Electric fuel pump

Vane pieces (31) which are in an outer peripheral edge portion of an impeller (30) are divided into front and rear groups by a partition wall (32), and arranged in a staggered pattern, and outer peripheral faces of the vane pieces (31) are protruded toward the outer peripheral side with respect to the outer peripheral face of the partition wall (32). Therefore, fuel portions respectively entering vane grooves (33) which are divided into front and rear groups do not simultaneously collide against end faces (9b) of radial seal portions (9a). Consequently, the level of noises due to the fuel collision can be lowered. Furthermore, a reverse-flow region is prevented from being produced immediately above the partition wall (32). Therefore, the pump efficiency can be improved.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The present invention relates to an electric fuel pump which is mounted in
 a fuel tank of an automobile or the like, and which forcedly delivers fuel
 to an engine, and particularly to an electric fuel pump in which the noise
 level can be lowered and the efficiency can be improved.
 2. Description of the Related Art
 FIGS. 6 and 7 are an enlarged partial perspective view of an impeller of an
 electric fuel pump of the conventional art which is disclosed in, for
 example, JP-B-63-63756, and an enlarged perspective view of the periphery
 of a radial seal portion of a pump base of the pump.
 In the figures, 10 denotes the impeller which has many vane pieces 21 in an
 outer peripheral edge portion of a disk-like shape. The vane pieces 21 are
 divided into front and rear groups by a partition wall 22, and a vane
 groove 23 is formed between the vane pieces 21. The reference numeral 9
 denotes the pump base which constitutes a pump casing (not shown), and
 which has an arcuate strip-like pump passage 13, a suction port 14, a
 discharge port 15, the radial seal portion 9a for preventing a reverse
 flow of fuel from occurring, and an end face 9b which changes the flow
 direction of the fuel.
 When the impeller 10 is rotated in the pump casing (not shown), the fuel
 sucked from the suction port 14 flows into the vane grooves 23, is
 provided with a kinetic energy by the vane pieces 21, and then forcedly
 sent through the pump passage 13 toward the discharge port 15. The fuel
 which is forcedly sent to the discharge port 15 as described above
 collides against the end face 9b of the radial seal portion 9a which is
 formed in the final end of the pump passage, and is then discharged from
 the discharge port 15 while the direction is changed.
 In this configuration, therefore, the fuel portions respectively entering
 the right and left vane grooves 23 which are divided into front and rear
 groups by the partition wall 22 simultaneously collide against the end
 faces 9b of the radial seal portions 9a. Consequently, the configuration
 has a problem in that the level of noises due to the fuel collision is
 high.
 As a countermeasure against this problem, for example, known is the
 configuration which is disclosed in JP-A-60-173390 and shown in FIG. 8. In
 an impeller 10 of the configuration, vane pieces 21 on both the sides of a
 partition wall 22 are shifted from each other by 1/2 pitch, so that
 timings when the fuel portions respectively entering vane grooves 23 on
 both the sides of the partition wall 22 collide against end faces 9b of
 radial seal portions 9a are shifted from each other. As a result, the
 impact force due to the fuel collision is reduced, thereby lowering the
 noise level. The periphery of the radial seal portion is configured in the
 same manner as above-described FIG. 7.
 In the configuration which is disclosed in JP-A-61-59283 and shown in FIGS.
 9 and 10, a step 9c is disposed in an end face 9b of each radial seal
 portion 9a of a pump base 9 which constitutes a pump casing (not shown),
 whereby timings of fluid collision are shifted from each other to lower
 the noise level. Furthermore, the outer peripheral face of each vane piece
 21 is protruded from that of a partition wall 22 in an outer peripheral
 direction, so that a reverse-flow region (a region where the pumping
 function is impeded) is prevented from being produced immediately above
 the partition wall 22, whereby the pump efficiency is improved.
 Recently, needs for lowering the operating sound level and reducing fuel
 consumption are increasing. In order to satisfy the needs, in an electric
 fuel pump of the conventional art, a countermeasure in which the shape of
 an impeller is changed so as to lower the operating sound level as
 described above, or that in which the shape of an impeller is changed and
 the shape of a pump base is changed so as to lower the operating sound
 level and improve the pump efficiency is taken. From the viewpoints of
 dimensional accuracy and mechanical strength, however, a pump base is
 usually produced by aluminum die casting. Consequently, there is a problem
 in that modification or production of production dies is very expensive.
 SUMMARY OF THE INVENTION
 The invention has been conducted in order to solve the above-discussed
 problems. It is an object of the invention to provide an electric fuel
 pump in which the noise level during operation is lowered and the pump
 efficiency is high, without changing the shape of a pump base.
 To achieve the above object, according to the invention, there is provided
 an electric fuel pump comprising: an impeller which has many vane pieces
 in an outer peripheral edge portion of a disk-like shape; a motor section
 which rotates the impeller; and a pump casing which houses the impeller,
 which forms an arcuate strip-like pump passage that elongates along the
 outer peripheral edge portion of the impeller, and which has a suction
 port in one end portion of the pump passage, and a discharge port in
 another end portion, wherein, in the impeller, the vane pieces which are
 divided into front and rear groups by a partition wall are arranged in a
 staggered pattern, and outer peripheral faces of the vane pieces are
 protruded toward an outer peripheral side with respect to an outer
 peripheral face of the partition wall.
 Also, according to the invention, an inclined face wall of the partition
 wall is formed so that, as the inclined face wall approaches nearer to a
 side face wall of each of the vane pieces, a distance between the inclined
 face wall of the partition wall and an end face of the impeller on a side
 of the vane piece is further reduced.
 Further, according to the invention, the inclined face wall of the
 partition wall is formed into a spherical shape.
 Furthermore, as seeing each of the vane pieces in a circumferential
 direction, the vane piece stands with overlapping another adjacent vane
 piece.
 Further, according to the invention, inner face walls of the vane pieces
 are formed to obliquely intersect with the outer peripheral face of the
 partition wall.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
 Now, a description will be given in more detail of preferred embodiments of
 the invention with reference to the accompanying drawings.
 FIG. 1 is a side view showing an electric fuel pump of an embodiment of the
 invention, partially in section, FIG. 2 is an enlarged perspective view of
 a vane piece portion of an impeller, and FIG. 3 is an enlarged section
 view of the vane piece portion of the impeller and taken along the line
 III--III of FIG. 2. Hereinafter, description will be made with reference
 to FIGS. 1 to 3. The electric fuel pump 1 is configured by a pump section
 2, and a motor section 3 which drives the pump section 2. For example, the
 motor section 3 is a DC motor having brushes which are not shown, and has
 a configuration in which permanent magnets 5 are annularly arranged in a
 cylindrical housing 4 and an armature 6 is concentrically placed on the
 inner peripheral side with respect to the permanent magnets 5.
 The pump section 2 is configured by a pump casing 7 consisting of a pump
 cover 8 and a pump base 9, and an impeller 30 which is housed in the pump
 casing 7. The pump cover 8 and the pump base 9 are formed by, for example,
 aluminum die cast molding.
 The pump base 9 is pressingly inserted and fixed to one end of the housing
 4. A rotary shaft 12 which is formed integrally with the armature 6 is
 passed through and held by a bearing 11 which is fittingly attached to the
 center of the one end. By contrast, the pump cover 8 is fixed to one end
 of the housing 4 by crimping or the like under a state where the cover is
 put on the pump base 9.
 An insertion hole 30a having a substantially D-like shape is formed in the
 center of the impeller 30. A D-cut portion 12a of the rotary shaft 12 is
 loosely inserted into the insertion hole 30a. According to this
 configuration, the impeller 30 is rotated integrally with the rotary shaft
 12 and slidable in the axial direction.
 An arcuate strip-like pump passage 13 is formed in inner side faces of the
 pump cover 8 and the pump base 9 which form the pump casing 7. A suction
 port 14 which communicates with one end of the pump passage 13 is formed
 in the pump cover 8. A discharge port 15 which communicates with the pump
 passage 13 is formed in the pump base 9. A radial seal portion 9a (see
 FIG. 7) for preventing a reverse flow from occurring is formed between the
 suction port 14 and the discharge port 15. The discharge port 15
 communicates with the space in the motor section 3, so that the fuel
 discharged from the discharge port 15 is passed through the motor section
 3 and then forcedly delivered to an engine (not shown) via a fuel outlet
 pipe 16 which is adjacent to the motor section 3.
 The impeller 30 is integrally formed by, for example, phenol resin or the
 like. Many vane pieces 31 which are protruded into the arcuate strip-like
 pump passage 13 are formed in the outer peripheral portion. The vane
 pieces 31 are divided into front and rear groups by a partition wall 32
 and arranged in a staggered pattern. On the same face (the front face or
 the rear face), a vane groove 33 is formed between each of the vane pieces
 31 and another adjacent vane piece 31. Outer peripheral faces of the vane
 pieces 31 are protruded toward the outer peripheral side with respect to
 the outer peripheral face of the partition wall 32.
 Next, the operation of the thus configured electric fuel pump will be
 described.
 When coils (not shown) of the armature 6 of the motor section 3 are
 energized, the armature 6 is rotated, so that the rotary shaft 12 which is
 formed integrally with the armature 6, and the impeller 30 having the
 insertion hole 30a which is engaged with the D-cut portion 12a of the
 rotary shaft 12 are rotated. Therefore, the vane pieces 31 which are in
 the outer peripheral portion of the impeller 30 are rotated along the
 arcuate strip-like pump passage 13, a turning flow is generated in the
 vane grooves 33, and the vane grooves 33 are rotationally moved in the
 pump passage 13, whereby the kinetic energy is increased to produce the
 pumping function.
 As a result, the fuel in a fuel tank (not shown) is sucked into the pump
 passage 13 via the suction port 14, flows into the vane grooves 33, and is
 rotationally moved in the pump passage 13. Thereafter, the fuel is
 forcedly sent toward the discharge port 15, passed through the motor
 section 3, and then forcedly delivered to the engine (not shown) via the
 fuel outlet pipe 16.
 The outer peripheral faces of the vane pieces 31 have a shape in which the
 faces are protruded toward the outer peripheral side with respect to the
 outer peripheral face of the partition wall 32, and a reverse-flow region
 (a region where the pumping function is impeded) is hardly produced
 immediately above the partition wall 32. Therefore, a turning flow is
 efficiently generated in each of the vane grooves 33, so that the pump
 efficiency is improved.
 Each of the vane pieces 31 of the impeller 30 is shifted by 1/2 pitch with
 respect to an adjacent one of the vane pieces 31, so that timings when the
 fuel portions respectively entering the vane grooves 33 on the front and
 rear sides of the partition wall 32 collide against the end faces 9b (see
 FIG. 7) of the radial seal portions 9a are shifted from each other. As a
 result, the noise level in the fuel collision is lowered.
 Next, another embodiment of the invention will be described. FIG. 4 is an
 enlarged perspective view of a vane piece portion of an impeller of the
 other embodiment of the invention, and FIG. 5 is an enlarged section view
 of the vane piece portion of the impeller and taken along the line V--V of
 FIG. 4. Hereinafter, description will be made with reference to FIGS. 1,
 4, and 5.
 In the figures, 40 denotes the impeller. The vane pieces 41, a partition
 wall 42, and vane grooves 43 are configured in the same manner as those of
 the embodiment described above. The reference numeral 41a denotes inner
 face walls, and 41b denotes side face walls which are formed on faces
 where the vane pieces 41 abut against the partition wall 42. The reference
 numeral 42a denotes inclined face walls corresponding to front and rear
 inclined faces of the partition wall 42, and 42b denotes leak grooves
 which are produced in the outer peripheral portion of the partition wall
 42 and between each of the vane pieces 41 and one of the vane pieces 41
 which is on the rear face side with respect to the vane piece.
 Each of the inclined face walls of the partition wall is configured so
 that, as the inclined face wall approaches nearer to the side face wall of
 the corresponding one of the vane pieces, the distance between the
 inclined face wall of the partition wall and the end face of the impeller
 on the side of the vane piece is further reduced.
 Each of the inclined face walls 42a of the partition wall 42 is formed so
 that, as the inclined face wall approaches nearer to the side face wall
 41b of the corresponding one of the vane pieces 41, the distance between
 the partition wall 42 and the impeller face on the side of the vane piece
 41 is further reduced. Preferably, the inclined face walls 42a are formed
 into a spherical shape. As seeing the vane pieces 41 in the
 circumferential direction, the vane pieces are arranged in positions where
 they overlap respective adjacent vane pieces, and in a staggered pattern.
 Each of the inner face walls 41a which intersects with the outer
 peripheral face of corresponding one of the vane pieces 41, and also with
 that of the partition wall 42 is formed so as to obliquely intersect with
 the outer peripheral face of the vane piece 41 and that of the partition
 wall 42.
 Next, the operation will be described. The basic operation as an electric
 fuel pump is identical with that of the embodiment described above, and
 its description is omitted.
 When the vane pieces 41 on the outer peripheral portion of the impeller 40
 are rotated along the arcuate strip-like pump passage 13, turning flows A,
 B, and C (in FIG. 4, only three turning flows are shown) are generated in
 the vane grooves 43. The rotational movement of the vane grooves 43 in the
 pump passage 13 causes the kinetic energies of these turning flows A, B,
 and C to be increased, so that the pressure is raised and the pumping
 function is performed. In the pressure rising process, the turning flows
 are shifted from one another in rotational angle position in the pump
 passage 13, and a pressure difference is generated among the turning
 flows. Therefore, the fuel leaks from the higher pressure side to the
 lower pressure side through the leak grooves between the vane pieces 41.
 The fuel leakage prevents the pressure in the pump passage 13 from rising,
 and hence lowers the pump efficiency.
 In the invention, the inclined face walls 42a of the partition wall 42 of
 the impeller 40 intersect with the side face walls 42b of the vane pieces
 41 so that the thickness of the partition wall 42 is increased. When a
 turning flow is produced along the shape of one of the inclined face walls
 42a, therefore, interference with another turning flow is reduced, whereby
 fuel leakage between turning flows is reduced, so that the pump efficiency
 can be improved. As seeing the vane pieces 41 in the circumferential
 direction, the vane pieces are arranged in positions where they overlap
 other respective adjacent vane pieces 41. When the impeller 40 is rotated,
 therefore, the overlapping portion of each of the side face walls 41b
 functions as a wall which prevents fuel leakage in the rotation direction
 from occurring. As a result, fuel leakage between turning flows which are
 generated in the vane grooves 43 is reduced, and the pump efficiency can
 be improved.
 Moreover, the inner face wall 41a of each of the vane pieces 41 and
 intersecting with the partition wall 42 is formed so as to obliquely
 intersect from the outer peripheral face of the partition wall 42 with
 that of the vane piece 41. Each turning flow is smoothly formed along the
 inclination angle of the inner face wall 41a. Therefore, the pump
 efficiency can be improved.
 In the above, the case where the impeller 40 has the shape in which the
 outer peripheral faces of the vane pieces 41 are protruded toward the
 outer peripheral side with respect to the outer peripheral face of the
 partition wall 42 has been described. In the impellers of the conventional
 art shown in FIGS. 6, 8, and 10, when the inclined face walls 42a of the
 partition wall 42 intersect with the side face walls 42b of the vane
 pieces 41 so that the thickness of the partition wall 42 is increased,
 fuel leakage between turning flows is reduced, and the pump efficiency can
 be improved.
 In the electric fuel pump according to the invention, vane pieces of an
 impeller are divided into front and rear groups by a partition wall, and
 arranged in a staggered pattern, and outer peripheral faces of the vane
 pieces are protruded toward the outer peripheral side with respect to the
 outer peripheral face of the partition wall. Therefore, it is possible to
 obtain an electric fuel pump in which the noise level during operation is
 low and the pump efficiency is high, without changing the shape of a pump
 base.
 Since an inclined face wall of the partition wall is formed so that, as the
 inclined face wall approaches nearer to a side face wall of each of the
 vane pieces, the distance between the inclined face wall of the partition
 wall and an end face of the impeller on the side of the vane piece is
 further reduced, fuel leakage is reduced, and the pump efficiency can be
 improved.
 Since, as seeing each of the vane pieces of the impeller in a
 circumferential direction, the vane piece with overlapping another
 adjacent vane piece, fuel leakage is reduced, and hence the pump
 efficiency can be improved.
 Since the inner face wall of each of the vane pieces of the impeller and
 intersecting with the partition wall is formed so as to obliquely
 intersect from the outer peripheral face of the partition wall with that
 of the vane piece, a turning flow is smoothly formed along the inclination
 angle of the inner face wall. Therefore, the pump efficiency can be
 improved.
 As described above, in the electric fuel pump according to the invention,
 the shape of the impeller is changed, thereby enabling an electric fuel
 pump in which the noise level during operation is low and the pump
 efficiency is high, to be provided. The electric fuel pump can be used not
 only as a pump for an automobile, but also as a pump for forcedly
 delivering a fluid such as water.