Internal-combustion engines – Charge forming device – Having fuel vapor recovery and storage system
Patent
1993-10-12
1996-04-09
Miller, Carl S.
Internal-combustion engines
Charge forming device
Having fuel vapor recovery and storage system
123198D, F02M 3302
Patent
active
055051820
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The following relates to a method and an arrangement for checking the operability of a tank-venting system for a motor vehicle having an internal combustion engine.
BACKGROUND OF THE INVENTION
Tank-venting systems having the following features are known for a long time: connecting line to the tank; intake pipe of the engine and the intake end of the adsorption filter; and,
The drive unit drives the tank-venting valve in a fixed pregiven time pattern, for example, the drive unit alternately holds the valve closed for 1.5 minutes and then opens the valve for 4 minutes in order to make a regeneration of the adsorption filter possible. The opening cross section of the tank-venting valve is determined via a pulse-duty factor dependent upon the particular operating state of the engine.
It is apparent that tank-venting systems of this kind can only then operate completely satisfactorily when they are tight and when the tank-venting valve opens and closes properly. Various methods are known for checking the tightness and the operability of the tank-venting valve. However, it has been shown that these methods are not adequate in order to satisfactorily consider all aspects with reference to the operability of the tank-venting system.
Accordingly, the problem is present to provide a method and an arrangement with which a tank-venting system can be checked differently than previously with respect to operability.
SUMMARY OF THE INVENTIONS
A first method of the invention for checking the operability of a tank-venting system of the above-mentioned type is characterized in that: difference between the venting end and the intake end of the adsorption filter; and, when the measured difference pressure exceeds a threshold value.
A second method according to the invention is characterized in that: duration has run wherein an underpressure has developed in the tank-venting system and a difference pressure (Dp) is measured essentially when closing the tank-venting valve with this difference pressure being a measure for the pressure difference between the venting end and the intake end of the adsorption filter; is determined after closing of the tank-venting valve with the aid of at least one further difference pressure measurement; and, adsorption filter when the determined time constant is longer than a threshold value time constant (.tau..sub.-- SW).
A third method according to the invention is for a system which is so configured that, when tanking, the filling nozzle seals tightly against the tank stub (OBVR-system=on-board-vapor-recovery system) and the method is characterized in that: is measured which corresponds to the difference between the inner pressure of the tank-venting system and the ambient pressure; and, difference overpressure exceeds a difference overpressure threshold value (Dp>DSP.sub.-- SW).
These methods investigate the throughput capacity of the system and especially of the adsorption filter as a new aspect of the operability of a tank-venting system. This throughput capacity can, for example, be reduced either in that the venting opening is entirely or partially clogged or in that the charge of the adsorption filter, which as a rule is active charcoal, is so caked or dirtied that the charge greatly hinders the flow of venting air through the filter. In both cases, the adsorption filter can no longer correctly perform its task of adsorbing fuel vapor and desorbing the same with the aid of venting air. The inventions are based on the realization that this defect becomes manifest in that, for a pregiven intake capacity, the underpressure at the intake end is that much greater the less venting air can flow to this end and that, when closing the tank-venting valve, the decay of the above-mentioned underpressure takes place that much slower the slower the venting air (and fuel vapor) flows. Each of these effects, that is, the effect of amplified underpressure and the effect of slowed pressure decay can be applied separately to determine inadequate throughput capacity of the ad
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Blumenstock Andreas
Denz Helmut
Miller Carl S.
Ottesen Walter
Robert & Bosch GmbH
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