Internal-combustion engines – Charge forming device – Having fuel vapor recovery and storage system
Patent
1991-02-25
1992-09-01
Miller, Carl S.
Internal-combustion engines
Charge forming device
Having fuel vapor recovery and storage system
123516, F02M 3302
Patent
active
051430410
DESCRIPTION:
BRIEF SUMMARY
PRIOR ART
The invention starts from a venting device for a fuel tank of an internal combustion engine as set forth hereinafter.
Such a venting devices (sic) serves to prevent fuel which evaporates in the fuel tank, so-called fuel vapour, which arises, in particular, during the filling of the fuel tank or in the hot shut-off phase of the internal combustion engine, from escaping into the atmosphere, instead being stored in a fuel vapour filter. During the operation of the internal combustion engine, the filter is then regenerated by flushing with fresh air which is sucked in by the intake system of the internal combustion engine via the fuel filter. The fuel-laden flushing air is then fed to the internal combustion engine in metered fashion for combustion (DE 33 46 103 C2, DE 38 02 664 C1).
In the U.S.A., such venting devices must be subjected to a so-called "on-board-refuelling test" to prove their efficiency, in which test a fixed limiting value for the hydrocarbons set free with the evaporation of fuel must be complied with. In such a test, a number of operating cycles of the internal combustion engine with intermediate shut-off phases are performed, starting from a fully laden fuel vapour filter. After the last shut-off phase, the fuel tank is filled. The hydrocarbon values measured at the filter outlet during this procedure must be below the limiting value.
In order to be able to comply with this limiting value at a volume of the fuel vapour filter which is still acceptable, it is necessary to remove the fuel vapour arising in shut-off phases of the internal combustion engine again during the operating phases of the internal combustion engine in order in this way, at the end of the test cycles, to achieve a loading condition of the fuel vapour filter in which the latter is still capable of reliably absorbing the quantity of fuel vapour arising during refuelling. The quantity of flushing air required to remove a certain mass of fuel vapour in the regeneration of the fuel filter increases exponentially with increasing unloading of the fuel vapour filter, i.e. as the degree of loading of the fuel vapour filter decreases. This means that, given the relatively low loading condition which the fuel vapour filter reaches during one shut-off phase of the internal combustion engine within the test cycles, a very large quantity of flushing air is required in the subsequent operating phase of the internal combustion engine in order to remove the fuel vapour from the filter again.
Advantages of the invention
In contrast, the venting device according to the invention has an advantage that, while a relatively small total filter volume is retained, the quantity of flushing air required for the regeneration of the fuel vapour filter in the operating phases of the internal combustion engine is small. The subdivision of the filter into two filter parts opens up the possibility of making the first filter part very small, with the result that it achieves a very high degree of loading in each shut-off phase of the internal combustion engine and can thus be unloaded again reliably and with certainty during the subsequent operating phase of the internal combustion engine using only a small quantity of flushing air. The dimensions of the second filter part are then to be made sufficiently large to enable it, at the end of the test cycles concluding with a shut-off phase of the internal combustion engine--and hence with the first filter part fully laden--to absorb the volume of fuel vapour arising during refuelling. The diffusion-hindering connection between the two filter parts ensures that fuel vapour does not already pass into the second filter part when the first filter part is not yet laden to the maximum extent, thus resulting in a premature, slight loading, of the second filter part, which cannot be removed because of the small quantity of flushing air during the individual test cycles. The flushing air is always sucked in via the outlet of the second filter part and flows through the two filter parts in the reverse
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Greigg Edwin E.
Greigg Ronald E.
Miller Carl S.
Robert & Bosch GmbH
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