Arrangement for the Detection of Deficiencies in a Tank Ventilation System

The relates to an arrangement for the detection of defects in a tank ventilation system. In the case of known tank ventilation systems, the fuel vapors that develop in the fuel tank are stored in an active carbon filter and are guided into the combustion chamber of the engine periodically after the opening of a ventilation valve.

In these known tank ventilation systems, deficiencies can occur at the connecting lines and the air valve without every defect being immediately recognized. The connecting pipes can be plugged up or leaky, or the air valve can no longer open or close. The consequence thereof is that, until the defect has accidentally been discovered, the tank ventilation system does not operate correctly and the fuel vapors escape into the atmosphere.

Therefore, it is an object of the invention to create a tank ventilation system whereby deficiencies in the system are detected as promptly as possible.

This problem is solved by providing a system for the detection of defects in a tank ventilation system wherein in a line between an output of the filter to an intake portion of the internal combustion engine a flow sensor is arranged which supplies a flow signal to the control unit. A lambda probe may also be provided which supplies a probe signal to the control unit, the lambda probe being provided at an exhaust portion of the internal combustion engine. Means are provided for comparing the at least one of flow signal from the flow sensor or the probe signal from the lambda probe to a control signal which actuates the tank ventilation valve. An error signal is provided in the case of a logically unreasonable comparison of these signals which is indicative of a defect in the tank ventilation system.

FIG. 1 illustrates in schematic fashion an arrangement according to the invention for the detection of defects in a tank ventilation system; and

FIG. 2 is a table showing the defect conditions identified by the control unit 4 according to the invention.

The drawing FIG. 1 shows schematically the elements of a tank ventilation system with defect detection according to the invention. The fuel vapors developing in the tank 1 are directed via a connecting pipe 11 into the active carbon filter 2. From the active carbon filter 2 a connecting line 21 leads to the intake section 51 of the internal combustion engine 5 via a tank ventilation or air valve 3. Via a control signal, the tank ventilation valve 3 can be electrically actuated and controlled by the control unit 4. Between the active carbon filter 2 and the tank air valve 3, a flow sensor 7 is arranged which supplies a flow signal to the control unit 4 given a gas flow in the connecting line 21. In the exhaust section 52 sits a lambda probe 521, which delivers a probe signal to the control unit 4.

The following describes the proper functioning of the tank ventilation. The fuel 12 in the fuel tank 1 vaporizes and is guided via the connecting pipe 11 into the filter insert 23 of the active carbon filter 2. The filter insert 23 has a limited reception capacity and must therefore be emptied out periodically with rinsing or cleaning air 6. For this, the tank air valve 3 is opened by the control unit 4. The underpressure prevailing in the intake section 51 of the internal combustion engine 5 continues via the connecting line 21, the tank air valve 3 and an excess pressure valve 211 into the active carbon filter 2. The under-pressure prevailing in the active carbon filter 2 causes the cleaning or rinsing air 6 to pass onto the active carbon filter 2 via the air inlet opening 22, and causes this air to stream through the filter insert 23. Thus, the fuel vapors contained in the filter insert 23 are released and flow all the way into the intake section 51 of the internal combustion engine 5. The flow sensor 7 detects whether gas is leaking from the active carbon filter 2. The excess pressure valve 211 prevents the overincreases of pressure in the intake section 51 which occur during the dynamic operation of the internal combustion engine 5 (known to the person skilled in the art as pulsations or resonances) from reaching the active carbon filter 2.

In the event that the connecting line 11 is leaky, fuel vapors get into the atmosphere at the leaky location. If the connecting line 11 is plugged up, however, the fuel vapors get into the atmosphere via the excess pressure valve 13 of the fuel tank 1. In case of a disturbance in or at the connecting line 11, thus no fuel vapor gets into the active carbon filter 2. When the active carbon filter 2 is cleaned or rinsed via actuation of the tank air valve 3, the air supplied to the intake section 51 would thus contain no fuel portions. In the case of a normal functioning of the tank ventilation, however, fuel portions would be supplied to the engine which would be noticeable as a change of the probe signal delivered by the lambda probe 521 to the control unit 4. Thus, the control unit 4 recognizes the existing defect since, given an open tank air valve 3, no change of the values provided by the lambda probe 521 occurs. Thus, the case may occur that, after the actuation of the tank air valve 3, the mixture supplied to the intake section 51 accidentally has the same distribution of air and fuel as the mixture delivered to the internal combustion engine via a mixture generation unit not shown here. Although at first no change of the probe signals will result, a continued cleaning or rinsing of the filter insert 23 results in a change of the ratio of air and fuel which, in turn, is noticeable as a change of the probe signals.

When the sectional piece 212 of the connecting line 21 between the active carbon filter and the tank air valve 3 is clogged up or leaky, no under-pressure effects the active carbon filter 2. Thus, the flow sensor 7 detects no more flow. From the logical operation "tank ventilation valve open--flow sensor 7 delivers no signal", the control unit 4 recognizes that a defect exists.

Two types of defects can occur at the tank ventilation valve 3: The tank ventilation valve 3 does not open--defect (A)--or does not close--defect (B).

If the tank ventilation valve 3 does not open, the flow sensor 7 detects no air flow. From the logical connection "tank ventilation valve 3 open--no flow signal from the flow sensor 7", a defect is detected. If the tank ventilation valve 3 does not close, the logical connection "tank ventilation valve closed--flow sensor 7 delivers signal" reveals a defect.

Given a defect in the sectional part 213 of the connecting line 21 between valve 3 and intake section 51, the situation is the same as in the case of a defect in the part 212 of the connecting line 21. Here, too, the control unit 4 recognizes from the logical operation "tank ventilation valve open--flow sensor 7 delivers no flow signal" that a defect exists.

FIG. 2 in the drawings is a table summarizing the above described defect detection performed by simple logic circuitry or programming of the control unit 4.

Regarding the technical realization it would be favorable to use a thermal mass flow sensor as flow sensor 7. Based on the self-regulation effect in the case of ceramic PTC resistors and the small circuit expense associated therewith, preferably a ceramic PTC resistor is employed as a flow sensor 7.

Although various minor changes and modifications might be proposed by those skilled in the art, it will be understood that we wish to include within the claims of the patent warranted hereon all such changes and modifications as reasonably come within our contribution to the art.