FUEL PUMP FOR INTERNAL COMBUSTION ENGINES

POMPE A CARBURANT POUR MOTEURS A COMBUSTION INTERNE

English Abstract

The invention relates to a fuel pump, especially the
prefeed pump for feeding aircraft fuel to the high pressure
pump, wherein the form-fit connection between the drive
shaft (4) and the driven impeller (2) is produced by a
regular, convex, triangular polygonal contour having
rounded-off lateral faces and corner faces, the drive shaft
and the impeller being provided with said polygonal
contour. In this manner, the wear resulting from the poor
lubricating power of the kerosene-based aircraft fuel can
be reduced and the service life of the fuel pump can be
increased.

French Abstract

Sur une pompe à carburant, en particulier la pompe d'alimentation envoyant du carburant pour avion à la pompe à haute pression, la liaison avec complémentarité de forme entre l'arbre d'entraînement (4) et la roue de pompe entraînée (2) est formée par un contour polygonal régulier, convexe et triangulaire réalisé sur ceux-ci, ayant des surfaces latérales et d'angle arrondies. De ce fait, les phénomènes d'usure qui s'expliquent par le faible effet lubrifiant du carburant pour avion à base de kérosène sont réduits et la durée de vie de la pompe à carburant est augmentée.

Claims

CLAIMS
1. A fuel pump, particularly prefeed pump for internal
combustion engines comprising a gear pump with a pump
gear driven via a driveshaft, more preferably for
diesel engines operated with aircraft fuel,
characterized by a form-fit connection embodied as
regular convex polygon having lateral faces and corner
regions curved to the outside between the driven pump
gear (2) and the driveshaft (4).
2. The fuel pump according to Claim 1, characterized in
that the form-fit polygon connection comprises a
coupling disc (5) provided on the driveshaft (4) and a
recess (6) moulded into the driven pump gear (2) with
corresponding polygonal contour.
3. The fuel pump according to Claim 1 or 2, characterized
in that the convex polygonal contour is triangular and
in the radius Rs comprises lateral faces curved to the
outside and in the radius R E corner regions curved to
the outside.
4. The fuel pump according to Claim 1 or 2, characterized
in that the regular convex polygonal contour is
designed as tetragon or pentagon.

Description

CA 02747074 2011-05-19
WO 2010/057838 A2
Fuel pump for internal combustion engines
DESCRIPTION
The invention relates to a fuel pump, especially prefeed
pump for internal combustion engines comprising a gear pump
with a pump impeller driven via a driveshaft, more
preferably for diesel engines operated with aircraft fuel.
The fuel feed to the combustion chamber of aircraft engines
operated in common-rail technology using aircraft fuel
takes place from a tank via a prefeed pump and a high-
pressure pump to a common distribution pipe (rail)
connected to the individual cylinders, as is well known.
Since a failure of a fuel pump invariably results in engine
stoppage, an extremely high reliability is demanded
particularly with aircraft engines. The reliability and the
maximum operating duration of the fuel pumps are
particularly limited in that they are lubricated with the
delivered fuel and the bearings and sliding surfaces are
under more or less load corresponding to the lubricating
power of the fuel. The lifespan of the fuel pumps is thus
decisively influenced by the lubricating properties of the
respective fuel. Since the diesel engines employed in
aircraft are operated with a kerosene-based aircraft fuel
with significantly lower lubricating power compared with
diesel fuel, the lifespan of the fuel pumps in this case is
particularly low.
In the case of a prefeed pump designed as a gear pump the
pump gear (drive gear) of said prefeed pump is connected to
a drive shaft by way of a splined shaft toothing, whose
outer toothing (outer profile) present on a shaft end form-
fittingly engages in an internal toothing (inner profile)
present on the drive gear of the prefeed pump. The prefeed
pump designed in this manner only has a very short lifespan
when used for a diesel engine operated with aircraft fuel

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since the driveshaft and the driven pump gear and
consequently also the pump housing are subjected to high
wear and the prefeed pump has to be replaced completely
even after a short operating time.
DE 100 14 548 Al describes a gear feed pump for diesel fuel
with which the form-fit connection between the drive shaft
and the one pump gear is established through a flattened
circle geometry or via a profiling provided with recesses
and protrusions.
The invention is therefore based on the object of designing
the prefeed pump connected upstream of the high-pressure
pump in such a manner that even when using fuel with
reduced lubricating power a long lifespan is guaranteed.
According to the invention, this object is solved with a
fuel pump or prefeed pump designed as gear pump according
to the features of Patent Claim 1. Practical configurations
of the invention are the subject of the subclaims.
The essence of the invention in other words consists in
that the form-fit connection between the driveshaft and the
driven pump gear is established through a convex polygonal
contour designed on the driveshaft and on the pump gear.
In a further embodiment of the invention the driveshaft
comprises a coupling disc in the shape of a polygon shaped
as triangle with lateral faces curved outwardly at a
certain radius and corner regions rounded towards the
outside, while in the driven pump gear a recess
corresponding in shape and size to the coupling disc is
formed, so that the coupling disc engages in the recess as
an accurate fit.
Surprisingly it was discovered that the connection between
driveshaft and pump gear established via two polygons form-

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fittingly engaging into each other guarantees a secure
power transmission and results in a significant reduction
of the wear on the form-fit connection point and thus the
driveshaft, the pump gears and the pump housing and thus
the lifespan of the fuel pump provided for delivering fuel
with low lubricating power is increased and its especially
for aviation indispensable reliability is improved. In a
further configuration of the inventions the convexly curved
polygonal contours form-fittingly engaging into each other
can also be embodied as polygon, for example as tetragon.
An exemplary embodiment of the invention is explained in
more detail by means of the drawing. It shows:
Fig. 1 a perspective representation of a prefeed pump
designed as gear pump in a disassembled state;
Fig. 2 a front view of the driveshaft designed with a
coupling disc designed as polygon; and
Fig. 3 a front view of the drive gear of the prefeed
pump with an inner profile designed as polygon.
The prefeed pump shown in a disassembled state in Fig. 1 is
designed as gear pump and comprises a pump housing 1, in
which a driven first pump gear 2 and a second pump gear 3
are mounted. In addition, a driven driveshaft 4 is mounted
in the pump housing 1. A coupling disc 5 moulded onto the
driveshaft 4 has the shape of a convex, regular, in this
case, triangular polygon, i.e. of a triangle with three
curved lateral faces of the same length and the same size
internal angles. The coupling disc 5 engages in a recess 6
formed in the driven pump gear 2 whose contour shaped as
polygon corresponds to the contour of the coupling disc 5.
Subject to the intermediate connection of a sealing ring 8
the pump housing 1 is closed-off through a housing cover 9
which is fastened by means of cheese-head screws.

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The polygonal outer contour of the coupling disc 5 and the
recess 6 provided in the driven pump gear 2 is shown in
more detail in the Figures 2 and 3. The regular triangular
polygon of the coupling disc 5 and of the recess 6 has a
circumcircle with the diameter du and an incircle with the
diameter dI. However, the polygon has no straight lateral
edges (lateral faces) but is convexly shaped, i.e. with
crowned lateral faces curved outwardly in the radius RS and
within the radius RE rounded corner regions of the polygon
of the coupling disc 5 and of the recess 6. The maximum
width of the polygon of the recess 6 or of the coupling
disc 5 is designated W in the drawing.
With the form-fit between the driveshaft 6 and the driven
pump gear embodied as convex polygonal connection the wear
of the first and also of the second pump gear as well as of
the driveshaft and of the housing can be significantly
lowered and the lifespan of the prefeed pump designed as
gear pump can be increased by up to three times even when
using a fuel with low lubricating power.
The invention is not restricted to the exemplary embodiment
described before. For example, the form-fit connection can
also be formed through regular convex polygons with more
than three corners such as a tetragon or pentagon and also
be employed with other fuel pumps with rotating pump
wheels.

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List of reference characters
1. Pump housing
2. First, driven pump gear
3. Second pump gear
4. Driveshaft
5. Coupling disc, triangular convex polygon
6. Recess, triangular convex polygon
7. Cheese-head screws
8. Sealing ring
9. Housing cover
Du Circumcircle of polygon
DI Incircle of polygon
W Maximum width of the polygon
Rs Radius of the lateral faces of the polygon
RE Radius of the corner faces of the polygon

Representative Drawing