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BACKGROUND OF THE INVENTION
The present invention relates to an electric fuel pump device for use in
pumping a liquid fuel from a fuel reservoir to a fuel consuming equipment.
More particuarly, the invention is concerned with an electric fuel pump
device for pumping a liquid fuel from a fuel tank to the combustion
chamber of an engine of a vehicle.
In general, electronic fuel injecting pump system of vehicle engine
incorporates an electric fuel pump which is adapted to pump a liquid fuel
from the fuel tank to the combustion chamber of the engine, at a
comparatively high pressure of 2 to 3 Kg/cm.sup.2. In order to obtain the
comparatively high pressure, constant volume type pump is used in the
electric fuel pump used for this purpose.
Although some fuel pump devices incorporate centrifugal pumps, the use of
such fuel pump devices is limited only to the cases where the discharge
pressure is as low as or less than 1 Kg/cm.sup.2. The fuel pump apparatus
employing a constant volume type pump cannot acquire the desired
performance unless it is fabricated at a high precision, so that the
production cost is raised and, in addition, the levels of the vibration
and noise are inconviniently increased due to a large pulsation of the
discharge pressure. To the contrary, the fuel pump device incorporating a
centrifugal pump is hardly operative to provide a high discharge pressure
at small flow rate, although it is suitable for providing a large flow
rate at a comparatively low pressure.
In order to obviate the above-described shortcomings of the prior art, the
present inventors have proposed a fuel pump device incorporating a
regenerative pump in the pumping section thereof. The regenerative pump,
which is referred to also as "Wesco pump" can provide a high discharge
pressure without any pulsation at a reduced level of noise. It is possible
to easily obtain a high pressure of 2 to 3 Kg/cm.sup.2 by using a
regenerative pump, particuarly a regenerative pump having an impeller of
closed vane type. In the use of the regenerative pump of this type,
however, it is necessary to keep suitable distances or clearances between
both axial end surfaces of the impeller and the axial inner surfaces of
the pump casing, for otherwise the axial end surface may inconveniently
contact the opposing axial inner surface of the casing to generate a
friction which in turn increases the driving torque to seriously
deteriorate the pump performance. The following two ways can be taken as
countermeasures for overcoming these problems. The first way is to
precisely locate and fix the impeller on the rotor shaft, while the second
way is to maintain a balance of pressure between both sides of the
impeller while mounting the latter axially movable. These countermeasures,
however, require the parts have to be fabricated at a considerably high
precision, resulting in a raised cost of production.
SUMMARY OF THE INVENTION
Accordingly, an object of the invention is to provide an electric fuel pump
device capable of pumping a liquid fuel at a high discharge pressure
without any pulsation and at a reduced level of noise.
Another object of the invention is to provide an electric pump device in
which the deterioration in the durability and performance of the pump, as
well as generation of noise, attributable to the accidental contact
between the inner surface of the casing and the opposing axial end surface
of the impeller is eliminated and, at the same time, the production cost
is lowered economically.
To these ends, according to an aspect of the invention, there is provided
an electric fuel pump device comprising a regenerative pump section and an
electric motor section for driving the regenerative pump section, wherein
the improvement comprises that the regenerative pump section includes a
pump casing having a first inner surface and a second inner surface spaced
axially from each other to define therebetween a pump chamber, and an
impeller accomodated by the pump chamber and mounted on a rotor shaft for
rotation as a unit therewith but axially movably relatively to the rotor
shaft, the rotor shaft being adapted to be rotated by the electric motor
section, the impeller having a first axial end surface opposing to the
first inner surface of the pump casing leaving a first gap therebetween
and the other axial end surface opposing to the second inner surface of
the pump casing with a second gap left therebetween, each of the first
inner surface and the second inner surface of the pump casing having an
axial thrust generating surface of such a shape that the gap is gradually
decreased towards the downstream side of the fuel introduced into the gap,
thereby to prevent the accidental contact between the impeller and the
first and second inner surfaces of the pump casing during operation of the
pump.
The above and other objects, features and advantages of the invention will
become clear from the following description of the preferred embodiments
taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a sectional view of an electric fuel pump in accordance with an
embodiment of the invention, taken along the axis thereof;
FIG. 2 is a sectional view taken along the line II--II of FIG. 1;
FIG. 3 is a view of the fuel pump device shown in FIG. 1 as viewed in the
direction of arrows III--III, showing particularly the thrust generating
surface formed on the second inner surface of the pump casing;
FIG. 4 is a sectional view taken along the line IV--IV of FIG. 3;
FIG. 5 is a sectional view taken along the line V--V of FIG. 3;
FIG. 6 is a sectional view taken along the line VI--VI of FIG. 3;
FIG. 7 is a sectional view taken along the line VII--VII of FIG. 3;
FIG. 8 is a view of the fuel pump device shown in FIG. 1 as viewed in the
direction of the arrows VIII--VIII showing particularly a thrust
generating surface formed on the first inner surface of the pump casing;
FIGS. 9A to 9C are illustrations of wedging effect;
FIG. 10 is an illustration of the state of flow of fuel introduced into the
second gap;
FIG. 11 is an illustration of the behaviour of the impeller in the
operating state of the fuel pump device;
FIG. 12 is an illustration of the performance of the fuel pump device in
comparison with the device having no thrust generating surface;
FIG. 13 is a view similar to that in FIG. 3 showing a thrust generating
surface provided in the fuel pump device in accordance with a second
embodiment of the invention;
FIG. 14 is a sectional view taken along the line XIV--XIV of FIG. 13;
FIG. 15 is a sectional view taken along the line XV--XV of FIG. 13;
FIG. 16 is a sectional view taken along the line XVI--XVI of FIG. 13;
FIG. 17 is a sectional view taken along the line XVII--XVII of FIG. 13;
FIG. 18 is a view similar to that in FIG. 3, showing the thrust generating
surface in a fuel pump device constructed in accordance with a third
embodiment of the invention;
FIG. 19 is a sectional view taken along the line XIX--XIX of FIG. 18;
FIG. 20 is a sectional view taken along the line XX--XX of FIG. 18;
FIG. 21 is a view similar to that in FIG. 3, showing the thrust generating
surface in a fuel pump device in accordance with a fourth embodiment of
the invention;
FIG. 22 is a sectional view taken along the line XXII--XXII of FIG. 21;
FIG. 23 is a sectional view taken along the line XXIII--XXIII of FIG. 21;
FIG. 24 is a sectional view taken along the line XXIV--XXIV of FIG. 21;
FIG. 25 is a view similar to that in FIG. 3, showing the thrust generating
surface in a fuel pump device in accordance with a fifth embodiment of the
invention;
FIG. 26 is a sectional view taken along the line XXVI--XXVI of FIG. 25;
FIG. 27 is a sectional view taken along the line XXVII--XXVII of FIG. 25;
FIG. 28 is a sectional view taken along the line XXVIII--XXVIII of FIG. 25;
FIG. 29 is a sectional view taken along the line XXIX--XXIX of FIG. 25; and
FIGS. 30A and 30B are sectional views showing modifications of the thrust
generating surface.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIGS. 1 thru 8 show an electric fuel pump in accordance with a first
embodiment of the invention. This fuel pump device is adapted to be
immersed, for example, in a liquid fuel contained by a fuel tank of a
vehicle. Referring first to FIG. 1, the pump device has a generally
cylindrical housing 10 having two end walls 13 and 14 which are provided
with openings 11 and 12, respectively. The pump device is further provided
with a regenerative pump section 15 disposed in the housing in contact
with one axial end surface of the housing 10, and an electric motor
section 16 disposed in the housing 10 to take a position adjacent to the
regenerative pump section. The motor section 16 is operatively connected
to the pump section 15 to drive the latter. The regenerative pump section
15 has a pump casing which is composed of a first casing part 18 having an
inner surface 17 and an outer surface which materially closes the opening
11 in one axial end wall of the housing 10, and a second housing part 21
having an inner surface 19 which cooperates with the inner surface 17 of
the first casing part in defining therebetween a pump chamber.
A rotor shaft 25 extends coaxially with the housing 10 and is rotatably
supported at its one end 26 by a bearing 28 which is press-fitted into the
axial central bore 27 formed in the second casing part 21. The
above-mentioned axial end 26 of the shaft 25 extends through the pump
chamber and has an axial end surface which is received by a central recess
31 formed in the inner surface 17 of the first casing part 18.
A substantially disk-shaped impeller 32 is mounted on the rotor shaft 25 in
such a manner as to be able to rotate within the pump chamber. The
impeller 32 is provided with an axial central bore 33 (See FIG. 2) adapted
to be fit by the axial end portion 26 of the shaft 25. The wall defining
the central bore 33 is provided with a pair of diametrically opposing
axial grooves 34. A pin 36 having a circular cross-section extends through
the axial end portion 26 of the shaft 25. Both ends of the pin 36 are
received by the pair of axial grooves 34. The impeller 32 is mounted on
the shaft 25 for rotation as a unit with the latter but axially movably
relatively thereto. The impeller 32 has one axial end surface 38 which
opposes to the first inner surface of the pump casing, i.e. the inner
surface 17 of the first casing part 18, with a first gap w.sub.1 left
therebetween, and the other axial end surface 39 opposing to a second
inner surface of the pump casing, i.e. the inner surface 19 of the second
casing part 21, with a second gap w.sub.2 left therebetween. Although
shown in FIG. 1 in an exaggerated manner, these gaps w.sub.1 and w.sub.2
are actually very small.
The recess 31 formed in the first casing part 18 defines a chamber 43 in
cooperation with the outer peripheral surface and axial end surface of the
axial end portion 26 of the rotor shaft 25. The axial central bore 27
formed in the second casing part 21 defined a chamber 44 in cooperation
with the axial end surface of the bearing 28 and the outer peripheral
surface of the axial end portion 26 of the shaft 25. As clearly shown in
FIG. 2, the wall surface of the axial central bore 33 provided in the
impeller 32 is provided with a second pair of axial grooves 45 opposing
diametrically to each other. The chambers 43 and 44 are communicated with
each other through the second pair of axial grooves 45 thereby to keep
balance of pressure between the chambers 43 and 44.
The impeller 32 has an outer peripheral portion which defines a
substantially annular passage 46 in the pump casing parts 18 and 21. A
plurality of radial vane grooves 47 are formed in the outer peripheral
portion of the impeller at both axial end surfaces 38 and 39 of the latter
at an equal circumferential pitch. In the illustrated impeller, the bottom
surfaces of the vane grooves 47 formed in one axial end surface 38 do not
intersect the other axial end surface 39 of the impeller. Similarly, the
bottom surfaces of the vane grooves 47 formed in the other axial end
surface 39 do not intersect the one axial end surface 38 of the impeller.
Thus, the illustrated embodiment is a socalled closed vane type impeller.
The pump passage 46 is communicated with a liquid fuel in a fuel reservoir
(not shown) through a suction port 51 formed in the first casing part 18
and also with a space in the housing 10 through a discharge port 52 formed
in the second casing part 21.
The electric motor section 16 has a couple of semi-cylindrical permanent
magnets 61 disposed in the housing 10 concentrically with the rotor shaft
25, an armature fixedly mounted on the rotor shaft 25 concentrically with
the permanent magnets 61, and a commutator 63 connected to the armature 62
and fixed to the rotor shaft 25. Brushes 64 are held in sliding contact
with the commutator 63. Brushes 64 are held by brush holders 66 fixed to
an end block 67 which is disposed in the housing in such a manner as to
materially close the opening 12 formed in the other axial end wall 14 of
the housing 10. The end block 67 has a central recess 71 formed in one
axial end surface facing the space in the housing 10 and a second recess
72 formed in the bottom of the central recess 71. A plurality of
circumferentially spaced grooves 73 are formed in the wall of the second
recess 72. Each groove 73 is provided with a tapered bottom surface. The
end block 67 is provided with a hollow projection 74 projecting outwardly
from the other axial end surface thereof. The space in the hollow
projection 74 is communicated with the second recess 72. The hollow
projection 74 is connected to fuel consuming equipment such as an engine
which is not shown.
The shaft 25 is rotatably supported at its other end 81 by a bearing 82
which is seated on a chambered seat 83 in the recess 72 and is held at the
predetermined position by an annular retainer 85 disposed in the central
recess 71. The retainer 85 is provided with a plurality of
circumferentially spaced holes 86.
The shaft 25 is adapted to be held at a predetermined axial position by a
spacer 87 which is mounted on the shaft 25 in contact with one axial end
surface of the bearing 82 and by a spacer 88 which is mounted on the shaft
25 in contact with one axial end surface of the bearing 28.
The electric fuel pump device having the described construction operates in
a manner explained hereinunder. As electric power is supplied from a power
source (not shown) through the brushes 64, the armature 62 starts to
rotate and the rotation of the armature 62 is transmitted to the impeller
32 through the shaft 25, so that the impeller 32 rotates in the clockwise
direction as indicated by an arrow in FIG. 2. In consequence, the liquid
fuel is sucked from the fuel reservoir into the pump passage 46 through
the suction port 51. The fuel thus sucked is boosted by the vane grooves
47 of the impeller 32 as it flows along the pump passage 46 and is
discharged into the space in the housing 10 through the discharge port 52,
and is sent to the fuel consuming equipment through the annular gap
between the permanent magnet 61 and the armature 62, holes 86 formed in
the retainer 85, grooves 73 formed in the end block 67 and the bore in the
hollow projection 74.
During the operation of the pump, a flow of fuel is formed as shown in FIG.
10, in the second gap w.sub.2 formed between the other axial end surface
39 of the impeller 32 and the second inner surface 19 of the pump casing.
On the other hand, a flow of fuel is generated in the first gap w.sub.1
between one axial end surface 38 of the impeller 32 and the first inner
surface 17 of the pump casing, in symmetry to the first-mentioned flow of
fuel shown in FIG. 10 respect to a plane which is perpendicular to the
axis of the rotor shaft 25. Namely, when a pumping action is made by the
rotation of the impeller 32, the pressure of the fuel in the pump passage
46 is successively increased substantially linearly from the suction side
to the discharge side. Meanwhile, fuel is introduced into the portions 43,
44 of the pump chamber surrounding the shaft 25 from the pump passage 46
through the first and second gaps w.sub.1 and w.sub.2 and the pressure in
the chamber portions 43, 44 is increased up to 40 to 45% of the discharge
pressure. The flow of fuel in the first and second gaps w.sub.1 and
w.sub.2 is influenced by the pressure differential between the pump
passage 46 and the chambers 43, 44. More specifically, in the upstream
half part of the pump passage 46 extending between the suction port 51 and
the discharge port 52, a radial flow of fuel is generated to flow from the
chambers 43, 44 to the pump passage 46, whereas, in the downstream half
part of the pump passage 46, a flow of fuel is generated to flow from the
pump passage 46 to the chambers 43, 44. In addition, since the impeller 32
is rotating, circumferential flow of fuel is generated in each of the
first and second gaps w.sub.1 and w.sub.2 accompanying the surfaces of the
impeller 32 because of the viscosity of the fuel. Thus, in each gap, the
flow of fuel is formed as a vector sum of the radial flow component and
the circumferential flow component. In consequence, a flow of fuel as
indicated by arrow in FIG. 10 is formed in the second gap w.sub.2, whereas
the flow of fuel is generated in the first gap w.sub.1 in symmetry to that
shown in FIG. 10 with respect to a plane perpendicular to the axis of the
shaft 25.
FIG. 8 shows the result of an experiment conducted by the present
inventors. This experiment was conducted with a model of the pump device
having a regenerative pump section which is enlarged to a size 8 times as
large as that of the actual one and having a pump casing made of a
transparent acrylic resin to permit the inspection of the inner side. The
pump was constructed such that the Reynolds number and the flow direction
in the first and second gaps are identical to those in the actual
regenerative pump section to create a flow in each gap similar to that
obtained in the actual gap. The pump casing used in this experiment was
devoid of a later-mentioned thrust generating surface.
As stated before, in order to obtain a higher performance of the fuel pump
device, it is desirable to maintain the first and second gaps w.sub.1 and
w.sub.2 substantially equal to each other to minimize the chance of
contact between the end surfaces 38, 39 of the impeller 32 and the inner
surfaces 17, 19 of the pump casing, during rotation of the impeller 32. To
this end, the fuel pump device of the invention employs an arrangement
which acts to hold the impeller 32 substantially at the mid position
between the inner surfaces 17 and 19 of the pump casing and, when the
impeller is moved axially towards the inner surface 17 or 19 of the pump
casing, to push back the impeller 32 in the opposite direction.
Namely, as shown in FIGS. 3 thru 7, the fuel pump device of the first
embodiment has five recesses 100a to 100e having tapered bottom surfaces,
i.e. thrust generating surfaces 100a' to 100e', formed in the second inner
surface of the pump casing, i.e. in the inner surface 19 of the second
casing part 21. As shown in FIG. 6, a plurality of recesses 101a to 101e
having similar thrust generating surfaces 101a' to 101e' are formed in the
first inner surface of the pump casing, i.e. in the inner surface of the
first casing part 18.
As will be understood from a comparison between the arrangements shown in
FIGS. 3 and 10, the bottom surfaces of the recesses 100a to 100e formed in
the inner surface 19 of the second casing part 21, i.e. the thrust
generating surfaces 100a' to 100e', extend in the direction of flow of the
fuel in the second gap w.sub.2. The recess 100a and the thrust generating
surface 100a' of the same have cross-sectional configurations as shown in
FIGS. 4 and 5. The recess 100b and its thrust generating surface 100b'
have similar cross-sections. These recesses 100a and 100b open at their
innermost portions to the chamber 44 constituting the part of the pump
chamber surrounding the rotor shaft 25. The thrust generating surfaces
100a', 100b' of these recesses are inclined in such a manner as to
gradually decrease the depth of the recesses 100a, 100b from the portions
communicating with the chamber 44 along the length of these recesses 100a,
100b thereby to gradually decrease the second gap w.sub.2 towards the
downstream side as viewed in the direction of flow of fuel.
The recess 100e and the thrust generating surface 100e' have shapes as
shown in FIGS. 6 and 7, as well as the recesses 100c, 100d and their
thrust generating surfaces 100c', 100d'. Namely, these recesses 100c to
100e communicate with the pump passage 46 at their innermost portions, and
the thrust generating surfaces 100c' to 100e' of these recesses are so
inclined as to gradually decrease the depth of the recesses 100c to 100e
from the portions communicating with the pump passage 46 along the length
of these recesses thereby to gradually decrease the second gap w.sub.2
gradually towards the downstream side as viewed in the direction of flow
of the fuel.
The recesses 101a to 101e formed in the inner surface 17 of the first
casing part are similar to the recesses 100a to 100e formed in the inner
surface 19 of the second casing part 21. The recesses 101a to 101e are
formed in symmetry to the recesses 100a to 100e with respect to the plane
perpendicular to the axis of the shaft 25. The thrust generating surfaces
101a' to 101e' of the recesses 101a to 101e extend in the direction of
flow of the fuel in the first gap w.sub.1. The innermost portions of the
recesses 101a, 101b open to the chamber 43 constituting the portion of the
pump chamber surrounding the shaft 25, and the innermost portions 101c,
101d, 101e open to the pump passage 46. The thrust generating surfaces
101a' to 101e' of these recesses 101a to 101e are so inclined as to
gradually decrease the first gap w.sub.1 towards the downstream side as
viewed in the direction of flow of the fuel.
In FIGS. 3 and 8, a number of laterally extending lines in recesses are the
lines of equal depth.
Thanks to the provision of the thrust generating surfaces 100a' to 100e'
and 101a' to 101e', axial thrust forces act on the impeller 32 due to a
wedging action which will be detailed later, so that the impeller 32 can
be maintained substantially at the mid point between the inner surface 17
of the first casing part 18 and the inner surface 19 of the second casing
part 21.
The wedging action mentioned before will be explained with specific
reference to FIGS. 9A to 9C. Referring first to FIG. 9A, a stationary wall
110 has an inclined surface 110a which oposes to a horizontal surface 111a
of a movable wall 111 with a small gap C. Then, as the horizontal surface
111a is moved in the direction of the arrow U, a flow of fluid is
generated in the gap C to flow from the wider side to the narrower side as
indicated by an arrow V. This flow of fluid acts just like as a wedge
driven into the gap C to produce a so-called wedging effect to generate a
load W which acts on the horizontal surface 111a to move the same away
from the inclined surface 110a. A curve Z shows the distribution of the
pressure P acting on the horizontal surface 110a.
The load W is increased as the horizontal surface 111a gets closer to the
inclined surface 110a, i.e. as the gap C is decreased. The wedging action
is produced to apply a load W on the horizontal surface 111a, even when
the horizontal surface 111a is stationed without being moved in the
direction of the arrow U, provided that the flow of fluid as indicated by
the arrow V is produced.
The relationship between the thrust generating surfaces 100a' to 100e' and
the opposing end surface 39 of the impeller 32 a shown in FIGS. 3 thru 6
is similar to the relationship shown in FIG. 9A between the inclined
surface 110a and the horizontal surface 111a.
FIG. 9B schematically shows the relationship between one 100a' of the
thrust generating surfaces and the end surface 39 of the impeller 32.
Namely, referring to FIG. 9B, the impeller 32 rotates in the direction of
the arrow U, while the fuel flows in the second gap w.sub.2 from the wider
side to the narrower side of the second gap w.sub.2 as indicated by an
arrow V. Therefore, a load W is applied to the end surface 39 of the
impeller 32 to move the same away from the thrust generating surface 100a.
FIG. 9B illustrates only the relationship between the thrust generating
surface 100a' and the end surface 39 of the impeller 32, but the same
relationship applied also to that between the thrust generating surfaces
100b' to 100e' and the end surface 39, as well as to that between the
thrust generating surfaces 101a' to 101e' and the end surface 38 of the
impeller 32.
As stated before, the innermost portion of the recess 100a in the first
embodiment opens to the chamber 44. This, however, is not exclusive and it
is possible to adopt a recess 100 shown in FIG. 9C, insteadly of opening
the same to the chamber 44. However, in the case where the recess 100 as
shown in FIG. 9C is used, there is a fear that the fuel does not smoothly
flow along the thrust generating surface 100' of the recess 100 to fail to
apply sufficient load to the end surface 9. In contrast to the above, by
making the innermost portion of the recess 100a open to the chamber 44 as
in the first embodiment, it is possible to smoothly introduce the fuel
into the second gap w.sub.2 along the thrust generating surface 100a' of
the recess 100a as shown in FIG. 9B, so that a sufficiently large wedging
effect is produced to apply a sufficiently large load W to the end surface
39 of the impeller 32. For the same reason as above, the innermost portion
of the recess 100b and the innermost portions of the recesses 100c to 100e
in the first embodiment open to the chamber 44 and the pump passage 46,
respectively. Meanwhile, the innermost portions of the recesses 101a, 101b
and the innermost portions of the recesses 101c to 101e are made to open
to the chamber 43 and the pump passage 46, respectively.
As will be clearly seen from the foregoing description, thanks to the
provision of the thrust generating surfaces 101a' to 101e' and 100a' to
100e' on the inner surfaces 17 and 19 of the pump casing, the impeller 32
is urged during operation of the pump device to the left as viewed in FIG.
1 by the fuel introduced into the first gap w.sub.1 and to the right as
viewed in FIG. 1 by the fuel introduced into the second gap w.sub.2
respectively. Assuming here that the impeller 32 is urged to the left as
viewed in FIG. 1 by an external force to increase the first gap w.sub.1
while decreasing the second gap w.sub.2, the pressure for urging the
impeller to the left by the weding effect of the fuel introduced into the
first gap w.sub.1 is decreased while the rightward pressing force caused
by the wedging effect of the fuel introduced into the second gap w.sub.2
is increased. Therefore, the impeller 32 is pushed back rightwardly to the
position where the first and second gaps w.sub.1 and w.sub.2 are
substantially equal to each other. Similarly, the impeller is forced back
to the above-mentioned position to substantially equalize the first and
second gaps w.sub.1 and w.sub.2 when the impeller 32 is happened to be
moved to the right by an external force. Thus, the impeller 32 is held
substantially at the mid point between the first inner surface 17 and the
second inner surface 19 of the pump casing to remarkably reduce the chance
of contact between the impeller and both inner surfaces 17, 19 of the pump
casing.
FIG. 11 shows the behaviour of the impeller 32 of the fuel pump device of
the first embodiment in relation to time. As shown by a line S, the
impeller 32 is moved to the substantially mid point between the inner
surfaces 17 and 19 of the pump casing soon after the fuel pump device is
started and held substantially at a position near the above-mentioned mid
point during the operation of the pump device. Therefore, the undesirable
contact between the impeller 32 and the inner surfaces 17, 19 of the pump
casing is avoided perfectly.
FIG. 12 shows the result of an experiment conducted to compare the
performance of the fuel pump device of the first embodiment having the
above-mentioned recess 101a to 101e and the recesses 100a to 100e formed
in the inner surfaces 17 and 19 of the pump casing with the performance of
a fuel pump device having no recesses. More specifically, in FIG. 12,
full-line curves X and Y represent the efficiency % and the discharge
pressure P (Kg/cm.sup.2) in relation to the discharge rate as observed in
the fuel pump device of the first embodiment, while broken line curves X'
and Y' show the efficiency and dischage pressure in relation to the
discharge rate as observed in the fuel pump device having no recess. From
this Figure, it will be seen that the discharge pressure and the
efficiency are considerably increased to improve the performance of the
fuel pump device remarkably, by the provision of the recesses 101a thru
101e and 100a thru 100e in the inner surfaces 17 and 19 of the pump
casing.
A second to fifth embodiments of the invention, employing different shapes
and numbers of the thrust generating surfaces 100a' to 100e' and 101a' to
101e' will be explained hereinafter with reference to FIGS. 13 thru 29. In
the first embodiment described hereinbefore, the thrust generating
surfaces 101a' to 101e' formed in the first inner surface of the pump
casing, i.e. in the inner surface 17, are positioned in symmetry to the
thrust generating surfaces 100a' to 100e' formed in the second inner
surface 19 with respect to the plane perpendicular to the axis of the
shaft 25. Also, the shapes of the thrust generating surfaces formed in the
inner surface 17 and the thrust generating surfaces formed in the inner
surface 19 are in symmetry with respect to the above-mentioned plane. This
symmetrical arrangement applied also to the second to fifth embodiments.
Therefore, in the following description of the second to fifth embodiments
of the invention, the explanation will be made only to the thrust
generating surface formed in the second inner surface of the pump casing,
while the explanation of the thrust generating surface in the first inner
surface 17 is omitted.
FIGS. 13 thru 17 show a second embodiment of the invention in which
recesses 200a to 200e having respective thrust generating surfaces 200a'
to 200e' are formed in the inner surface 19 of the pump casing. These
recesses 200a to 200e resemble the recesses 100a to 100e of the first
embodiment but are different from those in the first embodiment in that
the recesses 200a and 200b do not open at their innermost portions to the
chamber 44 and that the innermost portions of the recesses 200c to 200e do
not open to the pump passage 46. Although the advantages of the invention
are achieved by the arrangement of the second embodidment, the first
embodiment is preferred to the second one for the reasons stated before in
connection with FIGS. 9B and 9C.
FIGS. 18 to 20 show a third embodiment of the invention in which a single
recess 300e having a thrust generating surface 300e' is formed in the
inner surface 19 of the pump casing. The recess 300e resembles the recess
100e of the first embodiment but has greater width and length than the
latter. In addition, the recess 300e extends in the longitudinal direction
at such a slight curvature as to project outwardly. The recess 300e opens
at its innermost portion to the pump passage 46. The thrust generating
surface 300e' extends at such an inclination that the depth of the recess
300e is gradually decreased from the position of the pump passage 46 along
the length of the recess 300e which extends at a curvature. In FIG. 18, a
multiplicity of lines extending across the recess 300e are the lines of
equal depth. In the third embodiment also, the thrust generating surface
300e' gradually decreases the gap w.sub.2 towards the downsream side as
viewed in the direction of flow of the fuel introduced into the second gap
w.sub.2, so that an axial thrust force is applied to the impeller by the
wedging effect explained before. In addition, since the recess 300e and
the thrust generating surface 300e' have substantial size, the weding
effect will be never suppressed largely even if the state of flow of fuel
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