DE102021104511B3 - Method for operating a drive device and corresponding drive device - Google Patents

Abstract

The invention relates to a method for operating a drive device with an internal combustion engine that generates exhaust gas, wherein a measured value describing the residual oxygen content in the exhaust gas is measured using a lambda probe and the combustion air ratio of a fuel-air mixture used to operate the internal combustion engine is adjusted on the basis of the measured value. It is provided that to compensate for different reaction speeds of the lambda probe when the combustion air ratio is adjusted in the direction of air shortage and when the combustion air ratio is adjusted in the direction of excess air, the measured value of the lambda probe is corrected using a rotational acceleration of a driven shaft of the internal combustion engine. The invention further relates to a drive device.

Description

The invention relates to a method for operating a drive device with an internal combustion engine that generates exhaust gas, wherein a measured value describing the residual oxygen content in the exhaust gas is measured using a lambda probe and the combustion air ratio of a fuel-air mixture used to operate the internal combustion engine is adjusted on the basis of the measured value. The invention further relates to a drive device.

From the prior art, for example, the publication U.S.A. 4,271,798 famous. This describes a control system for controlling the air-fuel ratio of an internal combustion engine. An oxygen sensor is connected to the control circuit after the engine has warmed up, when the temperature has reached its operating temperature, in order to keep the air/fuel ratio close to stoichiometric. A rough running sensor is connected to the control loop before the oxygen sensor has reached its operating temperature to keep the air/fuel ratio close to a predetermined lean limit. A temperature sensor and switching means controlled thereby are provided in order to alternately connect the rough-running sensor and the oxygen sensor to the control loop.

The publication is also from the state of the art US 2014/0345584 A1 famous. This describes a method for converting an asymmetrical wear behavior of an exhaust gas sensor into a more symmetrical wear behavior. In one example, a method includes adjusting fuel injection depending on a changed exhaust gas oxygen feedback signal from an exhaust gas sensor, the changed exhaust gas oxygen feedback signal being modified by converting an asymmetric response of the exhaust gas sensor to a more symmetric response. Further, the method may include adjusting one or more parameters of an anticipatory control of the exhaust gas sensor depending on the changed symmetric response.

The object of the invention is to propose a method for operating a drive device with an internal combustion engine that generates exhaust gas, which has advantages over known methods, in particular enabling the combustion air ratio to be set more precisely to a desired value.

According to the invention, this is achieved with a method for operating a drive device with an internal combustion engine that generates exhaust gas and has the features of claim 1 . It is provided that to compensate for different reaction speeds of the lambda probe when the combustion air ratio is adjusted in the direction of air shortage and when the combustion air ratio is adjusted in the direction of excess air, the measured value of the lambda probe is corrected using a rotational acceleration of a driven shaft of the internal combustion engine.

Advantageous configurations with expedient developments of the invention are specified in the dependent claims.

The drive device is preferably provided and designed to drive a motor vehicle and in this respect serves to provide a drive torque aimed at driving the motor vehicle. The drive device is preferably part of the motor vehicle, but can of course also be present separately from it and in this case is used solely to provide the drive torque.

The drive torque is provided by the drive device using a drive unit, which is in the form of the internal combustion engine. The internal combustion engine is operated with the fuel/fresh gas mixture that is supplied to the internal combustion engine or is only generated in the internal combustion engine. In any case, fresh gas and fuel are supplied to the internal combustion engine, for example separately or together, with the fresh gas at least temporarily and at least partially containing fresh air from an external environment of the drive device. The internal combustion engine is preferably in the form of a diesel internal combustion engine or an Otto internal combustion engine.

During its operation, the internal combustion engine generates exhaust gas, which means that during the operation of the drive assembly, exhaust gas is produced, which is supplied to an exhaust tract and discharged via this in the direction of the outside environment. The exhaust tract can—optionally—have an exhaust gas aftertreatment device. This is preferably designed as a vehicle catalytic converter, ie it serves to catalytically convert pollutants contained in the exhaust gas into less hazardous products. The vehicle catalytic converter is present in particular as a three-way catalytic converter or as a storage catalytic converter.

The fuel/fresh gas mixture used to operate the internal combustion engine has the specific combustion air ratio. The determined combustion air ratio describes the mass ratio of air to fuel relative to the stoichiometrically ideal ratio. With a combustion air ratio of one the fuel/fresh gas mixture is stoichiometric insofar as there is a lack of air at a combustion air ratio of less than one and there is excess air at a combustion air ratio of greater than one.

The combustion air ratio of the fuel-air mixture is set based on a measured value that is measured using a lambda probe. The measured value describes the residual oxygen content of the exhaust gas. The combustion air ratio is particularly preferably set using two measured values, namely using a first measured value and a second measured value. One of the measured values is determined using the lambda probe and another of the measured values is determined using a further lambda probe. The lambda probe can also be referred to as the first lambda probe and the further lambda probe as the second lambda probe.

Both the first lambda probe and the second lambda probe are arranged downstream of the drive unit. For example, in terms of flow, the first lambda probe is located between the drive assembly and the exhaust gas aftertreatment device. The second lambda probe is located downstream of the first lambda probe, in particular downstream of the exhaust gas aftertreatment device, that is to say downstream of the exhaust gas aftertreatment device in terms of flow. In this respect, the exhaust gas aftertreatment device is preferably arranged in terms of flow between the first lambda probe and the second lambda probe.

The first measured value describes the residual oxygen content of the exhaust gas downstream of the drive unit, in particular upstream of the exhaust gas aftertreatment device, and the second measured value describes the residual oxygen content of the exhaust gas downstream of the first lambda probe, preferably downstream of the exhaust gas aftertreatment device. The first measured value is preferably in the form of a lambda value, ie as a combustion air ratio. The second measured value is, for example, an electrical voltage supplied by the second lambda probe.

It is preferably provided that a broadband lambda probe is used as the first lambda probe and a jump lambda probe is used as the second lambda probe. The broadband lambda probe is preferably composed of several measuring cells, namely a pump cell and a Nernst cell. With such a structure, an accurate measurement of the residual oxygen content of the exhaust gas is also possible outside of a stoichiometric combustion air ratio by means of the broadband lambda probe. The jump lambda probe, on the other hand, preferably has only a single Nernst cell. In this respect, it can also be referred to as a Nernst probe or voltage jump probe. The broadband lambda probe has the advantage of a large measuring range, the jump lambda probe has the advantage of higher accuracy. A combination of broadband lambda probe and jump lambda probe can correspondingly achieve high accuracy of a lambda control and thus high efficiency.

The measured value or the first measured value is preferably regulated by setting the combustion air ratio to the desired value. This process is also referred to as lambda control. In this case, the target value is particularly preferably defined on the basis of the second measured value. In order to achieve efficient operation of the drive assembly, as soon as the second measured value reaches a threshold value, the combustion air ratio is adjusted by a differential value in a specific direction within a first time period. The combustion air ratio is then adjusted in the same direction at a specific speed over a second period of time. Incidentally, the threshold value can also be referred to as a lambda threshold value or as a control threshold value.

Provision is therefore preferably made for the combustion air ratio to be set in different ways during the two time periods. In this case, the second period of time preferably follows directly after the first period of time. During the first period of time, the combustion air ratio is changed by the differential value. The first period of time has a specific period of time, which is particularly preferably significantly less than a period of time of the second period of time. In particular, the combustion air ratio is adjusted instantaneously or essentially instantaneously by the differential value, so that the first time period is very short, in particular infinitesimally short.

In contrast, the adjustment of the combustion air ratio within the second period of time takes place over a longer period of time. There is no provision here for the combustion air ratio to be changed directly by a specific value, rather the combustion air ratio is adjusted at the specific speed. The speed is to be understood in particular as a gradient of the combustion air ratio over time. For example, both the difference value and the speed are permanently stored values.

The combustion air ratio is adjusted in particular by adjusting the setpoint value already mentioned. It is therefore provided that when the threshold is reached by the second measurement to understand the target value within the first period of time to understand the differential value in the given direction and then over the second period of time at the speed in the same direction. The first measured value is then regulated to the desired value as part of the lambda control explained, namely by adjusting the combustion air ratio.

Basically, the direction in which the combustion air ratio is adjusted depends on the direction in which the second measured value reaches the threshold value. If the second measured value reaches the threshold value in a first direction, for example from below, the combustion air ratio is adjusted in a specific first direction. If, on the other hand, the second measured value reaches the threshold value from a second direction that is different from the first direction, for example from above, the combustion air ratio is adjusted in a second specific direction opposite to the first specific direction. As a result, a so-called natural frequency control of the combustion air ratio is implemented. The threshold value required for this can basically be chosen in any way, for example it corresponds to a combustion air ratio of one or at least almost one or a corresponding voltage of the second lambda probe.

In order to achieve high accuracy of the lambda control, it is necessary to measure the residual oxygen content in the exhaust gas in the form of the measured value with high accuracy. However, due to its dynamic properties, the lambda probe detects a change in the residual oxygen content in the direction of a lack of air more quickly than a change in the residual oxygen content in the direction of an excess of air. This property of the lambda probe can be explained by a higher diffusion rate of the fat gas component H ₂ . The behavior of the lambda probe described is particularly relevant when the residual oxygen content changes from excess air to insufficient air or vice versa. Such a lambda change from lean (excess air) to rich (lack of air) is recognized by the lambda probe more quickly than a lambda change from rich (lack of air) to lean (excess air).

For this reason, these different reaction speeds of the lambda probe are to be compensated within the scope of the invention. In other words, compensation takes place based on the difference between the reaction speed of the lambda probe when the combustion air ratio is adjusted in the direction of a lack of air and the reaction speed of the lambda probe when the combustion air ratio is adjusted in the direction of excess air. Compensation takes place by correcting the measured value of the lambda probe based on the rotational acceleration of the driven shaft of the internal combustion engine. The driven shaft is to be understood as meaning a shaft which is driven during the operation of the internal combustion engine and is in particular in drive connection with at least one piston of the internal combustion engine. A crankshaft of the internal combustion engine is particularly preferably used as the driven shaft. Of course, the driven shaft can also be a camshaft, a balancer shaft or the like.

The rotational acceleration of the driven shaft gives an indication of the actual combustion air ratio. In particular, based on the rotational acceleration, a difference between the combustion air ratios present in different cylinders of the internal combustion engine can be inferred. The different combustion air ratios in the cylinders of the internal combustion engine are due, for example, to alternating operation of the internal combustion engine when there is a lack of air and when there is excess air.

Overall, it is therefore intended to measure the residual oxygen content in the exhaust gas in the form of the measured value and to determine the rotational acceleration of the driven shaft of the internal combustion engine. The measured value is then corrected using the angular acceleration. Only then is the measured value used to carry out the lambda control. A particularly high degree of accuracy in the lambda control can be achieved as a result, since the different reaction speeds of the lambda probe are taken into account.

A development of the invention provides that the rotational acceleration is determined from a speed of the driven shaft. The speed of the shaft is preferably measured, in particular by means of a speed sensor. For example, a sensor wheel is coupled to the shaft in terms of drive technology, and it is preferably seated directly on the shaft. A sensor interacts with the sensor wheel in order to determine a rotational angle position of the shaft, in particular to determine it incrementally. The speed of the shaft can be measured directly using the encoder wheel and the sensor. The rotational acceleration is determined from the speed, namely by deriving it from time. This enables the rotational acceleration to be determined precisely and the measured value to be corrected accordingly with a high level of accuracy.

A development of the invention provides that the rotational acceleration is determined for a specific acceleration period immediately after ignition in a cylinder of the internal combustion engine. The internal combustion engine has at least one cylinder, preferably multiple cylinders. In the cylinder or in each of the cylinders, a piston is arranged, which is connected via a connecting rod to the crankshaft of the internal combustion engine in terms of drive technology. The piston is arranged to be linearly displaceable in the cylinder. A cylinder wall of the cylinder and the piston therefore jointly delimit a variable-volume combustion chamber.

The fuel-air mixture is periodically burned in the combustion chamber or the cylinder in order to generate the drive torque. Once the fuel-air mixture has ignited, a force acts on the piston, which in turn causes a torque on the crankshaft, so that its rotational speed and, correspondingly, the rotational speed of the driven shaft change. The period of time relevant for determining the combustion air ratio of the fuel/air mixture present in the cylinder begins with the ignition. For this reason, provision is made for the rotational acceleration used to correct the measured value of the lambda probe to be determined in a period of time immediately following ignition. This achieves a particularly high level of accuracy for the correction and, accordingly, for the lambda control.

A further development of the invention provides that a rotational acceleration difference is determined from the rotational acceleration and a further rotational acceleration, with the further rotational acceleration being determined immediately after ignition in a further cylinder of the internal combustion engine that is different from the cylinder, and with the measured value of the lambda probe being determined on the basis of the rotational acceleration difference is corrected. The measured value is therefore not corrected directly on the basis of the rotational acceleration, but using a variable derived from the rotational acceleration, namely the difference in rotational acceleration. In this respect, not only the rotational acceleration but also the further rotational acceleration flows into the correction.

While the rotational acceleration for the cylinder is present, namely in the period of time following the ignition, the further rotational acceleration for the other cylinder is present, here for the period of time following the further ignition. The rotational acceleration difference is calculated from the rotational acceleration and the further rotational acceleration. The cylinder with the lower combustion air ratio usually has the greater rotational acceleration and vice versa. Based on the difference in rotational acceleration, it can be determined whether there is a deviation in the combustion air ratios between the cylinders. With the procedure described, a particularly high accuracy of the measured value and consequently of the lambda control is achieved.

A further development of the invention provides that the cylinder and the additional cylinder are selected in such a way that they follow one another directly in an ignition sequence of the internal combustion engine. The firing order is the order in which the fuel-air mixture in the cylinders of the internal combustion engine is ignited. The firing order does not necessarily correspond to a geometric arrangement of the cylinders. The cylinders that follow one another in the ignition sequence are preferably operated in such a way that in one working cycle of the internal combustion engine, during which ignition takes place in all of the cylinders, there is a lack of air in one of the cylinders during ignition and an excess of air in another of the cylinders. This results from the lambda regulation or natural frequency regulation already described above. The procedure described in turn ensures a high degree of accuracy of the measured value.

A development of the invention provides that the measured value of the lambda probe is corrected further in the direction of excess air, the greater the difference in rotational acceleration. Due to the properties of the lambda probe already described, the measured value actually measured shifts further in the direction of air deficiency, the greater the difference between the combustion air ratios present in the cylinders of the internal combustion engine. An error in the direction of excess air does not occur. Accordingly, the measured value is corrected exclusively in the direction of excess air and this as a function of the difference in rotational acceleration. The greater the rotational acceleration difference, the further the measured value is corrected in the direction of the excess air. A specific relationship between the difference in rotational acceleration and a correction value by which the measured value is corrected in the direction of excess air depends on the configuration of the drive device, in particular on the lambda probe, and is preferably determined as part of a calibration. A particularly high level of accuracy is achieved as a result.

A development of the invention provides that the combustion air ratio of the fuel-air mixture is alternately adjusted to air deficiency and air excess. Such an approach way is provided in particular in the context of natural frequency control. The alternating adjustment to air deficiency and excess air will have an effect in particular on the combustion air ratio in the cylinders that follow one another in the ignition sequence. As already explained, there is preferably excess air in one of the cylinders and a lack of air in another of the cylinders, which immediately follows the cylinder in the firing order. With such a mode of operation, the advantages of correcting the measured value are particularly evident.

A development of the invention provides that the combustion air ratio of the fuel-air mixture is adjusted in such a way that there is a lack of air in the cylinder and an excess of air in the other cylinder. This corresponds to the already explained alternating adjustment to air deficiency and air excess and allows a particularly effective after-treatment of the exhaust gas.

A development of the invention provides that a broadband lambda probe is used as the lambda probe. This too has already been addressed.

The invention also relates to a drive device, in particular for carrying out the method according to the statements made within the scope of this description, the drive device having an internal combustion engine that generates exhaust gas and being provided and designed to use a lambda probe to measure and measure a measured value describing the residual oxygen content in the exhaust gas set the combustion air ratio of a fuel-air mixture used to operate the internal combustion engine based on the measured value. The drive device is also provided and configured to compensate for different reaction speeds of the lambda probe when the combustion air ratio is adjusted in the direction of a lack of air and when the combustion air ratio is adjusted in the direction of excess air, by correcting the measured value of the lambda probe using a rotational acceleration of a driven shaft of the internal combustion engine.

The advantages of such a procedure or such a configuration of the drive device have already been pointed out. Both the drive device and the method for operating it can be further developed according to the statements made within the scope of this description, so that reference is made to them in this respect.

The features and feature combinations described in the description, in particular the features and feature combinations described in the following description of the figures and/or shown in the figures, can be used not only in the combination specified in each case, but also in other combinations or on their own, without going beyond the scope of the leave invention. The invention is therefore also to be regarded as encompassing embodiments which are not explicitly shown or explained in the description and/or the figures, but emerge from the explained forms of expression or can be derived from them.

• 1 ein Diagramm, in welchem ein Verlauf eines Verbrennungsluftverhältnisses eines zum Betreiben einer Brennkraftmaschine verwendeten Kraftstoff-Luft-Gemischs und ein Verlauf eines mittels einer Lambdasonde gemessenen Messwerts sowie die entsprechenden Mittelwerte aufgetragen sind.

The invention is explained in more detail below with reference to the exemplary embodiments illustrated in the drawing, without the invention being restricted. It shows the only

• 1 a diagram in which a curve of a combustion air ratio of a fuel-air mixture used to operate an internal combustion engine and a curve of a measured value measured by means of a lambda probe as well as the corresponding mean values are plotted.

the 1 shows purely by way of example a diagram in which curves 1, 2, 3 and 4 are reproduced. Each of curves 1, 2, 3 and 4 shows a combustion air ratio or a residual oxygen content λ over time t. Curve 1 describes the combustion air ratio of a fuel-air mixture used to operate an internal combustion engine, ie ultimately the ratio between fuel and air that is supplied to the internal combustion engine to operate it. It can be seen that the combustion air ratio alternates between lack of air and excess air. This means that the internal combustion engine is operated at times with a combustion air ratio corresponding to a lack of air and at times with a combustion air ratio corresponding to excess air, namely alternately.

In particular, it is provided here that this alternating operation in the event of a lack of air and excess air is provided for cylinders of the internal combustion engine that are immediately adjacent in the ignition sequence. In a specific working cycle of the internal combustion engine, a first of the cylinders is operated with a lack of air and a second cylinder immediately following the first cylinder in the firing sequence with excess air, and so on. Curve 2 corresponds to a curve of the mean value of the combustion air ratio over time. It can be seen that the mean value is at a stoichiometric combustion air ratio, ie at lambda = 1.0.

During the operation of the internal combustion engine, exhaust gas is produced, which is discharged in the direction of the outside environment. The residual oxygen content of the exhaust gas is measured using a lambda probe. With the help of the lambda probe, a measured value is determined which describes the residual oxygen content of the exhaust gas. Based on this measured value, the combustion air ratio of the fuel-air mixture is set as part of a lambda control. It can be seen that the measured value according to curve 3 also alternates between lack of air and excess air. However, it is also clear that a reaction speed of the lambda probe in the direction of a lack of air is greater than a reaction speed of the lambda probe in the direction of an excess of air. A mean value over time of the measured value results from these different reaction speeds, which is indicated by curve 4 . It is clear that the different reaction speeds of the lambda probe cause a deviation in the measured value and therefore in the mean value, so that the mean value according to curve 4 deviates from the mean value according to curve 2.

In order to compensate for these different reaction speeds of the lambda probe, provision is made for a rotary acceleration of a driven shaft of the internal combustion engine to be determined, for example by means of a speed sensor assigned to the shaft. The rotational acceleration is used to determine whether the internal combustion engine is being operated with a combustion air ratio corresponding to a lack of air or with a combustion air ratio corresponding to an excess of air. Based on this knowledge, the measured value is corrected. In summary, the measured value of the lambda probe is corrected using the rotational acceleration of the driven shaft of the internal combustion engine.

Provision is preferably made to determine the rotational acceleration for the first cylinder and a further rotational acceleration for the second cylinder, so that the rotational acceleration is present for a combustion air ratio corresponding to a lack of air and the further rotational acceleration for a combustion air ratio corresponding to excess air. A rotational acceleration difference is calculated from the rotational acceleration and the further rotational acceleration, ie a difference between the rotational acceleration and the further rotational acceleration. This rotational acceleration difference is used to correct the oxygen sensor reading. In this case, the measured value of the lambda probe is preferably corrected further in the direction of excess air, the greater the difference in rotational acceleration.

With the procedure described, an extremely precise measurement of the residual oxygen content in the exhaust gas is made possible. Ultimately, this leads to a highly precise implementation of the lambda control, so that exhaust gas aftertreatment can take place particularly effectively.

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Claims (10)

Method for operating a drive device with an internal combustion engine that generates exhaust gas, a measured value describing the residual oxygen content in the exhaust gas being measured by means of a lambda probe and the combustion air ratio of a fuel-air mixture used to operate the internal combustion engine being adjusted on the basis of the measured value, characterized in that Compensating for different reaction speeds of the lambda probe when the combustion air ratio is adjusted in the direction of a lack of air and when the combustion air ratio is adjusted in the direction of excess air, the measured value of the lambda probe is corrected using a rotational acceleration of a driven shaft of the internal combustion engine. procedure after claim 1 , characterized in that the rotational acceleration is determined from a speed of the driven shaft. Method according to one of the preceding claims, characterized in that the rotational acceleration for a specific acceleration period is determined immediately after ignition in a cylinder of the internal combustion engine. Method according to one of the preceding claims, characterized in that a rotational acceleration difference is determined from the rotational acceleration and a further rotational acceleration, the further rotational acceleration being determined immediately after ignition in a further cylinder of the internal combustion engine which is different from the cylinder, and the measured value of the lambda probe is corrected using the rotational acceleration difference. Method according to one of the preceding claims, characterized in that the Cylinder and the other cylinder are selected in such a way that they follow one another directly in an ignition order of the internal combustion engine. Method according to one of the preceding claims, characterized in that the greater the difference in rotational acceleration, the further the measured value of the lambda probe is corrected in the direction of excess air. Method according to one of the preceding claims, characterized in that the combustion air ratio of the fuel-air mixture is set alternately to air deficiency and air excess. Method according to one of the preceding claims, characterized in that the combustion air ratio of the fuel-air mixture is set in such a way that there is a lack of air in the cylinder and an excess of air in the other cylinder. Method according to one of the preceding claims, characterized in that a broadband lambda probe is used as the lambda probe. Drive device, in particular for carrying out the method according to one or more of the preceding claims, wherein the drive device has an exhaust-gas-generating internal combustion engine and is provided and designed to use a lambda probe to measure a measured value describing the residual oxygen content in the exhaust gas and to operate the combustion air ratio the fuel-air mixture used in the internal combustion engine on the basis of the measured value, characterized in that the drive unit is also provided and designed to compensate for different reaction speeds of the lambda probe when the combustion air ratio is adjusted in the direction of a lack of air and when the combustion air ratio is adjusted in the direction of excess air To correct the measured value of the lambda probe based on a rotational acceleration of a driven shaft of the internal combustion engine.

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