Fuel tank having a venting system

A venting system for a fuel tank has an inlet opening that is communicated with a liquid separator arranged between the inlet opening and a vapor canister that preferably has an activated carbon filter. The liquid separator is preferably arranged in the interior of the fuel tank. In a preferred embodiment of the invention, a plurality of vent lines are arranged in the interior of the tank with the inlet openings of the vent lines spaced apart from each other so that there is always at least one inlet opening not exposed to liquid fuel. A line between the liquid separator and the activated carbon filter communicates with the upper region of the liquid separator. These measures ensure that the fuel vapors which are to be vented can pass undisturbed through the liquid separator while any liquid fuel which enters the separator collects in its lower region.

Applicant claims the benefit of German Patent Application Serial No. DE 102 09 491.8 filed Mar. 5, 2002.

FIELD OF THE INVENTION

The invention relates to a fuel tank, and more particularly to a fuel tank having a venting system.

BACKGROUND OF THE INVENTION

In addition to the liquid fuel volume, fuel tanks also contain a gas volume, which is formed by fuel vapors and/or air. Temperature fluctuations lead to corresponding internal-pressure fluctuations in the tank. Excess pressures which occur have to be reduced, but emission regulations mean that fuel vapors must not escape into the atmosphere. The pressure is therefore reduced via an activated carbon filter (ACF) into which a vent line leads. However, it has to be ensured that liquid fuel does not pass into the activated carbon filter via the vent line. Up to now, a valve, for example a float valve, has therefore been arranged at the inlet opening of the vent line, the valve closing in the presence of liquid fuel, such as may occur if the vehicle is on a slope and/or during sloshing of the fuel. To ensure that the fuel tank can be vented during a wide range of circumstances which occur, two or more venting locations are provided with corresponding lines and valves, with the result that if one valve dips into liquid fuel, another valve, which is preferably arranged in the opposite region of the tank, may be open. These valves are subject to mechanical faults and cause additional costs during production of the fuel tank.

SUMMARY OF THE INVENTION

A venting system for a fuel tank has an inlet opening that is communicated with a liquid separator arranged between the inlet opening and a vapor canister that preferably has an activated carbon filter. The liquid separator is preferably arranged in the interior of the fuel tank. In a preferred embodiment of the invention, a plurality of vent lines are arranged in the interior of the tank with the inlet openings of the vent lines spaced apart from each other so that there is always at least one inlet opening not exposed to liquid fuel. The vent lines may each be connected individually to the liquid separator, but they preferably lead into a manifold or branch section which communicates with the liquid separator through a short connecting line. A line between the liquid separator and the activated carbon filter communicates with the upper region of the liquid separator. These measures ensure that the fuel vapors which are to be vented can pass undisturbed through the liquid separator while any liquid fuel which enters the separator collects in its lower region.

In a preferred embodiment of the invention, at least one vent line is arranged in the interior of the tank in such a manner that, during changes in inclination of the tank and/or fuel-sloshing movements which occur in the operation of a motor vehicle, at least a subregion of the line runs above the fuel level. This forms a siphon which prevents relatively large quantities of liquid from entering into the vent line.

The removal of liquid fuel from the separator preferably takes place via a line which is connected to the lower region of the liquid separator and is connected to a low-pressure source, which is preferably a jet pump arranged in the container and driven by a portion of the fuel discharged from a fuel pump arranged in the fuel tank.

In order to prevent liquid fuel from entering into the line leading from the separator to the activated carbon filter, the liquid separator preferably has a baffle plate arrangement arranged upstream of the line.

A preferably electromagnetically actuable shutoff valve can be arranged at an outlet of the activated carbon filter leading into the atmosphere, the shutoff valve can be switched in accordance with an electronic engine control system and/or a position sensor or filling-level sensor. The shutoff valve may be closed, for example for building up a counterpressure when filling the tank, so that the counterpressure causes the fuel nozzle to shut-off before the tank is overfilled, i.e. before the fuel level reaches the inlet openings of the vent lines, or to prevent fuel from running out in the event of the vehicle overturning.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring in more detail to the drawings,FIGS. 1-4illustrate a fuel system including a fuel tank10having an interior for a supply of fuel in which two vent lines12,14having open inlet openings16,18are arranged in the upper region of the tank interior. The vent lines12,14have another end opposite the inlet openings16,18leading a liquid separator20. From there, a line22leads to a vapor canister34preferably providing an activated carbon filter (ACF) which is preferably arranged outside the tank and in which the vented fuel vapors can be collected and either added to the combustion air fed to an engine via a line24(cyclic regeneration in accordance with an electronic control system) or the cleaned air can be passed into the atmosphere via a line26.

Also arranged in the tank are a fuel pump28and a jet pump30. The latter has the following function: A portion of the fuel discharged from the fuel pump28(which may discharge fuel at a relatively high pressure, for example, without limitation,4bar) is routed to the jet pump30by line32. This flow of fuel is the driving flow for the jet pump30, and causes a low pressure to be produced in the area of the jet pump housing. The low pressure pumps liquid fuel from the tank10into a storage tank or container (not illustrated) and/or out of a second tank chamber when the tank is designed as a “saddle tank”. A solenoid valve36can be arranged at the output of the vapor canister34leading into the atmosphere, the solenoid valve may have the function of providing an onboard diagnosis. If the solenoid valve is closed, pressure builds up in the tank. If the pressure which has built up and is measured by a pressure sensor is not within certain limits, this may indicate a malfunction of the valve36or possible leakages from the tank10. Within the context of the invention, this valve36may carry out an additional function, which is explained in more detail below.

Even when the tank is fully filled, the open vent lines12,14are open at least partially in the gas space38above the fuel level40. During operation of the vehicle, however, static or dynamic operating states occur, in which, as illustrated inFIG. 2, one of the inlet openings16,18is situated below the fuel level. The line routing ensures, however, that at least part of the line12,14from this inlet opening to the liquid separator20lies above the liquid level40(formation of a siphon) in at least a wide range of and preferably substantially all orientations, attitudes, or inclinations of the fuel tank, with the result that a relatively large amount of fuel cannot flow through the respective line12,14into the separator20. In such a case, the venting function is ensured by the other vent line which has its inlet opening above the level of liquid fuel in the fuel tank.

If an excess pressure does not prevail in the tank and the inlet openings16,18are normally situated above the liquid level, the vapor is sucked or drawn via the jet pump, which is arranged on the outlet side of the separating tank, and recycled into the tank. This corresponds to the situation as known from prior art, for example in the case of a saddle tank construction. Although fuel does not foam up to a great extent, it is nevertheless ensured that the fuel pump does not suck up any air.

Although liquid fuel can pass via the lines12,14into the separator20, it collects there in its lower region and is removed from there by the jet pump30while a gas space is formed above the liquid level in an upper region of the separator20. An arrangement of baffle plates42(FIG. 3) is provided upstream of the vent line22and ensures that liquid cannot enter into the vent line22even during sloshing movements.

In the event of the vehicle overturning, an upside-down position of the fuel tank and other components may occur. In this case, even the baffle plate arrangement42cannot prevent liquid fuel from entering into the line22and the vapor canister34. It then has to be ensured in another manner that liquid fuel does not pass to the outside. In order to prevent the liquid from escaping to the outside, the solenoid valve36at the outlet of the vapor canister is activated by a position sensor arranged on the vehicle.

As an alternative, relatively large quantities of fuel can also be prevented from running out by use of a suitable routing of the line22in the tank10by providing the line22with a siphon in the form of a loop44(shown in dashed line inFIG. 2) guided to the bottom of the tank.

The venting of the tank10as it is being filled can be realized in two ways. Firstly, a vent line (not illustrated) from or on the tank filler neck can protrude into the tank. As soon as the vent line is flooded by the rising liquid level, the fuel fill nozzle is shut off. Secondly, legal regulations may make it necessary to conduct the fuel vapors displaced during filling of the tank through the activated carbon filter. In this case, it can be ensured with the venting system according to the invention that the fuel level does not reach the open inlet openings16,18of the vent lines12,14. In order to achieve this, a signal of a filling-level transmitter arranged in the tank10is used to establish when the desired level is reached. The signal tapped off from the filling-level transmitter is used for actuating the solenoid valve36at the outlet of the vapor canister filter34. When the valve36is closed, a counterpressure builds up in the tank10resulting in the fuel nozzle being shut off and therefore ending the filling process.