EP0191170B2 - Fuel vapour purging device for a fuel tank - Google Patents

Description

State of the art

The invention relates to a device according to the preamble of claim 1. In a known device of this type (US-A-4 275 697), the composition of the exhaust gas-sensing lambda probe is used to control tank ventilation valves in such a way that depending on the signal of the lambda probe such valve is opened or closed continuously. The tank ventilation valve is 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.

DE-A-2 633 617 discloses a combination of precontrol and regulation of setting variables in internal combustion engines, but without going into the special conditions when venting fuel tanks.

What is remarkable in all known embodiments of tank ventilation systems, however, is the dependence 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 intended 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 processing 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 the tank ventilation off 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 any major influence and ultimately, namely indirectly via the reaction of the λ probe, affect the mixture composition, albeit with a time delay and below Circumstances, roughly corrected.

The publications mentioned are examples of the fact that in the operation of internal combustion engines, efforts are made not only to vent the fuel vapors into the open due to and depending on certain parameters (fuel temperature, quantity, vapor pressure, air pressure, flushing quantity ...) , but to feed the internal combustion engine again; Usually so that the aforementioned, filled with activated carbon 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. In this context, it is also known to prevent or minimize an increase in the exhaust gas emission that is possible due to such an additional quantity of fuel / air mixture attributable to the tank ventilation, by permitting the tank ventilation only in certain operating states of the internal combustion engine (see Bosch "Motronic" - Technical Description C5 / 1 of August 1981; DE-OS-2 829 958).

The intermediate storage container containing the activated carbon filter is able to store fuel vapors up to a certain maximum quantity, 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. Therefore, if you only allow the buffer to be flushed under certain operating conditions, an additional fuel-air mixture that is attributable to this tank ventilation results, which, as a mixture that has not been measured or cannot be measured with reasonable effort, results in the fuel metering signal that is normally produced very precisely with a high level of computation a fuel injection system, the duration of the injection control command t _i - and the resulting quantity of fuel supplied to the internal combustion engine falsifies. 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 refers to 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 to provide a device which in terms of its proportions or its quantities, the tank ventilation mixture, which cannot be predetermined, can be fed to the intake tract of the respective internal combustion engine in such a way that, on the one hand, there is an effective ventilation of the intermediate storage, but on the other hand no disturbing influence on the fuel metering device operating under the guidance of a λ regulation the internal combustion engine results.

Advantages of the invention

The invention solves this problem with the characterizing features of claim 1 and has the decisive advantage that the tank ventilation influence is removed from the area of arbitrary connections and is deliberately fine-tuned to the respective internal combustion engine behavior with continuous change of the maximum quantity to be supplied, the tank ventilation depending on in internal combustion engines already existing λ control of the operating mixture is controlled and regulated so that negative influences neither on the driving behavior nor on the basic control of the fuel supply are possible.

It is particularly advantageous to control the tank ventilation in the sense of a pre-control from a load-speed map, this pre-control then being made even more dependent on the λ control factor.

It is also particularly advantageous to introduce an additional limit value control, or one that is effective solely in connection with the load-speed characteristic map, around the limit value of a minimally permissible λ control factor.

The tank ventilation valve in the tank ventilation line between the filter and the suction tract is controlled periodically by the assigned control unit, the period resulting from the change between opening and closing the valve and a variation of this ratio of opening time to closing time (which corresponds to the duty cycle of the tank ventilation control) appropriate adjustment of the tank ventilation mixture amount can be achieved. In this way, tank ventilation can also be included and implemented in the overall behavior of the internal combustion engine over a wide range depending on the λ control factor.

Advantageous further developments and improvements of the device specified in the main claim are possible through the measures listed in the subclaims.

drawing

Exemplary embodiments of the invention are shown in the drawing and are explained in more detail in the following description. 1 shows the basic principle of tank ventilation with tank ventilation valve with a continuously changeable opening cross section and electronic control unit, FIG. 2 shows the approximately linear course of the characteristic curve of the tank ventilation valve over the pulse duty factor of the control pulse sequence, Control pulse sequence for the tank ventilation valve via load and speed, Fig. 4 shows the characteristic curve of the mean value of the lambda control factor for lambda control-dependent control of the tank ventilation, Fig. 5 characteristic curves of the duty cycle, tank ventilation and lambda control factor over time each with pure control via the tank ventilation Map and additionally with a control dependent on the mean value of the lambda control factor, FIG. 6 the characteristic curve course of the duty cycle of the control pulse sequence, the tank ventilation and the mean value of the lambda control factor over time at pre-control via the tank venting map and additional limit control, Fig. 7 shows the block diagram schematic of the tank ventilation with pilot control map and optional supplementary engagement of a lambda control dependent control and a threshold control.

Description of the embodiments

1 shows a fuel tank or tank 10 which is vented and vented exclusively via an activated carbon filter located in a temporary storage tank 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 while the internal combustion engine is running - 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 control of the tank ventilation valve 13 takes place on its magnetic part 13a by a control device 14, this one Control pulse sequence outputs with variable duty cycle 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 specific 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 of 2 <Q ≦ 4 m³ / h and a minimum throughput at the same pressure difference of 0 <Q ≦ 0.1 m³ / h at a pressure difference Δp = 20 mbar, in this preferred exemplary embodiment the one that can be produced via the pulse duty factor Variation between Qmin and Qmax is 1:20. A corresponding characteristic curve is shown qualitatively in FIG. 2.

For the further functions of the tank ventilation TE, reference is made to the block diagram of FIG. 7; Here, a first embodiment, which is independent of other, possibly supplementary and supportive control and regulation options for tank ventilation, has inventive importance, the control of the tank ventilation valve via a tank ventilation map or pilot control map, which is dependent on the load (shown as pilot control Injection pulse t _L here a fuel injection system) and the speed n via 4x4 support points with the possibility of interpolation each outputs quantized duty cycle variables and feeds, for example, a multiplier 15 for the tank ventilation valve control. In the illustration in FIG. 7, such a pilot control map is denoted by 16 and shown in FIG. 3 as a diagram, the map being designed so that the percentage enrichment of the combustion mixture supplied to the internal combustion engine is the same in all areas for a given TE mixture .

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 the Possible application with any fuel metering devices for internal combustion engines.

The duty cycle of the control pulse sequence for the tank ventilation valve can be quantized continuously or in steps of, for example, 10% each in the range between 0 and 100%. In Fig. 7 the control of the further processing point 15 from the pilot control map 16 is shown via a switch S1, which is useful so that in certain operating states (idling, overrun cut-off) the tank ventilation can be completely prevented, if necessary, or also to do without to enable the pilot control map control to take effect other control and regulating methods to be explained below.

7 also shows the lambda control circuit for generating the fuel metering signal of the internal combustion engine 17, in this case a spark ignition internal combustion engine (Otto engine) with injection, in a multiplier stage 18, starting from the output signal of a load sensor (not shown), For example, an air flow meter, and a speed sensor generates a load signal, namely an injection time duration signal t _L and is fed to a further, downstream multiplier stage 19, ultimately for the control of the injection valve or valves. A correction factor F _{R is} applied to the injection time period at the multiplier 19, which is generated as a lambda correction factor behind a comparator 20 from the actual lambda value generated by the lambda probe 21 and a lambda target value from a lambda controller 22.

In one embodiment of the present invention, this lambda correction factor F _R , which is present anyway on the basis of the lambda control loop, is used in order to make possible a lambda control-dependent control of the tank ventilation as well.

For this purpose, the averaged value generated via an intermediate low-pass filter 23 is used F _{R of} the lambda correction factor is used and also reaches a multiplication point 15 for the TE valve control via a characteristic curve block 24.

The characteristic curve of the tank ventilation change or influence above the mean value of the lambda control is again shown separately in FIG. 4 and comprises four support points with interpolation, the basic function being such that an increasing enrichment of the tank ventilation mixture (TE mixture) over the mean value F _{R of} the lambda correction factor is recognized, since this shifts to lower values, and the tank ventilation is closed accordingly by correspondingly changing the duty cycle of the control pulse sequence for the tank ventilation valve.

Finally, the block diagram of FIG. 7 also contains a second possible variant for characteristic curve mean value control, which can be used as an alternative to this and comprises limit value regulation of the mean value of the lambda correction factor. For this purpose, a further comparison point 25 is provided, which has a limit value F _{RGW of} the mean value of the lambda correction factor is supplied, together with the actual value mean value F _{R of} the correction factor. Via a switch S2, the comparison result is sent to a comparator 26, which decides whether the mean value F _{R of} the correction factor is above or below the predetermined limit value; Depending on the result, a downstream integrator 27 is driven as an I controller for limit value control with appropriate polarity, the output signal of which is then likewise fed to the multiplication point 15.

The functions resulting from the possible tank ventilation control method are explained below on the basis of the diagram profiles of FIGS. 5 and 6.

The diagrams on the left-hand side of FIG. 5 show the states that result from the pilot control map 16 with pure control; assume that the duty cycle of the controller is at 0.25 due to the speed and load values; occurs at a predetermined time t 1 (see diagram b) of Fig. 5) a sudden increase in the fuel content in the TE mixture (illustrated by three different curves (1); (2); (3)), then the controller responds Not at all via the pilot control map and the lambda correction factor F _R only shifts accordingly in the direction of a lean mixture as a result of the "fuel cloud" (theoretical step function) in the TE mixture (see c) of FIG. 5), ie the Regulator leans.

This is different with the diagram courses on the right side of FIG. 5; if one also starts with a duty cycle of 0.25 from the map control, then the influence of F _R -dependent control, depending on the fuel cloud in the TE mixture, lower duty cycle values, as shown in (2) and (3); this change in the duty cycle results from the pilot control component above the characteristic block of the mean value lambda control and also shows a less pronounced drop in the lambda correction factor F _R in c).

In contrast, the effect of the limit value control, shown in the diagram curves of FIG. 6 at a), b) and c) without an FR-dependent control, is such that the tank ventilation TE via the duty cycle of the control pulse sequence from the pilot control map of the tank ventilation KFTE of block 16 (maximum) is open (numerical value at a) in Fig. 6: TV = 0.25) until the time t 1 the TE fuel enrichment in this case one assumed value of 100% results (see b) in FIG. 6).

Corresponding to the characteristic curve at c) of FIG. 6 for the lambda correction factor (= solid line following a triangular curve, with the mean value F _{R of} the correction factor is shown in dashed lines in this diagram), the enrichment now caused by the tank ventilation shifts the mean value F _R beyond the limit value GW, which occurs at time t₂. From here, the duty cycle of the drive pulse sequence is (increasingly) closed via the I controller 27, that is, it decreases from the time t 3 to the mean value F _{R has} returned above the limit; from this point in time, the pulse duty factor increases again in accordance with the adjustment of the I-controller 27, whereby multiple oscillations, as shown at c) in FIG. 6, can also result around the limit value GW until the cloud formation has subsided at the point in time t and Average F _R and duty cycle return to previous values.

It is ascertained that the time constant of the I controller 27 for the tank ventilation must be greater than the time constant of the known I controller of the lambda control for the fuel metering or the calculation of the fuel injection pulses, one for the entire speed / load range constant time constant is sufficient for the tank ventilation. Furthermore, a maximum _limitation I _TEmax should be provided for the I controller and the quantization of the I controller should be about four times finer than the output quantization for the pulse duty factor.

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

The overall function of the tank ventilation in accordance with the block diagram representation of FIG. 7 can therefore look like the two following formulas alternatively indicate and the alternatively provided additional control options occur via the mean value of the lambda control or the limit value control in addition to the map control:

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

• 1. Die Ausgabe des Tastverhältnisses TV ist unterbunden (TV = 0), also die Tankentlüftung gesperrt, wenn
  • a) die Lambda-Regelung der Brennkraftmaschine selbst unwirksam ist.
  • b) der Betriebszustand Schubabschneiden vorliegt oder
  • c) gegebenenfalls bei Leerlauf.
• 2. Erfolgt die Kraftstoffzuführung oder -dosierung, etwa bei einer Kraftstoffeinspritzanlage mit adaptiver Vorsteuerung der Lambda-Regelung (LRA), dann würden diese beiden Funktionen (LRA und TE) sich gegenseitig beeinflussen und zu einem Fehlverhalten führen. Die TE ist daher abzuschalten, wenn LRA aktiv ist oder umgekehrt, die adaptive Lambda-Regelung ist abzuschalten, wenn die Tankentlüftung TE aktiv ist.
• 3. Dabei können noch folgende Bedingungen gelten:
  • a) Bei Start mit Motortemperatur T_MOT < 30° und T_ANS < 30° ist die Tankentlüftung TE für ca. 10 Minuten geschlossen; währenddessen ist die erwähnte adaptive Vorsteuerung der Lambda-Regelung (LRA) aktiv.
  • b) Es schließt sich eine TE-Phase von ca. 5 Minuten an, dann wird TE mit Änderungsbegrenzung geschlossen. Unter Beachtung des Korrekturfaktors FR wird dann, wenn die Abweichung ΔF_R > 5 % vom Normalwert F_R = 1 ist, die LRA aktiviert und abgewartet, bis ΔF_R < 5 % ist oder maximal 5 Minuten vergangen sind. Anschließend kann die TE wieder mit Änderungsbegrenzung zugelassen werden.

The following boundary conditions must generally be observed as switch-on conditions:

• 1. The output of the duty cycle TV is prevented (TV = 0), so the tank ventilation is blocked when
  • a) the lambda control of the internal combustion engine itself is ineffective.
  • b) the operating status of thrust cutting is present or
  • c) if necessary at idle.
• 2. If the fuel supply or metering takes place, for example in a fuel injection system with adaptive pilot control of the lambda control (LRA), then these two functions (LRA and TE) would influence one another and lead to incorrect behavior. The TE must therefore be switched off when LRA is active or vice versa, the adaptive lambda control must be switched off when the tank ventilation TE is active.
• 3. The following conditions may also apply:
  • a) When starting with engine temperature T _MOT <30 ° and T _ANS <30 °, the tank ventilation TE is closed for approx. 10 minutes; the aforementioned adaptive feedforward control of the lambda control (LRA) is active.
  • b) A TE phase of approx. 5 minutes follows, then TE is closed with a change limit. Taking the correction factor FR into account, if the deviation ΔF _R > 5% from the normal value F _R = 1, the LRA is activated and waited until ΔF _R <5% or a maximum of 5 minutes have passed. The TE can then be permitted again with a change limit.

Claims (5)

1. Device for purging fuel tanks (10) in the case of internal combustion engines in combination with a fuel metering of the operating mixture, controlled by a λ-control factor, with an intermediate reservoir which accommodates fuel vapours forming, particularly an active carbon filter container (11), and means (14, 13a, 13) for the controlled emission of the tank purging mixture (TE mixture) to the internal combustion engine in dependence on selected operating conditions comprising at least the output signal of a λ probe by changing of the passage opening cross-section of an electrically controlled tank purging valve (13) connected between the intermediate reservoir and the internal combustion engine, characterized in that the passage opening cross-section of the tank purging valve (13) is determined in a controlled manner between predetermined values (0% - 100%) via a set of preliminary control characteristics (16) (Fig. 3) in dependence on load (t_L) and speed (n) and is additionally controlled in a closed effective circuit in dependence on the λ-probe signal, in that the tank purging valve (13), constructed as a solenoid valve, particularly a lifting solenoid, is actuated by a control circuit (14) by means of a clocked actuating pulse sequence, the duty ratio (TVTE) of which is variable for changing the passage opening cross-section, in such a manner that, with an increasing duty ratio, the passage opening cross-section increases continuously and in that, for the λ-probe signal-dependent controlling of the duty ratio (TVTE) in the abovementioned closed effective circuit, either means (23, 24, 15) are provided, which control the duty ratio along a mean value characteristic of the λ-control factor (F_R) in such a manner that an increasing enrichment of the tank purging mixture is detected via the mean value of the λ-control factor (F_R) and the tank purging valve is closed correspondingly by corresponding reduction of the duty ratio, or a comparison location (25) is provided which is supplied with a limit value (GW) of the mean value of the λ-control factor (F_R) and the latter, with a subsequent comparator (26) for determining the sign and an integrator (27) which generates, in continuous adjustment with a predetermined constant, a changing duty ratio for the actuating pulse sequence and supplies it to a multiplier stage (15), to which the duty ratio (KFTE) output by the preliminary set-of-characteristics control is also supplied, in such a manner that, alternatively to the controlling via the mean value of the λ-control factor, a controlling of the mean value of the λ-control factor to a limit value is carried out by means of changing the duty ratio (TVTE) of the actuating pulse sequence, the duty ratio (TVTE) being changed in the direction of a reduction of the opening cross-section when a predetermined limit value (F_RGW) is exceeded by the mean value of the λ-control factor (F_R) and being changed in the direction of an increase of the passage opening cross-section when it goes back (Figure 6).
2. Device according to Claim 1, characterized in that the set of preliminary control characteristics (KVTE) comprises at least 4 × 4 data points with the possibility of interpolation and is designed in such a manner that the percentage enrichment of the combustion mixture is continuously of equal magnitude with the given tank purging mixture.
3. Device according to Claim 1, characterized in that, as alternative to the characteristic-dependent control via the mean value, the basic adaptation remains uninfluenced by the tank purging.
4. Device according to one of Claims 1 to 3, characterized in that a preliminary set-of-characteristics control block (16), which contains duty ratio values for the actuating pulse sequence of the tank purging valve stored, is provided which outputs values, which are predetermined in dependence on load (t_L) and speed (n), of the duty ratio and supplies these values to an intervention location, particularly a multiplier stage (15) (Figure 7).
5. Device according to Claim 4, characterized in that the intervention location (multiplier stage 15) is supplied with a further output signal of a block of characteristics (24) which generates values, which are predetermined in dependence on the variation of the mean value (F_R) of the λ-control factor, of the duty ratio for the sole evaluation or in combination with the information of the set of preliminary control characteristics.

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