JP6130095B2 - Method for the operation of an actively heated exhaust gas sensor heater - Google Patents

Description

  The present invention relates to a method for the operation of a heater of an actively heated exhaust gas sensor, in particular a lambda sonde.

  Lambdasonde is used in today's engine control systems to measure the oxygen concentration in the exhaust gas of internal combustion engines. The oxygen concentration in the exhaust gas of the internal combustion engine is determined by the lambda sonde, and as a result, the exhaust gas aftertreatment by the catalyst provided in the exhaust gas path of the internal combustion engine is supplied to the air and fuel of the internal combustion engine through the lambda control circuit. So that an optimal exhaust gas composition can be achieved.

  Several forms of lambda sonde are known. For a two-point lambda sonde, also called a voltage jump lambda sensor, the characteristic curve shows a drop that jumps when λ = 1. In doing so, the voltage jump sonde essentially allows a distinction between rich exhaust gas when operating an internal combustion engine with excess fuel and lean exhaust gas when operating with excess air. A so-called wideband lambda sonde, also called a continuous lambda sonde or linear lambda sonde, can measure the lambda value of the exhaust gas in a wide area around λ = 1. Thus, the wideband lambda sonde can be used, for example, for control of an internal combustion engine for lean operation with excess air.

  Lambdasonde is based on a galvanic oxygen concentration cell using a solid electrolyte in principle. Solid electrolytes have the property that oxygen ions can be transported electrolytically at high temperatures, which causes voltage jumps. This property makes it possible to determine the difference between two different gases, in particular the exhaust gas flow and the oxygen-based oxygen partial pressure. In general, the solid electrolyte becomes conductive to oxygen ions at an activation temperature of about 350 ° C. The rated temperature of the sonde is generally much higher than that, usually between 650 ° C and 850 ° C. In order to achieve the temperature required for the operation of the sonde, a heater for the exhaust gas sonde is generally provided, but this heater may be incorporated, for example, in a sensor.

  The output signal of the lambda sonde is highly dependent on the temperature of the sensor element. Therefore, in order to improve signal accuracy, it is desirable to keep the temperature of the sensor element as constant as possible by separating it from changes in the exhaust gas temperature. It is known to control this temperature through a heater voltage. For this purpose, for example, an operating point-dependent characteristic map using the exhaust gas temperature and the exhaust gas mass flow rate as input values can be used.

  Lambdasonde temperature control can be used for higher temperature accuracy. At that time, the internal resistance Ri of the sonde can be used as the control value. In this case, it is assumed that a unique relationship is established between the internal resistance of the sonde and the temperature of the sonde element. Yes.

  By employing operating point dependent pre-control along with temperature control, the very high accuracy of temperature control can be combined with a quick response to changes in engine operating points due to pre-control. Therefore, characteristic map preliminary control by superimposition control aiming at a certain sonde internal resistance is already known. However, the characteristic map preliminary control by the superimposition control aiming at a certain internal resistance of the sonde has a drawback that the signal accuracy may be lowered due to a deterioration phenomenon during the use period of the sonde. In addition, the sonde may overheat and possibly be damaged. This is particularly related to the fact that the internal resistance of the sonde generally varies with the age of the sonde. For example, in the case of a lambda sonde, the internal resistance of the sonde increases even under the same sensor element temperature with the age of the sonde. As a result, in the case of control using a certain internal resistance of the sonde as the guide value, the sonde is gradually heated strongly with the years of use. Therefore, the control using the target value of the constant internal resistance as a guide is effective only when the change in the internal resistance can be ignored. When this is not the case, automatic adjustment of the target value of the internal resistance is required, which is often impossible in practice. Therefore, in general, when the change in the internal resistance is significant, the temperature control is given up and only the sonde heater is controlled.

  The object of the present invention is to provide an improved method for the operation of heaters of actively heated exhaust gas sensors. In so doing, the exhaust gas sensor is actuated too hot on the one hand and prevented from being cooled too strongly on the other hand. According to the method according to the invention, the exhaust gas sensor or the sonde is operated as close as possible to the rated temperature of the sensor, so that no deterioration of the signal accuracy occurs during the sensor usage period. This reduces the emissions of the internal combustion engine and enables a robust diagnosis.

  The above problem is solved by the method as claimed. Preferred embodiments of the method are subject to the dependent claims.

  In the method for the operation of an actively heated exhaust gas sensor heater according to the present invention, deadband control is used for adjusting the temperature of the sensor, wherein the sonde heater has a temperature dependent value of the sensor. , Adjusted and controlled so as to be within a predetermined target band. According to this method, a value that undergoes some fluctuation or change during the use period of the sensor can be used for adjusting the temperature of the sensor. In particular, according to the method of the present invention, the internal resistance of the exhaust gas sensor can be used as a guide value for dead zone control. There is a unique relationship between the internal resistance of the sonde and the temperature of the sensor element, although it usually changes during the sensor usage period. In general, internal resistance increases with length of service time and decreases with increasing sensor element temperature. However, the method according to the invention is also applicable to sensors in which the internal resistance decreases, for example with increasing usage time and increases with increasing sensor element temperature. The dead band control provided in accordance with the present invention, in which one target band is given in advance for the guide value, can take into account changes between the sensor usage time lengths, so Almost optimal control can be performed without automatic adjustment. In that way, the bandwidth is chosen as narrow as possible in order to achieve the control as optimally as possible. This band boundary is preferably defined such that the sensor or sonde is activated without being too hot or too cold. In the dead zone control provided based on the present invention, it is certainly impossible to stabilize the sensor element temperature as well as the control aimed at a constant target value. However, this deadband control has the advantage that it takes into account disturbances that cannot be measured by the control, compared to pure temperature control. This allows essentially better temperature stabilization compared to pure temperature control with the method according to the invention.

  Preferably, in addition to the dead zone control, preliminary control for controlling heating, preferably characteristic map preliminary control is performed. Here, the preliminary control refers to preliminary control that is particularly dependent on the operating point, and thus dependent on the engine operating point. This preliminary control can be realized by, for example, a characteristic map in which, for example, exhaust gas temperature or exhaust gas mass flow rate is sent. Using such a characteristic map, the heater target voltage depending on the operating point can be calculated. Due to the operating point dependent preliminary control, the method according to the invention makes it possible to react to changes in the engine operating point very quickly during the operation of the heater. This is combined with high control accuracy according to the invention. Therefore, the preliminary control of the characteristic map superimposed with the dead zone control can be used in a very advantageous way for the almost optimal operation of the sensor heating device, in which case the sensor changes during the sensor usage period. Characteristics are taken into account.

  In order to determine the dead band or target band for the guide value, the first boundary of the dead band, in particular the lower boundary, is the internal resistance threshold when the new exhaust gas sensor is overheated and the rated internal resistance of the new exhaust gas. And determined. The second boundary of the dead zone, in particular the upper boundary, is preferably determined between the internal resistance threshold at which the deteriorated exhaust gas sensor is heated and the internal resistance threshold at which the new exhaust gas sensor can still operate. By defining the target zone in this region, it is possible in particular to prevent the sonde from being heated too strongly as aging progresses. On the other hand, it is possible to prevent the new sonde from being cooled too strongly. In addition, such determination of the target zone or dead zone ensures that the sonde is operated as close to the rated temperature as possible over the entire period of use, in which case the internal resistance of the sonde during the period of use Changes in the characteristics of the sonde are taken into account.

  Preferably, the lower and upper boundary of the dead zone is such that the internal resistance of the exhaust gas sensor deviates from the "region where the new exhaust gas sensor can still function but will not be overheated" during the transient oscillation of the controller. It is determined that there is no. In order for the signal accuracy of the sonde to be optimized, the internal resistance of the sonde should remain as close as possible to the dead zone.

  In the dead zone, the gain of the controller to be operated is preferably 0 by the guide value adjusted by the dead zone. In this way, the control intervention of the controller is frozen as soon as the internal resistance enters the dead zone. For example, when the PI controller is used, the P component becomes 0 in the dead zone, while the I component remains in the value learned outside the dead zone in the dead zone. In this case, in the dead zone, if used temporarily, only preliminary control and learned I component are taken in for calculation of the control value.

  In one preferred embodiment of the method according to the invention, the preliminary control in controlling the heating does not depend on the internal resistance of the exhaust gas sensor. In this case, all of the internal resistance, and therefore the value that changes during the sensor usage period, is sent into the dead zone control and not into the preliminary control.

  The method according to the invention is particularly advantageously applied, for example, in the case of a lambda sonde having the above-mentioned relationship between the internal resistance of a sonde and temperature and whose internal resistance generally increases with the length of use. Is possible. In principle, the method according to the invention can be applied to any kind of actively heated exhaust gas sensor operating within a specific temperature zone.

  With the method according to the invention, improved signal stabilization makes it possible to achieve higher signal accuracy in a particularly advantageous manner. For example, in the case of a lambda sonde, in the case of a warm-up engine, it is sensed that the sensor element temperature is unacceptably low as soon as the internal resistance of the sonde exceeds the upper boundary of the dead zone. In this case, the control device operates to increase the heater output, ensuring that the function of the sonde is retained. As soon as the lower boundary of the dead zone is interrupted, it is sensed that the sensor element temperature is unacceptably high. In this case, the control device operates to lower the heater output, and damage to the sonde due to heating is prevented.

  The method according to the invention can also be used advantageously in the warm-up phase of an engine or internal combustion engine. If during this phase of the internal combustion engine it is desired to use the sonde signal for control and / or diagnostic purposes, the sonde is preferably narrow above the activation temperature and below the heat shock temperature. Operated in the temperature range. In this case, the heat shock temperature means that water droplets still exist in the exhaust gas path above that temperature, which hits the hot sonde surface and causes the sonde to enter the material of the sonde element due to local temperature differences. It refers to the temperature that generates thermal stress that can be destroyed. The risk of this overheating and damage of the sonde is very high, especially during the warm-up phase of the internal combustion engine. With the proper setting of the dead zone boundary, dead zone control senses an internal resistance of the sonde that is too low during this phase of the operation of the internal combustion engine and acts to prevent the sonde from being operated at excessively high temperatures by lowering the heater output. On the other hand, deadband control senses when the sensor element temperature is lower than the activation temperature. In this case, since the internal resistance of the sonde is too high, the dead zone control works so that the heater output is increased and the sonde is sufficiently warmed. Preconditions for control and / or diagnostic purposes are obtained because the sonde does not accurately indicate the state of the mixture (lean or rich) when the activation temperature has not been reached or maintained. Absent.

  In order to achieve these advantages on the one hand in the case of a warm-up engine and on the other hand in the case of a warm-up operation of the engine, according to the invention, a dead zone is provided after each operating phase of the internal combustion engine. An appropriately adapted boundary is set. The heat shock temperature that must not be exceeded during the start-up phase is generally well below the rated temperature of the sonde when the engine is warm. Correspondingly, the internal resistance of the sonde during the start-up phase is advantageously maintained in a region that is sufficiently higher than for a warm-up engine, for example between 1K ohms and 2K ohms. In the case of an engine in a warm-up state, for example, a region between 200 ohms and 240 ohms is suitable as an internal resistance.

  The method according to the invention as a whole makes it possible to operate an exhaust gas sensor, for example a lambda sonde, which cannot be controlled with the aim of a constant internal resistance target value or an automatic adjustment of the internal resistance target value, with temperature control, In so doing, according to the invention, the sensor element temperature is stabilized in the target zone or dead zone. This prevents the sonde from being overheated on one side and being cooled to an unacceptable level on the other side. The method according to the invention ensures that the sonde is operated as close to the rated temperature as possible, taking into account the degradation of the sonde internal resistance. Since the signal accuracy of the sonde increases as its operating temperature is adjusted to be constant regardless of the exhaust gas temperature, the method according to the present invention provides improved signal accuracy and thereby for lambda control. Emissions can be reduced and diagnostics can be performed with improved robustness in improved output conditions.

  The invention further includes a computer program that, when executed on a computing device or control device, executes all the steps of the method according to the invention. Finally, the present invention includes program code stored on a machine readable medium for performing the method according to the present invention when the above program is executed on a computing device or control device. Includes computer program products. Here, the control device can be considered as a central control device of an automobile or an internal combustion engine or a control unit of an exhaust gas sensor. The embodiment of the invention as a computer program or as a computer program product has the particular advantage that no other components need to be mounted on the vehicle for the adoption of the method according to the invention. The method according to the invention for the operation of the heater of the exhaust gas sensor can use the normal wiring of the sensor. All that is required is, for example, to install the corresponding computer program, and the method according to the invention can therefore be employed particularly advantageously in the case of existing vehicles.

  Other Merckmars and advantages of the present invention will become apparent from the description of the following examples in conjunction with the drawings. In that case, each Merck Mar can be realized individually or in combination with each other.

FIG. 1 shows a schematic diagram of the relationship between the sonde internal resistance Ri and the sonde element temperature. FIG. 2 shows a schematic diagram of a preferred embodiment of the method according to the invention for the control of a sonde heater. FIG. 3 shows a schematic diagram of a preferred embodiment of deadband control according to the present invention. FIG. 4 shows a schematic diagram of relevant preferred thresholds for deadband control according to the present invention.

  FIG. 1 shows the relationship between the temperature of the sensor ceramic and the internal resistance Ri of the sensor or sonde, where the new sensor's internal resistance and the sensor's internal resistance are degraded. Contrast. The solid line shows the internal resistance of the new sensor. The broken line indicates the internal resistance of the deteriorated sensor. In this example, if the rated temperature of the sonde is 780 ° C., the internal resistance is 220 ohms for the new sensor. Therefore, this value is the rated internal resistance. However, in the case of a degraded sonde, when the rated internal resistance is 220 ohms, the temperature is 820 ° C., which is much higher. Therefore, if the internal resistance of the sonde is used as a constant target value during the temperature control of the sonde heater, the deteriorated sonde will be overheated.

  In order to prevent the sonde from being overheated after a long period of use, the method according to the invention uses dead-zone control for the operation of the actively heated sensor heater. Taking the case of lambda sonde as an example, in particular the internal resistance of the sonde is used as a guide value, in which the sonde heater is not controlled towards a constant Ri = target value, but the sonde internal resistance is fixed. It is controlled so that it is adjusted to be within the target zone (dead zone). As a result, it is possible to take into account the deterioration phenomenon regarding the value which is the basis of the control, in particular the deterioration phenomenon regarding the internal resistance of the sonde suitable for the temperature control. By presetting an appropriate target zone as a control value, the sonde is rated as much as possible without the sonde being overheated or being cooled so hard that the sonde is not allowed over the entire period of use of the sonde. Can operate near temperature.

  This dead band control in the case of heater operation is preferably combined with preliminary control depending on the engine operating point. For this purpose, the preliminary control map is preferably applied so that a constant rated internal resistance corresponding to the rated temperature of the sonde is obtained over the entire characteristic map, for example in steady operation when using a new intermediate layer sonde. . Deviations from this rated internal resistance can occur during operation of the internal combustion engine for various reasons. For example, since the preliminary control characteristic map is applied during steady operation, the rated internal resistance is exceeded or interrupted during dynamic traveling operation. For example, high transient resistance in the heater circuit of a sonde caused by plugs and wire harnesses can cause the sonde to overheat and thereby cause higher internal resistance. Other effects that are not taken into account in the preliminary control can also lead to cooling and heating of the sound and thereby higher or lower internal resistance. In these various cases, another control aiming at the rated internal resistance can be performed using the target value of the fixed internal resistance. However, as a result of the aging phenomenon of the sonde, the internal resistance of the sonde changes during the usage period of the sonde, so that when the sensor element temperature becomes equal to the rated temperature, the internal resistance exceeds the rated internal resistance. Arise. In this case, control using a constant internal resistance target value will not give a favorable result. In addition, control using such a constant internal resistance target value may cause overheating of the sonde. Thus, according to the present invention, the characteristic map preliminary control is combined with the dead zone heater control. In this case, the sonde internal resistance Ri is used as a guide value, and the gain of the control device is set to 0 in the dead zone defined around the rated internal resistance. This measure freezes the control intervention of the controller as soon as the internal resistance enters the dead zone. This is illustrated, for example, in FIG. In the lower part of the figure, the change of the controller with respect to time is shown. In the upper part of the figure, the change of the internal resistance Ri of the sound with respect to time is shown inside and outside the boundary of the dead zone 40. As soon as the internal resistance exceeds the threshold 21 or 22 defined by the dead zone 40, the controller is activated. If the sonde internal resistance Ri is in the dead zone 40 and thus in the boundaries 21 and 22, the controller does not operate, i.e. the control intervention of the controller is frozen.

  FIG. 3 shows an example of the control of the sonde heater according to the present invention including the characteristic map preliminary control means 31 and the superimposed dead zone control means 32. For example, the exhaust gas temperature 35 and the exhaust gas mass flow rate 36 are sent to the characteristic map preliminary control means 31. The dead zone controller that causes the dead zone control means 32 to function is made, for example, as a PI controller. When the internal resistance is in the dead zone, the P component is 0, while the I component in the dead zone remains at the value learned outside the dead zone. That is, when the internal resistance value is in the dead zone, only the I component learned as the preliminary control is taken into the calculation of the control value. The calculated control value is fed into the control device of the sonde heater 33. The internal resistance value Ri_ist measured by the internal resistance measuring device 34 is processed by the dead zone control means 32 together with the target value Ri_soll. For example, the control difference Ri_soll-Ri_ist may be input to a normal PI controller for this purpose. Thereby, the PI controller becomes a dead zone controller that sets the control difference to 0 when Ri_ist is in the dead zone. As a result, the P component of the controller automatically becomes zero. The I component is frozen. When Ri_ist is outside the dead zone, the control difference is passed to the PI controller without change.

  FIG. 4 shows a possible setting of the boundary or threshold value of the dead band 40 in the case of a lambda sonde where the internal resistance value increases with the years of use when the temperature of the sensor elements is the same. A possible area 41 for the lower boundary of the dead zone is set between the Ri threshold 42 at which the new sonde is overheated and the rated internal resistance 43 of the new sonde. The possible region 44 for the upper boundary of the dead zone 40 is set between the Ri threshold 45 at which the degraded sonde is overheated and the Ri threshold 46 at which the new sonde is still functional. Here, the expression “functional” may have different meanings for a warm-up engine and a warm-up engine. In the case of a warm-up engine, functionability means, for example, that the requirements for signal accuracy and sonde dynamics are met, whereas in the case of a warm-up engine, it can function. Sex may simply mean a sonde's ability to indicate the state of the mixture.

  The aged sonde rating 47 is generally within the possible region 44 for the upper boundary of the deadband 40. The Ri threshold 48 for the functionality of an aged sonde is generally above the possible region 44 for the upper boundary of the dead zone 40. The arrows in the possible areas 41 and 44 with respect to the lower or upper boundary of the dead zone indicate the direction of action of the dead zone controller. Within the dead zone, the controller gain is set to zero. The table below shows numerical values for various temperatures and internal resistance values for the new and old sondes as an example.

  The rated internal resistance of the characteristic map preliminary control when using a new sonde is, for example, Ri_nom = 100 ohms. A possible area for the lower boundary of the deadband in this case is 80 ohms <Ri_min <100 ohms. A possible area for the upper boundary of the dead zone is 240 ohms <Ri_max <400 ohms.

  Therefore, the lower boundary of the dead zone is used to prevent overheating of the new sonde. This boundary is therefore defined using a new sonde without Ri degradation. When the internal resistance value falls below the lower boundary of the dead zone, the heating power and, along with that, the sonde temperature decreases. The upper boundary of the dead zone is used to prevent unacceptably strong cooling of the new sonde and at the same time prevent overheating of the degraded sonde. This boundary is therefore defined so that the new sonde is still functional and the maximum Ri-degraded sonde is not overheated. What is important in this case is that the Ri threshold for overheating of the degraded sonde is smaller than the threshold for the functionality of the new sonde. This is because otherwise there will be no overlap area where both the new and old sondes can operate reliably and functionally. When the internal resistance value exceeds the upper boundary of the dead zone, the heating output and the sonde temperature are increased accordingly.

  The lower and upper bounds of the dead zone controller and dead zone are actually the sonde's internal resistance that can be used to optimize the signal accuracy of the sonde. It is preferable that it is determined so that it does not come off during vibration and stays on the dead zone as closely as possible.

21 Lower boundary of the dead zone (threshold)
22 Upper boundary (threshold) of dead zone
31 Characteristic map preliminary control means 32 Dead zone control means 33 Sonde heater 34 Internal resistance measuring device 35 Exhaust gas temperature 36 Exhaust gas mass flow rate 40 Dead zone 41 Possible area of lower boundary of dead zone 42 Ri threshold value 43 over which new sonde is overheated New sonde internal resistance 44 Possible area of upper boundary of dead zone 45 Ri threshold 46 at which degraded sonde is overheated Ri threshold at which new sonde can still function 47 Aged (degraded) sonde rating 48 Ri threshold for functional possibility of degraded sonde

Claims (6)

In a method for operation of an actively heated exhaust gas sensor heater (33),
Dead zone control (32) is performed for the operation of the heater (33), and the guide value for the dead zone control (32) is the internal resistance of the exhaust gas sensor,
The dead zone control is performed by a PI controller that processes a control difference (Ri_soll−Ri_ist) between a measured internal resistance value (Ri_ist) and a target value (Ri_soll) of the internal resistance,
When the internal resistance value is in the dead zone, the P component of the PI controller is set to 0, dead zone control is performed to freeze the I component, and preliminary control is performed to calculate the target voltage of the heater. Being
When the internal resistance value is outside the dead band, the control difference is handed over to the PI controller, and the preliminary control is further performed;
The preliminary control (31) can be realized by a characteristic map into which exhaust gas temperature and exhaust gas mass flow rate are sent,
A method characterized by. The lower boundary of the dead band control dead zone (40) (21; 41) is, as the internal resistance threshold (42), preset by the superheated work movements of the exhaust gas sensor unused, the internal resistance value of the new exhaust gas sensor When a method according to claim 1, characterized in that between the nominal internal resistance of the new exhaust gas sensor (43). The upper boundary of the dead band control dead zone (40) (22; 44) is, as the internal resistance threshold (45), preset by the superheated work movement of the exhaust gas sensor is used, the internal resistance of the exhaust gas sensor is used 3. A method according to claim 1 or 2, characterized in that the value is between an internal resistance value (46) at which the new exhaust gas sensor can function.   The measured value of the internal resistance (Ri_ist) and the target value of the internal resistance (Ri_soll) are processed by a dead zone controller, and the lower boundary of the dead zone controller and the dead zone (40) of the dead zone control (40) 21; 41) and the upper boundary (22; 44) are determined so that the region where the internal resistance of the exhaust gas sensor is surrounded by the boundary is not removed during the transient vibration of the dead zone control. The method of claim 1, wherein:   A computer program that, when executed by an arithmetic device or a control device, implements the steps of the method according to claim 1.   A computer program product comprising program code stored on a machine readable medium for performing the method according to any of claims 1 to 4 when the program is executed on a computing device or control device.

Images