EP0288090B1 - Fuel vapour purging device for a fuel tank - Google Patents

Description

State of the art

The invention relates to an object according to the preamble of claim 1 or. 15.> In known devices of this type (US-A-4 275 697; US-A-4 013 054) the composition of the exhaust gas λ-probes are used to control tank ventilation valves so that depending on the signal of the λ-probe such valve is opened or closed continuously. The tank ventilation valve is in each case arranged between an intermediate store and the inlet of the internal combustion engine and is electrically controlled; a corresponding, but pneumatically controlled tank ventilation valve is also known from DE-A-2 612 300.

However, it is noteworthy in all known embodiments of tank ventilation systems that are dependent for the output signal of a λ probe or, depending on a fuel control pulse, actuate tank ventilation valves so that the release of vapors from the intermediate storage is always permitted if the output signal of the λ probe results in a lean mixture composition while the tank ventilation valve is closed or almost closed when the λ probe indicates a rich mixture composition. This is to achieve a balancing effect with regard to a steady ratio of the fuel air mixture supplied to the internal combustion engine as a whole, but the treatment of the fuel air mixture via the gasification provided in both US patents remains unaffected by the tank ventilation means. This means that when a correspondingly lean mixture is indicated by the λ probe, the enrichment takes place simultaneously and therefore in parallel via the mixture preparation system and the tank ventilation.

The only difference is the tank ventilation device according to US Pat. No. 4,275,697, which parallelly converts the output signal of the λ probe, which is converted into a clock pulse sequence, and which is originally fed to the solenoid of a control nozzle in the carburetor, in order to ensure a stoichiometric mixture used to switch off the tank ventilation or to keep it to minimum values when either a minimum or a maximum fuel is added via the carburetor. In these two cases, the additional tank ventilation should lead to an undesirable over-greasing of the mixture; in normal operation, the additional fuel quantities coming from the tank ventilation remain without major ones Influence and ultimately, also indirectly, namely indirectly via the reaction of the λ probe, in its effect on the mixture composition, albeit with a time delay and possibly out of phase, are approximately corrected.

The publications mentioned are examples of the fact that efforts are made in the operation of internal combustion engines not only to vent the fuel vapors due to and depending on certain parameters (fuel temperature, quantity, vapor pressure, air pressure, flushing volume ...), but to feed the internal combustion engine again; Usually so that the aforementioned, filled with active hollow buffer is provided, which absorbs the fuel vapors that form, for example when the vehicle is stationary, and feeds it to the intake area of the internal combustion engine via a line. The publications mentioned so far do not contain any adaptive learning systems for the correction of fuel pilot variables. Such an adaptive feedforward control is disclosed, for example, in DE 3341015. There, a lambda control method with adaptive precontrol is described, in which different adaptation processes take place depending on the existing operating state. The problem of the adaptation disruption due to the tank ventilation is not considered. US-A-4 467 769 describes lambda-controlled mixture formation with tank ventilation and adaptive correction of pilot control values for the fuel metering. Depending on the operating parameters, the tank ventilation only takes place in the phases in which the adaptation is at a standstill. In this context it is also known that the tank ventilation is only permitted under certain operating conditions of the internal combustion engine (see Bosch "Motronic" - Technical Description C5 / 1 from August 1981; DE-OS 28 29 958).

The intermediate storage container containing the activated carbon filter is able to store fuel vapors up to a certain maximum amount, the filter being flushed during engine operation by the vacuum developed by the internal combustion engine in the intake tract, for which purpose the filter has an opening to the outside air. Necessarily Therefore, if you only allow the buffer to be flushed under certain operating conditions, there is an additional fuel-air mixture that can be traced back to this tank ventilation, which, as a mixture that is not measured or cannot be measured with reasonable effort, produces the fuel metering signal, which is usually very precisely calculated at great expense - with one Fuel injection system falsifies the duration of the injection control command t _i - and the resulting quantity of fuel supplied to the internal combustion engine. Such an additional amount of fuel, which in particular also influences the driving behavior under certain conditions, which in extreme cases can consist of almost 100% air or 100% fuel vapor as a tank ventilation mixture, is also not acceptable if the influence of this disturbance variable is directly influenced by pneumatic actuators obtains the intake manifold pressure developed by the internal combustion engine or completely excludes the supply of the tank ventilation mixture by means of an electronic on / off control for particularly sensitive operating conditions, such as idling.

The invention is therefore based on the object of providing a device which supplies the tank ventilation mixture, which cannot be predetermined in terms of its proportions or quantities, to the intake tract of the respective internal combustion engine in such a way that, on the one hand, there is effective ventilation of the buffer store, but on the other hand none disruptive influence on the fuel metering for the internal combustion engine operating under the guidance of a λ control results.

Advantages of the invention

The invention solves this problem with the characterizing features of claim 1 or. 15> and has the advantage that, despite the fact that the extent of the tank ventilation influence is beyond a mathematical prediction, the actual fuel metering can still be adjusted to the tank ventilation influence and measures can be taken to adapt the so-called adaptive learning systems (adaptive pilot control systems ) to ensure that the unavoidable, long-term deviations of the controller output in the presence of a tank ventilation, which can only be attributed to this additional influence, do not introduce unwanted input tax corrections per se, which would permanently impair the adaptation behavior overall.

In this way, it is also possible to adaptively pre-control the tank ventilation area, the TE being set to a minimum value at start, overrun fuel cutoff and when the lambda control is inactive; it is also possible to introduce a limit control around the limit of a minimum permissible adaptation value of the tank ventilation.

Basically, the deviation of the control factor from the setpoint value caused by the tank ventilation causes a correction value to run away, which in the present case In this case, however, it is advantageously taken into account in the calculation of the normal injection signal, here based on a fuel injection system, that a constant amount of fuel or air is compensated for regardless of load and speed. In this way it is possible to switch off the influence of the tank ventilation on the lambda control and the associated adaptation of the pilot control of the fuel injection signal. With changes in the tank ventilation mixture composition and with load changes, an impairment of driving behavior can be avoided.

Advantageous further developments and improvements of the device specified in the main claim are possible through the measures listed in the subclaims. It is advantageous here that the tank ventilation valve in the tank ventilation line between the filter and the suction tract is periodically controlled by an associated control device, the period resulting from the change between opening and closing the valve and by varying this ratio of opening duration to closing duration (which is the duty cycle of the Tank ventilation control corresponds) a corresponding adjustment of the tank ventilation mixture amount can be achieved. In this way, tank ventilation can also be incorporated and implemented in the overall behavior of the internal combustion engine over a wide range depending on the lambda control factor.

drawing

Fig. 1

stark schematisiert das Grundprinzip der Tankentlüftung mit Tankentlüftungsventil mit kontinuierlich änderbarem Öffnungsquerschnitt und elektronischem Steuergerät,

Fig. 2

ein Blockschaltbild einer adaptiven Tankentlüftungsregelung mit möglicher Einflußnahme auf die vom Kraftstoffdosiersystem der Brennkraftmaschine zugeführten Kraftstoffmenge,

Fig. 3

Kurvenverläufe über der Zeit des Tankentlüftungsverlaufs, des Tastverhältnisses der Ansteuerimpulsfolge, der adaptiven Vorsteuerung bei Tankentlüftung und des Lambda-Regelfaktors und

Fig. 4

den Bereich der Tankentlüftungsadaption im Lastdrehzahldiagramm.

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

Fig. 1

highly schematized the basic principle of tank ventilation with tank ventilation valve with continuously changing opening cross-section and electronic control unit,

Fig. 2

2 shows a block diagram of an adaptive tank ventilation control with possible influence on the fuel quantity supplied by the fuel metering system to the internal combustion engine,

Fig. 3

Curves over the time of the tank ventilation process, the duty cycle of the control pulse sequence, the adaptive pilot control for tank ventilation and the lambda control factor and

Fig. 4

the area of the tank ventilation adaptation in the load speed diagram.

Description of the embodiments

1 shows a fuel tank or tank 10 which is ventilated and vented exclusively via an activated carbon filter located in a temporary storage container 11, the fuel evaporating from the tank being stored in the activated carbon filter up to a limited maximum amount. This stored fuel is then sucked into the engine by the running internal combustion engine - only the intake area 12 with the throttle valve 12a is shown in FIG. 1.

The metering of the fuel drawn off from the area of the tank ventilation or of the fuel air mixture formed there, the proportions of which cannot be determined, takes place via a special tank ventilation valve 13 in such a way that in all operating states of the system there is no impairment of driving behavior and exhaust gas behavior and no impairment of the control circuits involved in the fuel metering and adaptive systems occurs.

The tank ventilation valve 13 is actuated on its magnetic part 13a by a tank ventilation control (TE) 34, which outputs a control pulse sequence with a variable pulse duty factor TV, whereby a suitable variation of the opening cross section of the tank ventilation system 13 can be set. The characteristic curve of the tank ventilation valve 13 between the minimum throughput Qmin and Qmax over the pulse duty factor can be approximately linear, possibly also exponential, which can be included in the calculation.

The following information relates to special numerical data of a suitable tank ventilation valve with a passage cross-section that can be changed continuously depending on the duty cycle of the control pulse sequence.

The tank ventilation valve is advantageously based on the solenoid principle, which is open when de-energized and controlled by a suitable pulse frequency pulse sequence of 10 Hz. This results in a maximum throughput at a pressure difference Δp = 20 mbar of 2 <Q ≦ 4 m³ / h and a minimum throughput at the same pressure difference of 0 <Q ≦ 0.1 m³ / h, whereby in this preferred exemplary embodiment the variation between Qmin and Qmax that can be produced via the pulse duty factor can be 1:20.

In this context, it is pointed out that the following explanations essentially relate to the application of the tank ventilation to a fuel injection system, so that common names for the injection are used in the following. As a result, however, the invention is not restricted to the assignment to a fuel injection system, but rather includes possible applications with any fuel metering devices for internal combustion engines.

The basic function of a fuel injection system can therefore be such that for the generation of the fuel metering signal in connection with a lambda control circuit in a multiplication stage, starting from the output signal of a load sensor shown, for example an air flow meter, and a speed sensor, a load signal, namely an injection time duration signal t _{L, is} generated and a further, downstream multiplier stage, ultimately for the control of the or injection valves. The second multiplier stage corrects the injection duration with a correction factor F _R , which is generated as a lambda correction factor behind a comparator from the actual lambda value generated by the lambda probe and a desired lambda value from a lambda controller 22, which is shown in FIG. 2 is shown.

The invention now succeeds in also adaptively adapting the tank ventilation TE, in other words, the components, switching means, regulating and control processes involved in the tank ventilation are such that what the tank ventilation brings to the mixture for the internal combustion engine the actual mixture formation is subtracted again, which results in a particular advantage in those mixture preparation systems and fuel injection systems which themselves have an adaptive pilot control for lambda control and in which tank ventilation can therefore cause certain difficulties because this adaptive pilot control (basic adaptation) is customary uses the longer-term deviations of the controller output (lambda controller) as a measure for a correction of the pilot control - the invention makes it possible to maintain the advantages of adapting the pilot control in its extent.

The block diagram of FIG. 2 therefore shows schematically and without going into special detailed solutions, in the upper area the lambda control circuit for the mixture preparation, for example by a fuel injection system with basic adaptation, and in the lower part the extension of this basic principle to an adaptive pilot control of the tank ventilation.

2, the lambda controller 22 connected downstream of the actual value setpoint comparison point 20 for the output signal of the lambda probe generates the lambda correction factor F _R , which leads to an intervention point 19, where, multiplicative and additive, preferably multiplicative, an effective injection time period t _L · π _i · F _i generated by other components of the mixture preparation system, for example fuel injection system, is supplied.

A further intervention in the injection period then takes place at 30; this intervention serves or is represented representatively for adapting the pilot control (basic adaptation). For this purpose, the output signal F _{R of} the lambda controller 22 is smoothed via a low-pass filter 23, that is to say subjected to averaging, and the smoothed or mean value signal F _{R of} the correction factor is led after a comparison point 31 via a switch S3 to the basic adaptation block 32, which is usually a controller. In a downstream multiplier block 33 there is also a multiplication by a normalized speed value; memory (not shown) can also be provided, which temporarily stores the value of the basic pre-control adaptation, for example, for periods during which a lambda signal is not available, for example due to an inactive lambda probe.

The controller 32 for the basic adaptation adjusts its output variable for the multiplicative or additive factor resulting at the point of engagement 30, which originates from it, until the mean value of the output variable of the lambda controller 22 matches the setpoint at the comparison point 31, which is preferably the assumes neutral value 1, corresponds. It is understood that this basic pilot control adaptation can include various correction values - speed-proportional, speed-independent, which, depending on the load state of the internal combustion engine, intervene in the calculated injection period in an additive or multiplicative corrective manner, which is not shown.

The adaptive pilot control of the tank ventilation, which is assigned to the pilot control adaptation of the injection duration, initially comprises a logic circuit or sequence control circuit, which is represented at 34 as representative of all conceivable embodiments, also in software version, and an assigned block 35 for the TE adaptation, which alternatively via the already mentioned switch S3 from the mean value of the lambda correction factor F _{R is} applied. Therefore, in this exemplary embodiment the control factor F _{R is} used to intervene in the tank ventilation, an adaptation to the load value t _L , for example additively, would of course also be conceivable.

Furthermore, block 35 for the TE adaptation passes information from block 34 of the sequence control TE, mainly via the duty cycle of the control pulse sequence for the tank ventilation valve 13, active lambda control, transition to pilot control map and the like. The result of a limit value detection block 36 from the output of the TE adaptation block 35, at which a value of the adaptive pilot control for tank ventilation (ATE) is present, is whether this correction factor ATE (adaptation value) has a negative threshold value (ATEmin) or has reached a positive threshold value ATEpos, which threshold values can also be referred to as fat or lean. The adaptation value ATE passes through an intermediate multiplication stage 37, at which in turn, so that the two intervention values of the basic adaptation and the TE adaptation are equivalent, a standardized speed value is supplied, and via a switch S4 to a further intervention point 38 in the course of the t _i preparation where multiplicative or additive interventions can be made.

A multiplier 39 with a speed value n is then connected downstream, so that a fuel / time-air mass / time mixture information is obtained at an addition point 40, which is then fed to the TE mixture at point 41.

${\text{Q}}_{\text{TE}}{\text{= const · TVTE · (Δp)}}^{\text{1/2}}$

In this case, the tank ventilation line leading the TE mixture from the tank ventilation valve 13 in front of the throttle valve can be connected to the intake tract of the internal combustion engine, as a result of which the amount of the extracted TE mixture remains approximately constant while the cross section of the TE valve 13 remains the same, since the negative pressure in front of the throttle valve in is approximately constant and the amount increases with the root of the negative pressure. In fact, the negative pressure varies somewhat above the load and speed even in front of the throttle valve, so that the opening of the TE valve 13 in the map KFTE = f (n, t _L ) mentioned earlier must be corrected somewhat in order to obtain a constant amount Q _TE to reach. A constant amount is also helpful for adaptive control as it is based on an additive correction value can be compensated. As mentioned, the following equations therefore apply:

${\text{Δp = p}}_{\text{AIR}}{\text{- p}}_{\text{DK}}$

${\text{Q}}_{\text{TE}}{\text{= constTVTE (Δp)}}^{\text{1/2}}$

If the TE mixture was likewise introduced behind the throttle valve - this will be discussed further below with the aid of a table - the vacuum and thus the quantity would vary considerably more so that especially when idling, where the tank ventilation can be particularly troublesome, this amount of TE would be greatest and with increasing load, where it is less and less disturbing, the amount of flushing would be less and less.

Based on the block diagram of FIG. 2, the following basic functions apply.

The deviation of the lambda control factor from the nominal value F _R = 1 causes a correction value to run away, which is included in the calculation of the injection signal in addition to the air quantity, as explained further above, so that a constant fuel or air quantity is compensated for regardless of load and speed (adaptive feedforward control). According to the block diagram of FIG. 2, this then results in

${\text{t}}_{\text{i}}{\text{= (t}}_{\text{L}}{\text{+ ATE · n}}_{\text{O}}{\text{/ n) · π}}_{\text{i}}{\text{F}}_{\text{i}}\text{+ TVTE}$

The tank ventilation is activated at the start, when the overrun is switched off and also set a minimum value when the lambda control is inactive; a defined mixture should enable starting and reinsertion after overrun fuel cutoff.

The further course of the adaptive pilot control for tank ventilation in accordance with the block diagram of FIG. 2, including the information from the pilot control map, is explained in more detail below with the aid of the curves of FIG. 3 "time sequence of the tank ventilation": these functional details are therefore part of the inventive overall concept for the Tank ventilation.

If the lambda control is active, that is to say the switch S5 in front of the lambda controller 22 is closed, and a corresponding signal also reaches the sequence control 34, then the TE control starts softly and the duty cycle of the tank ventilation becomes TVTE, as in b) in 3 shown, ramped, but with change limitation 1, increased starting from a predetermined minimum value TVTEmin1. The slope of the duty cycle of the control pulse sequence for the TE valve is chosen so that the pilot control to be explained further below can compensate for the resulting disturbance in the mixture balance of the internal combustion engine in good time.

The deviation of the lambda control factor caused by this change - compare the curve at a), where a fuel share in the TE mixture of 100% (as required) is assumed at the time of the TVTE increase, from the target value F _R = 1 (compare 3 in the direction bold causes the correction value to run away, which is then included in the calculation of the injection signal in such a way that a constant amount of fuel or air is compensated for regardless of load and speed, so that the adaptive pilot control results in tank ventilation - see also the course of the adaptation value ATE at c) in FIG. 3, which increases to a maximum negative value ATEmax and, as already explained further above in the block diagram in FIG. 2, acts on the lambda control as adaptive pilot control in tank ventilation.

The pulse duty factor is increased until the adaptation value ATE has reached a minimum negative threshold value ATEmin, which can also be referred to as a fat stroke in relation to the adaptation value. A limit control then starts. Before that, the duty cycle TVTE can already have reached a pre-control stop value at t 1, which can result from the pre-control map; therefore, the duty cycle is not changed until the time t₂, at which the negative threshold ATEmin is reached. Then, from t₂, the duty cycle TVTE is decremented until the threshold falls below (in the positive direction) again. From then on, the pulse duty factor is incremented again until the threshold is exceeded again in the negative direction, etc. This results in continuous oscillation around the negative minimum value (limit value control), the change limitation in the adjustment of the pulse duty factor being an integral part (ITE ) works, therefore yields yourself

${\text{TVTE = KFTE (n, t}}_{\text{L}}\text{) - ITE (ATEmin)}$

In general, the operating time of the fuel from the intermediate storage decreases, so that with this limit value control the pilot control value from the map is reached and therefore the pulse duty factor remains constant for a predetermined period of time during which the adaptation value ATE runs from the negative stop in the positive direction.

If the adaptation value reaches a positive threshold value ATEmax, then this means that the filter has been sufficiently rinsed - the two threshold values go to the sequence control 34 via the threshold value block 36 - and the pulse duty factor is then gradually moved to a second minimum value TVTEmin2, namely from time t₃.

At the same time and after reaching this minimum value, it is then possible to enable the basic adaptation via block 32 (= adaptation without TE) by switching switch S3 for a predetermined (programmable) time (on the order of a few minutes).

After this time has elapsed, the TE mixture is checked in that the control sequence just explained begins in block 34 by regulating the duty cycle from the beginning - it should also be pointed out that the duty cycle is reduced with a change limit 2 to the minimum value TVTEmin2, which enables a faster change of the duty cycle to small passage cross-sections of the tank ventilation valve.

This adaptation of the tank ventilation pre-control is expediently limited to a load-speed range which is only effective below the air quantity threshold, as shown in FIG. 4, since it can only be calculated precisely enough in this range. Otherwise, the adapted value ATE is expediently only stored in a memory (not mentioned) assigned to block 35 of the TE adaptation when the engine is running - for use, for example, in the case of a temporarily inactive λ probe, and deleted when the engine is switched off.

The TE precontrol adaptation is interrupted above the range indicated in FIG. 4, and the last adapted value ATE is buffered in the memory (not shown) assigned to block 35. Above the effective range of the TE pilot control adaption according to Fig. 4, so much tank ventilation mixture can be output via the KFTE map that the influence on the lambda control can be neglected (the TE amount is proportional to the air volume), so that basic adaptation in this sub-area can also be effective during the tank ventilation - in other words, the switch S3 is switched to the block 32 in this case, which can also be done by the sequence control 34 by evaluating corresponding load and speed information.

ständnis anhand eines Blockschaltbilds unter Verwendung von Einzelkomponenten erläutert wurde, auch eine softwaremäßige Ausführung der erfindungsgemäßen Einrichtung mittels eines Mikrorechners oder Mikrocomputers ohne weiteres innerhalb des erfindungsgemäßen Rahmens liegt und durchgeführt werden kann; eine solche Ausführungsform stellt für den Fachmann auf dem Gebiet der Kraftstoffzumessung bei Brennkraftmaschinen kein Problem dar, da er notfalls auch Fachleute auf dem Gebiet der Datenverarbeitungstechnik heranziehen kann.The sequence control specified on the next page 11 for the control of the tank ventilation valve in the form of a flow chart indicates the function of the sequence control 34 in software terms. It is therefore understood that, although the invention has been improved for better ver

was explained on the basis of a block diagram using individual components, and a software version of the device according to the invention by means of a microcomputer or microcomputer is easily within the scope of the invention and can be carried out; Such an embodiment is not a problem for the person skilled in the field of fuel metering in internal combustion engines, since he can also call in experts in the field of data processing technology if necessary.

• 1. Zur Erzielung einer konstanten TE-Menge pro Zeit (Variante 1.1) wird die Tankentlüftungsleitung vor der Drosselklappe dem Ansaugtrakt zugeführt, wie weiter vorn schon erläutert. Da in diesem Fall die Menge des abgesaugten TE-Gemisches bei gleichbleibendem Querschnitt des Tankentlüftungsventils in etwa konstant ist, braucht dieses, um die weiter vorn erwähnten Funktionen und Werte zu realisieren, nur eine vergleichsweise kleine Variationsfähigkeit aufzuweisen, zur Einhaltung der Minimal- und Maximalwerte, die bei etwa 1:20 liegt.
  Die weiteren Alternativen der Vorsteuerung sind nach den verschiedenen Bewertungskriterien in Form der weiter vorn schon erwähnten tabellenartigen Entscheidungsmatrix zusammengefaßt (S. 24).
• 2. Um einen konstanten relativen TE-Fehler zu erzielen (Var. 1.2), wird auch hier die Tankentlüftung vor der Drosselklappe eingeleitet. Das Kennfeld wird so ausgelegt, daß die TE-Menge proportional zur Luftmenge ist (bis zu einer bestimmten maximalen Luftmenge, ca. das 10 fache der Leerlaufmenge). Dann ist der relative Fehler in diesem Last- und Drehzahlbereich konstant. Allerdings ist die Spülmenge im Leerlaufgebiet relativ klein; mit:
  
  ${\text{KFTE ∼ (Δp)}}^{\text{-1/2}}{\text{·Q}}_{\text{L}}$
  
  Variation 1:8
  
  folgt:
  
  ${\text{Q}}_{\text{TE}}{\text{= const·Q}}_{\text{L}}$
  
  
  
• 3. Zur Erzielung einer konstanten TE-Menge pro Umdrehung (Var. 2.1) müßte die Einleitung der Tankentlüftung hinter die Drosselklappe im Saugrohr erfolgen, wobei jedoch der Unterdruck wesentlich stärker variieren würde. Bei steigendem Unterdruck ist dann die Strömung nicht mehr laminar, sondern auf jeden Fall turbulent, bis zum Erreichen des kritischen, Druckverhältnisses, bei dem die Strömung die Schallgeschwindigkeit erreicht; bei überkritischem Druckverhältnis ist dann die Menge konstant. Die Berechnung hierfür ist komplex, und die folgenden Angaben stellen lediglich eine grobe Abschätzung dar, die auf der Annahme beruhen, daß die Gleichung nach Bernoulli gilt.
  Dabei muß einerseits das TE-Ventil eine wesentlich größere Variation bewältigen, um die obengenannten Minimal- und Maximalmengen einzuhalten, und zwar eine Variation von 1:110; wegen Q_TEmin/max = 1/20; Δp_min/max = 30/900.
  Andererseits müßte, um zu erreichen, daß der Fehler durch die Tankentlüftung pro Umdrehung konstant ist, das Tankentlüftungskennfeld eine größere Variation aufweisen, was für eine additive Adaption - hier additiv auf t_L) hilfreich ist.
  Es gilt dann näherungsweise:
  
  ${\text{Q}}_{\text{TE}}{\text{= const·KFTE(Δp)}}^{\text{1/2}}$
  
  
  ${\text{Δp = p}}_{\text{LUFT}}{\text{- p}}_{\text{SAUG}}$
  
  
  30 < Δp < 900 mbar
  
  mit KFTE ∼ (Δp)^-1/2/n Variation 1:22 (bei Variation Drehzahl 1:4)
  folgt: Q_TE = const/n → Δt_L = const
• 4. Zur Erzielung eines konstanten Vorsteuerwerts (Variante 2.2)erfolgt die Einleitung der Tankentlüftung ebenfalls im Saugrohr, also hinter der Drosselklappe, wobei bei der einfachsten Vorsteuerung, einem Festwert anstelle des Kennfeldes, Unterdruck und damit die Menge viel stärker variieren würden, so daß gerade im Leerlauf-und Anfahrt-Bereich, wo die Tankentlüftung besonders stört, die Tankentlüftungsmenge am größten wäre, und bei steigender Last, wo die Tankentlüftung immer weniger stört, die Spülmenge immer geringer würde, wie es aus dem seitherigen System bekannt ist. Der Fehler wäre in einem luftmengenmessenden System von verschiedenen Größen wie Last (aus Luftmenge) und Drehzahl abhängig; eine Adaption daher besonders aufwendig, wobei näherungsweise gilt:
  
  Q_TE = const·(Δp)^1/2
  
  Dabei sind die Varianten 1.1 und 1.2 für Systeme geeignet, die einen näherungsweise konstanten Druckabfall vor der Drosselklappe erzeugen (Luftmengenmesser mit Stauklappe). Systeme mit vor allem im Leerlauf sehr kleinem Druckabfall (HLM, Alpha/n, P/n) sind nur mit Variante 2.1 abzudecken. Wenn diese Variante 2.1 der Vorsteuerung der TE gewählt werden muß (additiv auf t_L), sind entsprechende Maßnahmen einzusetzen. Die Einrechnung der TE-Adaption erfolgt dann additiv auf t_L, der Adaptionsbereich ist dann durch eine t_L-Schwelle nach oben zu begrenzen.

The following variants of the pilot control of the tank ventilation are also mentioned and are clearly summarized in the table on page 24.

• 1. To achieve a constant amount of TE per time (variant 1.1), the tank ventilation line in front of the throttle valve is fed to the intake tract, as already explained earlier. In this case, since the amount of extracted TE mixture is approximately constant with the cross-section of the tank ventilation valve remaining the same, in order to implement the functions and values mentioned above, it only needs to have a comparatively small variability to comply with the minimum and maximum values, which is around 1:20.
  The other pre-control alternatives are summarized according to the various evaluation criteria in the form of the table-like decision matrix mentioned earlier (p. 24).
• 2. In order to achieve a constant relative TE error (Var. 1.2), the tank ventilation in front of the throttle valve is also initiated here. The map is designed so that the TE quantity is proportional to the air volume (up to a certain maximum air volume, approx. 10 times the idling volume). Then the relative error in this load and speed range is constant. However, the amount of flushing in the idle area is relatively small; With:
  
  ${\text{KFTE ∼ (Δp)}}^{\text{-1/2}}{\text{· Q}}_{\text{L}}$
  
  Variation 1: 8
  
  follows:
  
  ${\text{Q}}_{\text{TE}}{\text{= const · Q}}_{\text{L}}$
  
  
  
• 3. To achieve a constant TE quantity per revolution (Var. 2.1), the tank ventilation would have to be introduced behind the throttle valve in the intake manifold, although the vacuum would vary considerably more. When the vacuum increases, the flow is no longer laminar, but in any case turbulent, until the critical pressure ratio is reached, at which the flow reaches the speed of sound; at a supercritical pressure ratio, the quantity is constant. The calculation for this is complex, and the following information is only a rough estimate based on the assumption that the Bernoulli equation holds.
  On the one hand, the TE valve has to cope with a much larger variation to the above Observe minimum and maximum quantities, namely a variation of 1: 110; because of Q _{TEmin / max} = 1/20; Δp _{min / max} = 30/900.
  On the other hand, in order to ensure that the error caused by the tank ventilation per revolution would have to be constant, the tank ventilation map would have to have a greater variation, which is helpful for an additive adaptation - here additive to t _L ).
  The following then approximately applies:
  
  ${\text{Q}}_{\text{TE}}{\text{= const · KFTE (Δp)}}^{\text{1/2}}$
  
  
  ${\text{Δp = p}}_{\text{AIR}}{\text{- p}}_{\text{SUCTION}}$
  
  
  30 <Δp <900 mbar
  
  with KFTE ∼ (Δp) ^-1/2 / n variation 1:22 (with variation speed 1: 4)
  follows: Q _TE = const / n → Δt _L = const
• 4. To achieve a constant pilot control value (variant 2.2), the tank ventilation is also initiated in the intake manifold, i.e. behind the throttle valve, whereby with the simplest pilot control, a fixed value instead of the map, the vacuum and thus the quantity would vary much more, so that straight in the idle and start-up area, where the tank ventilation is particularly troublesome, the tank ventilation amount would be greatest, and with increasing load, where the tank ventilation is less and less disturbing, the amount of flushing would decrease, as is known from the system since then. In an air volume measuring system, the error would depend on various variables such as load (from air volume) and speed; an adaptation is therefore particularly complex, the following roughly applies:
  
  Q _TE = const · (Δp) ^1/2
  
  Variants 1.1 and 1.2 are suitable for systems that generate an approximately constant pressure drop in front of the throttle valve (air volume meter with damper). Systems with a very low pressure drop (especially when idling) (HLM, Alpha / n, P / n) can only be covered with variant 2.1. If this variant 2.1 of the pre-control of the TE has to be selected (additive to t _L ), appropriate measures must be taken. The TE adaptation is then calculated additively to t _L , the adaptation range is then to be limited by a t _L threshold.

Claims (15)

1. Method for venting fuel tanks in internal combustion engines or the like, the mixture composition of which is determined by a lambda closed-loop control with precontrol adaptation, and in which the fuel vapours forming in the fuel tank are collected in an activated-carbon filter canister and released in controlled fashion to the internal combustion engine as tank venting mixture as a function of selected operating conditions comprising at least the output signal of a lambda probe by continuous variation of the cross-section of a passage opening of an electrically controlled tank venting valve switched between the intermediate store and the internal combustion engine, characterised in that

   - to compensate the influence of the tank venting mixture on the composition of the overall mixture, an adaptation factor (ATE) is formed as a function of the averaged lambda control factor,

   - the adaptation factor (ATE) influences the basic injection quantity additively or multiplicatively,

   - the adaptation factor (ATE) is compared (36) to one or more values

   - and, depending on the result of the comparison, a reduction or enlargement of the cross-section of the passage opening of the tank venting valve is performed.
2. Method according to Claim 1, characterised in that the adaptive tank venting by influencing the calculated value of the fuel quantity is furthermore dependent on the load (t_L) and/or the speed (n) of the internal combustion engine in the sense of a limitation to a predetermined load/speed range.
3. Method according to Claim 1 or 2, characterised in that the adaptation is effected multiplicatively or additively per unit time to the air quantity (Q_L) or additively to the injection quantity/stroke or to load signal (t_L).
4. Method according to Claim 1, 2 or 3, characterised in that, at certain values of air flow rate and speed, the averaged output signal as λ control factor F _R of the λ controller (22) is switched between a basic adaptation block (32) for the adaptive corrective influencing of the calculated fuel quantity and a tank-venting adaptation block (35) for the issuing of an adaptation value (ATE) of the tank venting, with the result that the basic adaptation remains unaffected by the tank venting.
5. Method according to Claim 4, characterised in that a sequence control circuit (34) is provided for adaptive precontrol in the case of tank venting, said circuit also driving the tank-venting adaptation block (35), starting from which the precontrol adaptation value (ATE) intervenes in the calculation process for the fuel quantity to be fed to the internal combustion engine, with the result that a constant fuel or air quantity per unit time is compensated irrespective of load and speed.
6. Method according to Claim 5, characterised in that a limiting-value detection block (36) which responds at predetermined maximum and minimum values (ATE_max, ATE_min) of the adaptive precontrol correction value in the case of tank venting (ATE) and drives the sequence control circuit (34) in the sense of a correspondingly directed alteration of the duty factor (TVTE) is provided.
7. Method according to one of Claims 4, 5 or 6, characterised in that in the case of active λ closed-loop control, the duty factor (TVTE) of the drive pulse sequence for the tank venting valve (13) is increased in the form of a ramp with a predetermined first alteration limit, starting from a minimum value (TVTE_min1), until a negative maximum threshold value ATE_min of the adaptation value (ATE) is reached, with a resulting in reduction of the duty factor of the drive pulse sequence until the undershooting of the threshold value and a subsequent gradual increase, to form a sustained oscillation around the negative minimum threshold value (ATE_min) - limit control.
8. Method according to Claim 7, characterised in that as the rise in the adaptation value (ATE) from the negative stop in the positive direction proceeds, the duty factor (TVTE) of the drive pulse sequence is held constant at a predetermined value, preferably a value stemming from the precontrol characteristic map, and, when a positive maximum stop value (ATE_max) is reached, an alteration of the duty factor, preferably with a second, steeper alteration limitation, is initiated, with simultaneous enabling of the basic adaptation in the λ control loop of the fuel-quantity calculation, in particular injection-signal calculation.
9. Method according to Claim 8, characterised in that, following the enabling of the basic adaptation corresponding to an adaptation without tank venting, a recheck of the tank venting mixture is effected for a fixed, predetermined, programmable time by increasing the duty factor in a controlled fashion.
10. Method according to one of Claims 5-9, characterised in that the tank-venting precontrol adaptation is limited to a predetermined load/speed range effective below a particular air flow rate limit and below a particular speed limit, and above this range, upon interruption of the tank-venting precontrol adaptation and enabling of the basic adaptation for the fuel-quantity calculation, the determination of the duty factor for the release of the tank venting mixture is effected via the stored characteristic map as a function of the speed and load.
11. Method according to Claim 10, characterised in that, upon transition from the range of the tank-venting precontrol adaptation into the controlled characteristic map range of the tank-venting mixture delivery, a temporary storage of the last adaptation value (ATE) is effected, with which value the adapted tank venting precontrol starts after the return to the adaptation range.
12. Method according to one of Claims 7-11, characterised in that the tank-venting mixture quantity is formed proportionally to the air quantity and the adaptation acts multiplicatively.
13. Method according to one of Claims 7-11, characterised in that the tank-venting mixture quantity is formed additively per stroke irrespective of the speed and the adaptation acts additively on the calculated precontrol injection signal (t_L).
14. Method according to Claim 13, characterised in that the range of adaptation is limited at the top by a t_L threshold (Fig. 4).
15. Device for venting fuel tanks in internal combustion engines or the like and for carrying out the method according to one of Claims 1-14, the mixture composition being determined by a lambda closed-loop control with precontrol adaptation, and in which the fuel vapours forming in the fuel tank are collected in an activated-carbon filter canister and released in controlled fashion to the internal combustion engine as tank venting mixture as a function of selected operating conditions comprising at least the output signal of a lambda probe by continuous variation of the cross-section of a passage opening of an electrically controlled tank venting valve switched between the intermediate store and the internal combustion engine, characterised in that

    - there are means (23, 31, S3, 35) for the formation of an adaptation factor (ATE) as a function of the averaged lambda control factor in order to compensate the influence of the tank venting mixture on the composition of the overall mixture,

    - in that, furthermore, there are means (38) for the additive or multiplicative influencing of a basic injection quantity by the adaptation factor (ATE) and

    - means (36) for comparing the adaptation factor (ATE) to one or more values

    - and means which, depending on the result of the comparison, perform a reduction or enlargement of the cross-section of the passage opening of the tank venting valve.

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