exclusively): energy input as a function of heater resistance; convective energy exchange between the exhaust gas and a ceramic element of the exhaust gas sensor, in particular the probe ceramic, and between the exhaust gas and a housing of the exhaust gas sensor, in particular the probe housing; conductive energy exchange between a ceramic element of the exhaust gas sensor, in particular the probe ceramic, and a housing of the exhaust gas sensor, in particular the probe housing, and between a housing of the exhaust gas sensor, in particular the probe housing, and the environment; thermal radiation between a ceramic element of the exhaust gas sensor, in particular the probe ceramic, and a housing of the exhaust gas sensor, in particular the probe housing, or between a ceramic element of the exhaust gas sensor, in particular the probe ceramic, and a protective tube.

[0045] During the heating phase, convective energy exchange, conductive energy exchange, and thermal radiation typically act in the form of heat losses in the probe ceramic, which can sometimes be considered as a total power loss. The course of the effective heater voltage during the heating phase is generally specified by the manufacturer, taking into account the allowable tensile stress. In particular, a heating duration that can be variably configured for each application can basically be realized by simply specifying an appropriate modeled energy or temperature threshold. In principle, the exhaust gas sensor can be operated with the maximum allowable effective heater voltage up to the specified threshold, and basically, the fastest possible transition to closed-loop controlled operation can be realized.

[0046] Further optional details and features of the invention will become apparent from the following description of preferred embodiments which are illustrated diagrammatically in the drawings. [Brief explanation of the drawings]

[0047] [Figure 1] FIG. 1 is an exploded view of a broadband lambda probe. DETAILED DESCRIPTION OF THE INVENTION

[0048] Embodiments of the invention 1 shows an exploded view of a broadband lambda probe 110. The broadband lambda probe 110 may have a pump cell 114 with a porous protective layer 112. Additionally, the broadband lambda probe 110 may have a Nernst cell 116. FIG. 1 shows a hollow space 118 and a diffusion barrier 120. Additionally, the broadband lambda probe 110 may have a heating element 122. The broadband lambda probe 110 may have multiple substrate electrodes 124. The conductive connections are shown schematically in FIG. 1 by lines 126. In FIG. 1, I p represents the pump current, and U R represents the reference voltage, and U H represents the heater voltage, and R represents the electrical resistance.

Claims

1. 1. A method for heating an exhaust gas sensor including at least one heating element, comprising: The method comprises the following steps: a) providing an energy model of the exhaust gas sensor, the energy model describing energy input via an effective heater voltage of the heating element and a heater resistance of the heating element; b) determining an energy threshold; c) continuously calculating the energy input using the energy model, thereby obtaining a calculated energy input; d) heating the exhaust gas sensor with the heating element until the calculated energy input reaches the energy threshold; Including, The method, wherein the energy threshold is selected such that a temperature-target corridor is achieved by the energy threshold.

2. The method is a computer-implemented method. The method of claim 1.

3. Steps a) to d) are performed by a computer program when the computer program is executed on a computer, When the computer program is run, step c) is initiated. The method of claim 2.

4. The energy model is convective energy exchange between the exhaust gas and the ceramic element of the exhaust gas sensor and / or the housing of the exhaust gas sensor; conductive energy exchange between the ceramic element of the exhaust gas sensor and the housing of the exhaust gas sensor; conductive energy exchange between the housing of the exhaust gas sensor and an environment external to the exhaust gas sensor; heat radiation between the ceramic element of the exhaust gas sensor and the housing of the exhaust gas sensor; Heat radiation between the ceramic element of the exhaust gas sensor and the protective tube of the exhaust gas sensor using at least one parameter selected from the group consisting of: The method of claim 1.

5. In step d), the exhaust gas sensor is heated by a maximum allowable effective heater voltage of the heating element. The method of claim 1.

6. After step d), the heating element is operated under closed-loop control. The method of claim 1.

7. 1. A system including at least one exhaust gas sensor and at least one controller, the control device includes at least one processor; The control device is configured to perform the steps according to the method of claim 1. system.

8. The exhaust gas sensor is selected from the group consisting of a nitrogen oxide sensor, a particle sensor, a lambda probe, and a binary jump probe. The system of claim 7.

9. A computer program comprising a program code which, when executed on a computer, causes said computer to carry out the method of claim 1.

10. 10. A data carrier having stored thereon a program code for causing a computer to carry out the method according to claim 1 after being loaded into the working memory and / or main memory of said computer.

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