Breather for an internal combustion engine fuel tank

Details Breather for an internal combustion engine fuel tank Breather for an internal combustion engine fuel tank

1993-08-06

1994-11-08

Cross, E. Rollins

Internal-combustion engines

Charge forming device

Having fuel vapor recovery and storage system

123520, F02M 2508, F02M 2102

Patent

active

053617436

DESCRIPTION:

BRIEF SUMMARY
PRIOR ART

The invention is based on a breather for an internal combustion engine fuel tank. Such a breather with an adsorption filter, an active carbon filter for example, is known from the DE-OS 40 03 751 which prevents the escape of fuel vapours from a fuel tank into the atmosphere. The fuel vapours arise as soon as the fuel exceeds the saturation temperature which is dependent on the ambient pressure. Initially, those parts of the fuel will evaporate which have the lowest saturation temperature. With increasing fuel temperature or reducing ambient pressure, the rate of fuel evaporation increases. The fuel vapour represents a severe burden for the environment and a health hazard for people, in particular when it is inhaled.
The adsorption filter is connected to the fuel tank by means of a filter line which terminates in the interior of the adsorption filter, for example in that region which is filled with activated carbon. A suction line which is controlled by a tank breather valve, links the adsorption filter with that part of the induction manifold of the internal combustion engine which is downstream from a throttle.
With the engine running, the fuel vapour is drawn in by the vacuum which exists, in the induction manifold behind the throttle, and is fed to the engine, for combustion. At periods of rest or when the tank breather valve is closed, or when the vacuum being accumulated in the induction manifold is insufficient due to the load conditions of the engine to allow the fuel vapours to be exhausted, these are adsorbed in the adsorption filter.
The limited design space of the adsorption filter provides for a limited storage capacity. For regeneration, the adsorption filter is flushed with fresh air which is fed to the filter via a breather line which is linked to the atmosphere. With negative pressure prevailing in the suction pipe and the tank breather valve open, the fresh air will pass first through a shut-off valve, which controls the breather line, into the adsorption filter, where it absorbs the fuel vapours and feeds these through the suction line and the suction pipe to the engine.
With both the shut-off valve and the tank breather valve closed, it is required for reasons of function and environment protection, that the fuel tank, the filter line, and the adsorption filter form a single unit which is hermetically sealed from the atmosphere. To check the sealing efficiency, a negative pressure is set in this unit (see DE-OS 40 03 751). If one of the components is leaky, the negative pressure cannot be maintained, since air from the outside will flow into this unit. Following this leak diagnosis, the shut-off valve is opened, and with the tank breather valve open, fresh air will flow via the shut-off valve into the adsorption filter, regenerating the adsorption filter, and is then fed as a mixture to the engine.
With such a shut-off valve, there is the risk that condensate will accumulate in its electrical region and cause faults or failure of the shut-off valve.
Furthermore, with such a shut-off valve, there is the risk that any fault in the electromagnetic circuit will unintentionally keep the valve closed and that, with the tank breather valve closed, an inadmissibly high pressure will build up in the fuel tank, the lines, and the adsorption filter, causing faults.
The fresh air flowing into the adsorption filter contains impurities, for example in the form of dust and dirt particles. These impurities will partly deposit in the interior of the shut-off valve, for example, on the sealing faces of a valve closing body and the valve seat. When the valve closes again, the deposited impurities will prevent repeated tight closing of the shut-off valve. If the unit is to be subjected to a further leak test, air will enter into the unit from outside through the defective shut-off valve which has negative pressure. This makes it impossible to positively assess whether the leak stems from a possibly existing leak somewhere in the unit or from insufficient sealing of the shut-off valve.
In known br

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