EP0470960B1 - Process and device for checking the controllability of a tank ventilation valve - Google Patents

Abstract

A process is described for checking the controllability of a tank ventilation valve through which supplementary air carrying fuel vapours is supplied to the intake zone of an internal combustion engine. This process is carried out by measuring, in the region of the tank ventilation valve, parameters which change when a flow exists through the valve. This is preferably done by comparing the differences between the values of these parameters before and after signalling a command to the valve. The check can also be made dependent on the pressure in the intake zone, as necessary, for instance when required by the sensitivity of the sensors used.

Description

State of the art

The invention relates to a diagnostic method according to the preamble of claim 1 and a diagnostic device according to the preamble of claim 8. A diagnostic method is already known (DE-PS 36 24 441), in which the controllability of a tank ventilation valve and an idle actuator is checked . The tank ventilation valve is arranged in a feed line that connects an intermediate container, which receives fuel vapors from a fuel tank, to the intake area of an internal combustion engine. The intermediate container usually contains an activated carbon filter, which only allows a certain maximum degree of loading, i. H. can only absorb a maximum amount of fuel in the form of fuel vapors.

Therefore it is necessary to rinse it regularly. This is usually done by supplying air to the intake area of the internal combustion engine via the activated carbon filter after actuation of the tank ventilation valve. Since this amount of additional air is enriched with fuel, the higher the degree of loading of the activated carbon filter, the addition thereof leads to a falsification of the air / fuel ratio supplied to the internal combustion engine.

This must then be compensated for by a control loop, a so-called lambda control. Since the control process carried out by the lambda control is normally quite slow, methods have been introduced which redetermine pilot control values for the fuel supply during operation of the internal combustion engine, i. H. learn adaptively (DE-OS 36 39 946). A distinction is made as to whether an existing tank ventilation valve is activated or not, it being assumed that the tank ventilation valve is open or closed depending on the activation.

When carrying out the diagnostic method, which is presented in DE-PS 36 24 441, it is assumed that the additional air quantity that can be supplied through the tank ventilation valve is so weakly enriched with fuel vapors that this additional air (Q _TEV ) is supplied with additional air supplied by the idle actuator (Q _LLR ) is comparable. Through targeted control of the tank ventilation valve and the idle controller that can be controlled by an idle control, responses from the idle control and the lambda control to the functionality of the tank ventilation valve and the idle controller are concluded. For the sake of completeness, it should be mentioned that the functionality of the associated control chains, which essentially consist of the control logic downstream amplifier stages and electrical connection lines, is also concluded. The control chains are no longer explicitly mentioned in the following.

Advantages of the invention

The method according to the invention with the characterizing features of the main claim has the advantage that it works regardless of how much the amount of additional air that can be supplied via the tank ventilation valve is enriched with fuel. That is, that Diagnostic procedures can be used at any time, even if the activated carbon filter and therefore the additional air that can be supplied is heavily loaded with fuel.

This is the case, for example, if the internal combustion engine has not been in operation for a long time. But then it is particularly important to know whether the tank ventilation valve can be activated, since an internal combustion engine tends to malfunction in the cold state when the air / fuel ratio to be supplied deviates from it. In addition, the likelihood that an electromechanically functioning tank ventilation valve will no longer function properly after a long period of inactivity is particularly high.

Since variables are used for the diagnostic method that change when an air / fuel mixture flows through the tank ventilation valve and can be measured in the area of the tank ventilation valve by sensors intended for this purpose, it is not necessary to evaluate reactions of the internal combustion engine or one of its control devices. This means that their functionality is not a prerequisite for the diagnostic method according to the invention.

Furthermore, it should be pointed out that, in the case of the quantities measured by the sensors, it is generally sufficient if only the differences between the quantities measured at the time before and after the activation of the tank ventilation valve are evaluated.

drawing

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

Show it

• Figure 1a: highly schematic in the form of a block diagram of a possible implementation of electronic, electrical and electromechanical regulation and control elements and actuators for the operation of an internal combustion engine, in particular the area of the tank ventilation is indicated with sensors necessary for first embodiments of the diagnostic method.
• FIG. 1b: an enlarged representation of the tank ventilation valve with its inlet and outlet line, as well as a differential pressure sensor necessary for one embodiment,
• FIG. 2: the flow chart of the diagnostic procedure with pressure measurement,
• Figure 3: the flow chart of the diagnostic method with mass flow rate measurement and
• Figure 4: the flow chart of the diagnostic procedure with differential pressure measurement.

Description of the embodiments

The basic idea of the present invention is to carry out an actuator diagnosis for the area of the tank ventilation in the operation of a motor vehicle and with the engine running, in which a real physical reaction results, regardless of the air / fuel ratio of the regeneration gas flow of the activated carbon filter. The diagnosis is based on the fact that actuation of the tank ventilation valve directs an additional air quantity through the activated carbon filter to the intake area of the internal combustion engine and that the flow of this air quantity changes quantities which are registered by sensors upstream and downstream of the tank ventilation valve. Corresponding error states can then be identified in this way.

Before the invention is discussed in the following, it is expressly pointed out that the block diagram shown in FIG. 1, which is based on discrete switching stages, does not limit the invention, but in particular serves to illustrate the basic functional effects of the invention and special functional sequences in one possible way Specify the form of implementation. It is understood that the individual blocks and blocks can be constructed using analog, digital or hybrid technology. Furthermore, it is also possible that they can be combined in whole or in part, corresponding areas of program-controlled digital systems, for example microcomputers, microprocessors, digital or analog logic circuits and the like. The descriptions given below are therefore only to be evaluated as a preferred exemplary embodiment with regard to the overall functional and time sequence, the mode of operation achieved on the respective blocks discussed and with regard to the respective interaction of the sub-functions represented by the individual components, with the references to the respective circuit blocks being evaluated For reasons of better understanding.

In FIG. 1, an internal combustion engine is designated by 10 and its intake area by 11, in which a throttle valve 11a is rotatably arranged. A deflection from the rest position is indicated by the angle α. The other components that ensure the operation of the internal combustion engine are dealt with only to the extent necessary for understanding the present invention and for the basic relationships.

• der Last L der Brennkraftmaschine 10 von einem Luftmengenmesser 13, der eine Stauscheibe, ein Druckmesser, ein Hitzdrahtgeber oder dergleichen sein kann,
• der Drehzahl n von einem Drehzahlgeber 14,
• dem der Brennkraftmaschine zugeführten Luft/Kraftstoff-Verhältnis, das durch das Ausgangssignal einer Lambda-Sonde 15, die im Abgaskanal 16 angeordnet ist und eine Istwert-Angabe über den jeweiligen Betriebszustand der Brennkraftmaschine, genauer über den Sauerstoffgehalt im Abgas vermittelt, bestimmt wird.

An electronic control unit 12, which is usually a microcomputer with a microprocessor, associated memory, power supply and peripheral sensors and actuators, receives multiple operating status data, at least with respect to

• the load L of the internal combustion engine 10 from an air flow meter 13, which can be a baffle plate, a pressure meter, a hot wire sensor or the like,
• the speed n from a speed sensor 14,
• the air / fuel ratio supplied to the internal combustion engine, which is determined by the output signal of a lambda probe 15 which is arranged in the exhaust gas duct 16 and an actual value indication of the respective operating state of the internal combustion engine, more precisely of the oxygen content in the exhaust gas.

From this data and a large number of other supplied information such as temperature, air pressure and the like, the electronic control unit 12 creates an output signal calculated with high accuracy, in the case of a fuel injection system, for example, an injection control command ti for actuating injection valves symbolically represented by 17 in the intake area.

A control unit 18, which is drawn separately for reasons of clarity, is also provided for the tank ventilation, but can also be part of the central microcomputer and which controls the tank ventilation valve 19. This is arranged in a line which leads from an intermediate container 20, which receives vapors from a fuel tank 21, to the intake area 11 of the internal combustion engine at point 22.

• des Drehzahlgebers 14 bezüglich der Drehzahl n,
• bezüglich der Auslenkung α der Drosselklappe 11a,
• eines Sensors 24, der in der Zuleitung des Tankentlüftungsventils 19 angeordnet ist,
• eines Sensors 25, der in der Abgangsleitung des Tankentlüftungsventils 19 angeordnet ist.

To carry out the diagnostic method according to the invention, a diagnostic block 23 is also provided, which is shown separately in FIG. 1, but can also be part of the central microcomputer. This diagnostic block emits a signal via a signal line to the tank ventilation control unit 18, by means of which the usual tank ventilation function is switched off and the diagnostic method is initiated. The diagnostic block receives signals

• of the speed sensor 14 with respect to the speed n,
• with respect to the deflection α of the throttle valve 11a,
• a sensor 24, which is arranged in the feed line of the tank ventilation valve 19,
• a sensor 25 which is arranged in the outlet line of the tank ventilation valve 19.

The sensors 24 and 25 are designed such that they detect quantities that change when an air / fuel mixture flows through the tank ventilation valve 19.

Furthermore, the diagnostic block 23 can also receive a signal from the electronic control unit 12, which only allows the diagnostic method to be carried out. Finally, a signal relating to the load L can also be supplied to the diagnostic block 23 by the air flow meter 13, in particular if the latter is designed as a pressure meter.

The diagnostic block 23, also as part of the microcomputer or of its programming, comprises memories in which the measured values of the sensors 24 and 25 and results of the diagnosis can be stored, and comparison means which can carry out the necessary comparisons of the measurement signals.

A display device 26 can also be actuated by the diagnostic block 23, which, depending on the result of the diagnosis, lights up indicator lamps, for example. It goes without saying that this display can in principle be implemented in any form, including as a letter display, and can also display intermediate values of the diagnosis.

Due to the operation of the internal combustion engine 10, a negative pressure is generated in the intake area 11, ie a pressure pA that is less than Is atmospheric pressure and which depends on operating parameters, such as the speed n and the deflection α of the throttle valve 11a.

In a first version of the present invention, the sensors 24 and 25 are designed such that they measure the pressure in the inlet and outlet line of the tank ventilation valve 19. The sequence of the diagnostic procedure is explained with the aid of FIG. 2.

First of all, such operating parameters are measured on which the pressure in the intake area 11 depends (step 100), such as the rotational speed n and the angle of attack α of the throttle valve 11a. On the basis of the operating parameters, the pressure pA in the intake area 11 of the internal combustion engine 10 is calculated in step 101.

Step 100 can also be designed such that the pressure pA in the suction area 11 is detected by a sensor provided for this purpose; the signal it emits can also be used as a measure of the load state of the internal combustion engine.

In step 102, pA is compared with a maximum permissible pressure pAMAX, which is at most permissible in order to be able to measure a pressure change after activation of the tank ventilation valve 19 by the sensors 24 and 25. If pA is greater than pAMAX, the diagnostic procedure is aborted (103). If, however, pA is less than or equal to pAMAX, the pressures p124 and p125 are measured in step 104 by the sensors 24 and 25, respectively. These values are stored in step 105, and then a control signal AS is sent by the diagnostic block 23 to the tank ventilation control unit 18 submitted (106).

In step 107, pressures p224 and p225 are measured again by sensors 24 and 25, respectively.

$$\text{(2) p25 = p125 - p225}$$

$$\text{(3) p = (p125 - p124) - (p225 - p224).}$$

In step 108, the actual evaluation is carried out by forming difference values, especially by $$\text{(1) p24 = p124 - p224}$$

$$\text{(2) p25 = p125 - p225}$$

$$\text{(3) p = (p125 - p124) - (p225 - p224).}$$

In step 109, the pressure differences from at least one of the equations (1) to (3) are compared with target values. If one or more of these differences are smaller than the associated target values DMIN, an error state is determined in step 111. A multitude of minimum values with respect to equations (1) - (3) are thus designated here by DMIN.

If the measured differences are greater than the associated minimum values, it is concluded that the tank ventilation valve 19 can be activated (110), which can be referred to here as a “good condition”.

The results of the diagnosis (103, 110, 111) can be stored in the memory provided for this purpose, which is part of the diagnosis block 23 and / or can be displayed by the display device 26.

In a second version of the diagnostic method, the sensors 24, 25 are designed such that they measure a mass flow rate Q, usually of an air / fuel mixture, flowing through the inlet or outlet line of the tank ventilation valve.

The process is explained with the help of Figure 3. Steps that proceed as in the first version of the diagnostic procedure are identified exactly as they are, and they are only dealt with to the extent necessary for understanding the procedure.

At the beginning of the method, a variable K = 0 is set in step 200.

If it is determined in step 102 that the pressure in the intake area is less than or equal to a maximum pressure pAMAX, sensors 24 and 25 measure the mass flow in the inlet and outlet line of the tank ventilation valve 19 and store the associated values Q124 and Q125 (Step 204).

If it is found that this flow has a value that deviates significantly from 0, then there is at least one defect in the inlet or outlet line of the tank ventilation valve or in it itself such that the tank ventilation system is leaking or that the tank ventilation valve is open. For a more precise analysis, a variable K = 1 is set in step 205a, and the method is then continued in step 106.

If no noticeable mass flow is determined in step 205, K = 0 remains and the method is continued in step 106.

$$\text{(5) Q25 = Q225 - Q125.}$$

After a renewed measurement of mass flows Q224 and Q225 by sensors 24 and 25, respectively, after actuation of the tank ventilation control unit 18 by the diagnostic block 23, a difference is calculated in step 108, preferably of $$\text{(4) Q24 = Q224 - Q124}$$

$$\text{(5) Q25 = Q225 - Q125.}$$

In step 209, a query is made as to whether the variable K = 1. If yes, that is to say if Q124 and / or Q125 have a value other than 0, the method continues at step 109a.

There the query is made as to whether differences from (3), (4) are smaller than a predetermined minimum value. If so, it follows that the tank ventilation valve is not controllable and that the tank ventilation system is leaking and / or the tank ventilation valve is open (211).

If the query at step 109a shows that differences are greater than or equal to DMIN, this means that the tank ventilation valve can be actuated, but the tank ventilation system is leaking. This leak means that the air / fuel mixture gets outside the tank ventilation system or that the tank ventilation valve was not completely closed before actuation. An exact diagnosis, which will not be discussed further, can be obtained in step 210 through a selective evaluation of the output signals of the sensors 24, 25.

If, however, the variable K is not equal to 1, the question is asked in step 109 as to whether differences from equations (4) and (5) are smaller than the minimum target values DMIN. If "yes", the tank ventilation valve cannot be activated and is closed before and after activation by the diagnostic block 23 (111).

If the query at step 109 is "no", this means that the tank ventilation system is tight in the area which the sensors 24, 25 detect and that the tank ventilation valve can be activated.

This means that according to this variant of the diagnostic method, a "good condition" is inferred.

In the second embodiment of the diagnostic method, DMIN denotes minimum values with respect to equations (4) and (5).

The possible results of the diagnostic method (103, 110, 111, 210, 211) can be stored in the memory provided for this purpose, which is part of the diagnostic block 23 and / or can be displayed by the display device (26).

A possible variation of the second embodiment, which will not be discussed further, uses sensors 24, 25 in such a way that volume flows are measured instead of mass flows.

In addition, it should be pointed out that the two versions of the diagnostic method according to the invention presented so far can also be modified such that one of the two sensors 24, 25 is dispensed with. The number of differences that can be calculated in step 108 naturally decreases accordingly.

A third version of the diagnostic method uses a single 27 (FIG. 1b) instead of the two sensors 24, 25, which outputs an output signal to the diagnostic block 23, which is a measure of the differential pressure between the outgoing and the supply line of the tank ventilation valve 19. The process this version of the diagnostic method is explained with the aid of FIG. 4. Steps which proceed as in the first version of the diagnostic method are designated as in FIG. 2. These are only dealt with to the extent necessary for understanding.

After a pressure pA that is less than or equal to PMAX was determined in step 102, a measurement of the differential pressure p127 between the discharge and the supply line of the tank ventilation valve 19 follows in step 304. The value of this measurement is stored in step 305 and then (106 ) a control signal AS for the tank ventilation valve is emitted to the tank ventilation control unit 18 by the diagnostic block 23.

In step 307, the differential pressure is measured again, which gives the value p227.

und anschließend (109) wird abgefragt, ob diese Differenz kleiner als eine minimal zulässige Differenz DMIN ist, wobei DMIN sich hier speziell auf G1. (6) bezieht.In step 108, differences, in particular, are calculated $$\text{(6) p27 = p227 - p127}$$

and then (109) a query is made as to whether this difference is smaller than a minimum permissible difference DMIN, DMIN specifically referring to G1. (6) relates.

If "yes", the diagnostic method concludes that there is a fault in the control chain of the tank ventilation valve (111), otherwise ("no") the tank ventilation valve has responded to the control signal and a "good condition" is registered (110).

The results from 110 or 111 can then be displayed and / or saved.

The method according to the invention has the particular advantage that it works independently of engine reactions and therefore does not require any restriction of the air / fuel ratio of the flow rate.

Claims (8)

1. Diagnostic method for checking the controllability of a tank venting valve, via which an additional quantity of air charged with fuel vapours can be supplied to the intake area of an internal combustion engine, characterized in that

   - output signals from at least one sensor which detects quantities which can be measured in the inlet and/or outlet line of the tank venting valve and which change when the additional quantity of air flows through the tank venting valve are used as measurement signals,

   - in dependence on at least one of these measurement signals with a given activation signal AS for a control chain associated with the tank venting valve, the controllability of the tank venting valve and/or the state of sealing of the inlet and/or outlet line of the tank venting valve is inferred.

   - and that before the evaluation of measurement signals a check is made whether the pressure pA existing in the intake area of the internal combustion engine is below a maximum permissible value and an evaluation is omitted at a pressure pA above the maximum value.
2. Diagnostic method according to Claim 1, characterized in that, in addition to at least one measurement signal with a given activation signal AS, at least one measurement signal is evaluated before emission of the activation signal AS.
3. Diagnostic method according to Claim 2, characterized in that at least one difference of measurement signals before emission of and with a given activation signal AS is evaluated.
4. Diagnostic method according to Claim 1, characterized in that the pressure pA is calculated by means of operating characteristics of the internal combustion engine, at least the rotational speed and the load.
5. Diagnostic method according to one of Claims 1 to 4, characterized in that the detectable quantities represent pressures in the inlet and/or outlet line of the tank venting valve.
6. Diagnostic method according to one of Claims 1 to 4, characterized in that the detectable quantities represent rates of flow in the inlet and/or outlet line of the tank venting valve.
7. Diagnostic method according to one of Claims 1 to 4, characterized in that the detectable quantities represent differential pressures between inlet and outlet line of the tank venting valve.
8. Device for carrying out a diagnostic method according to one of Claims 1 - 7 for checking the controllability of a tank venting valve via which an additional quantity of air charged with fuel vapours can be supplied to the intake area of an internal combustion engine and which exhibits means which can output activation signals (AS) of the control chain allocated to the tank venting valve, and that means exist for indicating or storing the results of the diagnostic method, characterized in that further means are provided which

   - measure, or calculate from measured quantities, the pressure pA existing in the intake area of the internal combustion engine and compare this pressure with a threshold value and only permit a diagnosis when the pressure pA is below this threshold value,

   - which exhibit at least one sensor which detects quantities in the inlet and/or outlet line of the tank venting valve, which change when the additional quantity of air flows through the tank venting valve,

   - which store values of the output signals of the sensors and compare these values with predetermined values and, as a result, infer an operability of the control chain of the tank venting valve.

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