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] In order to comply with current exhaust gas regulations, the use of different exhaust gas sensors for exhaust gas aftertreatment for modern internal combustion engines is fundamentally essential. Usually, nitrogen oxides (NO 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, for metering the fuel amount, for improving the exhaust gas aftertreatment and for monitoring the efficiency of the three-way catalyst. On the basis of the nitrogen oxide sensor, it is basically possible to determine the nitrogen oxide concentration and / or the oxygen concentration in the exhaust gas. If an SCR catalyst is used, the ammonia concentration can additionally be determined. In the case of a nitrogen oxide storage catalyst, this basically allows the detection of the accumulation or the end of the storage possibility, while in the case of an SCR catalyst, a precise metering of the urea-water solution is basically carried out. [Background technology]

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

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

[0004] In order to guarantee overheating protection of the sensor, a maximum heating time is basically defined. If no valid temperature signal is available, the probe heater must basically be switched off after this time or a safe operating mode with a significantly reduced effective heater voltage must be entered. The above-mentioned maximum time is basically designed for battery voltages typically above 12 V, taking into account manufacturing variations of the heater resistor at the specified heating gradient and critical ambient conditions. However, the actually required heating time of the sensor can deviate significantly from this maximum time, for example due to low ambient temperatures, long propulsion phases and reduced battery voltages. For example, the installation position of the sensor, residual moisture and water in the exhaust gas pipe can be further influencing factors.

[0005] It is basically known how the heating method should be adapted in the event of a drop in the 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 influences on the actual sensor temperature are essentially negligible during the heating phase.

[0006] Some diagnostics of heated exhaust gas sensors can essentially only be performed robustly when the probe is very hot or hot. To make this possible, the activation of diagnostics based on energy models is essentially 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 disadvantages of the known devices and methods mentioned above. In particular, there is a need to enable a 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 sector. 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 for heating 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 for regenerating the exhaust gas sensor, in which case the burning off of particles, in particular soot, is performed 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 allow in particular an accurate control of the regeneration.

[0012] The further exhaust gas sensor can essentially only function if the operating temperature of the ceramic element of the exhaust gas sensor is sufficiently high and is therefore essentially heated continuously 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 the 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 denote 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 in particular be or include the battery voltage of the battery of the heating element. The effective heater voltage can be varied using the duty ratio. Within the context of the present invention, the duty ratio is to 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 in particular be calculated from the product of the heater voltage and the duty ratio.

[0020] The energy model can furthermore take into account 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 external environment of the exhaust gas sensor, thermal radiation between the ceramic element of the exhaust gas sensor and the housing of the exhaust gas sensor, 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 also be taken into account as a total power loss. 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 mentioned 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 the physical system to activate a certain reaction. The energy threshold can be determined with the WPA model, especially in the real operation of the exhaust gas sensor, especially under adverse ambient conditions. In particular, the energy threshold can be determined with the WPA model at cold start. Furthermore, the energy threshold can be determined with the WPA model in cold ambient conditions. Furthermore, the energy threshold can be determined with the BP model. The BP model (Best Performance Model) is basically an error-free system. An error-free system may have a specified minimum heater resistance, especially depending on the manufacturing tolerances.

[0022] The energy threshold can be selected such that the temperature-target corridor is achieved by the energy threshold. The temperature-target corridor can be determined by probing the boundary positions. 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 means 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 fault-free system, i.e. the system is still barely capable of maintaining the exhaust gas limit values. The system may be particularly a vehicle at the end of its life. All validation measurements required on the fault system for approval by the authorities are also essentially carried out on the basis of the aged system. The WPA model can take into account particularly the critically high heater resistance of the heating element.

[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. The term "continuously calculated" is to be understood within the scope of the present invention as meaning that the energy input is calculated as soon as the control device (English: electronic control unit, ECU) is ready for operation and the software is executed. Additional special switch-on conditions and / or boundary conditions can be omitted. There are therefore no special switch-on conditions and / or boundary conditions.

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

[0027] As mentioned above, in step d) the exhaust gas sensor is heated by means of a heating element until the energy input reaches an 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 square root of the input current (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: ohms) 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: amperes).

number

[0031] The energy E of the exhaust gas sensor (unit: Joule) is calculated from the time integral: h corresponds to the heating power (unit: watts), 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 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 carry out a method as described 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 a working memory and / or a main memory of a computer or a computer network.

[0038] In a further aspect of the invention, a computer program product is proposed comprising program code means stored on a machine readable carrier for carrying out a method as mentioned 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 be a program 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 a non-transitory data memory, for example a hardware data memory medium 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 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 the diagnosis. Whereas in known heating methods, essentially only the battery voltage is taken into account, the energy modeling is based in particular 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 the environmental conditions, and a reliable transition to closed-loop controlled operation can be made.

[0043] In addition to the above mentioned advantages, the present invention essentially reduces the application costs significantly. Furthermore, it requires essentially fewer parameters, 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 several influencing parameters, which according to the current prior art would essentially not be reproducible if they were 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 quantity (energy or temperature), the following influence quantities can be taken into account in particular (but not exclusively): energy input as a function of the heater resistance; convective energy exchange between the exhaust gas and the ceramic element of the exhaust gas sensor, in particular the probe ceramic, and between the exhaust gas and the housing of the exhaust gas sensor, in particular the probe housing; conductive energy exchange between the ceramic element of the exhaust gas sensor, in particular the probe ceramic, and the housing of the exhaust gas sensor, in particular the probe housing, and between the housing of the exhaust gas sensor, in particular the probe housing, and the environment; thermal radiation between the ceramic element of the exhaust gas sensor, in particular the probe ceramic, and the housing of the exhaust gas sensor, in particular the probe housing, or between the ceramic element of the exhaust gas sensor, in particular the probe ceramic, and the protective tube.

[0045] During the heating phase, convective energy exchange, conductive energy exchange and heat radiation typically act in the form of heat losses in the probe ceramic, which may also be considered as a total power loss. The course of the effective heater voltage during the heating phase is basically specified by the manufacturer, taking into account the permissible tensile stresses. The heating duration, which is to be variably configured, particularly for each application, can basically be realized by simply specifying suitable modeled energy or temperature thresholds. In principle, the exhaust gas sensor can be operated with the maximum permissible effective heater voltage up to the specified threshold, and in principle, 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 description of the drawings]

[0047] [Figure 1] FIG. 2 is an exploded view of a broadband lambda probe. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0048] EMBODIMENTS OF THE PRESENTINVENTION In Fig. 1, an exploded view of a broadband lambda probe 110 is shown. The broadband lambda probe 110 may have a pump cell 114 with a porous protective layer 112. In addition, the broadband lambda probe 110 may have a Nernst cell 116. A hollow space 118 and a diffusion barrier 120 are shown in Fig. 1. In addition, the broadband lambda probe 110 may have a heating element 122. The broadband lambda probe 110 may have a number of substrate electrodes 124. The electrically conductive connections are indicated diagrammatically in Fig. 1 by lines 126. In Fig. 1, the 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 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; d) heating the exhaust gas sensor with the heating element until the calculated energy input reaches the energy threshold; A method comprising:

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

3. said method steps a) to d) being carried out by a computer program when said computer program is executed on a computer or a computer network, Step c) is initiated as soon as the computer program is running. The method according to claim 1 or 2.

4. The energy model is - convective energy exchange between the exhaust gases 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 a protective tube of the exhaust gas sensor. taking into account at least one parameter selected from the group consisting of:

4. The method according to any one of claims 1 to 3.

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

5. The method according to any one of claims 1 to 4.

6. After step d), the heating element is operated under closed-loop control.

6. The method according to any one of claims 1 to 5.

7. A system including at least one exhaust gas sensor and at least one control device, The control device includes at least one processor; The control device is configured to carry out the method steps according to any one of claims 1 to 6. system.

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

9. A computer program arranged to carry out the method according to any one of claims 1 to 6 when executed on a computer or on a computer network.

10. 7. A data carrier having stored thereon a data structure configured for carrying out the method according to any one of claims 1 to 6 after being loaded into the working memory and / or main memory of a computer or computer network.

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