Method for verifying the tightness of a tank system in a motor vehicle

Abstract

A method for checking the tightness of a tank system, especially of a tank-venting system of a vehicle, wherein an overpressure or an underpressure relative to the atmospheric pressure is introduced into the tank system by means of a pressure source and the time-dependent trace of at least one operating characteristic variable of the pressure source is detected when introducing the overpressure / underpressure up to reaching a first time point or a first pressure level and is compared to a time-dependent trace of the operating characteristic value up to this time point or up to this pressure level (expected diagnostic trace), the time-dependent trace being expected in the case of a tight tank system, and, a conclusion as to non-tightness is drawn when the detected time-dependent trace deviates from the expected diagnostic trace by at least a pregiven value, characterized in that, when a deviation is determined, the overpressure / underpressure in the tank-venting system is further increased up to reaching a second time point or a second pressure level; the operating characteristic value of the pressure source continues to be detected and compared to an expected further time-dependent trace of the operating variable in the case of a tight system (further diagnostic trace) and, a fault announcement is only then outputted when the detected time-dependent trace during the introduction of the further overpressure / underpressure deviates from the further diagnostic trace.

Description

STATE OF THE ART[0001] The invention relates to a method for checking the tightness of a tank system, especially a tank-venting system, in accordance with the preamble of claim 1.[0002] A method for checking the tightness of the tank-venting system of a vehicle is disclosed, for example, in DE 198 09 384 A1 as well as in DE 196 36 431 A1.[0003] In the above, an overpressure is introduced into a tank-venting system by means of a pressure source and the time-dependent trace of at least one operating characteristic variable of the pressure source is detected while introducing the overpressure. This time-dependent trace is compared to a time-dependent trace of the operating characteristic variable (diagnostic trace), which is expected in the case of a tight tank system. This expected time-dependent trace is, for example, previously measured, computed or estimated. A conclusion is then drawn as to non-tightness when the detected time-dependent trace deviates from the diagnostic trace by ...

AI Technical Summary

Benefits of technology

[0008] This task is solved in accordance with the invention with the features of claim 1 with a method for checking the tightness of a tank system of the kind described initially herein.[0009] Advantageous further improvements of the invention are the subject matter of the dependent claims.[0010] The advantage of the method of the invention is that, to a certain extent, it is possible to verify an initially expected untightness or to show that it is false via the following: a further diagnostic trace (that is, a further introduction of an overpressure or underpressure into the tank system); the detection of the operating variable of the pressure source when introducing this additional overpressure or underpressure until reaching a second time point or a second pressure level; a comparison of the so detected operating characteristic variable to a time-dependent trace of the operating characteristic variable (expected for a tight tank system) when introducing the additional overpressure; and, the output of a fault announcement only when a determination is made of a deviation of the detected operating characteristic variable from the diagnostic trace by at least a pregiven value and when there is a deviation of the operating characteristic variable from the further diagnostic trace by at least a pregiven value. With this verification or showing to be false, faults can be eliminated which are caused especially by ambient influences or component tolerances.[0011] With the method of the invention, large leaks having a diameter of 1 mm or greater than 1 mm can be recognized with high accuracy. On the other hand, leaks having a diameter of less than 1 mm do not lead to fault announcements.[0012] The electric current of an overpressure pump / underpressure pump is advantageously detected as an operating characteristic variable of the pressure source. For this reason, it is not only possible to accurately detect significant changes of the operating state of the pressure source but the detected electric current can also be directly further processed in evaluation circuits or the like in an advantageous manner.[0013] As to the time-dependent trace of the operating characteristic variable (that is, the electric current), the current could, in principle, be detected continuously over time and the functional trace shown in this manner could be compared to a time-dependent trace which was previously measured, computed or estimated.[0014] An especially advantageous embodiment provides that the pump current is compared to the expected current values for a tight tank system after the elapse of pregiven time intervals and a fault announcement is only outputted when the detected pump current, after the elapse of the first time interval, deviates from an expected current value for a tight tank system as well as, after the elapse of the second time interval, deviates from a second expected current value for a tight tank system.[0015] With the comparison of these values, a very accurate leak detection of a tank-venting system is also possible. A significantly reduced storage complexity is required when compared to the detection of the time-dependent trace of the current intensity.

Problems solved by technology

A reliable decision is therefore not possible in this manner as to whether a large is leak is present having a diameter of 1 mm or more.

On the other hand, for other tolerances, a pregiven current threshold can be reached also for a leak having a diameter of more than 1 mm in a time interval, which is less than a pregiven diagnostic time interval and this would lead to the situation that a fault output would not take place.

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