EP0364522B1 - Process and device for adjusting a fuel tank ventilator valve - Google Patents

Abstract

In a process for obtaining adjustment values for controlling a fuel tank ventilator valve connected to an internal combustion engine, the adjustment factor used is obtained from a calculating step for lambda control. The adjustment factor modifies a loading factor until such time as a quantity of regenerated fuel which does not lead to a deviation in the lambda target value is delivered through the fuel tank ventilator valve. The adjusted loading factor modifies pre-control values for the quantity of regenerated fuel to be supplied in the preceding operating mode. The process disclosed is characterized in that allowance is made for pressure, conditions prevailing in the fuel tank ventilator valve. The opening of the fuel tank ventilator pipe into the intake manifold of an internal combustion engine can therefore be located behind the throttle valve, where there is a high negative pressure which can nevertheless vary within wide limits. The process makes allowance for these fluctuations in the context of pre-control with overriden control, making it possible to operate reliably with high regenerated gas flow rates. The device disclosed comprises, in particular, means (33) for determining the flow rate which make allowance for the pressure conditions in the fuel tank ventilator valve, as well as means (31) for controlling the load which adapt a temporarily assumed loading factor to the actual loading factor.

Description

The invention relates to a method and a device for setting a tank ventilation valve, which connects a container in which fuel vapors are temporarily stored to the intake manifold of an internal combustion engine.

State of the art

A method and a device for setting a tank ventilation valve are known from DE-A1-35 02 573 (US patent application 822.012 / 86). The method described there uses the lambda control factor, which is supplied by a lambda controller functional unit for controlling the lambda value of the air / fuel mixture to be supplied to the internal combustion engine. This factor serves to modify values of a pilot control variable for a pulse duty factor for actuating the tank ventilation valve, which values are stored in an addressable manner via the speed and a load-dependent variable.

The known method presupposes that on the negative pressure side of the tank ventilation valve, that is to say at the junction the tank ventilation in the air duct of the internal combustion engine, essentially the same negative pressure prevails. This presupposes that the mentioned junction is in front of the throttle valve. If different negative pressures occur depending on different loads, this is taken into account by the load-dependent values of the pilot variable. In the cited document, however, it is expressly mentioned that larger pressure differences between different load conditions cannot be adequately taken into account.

Behind the throttle valve, there is a much stronger negative pressure in the intake manifold than before, especially when the valve is not fully open. The result of this is that if the tank ventilation behind the throttle valve opens into the air duct, i.e. into the intake manifold, instead of in front of it, significantly higher gas throughputs can be achieved with the same cross sections of the tank ventilation lines and thus the intermediate store, which is usually filled with activated carbon is regenerated faster and better. However, the known method and the known device are not able to carry out a satisfactory regulation of the quantity of fuel to be supplied to the internal combustion engine in this case.

The invention is based on the object of specifying a method and a device for setting a tank ventilation valve, which method and which device also lead to good control results for the total amount of fuel to be supplied to an internal combustion engine if the method or the device is to be used on a system , in which the tank ventilation is guided behind the throttle valve in the air duct of an internal combustion engine.

Advantages of the invention

The invention is given for the method by the features of claim 1 and for the device by the features of claim 2. Advantageous further developments and refinements of the device are the subject of the dependent claims.

It is of particular importance for the method according to the invention that it calculates the maximum possible gas flow through the tank ventilation valve under the pressure conditions prevailing in a particular operating state. This maximum gas flow is taken into account when modifying predetermined pilot control values of a size that is a measure of the desired amount of regeneration fuel. These pilot control values are advantageously set in inverse proportion to the calculated maximum gas flow. The dependency can be done either by addressing a memory with pre-control values stored there via the maximum gas flow calculated for the respective operating state, or by dividing a pre-control value determined without the dependence on the maximum gas flow by the value of the respective maximum gas flow. The pilot values are also set in proportion to the air mass flow through the intake manifold. This dependency can also be done in one of the two ways just described.

The pilot control values are modified by division by a loading factor, which, based on its present value, is preferably changed step by step depending on the respective present value of the lambda control factor in such a way that it leads to a change in the amount of regenerative fuel to be output in the respective direction that changes the Lambda control factor on one Control factor setpoint. The setpoint is typically one. A modification to the divided value also belongs to the modification. The modification mentioned can be carried out on the pre-control values before they are set to the dependency mentioned in the previous section or afterwards.

The modified and set values are finally converted into a manipulated value for the tank ventilation valve, typically a duty cycle.

If fuel is supplied to an internal combustion engine via a tank ventilation valve and not only via a fuel metering device, typically an injection valve arrangement, this has the consequence that the two fuel subsets have to be matched to one another for correct operation. For this purpose, the control value to be supplied to the fuel metering device is reduced in the method according to the invention in order to reduce the amount of fuel supplied by this device to the internal combustion engine compared to the state in which no fuel is supplied via the tank ventilation valve. The reduction takes place to such an extent that the metering device essentially supplies the internal combustion engine with the amount of fuel which is supplied to it more via the tank ventilation valve.

In order to carry out the above-mentioned method, a device according to the invention requires at least one regeneration pre-control value memory, a flow determination means, a load control means, a conversion means and a compensation means. The regeneration pilot control value memory stores provisional values for the regeneration gas flow in an addressable manner via values of the rotational speed, the air flow and the maximum possible gas flow through the tank ventilation valve. The maximum possible values for the gas flow through the tank ventilation valve are determined by the flow determining means for the respective operating state. The load controller means determines the load factor mentioned above and divides the pilot values read out for a given set of values of addressing operating variables by this load factor. In a subsequent step within the load regulator means, the divided value is then regulated. The regulated value is converted by the conversion means into a manipulated value for the actuator of the tank ventilation valve. The compensation means carries out the aforementioned reduction in the control value to be supplied to the fuel metering device.

Said means of the device can be implemented by individual hardware-specific special assemblies or by the known functions of a suitably programmed microcomputer, with the second possibility being preferred according to today's technology.

Instead of using the minimum number of functional means mentioned, the method according to the invention can also be implemented with a larger number of such means, specifically with the less information that is already taken into account in the regeneration pilot control value memory. The dependencies not taken into account must then be created in special functional means.

Of particular advantage is a device which has a regeneration pre-control value memory which stores fuel ratio numbers for the ratio of regeneration fuel mass / total fuel mass in an addressable manner via values of the rotational speed and a load-dependent quantity.

The values to be stored in the memory in this case correspond exactly to what is ultimately desired, namely to replace a certain proportion of the total fuel with regeneration fuel. In order to convert the value read in each case into a regeneration gas stream, i.e. into a variable that can be controlled by the tank ventilation valve, the device has a load regulator means directly behind the pilot control value memory, which means that a gas ratio number is obtained by dividing the fuel ratio by the load factor. From this ratio, the actually required regeneration gas flow is obtained by multiplying it with the air flow through the intake manifold and a constant in a multiplication step. In a dividing step, the maximum gas flow that is possible at the moment is taken into account, the value of which is determined by a flow determining means. A conversion means calculates a manipulated variable for the actuator of the tank ventilation valve. A compensation means reduces the manipulated value which is fed to the fuel metering device in accordance with the amount of regenerating fuel supplied.

In practice, the device working with these means can be adapted particularly well to different engine systems, since it takes into account important variables that are important for the function of the overall device in separate calculation steps.

Any valve whose flow can be controlled can be used as a tank ventilation valve. The use of a clocked valve is particularly advantageous. DE-A1-35 02 573, already mentioned at the beginning, mentions a clock frequency of 10 Hz as advantageous. Without changing the frequency, the clock ratio for ice creaming is required Gas flow varies. The opening and closing times of the valve are therefore within wide limits.

In an advantageous embodiment of devices according to the invention, which, however, can also be used with any other devices for controlling a tank ventilation valve, the opening time or the closing time, depending on the duty cycle just required, is set to the minimum value at which the tank ventilation valve can still operate properly is. It is not the cycle frequency that is kept constant, but the opening time when the valve is mostly closed. This has the advantage that even with unfavorable duty cycles, the fastest possible change between opening and closing and thus good driving properties of the vehicle in which the device is used are achieved. Only with extreme duty cycles, the clock frequency is so low that z. B. the opening time is so large that it overlaps with the intake periods of several cylinders. In order to prevent this, the clock frequency is limited to a minimum value according to an advantageous further embodiment. If this value is reached, the frequency is maintained and the closing or opening time of the tank ventilation valve is set below the value that is actually required for correct operation. Although this leads to deviations from the desired values, this is less serious than poor driving behavior due to a too low clock frequency.

drawing

Fig. 1

eine in Blockschaltbildform ausgeführte Funktionsdarstellung eines Verfahrens zum Stellen eines Tankentlüftungsventiles, mit einem Beladungsreglermittel und einem Durchflußbestimmungsmittel;

Fig. 2

eine in Blockschaltbildform ausgeführte Funktionsdarstellung des Beladungsreglermittels im Verfahren von Fig. 1;

Fig. 3

eine in Blockschaltbildform ausgeführte Funktionsdarstellung des Durchflußbestimmungsmittels im Verfahren von Fig. 1; und

Fig. 4

eine in Blockschaltbildform ausgeführte Funktionsdarstellung einer anderen Ausführungsform eines Verfahrens zum Stellen eines Tankentlüftungsventiles, mit einem Regenerier-Vorsteuerwertspeicher, der unter anderem mit dem Ausgangswert von einem Durchflußbestimmungsmittel adressiert wird.

Embodiments of the invention are shown in the drawing and explained in more detail in the following description. Show it:

Fig. 1

a functional block diagram of a method for setting a tank ventilation valve, with a load control means and a flow determining means;

Fig. 2

a functional diagram of the load controller means executed in block diagram form in the method of Fig. 1;

Fig. 3

a functional diagram of the flow determining means executed in block diagram form in the method of Fig. 1; and

Fig. 4

a functional diagram in block diagram form of another embodiment of a method for setting a tank ventilation valve, with a regeneration pilot control value memory, which is addressed inter alia with the output value by a flow determining means.

Description of exemplary embodiments

1 shows an internal combustion engine 10 with regulation of the injection time TI of an injection valve 11 and regulation of the duty cycle TAU of a tank ventilation valve 12.

The injection time is regulated as follows. Preliminary injection times TIV are read out from an injection pilot control value memory 13 as a function of the speed n and a load-dependent variable TL. The values arrive at a compensating-multiplying step 14, the function of which is discussed in connection with the regulation of the tank ventilation valve. After this multiplication step, the modified values arrive at a control factor multiplication step 15, where they are compared with a control factor FR can be multiplied, which is supplied by a lambda control means 16 as a function of a target / actual difference. The actual value is obtained with the aid of a lambda probe 17. The setpoint comes from a lambda setpoint memory 18 which can be addressed via the speed n and the load-dependent variable TL. If control is also not performed on lean values, but only on lambda value one, the lambda setpoint memory 18 is not available. In addition to the control factor multiplying step 15, the control factor is also led to an injection adaptation means 19 which carries out a learning process when a corresponding adaptation instruction is fulfilled, which is indicated by a closable injection adaptation switch 20. The output signal of the injection adapter 19 also modifies the injection time. This is done in a linking means 21 which, for. B. works multiplicatively or multiplicatively and additively, depending on the structure and function of the injection adapter 19.

The described control loop for the injection time works in such a way that an injection pilot control time TIV is read out of the injection pilot control value memory 13 for the respective operating state. This time is modified by the above-mentioned calculation steps with the aid of the control factor FR in such a way that the lambda setpoint specified for the relevant operating state is set.

The compensating-multiplying step 14 has already been mentioned. This serves to reduce the injection pre-control time when fuel is supplied to the intake manifold 22 of the internal combustion engine 10 not only via the injection valve 11, but also via a tank ventilation pipe 23.

The tank ventilation has an intermediate store 24, which is usually filled with activated carbon. Its vent inlet 25E is connected to the fuel tank. When regenerating, air flows into it through a vent inlet 25B at ambient pressure PAMB. Its outlet 26 leads to the tank ventilation valve 23, which is connected to the suction pipe 22 via the tank ventilation pipe 23. The suction pressure PSAUG prevails in both pipes mentioned. The tank ventilation pipe 23 opens into the intake manifold behind a throttle valve 27. As a result, the suction vacuum is particularly strong, which leads to a high gas flow through the intermediate store 24 and thus to good regeneration results of the activated carbon.

In addition to the injection valve 11 and the throttle valve 27, an air mass meter 28 is also arranged in the air duct, which measures the air flow, that is to say the air mass per unit of time, through the air duct. The output signal from the air mass meter 28 is converted by an evaluation means 29, which is also supplied with the speed signal n, into an air flow signal ML and the load signal TL already mentioned, the latter being proportional to the quotient of air flow and speed.

It should be noted at this point that the load detection does not have to be done by an air mass meter, but can be done in any way, for. B. by measuring the position of the accelerator pedal or the throttle valve.

Before the calculation steps for controlling the tank ventilation valve 12 are discussed in more detail, it should first be explained which considerations the invention makes use of.

The tank ventilation valve 12 is not able to directly control the regeneration fuel mass, but it can only directly influence the regeneration gas flow. However, a certain amount of fuel from the injection valve 11 and a certain amount of fuel from the tank ventilation pipe 23 are actually desired for each operating state. Specified values must therefore always be a measure of the ratio of regeneration fuel mass / total fuel mass. What type of regeneration gas flow corresponds to the desired fuel mass depends on the loading factor FTEAD of the regeneration gas, i. H. of the ratio of regeneration fuel mass to regeneration gas mass. If all of the regeneration gas is fuel gas, the loading factor is one; if the regeneration gas consists only of air, the loading factor is zero.

The loading factor present in each case is determined by first assuming a certain value and using this assumption to determine the regeneration gas flow. If the assumption was incorrect, the internal combustion engine 10 is supplied with a different total fuel mass than assumed. This leads to a deviation of the control factor FR from one. Depending on the direction in which the control factor FR deviates from one, the loading factor FTEAD initially assumed is changed, in each case in the direction which counteracts the measured deviation of the control factor FR from one. Thus, based on the initially assumed value of the load factor FTEAD, the load factor applicable to the present operating conditions is adjusted.

Of particular importance for the function of the device for setting the tank ventilation valve 12 is the knowledge that the gas flow through the tank ventilation valve from Pressure ratio between inlet-side pressure PAMB and outlet-side pressure PSAUG depends. For each ratio, there is a certain maximum possible gas flow through the valve, which is present when the valve is constantly fully open. This maximum possible current is reduced to the desired value by setting a pulse duty factor. The maximum gas flow that is possible in a particular operating state, ie certain pressure ratios, must be calculated.

When determining the regeneration gas flow, it must also be taken into account that this is to be changed in proportion to the air flow ML through the intake manifold 22 in order to obtain a desired ratio of regeneration fuel mass / total fuel mass.

The device for setting the tank ventilation valve includes a regeneration pilot control memory 30, a load regulator means 31, the function of which is shown in detail in FIG. 2, an air mass multiplier 32, a flow determining means 33, the function of which is shown in detail in FIG. 3 Flow dividing means 34, a normalizing multiplier 35, a conversion means 36 and a compensating means, which acts as a loading multiplier 37, subtracting means 38 and already mentioned compensating multiplier 14.

The regeneration pilot control value memory stores fuel ratio numbers for the ratio of regeneration fuel mass / total fuel mass addressable via values of the speed n and the load-dependent variable TL, z. B. the value 0.1 for medium speed and medium load. This example number means that when an operating state occurs with those predetermined values of speed and load, for which the value 0.1 is stored, up to 10% of the total fuel mass may be applied by regenerating fuel mass. For the further explanations, it is initially assumed that the regeneration gas stream contains a sufficient proportion of fuel gas that the permissible 10% can be supplied.

The fuel ratio FTEFMA read out for the respective operating state is given to the load control means 31, to which the control factor FR is also supplied by the lambda control stage 16. The loading control means 31 works in two sub-steps, namely a recurrence means 39 and a control means 40, which will now be explained in more detail with reference to FIG. 2.

wobei ΔFR die positive oder negative Abweichung des Regelfaktors FR vom Sollwert Eins ist. Diese Differenz wird durch einen Sollwert-Subtrahierschritt 42 im Rekursionsmittel 39 gebildet. LEKTE ist ein Abschwächungsfaktor, der dazu führt, daß, je nach dem für ihn festgelegten Wert, der Adaptionsprozeß für die Ansteuerung des Tankentlüftungsventiles nicht zu schnell, sondern sozusagen gedämpft erfolgt, um Regelschwingungen zu vermeiden.The recurrence means 39 has a sample / hold step 41 which, for. B. can be performed by a memory cell in a microcomputer. This step 41 stores an assumed value for the loading factor FTEAD, e.g. B. the value zero at first start-up or the value that was last calculated. With each program run i, if the device is implemented by a microcomputer, a new load factor FTEAD (i - 1) is calculated from the load factor FTEAD (i - 1) calculated in the previous cycle according to the following recursion formula: $$\text{FTEAD (i) = FTEAD (i - 1) - ΔFR * LEKTE}$$

where ΔFR is the positive or negative deviation of the control factor FR from the setpoint one. This difference is formed by a setpoint subtracting step 42 in the recursion means 39. LEKTE is a mitigating factor that, depending on the value set for it, causes the Adaptation process for the control of the tank ventilation valve is not too fast, but rather damped, so to speak, to avoid control vibrations.

In order to carry out the recursion mentioned, the recursion means 39 works with a recursion subcarrier step 43, to which the loading factor FTEAD (i-1) from the previous calculation cycle and the quantity ΔFR * LEKTE are supplied and which the newly calculated value FTEAD (i) for the loading factor to sample / hold step 41.

From the fuel ratio FTEFMA and the loading factor FTEAD, a gas ratio is obtained by division, which represents the ratio of mass of regeneration gas to mass of total fuel. If the loading factor FTEAD is set to zero or to a very small value at the start of the operation of the device, this would result in a high gas ratio and thus a senselessly high value for the gas flow that the tank ventilation valve should enforce. Very high values for the required gas throughput can also occur during operation if the operating state changes suddenly and the fuel ratio number read from the regeneration pilot control value memory 30 jumps compared to the previously read number. In order to avoid abrupt changes in the required value for the regeneration gas flow and in particular the jump to senselessly high values, the recurring means 39 is followed by the said regulating means 40. In the calculation steps there, the quotient of the read fuel ratio FTEFMA and the loading factor FTEAD determined by the recursion formula is formed. This variable is supplied as a setpoint via a setpoint / actual comparison step 44 to an I control step which has a normalizing comparator step 45 and an integrator step 46. Only the initial value supplied by integrator step 46 is evaluated as the gas ratio number FTEFVA. This output variable is subtracted from said target value in target / actual comparison step 44. If the difference is positive, the normalizing comparator step 45 outputs the signal "plus 1", which leads to a further high integration of the gas ratio number FTEFVA by the integrator step 46. If the output actual value finally reaches and even exceeds the target value, the result of the normalizing comparator step 45 tilts to the output signal "minus 1", whereupon each integrator step 46 integrates downwards, that is to say the gas ratio FTEFVA is reduced again.

The gas ratio number is supplied to the air mass multiplying step 32, where it is multiplied by the current value for the air mass ML. If a multiplication by a normalization factor took place at the same time, there would be a quantity that would be a direct measure of the required regeneration gas flow for the current air flow ML. In the exemplary embodiment shown, however, this standardization only takes place after the flow dividing step 34 in the standardization multiplication step 35, so that it can be normalized to a predetermined maximum gas flow at the same time.

The flow determining means 33 has gem. 3 shows a suction pressure characteristic curve memory 47, a pressure dividing step 48, a flow characteristic curve memory 49 and a pressure multiplying step 50. These calculation steps simulate the following physical relationship: $$\text{VREGNULL = PAMB x F (PSAUG (TL) / PAMB)}$$

The intake manifold pressure PSAUG is present via the tank ventilation pipe 23 at the outlet 26 of the tank ventilation valve 12 and changes essentially in proportion to the value of the load-indicating quantity TL. This proportional relationship is stored in the suction pressure characteristic curve memory 47. It could also be calculated, but this would require additional computing time. The relationship between the maximum possible gas flow VREGNULL through the permanently open tank ventilation valve 12 and the quotient QUOP between suction pressure PSAUG and ambient pressure PAMB is complex and can only be calculated with difficulty. The relationship is therefore stored in the flow characteristic curve memory 49.

The flow determining means 33 are each supplied with values of the load-indicating quantity TL and the ambient pressure PAMB. It takes the suction pressure characteristic curve memory 47 from the suction pressure valid for the predetermined load size and divides it by the ambient pressure PAMB in order to be able to use the quotient obtained in this way to obtain a provisional value for the maximum gas flow through the tank ventilation valve 12 from the flow characteristic curve memory 49. This value is then multiplied by the ambient pressure PAMB in the pressure multiplication step 50 and normalized to the ambient pressure for which the remaining characteristic curve and characteristic map values of the entire device are intended in the normalization multiplication step 35 already mentioned.

After all of these measures, the conversion means 36 receives a signal that is a direct measure of the open time of the tank ventilation valve 12. The present value is converted into a duty cycle by the conversion means 36 TAU converted for the actuator 51 of the tank ventilation valve 12. It is already taken into account with the aid of the flow determining means 33 that different duty cycles are required to achieve the same gas flow under different pressure conditions. The flow determination means 33 is thus functionally closer to the conversion means 36 than those arithmetic steps which are used to actually calculate the desired regeneration current. This value would already be present at the output of the air mass multiplication step 32 if the normalization mentioned above had already been carried out there.

The function of the function groups of the device for setting the tank ventilation valve 12 described so far is as follows: It is assumed that the entire system is in balance, that is to say the injection time TI has been chosen correctly and that the tank ventilation pipe 23 has exactly the desired amount of regeneration fuel in relation to Total amount of fuel supplied. Now suddenly the loading factor of the regeneration gas stream, e.g. B. in that the activated carbon is largely regenerated in the intermediate storage 24. This leads to an excessively lean mixture being supplied to the internal combustion engine 10. The control factor FR then rises above the value one, as a result of which the difference ΔFR from the setpoint one becomes positive. This positive value is subtracted from the value FTEAD (i-1) for the loading factor still stored in the sample / hold step, whereby a new, smaller value FTEAD (i) is obtained. The fuel ratio number FTEFMA which is read out unchanged is divided by this smaller value in the loading dividing step 52, as a result of which the value supplied to the target / actual comparison step 44 becomes larger. The gas ratio FTEFVA is thereby reduced to integrates a higher value than the previous one until it reaches the specified target value. This increase in the gas ratio FTEFVA increases the regeneration gas flow and thus the amount of regeneration fuel supplied to the intake manifold 22 through the tank ventilation pipe 23 so that the internal combustion engine 10 is operated again with the predetermined lambda setpoint, at which the control factor FR is again one.

To complete the functional description of the system, the function of the compensating means will now be explained.

As soon as the loading factor FTEAD is adjusted to the value that actually applies in the regeneration gas flow by the loading regulator means 31, the product of its value and the value of the gas ratio FTEFVA by definition gives exactly the ratio of the regeneration fuel mass to the total fuel mass, that is to say the value 0 in the example. 1. This value from the load multiplying step 37 is subtracted from the fixed value one in the subtracting step 38, whereby the compensating multiplying step 14 is supplied with a difference value, in the example the value 0.9, by which the preliminary injection time TIV is multiplied. This is thus reduced, in the example by 10%. The control value supplied to the injection valve 11 is thus reduced to such an extent that the fuel supplied by the injection valve of the internal combustion engine 10 is reduced in each case to the extent that the injection valve 11 is the one in which no fuel is supplied via the tank ventilation valve 12 Internal combustion engine 10 essentially supplies the amount of fuel that is supplied to it more via the tank ventilation valve 12.

Various special conditions can occur when operating the device mentioned. Such special conditions are taken into account separately in the exemplary embodiment. While the injection time is being adapted, there must be no tank ventilation and vice versa. For this purpose, the already mentioned injection adaptation switch 20, a ventilation adaptation switch 53 and an actuator switch 54 are provided. The function of the vent adaptation switch 53 acts between the load multiplying step 37 and the subtracting step 38, which leads to the fact that it gives the setpoint one to the compensating multiplying step 14 in the open state. The function of the actuator switch 54 is to switch the actuator 51 for the tank ventilation valve 12 so that the tank ventilation valve is permanently closed when the switch is open. During an adaptation period for the injection time, the vent adaptation switch 53 and the actuator switch 54 are open (the adaptation of the loading factor FTEAD by the recurrence means 39 is stopped), and the injection adaptation switch 20 is closed, while it is exactly the opposite in periods for the adaptation ventilation . The period for the injection time adaptation is z. B. about a minute, the period for the adaptation of the tank ventilation z. B. two minutes. At full load there is constant regeneration, the load factor remains unchanged and FTEFVA = FTEFMA is set temporarily.

The following conditions apply in particular as special conditions as are taken into account by a special condition level in the control means 40. If the tank ventilation valve 12 is fully open, the normalizing comparator step 45 inevitably outputs the value "minus 1" so that the integrator step 46 integrates again downwards. Thereby there is a limit control. The same applies if the control factor FR to limit values for rich or lean operation, z. B. runs to the values 0.8 or 1.2. In other special conditions, the special condition means 55 directly influences the integrator step 46. For example, it sets its output value directly to the quotient of the fuel ratio FTEFMA and the loading factor FTEAD if this quotient becomes smaller than the current output value FTEFVA, which is the case when the load is reduced . In this case, less fuel should be delivered suddenly. Another measure is to influence the speed of integration. The integration speed is normally chosen to be relatively low, so that vibrations do not occur when superimposed on the integration behavior of the lambda control means 16. However, rapid integration is selected at the beginning of each adaptation period for the tank ventilation until the control factor FR runs to one of the limits already mentioned or until the tank ventilation valve is fully open.

In order to be able to react quickly under special operating conditions, a special measure is also taken in recursion means 39. This is because a learning factor dividing step 56 is used which divides a predetermined weakening constant KONSTL for learning by the initial value FTEFVA of integrator step 46 and thus gains the weakening factor LEKTE. This has the effect that if the gas throughput through the tank ventilation is still relatively low, the learning process takes place quickly, whereas the learning process, that is to say the recursion in the recursion means 39, takes place increasingly slowly when the regeneration gas flow increases. This also reduces the tendency to control vibrations.

FIG. 4 shows a variant of that part of the functional sequence of FIG. 1 which in FIG. 1 lies below the horizontal dash-dotted line drawn there. These are the arithmetic steps between reading values from the regeneration pilot value memory 30 and the conversion means 36. In the embodiment according to FIG. 4, there are only four arithmetic step groups, namely the flow determining means 33, a read from a modified regeneration pilot value memory 30.4, the load control means 31 and the conversion means 36.

In contrast to that of the embodiment according to FIG. 1, the regeneration pre-control value memory 30.4 of the embodiment according to FIG. 4 can be controlled not only via values of two operating variables, but via values of four operating variables, namely via values of the load-indicating variable TL, the speed n, the air flow ML and the maximum gas flow VREGNULL. One of the two addressing variables, load-indicating variable TL and airflow ML, can be omitted, since these variables can be converted into one another using the speed n and a constant. Because the values stored in the aforementioned memory 30.4 already take the air flow ML and the maximum gas flow VREGNULL into account, the air mass multiplying step 32, the flow dividing step 34 and the normalizing multiplying step 35 are omitted in comparison to the embodiment according to FIG. 1. The load controller means 31 thereby no longer receives fuel ratio numbers, but rather provisional values for duty cycles, namely in that the duty cycle dependency of pressure ratios for predetermined regeneration gas flows is already taken into account via values for the maximum gas flow VREGNULL through the tank ventilation valve 12. The load control means 31 uses these more complex values instead of the fuel ratio numbers.

The embodiment according to FIG. 4 has the advantage of very short computing time, since fewer arithmetic computing steps are to be carried out than with the embodiment according to FIG. 1. This requires a larger regeneration pre-control value memory 30.4 and the method is less adaptable to different operating conditions.

A step in the opposite direction would mean that instead of the regeneration pilot control value memory 30 of the embodiment according to FIG. 1, a memory was used in which only the relationship between fuel ratio numbers and the load variable TL is stored, while the dependence of the engine speed n would be taken into account by a subsequent multiplication step. In the event of further progress in the direction of arithmetic, the memory just mentioned could also be dispensed with and a fuel ratio number required for each value of the load variable TL could be calculated from a mathematical function.

It is up to the person skilled in the art to determine which arithmetic functions are actually carried out and which functions are already taken into account in stored values. The embodiment according to FIG. 1 forms a good optimization. However, all of the methods according to the invention are distinguished by the fact that they have a flow determination means and a load control means for modifying read or calculated values.

The conversion means 36 in the exemplary embodiment according to FIGS. 1 and 4 works according to a method for determining the duty cycle which is particularly advantageous for the present application. This is because the opening and closing times of the tank ventilation valve 12 are as short as possible.

It is assumed that the tank ventilation valve 12 has a minimum open time of 5 ms and a closing time of the same value in reliable operation. Are these times shortened, e.g. B. to 3 ms, it is no longer guaranteed that the selected time is really kept. If a duty cycle of 50% is to be set, an open time of 5 ms and a closing time of 5 ms are selected. For a duty cycle of 4: 1, 20 ms open time and 5 ms closing time are used, conversely for a duty cycle of 1: 4, an open time of 5 ms and a closing time of 20 ms. The frequency for the duty cycle is 1: 1 100 Hz, in the other two examples, however, 40 Hz. Is a minimum frequency, z. B. 10 Hz, this is no longer reduced, but the open or closing time is now reduced below the value for reliable operation, so with a duty cycle of 20: 1 for an open time of about 99 ms and a closing time of about 1 ms used. Because of the unreliable way of working with this short closing time, there is no guarantee that the desired duty cycle will actually be set, however, deviations are insignificant for practical operation in these extreme cases.

The measure mentioned has the effect that clock frequencies and open or close times are never obtained, in which the alternating opening and closing of the tank ventilation valve leads to noticeable torque changes.

The external air pressure PAMB is used in the method step, which is particularly important for the invention, of taking into account the pressure conditions at the tank ventilation valve by means of the flow determination stage. This can either be measured directly, or it can be calculated from adaptation variables of the injection adaptation stage 19. The latter is based on the knowledge that it is necessary to adapt the pilot control values for the injection, in particular because of fluctuations in air pressure.

Claims (8)

1. Method of actuating a tank venting valve (12), which is connected to the intake stub of an internal-combustion engine, the supply of which with air/fuel mixture is set with the aid of a lambda control which influences a fuel metering device (11) via a lambda control factor (FR), in which method the following method steps are carried out, the order of which is fixed only where expressly specified:

   - Calculating the maximum possible gas flow (VREGNULL) through the completely opened tank venting valve (12) under the pressure conditions prevailing in their respective operating state, from intake pressure to ambient pressure (PSAUG/PAMB),

   - Predetermining pre-control values (FTEFMA) of a variable which is a measure of a required regenerating fuel quantity, i.e. a quantity of fuel to be supplied via the tank venting, in dependence on at least one load-dependent variable (TL) and the rotational speed (n),

   - Multiplying the possibly modified pre-control values by a value for the airflow (ML) supplied to the internal-combustion engine through the intake stub,

   - Recalculating the possibly further modified pre-control value into a pulse duty factor for actuating the tank venting valve,

   - Compensating for the influence to be expected of the quantity of fuel supplied via the tank venting on the overall fuel balance by a compensation step (means 14) performed in addition to the lambda control intervention (means 16) on a fuel metering signal to be supplied to the fuel metering device (11), which compensation step effects a reducing of the setting value (TI) to be supplied to the fuel metering device (11), as a result of which the quantity of fuel supplied from the fuel metering device (11) to the internal-combustion engine is reduced in comparison with the state in which no fuel is supplied via the tank venting valve (12), in each case to such an extent that the fuel metering device (11) supplies to the internal-combustion engine that quantity of fuel less which is supplied to it more via the tank venting valve (12) in the case of the influence to be expected of the quantity of fuel supplied via the tank venting on the overall fuel balance,

   - Sensing of the overall mixture composition resulting when the tank venting valve is open,

   characterized by the following further steps:

   - Modifying the pre-control values by division by an initially assumed loading factor (FTEAD), which designates the proportion of the fuel mass (regenerating fuel quantity) of the mass of the tank venting mixture (gas flow through the tank venting valve),

   - Dividing the possibly modified and multiplied pre-control values by the maximum possible gas flow (VREGNULL) through the tank venting valve (12)

   - parallel to the lambda control intervention (means 16) on a fuel metering signal to be supplied to the fuel metering device (11), changing of the loading factor (FTEAD), starting from its present value, in a manner dependent on the respectively present value of the lambda control factor (FR), in such a way that it is reduced whenever a lean overall mixture (FR>1) results when the tank venting valve is open and that it is increased whenever a rich overall mixture (FR<1) results when the tank venting valve is open.
2. Device for carrying out the method according to Claim 1, having

   - Means (17, 16, 15) for lambda control

   - a flow-determining means (33) for determining the maximum possible gas flow through the completely opened tank venting valve under the pressure conditions prevailing in a respective operating state, from intake pressure to ambient pressure (PSAUG/PAMB),

   - a regenerating pre-control value memory (30), which in dependence on operating parameters of the internal-combustion engine (n, TL) stores pre-control values of a variable which is a measure of a required regenerating fuel quantity, i.e. a quantity of fuel to be supplied via the tank venting,

   - a compensating means (37, 38, 14) for compensating for the influence to be expected in the case of a correctly assumed loading factor (FTEAD) of the quantity of fuel supplied via the tank venting on the overall fuel balance by a compensation step (means 14) performed in addition to the lambda control intervention (means 16),

   - a recalculating means (36) which recalculates the modified pre-control values into a setting value (TAU) for the actuator (51) for the tank venting valve,

   characterized by the following further means

   - a loading control means (31), which outputs an initially assumed loading factor (FTEAD), which designates the proportion of the fuel mass (regenerating fuel quantity) of the quantity of the tank venting mixture (gas flow through the tank venting valve) and which loading control means modifies the said pre-control values by division by the said loading factor and which loading control means changes the said loading factor (FTEAD), starting from its present value, in a manner dependent on the respectively present value of a lambda control factor (FR) in such a way that it is reduced whenever a lean overall mixture (FR>1) results when the tank venting valve is open, and that it is increased whenever a rich overall mixture (FR<1) results when the tank venting valve is open,

   - a division means (34), which divides the modified pre-control values by the maximum possible gas flow (VREGO) through the tank venting valve.
3. Device according to Claim 2, characterized in that the flow-determining means (33) exhibits a flow characteristics memory (49) which stores values for the maximum possible gas flow at a predetermined pressure ratio (PSAUG/PAMB), addressibly via predetermined values of the pressure ratio.
4. Device according to one of Claims 2-3, characterized in that the flow-determing means (33) exhibits an intake pressure characteristics memory (47) which stores values for the intake pressure (PSAUG) behind the throttling valve (27), addressibly via predetermined values of a load variable (TL).
5. Device according to one of Claims 2-4, characterized in that the flow determing means (33) is supplied with values indicating the ambient pressure (PAMB).
6. Device according to one of Claims 2-5, characterized by a special-condition stage (55) which sets the loading control means (31, 40) to predetermined operating conditions when predetermined operating conditions occur.
7. Device according to one of Claims 1-6, characterized in that the recalculating means (36) calculates pulse duty factor values (TAU) in such a manner that, with an opening pulse duty factor of greater than 50 %, the opening time for the tank venting valve is kept at the minimum possible value for proper operation and the closing time is varied and that, with an opening pulse duty factor of less than 50 %, the closing time is kept at the minimum possible value for proper operation and the open time is varied.
8. Device according to Claim 7, characterized in that the recalculating means (36) limits the pulse frequency to a minimum value and, when it is reached, lowers the open time or the closing time below the said respective minimum value for proper operation, depending on the pulse duty factor which is currently required.

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