Internal-combustion engines – Charge forming device – Having fuel vapor recovery and storage system
Patent
1993-10-04
1995-11-07
Miller, Carl S.
Internal-combustion engines
Charge forming device
Having fuel vapor recovery and storage system
123198D, F02M 3302
Patent
active
054639980
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The following description relates to a method and an arrangement for checking the operability of a tank-venting system on a vehicle having an internal combustion engine.
BACKGROUND OF THE INVENTION
U.S. Pat. No. 5,193,512 discloses a tank-venting system which has a tank with a tank-pressure sensor, an adsorption filter connected to the tank via a tank-connecting 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 venting line which can be closed by means of a shut-off valve. The tank-venting system configured in this way is checked for operability by the following method:
checking to determine whether an operating state is present, for example full load, in which no significant underpressure can build up in the tank after the closure of the shut-off valve and the opening of the tank-venting valve;
if such a state is present, the method is terminated; otherwise, the following steps follow:
closing the shut-off valve;
opening the tank-venting valve;
measuring of the underpressure building up in the tank; and,
evaluating of the tank-venting system as non-operative if a pregiven underpressure is not reached.
U.S. Pat. No. 5,205,263 discloses a method which operates on a tank-venting system without a shut-off valve and has the following method steps:
opening the tank-venting valve;
determining the build-up gradient of the underpressure building up in the tank; and,
comparing the build-up gradient and/or the decay gradient with a respective threshold value and evaluation of the system as operative if the at least one gradient and the corresponding threshold value fulfill a pregiven relationship.
U.S. patent application Ser. No. 08/070,334, filed May 26, 1993, discloses a similar method which is however carried out on a tank-venting system with a shut-off valve. Measurements for determining the build-up and the decay gradient are only taken into account once it has been ensured that the measurements are not influenced by vaporizing fuel. For this purpose, a leanness correction check is used with the aid of a lambda controller and/or a check as to whether the vehicle and hence also the contents of the tank are presumably in motion.
It has been shown that the known and proposed methods require further refinement in order to be able to detect small leaks in the order of 2 mm.
SUMMARY OF THE INVENTION
The method according to the invention for checking the operability of a tank-venting system of the kind mentioned above has the following steps:
closing the shut-off valve;
opening the tank-venting valve;
determining the build-up gradient of the underpressure building up in the tank;
closing the tank-venting valve;
determining the decay gradient of the decaying underpressure in the tank;
mathematically combining the build-up and decay gradients in such a manner that the influence of the fill level has as little effect as possible on the evaluation variable formed by the combination;
comparing the value of the evaluation variable to a threshold value and evaluating the system as non-operative if the value of the evaluation variable and the threshold value fulfill a pregiven relationship.
The arrangement according to the invention has a sequence controller for driving the shut-off valve and the tank-venting valve; a gradient determination device for determining the above-mentioned gradients; an evaluation-variable formation device for forming the above-mentioned quotient and a comparison/evaluation device for carrying out the above-mentioned comparison and the corresponding evaluation.
It is noted that when reference is made below to gradients of the underpressure build up or decay, almost always positive (absolute) values (in terms of magnitude) are meant. Only FIGS. 2a and 2b relate to these gradients with reference to the sign.
It has been shown that the method according to the invention provides evaluation results which are hardly influenced by the fill level of the tank. If the tank is almost full, both
REFERENCES:
patent: 5193512 (1993-03-01), Steinbrenner et al.
patent: 5205263 (1993-04-01), Blumenstock et al.
patent: 5275144 (1994-01-01), Gross
patent: 5295472 (1994-03-01), Otsuka
patent: 5299545 (1994-04-01), Kuroda
patent: 5327873 (1994-07-01), Ohuchi
patent: 5339788 (1994-08-01), Blumenstock
patent: 5355863 (1994-10-01), Yamanaka
patent: 5363828 (1994-11-01), Yamashita
Blumenstock Andreas
Denz Helmut
Miller Carl S.
Ottesen Walter
Robert & Bosch GmbH
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