Note: Descriptions are shown in the official language in which they were submitted.
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The invention concerns an electric fuel pump and a pump mechanism
for a fuel pump.
An electric fuel pump may typically comprise at least one pump
mechanism which for example may be in the form of a side-channel pump
mechanism, with an electronically switched do motor for driving the pump
mechanism. The pump may have a pump housing with at least one inlet
and at least one outlet, while there is at least one pump impeller mounted
rotatably in the pump housing and at the same time forming the rotor of
the do motor.
it will be noted that fuel pumps are generally in the form of single-
stage or dual-stage units, either in the form of positive-displacement
pumps or in the form of flow or turbine pumps, wherein the pump
mechanism is generally driven by way of a do motor. The pump mechanism
and the electric motor are combined in a housing with an inlet and an
outlet, the pump mechanism drawing in the fuel through the inlet and
pumping it through the do motor to the outlet. In that situation the motor is
cooled by the fuel flowing through the unit. The do motors which are
usually employed in such a case involve do motors with separate excitation
with permanent magnets and which are operated either on 12V or 24V
voltage. The pump mechanisms used are typically for example toothed ring
pump mechanisms, side-channel pump mechanisms, peripheral channel
pump mechanisms, vane or roller pump mechanisms and screw or axial
pump mechanisms.
Fuel pumps of such a kind require a comparatively large installation
volume, more particularly they require a considerable installation height. In
principle however the dimensions of an electric fuel pump should be as
small as possible so as to ensure that the components required are
assembled in a compact and space-saving manner, to constitute what can
be referred to as the tank installation unit. The term tank installation unit
is
generally used to designate a fuel delivery unit which includes all
components required for the reliable supply of fuel to an engine. The
dimensions of a fuel pump can be reduced to a limited extent by virtue of
the choice of smaller pump diameters. A reduction in the pump diameter
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however entails higher speeds of pump rotation which are required to
achieve the same delivery. High speeds of rotation however involve higher
levels of thermal and mechanical stress for motor and pump components as
well as higher levels of acoustic emissions. This means that minimising the
dimensions of a fuel pump is to be implemented in part only at the expense
of the robustness and longevity thereof.
On the other hand a reduction in the dimensions of fuel pumps is
often desirable, having regard to the external contour of a tank with which
such a pump is to be used. Particularly when the fuel tank involved is a
blow-molded plastic tank, the tank enjoys a particular degree of flexibility
in regard to the configuration thereof. Different locations for installation
of
tanks in a vehicle mean that there are very different tank design
configurations which however must take account of fitments which are
disposed in the tank. In that respect particular significance is to be
attributed to the dimensions of a fuel pump to be fitted to the tank.
In order to reduce the installation height of fuel pumps and in order
to reduce the number of moving parts of such electric fuel pumps, the
impeller of the pump may be designed at the same time as the rotor of the
electric motor driving the pump. An electric fuel pump of that kind is to be
found for example in JP 63-120888 A, Patent Abstracts of Japan, M-748,
1988, Volume 12, No 371. That design of electric fuel pump provides that a
plurality of windings pass through the impeller of the pump or the rotor of
the motor, with the windings being put under voltage in the usual fashion
by way of a brush and a commutator. A similar electric fuel pump is also to
be found for example in DE 43 41 564.
Reference may also be made to German laid-open application (DE-
OS) No 20 12 560 disclosing still another similar electric fuel pump in which
the rotor is in the form of a permanent-magnetic rotor and the do motor is
of a brushless configuration with magnet-controlled external commutator.
The use of a brushless do motor is proposed in that specification from
points of view related to safety and wear, but nonetheless it will be
apparent that a saving is additionally made in respect of axial installation
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height, by virtue of omission of the otherwise usual commutator with
brushes.
Attention may also be directed to DE 197 52 884.8 for example
which discloses another form of fuel pump in which the electric motor is
also a brushless design, to achieve an extremely flat structure in the axial
direction, while its rotor is formed by the impeller of the delivery pump
unit. The pump impeller is contained in a cylindrical pump chamber with
radially extending, axially mutually spaced side walls and a peripheral wall
which connects the two side walls together along their circular periphery.
The impeller is disposed in opposite relationship to the side walls with a
very small gap in relation to the respective ones thereof, and the inside
surface of a stator formed by a grooved lamination assembly forms the
peripheral wall of the pump chamber. The pump mechanism of that pump
is in the form of a side-channel pump mechanism and the two mutually
axially spaced side walls are each provided with groove-like side channels
which are open towards the pump chamber and which extend concentrically
with respect to the axis of the impeller.
That design configuration is advantageous in terms of the
requirement for a small axial structural height. In addition, the outside
diameter of the electric fuel pump, which is increased by virtue of that
structural design, is also advantageous in regard to improving the efficiency
of the pump.
It will be noted however that production of the pump housing is an
extremely complicated and expensive procedure as the pump housing in
part forms both the stator and also in part the flow passages or ducts of the
side-channel pump mechanism. In particular, the mutually contacting
surfaces of the impeller and the pump housing portions forming the side
channels, that is to say the sliding or bearing surfaces of the housing, must
be produced with the maximum possible degree of flatness and evenness
and the smallest possible roughness depth in order to minimise the axial
play and clearance of the pump and thus any leakage losses. With the
integral configuration of hydraulically operative parts of the pump housing
and the electric motor stator, the surface treatment thereof is extremely
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complicated and expensive, having regard to the complex contour of the
component involved.
In accordance with the present invention there is provided an electric
fuel pump comprising at least one pump mechanism including a pump
housing having at least one inlet and at least one outlet, at least one pump
impeller and means mounting the impeller rotatably in the pump housing
and an electronically commutated do motor for driving the pump
mechanism and having a stator and a rotor which is formed at the same
time by the impeller, wherein the pump housing is partially penetrated by
parts of the stator.
As will be seen from a description hereinafter of preferred
embodiments of the invention, the arrangement in accordance with the
invention affords a structural separation between the do motor and the
pump housing, which latter can thus be produced separately and can thus
be optimised in terms of its structure in regard to the required surface
quality of the sliding or bearing surfaces thereof. Such an electric fuel pump
design configuration in accordance with the invention also affords the
advantage that the do motor and the pump mechanism can be made
available as mutually separable units.
In accordance with a preferred feature of the fuel pump the pump
housing, preferably at the pressure side, has a plurality of peripheral
openings which are so arranged in relation to the impeller that they permit
magnetically permeable extension portions of the stator to engage into the
pump housing in such a fashion that a magnetically operative gap is formed
between the impeller and the stator extension portions. That structure
provides for guidance of both the magnetic flux in the form of a radial gap
arrangement and also the flow of fuel. It will be appreciated that the fuel
also flows through the do motor for cooling thereof. The structural
combination of the pump impeller and the motor rotor is in effect detached
by virtue of the partial interpenetration of the stator and the pump housing,
with the stator and the pump housing forming separate components.
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A preferred feature of the invention provides that the extension
portions of the stator extend axially, that is to say in parallel relationship
with and concentrically with respect to the axis of the impeller.
It will be noted at this point that an electronically switched do motor
whose stator is of a design configuration as set forth hereinbefore is
disclosed for example in US patents Nos 4 949 000, 4 837 474, 4 745 345,
5 659 217 and 5 874 797 to Petersen, to which attention is directed for
incorporation herein of the full content thereof. A do motor of that kind
involves an extremely small axial height, the motor is brushless and the
rotor of the motor does not have any electrical terminals so that such a
motor is ideally suited to use in an electric fuel pump. In particular the
electronically switched do motor described in US patent No 5 659 217 is in
the form of a radial gap motor of extremely shallow structure while being of
comparatively large diameter.
In accordance with a further preferred feature of the invention the
openings in the pump housing are arranged arcuately and concentrically
with respect to the impeller and the diameter of that arrangement is larger
than the inside diameter of the enclosed impeller so that the magnetically
permeable extension portions of the stator embrace the pump impeller as a
rotor.
A further preferred embodiment of the pump mechanism according
to the invention provides that a ring of permanent-magnetic material
encloses the impeller, while in a further preferred feature the ring is
mounted axially displaceably with respect to the pump impeller. A loose
arrangement of the ring and the impeller relative to each other in that way
represents a simplification in terms of assembly.
In that arrangement it is preferably provided that the impeller and
the ring of permanent-magnetic material co-operate in positively locking
non-rotatable relationship with respect to each other.
Preferably, the pump housing is formed by disks respectively
providing the side channels, wherein the disks can be fixed at a spacing
relative to each other by way of at least one spacer ring. The advantage of
such an arrangement is that all the individual parts of the pump mechanism
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can be produced and machined by grinding and lapping procedures. Those
procedures afford a greater degree of flatness and smoothness at their
surfaces and a lesser depth of roughness in respect of the sliding or bearing
surfaces of the housing, as well as greater flatness and a lower depth of
roughness in respect of the impeller which is in the form of a vane impeller.
That configuration also affords lower levels of leakage and an improved fuel
delivery characteristic. Finally, at the same time a cost advantage is to be
expected as the pump housing and the impeller do not have to be
machined by turning processes. The production tolerances to be achieved
are overall smaller.
It will be noted that, instead of a spacer ring as referred to above,
annular grooves can be provided in the disks, to receive the magnetic ring.
Further in accordance with the invention there is provided a pump
mechanism for a fuel pump which has a do motor as a flow pump having a
i5 multi-part pump housing having at least one inlet and at least one outlet,
at least one impeller, means rotatably supporting the impeller in the pump
housing, wherein the pump mechanism forms a separate unit, and further
including means for releasably connecting the pump mechanism to the do
motor of a fuel pump.
As will be seen in greater detail hereinafter, that provides that the
motor on the one hand and the pump mechanism on the other hand occur
as units which can thus be handled separately and which can also be
separately subjected to operational testing and checking. Hitherto the usual
practice was for electric fuel pumps to be checked in production in the form
of a complete unit with a motor in a fuel substitute for testing purposes.
The residual fuel which in those procedures then remains in the housings
repeatedly gave rise to problems in subsequent procedures, for example
upon integration into the delivery unit or into a tank. The pump mechanism
according to the invention in contrast can be subjected to functional testing
and checking without the motor and the associated electronics, while the
residual fuel can be removed from the pump housing before assembly to
the motor.
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Embodiments of the invention will now be described by way of
example with reference to the accompanying drawings in which:
Figure 1 is a view in longitudinal section through an electric fuel
pump according to the invention,
Figure 2 is a simplified diagrammatic perspective view of an
electronically commutated do motor of the electric fuel pump according to
the invention,
Figure 3 is a diagrammatic exploded view of a pump mechanism in
accordance with a first embodiment of the invention, and
Figure 4 is a diagrammatic exploded view of a pump mechanism in
accordance with a second embodiment of the invention.
Referring now to Figure 1, an electric fuel pump according to the
invention as illustrated therein comprises a hydraulic part and an electric
part, with the hydraulic part being formed by a pump mechanism generally
indicated by reference numeral 1 while the hydraulic part is formed by an
electronically switched do motor which is generally indicated by reference
numeral 2 and which for the sake of convenience will be referred to
hereinafter in this description as the motor 2. As already mentioned above,
the precise structure and mode of operation of the motor in various
different configurations are to be found in US patents Nos 4 949 000, 4 837
474, 4 745 345, 5 659 217 and 5 874 796 to Petersen, the disclosure of
which is to be suitably incorporated herein by virtue of reference thereto.
The pump mechanism 1 and the motor 2 are each in the form of
units which can be releasably connected together, as shown they are
secured to each other by way of screws 3 in a casing 4.
The motor 2 has a generally plate-shaped stator which is generally
identified by reference numeral 5 in Figure 1 and which has an annular
laminated stator assembly 6. The laminated stator assembly 6 forms
magnetically permeable extension portions 7 which as shown in Figure 2
each extend in a finger-like configuration in the axial direction of the
assembly, that is to say in parallel relationship with the axis of rotation of
the impeller of the pump and the rotor of the motor. In their base or root
region the extension portions 7 are each surrounded by field windings
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diagrammatically indicated at 8 in Figure 1. The stator 5 and the extension
portions 7 are of such a configuration that a permanent-magnet rotor can
fit into the hollow space enclosed by the extension portions 7, forming a
magnetic gap. A rotating electromagnetic field can be produced by way of
the field windings, which drives the rotor across a radial gap.
As can be seen for example from Figures 1 and 3, the electric fuel
pump according to the invention is designed in such a way that the
extension portions 7 of the stator 5 partially pass through the two-part
pump housing which is identified by reference numeral 9. The pump
i0 mechanism 1 which as shown in Figure 3 is in the form of a dual-stage
side-channel pump mechanism comprises a first housing portion 10 with a
fuel inlet 11, a second housing portion 12 with a fuel outlet 13, and a pump
impeller in the form of a vane impeller 14 mounted rotatably between the
housing portions 10 and 12. The impeller 14 co-operates with a first side
i5 channel 15 of the first housing portion 10 and a second side channel (not
shown) in the second housing portion 12. The side channels extend
substantially concentrically with respect to the axis of the impeller 14. As
already mentioned above, the pump mechanism shown in Figure 3 is of a
two-stage design configuration, and it will be appreciated that the pump
20 chamber formed by the pump housing 9 is cylindrical.
The impeller 14 of the pump mechanism is enclosed by a magnetic
ring 16 having permanent-magnetic properties. The magnetic ring 16 can
be composed of magnets which are arranged in a discretely distributed
array around the periphery of the impeller 14. It will be appreciated
25 however that the ring 16 can also be formed in one piece from plastic
material with suitably magnetised ferrite portions incorporated therein.
The second housing portion 12 is provided with peripherally arcuately
arranged openings 17 therethrough, as can be particularly clearly seen
from Figures 3 and 4. The contour of the openings 17 corresponds to the
30 contour of the extension portions 7 of the stator 5. The openings are
arranged concentrically with respect to the impeller 14 and the inside
diameter of that arrangement is slightly larger than the outside diameter of
the impeller 14 enclosed by the magnetic ring 16, so that the magnetically
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permeable extension portions 7 of the stator can extend into the pump
housing 9, concentrically surrounding the magnetic ring 16 and the impeller
14. As noted above, the extension portions 7 extend axially and
concentrically with respect to the axis of the impeller 14. In that way,
formed between the extension portions 7 and the magnetic ring 16 is a
magnetically effective gap in the form of a radial gap so that the impeller
14 performs both the function of the pump impeller and also acts as the
rotor of the motor 2. This highly compact arrangement of the pump
mechanism 1 and the motor 2 relative to each other also permits effective
guidance for the flow of fuel which flows with a cooling action around the
field windings 8 of the stator 5.
The housing portions 10 and 12 are of a circular or disk-shaped
configuration, as can be seen for example from Figure 3, and it will be
appreciated that the diameter thereof is larger than the diameters of the
stator 5 and the impeller 14.
Referring now to Figure 4, in the embodiment of the pump
mechanism 1 illustrated therein it is in the form of a dual-flow pump
mechanism. With the pump impeller being of a dual-flow configuration, its
thickness is markedly less than the thickness of a dual-stage impeller. The
magnetic ring 16 however must be of a certain minimum thickness in order
to achieve the desired output or in order to be able to apply a
correspondingly high level of torque.
In order to achieve a simplification of the pump mechanism 1
according to the invention in terms of production processes and
engineering, the embodiment of the pump mechanism 1 shown in Figure 4
provides that the housing portions 10 and 12 and also the impeller 14 and
a spacer ring which is identified by reference 18 are in the form of flat
disks. The magnetic ring i6 is arranged floatingly, that is to say axially
displaceably, with respect to the impeller 14, while the magnetic ring 16
and the impeller 14 are connected together in positively locking relationship
in the peripheral direction by way of entrainment portions indicated at 19 in
Figure 4 on the impeller 14 and corresponding recesses indicated at 20 in
the magnetic ring 16 so that the magnetic ring 16 and the impeller 14 are
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guided one within the other in non-rotational relationship with each other,
that is to say, so that they can rotate together with each other but they are
not rotatable relative to each other. So that all components can be in the
form of disks with the pump housing being of a suitable depth, the first
housing portion 10 and the second housing portion 12 are screwed together
with the interposition of the spacer ring 18. This arrangement affords the
advantage that all the disk-shaped components can be subjected to
finishing machining by lapping and grinding, whereby the housing sliding
and bearing surfaces enjoy a greater degree of flatness and smoothness
and a smaller depth of roughness in their surface. The recesses 20 in the
magnetic ring 16 are so selected that the impeller 14 is axially centered in
the magnetic ring 16 by way of the sliding surfaces of the first housing
portion 10 and the second housing portion 12. As already indicated above
and as will be readily apparent such an arrangement also affords cost
advantages.
As an alternative to the structure shown in Figure 4, it is also
possible for the magnetic ring 16 to be in the form of a component which
can be fitted on to the impeller 14 by snap engagement or by latching or
detent engagement.
As will be seen from the foregoing, the invention can provide an
electric fuel pump of an improved structural configuration, while retaining
the advantages of a design which is shallow in the axial direction, that is to
say in the direction of the pump impeller axis. The electrically operated fuel
pump can be of such a design configuration that it is relatively simple to
manufacture and can be easily produced as a high-quality unit, as well as
affording enhanced versatility of design options.
It will be appreciated that the above-described embodiments of the
invention have been set forth solely by way of example and illustration of
the principles thereof and that further modifications and alterations may be
made therein without thereby departing from the spirit and scope of the
invention.
