Internal-combustion engines – Charge forming device – Having fuel vapor recovery and storage system
Reexamination Certificate
1999-08-11
2001-06-26
Yuen, Henry C. (Department: 3747)
Internal-combustion engines
Charge forming device
Having fuel vapor recovery and storage system
C123S1980DA, C073S118040
Reexamination Certificate
active
06250288
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a method for checking the operability of a tank-venting system of a motor vehicle. The tank-venting system includes a tank and an absorption filter which has a venting line. The adsorption filter is connected to the tank via a connecting line and the system also includes a tank-venting valve which is connected to the adsorption filter via a valve line. In the method, an overpressure compared to ambient pressure is introduced into the system and at least one operating characteristic variable is detected when introducing the overpressure for determining the pressure trace and a conclusion is drawn as to the presence of a leak (tightness check). The operating characteristic variable which is detected is preferably of the pressure source.
BACKGROUND OF THE INVENTION
A method and an arrangement of this kind for checking the operability of a tank-venting system is disclosed, for example, in U.S. Pat. No. 5,890,474 as well as in U.S. Pat. No. 6,131,550.
From U.S. Pat. No. 6,131,550, a method is known wherein the time-dependent trace of at least one operating characteristic variable is detected during standstill of the vehicle and this variable is compared to a previously measured, computed or estimated time-dependent trace of the at least one operating characteristic variable which is not disturbed by a tanking operation. A fault announcement is not outputted when the detected time-dependent trace deviates by a pregivable value from the diagnostic trace. The operating characteristic variable is advantageously the electric current of an overpressure pump with which an overpressure is generated in the tank-venting system.
For this method, it is problematic that the time-dependent trace of the operating characteristic variable must be continuously detected and compared to a computed, stored or measured operating characteristic variable. A leak is here only detected when a significant change of the operating characteristic value is detected within this diagnostic trace.
It is not infrequent that the driver of a motor vehicle, for example, stops at a gas station, switches off the engine, opens the cap of the tank but does not immediately start tanking. In this case, the tightness check starts with the standstill of the vehicle and erroneously determines a leak because of the removed tank cap which leak is no longer present after the tanking operation and the closing of the tank. In a case such as this, an erroneous entry into a memory of a control apparatus or the like should be avoided. In the arrangement disclosed in U.S. Pat. No. 6,131,550, an opening of the tank can only be detected when this takes place during the course of a diagnosis. For this reason, a tank, which has already been opened in advance of the diagnostic sequence, cannot be distinguished from an actually present leak in the tank-venting system.
SUMMARY OF THE INVENTION
In view of the foregoing, it is an object of the invention to improve a method for checking the operability of a tank-venting system in such a manner that an erroneously diagnosed leak based on an improper use of the vehicle can be reliably detected.
The method of the invention is for checking the operability of a tank-venting system of a vehicle having an engine. The tank-venting system includes: a tank; an adsorption filter having a venting line; a first connecting line connecting the adsorption filter to the tank; a tank-venting valve; and, a second connecting line connecting the tank-venting valve to the adsorption filter. The method includes the steps of: providing a pressure source and operatively connecting the pressure source to the tank-venting system; determining and storing a first fill level of the tank at the start of a standstill of the vehicle; introducing an overpressure relative to atmospheric pressure into the tank-venting system during the standstill of the vehicle; detecting an operating characteristic variable of the pressure source as the overpressure is introduced into the tank-venting system; drawing a conclusion as to the presence of a leak in the tank-venting system from the operating characteristic variable; determining and storing a second fill level of the tank at the end of the standstill; forming the difference of the first and second fill levels and determining whether the difference is less than a pregiven threshold value; and, only if the difference is less than the threshold value, outputting a fault announcement.
An actually present leak can be distinguished from an erroneous leak based on an open tank cap by means of the detection of the fill level of the tank at the start of the standstill of the vehicle and at the end of the standstill in a simple and advantageous manner. In this context, it is of no significance whether the tank was impermissibly open over a longer time duration as described above or was open only for the actual tanking operation.
In each case, a significant change of the tank fill level is detected for a tanking operation so that the presence of such a change permits a conclusion to be drawn as to a tanking operation and therefore to an opening of the tank. The end of the standstill can then be determined in various ways.
In an advantageous embodiment, it is provided that the end of the standstill is defined as a renewed start of the engine.
In another very advantageous embodiment of the invention, it is provided that the end of the standstill is defined as the renewed start of the vehicle and the travel over a pregiven road distance or the elapse of a pregivable duration of operation of the engine. This embodiment affords especially the advantage that erroneously outputted leak announcements, which occur during driving with an open tank (for example in the vicinity of a gas station), can be excluded.
If the driver opens the tank at a gas station and moves the vehicle with the open tank to advance, for example, in a waiting line, then, for a definition of the end of standstill as a renewed start of the engine, an incorrectly outputted leak announcement cannot be precluded which is based on such an improper operation of the vehicle during a tanking operation. In this case, a leak announcement would be outputted because the end of standstill would be detected by the renewed start of the engine and, even after the standstill of the vehicle, an open tank would be present and therefore a leak would be outputted.
The above would be precluded by the above-mentioned advantageous embodiment in that the end of standstill is defined only after a pregiven distance has been traveled which, for example, could be five hundred meters or the like.
In principle, the most different operating characteristic variables can be considered with respect to the detection of the time-dependent trace of the operating characteristic variables of the pressure source.
An advantageous embodiment provides that the electric current of an overpressure pump is detected as an operating characteristic variable of the pressure source. By detecting the current, not only can significant changes of the operating state of the pressure source be precisely detected but the detected current can also be processed in an especially advantageous and simple manner.
The fill level can be advantageously determined in one or more of the following ways: with a fill level transducer; from the injected fuel quantity determined by an engine control; and, with contactless fill level sensors.
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Gimie Mahmoud
Ottesen Walter
Robert & Bosch GmbH
Yuen Henry C.
LandOfFree
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