EP0578795B1 - Process and device for testing the operativeness of a tank ventilation system - Google Patents

Abstract

A process for testing the operativeness of a tank ventilation system in a vehicle with an internal combustion engine which has a pressure sensor fitted in the tank, an adsorption filter connected to the tank via a line and a tank ventilation valve connected to the adsorption filter via a valve line, in which system the adsorption filter has a ventilation line which can be closed off by a stop-valve. The process makes use of the knowledge that both the build-up and the decrease gradient for the underpressure in the tank depend substantially similarly on the level in the tank. If, for instance, the quotient of the build-up and decrease gradient is used as the evaluation quantity, it is therefore substantially independent of the level, permitting a very reliable comparison with a threshold value. If the build-up/decrease gradient quotient is found to be greater than the threshold value, the system is regarded as non operative. This procedure makes it possible to detect leaks with diameters of the order of 2 mm.

Description

The following relates to a method and a device for checking the functionality of a tank ventilation system on a vehicle with an internal combustion engine.

State of the art

• es wird untersucht, ob ein Betriebszustand vorliegt, z. B. Vollast, bei dem im Tank nach Schließen des Absperrventils und öffnen des Tankentlüftungsventils kein wesentlicher Unterdruck aufgebaut werden kann;
• liegt ein derartiger Zustand vor, wird das Verfahren abgebrochen, andernfalls schließen sich die folgenden Schritte an:
• Schließen des Absperrventils;
• öffnen des Tankentlüftungsventils;
• Messen des sich im Tank aufbauenden Unterdrucks; und
• Beurteilen der Tankentlüftungsanlage als nicht funktionsfähig, wenn ein vorgegebener Unterdruck nicht erreicht wird.

From DE-A-40 03 751 or from DE-A-4030948 a tank ventilation system is known which has a tank with a tank pressure sensor, an adsorption filter connected to the tank via a tank connection line and a tank ventilation valve which is connected to the adsorption filter via a valve line is in which system the adsorption filter has a ventilation line that can be closed by a shut-off valve. The tank ventilation system constructed in this way is checked for functionality using the following procedure:

• it is examined whether there is an operating state, e.g. B. full load, in which no significant negative pressure can be built up in the tank after closing the shut-off valve and opening the tank ventilation valve;
• if such a condition exists, the process is terminated, otherwise the following steps follow:
• Closing the shut-off valve;
• opening the tank vent valve;
• Measuring the negative pressure building up in the tank; and
• Assess the tank ventilation system as not working if a given vacuum is not reached.

• öffnen des Tankentlüftungsventils;
• Bestimmen des Aufbaugradienten des sich im Tank aufbauenden Unterdrucks; und
• Vergleichen des Aufbaugradienten und/oder des Abbaugradienten mit einem jeweils zugehörigen Schwellenwert und Beurteilen der Anlage als funktionsfähig, wenn der mindestens eine Gradient und der zugehörige Schwellenwert eine vorgegebene Beziehung erfüllt.

In the document DE-A-41 11 361, which does not pre-publish and belongs to an application with an older seniority, a method is described which works on a tank ventilation system without a shut-off valve and has the following method steps:

• opening the tank vent valve;
• Determining the build-up gradient of the negative pressure building up in the tank; and
• Comparing the build-up gradient and / or the build-up gradient with a respective associated threshold value and assessing the system as functional if the at least one gradient and the associated threshold value fulfill a predetermined relationship.

A similar method is described in the document DE-A-41 32 055, which also belongs to another application with an older seniority and is not prepublished, but is carried out on a tank ventilation system with a shut-off valve. Measurements to determine the build-up and breakdown gradient are only taken into account if it is ensured that the measurements are not influenced by gassing fuel. For this purpose, a lean correction test with the help of a lambda controller and / or a check is carried out to determine whether the vehicle, and thus also the tank content, is probably moving.

It has been shown that the previously known and proposed methods have to be refined further in order to be able to detect very small leaks of the order of 2 mm.

Presentation of the invention

• Schließen des Absperrventils;
• öffnen des Tankentlüftungsventils;
• Bestimmen des Aufbaugradienten des sich im Tank aufbauenden Unterdrucks;
• Schließen des Tankentlüftungsventils;
• Bestimmen des Abbaugradienten des sich im Tank abbauenden Unterdrucks;
• mathematisches Verknüpfen des Aufbau- und des Abbaugradienten in solcher Weise, daß sich der Einfluß des Füllstandes auf die durch die Verknüpfung gebildete Beurteilungsgröße möglichst wenig auswirkt; und
• Vergleichen des Werts der Beurteilungsgröße mit einem Schwellenwert und Beurteilen der Anlage als nicht funktionsfähig, wenn der Wert der Beurteilungsgröße und der Schwellenwert eine vorgegebene Beziehung erfüllen.

The method according to the invention for checking the functionality of a tank ventilation system of the type mentioned at the outset has the following steps:

• Closing the shut-off valve;
• opening the tank vent valve;
• Determining the build-up gradient of the negative pressure building up in the tank;
• Closing the tank vent valve;
• Determining the degradation gradient of the negative pressure reducing in the tank;
• mathematically linking the build-up and degradation gradients in such a way that the influence of the fill level has as little effect as possible on the assessment variable formed by the link; and
• Comparing the value of the evaluation quantity with a threshold value and judging the plant as inoperable if the value of the evaluation quantity and the threshold value fulfill a predetermined relationship.

The device according to the invention has a sequence control for actuating the shut-off valve and the tank ventilation valve; gradient determining means for determining the gradients just mentioned; a judgment quantity formation device for forming the quotient just mentioned and a comparison / judgment device for making the comparison just mentioned and the associated assessment.

It is pointed out that when the following is used to speak of gradients in the build-up or reduction of negative pressure, positive (absolute) values are almost always meant. Only Figures 2a and 2b relate to these gradients below Consideration of the sign.

It has been shown that the method according to the invention provides assessment results which are hardly influenced by the fill level of the tank. When the tank is almost full, both gradients are quite high, while when the tank is almost empty they are both quite low. The relative changes of both gradients as a function of the fill level of the tank depend essentially on the fill level, so that the effects exerted by the fill level on the gradients are essentially canceled out by the formation of the quotient.

In a preferred embodiment, the quotient degradation gradient / buildup gradient is formed, and the system is judged to be inoperative if the quotient is greater than the stated threshold value. If there is a leak in the system, the degradation gradient becomes relatively large and the buildup gradient relatively small, as a result of which the quotient rises above the threshold value. If the system is blocked, the build-up gradient becomes very small, whereas there is no particular effect on the build-up gradient, so that the quotient also rises above the threshold value because of the small denominator.

Theoretically, the procedure is most precise when it is carried out with the vehicle at a standstill and the fuel out of gas. Gassing the fuel, be it through elevated temperature or through movements of the tank contents, influences the gradients in the same way as a leak and thus falsifies the measurement. During the build-up of the negative pressure, if the method is carried out on an internal combustion engine with a lambda regulator, it can easily be determined with the aid of a conventional lean correction test whether the fuel is gassing. It has been found that the gradient determination of gassing fuel even then is not significantly affected if the gassing can already be clearly determined with the lean correction test, e.g. B. by a correction in the range of 5 to 10%. The test method according to the invention is therefore preferably developed such that a lean correction test is carried out and the test method is terminated if lean correction is to be carried out which is stronger than a threshold lean correction.

A lean correction check is not possible while the vacuum is being reduced because the tank ventilation valve is closed. However, if no lean correction was required during the vacuum build-up and the vehicle is stationary during dismantling, the fuel is unlikely to gas. Standstill of the vehicle is therefore measured directly by appropriate signals, e.g. B. speed or acceleration measurement, or it is indirectly concluded to drive, z. B. from load signals or clutch / gear position signals. However, immediately after the last measurement to determine the degradation gradient, the tank ventilation valve can be opened again and it can be examined whether a lean correction is necessary. If this is not the case, it is assumed that the degradation gradient was not influenced by gassing fuel. However, it cannot be ruled out that the tank pressure was influenced by volume increases and decreases due to sloshing fuel. Such fluctuations cancel each other out over time and can accordingly be taken into account by time averaging the pressure measured to determine the degradation gradient.

drawing

• Fig. 1: Block diagram of a tank ventilation system with device to check the functionality of the same by evaluating a quotient degradation gradient / buildup gradient relating to the negative pressure in the tank;
• 2A and 2B: Diagrams relating to negative pressure change gradients or quotients from change gradients depending on different tank fill levels;
• 3a, 3b: flow chart for explaining a method for checking the functionality of a tank ventilation system;
• 4 and 5: partial flow diagrams relating to variations in the sequence according to FIG. 3.

Description of exemplary embodiments

The u. a. The tank ventilation system shown has a tank 10 with a differential pressure meter 11, an adsorption filter 13 connected to the tank via a tank connection line 12, with a ventilation line 14 with an inserted shut-off valve AV, and a tank ventilation valve TEV, which is inserted into a valve line 15 which connects the adsorption filter 13 with the suction pipe 16 an internal combustion engine 17 connects. The tank ventilation valve TEV and the shut-off valve AV are controlled by signals as they are output by a sequence control block 19. The tank ventilation valve TEV is also activated depending on the operating state of the engine 17, but this is not illustrated in FIG. 1.

A catalytic converter 20 with a lambda probe 21 located in front of it is arranged in the exhaust duct 30 of the engine 17. The latter sends its signal to a lambda control block 22, which determines an actuating signal for an injection device 23 in the intake manifold 16 and also outputs a lean correction signal MK.

The functionality of the tank ventilation system is assessed with the aid of a gradient determination block 24, a quotient calculation block 25 and a comparison / assessment block 26.

The sequence controller 19 starts a sequence for checking the functionality of the tank ventilation system as soon as an idling signal generator 27 cooperating with the throttle valve 28 of the engine indicates idling and an adaptation phase has ended. Adaptation phases for achieving learning processes in the lambda control block 22 alternate with tank ventilation phases; the former typically last 1.5 minutes, the latter 4 minutes. The sequence control then closes the shut-off valve AV and opens the tank ventilation valve TEV in such a way as is permitted in the context of a conventional tank ventilation; at the same time, it starts a process to be carried out by the gradient determination block 24 for determining the build-up of the negative pressure in the tank 10. As soon as this gradient has been determined, the sequence controller 19 closes the tank ventilation valve TEV and now causes the gradient determination block 24 to determine the reduction gradient for the negative pressure in the tank. As soon as both gradients are determined, the quotient degradation gradient / buildup gradient is calculated in the quotient calculation block 25, and this quotient is compared in the comparison / assessment block 26 with a quotient threshold value Q_SW. If the quotient is above the threshold value, an evaluation signal BS is output, which indicates that the system is not functional. This signal can also be output if the determined lean correction is weaker than a threshold lean correction and the build-up gradient is smaller than a threshold value.

The diagram of FIG. 2A illustrates negative pressure change gradients as they are with a 2.5 l six-cylinder engine at idle with the tank vent valve (flow 0.6 m³ / h) were measured on a tank with 80 l capacity for different fill levels. Two pairs of measured values, each with short lines, are entered for each fill level. The solid lines relate to measurements for the pressure reduction gradient (top) and the pressure build-up gradient (bottom) for a functional tank ventilation system, while the dashed lines represent the corresponding values for a system with a leak of 2 mm in diameter. FIG. 2B shows the quotient degradation gradient / buildup gradient for each gradient pair from FIG. 2A. The following can be seen from the figures. Even when the tank is empty, the build-up gradient with a dense system is still significantly larger than the build-up gradient with a full system, but a leak of 2 mm in diameter. A threshold value ṗ + _SW can therefore be specified, below which it is clear that there is a leak of at least 2 mm in diameter. If the leak is smaller, the quotient shown in FIG. 2B helps further. As can be seen, this is hardly dependent on the fill level. The value that is achieved for a dense system is very different from that for the system with a leak of 2 mm in diameter. A threshold value Q_SW can therefore be specified for the quotient, which is as close as possible to the smallest quotient as it applies to the dense system and which accordingly makes it possible to distinguish between a dense system and one with a small leak.

While a method for checking the functionality of the tank ventilation system was roughly discussed above with reference to the block diagram in FIG. 1 and the diagram in FIG. 2, a sequence is now explained in more detail with reference to the flow diagram in FIG. 3.

The method according to FIG. 3 uses signals from the differential pressure sensor 11. This can be done after opening the tank ventilation valve TEV only show significant changes in negative pressure if there is a high negative pressure in the intake manifold 16 and the tank ventilation valve can be opened relatively widely without influencing the fuel / air budget of the internal combustion engine 17 in a manner which is no longer quick and reliable by the lambda controller 22 could be corrected. These conditions are met with low gassing fuel, especially when idling. It should also be noted that the method described in the following provides particularly good results if the fuel in the tank gasses as little as possible during the measurement. This is especially the case when the fuel in the tank hardly moves. Such a movement is unlikely to occur when the engine is idling. It is therefore assumed for the following that the method of FIG. 3 is only started if idle operation has previously been determined. The vehicle may also be at a standstill. However, it is also possible to allow the engine to operate at medium load, where there is also good pumping action through the tank venting valve TEV, and to check whether the condition of the tank's little movement is satisfied by evaluating the signals from acceleration sensors, as they are e.g. B. are available in vehicles with chassis control.

At the beginning of the method of FIG. 3, the shut-off valve AV is closed (step s3.1) and the differential pressure pA between the pressure in the tank and the ambient pressure is measured (step s3.2). Subsequently, the tank ventilation valve TEV is opened (step s3.3), whereupon a time measurement loop with steps s3.4 to s3.6 follows. In step s3.4 it is examined whether a lean correction above a lean correction threshold is required. If this is the case, a process is achieved from a mark E, which process is described in more detail below. Otherwise, the gas throughput is determined by the tank ventilation valve (step s3.5), and it is queried whether a predetermined time interval Δt has elapsed since the tank ventilation valve opened (step s3.6). If the time period has not yet expired, steps s3.4 to s3.6 are repeated. Otherwise, the pressure p in the tank is measured (step s3.7) and the difference Δp = pA - p between the differential pressures pA and p at the beginning and end of the time period Δt is calculated (step s3.8). This pressure difference is standardized to a predetermined throughput by the tank ventilation valve (likewise step s3.8) in order to obtain a standardized pressure difference Δp_NORM. If the gas throughput totaled when step s3.5 is repeated is less than the predetermined throughput, the measured pressure difference is increased accordingly, otherwise decreased accordingly, which is done in each case by multiplying the measured pressure difference by the quotient of the predetermined and totaled throughput. It should be noted that the gas throughput per unit of time is determined with the aid of the duty cycle for the tank ventilation valve, as specified by the sequence control 19, the negative pressure in the intake manifold 16 and a map which describes the relationship between negative pressure, duty cycle and gas throughput. In this case, vacuum in the intake manifold 16 is either measured by a corresponding sensor or determined from the speed of the engine 17 and the position of the throttle valve 28.

With the aid of the standardized pressure difference Δp_NORM, the negative pressure build-up gradient is determined to be Δp_NORM / Δt (step s3.9), whereupon a comparison is made with a threshold value ṗ + _SW (step s3.10). If the threshold value has not been reached, an error message is output in step s3.11, and an error lamp is illuminated. Then the E mark is reached again.

If a decision about the functionality of the system is not yet possible with the built-up gradient comparison according to step s3.10, the tank ventilation valve is closed in step s3.12 and a new time measurement is started. As soon as a predetermined period of time Δt has elapsed since the tank ventilation valve closed (step s3.13), the negative pressure pE in the tank is measured (step s3.14) and the tank ventilation valve is opened (step s3.15) in order to carry out a lean correction test can (step s3.16), which corresponds to that of step s3.4, in which case either the mark E is reached or the method is continued if the required correction is below the threshold. If the method is continued, the degradation gradient ṗ- = (p-pE) / Δt is determined (step s3.17) and the quotient degradation gradient / buildup gradient is calculated (step s3.18). If the comparison of this quotient with a quotient threshold value (step s3.19) shows that this threshold value has been exceeded, a step s3.20 follows, which corresponds to the error message step s3.14. Otherwise, step s3.21 is reached via mark E, which has already been mentioned several times, in which the shut-off valve is opened, whereupon the end of the method is reached.

Instead of the quotient formed as above, the reciprocal of this quotient can also be used, in which case the system is judged to be inoperative if the quotient is less than a threshold value. Instead of a quotient, the amount of the difference between the (absolute) gradients can also be used, for example. Other changes are explained with reference to FIGS. 4 to 6. 4 is to be carried out between marks A and B in the flow of FIG. 3 instead of the partial flow there. It is used to get by as short as possible instead of a predetermined period. For this purpose, a step s4.1 is used to examine whether a maximum time period has elapsed since the tank ventilation valve opened. This is chosen so that a threshold pressure p_SW of, for example, -15 hPa can be reached even when the tank is empty but the system is tight. If it is determined that the span has expired, an error message step s4.2 takes place, which corresponds to step s3.11. Otherwise, step s4.3 follows, in which the gas throughput is determined in accordance with step s3.5. The current differential pressure p in the tank is then measured (step s4.4), and the measured value is compared with the threshold value p_SW mentioned (step s4.5). If this threshold value has not yet been reached, the sequence follows again from step s4.1, while otherwise, in a step s4.5, the time period Δt since the beginning of the opening of the tank ventilation valve is recorded in step s3.3. The method according to FIG. 3 then follows from step s3.8.

5 replaces the test of step s3.16 with step s5.1, which serves to determine whether the measurements can be used to determine the degradation gradient. For this purpose, step s5.1 examines whether the load of the motor 17 is above a threshold. If this is the case, it is assumed that the vehicle is moving. From this it is concluded that the tank contents are moving and therefore gassing, which makes it seem advisable to abort the test procedure. Therefore the brand E is reached. Otherwise, steps s5.2 to s5.4 are followed by steps s3.13 to s3.15, which are then followed by step s3.17 due to the omission of step s3.16.

In the description of error reporting step s3.11, it was stated that that the error message occurs the first time an error is detected. When processing errors in motor electronics systems, however, the procedure is generally such that an error is only output if it has occurred several times within a predetermined number of test sequences. Such details are not important here.

Claims (8)

1. Procedure for checking the ability to function of a tank venting system in a vehicle with an internal combustion engine, which tank venting system has a tank with a tank pressure sensor, an adsorption filter connected to the tank via a tank connection line, and a tank venting valve which is connected to the adsorption filter via a valve line, in which system the adsorption filter has a vent line which can be closed by means of a shut-off valve, the procedure having the following steps:

   - closure of the shut-off valve;

   - opening of the tank venting valve;

   - determination of the build-up gradient (ṗ+) of the vacuum building up in the tank;

   - closure of the tank venting valve;

   - determination of the reduction gradient (ṗ-) of the decreasing vacuum in the tank;

   - mathematical combination of the build-up and reduction gradients in a manner such that the influence of the filling level has as little effect as possible on the assessment variable (Q) formed by means of the combination;

   - comparison of the value of the assessment variable with a threshold value (Q_SW) and assessment of the system as non-functional if the value of the assessment variable and the threshold value fulfil a specified relationship.
2. Procedure according to Claim 1, characterized in that the assessment variable is formed by a quotient which comprises the build-up and the reduction gradient.
3. Procedure according to either of Claims 1 or 2, characterized in that a check is made to determine whether a lambda controller interacting with the internal combustion engine has to perform a leanness correction greater than a threshold leanness correction in the period during which the tank venting valve is open, and the checking procedure is aborted without a result if the leanness correction ascertained is greater than the threshold leanness correction.
4. Procedure according to one of Claims 1 to 3, characterized in that a check is made to determine whether a lambda controller interacting with the internal combustion engine has to carry out a leanness correction greater than a threshold leanness correction in the period during which the tank venting valve is open, and the checking procedure is concluded with the result that the system is not leaktight if the leanness correction ascertained is less than the threshold leanness correction and the build-up gradient is smaller than a threshold value (ṗ+ < ṗ+_SW).
5. Procedure according to one of Claims 1 to 4, characterized in that, after the last pressure measurement required to determine the reduction gradient, the tank venting valve is opened and a check is made to determine whether a lambda controller interacting with the internal combustion engine has to carry out a leanness correction greater than a threshold leanness correction, and the checking procedure is aborted without a result if the leanness correction ascertained is greater than the threshold leanness correction.
6. Procedure according to one of Claims 1 to 5, characterized in that, from the closing point of the tank venting valve, at least one operating parameter of the vehicle is checked, the measured values of this operating parameter indicating whether the vehicle and hence the contents of the tank are moving, and the checking procedure is aborted without a result if the measured value of the operating parameter is higher than a specified threshold value (step s5.1).
7. Procedure according to one of Claims 1 to 6, characterized in that the gas throughput through the tank venting valve is determined in the time period during which the said valve is open and the build-up gradient is normalized with respect to a specified gas throughput.
8. Apparatus for checking the ability to function of a tank venting system in a vehicle with an internal combustion engine (17), which tank venting system has a tank (10) with a tank pressure sensor (11), an adsorption filter (13) connected to the tank via a tank connection line, and a tank venting valve (TEV) which is connected to the adsorption filter via a valve line (15), in which system the adsorption filter has a vent line which can be closed by means of a shut-off valve (AV), with:

   - a sequence controller (19) for activating the shut-off valve and the tank venting valve;
   characterized by

   - a gradient determination device (24) for the determination of the build-up gradient of the vacuum which builds up in the tank when the shut-off valve is closed and the tank venting valve is open and for the determination of the reduction gradient of the decreasing vacuum in the tank after a closure of the tank venting valve;

   - an assessment-variable calculation device (25) for the mathematical combination of the build-up and reduction gradients in a manner such that the influence of the filling level has as little effect as possible on the assessment variable (Q) formed by the combination; and

   - a comparison/assessment device (26) for comparing the value of the assessment variable with a threshold value and for assessing the system as non-functional if the value of the assessment variable and the threshold value fulfil a specified relationship.

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