Internal-combustion engines – Charge forming device – Having fuel vapor recovery and storage system
Patent
1995-08-18
1996-07-09
Moulis, Thomas N.
Internal-combustion engines
Charge forming device
Having fuel vapor recovery and storage system
F02M 3302
Patent
active
055334792
DESCRIPTION:
BRIEF SUMMARY
STATE OF THE ART
The invention relates to a method for the ventilation of a fuel tank of a motor vehicle having an internal-combustion engine and to a tank ventilation system for carrying out the method.
A method of the relevant generic type for the ventilation of a fuel tank and a tank ventilation system for carrying out this method are known (see, for example, Bosch, Technische Unterrichtung [Technical Information], Motronic, 2nd edition, September 1985, page 26, 27, 35). In the known method and the known ventilation system, the scavenging of the adsorption filter is carried out by means of a scavenging-airstream which flows from the atmosphere through the adsorption filter by way of a ventilation orifice and a shut-off valve opened for the scavenging operation and which, by way of a tank ventilation valve opened for the scavenging operation, is introduced, downstream of the throttle flap and of the bypass bypassing the throttle flap and conventionally containing an idling adjuster, into the suction pipe leading to the internal-combustion engine.
It has been shown that this known ventilation method and the known tank ventilation system do not in all cases fully meet the requirements. In particular, the scavenging-airstream, which must contain considerable air quantity per unit time for the effective scavenging of the adsorption filter, constitutes, in relation to the metered air quantity sucked in by way of the suction pipe, an appreciable leakage stream which leads to a lambda fault when the internal-combustion engine is working. In addition, when there is a high gas content in the tank, an additional fuel quantity is fed to the suction pipe along with the scavenging air and can impair the optimization of the operating conditions of the internal-combustion engine.
Proceeding from the state of the art and from the problem indicated above, the object on which the invention is based is to specify an improved method for the ventilation of a fuel tank of a motor vehicle and an improved tank ventilation system, by means of which a disadvantageous impairment of the regulated mixture composition for an internal-combustion engine during the scavenging of the absorption filter is avoided.
The set object is achieved by means of a method as set forth herein and the tank ventilation system set forth hereinafter.
ADVANTAGES OF THE INVENTION
An important advantage of the method according to the invention is that the scavenging-airstream enters the suction pipe as a measured leakage stream, since it is branched off from the measured airflow in the suction pipe and in the bypass of the latter, so that an impairment of the set operating parameters for the internal-combustion engine by an additionally supplied scavenging-air quantity is avoided under all operating conditions.
In an embodiment of the method according to the invention, there is additionally the possibility, when the gas content of the tank is high, of throttling the scavenging-air quantity in such a way that the fuel component contained in the scavenging-airstream likewise does not lead to any impairment of the regulated fuel/air mixture supplied to the internal-combustion engine.
As regards the tank ventilation system for carrying out the method according to the invention, there is, furthermore, the important advantage that, besides the two valves already required according to the state of the art, namely the shut-off valve downstream of the ventilation orifice for the adsorption filter and the ventilation valve in the ventilation conduit for the tank, no additional valves are required. On the contrary, it is sufficient to replace these two valves by conventional commercially available controllable valves which are available relatively cheaply.
BRIEF DESCRIPTION OF THE DRAWINGS
Further particulars and advantages of the invention are explained in more detail below by means of drawings. In these:
FIG. 1 shows a schematic diagram of a preferred embodiment of a tank ventilation system for carrying out the method according to the invention, and
FIGS. 2 t
REFERENCES:
patent: 4926825 (1990-05-01), Ohtaka et al.
patent: 4961412 (1990-10-01), Furuyama
patent: 5005550 (1991-04-01), Bugin, Jr. et al.
patent: 5172672 (1992-12-01), Harada
patent: 5174265 (1992-12-01), Sekine
patent: 5203300 (1993-04-01), Orzel
patent: 5371412 (1994-12-01), Iwashita et al.
Mezger Werner
Wild Ernst
Greigg Edwin E.
Greigg Ronald E.
Moulis Thomas N.
Robert & Bosch GmbH
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