Internal-combustion engines – Accessories – Covers – trays – vibrators – corrosion inhibitors – air filters
Patent
1994-11-14
1997-05-27
Rivell, John
Internal-combustion engines
Accessories
Covers, trays, vibrators, corrosion inhibitors, air filters
123520, 138 44, B60K 15035, F02M 2508
Patent
active
056322429
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a fuel system for motor vehicles, comprising a fuel tank, a fuel filler pipe with an opening into the tank, a first gas conduit, one end of which is positioned within the tank and whose opening determines the highest fuel level in the tank when filling the tank, and a second gas conduit which extends from an expansion space in the tank above said highest fuel level to a filter device.
Fuel systems of the above type are known in which the filter device is a canister filled with active carbon, the purpose of which being to prevent fuel vapours escaping into the atmosphere from the expansion space when the fuel volume increases as its temperature rises. The gas conduit between the expansion space and the canister includes a restricted passage (just under 1.5 mm in diameter in a known embodiment) in order to slow down the gas flow from the tank to the canister, since otherwise overfilling of the tank into the expansion space would occur during filling up. This would happen due to the fuel not being forced along the normal breather pipe (the first gas conduit) to shut off the fuel nozzle when the fuel level reaches the opening to the breather pipe in the tank. The restriction is normally shaped so as to offer the same flow resistance in both flow directions. It is so adapted that fuel vapours and air can be forced out of the tank and sucked in with relatively low velocity at over-pressure and under-pressure respectively in the tank.
For environmental reasons, it is desirable if the air-tightness of a fuel system can be periodically checked so as to be able to quickly establish whether any leaks are present through which fuel vapour could escape.
It is an object of the present invention to develop in a simple manner a fuel system that can be subjected to repeated tightness testing without risk of damage when the vehicle is in use and to enable the driver to immediately detect any leakage.
This object is achieved in accordance with the present invention by means of the second gas conduit including a restriction device which is so arranged that the flow resistance of the gas flow in the direction from the tank to the filter device is greater than in the opposite direction, and a pressure sensor being arranged to detect the pressure in the gas volume above the surface of the fuel.
The invention is generally based on the known technique of firstly subjecting a pressure-vessel to pressure and then measuring any pressure changes during a certain period. When testing a vehicle fuel tank, the signals generated by any pressure changes can be processed in a known computerized diagnostic system in the vehicle and faults can be indicated on a display in the vehicle dashboard. In practice, it is important that the tank be subjected to pressure for only a short period to thereby restrict the duration of the mechanical stresses on the walls of the tank. This is particularly important when using fuel tanks made of plastics material. The restrictor with less resistance in the direction towards the tank permits the pressure in the tank to quickly reach atmospheric pressure after the test has been performed, whilst at the same time the previously mentioned high flow resistance is maintained to eliminate the risk of overfilling.
Such a restrictor can quite simply have the shape of a conical nozzle with its narrow opening directed towards the fuel tank. Depending on its shaping, in this way a flow resistance which is 4 to 20 times greater in one direction than the other can be achieved. The absence of moving parts such as flap valves imparts high reliability and low costs, as does the lack of voltage feed.
The invention will be described in greater detail by way of example only and with reference to the attached drawings in which
FIG. 1 shows schematically an embodiment of a fuel system according to the invention, and
FIG. 2 shows an enlargement of certain components of the system shown in FIG. 1.
In FIG. 1, reference numeral 1 denotes a fuel tank for a motor vehicle. N denotes the maximum fuel level
REFERENCES:
patent: 3702144 (1972-11-01), Loveland
patent: 4862856 (1989-09-01), Yokoe et al.
patent: 4949695 (1990-08-01), Uranishi et al.
patent: 5085194 (1992-02-01), Kuroda et al.
patent: 5143035 (1992-09-01), Kayanuma
patent: 5172672 (1992-12-01), Harada
patent: 5261379 (1993-11-01), Lipinski et al.
AB Volvo
Rivell John
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