FUEL PUMP

CROSS REFERENCE TO RELATED APPLICATION

This application is based on Japanese Patent Application No. 2015-108630 filed on May 28, 2015, the disclosure of which is incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a fuel pump.

BACKGROUND ART

There has been known a fuel pump provided with a motor, an impeller which is coupled to an output end portion of a rotary shaft of the motor, and a case in which the impeller is received. The case has a pump chamber, a suction hole which passes through to one end in an axial direction from the pump chamber, and a discharge hole which passes through to the other end in the axial direction from the pump chamber. In this type of fuel pump, the output end portion of the rotary shaft is fitted in a fitting hole of the impeller, whereby the impeller and the rotary shaft can be coupled to each other in such a way that rotation can be transmitted from the rotary shaft to the impeller. For example, as shown in Patent Document 1, a cross-sectional shape of a fitting hole is a non-circular shape and is a shape of a letter D or a polygonal shape.

PRIOR ART DOCUMENT
Patent Document

Patent Document 1: JP 2014-173456A

In the meantime, a conventional fuel pump has a problem that as the fuel pump is used, a fitting hole of the impeller is worn. According to a study conducted by the present inventors, it was found that wear of the fitting hole is mainly caused by a phenomenon such that the impeller is relatively moved in an axial direction with respect to a rotary shaft to thereby cause the fitting hole to slide on an output end portion. As a result of a further analysis, the following facts were found: that is, a pressure applied to the impeller from fuel is different between on a suction hole side and on a discharge hole side; and when a force by this pressure difference is larger than a frictional force between the output end portion and the impeller, a relative movement of the impeller is caused. In particular, when a high pressure pump is provided at a discharge portion of the fuel pump and a pulsation of a fuel pressure caused in this high pressure pump is transmitted to the fuel pump, the pressure difference is made larger and the wear of the impeller is easily caused.

SUMMARY OF INVENTION

The present disclosure addresses the above issues. Thus, it is an objective of the present disclosure to provide a fuel pump that can inhibit an impeller from being worn.

The present inventors conducted many studies on a shape of an output end portion of a rotary shaft and found that: (1) an outer wall surface of the output end portion may include a pair of parallel plane surfaces; and (2) as a two-surface width that is a distance between the pair of plane surfaces is made smaller, a binding force applied to an impeller from the output end portion is made larger and hence a frictional force between the output end portion and the impeller is made larger. When two parallel surfaces are made on a rotary shaft so as to transmit rotation, as is specified in JIS B 1002, the two-surface width is usually set to 0.8 times an outer diameter of the rotary shaft. In contrast to this, the present inventors came to the conclusion that the two-surface width of the output end portion is made smaller than usual to make a frictional force between the output end portion and the impeller larger than a force which is caused by a difference in the axial direction of a pressure applied to the impeller from the fuel and completed the present disclosure.

To achieve the objective, a fuel pump in an aspect of the present disclosure includes a motor, an impeller that includes a fitting hole fitted to an output end portion of a rotary shaft of the motor, and a case that includes a pump chamber receiving the impeller, a suction hole passing through the case from the pump chamber to one side in an axial direction of the rotary shaft, and a discharge hole passing through the case from the pump chamber to the other side in the axial direction. An outer wall surface of the output end portion includes a pair of first plane surfaces that are parallel to each other. An inner wall surface of the fitting hole includes a pair of second plane surfaces, which are parallel to each other on their cross section perpendicular to an axial center of the impeller and each of which is engaged with one of the pair of first plane surfaces or the other one of the pair of first plane surfaces when the rotary shaft rotates in a predetermined rotational direction. When a distance between the pair of first plane surfaces is referred to as a two-surface width, a value obtained by dividing the two-surface width by an outer diameter of the output end portion is 0.75 or smaller.

When the two-surface width is set in this manner, the binding force applied to the impeller from the output end portion is made larger and hence the frictional force between the output end portion and the impeller is made larger. For this reason, a state is unlikely to develop in which the force which is caused by a difference in the axial direction of a pressure applied to the impeller from the fuel is made larger than the frictional force between the output end portion and the impeller. Hence, it is possible to inhibit the fitting hole from sliding on the output end portion and hence to inhibit the impeller from being worn.

BRIEF DESCRIPTION OF DRAWINGS

The above and other objects, features and advantages of the present disclosure will become more apparent from the following detailed description made with reference to the accompanying drawings. In the drawings:

FIG. 1 is a figure to show a longitudinal section of a fuel pump according to a first embodiment;

FIG. 2 is a section view taken along a line II-II of FIG. 1;

FIG. 3 is a figure to show an impeller of FIG. 1;

FIG. 4 is an enlarged view of a IV portion of FIG. 1;

FIG. 5 is a section view taken along a line V-V of FIG. 4 and an enlarged view of an output end portion of a rotary shaft and a fitting hole of the impeller;

FIG. 6 is a figure to show a state in which the output end portion of the rotary shaft and the impeller of FIG. 5 are rotated in contact with each other at two portions;

FIG. 7 is a figure to show a state in which one first plane surface of the output end portion is moved in such a way as to be brought into contact with one second plane surface of the fitting hole from a state of FIG. 5; and

FIG. 8 is a figure to show a portion in which the output end portion of the rotary shaft is fitted in the impeller, on an enlarged scale, of a longitudinal section of a fuel pump according to a second embodiment.

EMBODIMENTS FOR CARRYING OUT INVENTION

Hereinafter, a plurality of embodiments will be described on the basis of the drawings. Constructions that are substantially equal to the respective embodiments will be denoted by the same reference signs and their descriptions will be omitted.

First Embodiment

A fuel pump according to a first embodiment is an in-tank type pump that is set in a fuel tank of a vehicle and sucks fuel from a suction port 14 shown in a lower portion of FIG. 1 and raises a pressure of the fuel and discharges the fuel to an engine (not shown) from a discharge port 18 shown in an upper portion of FIG. 1.

Firstly, a general construction of a fuel pump 10 will be described with reference to FIG. 1 to FIG. 3. The fuel pump 10 is roughly divided into an outer part, a drive part, and a pressure raising part. The outer part is constructed of a housing 11, a suction side cover 12, and a discharge side cover 15.

The housing 11 is formed in a cylindrical shape. The suction side to cover 12 is provided at one end portion of the housing 11. The suction side cover 12 has a suction hole 13 which passes though in an axial direction. The suction port 14 is an inlet of the suction hole 13. The discharge side cover 15 is provided at the other end portion of the housing 11. The discharge side cover 15 forms a cylinder part 16 which projects to the outside is of the housing 11 and has a discharge flow passage 17 which is formed inside the cylinder part 16. The discharge port 18 is an outlet of the discharge flow passage 17. The discharge side cover 15 has a bearing 19 which is provided in a central portion thereof.

The drive part is constructed of a motor 20 and is provided with a stator 21 and a rotor 22. The stator 21 is provided in the housing 11 and includes a stator core 23, an insulator 24, a winding 25, and a terminal 26. The stator core 23 is made of a magnetic material and forms a cylindrical yoke part 27 and a plurality of teeth parts 28 each of which projects inside in a radial direction from the yoke part 27. The insulator 24 is fitted to the teeth part 28 of the stator core 23. The winding 25 is wound by the insulator 24. In the present embodiment, the winding 25 includes a U-phase winding part, a V-phase winding part, and a W-phase winding part. There are provided three terminals 26 and each of the three terminals 26 can couple the winding part of each phase to an external control device.

A fuel flow passage 29 is formed between the housing 11 and the stator 21. The discharge side cover 15 has a fuel flow passage (not shown in the drawing) that connects the fuel flow passage 29 to the discharge flow passage 17. The rotor 22 is provided inside the stator 21 and has a rotary shaft 31, a rotor core 32, and a plurality of magnets 33 to 36. The rotary shaft 31 is supported by the bearing 19 and a bearing 43, which will be described later, in such a way as to rotate. The rotor core 32 is formed in a cylindrical shape and is fitted and fixed to the rotary shaft 31. The magnets 33 to 36 are provided in an outer peripheral portion of the rotor core 32. The respective magnets 33 to 36 are provided in such a way that polarities outside in a radial direction are different from each other in a circumferential direction.

In the motor 20 constructed in this manner, when electric currents each having a phase difference flow through the winding parts of the respective phases of the winding 25 of the stator 21, a rotating magnetic field is generated and the rotating magnetic field attracts magnetic poles of the rotor 22, whereby the rotor 22 is rotated.

The pressure raising part includes a casing 38, an impeller 39, and the suction side cover 12. The suction side cover 12 constructs the outer part of the fuel pump 10 and constructs also the pressure raising part. The casing 38 is formed in a shape of a cylinder having a closed end, is interposed between the stator 21 and the suction side cover 12 and is combined with the suction side cover 12. Further, the casing 38 forms a pump chamber 41 between itself and the suction side cover 12. The casing 38 has a through hole 42 formed in a central portion thereof. The through hole 42 has a bearing 43 fitted therein. An output end portion 37 of the rotary shaft 31 passes through the bearing 43 and protrudes into the pump chamber 41.

The impeller 39 is an impeller shaped like a circular disk and is received in the pump chamber 41. The impeller 39 has a fitting hole 44 formed in, a central portion thereof. The fitting hole 44 is fitted on the output end portion 37 of the rotary shaft 31 in such a way as to be able to transmit rotation from the rotary shaft 31 to the impeller 39.

In a wall portion opposite to the impeller 39 of the suction side cover 12, a suction side pressure raising flow passage 45 is formed which is extended in a circumferential direction and which is shaped like a letter C. The suction hole 13 communicates with an upstream side end portion, which is located at an end portion opposite to a rotational direction of the impeller 39, of the suction side pressure raising flow passage 45. In a wall portion opposite to the impeller 39 of the casing 38, a discharge side pressure raising flow passage 46 is formed which is extended in the circumferential direction and which is shaped like a letter C. The casing 38 has a discharge hole 47 communicating with a downstream side end portion, which is located at an is end portion in the rotational direction, of the discharge side pressure raising flow passage 46. The suction hole 13 is a hole passing through from the pump chamber 41 to one side in an axial direction, whereas the discharge hole 47 is a hole passing through from the pump chamber 41 to the other side in the axial direction. The casing 38 and the suction side cover 12 constructs a case 48.

In the pressure raising part constructed in this manner, when the impeller 39 is rotated along with the rotary shaft 31, the fuel is sucked into the pump chamber 41 through the suction hole 13 from the suction port 14. The fuel in the pump chamber 41 flows in a shape of a spiral between the impeller 39 and the pressure raising flow passages 45, 46 and has its pressure raised toward the discharge hole 47 from the suction hole 13. The fuel having a pressure raised is introduced into the discharge flow passage 17 through the discharge hole 47 and the fuel flow passage 29 and then is discharged from the discharge port 18.

Next, a characteristic construction of the fuel pump 10 will be described with reference to FIG. 4 to FIG. 7. Here, in FIG. 4 to FIG. 7, the construction will be schematically shown so as to make the construction easy to understand. A dimension, an angle, and a dimensional ratio of each part shown in the drawings will be not necessarily correct.

Here, a study conducted by the present inventors will be described. The inventors wanted to reduce wear of a fitting hole of an impeller and analyzed a cause of the wear. As a result, the inventors found that the wear of the fitting hole is mainly caused by a phenomenon such that the impeller is relatively moved in an axial direction with respect to a rotary shaft to thereby cause the fitting hole to slide on an output end portion. As a result of a further analysis, the following facts were found: that is, a pressure applied to the impeller from fuel is different between on a suction hole side and on a discharge hole side; and when a force by this pressure difference is larger than a frictional force between the output end portion and the impeller, a relative movement of the impeller is caused. In particular, when a high pressure pump is provided at a discharge portion of the fuel pump and a pulsation of a fuel pressure caused in this high pressure pump is transmitted to a fuel pump, the pressure difference is made larger and the wear of the impeller is easily caused.

In consideration of the above result, the fuel pump 10 employs the following construction for the purpose of making a frictional force between the output end portion 37 and the impeller 39 larger than a force caused by a difference in the axial direction of the pressure applied to the impeller 39 from the fuel. As shown in FIG. 4 to FIG. 6, an outer wall surface of the output end portion 37 includes a pair of first plane surfaces 51, 52 which are parallel to each other. The first plane surfaces 51, 52 are parallel to an axial center AX1 of the rotary shaft 31.

Further, the outer wall surface of the output end portion 37 includes a pair of first curved surfaces 53, 54 each of which is located between one first plane surface 51 and the other first plane surface 52 in the circumferential direction and each of which is protruded outwardly in the radial direction. In the first embodiment, a center of curvature of each of the first curved surfaces 53, 54 coincides with the axial center AX1. Further, a radius of the first curved surface 53 is equal to a radius of the first curved surface 54, that is to say, the first curved surface 53 and the first curved surface 54 are formed in such a way as to be along an imaginary cylindrical surface whose center is the axial center AX1. In other words, the output end portion 37 is a shaft which has the pair of first plane surfaces 51, 52 parallel to each other, that is, which is chamfered at two surfaces. The shaft which is chamfered at two surfaces is also referred to as an I-cut shaft or a double D-cut shaft.

An inner wall surface of the fitting hole 44 includes a pair of second plane surfaces 61, 62 which are parallel to each other. The second plane surfaces 61, 62 are parallel to an axial center AX2 of the impeller 39. The second plane surface 61 is opposed to the first plane surface 51 in the radial direction and when the rotary shaft 31 is rotated in a specified rotational direction, the second plane surface 61 is engaged with the first plane surface 51. The second plane surface 62 is opposed to the first plane surface 52 in the radial direction and when the rotary shaft 31 is rotated in a specified rotational direction, the second plane surface 62 is engaged with the first plane surface 52.

Further, the inner wall surface of the fitting hole 44 includes a pair of second curved surfaces 63, 64 each of which is located between one second plane surface 61 and the other second plane surface 62 in a circumferential direction and each of which is depressed outwardly in the radial direction. In the first embodiment, a center of curvature of each of the second curved surfaces 63, 64 coincides with the axial center AX2. Further, a radius of the second curved surface 63 is equal to a radius of the second curved surface 64. In other words, the second curved surface 63 and the second curved surface 64 are formed in such a way as to be along an imaginary cylindrical surface whose center is the axial center AX2.

As shown in FIG. 4 and FIG. 5, in a case where a distance between the pair of first plane surfaces 51, 52 is referred to as a two-surface width S, a value obtained by dividing the two-surface width S by an outer diameter D of the output end portion 37 is 0.75 or less. In the first embodiment, the value obtained by dividing the two-surface width S by the outer diameter D is, for example, 0.74. As shown in FIG. 7, in a state where one first plane surface 51 is in contact with one second plane surface 61, a value obtained by dividing a clearance C between the other first plane surface 52 and the other second plane surface 62 by the two-surface width S is 0.011 or less. In the first embodiment, the value obtained by dividing the clearance C by the two-surface width S is 0.011.

In the fuel pump 10 constructed in this manner, as compared with a conventional mode in which a two-surface width is set to a value of 0.8 times an outer diameter of a shaft, as specified in JIS B 1002, in a case where the clearance C and a transmission torque are in the same conditions, a binding force applied to the impeller 39 from the output end portion 37 is made larger. As shown in FIG. 6, a binding force Fb is a component in a direction vertical to the second plane surfaces 61, 62 of a force F which is applied to the impeller 39 from the output end portion 37 at a portion in which the output end portion 37 and the impeller 39 are brought into contact with each other.

Effects of the fuel pump 10 of the first embodiment will be described in the following. As described above, in the first embodiment, the outer wall surface of the output end portion 37 includes the pair of first plane surfaces 51, 52 which are parallel to each other. The inner wall surface of the fitting hole 44 includes the pair of second plane surfaces 61, 62 which are parallel to each other and which are engaged with one first plane surface 51 or the other first plane surface 52 when the rotary shaft 31 is rotated in a specified rotational direction. The value obtained by dividing the two-surface width S by the outer diameter D of the output end portion 37 is 0.75 or less.

When the two-surface width S is set in this manner, as compared with the conventional mode described above, the binding force applied to the impeller 39 from the output end portion 37 is made larger and a frictional force between the output end portion 37 and the impeller 39 is made larger. For this reason, a state is unlikely to develop in which a force caused by a difference in the axial direction of the pressure which is applied to the impeller 39 from the fuel is made larger than the frictional force between the output end portion 37 and the impeller 39. Hence, it is possible to inhibit the fitting hole 44 from sliding on the output end portion 37 and hence to inhibit the impeller 39 from being worn.

Further, in the first embodiment, in a state where one first plane surface 51 is in contact with one second plane surface 61, a value obtained by dividing the clearance C between the other first plane surface 52 and the other second plane surface 62 by the two-surface width S is 0.011 or less. The binding force applied to the impeller 39 from the output end portion 37 is made larger as the two-surface width S is smaller and as the clearance C is smaller. For this reason, it is possible to further inhibit the impeller 39 from being worn.

Second Embodiment

In a second embodiment, as shown in FIG. 8, an inner wall surface of a fitting hole 71 includes second plane surfaces 72, 73, third plane surfaces 74, 75, and second curved surface 63, 64. The second plane surface 72 and the second plane surface 73 are parallel to each other. The second plane surface 72 is opposed to the first plane surface 51 in the radial direction and when the rotary shaft 31 is rotated in a specified rotational direction, the second plane surface 72 is engaged with the first plane surface 51. The second plane surface 73 is opposed to the first plane surface 52 in the radial direction and when the rotary shaft 31 is rotated in a specified rotational direction, the second plane surface 73 is engaged with the first plane surface 52.

The third plane surface 74 and the third plane surface 75 are parallel to each other. The third plane surface 74 is formed between the second plane surface 72 and the second curved surface 64 in the circumferential direction. The second plane surface 72 and the third plane surface 74 form a protruded surface which is protruded to an axial center AX2 side. When the rotary shaft 31 is rotated in a direction opposite to the rotational direction, the third plane surface 74 is engaged with the first plane surface 51. The third plane surface 75 is formed between the second plane surface 73 and the second curved surface 63 in the circumferential direction. The second plane surface 73 and the third plane surface 75 form a protruded surface which is protruded to the axial center AX2 side. When the rotary shaft 31 is rotated in a direction opposite to the rotational direction, the third plane is surface 75 is engaged with the first plane surface 52.

On the other hand, a space W1 between one third plane surface 74 and the other third plane surface 75 is larger than a space W2 between one second plane surface 72 and the other second plane surface 73. The space W2 is a little larger than the two-surface width S. On the other hand, the space W1 is much larger than the two-surface width S.

In the second embodiment, a value obtained by dividing the two-surface width S by the outer diameter D of the output end portion 37 is 0.75 or less. For this reason, as is the case with the first embodiment, it is possible to inhibit the fitting hole 71 from sliding on the output end portion 37 and hence to inhibit the impeller 39 from being worn. Further, in the second embodiment, when the rotary shaft 31 is combined with the impeller 39, the output end portion 37 is inserted between the one third plane surface 74 and the other third plane surface 75. Then, when rotation is transmitted from the rotary shaft 31 to the impeller 39, the first plane surfaces 51, 52 are engaged with the second plane surfaces 72, 73, respectively. For this reason, without damaging the ease of assembling, the clearance between the output end portion 37 and the fitting hole 71 when the rotation is transmitted can be made as small as possible and the binding force applied to the impeller 39 from the output end portion 37 can be made larger. Hence, it is possible to further inhibit the fitting hole 71 from sliding on the output end portion 37.

Modifications of the above embodiments will be described. In a modification, an outer wall surface of the output end portion is not only constructed of a pair of first plane surfaces and a pair of first curved surfaces but also may be constructed of a pair of first plane surfaces and one or a plurality of other plane surfaces. In short, the outer wall surface of the output end portion needs only to include a pair of first plane surfaces. In another modification, an edge portion between a plane surface and a curved surface, or an edge portion between the plane surface and the plane surface, of the outer wall surface of the output end portion may be formed in a round shape. In still another modification, the impeller may be constructed of not only resin but also other material, for example, metal. The present disclosure is not limited to the embodiments described above but can be put into practice in various modes within a scope not departing from the gist of the present disclosure.

While the present disclosure has been described with reference to embodiments thereof, it is to be understood that the disclosure is not limited to the embodiments and constructions. The present disclosure is intended to cover various modification and equivalent arrangements. In addition, the various combinations and configurations, other combinations and configurations, including more, less or only a single element, are also within the spirit and scope of the present disclosure.

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