EP2089621B1 - Method for controlling an internal combustion engine, and internal combustion engine - Google Patents

Abstract

In order to improve the exhaust behaviour during tank ventilation, a method for controlling an internal combustion engine (1) is proposed, in which method a lambda regulator (33) of the internal combustion engine (1) is adjusted from a normal regulating mode into a dynamic regulating mode, in which the lambda regulator (33) has greater regulating dynamics than in the normal regulating mode, in such a way that the lambda regulator (33) is in the dynamic regulating mode at least temporarily during the tank ventilation period.

Description

The invention relates to a method for controlling an internal combustion engine with a tank ventilation device, by means of which during a tank ventilation period fuel vapors are introduced into an intake tract of the internal combustion engine, and an internal combustion engine with a control device which is designed such that it can perform the method.

Modern motor vehicles usually have a tank ventilation system. The resulting fuel vapors in a fuel tank are adsorbed in an activated carbon container. For regeneration of the activated carbon container, a tank vent valve, which is located in a connecting line between the activated carbon container and a suction pipe of the internal combustion engine, opened during operation of the internal combustion engine, so that the fuel vapors stored in the activated carbon container are introduced by a rinsing effect in the intake of the engine and at to participate in the burning. This results in a change in the composition of the fuel mixture, which can result in higher pollutant emissions.

According to a known method, the concentration of the additional hydrocarbons additionally supplied by the tank ventilation process is estimated by means of a lambda controller and a corresponding correction of the amount of fuel supplied by the injection valves of the internal combustion engine is carried out to limit the emission of pollutants. If the tank venting valve is opened, the concentration of the hydrocarbons supplied by the tank venting process is initially unknown. In known systems, a correction of the injected amount of fuel takes place only with considerable delay, which over a longer period there is an increased emission of pollutants. To an early To be able to correct the fuel mass to be injected, an accurate determination of the opening timing and the opening degree of the tank venting valve, as well as a precise correlation between the opening degree and the supplied amount of hydrocarbons would be required. However, the opening time of the tank vent valve is subject to tolerances. A pilot control of the correction of the injected fuel quantity is therefore not possible. In addition, the opening behavior of the tank vent valve is not linear. For example, if a certain activation pulse width is exceeded, the tank ventilation valve may suddenly open. The amount of hydrocarbons supplied is subject to significant fluctuations depending on the degree of loading of the activated carbon container. A targeted dosage of the introduced fuel vapors is therefore not possible.

In summary, it can be stated that, especially at idle and in operating points with low load, significant enrichment of the fuel mixture when opening the tank-venting valve can only be corrected to a limited extent and with considerable delay.

Out US 5,404,862 a method according to the preamble of claim 1 and an internal combustion engine according to the preamble of claim 25 is known.

Out US 5,941,224 For example, a method for controlling the air-fuel ratio for an internal combustion engine is known. In this case, the ratio of the air-fuel mixture conducted to the engine is regulated to a defined value using at least one control gain parameter. A purge valve flushes the fuel vapors in the fuel tank to the engine. The control gain parameter is set to a smaller value when the degree of influence of the fuel vapor purged by the purge valve on the air-fuel mixture ratio is larger, and set to a larger value when the degree of influence of the purged fuel vapors on the air-fuel-mixture ratio is smaller.

Out US 5,224,462 For example, a method is known in which a control system regulates the supply of fuel to achieve stoichiometric combustion in an internal combustion engine. The control system comprises a controller which generates a feedback variable by integration of the output value of a lambda sensor. Integration is prevented if a rich air-fuel ratio is detected.

Out US 5,727,537 For example, a method for controlling the air-fuel ratio for an internal combustion engine is known. The injected amount of fuel is controlled so that the output of a lambda sensor has a desired air-fuel ratio. An initial coefficient representing the concentration of the fuel supplied into the internal combustion engine is calculated according to the deviation caused by the purging operation. The amount of fuel injected is reduced according to the coefficient.

It is therefore the object of the present invention to provide a method and an internal combustion engine, which is characterized by a faster compensation of the addition of fuel through the tank ventilation.

This object is achieved by the method and the internal combustion engine according to the independent claims. Advantageous embodiments of the invention are the subject of the dependent claims.

A control method according to claim 1 relates to an internal combustion engine having a tank ventilation device, through which during a tank ventilation period fuel vapors be introduced in an intake tract of the internal combustion engine. According to the method, a lambda controller of the internal combustion engine is offset from a normal control mode in a dynamic control mode, in which the lambda controller has a higher control dynamic than the normal control mode, such that the lambda controller at least during the tank ventilation period temporarily in the dynamic control mode. According to the method, the fuel vapors are stored in a storage tank of the tank ventilation device and the lambda controller is set in the dynamic control mode only if a parameter which represents a measure of the loading of the storage tank with fuel vapors exceeds a predetermined limit.

As already explained above, the lambda controller is used to determine the fuel quantity additionally supplied by the tank ventilation and to compensate it by a corresponding correction of the injection quantity. However, the output value of the lambda controller only represents a representative measure of the fuel concentration of the fuel vapors introduced into the intake tract when the disturbance is approximately corrected. The interpretation of the lambda controller is usually a compromise between response and dynamics and stability, with a focus on the controller stability. Known lambda controllers are therefore not calibrated arbitrarily fast, but have for stability reasons a significant attenuation. For this purpose, for example, the I component can be designed to be correspondingly slow, so that it takes a certain time to correct the disruption of the fuel mixture caused by the tank ventilation. Consequently, it takes a correspondingly long in a conventionally calibrated lambda controller until an injection amount correction can be made. However, this also leads to a correspondingly long-lasting deterioration of the exhaust gas.

According to the invention, therefore, the lambda controller is so from a normal control mode in a dynamic control mode in which the lambda controller compared to the normal control mode has a higher control dynamics, offset that the lambda controller during the tank ventilation period, at least temporarily is in the dynamics control mode. Under the higher control dynamics is understood according to the invention a more spontaneous or improved response of the lambda controller. Due to the higher gradient of the controller output or the manipulated variable in the dynamic control mode, the controlled variable approaches the reference variable more quickly and also reaches it faster. The higher control dynamics in the dynamic control mode can be realized, for example, by a corresponding change in the controller parameters of the lambda controller. This ensures a faster control of the fault due to the tank ventilation. The amount of fuel or the concentration of the fuel vapors, which is additionally supplied by the tank ventilation, can be determined faster and an injection quantity correction can be made faster. Thus, the emission of pollutants of the internal combustion engine is significantly reduced.

An operation of the lambda controller in the dynamic control mode is limited to the cases in which to be expected with a high loading of the storage tank with fuel vapors. At low load, the lambda controller therefore remains in the normal control mode, which ensures a higher system stability.

In embodiments of the method according to claims 2 and 3, the lambda controller is put into the dynamic control mode only if, prior to the tank ventilation period, an output value of the lambda controller is within a predetermined first range of time over a predetermined first time period and / or Change in the output value of the lambda controller is less than a predetermined first change limit.

Similarly, the lambda controller according to the embodiments of claims 4 and 5 is only put into the dynamic control mode, if an operating variable of the internal combustion engine over a predetermined second period of time is within a predetermined second value range and / or the change of the operating size smaller is considered a predetermined second change threshold.

These refinements ensure that the lambda controller is put into the dynamic control mode only when both the lambda controller itself and the internal combustion engine have assumed a sufficiently stable state. The operating variable of the internal combustion engine may be, for example, the rotational speed or the supplied fresh air mass. This prevents that due to the higher control dynamics in dynamic control mode it comes to instabilities and vibrations in the control loop, which can have a negative effect on the ride comfort and the exhaust performance of the internal combustion engine.

In one embodiment of the method according to claim 6, the lambda controller is only placed in the dynamic control mode, if the internal combustion engine is in idle.

This embodiment of the invention, the switching of the lambda controller in the dynamic control mode is limited to the idling of the internal combustion engine. In the operating state of the idling, the internal combustion engine supplied fresh air mass flow is extremely low, and at the same time the intake manifold pressure is very low, whereby when opening the tank vent valve, a very strong rinsing effect is created and thus get a large amount of fuel vapors in the intake. As a result, the concentration of the fuel vapors additionally supplied by the tank ventilation during idling is particularly high. Therefore, a quick settlement of the changed fuel gas composition required. Outside idling, ie at partial or full load, this effect is much lower, so that waives the switching of the lambda controller in the dynamic control mode and can be maintained for stability reasons, the normal control mode.

In the embodiment of the method according to claim 7, the control dynamics of the lambda controller is increased in dynamic control mode the further, the larger the parameter is.

According to the embodiments of claims 8 and 9, the parameter may be the ambient temperature of the internal combustion engine or the period of time during which the internal combustion engine was switched off before the last start.

In these embodiments of the method, the control parameters of the lambda controller can be changed in the dynamic control mode with increasing loading, for example due to high ambient temperature or very long periods of inactivity of the engine so that there is an ever higher or improved control dynamics. As a result, the control dynamics are adapted to the loading of the storage container. Since at a higher loading of the storage tank and a larger amount of fuel vapors in the tank ventilation is supplied, simultaneously improved control dynamics causes a faster compensation of the disturbance.

According to the embodiments of the method according to claims 10, 11 and 12, the control dynamics of the lambda controller is changed in the dynamic control mode depending on an operating variable of the internal combustion engine. Thus, the control dynamics increases the further, the smaller the speed of the internal combustion engine and / or the smaller the load of the internal combustion engine.

These embodiments of the method are the fact that the supplied through the tank ventilation additional Fuel vapors affect the exhaust behavior more strongly, the lower the speed and the load or the fresh air flow rate into the internal combustion engine. By increasing the control dynamics with decreasing speed and decreasing load this disturbance can be corrected even faster.

In the embodiments of the method according to claims 13 and 14, the lambda controller is placed in the dynamic control mode immediately before or immediately after the introduction of the fuel vapors in the intake system.

The timing of the introduction of the fuel vapors can be determined, for example, by the output of a drive signal to the tank vent valve by the control device of the internal combustion engine. In both embodiments of the method, a very timely changeover of the lambda controller is achieved in the dynamic mode. This ensures that the change in the fuel composition can be detected very early and quickly corrected.

In embodiments of the method according to claims 15 and 16, the lambda controller is placed in the dynamic control mode a predetermined period of time after initiation of the fuel vapors in the intake system. The time span can correspond to the time it takes for the fuel vapors to reach from the point of introduction in the intake tract to a lambda sensor in the exhaust tract of the internal combustion engine.

In these embodiments of the method, the switching of the lambda controller is delayed as far as possible in the dynamic control mode. A changeover to the dynamic control mode occurs only when the change in the exhaust gas composition due to the fuel vapors supplied by the tank ventilation is detectable by the lambda sensor. Also in this embodiment, a rapid compensation of this disorder is possible, however, the lambda controller remains longer in normal-rule mode, which benefits the stability of the control loop.

In one embodiment of the method according to claim 17, the lambda controller is placed in the dynamic control mode after the lambda value of the exhaust gas of the internal combustion engine falls below a predetermined lambda limit value.

In a further embodiment of the method according to claim 18, the lambda controller is placed in the dynamic control mode after an output value of the lambda controller exceeds a predetermined output limit.

In these embodiments of the method, the lambda controller is placed in the dynamic control mode only after detection of the enrichment caused by the tank ventilation enrichment of the fuel mixture. Analogous to the embodiment of the method according to claim 16, the lambda controller is kept as long as possible in the normal control mode in this embodiment as well. This ensures that the lambda controller is put into the dynamic control mode only in the case of correspondingly strong faults in the exhaust gas composition.

In one embodiment of the method according to claim 19, upon fulfillment of a condition, the lambda controller is returned from the dynamic control mode back to the normal control mode.

This embodiment of the method ensures that, after overcoming the disturbance caused by the tank venting, the lambda controller is returned to the normal control mode, in which a higher stability of the control system prevails. This serves both the ride comfort, as well as the stability of the entire control loop.

According to the embodiments of the method of claims 20, 21, 22 and 23, the condition may be fulfilled when the

Lambda value of the exhaust gas of the internal combustion engine exceeds a predetermined second lambda limit value or when the change of an output of the lambda controller is smaller than a predetermined third change limit. Furthermore, it is also possible for the condition to be met when an output variable of the lambda controller is within a predetermined third range over a predetermined third time period or when the lambda value of the exhaust gas is within a predetermined fourth range within a predetermined fourth range ,

These criteria will ensure that the lambda control is returned to the more stable normal control mode once the tank venting problem is resolved to a certain extent.

In one embodiment of the method according to claim 24, the condition is fulfilled when the internal combustion engine leaves the operating state of the idling.

As already mentioned with respect to claim 6, the deterioration of the mixture composition by the tank ventilation is particularly strong, especially at idling. Following this finding, according to the embodiment of claim 24, the lambda controller is set back into the normal control mode again as soon as the internal combustion engine leaves the idling again.

An internal combustion engine according to claim 25 comprises a tank ventilation device, through which during a tank ventilation period fuel vapors are introduced into an intake tract of the internal combustion engine. Furthermore, the internal combustion engine comprises a storage container for storing fuel vapors. The internal combustion engine also has an injection system which supplies a given amount of fuel to a combustion chamber of the internal combustion engine. The internal combustion engine further comprises a lambda control device, which is coupled to the injection system and corrects the amount of fuel to be supplied as a function of the exhaust gas composition, wherein the lambda control device is designed such that a lambda controller of such a normal control mode in a dynamic control mode, in which the lambda controller against the normal control mode has a higher control dynamics, is offset, that the lambda controller during the tank ventilation period is at least temporarily in the dynamic control mode. The lambda controller is only placed in the dynamic control mode, if a parameter which represents a measure of the loading of the fuel vapor storage with fuel vapors exceeds a predetermined limit.

With regard to the advantages of the internal combustion engine, reference is made to the statements on claim 1.

Figur 1

eine schematische Darstellung einer Brennkraftma- schine mit einer Tankentlüftungsvorrichtung;

Figur 2

eine allgemeine Darstellung eines Lambda- Regelkreises;

Figur 3

eine schematisches Diagramm zur Darstellung des Reglerverhaltens im Normal-Regelmodus und im Dyna- mik-Regelmodus

Figur 4

das Grundprinzip eines erfindungsgemäßen Verfahrens in Form eines Ablaufdiagramms;

In the following, an embodiment of the present invention will be explained in more detail with reference to the accompanying figures. Show it:

FIG. 1

a schematic representation of an internal combustion engine with a tank ventilation device;

FIG. 2

a general representation of a Lambda control loop;

FIG. 3

a schematic diagram showing the behavior of the controller in the normal control mode and in the dynamic control mode

FIG. 4

the basic principle of a method according to the invention in the form of a flow chart;

In FIG. 1 an embodiment of an internal combustion engine 1 is shown. The internal combustion engine 1 has at least one cylinder 2 and one in the cylinder 2 up and down movable piston 3. The fresh air required for combustion is introduced via an intake tract 4 into a combustion space 5 bounded by the cylinder 2 and the piston 3. Downstream of a suction port 6 are located in the intake 4 is an air mass sensor 7 for detecting the air flow in the intake tract 4, which can be regarded as a measure of the load of the internal combustion engine 1, a throttle valve 8 for controlling the air flow, a suction pipe 9 and an intake valve 10, by means of which the combustion chamber 5 with the intake 4 optionally connected or disconnected.

The ignition of the combustion takes place by means of a spark plug 11. The drive energy generated by the combustion is transmitted via a crankshaft 12 to the drive train of the motor vehicle (not shown). A rotational speed sensor 13 detects the rotational speed of the internal combustion engine 1.

The combustion exhaust gases are discharged via an exhaust tract 14 of the internal combustion engine 1. The combustion chamber 5 is selectively connected to the exhaust tract 14 by means of an exhaust valve 15 or separated from it. The exhaust gases are purified in an exhaust gas purification catalyst 16. In the exhaust tract 14 is also a so-called lambda sensor 17 for measuring the oxygen content in the exhaust gas. The lambda sensor 17 may be both a binary lambda sensor 17 and a linear lambda sensor 17.

The internal combustion engine 1 further comprises a fuel supply device with a fuel tank 18, a fuel pump 19, a high pressure pump 20, a pressure accumulator 21 and at least one controllable injection valve 22. The fuel tank 18 has a closable filler neck 23 for filling fuel. The fuel is supplied by means of the fuel pump 19 via a fuel supply line 24 to the injection valve 22. In the fuel supply line 24, the high-pressure pump 20 and the pressure accumulator 21 are arranged. The high-pressure pump 20 has the task to supply the pressure accumulator 21, the fuel at high pressure. The pressure accumulator 21 is designed as a common pressure accumulator 21 for all injectors 22. From him, all injectors 22 are pressurized Fuel supplied. In the exemplary embodiment is an internal combustion engine 1 with direct fuel injection, in which the fuel is injected directly into the combustion chamber 5 by means of an injector 22 projecting into the combustion chamber 5. It should be noted, however, that the present invention is not limited to this type of fuel injection, but is applicable to other types of fuel injection such as port injection.

The internal combustion engine 1 also has a tank ventilation device. To the tank ventilation device includes a fuel damper 25, which is for example designed as an activated carbon container and is connected via a connecting line 26 to the fuel tank 18. The resulting in the fuel tank 18 fuel vapors are passed into the fuel vapor storage 25 and there adsorbed by the activated carbon. The fuel vapor storage 25 is connected via a vent line 27 to the intake manifold 9 of the internal combustion engine 1. In the vent line 27 is a controllable tank vent valve 28. Further, the fuel vapor reservoir 25 via a vent line 29 and an optionally disposed therein controllable vent valve 30 fresh air can be supplied. In certain operating areas of the internal combustion engine 1, in particular at idle or at partial load, there is a large pressure gradient between the environment and the suction pipe 9 due to the strong throttle effect through the throttle valve 8. By opening the tank ventilation valve and the vent valve 30 during a tank ventilation period, it comes to a Rinsing effect, in which the fuel vapors stored in the fuel vapor storage 25 are directed into the intake manifold 9 and participate in the combustion. The fuel vapors thus cause a change in the composition of the fuel gases and the exhaust gases.

The internal combustion engine 1 is assigned a control device 31, in which map-based engine control functions (KF1 to KF5) are implemented by software. The control device 31 is connected to all actuators and sensors of the internal combustion engine 1 via signal and data lines. In particular, the control device 31 with the controllable vent valve 30, the controllable tank vent valve 28, the air mass sensor 7, the controllable throttle valve 8, the controllable injection valve 22, the spark plug 11, the lambda sensor 17, the speed sensor 13 and an ambient temperature sensor 32 for measuring the Ambient temperature connected.

Parts of the internal combustion engine 1 and the control device 31 form a lambda control device. The lambda control device comprises, in particular, the lambda sensor 17, a lambda controller 33 implemented in software in the control device 31, and the injection valves 22 and their control mechanism with which the opening times of the injection valves 22 are controlled. The lambda control device forms a closed lambda control loop and is designed in such a way that a deviation of the exhaust gas composition detected by the lambda sensor 17 is corrected from a predetermined desired lambda value by means of an injection quantity correction. If the tank venting valve 28 is opened during the tank venting period, fuel vapors from the fuel vapor accumulator 25 flow into the intake tract 4 or the intake manifold 9 of the internal combustion engine 1 due to the pressure gradient. These fuel vapors, whose concentration in the intake air is initially unknown, lead to enrichment of the combustion mixture That is, to an excess of hydrocarbons in the fuel gas, and after combustion to a corresponding change in the exhaust gas composition. The lambda value measured by the lambda sensor 17 thereby drops below the desired value of lambda = 1, for example. So it comes to a control deviation, which is registered by the lambda controller 33 and by a corresponding Changing the controller 33 output is compensated. This is done by specifying a corresponding control variable to the injectors 22, whereby the injected fuel quantity is changed accordingly until the fault is corrected. This process is referred to below as injection quantity correction.

In FIG. 2 is shown schematically such a lambda control loop. This schematic representation is to be transferred to the lambda control circuit of the embodiment. The lambda value of the exhaust gas, which represents the controlled variable x, is determined by the lambda sensor 17, in FIG FIG. 2 the measuring element F _m , detected. The controlled variable x is supplied to the control device 31 via the data and signal lines. There, the control deviation e is determined from the desired lambda value or from the reference variable w, which is assumed to be lambda = 1, for example, and the controlled variable x is determined by subtraction. The control difference e is supplied to the lambda controller 33 as a controller input. The lambda controller 33 may, for example, be a PI controller 33. In this case, the transmission behavior of the P component of the lambda controller 33 can be described by the following functional relationship: $$y_P\left(t\right)=K_P\times e\left(t\right)$$

The I member follows the functional relationship: $$y_I=K_I\times \underset{0}{\overset{\tau }{\mathrm{\int }}}e\left(t\right)dt$$

In this case, K _{I represents} the amplification factor of the I element and K _{P represents} the amplification factor of the P element.

The regulator output variable y _R is supplied to the drive mechanism of the injection valves or the actuator F _ST , resulting in a certain valve opening time, which represents the manipulated variable Y results. From the injected fuel quantity, which the controlled system F _S (the combustion chamber 5) is supplied and the disturbance z, as which are to be regarded as the fuel vapors supplied by the tank vent, results from the combustion again a certain exhaust gas composition, which represents the controlled variable x.

The lambda controller 33 is designed such that it can be operated either in a normal control mode or in a dynamic control mode. In the dynamic control mode, the lambda controller 33 differs from the normal control mode by a more spontaneous response or by a higher control dynamics. For further illustration, the controller behavior is in the dynamics control mode and in the normal control mode in FIG. 3 shown schematically. The diagram shows the controller output variable Y _R and the control deviation e over time. At time t ₁ , the control deviation e (in FIG. 3 dashed lines) and remains at a certain value. Such a deviation can result, for example, in the internal combustion engine 1 by the initiation of the tank ventilation process. To illustrate the reaction of the lambda controller 33 to the change in the control difference e is in FIG. 3 the controller output Y _R once in the state of the normal control mode (dashed line) and in the state of dynamic control mode (solid line) shown. As can be clearly seen, the response of the lambda controller 33 is much more dynamic in the dynamic control mode, ie, the controller output Y _R (DM) in the dynamic control mode increases significantly more in the normal control mode compared to the controller output Y _R (NM) at. Due to this increased control dynamics results in the case of the embodiment of the internal combustion engine 1, a significantly increased dynamics of injection quantity correction. As a result, the control variable x, ie the lambda value of the exhaust gas, in the dynamic control mode compared to the normal control mode is approached and adjusted much faster to the lambda desired value or the reference variable w.

This improved controller dynamics can be achieved, for example, by increasing the amplification factors K _I and K _{P of} the I component and the P component of the lambda controller 33.

Hereinafter, an embodiment of a method for controlling the internal combustion engine 1 with reference to the flowchart of FIG. 4 explained in more detail. The method is started in step 301, for example when starting the internal combustion engine 1. In step 302, the lambda controller 33 is set in the normal control mode by default in order to ensure the greatest possible stability of the control loop in the normal control mode due to the lower control dynamics of the lambda controller 33.

In a step 303, it is first checked whether a condition 1 is fulfilled. Step 303 is repeated until Condition 1 is satisfied. By checking the condition 1, it is to be ensured that a switching of the lambda controller 33 from the normal control mode into the dynamic control mode takes place at a suitable time with respect to a tank venting process or the tank venting period.

For example, the condition 1 may be satisfied when the introduction of the fuel vapors in the intake tract 4 is imminent. This can be realized by monitoring a corresponding control signal from the control device 31 to the tank ventilation valve 28.

Alternatively, the condition 1 can also be fulfilled immediately after the introduction of the fuel vapors into the intake tract 4. As a criterion, the emission of a first control signal to the tank venting valve 28 by the control device 31 can be used for this purpose.

The condition 1 can also after expiration of a certain predetermined period of time after initiation of the fuel vapors be considered fulfilled in the intake 4. Advantageously, the time span thereby corresponds to the gas running time which the fuel vapors require in order to reach the position of the lambda sensor 17s in the exhaust gas tract 14 from the position in the intake tract 4 at which the fuel vapors are introduced into the intake tract 4. Depending on the operating point of the internal combustion engine 1, this gas running time can be measured and stored in a map of the control device 31.

Alternatively, condition 1 can also be considered fulfilled if, after the start of the tank ventilation period, the gradient of the output value y _{R of} the lambda controller 33 rises above a predetermined threshold value.

It should be noted that the alternative criteria for condition 1 can also be linked together, as appropriate.

After fulfilling condition 1, the method moves in the flowchart of FIG. 4 with step 304, in which it is checked whether a condition 2 is satisfied. Step 304 is repeated until Condition 2 is satisfied. With the condition 2, criteria are connected, which ensure that the lambda controller 33 is put into the dynamic control mode only in meaningful operating states of the internal combustion engine 1 in order largely to avoid instabilities in the lambda control loop.

For example, condition 2 may then be met if, prior to the tank ventilation period or before opening the tank ventilation valve, the controller output value y _{R of} the lambda controller 33 was within a predetermined first range over a predetermined first period of time or if before the tank ventilation period Change or the gradient of the controller output value y _{R was} less than a predetermined first change limit. The first value range and the first change limit value are to be specified in this way if condition 2 is met, it can be assumed that the controller state is stable before the start of the tank ventilation period. An excessively high gradient of the controller output value or a controller output value which is outside the first value range indicates a momentary strong dynamic of the lambda controller 33, so that switching to the dynamic control mode is prevented in this state as stability reasons should.

Alternatively, the condition 2 may also be satisfied if an operating variable of the internal combustion engine 1 is within a predetermined second value range over a predetermined second time period and / or the change of the operating variable is smaller than a predetermined second change limit value. The second value range and the second change limit value are to be specified in such a way that, when these criteria are satisfied, it is ensured that the internal combustion engine 1 is in an approximately stationary operating point. This is intended to prevent the lambda controller 33 from being switched into the dynamic control mode during a highly dynamic operation of the internal combustion engine 1, which could lead to instabilities in the lambda control circuit and to an uncomfortable driving behavior.

In a further alternative, the condition 2 is fulfilled if the internal combustion engine 1 is idling. At idle, ie at substantially closed throttle valve 8, maximum Saugrohrunterdruck and minimal supply of fresh air in the intake manifold 4, the influence of the addition of the tank ventilation additionally supplied fuel vapor to the combustion and thus to the exhaust gas composition is particularly large. In this embodiment, therefore, the lambda controller 33 can be put into the dynamic control mode only when the internal combustion engine 1 is idling. The dynamic control mode is thus limited to the idling of the internal combustion engine 1. This ensures, on the one hand, that a deterioration in exhaust emissions is rapid is regulated and at the same time but outside the idle, ie in partial load or full load operation, the lambda controller 33 is operated in the normal control mode and the lambda control circuit has a higher stability.

In a further advantageous embodiment, the condition 2 is then considered to be satisfied if a parameter which represents a measure of the loading of the fuel vapor storage 25 with fuel vapors, exceeds a predetermined limit. The parameter may be, for example, the ambient temperature of the internal combustion engine 1 or the period of time during which the internal combustion engine 1 was switched off before the last start. With increasing ambient temperature and the inclination of the fuel in the fuel tank 18 to the outgassing and thus the loading of the fuel vapor storage 25 increases. The same applies to the duration of the stoppage phase of the internal combustion engine 1. The longer the internal combustion engine 1 was switched off before the last start, the more fuel vapors are adsorbed in the fuel vapor storage 25. In this embodiment, therefore, the switching of the lambda controller 33 in the dynamic control mode is limited to the case of a high load of the fuel vapor storage 25. For small loads, the lambda controller 33 remains in the normal control mode, since the disturbances in the exhaust behavior are classified as low and therefore a more stable controller behavior of the lambda controller 33 in the normal control mode is preferred.

As a further alternative, the condition 2 is fulfilled if, after the start of the tank ventilation period or after opening the tank ventilation valve, the lambda value of the exhaust gas of the internal combustion engine 1 falls below a predetermined lambda limit value. This is possible when using a linear lambda probe.

Advantageously, condition 2 can also be regarded as fulfilled if, after the start of the tank ventilation period the output value y _{R of} the lambda controller 33 exceeds a predetermined output limit value.

In the latter two embodiments, the switching of the lambda controller 33 in the dynamic control mode is limited to the case that the fuel gases are very heavily enriched by the tank venting, that is, that the lambda value of the exhaust gas is well below one. With only slightly enriched mixture, the lambda controller 33 remains in the normal control mode.

It should be noted that the alternative criteria for Condition 2 can also be linked together, as appropriate.

After fulfilling the condition 2 takes place according to the flowchart of FIG. 4 In step 305, a switching of the lambda controller 33 from the normal control mode in the dynamic control mode. As already on the basis of FIG. 3 has been explained, while the controller parameters of the lambda controller 33 are changed so that the lambda controller 33 reacts with a higher control dynamics on the disturbances caused by the tank ventilation. This results in a faster compensation of the changed exhaust gas composition by means of the injection quantity correction. As a result, the deterioration of the exhaust gas due to the tank ventilation only has a significantly shorter duration, which significantly improves the overall exhaust gas behavior of the internal combustion engine 1.

In an advantageous embodiment, the control dynamics of the lambda controller 33 can be further increased, the greater the load of the fuel vapor storage 25. For the estimation of the loading of the fuel vapor accumulator 25, the characteristic described above can again be used.

Alternatively, the control dynamics can also be changed depending on an operating variable of the internal combustion engine 1. For example, the control dynamics can be further increased the smaller the speed of the internal combustion engine 1 or the smaller the load of the internal combustion engine 1 is. This is due to the fact that the introduction of the additional fuel vapors through the tank venting influence the exhaust behavior of the internal combustion engine 1 all the more, the lower the rotational speed and the lower the load.

Specifically, the dynamic adaptation of the controller parameters can be realized so that in the case of the dynamic control mode, the controller parameters of the lambda controller 33 are stored as maps depending on the parameter, the load and / or the speed in the control device 31. By means of this dynamic adaptation of the controller parameters, for example the amplification factors of the I component or the P component of the lambda controller 33, the control dynamics can be better adapted to the individual requirements.

In the flowchart of FIG. 4 Continuing with step 306, it is checked whether a condition 3 is satisfied. Step 306 is repeated until Condition 3 is satisfied. The condition 3 is used to set the time at which the lambda controller 33 is to be returned from the dynamic control mode back to the normal control mode.

For example, the condition 3 can then be regarded as fulfilled if the lambda value of the exhaust gas of the internal combustion engine 1 exceeds a predetermined lambda limit value. The lambda limit value is preferably less than one, ie still within the range of an exhaust gas composition with an excess of hydrocarbons. However, the lambda limit should be close to the setpoint of lambda = 1 so that the peaks of the disturbance caused by the tank ventilation are already largely compensated by the injection quantity correction, and Switching to the normal control mode makes sense. This alternative relates to linear lambda sensor systems.

Alternatively, condition 3 may also be satisfied if the change or the gradient of the controller output variable of lambda controller 33 is smaller than a predefined third change limit value or if the controller output variable y _{R is} within a predefined third value range over a predetermined third time period. The third change limit value and the third value range are to be predefined in such a way that, when the condition 3 is met, it can be assumed that the lambda controller 33 is in an at least almost stable control state and the fault due to the tank ventilation is almost completely corrected.

The same also applies to a further alternative in which condition 3 is satisfied when the lambda value of the exhaust gas is within a predetermined fourth range over a predetermined fourth period of time. Also in this case, the fourth range of values and the fourth period are to be specified such that, when condition 3 is met, the exhaust gas composition disturbance caused by the tank ventilation has been largely compensated by the lambda control device. This alternative relates to linear lambda sensor systems.

Furthermore, it is also possible for the condition 3 to be satisfied when the internal combustion engine 1 leaves the operating state of the idling again. As already mentioned above, the influence of the fuel vapors additionally supplied by the tank ventilation on the exhaust gas behavior at idling is greatest. Outside idling, the disturbance of the exhaust gas behavior by the tank venting under certain circumstances even in the normal control mode of the lambda controller 33 can be compensated quickly enough.

In summary, it can be said that the condition 3 ensures that the lambda controller 33 is returned as quickly as possible from the dynamic control mode to the normal control mode, to instabilities, such as a swinging of the lambda control loop and thus an impairment of ride comfort and to prevent the entire system stability. It should be noted that the alternative criteria for Condition 3 can also be linked together, as appropriate.

1

Brennkraftmaschine

2

Zylinder

3

Kolben

4

Ansaugtrakt

5

Brennraum

6

Ansaugöffnung

7

Luftmassensensor

8

Drosselklappe

9

Saugrohr

10

Einlassventil

11

Zündkerze

12

Kurbelwelle

13

Drehzahlsensor

14

Abgastrakt

15

Auslassventil

16

Abgasreinigungskatalysator

17

Lambda-Sensor

18

Kraftstofftank

19

Kraftstoffpumpe

20

Hochdruckpumpe

21

Druckspeicher

22

Einspritzventil

23

Einfüllstutzen

24

Kraftstoffversorgungsleitung

25

Kraftstoffdämpfespeicher

26

Verbindungsleitung

27

Entlüftungsleitung

28

Tankentlüftungsventil

29

Belüftungsleitung

30

Belüftungsventil^

31

Steuervorrichtung

32

Umgebungstemperatursensor

33

Lambda-Regler

According to the flowchart of FIG. 4 If the condition 3 is fulfilled, then the lambda controller 33 is returned to the normal control mode in step 307. In step 308, the method is either terminated or restarted.

1

Internal combustion engine

2

cylinder

3

piston

4

intake system

5

combustion chamber

6

suction

7

Air mass sensor

8th

throttle

9

suction tube

10

intake valve

11

spark plug

12

crankshaft

13

Speed sensor

14

exhaust tract

15

outlet valve

16

purifying catalyst

17

Lambda sensor

18

Fuel tank

19

Fuel pump

20

high pressure pump

21

accumulator

22

Injector

23

filler pipe

24

Fuel supply line

25

Fuel vapor reservoir

26

connecting line

27

vent line

28

Tank ventilation valve

29

vent line

30

Vent valve ^

31

control device

32

Ambient temperature sensor

33

Lambda control

Claims (25)

1. Method for controlling an internal combustion engine (1) having a tank purging apparatus by means of which fuel vapours are introduced into an intake system (4) of the internal combustion engine (1) during a tank purging period, with a lambda controller (33) of the internal combustion engine (1) being switched from a normal control mode to a dynamic control mode in which the lambda controller (33) has a higher control dynamic than in the normal operating mode in such a manner that the lambda controller (33) is at least temporarily in the dynamic control mode during the tank purging period, characterised in that
   the fuel vapours are stored in a storage container of the tank purging apparatus and the lambda controller (33) is switched to the dynamic control mode only if a characteristic variable which represents a measure of the loading of the fuel vapour storage unit (25) with fuel vapours exceeds a predetermined limit value.
2. Method according to claim 1, wherein the lambda controller (33) is switched to the dynamic control mode only if before the tank purging period an output value of the lambda controller (33) is within a predetermined first value range over a predetermined first time period.
3. Method according to claim 1, wherein the lambda controller (33) is switched to the dynamic control mode only if before the tank purging period the change in an output value of the lambda controller (33) is less than a predetermined first change limit value.
4. Method according to claim 1, wherein the lambda controller (33) is switched to the dynamic control mode only if an operating variable of the internal combustion engine (1) is within a predetermined second value range over a predetermined second time period.
5. Method according to claim 1, wherein the lambda controller (33) is switched to the dynamic control mode only if the change in an operating variable of the internal combustion engine (1) is less than a predetermined second change limit value.
6. Method according to claim 1, wherein the lambda controller (33) is switched to the dynamic control mode only if the internal combustion engine (1) is in no-load operation.
7. Method according to claim 1, wherein the control dynamic of the lambda controller (33) in the dynamic mode is increased to a greater degree, the greater the characteristic variable.
8. Method according to one of claims 1 and 7, wherein the characteristic variable is the ambient temperature of the internal combustion engine (1).
9. Method according to one of claims 1 and 7, wherein the characteristic variable is the time interval during which the internal combustion engine (1) was turned off.
10. Method according to one of claims 1 to 9, wherein the control dynamic of the lambda controller (1) in the dynamic control mode is changed as a function of an operating variable of the internal combustion engine (1).
11. Method according to claim 10, wherein the control dynamic of the lambda controller (33) in the dynamic control mode is increased to a greater degree, the lower the speed of the internal combustion engine (1).
12. Method according to claim 10, wherein the control dynamic of the lambda controller (33) in the dynamic control mode is increased to a greater degree, the smaller the load of the internal combustion engine (1).
13. Method according to one of claims 1 to 12, wherein the lambda controller (33) is switched to the dynamic mode immediately before the introduction of the fuel vapours into the intake system (4).
14. Method according to one of claims 1 to 12, wherein the lambda controller (33) is switched to the dynamic mode immediately after the introduction of the fuel vapours into the intake system (4).
15. Method according to one of claims 1 to 12, wherein the lambda controller (33) is switched to the dynamic mode a predetermined time interval after the introduction of the fuel vapours into the intake system (4).
16. Method according to claim 15, wherein the time interval corresponds to the time required for the fuel vapours to pass from the introduction position in the intake system (4) to a lambda sensor (17) of the internal combustion engine (1).
17. Method according to claim 1, wherein the lambda controller (33) is switched to the dynamic mode once the lambda value of the exhaust gas of the internal combustion engine (1) drops below a predetermined first lambda limit value.
18. Method according to claim 1, wherein the lambda controller (33) is switched to the dynamic mode once an output value of the lambda controller (33) exceeds a predetermined output limit value.
19. Method according to one of claims 1 to 18, wherein when a condition is met the lambda controller (33) is switched from the dynamic control mode back to the normal control mode.
20. Method according to claim 19, wherein the condition is met when the lambda value of the exhaust gas of the internal combustion engine (1) exceeds a predetermined second lambda limit value.
21. Method according to claim 19, wherein the condition is met when the change in an output variable of the lambda controller (33) is less than a predetermined third change limit value.
22. Method according to claim 19, wherein the condition is met when an output variable of the lambda controller (33) is within a predetermined third value range over a predetermined third time period.
23. Method according to claim 19, wherein the condition is met when the lambda value of the exhaust gas is within a predetermined fourth value range over a predetermined fourth time period.
24. Method according to claim 19, wherein the condition is met when the internal combustion engine leaves the operating state of no-load operation.
25. Internal combustion engine (1) having

    - a tank purging apparatus by means of which fuel vapours are introduced into an intake system (4) of the internal combustion engine 1 during a tank purging period and which has a storage container for storing fuel vapours,

    - a fuel supply device which feeds a predetermined quantity of fuel to a combustion chamber (5) of the internal combustion engine (1),

    - a lambda controller device which is coupled to the fuel supply device and corrects the quantity of fuel to be fed in as a function of the exhaust gas composition, with the lambda controller device being embodied in such a manner that a lambda controller (33) is switched from a normal control mode to a dynamic control mode in which the lambda controller (33) has a higher control dynamic than in the normal operating mode, in such a manner that the lambda controller (33) is at least temporarily in the dynamic control mode during the tank purging period,

    characterised in that
    the lambda controller device is embodied in such a manner that the lambda controller (33) is switched to the dynamic control mode only if a characteristic variable which represents a measure of the loading of the fuel vapour storage unit (25) with fuel vapours exceeds a predetermined limit value.

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