Venting device for fuel tanks

In a venting device for a fuel tank 1 of a motor vehicle having a filler neck and a venting valve, a circulation pipe is provided which, due to the suction jet effect when refueling circulates gas from the fuel tank back into the tank with the fuel so as to prevent an excessive inflow of fresh air, and which includes a venting pipe extending between venting valve 2 and a filter for discharging excess gases through a filter in order to prevent the escape of fuel vapors into the environment.

BACKGROUND OF THE INVENTION

The invention relates to a venting device for fuel tanks of vehicles having a venting valve and a filler neck, to which a venting pipe to the fuel tank is connected.

A venting device for a fuel tank for a motor vehicle is disclosed by DE 37 44 175 C2. In this case a first venting pipe with a switching valve extends from the fuel tank to a first filter and a second venting pipe extends from the fuel tank to the first filter or to a second filter. In addition, a venting pipe is provided between the filler neck and the compensating volume, in order that the fuel present in the filler neck can flow off.

The object of the invention is to provide a venting device in such a way that an excessive charging of the venting filter and an escape of fuel vapor from the tank filler neck is prevented.

SUMMARY OF THE INVENTION

In a venting device for a fuel tank1of a motor vehicle having a filler neck and a venting valve, a venting pipe is provided which, due to the suction effect of a fuel jet from the refueling nozzle and the fuel inlet opening tightly engaging the refueling nozzle, prevents an excessive inflow of fresh air, and which includes a recirculation pipe between the venting valve and the filler neck for removing venting gases in order to prevent their escape into the environment.

In this way, a recirculation volumetric flow is established between the fuel tank and the filler neck, which is equal to the fuel volumetric flow when refueling and which, even with a large volumetric refueling pump flow, generates a sufficient circulation volumetric flow, ensuring a suction jet effect of the entering fuel jet, between the fuel tank and the filler neck.

It is advantageous if the filler neck has a cross-section which is reduced to the diameter of a fuel pump nozzle and the venting pipe is arranged downstream of the reduced cross section of the filler neck in the direction of flow, the reduced opening cross section of the filler neck having a sealing element for the fuel pump nozzle in the form of a diaphragm or a flexible plastic lip. Due to the suction jet effect it is therefore largely the recirculation pipe which is subjected to a vacuum, since the reduced cross-section and/or the sealing element form a flow barrier for the fresh air. The inflow of fresh air is reduced to a minimum.

According to a preferred embodiment the reducing member is finally designed as a filling level-dependent float valve. This prevents liquid fuel from entering the venting pipe.

According to a another embodiment, it is additionally possible for the reducing member to be a flow-dependent needle valve or a circulation valve with a flow-dependent opening cross section. Preferably, the circulation valve has a valve chamber, a nozzle and a needle corresponding to the nozzle and a float, the needle being preloaded against the nozzle by a preloading element. The needle valve is therefore basically closed and opens its flow cross section according to the venting volumetric flow generated by the refueling.

It is also advantageous for this purpose if the circulation valve is arranged at the end of the venting pipe or directly upstream of the filler neck in respect of the venting flow. This prevents the venting pipe from being filled with fuel.

Finally, according to a preferred embodiment of the invention the venting pipe is connected by way of the venting valve indirectly to the fuel tank and directly to the venting valve. This provides a simple method of connection to the tank and, where desired, also facilitates retrofitting of the recirculation pipe.

Preferably, a filter is connected to the venting valve by way of a filter line, the venting pipe being arranged on the venting valve or in the filter line. The recirculation pipe or the recirculation valve in the form of a needle valve relieves the filter, since the suction jet effect during refueling does not draw in an excess volumetric flow of fresh air. The fuel tank air present at the venting valve can flow both directly from the venting valve and via the filter line into the recirculation pipe.

The opening of the venting pipe in the filler neck and the filler neck suck the air drawn in by the suction jet effect during refueling of the fuel tank out of the tank interior through the venting pipe. This prevents overloading of the activated charcoal filter and any excessive escape of fuel vapor into the surroundings.

The invention will become more readily apparent from the following description with reference to the accompanying:

DESCRIPTION OF A PREFERRED EMBODIMENT

FIG. 1shows a fuel tank1for motor vehicles, which has a filler neck3and a venting valve2. The venting valve2is arranged in the fuel tank top wall and has a separating chamber2.1. A reservoir cup pump6, which fills a reservoir cup (not shown) with fuel, is furthermore provided inside the fuel tank1.

The venting valve2is on the one hand connected by way of a filter line7to a filter8, by way of which excess gas can escape to the ambient air. The filter8is preferably an activated carbon filter. The venting valve2is further connected via a venting pipe4or a first part4.1of a venting pipe to the filler neck3. A reducing member5in the form of a float needle valve is provided inside the venting pipe4, that is to say, downstream of the first part4.1of the venting pipe and upstream of a second part4.2of a venting pipe.

The float needle valve5has a valve chamber5.1with a nozzle opening5.2and a needle5.3in the form of a float. The needle5.3is preloaded by a preloading element5.4against the nozzle opening5.2which forms a seat surface for the needle5.3. According toFIG. 2, an upper connection5.5of the float needle valve5is provided on the first part of the venting pipe4.1, this first part of the venting pipe4.1connecting the float needle valve5to the venting valve2. A lower connection5.6is furthermore provided, which connects the float needle valve5to the filler neck3by way of the second part of the venting pipe4.2.

The second part of the venting pipe4.2joins the filler neck3downstream of a cross sectional diaphragm of the filler neck3, with respect of the direction of flow of the fuel, the diaphragm3.1including an opening3.2for receiving a fuel pump nozzle N and having approximately the same diameter as a fuel pump nozzle.

Preferably, the diaphragm3.1is provided with a seal structure in the form of a flexible plastic lip to sealingly engage the fuel pump nozzle N when it is inserted into the filler neck3to prevent ambient air from being sucked into the tank pipe3.3during refueling but rather, gas sucked in with the fuel is supplied via the venting pipe4and the needle valve5from the fuel tank1. The needle float valve5controls the recirculation gas flow volume and prevents fuel from flowing back into the vent pipe4upon excessive filling of the tank. Charging of the filter8by fuel from fuel vapors is therefore minimal.