Turbine fuel pump

A turbine fuel pump includes an impeller having blades, each including a linear blade portion extending linearly in the radial direction of the impeller and a curved blade portion extending circularly curvedly from the head of the linear blade portion to the forward side of the impeller as viewed in the direction of rotation of the impeller. The linear blade portion has a length of (⅓ to ⅔)×H, where H is an overall length of the impeller.

BACKGROUND OF THE INVENTION

The present invention relates to a turbine fuel pump suitable for use, for example, in fuel supply to an injection valve for an automotive engine.

Typically, the vehicle such as a passenger car is provided with an electronically controlled fuel injection system for supplying fuel to an engine, which comprises an injection valve for injecting fuel to an engine combustion chamber, a fuel pump for delivering to the injection valve fuel within a fuel tank arranged, e.g. in the rear of the vehicle, etc. Recently, because of social requirements of the global environmental protection, there is an increasing demand for an improvement in fuel consumption of the vehicle. Thus, it is an important challenge for the fuel pump driven by an electric motor to achieve an enhancement in efficiency (i.e. reduction in electric power consumption) and a reduction in size and weight.

The fuel pump in general use includes a turbine fuel pump comprising a cylindrical casing for accommodating an electric motor, an upper cover arranged at one end of the casing, a housing arranged at another end of the casing so as to support the motor and having an annular fuel passage between fuel inlet and outlet ports, and an impeller rotatably arranged in the housing and for feeding fuel sucked through the inlet port to the outlet port via the fuel passage while being rotated by the motor.

The impeller is formed like a disc, and has blades arranged circumferentially at the outer periphery and extending radially and blade grooves formed between the blades. Fuel sucked through the inlet port is introduced into the blade grooves via the fuel passage to receive kinetic energy from the blades, and it is then discharged to the passage. Fuel discharged to the fuel passage is circulated through the passage, then introduced again into the blade grooves. Fuel within the passage is increased in pressure by repetition of the inflow and outflow, and discharged through the outlet port.

It is important for enhancement of both of the efficiency of the electric motor and that of the pump portion to improve the efficiency of the fuel pump. Specifically, the impeller is driven by the electric motor which rotates in fuel, producing a torque loss due to viscosity of fuel. When rotating in the housing, the impeller also produces a torque loss due to viscosity of fuel. Those torque losses are increased in proportion to the square of rpm, and thus become very great values when the fuel pump is operated at high rpm, resulting in a reduction in pump efficiency.

Then, a torque loss can be restrained by setting the specifications of the pump portion to allow achievement of a required flow rate at lower rpm. In this case, however, torque required for driving of the impeller is increased.

Moreover, because of requirements of downsizing of the fuel pump, the electric motor has been reduced in size. As described above, generation of high torque at low rpm needs operation of the electric motor in the low-efficiency range. Thus, it is important for enhancement of the pump efficiency to provide not only the specifications of the pump portion to minimize a torque loss, but also the specifications of the electric motor to allow its service in the high-efficiency range.

In connection with the art to improve the efficiency of the turbine fuel pump, various improvements in the impeller have been proposed. One of the improvements is disclosed in JP-A 8-100780 wherein each blade of the impeller has a root portion curved backward as viewed in the direction of rotation of the impeller, and a head portion extending radially outward from a curved portion to incline backward linearly. This shape of the blade allows smooth fuel flow from a blade groove to a passage even in the range of relatively low rpm, preventing a reduction in flow rate with respect to rpm, resulting in enhancement in the low-voltage characteristics and flow-rate controllability.

With the turbine fuel pump disclosed in JP-A 8-100780, as described above, each blade of the impeller has a root portion curved backward as viewed in the direction of rotation of the impeller, and a head portion extending radially outward from a curved portion to incline backward linearly. With this, the impeller allows prevention of the flow rate with respect to rpm in the range of relatively low rpm. However, since the impeller has a head portion inclining backward linearly, outflow of fuel from the blade groove is carried out in the rear direction, providing no higher kinetic energy to fuel. Thus, achievement of relatively great flow rate requires a considerable increase in rpm. This leads to an increase in torque loss in the range of relatively great flow rate, raising a problem of a reduction in pump efficiency.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide a turbine fuel pump which allows an enhancement in pump efficiency in the entire operating range.

The present invention provides generally a turbine fuel pump, which comprises: a casing for accommodating an electric motor; a housing provided to the casing, the housing comprising an annular passage between inlet and outlet ports; and an impeller rotatably arranged in the housing, the impeller comprising blades arranged on an outer periphery to extend in a radial direction of the impeller and feeding fuel through the passage while the blades are rotated by the electric motor, each blade comprising a linear portion extending linearly in the radial direction of the impeller and a curved portion extending circularly curvedly from a head of the linear portion to a forward side of the impeller as viewed in a direction of rotation of the impeller, the linear portion having a predetermined length, the predetermined length being (⅓ to ⅔)×H, where H is an overall length of the impeller.

An aspect of the present invention is to provide a turbine fuel pump, which comprises: a casing for accommodating an electric motor; a housing provided to the casing, the housing comprising an annular passage between inlet and outlet ports; and an impeller rotatably arranged in the housing, the impeller comprising blades arranged on an outer periphery to extend in a radial direction of the impeller and feeding fuel through the passage while the blades are rotated by the electric motor, each blade including a plate body of substantially rectangular section, the plate body comprising a front face located on the forward side of the impeller, a rear face located on a rearward side of the impeller, and a pair of side faces located between the front face and the rear face, each blade comprising a chamfer arranged on the root side of the blade to extend in the radial direction of the impeller, the chamfer being obtained by slantly cutting a corner between the side face and the rear face of the blade, the chamfer having a predetermined length, wherein the predetermined length is (⅖ to ⅗)×L, where L is a radial length of the passage.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the drawings, a turbine fuel pump embodying the present invention is described.

Referring toFIGS. 1–7, there is shown first embodiment of the present invention. Referring toFIG. 1, the turbine fuel pump comprises a cylindrical casing1which constitutes an outer shell of the pump and has axial ends closed by a delivery cover2and a pump housing9.

The delivery cover2of a covered cylinder is arranged at one end of the casing1. As shown inFIG. 1, the delivery cover2is provided with a delivery pipe2A and a connector2B which protrude upward and a bearing sleeve2C arranged in the center to extend downward.

A check valve3is arranged in the delivery pipe2A to hold the residual pressure. During rotation of an electric motor7, the check valve3is opened by fuel flowing into the casing1to allow fuel to be delivered from the delivery pipe2A to an outside fuel line (not shown). During halts of the electric motor7, the check valve3is closed to prevent fuel within the fuel line from returning to the casing1, thus holding the fuel line at a predetermined residual pressure.

Referring also toFIG. 2, a bush4is engaged in the bearing sleeve2C of the delivery cover2, whereas a bush5is engaged in a stepped hole12E of an inner housing12. The bushes4,5constitute a bearing for rotatably supporting a rotation shaft6.

The rotation shaft6is supported between the delivery cover2and the pump housing9through the bushes4,5. As shown inFIG. 2, the rotation shaft6extends axially in the casing1along an axis O—O to rotatably support a rotor7B, etc. of the electric motor7. Referring toFIG. 3, a chamfer6A is formed at a lower end of the rotation shaft6to engage with an impeller22in the rotation-stop state.

The electric motor7is accommodated in the casing1, and comprises a cylindrical yoke7A engaged in the casing1between the delivery cover2and the pump housing9and for supporting a stator (not shown) comprising a permanent magnet, a rotor7B and a commutator7C arranged inside the yoke7A with a clearance and mounted to the rotation shaft6for unitary rotation, and a pair of brushes (not shown) making slide contact with the commutator7C.

With the electric motor7, when energizing the rotor7B through the connector2B of the delivery cover2, the brushes, and the commutator7C, the rotor7B is rotated together with the rotation shaft6to drive the impeller20in the range of medium to high rpm, e.g. 5,000–8,000 rpm.

A fuel passage8is formed between the yoke7A and the rotor7B of the electric motor7, and serves to circulate to the delivery cover2through a clearance between the yoke7A and the rotor7B fuel discharged from an outlet port14of the pump housing9to the casing1.

The pump housing9is arranged at another or lower end of the casing1, and is obtained by vertically abutting an outer housing10and the inner housing12. The pump housing9serves to rotatably accommodate the impeller20.

As shown inFIGS. 1 and 2, the outer housing10of the pump housing9is engagedly mounted at the lower end of the casing1through fixing means such as calking to close the casing1from the outside. The outer housing10is integrally formed with a fuel inlet port11.

The outer housing10has a circular concave10A formed in the shaft center (axis O—O), and a circular groove10B of substantially semicircular section formed corresponding to the outer periphery of the impeller20to extend circumferentially with the axis O—O as center. As shown inFIG. 3, the circular groove10B extends circumferentially over the range of an angle θ, and cooperates with a peripheral-wall groove12D of the inner housing12to form a lower abutting-side passage18.

The inner housing12serves as a housing member for constituting, together with the outer housing10, the pump housing9. The inner housing12is engaged in the casing1in the state abutting on the outer housing10.

As shown inFIG. 2, the inner housing12is shaped like a covered flat cylinder, and comprises a cylinder portion12A for forming a cylindrical peripheral wall and a cover portion12B for covering the cylinder portion12A from above. The cylindrical portion12A is formed at the inner periphery with a circular turbine accommodating recess13to open on the side of an abutting face12C of the cylindrical portion12A with the outer housing10. Moreover, the cylindrical portion12A is formed with circular peripheral-wall groove12D located below an annular protrusion16. The circular peripheral-wall groove12D cooperates with the circular groove10B of the outer housing10to form the abutting-side passage18. The cover portion12B is formed with stepped hole12E into which the bush5is inserted, and at the outer periphery with the outlet port14to extend vertically.

An annular fuel passage15is formed through the pump housing9at the outer periphery of the turbine accommodating recess13to extend circumferentially in a roughly C-shaped manner with the axis O as center as shown inFIG. 3. The fuel passage15comprises two portions divided vertically by the annular protrusion16, i.e. an interior passage17and the abutting-side passage18.

The fuel passage15has a beginning communicating with the inlet port11, and a termination communicating with the outlet port14. Moreover, the fuel passage15includes on the beginning side an inlet passage portion15A for smoothly introducing into the fuel passage15fuel sucked through the inlet port11.

The annular protrusion16is provided to the cylindrical portion12A of the inner housing12. As shown inFIG. 2, the annular protrusion16protrudes from the cylindrical portion12A to the outer periphery of the impeller20radially inward in a mountain-shaped manner as viewed in section so as to divide the fuel passage15into upper and lower portions in the axial direction of the impeller20, i.e. the interior passage17and the abutting-side passage18.

The interior passage17is formed as a slot of C-shaped section arranged at an interior corner between the cylindrical portion12A and the cover portion12B of the inner housing12. The abutting-side passage18is formed as a slot of C-shaped section by the circular groove10B of the outer housing10and the peripheral-wall groove12D of the inner housing12.

The annular protrusion16extends, together with the passages17,18, in the circumferential direction of the impeller20over the range of the angle θ (=250–270°, for example) as shown inFIG. 3, thus restraining occurrence of stagnation, etc. of fuel flowing through the fuel passage15.

A sealing partition19is provided to the inner housing12on the side of the cylinder portion12A. As shown inFIG. 3, the sealing partition19is formed as a circular protrusion protruding from the cylindrical portion12A of the inner housing12to a point adjacent to the outer periphery of the impeller20. The sealing partition19seals the outer periphery of the impeller20between the inlet port11and the outlet port14, allowing fuel sucked through the inlet port11to surely flow along the fuel passage15.

The impeller20is shaped roughly like a disk out of a reinforced plastic material, for example, and is rotatably arranged in the turbine accommodating recess13of the pump housing9. The impeller20is rotated by the electric motor7in the direction of arrow A inFIG. 3to feed fuel sucked through the inlet port11to the outlet port14through the fuel passage15.

The impeller20has in the center of rotation (axis O—O) an engagement hole21in which the rotation shaft6is engaged. A plurality of (e.g. three) through holes22is arranged around the engagement hole21. Referring toFIG. 4, the impeller20comprises at the outer periphery a plurality of blades23arranged circumferentially to extend radially. A pair of circular recesses24is arranged between the adjacent blades23, each recess24having a curvature corresponding roughly to a circular shape of the passages17,18of the pump housing9.

The impeller20is driven, together with the rotation shaft6, by the electric motor11with the upper and lower faces being floating-sealed between the upper face of the outer housing10and the lower face of the cover portion12B in the turbine accommodating recess13. Each through hole22of the impeller20has a function of uniformizing the fuel pressure, etc. between the circular concave10A of the outer housing10and the stepped hole12E of the inner housing12.

Referring toFIG. 5, each blade23comprises a linear blade portion23A located on the root side and extending linearly in the radial direction of the impeller20, and a curved blade portion23B extending circularly curvedly from the head of the linear blade portion23A to the forward side of the impeller20as viewed in the direction of rotation thereof, i.e. in the direction of arrow A.

Next, the shape of the blade23is described in detail. As shown inFIG. 5, the length from a root position B of the linear blade portion23A to a head position C of the curved blade portion23B, i.e. overall length of the blade23, is referred to as overall length H; the length from the root position B of the linear blade portion23A to a staring-point position D at which the curved blade portion23B starts, i.e. head position D of the linear blade portion23A, is referred to as linear-portion length H1; and the length from the starting-point position D of the curved blade portion23B to the head position C thereof is referred to as curved-portion length H2.

The forward-tilt length of the curved blade portion23B between a most forward position E inclined forward in the direction of rotation and the linear blade portion23A is represented by an angle α with reference to the center of rotation (axis O—O) of the impeller20.

In the first embodiment, it is revealed that when the linear-portion length H1of the linear blade portion23A with respect to the overall length H of the blade23, i.e. the starting-point position D of the curved blade portion23B, is set in accordance with the following formula (1), excellent pump efficiency can be obtained:
⅓≦(H1/H)≦⅔  (1)

In this connection, it is revealed that when H1/H in the formula (1) is set within the range given by the following formula (2), more excellent pump efficiency can be obtained:
⅖≦(H1/H)≦⅗  (2)

Moreover, it is revealed that when the angle α corresponding to the forward-tilt length of the curved blade portion23B is set in accordance with the following formula (3), excellent pump efficiency can be obtained:
0.5≦α≦2.0  (3)

In this connection, it is revealed that when a in the formula (3) is set within the range given by the following formula (4), more excellent pump efficiency can be obtained:
1.0≦α≦1.5  (4)

Next, operation of the first embodiment is described. When energizing the pump from the outside through the connector2B of the delivery cover2, a drive current is supplied to the rotor7B of the electric motor7to rotate the rotor7B and the rotation shaft6together, driving the impeller20in the pump housing9. By rotation of the impeller20, fuel in a fuel tank (not shown) is sucked into the fuel passage15through the inlet port11, which is then fed along the fuel passage15by the blades23of the impeller20, and discharged into the casing1through the outlet port14.

Fuel discharged into the casing1is circulated in the casing1to the delivery cover2through the fuel passage8, etc. so as to open the check valve3in the delivery pipe2A. Then, fuel is supplied from the delivery pipe2A to an injection valve (not shown) of the engine main body through an outside fuel line (not shown) at the delivery pressure of 200–500 kPa and the delivery rate of 30–200 L/h, for example.

As a consequence of our study on the ratio of the linear-portion length H1of the linear blade portion23A to the overall length H of the blade23, it is confirmed that when the ratio H1/H is set within the range of ⅓–⅔ as shown in the formula (1), preferably, within the range of ⅖–⅗ as shown in the formula (3), higher pump efficiency can be obtained as shown by a characteristic curve inFIG. 6. In this case, the angle α corresponding to the forward-tilt length of the curved blade portion23B is set at about 1.2°.

Moreover, as a consequence of our study on the angle α corresponding to the forward-tilt length of the curved blade portion23B, it is confirmed that when the angle α is set within the range of 0.5–2.0° as shown in the formula (3), preferably, within the range of 1.0–1.5° as shown in the formula (4), higher pump efficiency can be obtained as shown by a characteristic curve inFIG. 7. In this case, the ratio of the linear-portion length H1 of the linear blade portion23A to the overall length H of the blade23is set at about ½.

In such a manner, it is revealed that when the ratio of the linear-portion length H1of the linear blade portion23A to the overall length H of the blade23is set at about ½ which is within the range of ⅖–⅗, and the angle α corresponding to the forward-tilt length of the curved blade portion23B is set at about 1.2° which is within the range of 1.0–1.5°, the highest pump efficiency can be obtained.

In the first embodiment, therefore, the starting-point position D at which the curved blade portion23B of the blade23of the impeller20starts to curve, i.e. the linear-portion length H1, is set at a position of ⅖–⅗ (about ½) with respect to the overall length H of the blade23, whereas the angle α corresponding to the forward-tilt length of the curved blade portion23B is set at 1.0–1.5° (about 1.2°).

This allows the blade23to have the curved blade portion23B curving mildly from the middle in the length direction with an appropriate forward-tilt length secured in the direction of rotation of the impeller20.

As a result, when rotating the impeller20, smooth fuel flow can be obtained from the blade grooves between the blades23to the fuel passage15even in the range of relatively low flow rate, preventing a reduction in flow rate with respect to rpm. Moreover, the impeller20provides an appropriate kinetic energy to fuel, allowing restraint of an increase in torque loss in the range of relatively great flow rate and operation of the pump in the higher efficiency range of the electric motor7, resulting in achievement of higher pump efficiency in the entire operating range of the pump.

Moreover, since the curved blade portion23B of the blade23is formed to curve circularly, fuel can smoothly flow along the circular surface of the curved blade portion23B, resulting in smoother outflow of fuel from the blade grooves between the blades23.

Referring toFIGS. 8–14, there is shown second embodiment of the present invention which is substantially the same in structure as the first embodiment except that a chamfer39obtained by slantly cutting a corner between the side face and the rear face of a blade35is arranged on the root side of the blade35to extend in the radial direction of an impeller32.

Referring toFIGS. 8 and 9, an annular fuel passage31is arranged in place of the fuel passage15in the first embodiment. The fuel passage31includes circular groove10B of the outer housing10, and is formed as a passage of larger vertical length and C-shaped section extending circumferentially with the axis O—O as center.

The fuel passage31has upper and lower ends formed circularly, along which fuel flows in a circulating manner as indicated by arrows inFIG. 9, so that the perimeter of the center of a circular portion of the fuel passage31forms a passage center F when fuel is fed through the fuel passage31. The passage center F with respect to a radial length L from an internal end31A of the fuel passage31to an external end31B thereof is positioned at a distance L1of about ½ from the internal end31A. The fuel passage31has a beginning communicating with the inlet port11, and a termination communicating with the outlet port14.

The impeller32is shaped roughly like a disk out of a reinforced plastic material, for example, and is rotatably arranged in the turbine accommodating recess13of the pump housing9.

The impeller32has in the center of rotation (axis O—O) an engagement hole33in which the rotation shaft6is engaged. A plurality of (e.g. three) through holes34is arranged around the engagement hole33. Referring toFIG. 10, the impeller20comprises at the outer periphery a plurality of blades35arranged circumferentially to extend radially. A pair of circular recesses36is arranged between the adjacent blades35in a mountain-shaped manner, each recess36having a curvature corresponding roughly to a circular shape of the fuel passage31of the pump housing9.

Referring toFIGS. 10 and 11, the blade35is formed as a plate body of substantially rectangular section comprising a front face35A located on the forward side as viewed in the direction of rotation of the impeller32, i.e. in the direction of arrow A, a rear face35B located on the rearward side as viewed in the direction of rotation, and a pair of side faces35C located between the front face35A and the rear face35B.

The blade35includes on the root side a linear blade portion37extending linearly in the radial direction of the impeller32, and on the head side a curved blade portion38curving circularly to the forward side as viewed in the direction of rotation of the impeller32. The shape and dimension of the blade portions37,38is set in accordance with the formulas (1) and (3), preferably, the formulas (2) and (4) as described above in connection with the first embodiment.

A pair of chamfers39is arranged on the root side of the blade35to extend in the radial direction of the impeller32. Referring toFIGS. 10–12, each chamfer39is obtained by slantly cutting a corner between the side face35C and the rear face35B of the blade35. An overall length T of the chamfer39is set roughly equal to the distance L1from the internal end31A to the passage center F of the fuel passage31, i.e. a value of (⅖–⅗)×L, where L is radial length of the fuel passage31, in accordance with the following formula (5):
⅖≦(T/L)≦⅗  (5)

The overall length T of the chamfer39is set, preferably, at a value of ( 9/20– 11/20)×L in accordance with the following formula (6):
9/20≦(T/L)≦ 11/20  (6)

The overall length T of the chamfer39within the range given by the formulas (5) and (6) is set, optimally, at a value of ½ with respect to the radial length L of the fuel passage31. With this, the chamfer39is formed to extend the passage center F which forms a center when fuel flows through the fuel passage31in a circulating manner, allowing the most excellent achievement of an effect of smooth fuel flow into the blade grooves between the blades35.

The chamfer39comprises a roughly rectangular root-side chamfer portion39A located on the root side and having substantially constant chamfer width, and a roughly triangular head-side chamfer portion39B having chamfer width gradually reduced from the head of the root-side chamfer portion39A.

The root-side chamfer portion39A is formed by cutting a corner to have substantially constant chamfer width, achieving smooth fuel flow into the blade grooves between the blades36from the root side thereof, allowing a reduction in resistance to fuel flow. On the other hand, the head-side chamfer portion39B is formed with chamfer width gradually reduced to the head thereof, achieving smooth connection between the rear face35B and side face35C of the blade35and the root-side chamfer portion39A, allowing smooth fuel flow therebetween.

Referring toFIG. 12, the shape of the root-side chamfer portion39A of the chamfer39is described in detail. An angle of inclination β of the root-side chamfer portion39A with respect to the side face35C of the blade35is set within the range of 30–70° in accordance with the following formula (7):
30≦β≦70  (7)

The angle of inclination β in the formula (7) is set, preferably, within the range of 40–60° in accordance with the following formula (8):
40≦β≦80  (8)

Referring toFIG. 9, a length T1of the root-side chamfer portion39A with respect to an overall length T of the chamfer39is set at a value of ( 1/15–⅘)×T in accordance with the following formula (9):
⅕≦(T1/T)≦⅘  (9)

The length T1of the root-side chamfer portion39A is set, preferably, at a value (⅖–⅗)×T in accordance with the following formula (10):
⅖≦(T1/T)≦⅗  (10)

As a consequence of our study on the angle of inclination β of the root-side chamfer portion39A with respect to the side face35C of the blade35, it is confirmed that when the angle of inclination β is set within the range of 30–70° as shown in the formula (7), preferably, within the range of 40–60°as shown in the formula (8), higher pump efficiency can be obtained as shown by a characteristic curve inFIG. 13.

In this case, the ratio of the length T1of the root-side chamfer portion39A to the overall length T of the chamfer39is set at about ½. With this, the angle of inclination β of the root-side chamfer portion39A can be set substantially equal to the flow angle of fuel running from the side face35C of the blade35to the rear face35B thereof, resulting in smooth fuel flow along the root-side chamfer portion39A.

Moreover, as a consequence of our study on the ratio of the length T1of the root-side chamfer portion39A to the overall length T of the chamfer39, it is confirmed that when the ratio T1/T is set within the range of ⅕–⅘ as shown in the formula (9), preferably, within the range of ⅖–⅗ as shown in the formula (10), higher pump efficiency can be obtained as shown by a characteristic curve inFIG. 14.

In this case, the angle of inclination β of the root-side chamfer portion39A with respect to the side face35C of the blade35is set at about 50°. With this, the root-side chamfer portion39A restrains swirls which may occur on the root side of the blade35through a large recess of constant width, allowing smooth fuel inflow.

Moreover, our study reveals that since the head-side chamfer portion39B having chamfer width gradually reduced to the head ensures smooth connection between the rear face35B and side face35C of the blade35and the root-side chamfer portion39A, fuel can flow smoothly from the side face35C of the blade35to the root-side chamfer portion39A and from the root-side chamfer portion39A to the rear face35B, allowing achievement of higher pump efficiency.

In such a manner, it is revealed that when the ratio T/L of the overall length T of the chamfer39to the radial length L of the fuel passage31is set at ½ which is within the range of 9/20– 11/20, the angle of inclination β of the root-side chamfer portion39A with respect to the side face35C of the blade35is set at500which is within the range of 40–60°, and the ratio T1/T of the length T1of the root-side chamfer portion39A to the overall length T of the chamfer39is set at ½ which is within the range of ⅖–⅗, the highest pump efficiency can be obtained.

In the second embodiment, the chamfer39obtained by slantly cutting a corner between the side face35C and the rear face35B is arranged on the side of the impeller32. Therefore, when rotating the impeller32, the chamfer39allows smooth flow of fuel along the root-side chamfer portion39A and the head-side chamfer portion39B.

Moreover, the chamfer39is designed such that the ratio of the overall length T extending in the radial direction of the impeller32with respect to the radial length L of the fuel passage31is set at 9/20– 11/20 (preferably, ½), and the angle of inclination β of the root-side chamfer portion39A with respect to the side face35C of the blade35is set at 40–60° (preferably, 50°), and the ratio of the length T1of the root-side chamfer portion39A to the overall length T of the chamfer39is set at ⅖–⅗ (preferably, ½).

Thus, in the second embodiment, the position and length of the chamfer39(root-side chamfer portion39A) and the angle of inclination of the root-side chamfer portion39A can be set to correspond to the inflow position of fuel flowing into the blade grooves between the blades35through the fuel passage31, the size required for smooth fuel inflow, and the angle allowing smooth fuel inflow, providing smoother fuel flow from the blade grooves between the blades35to the fuel passage31as compared with the first embodiment, allowing achievement of higher pump efficiency.

Referring toFIGS. 15–23, there is shown third embodiment of the present invention. Referring toFIG. 15, the turbine fuel pump comprises a cylindrical casing101which constitutes an outer shell of the pump and has axial ends closed by a delivery cover102and a pump housing109.

The delivery cover102of a covered cylinder is arranged at one end of the casing101. As shown inFIG. 15, the delivery cover102is provided with a delivery pipe102A and a connector102B which protrude upward and a bearing sleeve102C arranged in the center to extend downward.

A check valve103is arranged in the delivery pipe102A to hold the residual pressure. During rotation of an electric motor107, the check valve103is opened by fuel flowing into the casing101to allow fuel to be delivered from the delivery pipe102A to an outside fuel line (not shown). During halts of the electric motor107, the check valve103is closed to prevent fuel within the fuel line from returning to the casing101, thus holding the fuel line at a predetermined residual pressure.

Referring also toFIG. 16, a bush104is engaged in the bearing sleeve102C of the delivery cover102, whereas a bush105is engaged in a stepped hole112D of an inner housing112. The bushes104,105constitute a bearing for rotatably supporting a rotation shaft106.

The rotation shaft106is supported between the delivery cover102and the pump housing109through the bushes104,105. As shown inFIG. 16, the rotation shaft106extends axially in the casing101along an axis O—O to rotatably support a rotor107B, etc. of the electric motor107. Referring toFIG. 17, a chamfer106A is formed at a lower end of the rotation shaft106to engage with an impeller117in the rotation-stop state.

The electric motor107is accommodated in the casing101, and comprises a cylindrical yoke107A engaged in the casing101between the delivery cover102and the pump housing109and for supporting a stator (not shown) comprising a permanent magnet, a rotor107B and a commutator107C arranged inside the yoke107A with a clearance and mounted to the rotation shaft106for unitary rotation, and a pair of brushes (not shown) making slide contact with the commutator107C.

With the electric motor107, when energizing the rotor107B through the connector102B of the delivery cover102, the brushes, and the commutator107C, the rotor107B is rotated together with the rotation shaft106to drive the impeller117at 5,000–8,000 rpm, for example.

A fuel passage108is formed between the yoke107A and the rotor107B of the electric motor107, and serves to circulate to the delivery cover102through a clearance between the yoke107A and the rotor107B fuel discharged from an outlet port114of the pump housing109to the casing101.

The pump housing109is arranged at another or lower end of the casing101, and is obtained by vertically abutting an outer housing110and the inner housing112. The pump housing109serves to rotatably accommodate the impeller117.

As shown inFIGS. 15 and 16, the outer housing110of the pump housing109is engagedly mounted at the lower end of the casing101through fixing means such as calking to close the casing101from the outside. The outer housing110is integrally formed with a fuel inlet port111.

The outer housing110has a circular concave110A formed in the shaft center (axis O—O), and a circular groove110B of substantially semicircular section formed corresponding to the outer periphery of the impeller117to extend circumferentially with the axis O—O as center.

The inner housing112is arranged on the outer housing110, and is engaged in the casing101in the state abutting on the outer housing110. As shown inFIG. 16, the inner housing112is shaped like a covered flat cylinder, and comprises a cylinder portion112A for forming a cylindrical peripheral wall and a cover portion112B for covering the cylinder portion112A from above. The cylindrical portion112A is formed at the inner periphery with a circular turbine accommodating recess113to open on the side of an abutting face112C of the cylindrical portion112A with the outer housing110.

Moreover, the cylindrical portion112A is formed at the inner periphery with an annular fuel passage115. The cover portion112B is formed with stepped hole112D into which the bush105is inserted, and at the outer periphery with the outlet port114to extend vertically.

The fuel passage115is formed through the pump housing109at the outer periphery of the turbine accommodating recess113to extend circumferentially in a roughly C-shaped manner with the axis O as center as shown inFIGS. 16 and 18. The fuel passage15comprises circular groove110B of the outer housing110.

The fuel passage115has upper and lower ends formed circularly, along which fuel flows in a circulating manner as indicated by arrows inFIG. 18, so that the perimeter of the center of a circular portion of the fuel passage115forms a passage center C when fuel is fed through the fuel passage115. The passage center C with respect to a radial length L from an internal end115A of the fuel passage115to an external end115B thereof is positioned at a distance L1of about ½ from the internal end115A.

The fuel passage115has a beginning communicating with the inlet port111, and a termination communicating with the outlet port114. Moreover, the fuel passage115includes on the beginning side an inlet passage portion115C for smoothly introducing into the fuel passage115fuel sucked through the inlet port111.

A sealing partition116is provided to the inner housing112on the side of the cylinder portion112A. As shown inFIG. 17, the sealing partition116is formed as a circular protrusion protruding from the cylindrical portion112A of the inner housing112to a point adjacent to the outer periphery of the impeller117. The sealing partition116seals the outer periphery of the impeller117between the inlet port111and the outlet port114, allowing fuel sucked through the inlet port111to surely flow along the fuel passage115.

The impeller117is shaped roughly like a disk out of a reinforced plastic material, for example, and is rotatably arranged in the turbine accommodating recess113of the pump housing109. The impeller117is rotated by the electric motor107in the direction of arrow A inFIG. 17to feed fuel sucked through the inlet port111to the outlet port114through the fuel passage115.

The impeller117has in the center of rotation (axis O—O) an engagement hole118in which the rotation shaft106is engaged. A plurality of (e.g. three) through holes119is arranged around the engagement hole118. Referring toFIG. 19, the impeller117comprises at the outer periphery a plurality of blades120arranged circumferentially to extend radially. A pair of circular recesses121is arranged between the adjacent blades120, each recess121having a curvature corresponding roughly to a circular shape of the passage115of the pump housing109.

The impeller117is driven, together with the rotation shaft106, by the electric motor107with the upper and lower faces being floating-sealed between the upper face of the outer housing110and the lower face of the cover portion112B in the turbine accommodating recess113. Each through hole119of the impeller117has a function of uniformizing the fuel pressure, etc. between the circular concave110A of the outer housing110and the stepped hole112D of the inner housing112.

Referring toFIGS. 19 and 20, the blade120is formed as a plate body of substantially rectangular section comprising a front face120A located on the forward side as viewed in the direction of rotation of the impeller117, i.e. in the direction of arrow A, a rear face120B located on the rearward side as viewed in the direction of rotation, and a pair of side faces120C located between the front face120A and the rear face120B.

The blade120includes on the root side a linear blade portion122extending linearly in the radial direction of the impeller117, and on the head side a curved blade portion123curving circularly to the forward side as viewed in the direction of rotation of the impeller117. The linear blade portion122and the curved blade portion123are roughly half the overall length of the blade120.

A pair of chamfers124is arranged on the root side of the blade120to extend in the radial direction of the impeller117. Referring toFIGS. 19–21, each chamfer124is obtained by slantly cutting a corner between the side face120C and the rear face120B of the blade120. An overall length H of the chamfer124is set roughly equal to the distance L1from the internal end115A to the passage center C of the fuel passage115, i.e. a value of (⅖–⅗)×L, where L is radial length of the fuel passage31, in accordance with the following formula (11):
⅖≦(T/L)≦⅗  (11)

The overall length H of the chamfer124is set, preferably, at a value of ( 9/20– 11/20)×L in accordance with the following formula (12):
9/20≦(T/L)≦ 11/20  (12)

The overall length H of the chamfer124within the range given by the formulas (11) and (12) is set, optimally, at a value of ½ with respect to the radial length L of the fuel passage115. With this, the chamfer124is formed to extend the passage center C which forms a center when fuel flows through the fuel passage115in a circulating manner, allowing the most excellent achievement of an effect of smooth fuel flow into the blade grooves between the blades120.

The chamfer124comprises a roughly rectangular root-side chamfer portion124A located on the root side and having substantially constant chamfer width, and a roughly triangular head-side chamfer portion124B having chamfer width gradually reduced from the head of the root-side chamfer portion124A.

The root-side chamfer portion124A is formed by cutting a corner to have substantially constant chamfer width, achieving smooth fuel flow into the blade grooves between the blades120from the root side thereof, allowing a reduction in resistance to fuel flow. On the other hand, the head-side chamfer portion124B is formed with chamfer width gradually reduced to the head thereof, achieving smooth connection between the rear face120B and side face120C and the root-side chamfer portion124A, allowing smooth fuel flow therebetween.

Referring toFIG. 21, the shape of the root-side chamfer portion124A of the chamfer124is described in detail. An angle of inclination α of the root-side chamfer portion124A with respect to the side face120C of the blade120is set within the range of 30–70° in accordance with the following formula (13):
30≦β≦70  (13)

The angle of inclination α in the formula (13) is set, preferably, within the range of 40–60° in accordance with the following formula (14):
40≦β≦80  (14)

Referring toFIG. 18, a length H1of the root-side chamfer portion124A with respect to the overall length H of the chamfer124is set at a value of (⅕–⅘)×T in accordance with the following formula (15):
⅕≦(T1/T)≦⅘  (15)

The length H1of the root-side chamfer portion124A is set, preferably, at a value (⅖–⅗)×T in accordance with the following formula (16):
⅖≦(T1/T)≦⅗  (16)

Next, operation of the third embodiment is described. When energizing the pump from the outside through the connector102B of the delivery cover102, a drive current is supplied to the rotor107B of the electric motor107to rotate the rotor107B and the rotation shaft106together, driving the impeller117in the pump housing109. By rotation of the impeller117, fuel in a fuel tank (not shown) is sucked into the fuel passage115through the inlet port111, which is then fed along the fuel passage115by the blades120of the impeller117, and discharged into the casing101through the outlet port114.

Fuel discharged into the casing101is circulated in the casing101to the delivery cover102through the fuel passage108, etc. so as to open the check valve103in the delivery pipe102A. Then, fuel is supplied from the delivery pipe102A to an injection valve (not shown) of the engine main body through an outside fuel line (not shown) at the delivery pressure of 200–500 kPa and the delivery rate of 30–200 L/h, for example.

As a consequence of our study on the angle α of the root-side chamfer portion124A with respect to the side face120C of the blade120, it is confirmed that when the angle α is set within the range of 30–70° as shown in the formula (13), preferably, within the range of 40–60° as shown in the formula (14), higher pump efficiency can be obtained as shown by a characteristic curve inFIG. 22under the conditions of 300 kPa delivery pressure and 80 L/h delivery rate.

In this case, the ratio of the length H1of the root-side chamfer portion124A to the overall length H of the chamfer124is set at about ½. With this, the angle of inclination α of the root-side chamfer portion124A can be set substantially equal to the flow angle of fuel running from the side face120C of the blade120to the rear face120B thereof, achieving smooth fuel flow along the root-side chamfer portion124A, resulting in a reduction in resistance to fuel flow.

Moreover, as a consequence of our study on the ratio of the length H1of the root-side chamfer portion124A to the overall length H of the chamfer124, it is confirmed that when the ratio H1/H is set within the range of ⅕–⅘ as shown in the formula (15), preferably, within the range of ⅖–⅗ as shown in the formula (16), higher pump efficiency can be obtained as shown by a characteristic curve inFIG. 23.

In this case, the angle of inclination α of the root-side chamfer portion124A with respect to the side face120C of the blade120is set at about 50°. With this, the root-side chamfer portion124A restrains swirls which may occur on the root side of the blade120through a large recess of constant width, allowing a reduction in resistance to fuel flow.

Moreover, our study reveals that since the head-side chamfer portion124B having chamfer width gradually reduced to the head ensures smooth connection between the rear face120B and side face120C of the blade120and the root-side chamfer portion124A, fuel can flow smoothly from the side face120C of the blade120to the root-side chamfer portion124A and from the root-side chamfer portion124A to the rear face120B, allowing achievement of higher pump efficiency.

In such a manner, it is revealed that when the ratio H/L of the overall length H of the chamfer124to the radial length L of the fuel passage115is set at ½ which is within the range of 9/20– 11/20, the angle of inclination α of the root-side chamfer portion124A with respect to the side face120C of the blade120is set at 50° which is within the range of 40–600, and the ratio H1/H of the length H1of the root-side chamfer portion124A to the overall length H of the chamfer124is set at ½ which is within the range of ⅖–⅗, the highest pump efficiency can be obtained.

In the third embodiment, the chamfer124obtained by slantly cutting a corner between the side face120C and the rear face120B is arranged on the side of the impeller32. And the chamfer124is designed such that the overall length H extending in the radial direction of the impeller117is set at 9/20– 11/20 (preferably, ½) with respect to the radial length L of the fuel passage115, the angle of inclination α of the root-side chamfer portion124A with respect to the side face120C of the blade120is set at 40–60° (preferably, 50°), and the length H1of the root-side chamfer portion124A is set at ⅖–⅗ (preferably, ½) with respect to the overall length H of the chamfer124.

Thus, in the third embodiment, the position and length of the chamfer124(root-side chamfer portion124A) and the angle of inclination of the root-side chamfer portion124A can be set to correspond to the inflow position of fuel flowing into the blade grooves between the blades120through the fuel passage115, the size required for smooth fuel inflow, and the angle allowing smooth fuel inflow.

As a result, when rotating the impeller117, the chamfer124allows smooth fuel flow along the root-side chamfer portion124A and the head-side chamber portion124B to reduce the resistance to fuel flow, achieving efficient feeding of fuel to the outlet port114through the fuel passage115, leading to enhancement in the pump efficiency.

In the third embodiment, the fuel passage115is formed as a passage of larger vertical length and C-shaped section. Optionally, referring toFIG. 24, in a first variation, a fuel passage131may comprise two portions divided vertically by annular protrusions132protruding radially inward from the center of the fuel passage132, i.e. an interior passage133and the abutting-side passage134.

Further, in the third embodiment, each blade120of the impeller117includes on the root side linear blade portion122extending linearly in the radial direction of the impeller117, and on the head side curved blade portion123curving circularly to the forward side as viewed in the direction of rotation of the impeller117. Optionally, referring toFIG. 25, in a second variation, each blade141may include a linear structure extending linearly from the root to the head. Alternatively, the blade120may include a curved structure curved from the root to the head circularly forward in the direction of rotation.

Having described the present invention with regard to the illustrative embodiments, it is noted that the present invention is not limited thereto, and various changes and modifications can be made without departing from the scope of the present invention.

The entire teachings of Japanese Patent Application P2002-257988 filed Sep. 3, 2002 and Japanese Patent Application P2002-165946 filed Jun. 6, 2002 are hereby incorporated by reference.