Pump Driving Apparatus

Abstract

A pump driving apparatus that can suppress backflow of a liquid in a pump chamber and improve pump efficiency is provided. A guide tube 23 is provided coaxially with an output shaft 4 of a motor M inside a pump chamber 8, and the ends in the axial direction of the guide tube 23 are fitted into and make sliding contact with a case inner wall surface that forms the pump chamber 8 and a shaft core-side inner wall surface 25 of an impeller 9 enclosed inside the pump chamber 8.

Description

TECHNICAL FIELD

The present invention relates to a pump driving apparatus that draws liquid in an axial direction into a pump chamber and expels the liquid in a circumferential direction by rotating an impeller provided inside the pump chamber.

BACKGROUND ART

First, one example of a pump driving apparatus will now be described. In FIG. 6, a rotor magnet 53, which has been magnetized with two poles at 180° intervals, is provided on a back yoke 52 of a rotor 51. The back yoke 52 is connected to a magnet case 56. A coupling magnet 55 is fitted onto the upper surface of the magnet case 56. The magnet case 56 is rotatably fitted onto a motor-side fixed shaft 54a via a bearing 57. A pump-side fixed shaft 54b, which is connected to a motor-side fixed shaft 54a by screw engagement, is integrally provided on a pump chamber 58. A rotation vane (impeller) 59 is fitted onto the pump-side fixed shaft 54b via a bearing 60. The impeller 59 slidably rotates via the bearing 60 around the pump-side fixed shaft 54b. A coupling magnet 61 is provided on the impeller 59 so as to face the magnet 55. The magnets 55, 61 are magnetized with six poles, for example, and the rotor 51 and the impeller 59 rotate together due to magnetic coupling.

The pump chamber 58 is formed by screwing together a pump case 62 and a motor case 63 with a divider plate 64 in between. The pump chamber 58 is sealed by an O ring 67 provided between the pump case 62 and the divider plate 64. When the motor is driven, the impeller 59 that is magnetically coupled to the rotor 51 rotates and thereby draws liquid from an inlet 65 in the axial direction (i.e., the direction of the arrow P) into the pump chamber 58 and expels the liquid from an outlet 66 provided at the outer periphery of the pump case 62 in FIG. 7. In FIG. 8, protruding ribs 67 are formed on the impeller 59 so as to radiate outward from the inner periphery to the outer periphery. Due to centrifugal force caused by rotation of the impeller 59, the liquid is guided along the protruding ribs 67 from the shaft core in FIG. 6 toward the outer periphery in the direction of the arrow Q (see Non-Patent Document 1).

Non-Patent Document 1

Journal of Technical Disclosure 10,194,725

DISCLOSURE OF THE INVENTION

In the pump driving apparatus shown in FIG. 6, to ensure smooth rotation of the impeller 59 inside the pump chamber 58, a gap S is formed between the impeller 59 and the inner wall surface of the pump case 62. This gap S is provided for the reasons given below. Firstly, it is necessary to prevent interference due to insufficient precision in the dimensions of the pump case 62 that is integrally molded. In addition, centering is difficult for the impeller 59 which is formed by welding together an upper portion, where the radial protruding ribs 67 are formed, and a lower portion, where the coupling magnet 61 is enclosed, which means that it is difficult to manufacture a pump driving apparatus with components that are precisely concentric. Also, although it would be conceivably possible to increase the thickness of the divider plate 64 to prevent eccentricity of the impeller 59 due to inclination of the fixed shafts 54a, 54b, this would cause a drop in the magnetic attraction between the impeller 59 and the rotor 51 that are magnetically coupled.

Most of the liquid that is drawn in near the shaft of the pump chamber 58 from the inlet 65 is driven in the direction of the arrow Q toward the outer periphery of the pump chamber 58 and expelled from the outlet 66. However, a pressure difference is produced inside the pump chamber 58, resulting in the problem that high-pressure liquid in the outer periphery flows back, via the gap S between the impeller 59 and the pump case 62, in the direction of the arrow R toward the periphery of the shaft that is at low pressure and collides with the liquid being drawn in the direction of the arrow P. thereby lowering the pump efficiency. When the fixed shafts 54a, 54b are inclined, there is a further problem in that the gap S will vary, resulting in greater fluctuations in pressure inside the pump chamber 58, which makes the pump operation unstable.

It is an object of the present invention to provide a pump driving apparatus that can suppress backflow of a liquid in a pump chamber and improve pump efficiency.

To achieve the stated object, the present invention has the following construction.

A pump driving apparatus draws in a liquid in an axial direction into a pump chamber and expels the liquid in the circumferential direction using an impeller that is magnetically coupled to a rotor of a motor and rotates about a fixed shaft, the pump driving apparatus including a guide tube that is provided inside the pump chamber so as to be coaxial with the fixed shaft, wherein ends of the guide tube in the axial direction are fitted to and make sliding contact with a case wall surface that forms the pump chamber and a core-side wall surface of the impeller enclosed inside the pump chamber.

Several representative examples of sliding contact between the guide tube and the case wall surface and the core-side wall surface of the impeller are given below.

Surfaces of the guide tube that make sliding contact may be spherical surface portions which are produced by having an outer circumferential surface of the guide tube swell outward and whose respective centers lie on an axis of the fixed shaft, and both ends of the guide tube in the axial direction may be fitted into and make sliding contact with the pump case and an uprising wall surface of the impeller.

Alternatively, surfaces of the pump case and the impeller that make sliding contact may be spherical surface portions that are each produced by having an outer circumferential surface of an erected wall, which is erected in the axial direction inside the pump chamber, swell outward and whose centers lie on an axis of the fixed shaft, and may be fitted into a tube hole of the guide tube so as to make the sliding contact.

As another alternative, at one end in the axial direction, a spherical surface portion that is produced by having an outer circumferential surface of an erected wall, which is erected in the axial direction inside the pump chamber, swell outward and whose center lies on an axis of the fixed shaft may be formed on one of the pump case and the impeller and the spherical surface portion may be fitted into a tube hole of the guide tube so as to make sliding contact, and at another end in the axial direction, a spherical surface portion that is produced by having an outer circumferential surface of the guide tube swell outward and whose center lies on the axis of the fixed shaft may be formed on the guide tube and the spherical surface portion may be fitted into an erected wall on one of the pump case and the impeller.

EFFECT OF THE INVENTION

When the pump driving apparatus according to the present invention is used, a guide tube is provided inside the pump chamber so as to be coaxial with the fixed shaft, wherein ends of the guide tube in the axial direction are fitted to and make sliding contact with a case wall surface that forms the pump chamber and a core-side wall surface of the impeller enclosed inside the pump chamber. This means that when the impeller is rotated to draw in low-pressure liquid in the axial direction into the pump chamber and expel the liquid toward the outer periphery, high-pressure liquid that flows back toward the core from the outer periphery of the pump chamber via a gap between the impeller and the pump case due to the pressure difference in the pump chamber can be effectively blocked by the guide tube. Therefore, it is possible to prevent vigorous collisions between high-pressure liquid that has flowed back in the pump chamber and the low-pressure liquid drawn in at the core due to the pressure difference inside the pump chamber, and therefore pump efficiency can be improved. Also, since it is possible to reduce the gap between the impeller and the pump case, it is possible to reduce redundant capacity of the pump chamber and make the pump chamber more compact.

Also, since each sliding contact surface formed on the guide tube or on an erected wall, which is erected in the axial direction inside the pump chamber, of the pump case or the impeller is formed for example of a spherical surface portion that is produced by having an outer circumferential surface of the guide tube or the erected wall swell outward and whose center lies on an axis of the fixed shaft, the guide tube will become inclined in keeping with any inclination of the impeller due to fluctuations in pressure inside the pump chamber or the strength of the fixed shaft. This means that the sliding contact between the guide tube and the case wall surface and wall surface of the impeller is maintained. As a result, it is possible to prevent vigorous collisions between high-pressure liquid that flows back from the outer periphery and the low-pressure liquid drawn in at the core due to the pressure difference inside the pump chamber, so that stable pump operation with little fluctuation in pressure inside the pump chamber can be maintained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial cross-sectional view of a principal part of a pump driving apparatus.

FIG. 2 is a perspective view showing a state where a magnet case and a back yoke are assembled.

FIG. 3A is an exploded perspective view showing the assembled construction of a pump driving apparatus and FIG. 3B is a partially enlarged view of a guide tube.

FIG. 4 is a schematic diagram showing sliding contact of the guide tube.

FIG. 5A to FIG. 5C are schematic cross-sectional views showing sliding contact between the guide tube and a pump case and an impeller according to other examples.

FIG. 6 is a cross-sectional view of a conventional pump driving apparatus.

FIG. 7 is a top view of the conventional pump driving apparatus.

FIG. 8 is a perspective view of a conventional impeller.

BEST MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of the present invention will now be described in detail with reference to the attached drawings. First, the overall construction of a pump driving apparatus will be described with reference to FIG. 1 to FIG. 3.

In FIG. 1, an example is shown where an outer-rotor, single-phase, bipolar brushless motor M is used as one example of a drive source for driving a pump. In this single-phase, bipolar brushless motor M, a rotor magnet (not shown) that is magnetized with two poles at 180° intervals is provided on a back yoke 2 of a rotor 1. The back yoke 2 is connected to a magnet case 6. A coupling magnet 5 is fitted into an upper surface of the magnet case 6. The magnet case 6 is rotatably fitted via a bearing 7 onto a motor-side fixed shaft 4a. Note that the rotor 1 is energized in the axial direction toward the magnet case 6 by a precompressed spring provided at a fixed end of the stator.

Here, the single-phase, bipolar brushless motor M is driven as a DC brushless motor by subjecting an AC current from a single-phase AC power supply to full-wave rectification by a rectifying bridge circuit and having a control unit change the direction of the rectified current flowing in the coil in accordance with the rotational angle of the rotor 1 (i.e., the positions of the poles of the magnet). After this, once the rotational speed of the rotor 1 approaches a rotational speed that is synchronized with the power supply frequency, there is a switch to synchronous operation so that there is a transition to synchronous operation. Note that the drive source is not limited to the single-phase bipolar brushless motor M, and it is also possible to use various types of motor, such as a DC motor (as examples, a multipolar brushless motor, such as a single-phase four-pole brushless motor M, or a brush motor), an AC motor, or an induction motor. The motor is also not limited to an outer-rotor motor and may be an inner-rotor motor.

In FIG. 2, engagement holes 15 are formed around a protruding part, which protrudes downward in the axial direction, of a boss portion 14 of the magnet case 6 in which the bearing 7 is fitted. Engagement protrusions 17 are also provided in the circumferential direction so as to protrude into a base portion through-hole 16 of the back yoke 2 that is cup-shaped. Grease is applied to contacting parts of the magnet case 6 and the back yoke 2 to reduce the frictional torque, and the magnet case 6 and the back yoke 2 engage one another with a certain angle of play for relative rotation therebetween.

Next, the construction of the pump chamber 8 side will be described. The pump chamber 8 is provided with a pump-side fixed shaft 4b that is integrally connected to the motor-side fixed shaft 4a by screw engagement. A rotating vane (impeller) 9 is fitted onto the pump-side fixed shaft 4b via a bearing 10. The bearing 10 is constructed by attaching ceramic rings 12, which receive the load in the thrust direction, at both ends in the axial direction of a cylindrical carbon ring 11 that is impregnated with metal. The carbon ring 11 is bonded to the impeller 9. The impeller 9 slidably rotates around the pump-side fixed shaft 4b via the carbon ring 11. The impeller 9 is provided with a coupling magnet 13 that faces the magnet 5. The magnets 5, 13 are magnetized with six poles, for example, and the rotor 1 and the impeller 9 integrally rotate due to magnetic coupling. The impeller 9 is integrally formed by welding an upper portion, on which radiating protruding ribs 9a (see FIG. 3A) are formed, and a lower portion, in which the coupling magnet 13 is enclosed.

In FIG. 1, the pump chamber 8 is integrally formed by screwing together a pump case 18 and a motor case 19 via a divider plate 20. The pump chamber 8 is sealed by an O ring 28 provided between the pump case 18 and the divider plate 20. An inlet 21 for liquid is formed at the core of the pump case 18 and an outlet 22 for the liquid (see FIG. 3A) is provided at the outer circumferential edge. A guide tube 23 is provided coaxially with the pump-side fixed shaft 4b inside the pump chamber 8. That is, the guide tube 23 is fitted into and makes sliding contact with a case inner wall surface 24 that forms the pump chamber 8 and an inner wall surface 25 of an erected wall 26 erected at the core of the impeller 9. The ends of the guide tube 23 in the axial direction are restrained by the pump case 18 and the impeller 9. The impeller 9 slidably rotates in contact with an outer circumferential surface of the guide tube 23.

In FIG. 3B, a sliding contact surface of the guide tube 23 is produced by having an outer circumferential surface of the guide tube 23 swell outward. More specifically, a spherical surface portion 23a whose center O lies on the axis M of the pump-side fixed shaft 4b is formed at two positions. In FIG. 4, in the present embodiment, since the distance from the axis M to the case inner wall surface 24 and the distance from the axis M to the inner wall surface 25 of the erected wall provided at the core of the impeller 9 are both r, spherical surface portions 23a with the radius r are formed at two positions on the sliding contact surface. The respective radii r may differ in a case where the distance from the axis M to the case inner wall surface 24 and the distance from the axis M to the inner wall surface 25 of the erected wall of the impeller 9 differ. In FIG. 4, even if the pump-side fixed shaft 4b is inclined with respect to the axis M at the axis M′ and the impeller 9 is inclined in the same way, even though the contact positions between one spherical surface portion 23a and the case inner wall surface 24 and between the other spherical surface portion 23a and the inner wall surface 25 of the erected wall of the impeller 9 will change, there will be no change in the sliding contact between the guide tube 23 and the pump case 18 and impeller 9. This means that the gap S between the impeller 9 and the pump case 18 can be effectively blocked by the guide tube 23.

When the motor is started, the impeller 9 that is magnetically coupled to the rotor 1 rotates, liquid is drawn from the inlet 21 in the axial direction (the direction of the arrow P) into the pump chamber 8, and the liquid is guided by rotation of the impeller 9 from the core of the pump case 18 in the direction of the arrow Q toward the outer periphery and is expelled from the outlet 22 that is provided in the outer periphery of the pump case 18 as shown in FIG. 3A. A pressure difference is produced inside the pump chamber 8 due to the centrifugal force caused by the rotation of the impeller 9, and although liquid in the outer periphery that is at a high pressure attempts to flow back via the gap S between the impeller 9 and the pump case 18 in the direction of the arrow R toward the core that is at low pressure, such flow is effectively blocked by the guide tube 23. Accordingly, since there are no vigorous collisions between liquid that has flowed back toward the core and the liquid drawn in from the inlet 21, an improvement of 20 to 30% or more in pump efficiency can be expected.

Note that although there is a slight backflow of the liquid due to the sliding movement of the spherical surface portions 23a of the guide tube 23 and the case inner wall surface 24 and the inner wall surface 25 of the erected wall, this has very little effect on pump operation. Also, as shown in FIG. 4, since the guide tube 23 will become inclined in keeping with any inclination of the pump-side fixed shaft 4b and will maintain the sliding contact, there will be no vigorous collisions between liquid that has flowed back through the gap S and the liquid drawn in from the inlet 21.

Next, one example of an assembling process for the above pump driving apparatus will be described with reference to FIG. 3.

Since there are no particular limitations on the type of motor, the details of the assembling of the motor are omitted here, and the following description will focus on the assembling of the pump.

The magnet case 6 into which the coupling magnet 5 has been fitted is fitted via the bearing 7 onto the motor-side fixed shaft 4a of the motor M (see FIG. 1). The divider plate 20 that acts as a divider for the pump chamber is screwed to an upper surface of the motor case 19. The ceramic rings 12 are fitted at both ends of the carbon ring 11 on the pump-side fixed shaft 4b. The carbon ring 11 is fixed by bonding to the shaft hole of the impeller 9.

The impeller 9 is fitted via the carbon ring 11 onto the pump-side fixed shaft 4b that is provided so as to protrude on the pump side, and the coupling magnet 13 is magnetically coupled to the magnet 5 of the rotor. The erected wall 26 is provided at the core of the impeller 9 and the lower end of the guide tube 23 is fitted into the inner wall surface 25 of this erected wall so that sliding contact is achieved between one spherical surface portion 23a and the inner wall surface 25. In addition, the pump case 18 is placed on the motor case 19 and fixed by screws 27. When doing so, the upper end of the guide tube 23 is fitted into the case inner wall surface 24 at the core of the pump case 18 so that sliding contact is achieved between the case inner wall surface 24 and the guide tube 23a (see FIG. 1 and FIG. 4).

According to the pump driving apparatus described above, when liquid is drawn in the axial direction into the pump chamber 8 and driven in the circumferential direction by rotation of the impeller 9, due to the pressure difference inside the pump chamber 8, high-pressure liquid that flows back via the gap S between the impeller 9 and the pump case 18 is effectively blocked by the guide tube 23, which makes it possible to prevent collisions with low pressure liquid drawn in at the core and thereby improve the pump efficiency. Also, since it is possible to reduce the gap S between the impeller 9 and the pump case 18, it is possible to reduce redundant capacity of the pump chamber 8 and make the pump chamber more compact.

Next, other examples of sliding contact between the guide tube 23 and the pump case 18 and impeller 9 will be described with reference to FIG. 5A to FIG. 5C.

In FIG. 5A, an erected wall 29 and the erected wall 26, which are erected in the axial direction inside the pump chamber, are respectively formed on the pump case 18 and the impeller 9. Spherical surface portions 29a, 26a which are produced by having an outer circumferential surface swell outward and whose center O lies on the axis M of the fixed shaft are respectively formed on the erected walls 29, 26. These erected walls 29, 26 are fitted into a cylindrical hole of the guide tube 23 and make sliding contact with the guide tube 23.

In FIG. 5B, an erected wall 29 and the erected wall 26, which are erected in the axial direction inside the pump chamber, are respectively formed on the pump case 18 and the impeller 9. The guide tube 23 is formed with a large diameter portion 30 and a small diameter portion 31. A spherical surface portion 29a which is produced by having an outer circumferential surface swell outward and whose center O lies on the axis M of the fixed shaft is formed on the erected wall 29. A spherical surface portion 31a which is produced by having an outer circumferential surface swell outward and whose center O lies on the axis M of the fixed shaft is also formed on the erected wall 31. At one end in the axial direction, the erected wall 29 is fitted into the cylindrical hole of the guide tube 23 so that the spherical surface portion 29a makes sliding contact. At the other end in the axial direction, the small diameter portion 31 is fitted into the erected wall 26 so that the spherical surface portion 31a makes sliding contact.

Note that it is also possible to reverse the up-down positions of the large diameter portion 30 and the small diameter portion 31 of the guide tube 23 in FIG. 5B and to form a spherical surface portion, which is produced by having an outer circumferential surface swell outward and whose center O lies on the axis M of the fixed shaft, on the erected wall 26 of the impeller 9 instead of on the pump case 18.

In FIG. 5C, an erected wall 29 and the erected wall 26, which are erected in the axial direction inside the pump chamber, are respectively formed on the pump case 18 and the impeller 9. Protruding surface portions (such as curved surface portions or spherical surface portions) 29b, 26b are formed on the inner wall surfaces of the erected wall 29 and the erected wall 26. Although the protruding surface portions 29b, 26b are not necessarily limited to spherical surface portions, such portions need to contact the outer circumferential surface of the guide tube 23 at the top and the bottom. The guide tube 23 is fitted into the erected walls 29, 26 of the pump case 18 and the impeller 9 at both ends in the axial direction so as to make sliding contact with the protruding surface portions 29b, 26b. Note that although various examples of sliding contact have been described earlier, it is possible to produce various types of sliding surfaces by interchanging the spherical surface portions or protruding surface portions formed on the sliding surfaces.

Claims

1. A pump driving apparatus that draws in a liquid in an axial direction into a pump chamber and expels the liquid in the circumferential direction using an impeller that is magnetically coupled to a rotor of a motor and rotates about a fixed shaft,

the pump driving apparatus comprising a guide tube that is provided inside the pump chamber so as to be coaxial with the fixed shaft, wherein ends of the guide tube in the axial direction are fitted to and make sliding contact with a case wall surface that forms the pump chamber and a core-side wall surface of the impeller enclosed inside the pump chamber.

2. A pump driving apparatus according to claim 1,

wherein surfaces of the guide tube that make sliding contact are spherical surface portions which are produced by having an outer circumferential surface of the guide tube swell outward and whose respective centers lie on an axis of the fixed shaft, and both ends of the guide tube in the axial direction are fitted into and make sliding contact with the pump case and an uprising wall surface of the impeller.

3. A pump driving apparatus according to claim 1,

wherein surfaces of the pump case and the impeller that make sliding contact are spherical surface portions that are each produced by having an outer circumferential surface of an erected wall, which is erected in the axial direction inside the pump chamber, swell outward and whose centers lie on an axis of the fixed shaft, and are fitted into a tube hole of the guide tube so as to make the sliding contact.

4. A pump driving apparatus according to claim 1,

wherein at one end in the axial direction, a spherical surface portion that is produced by having an outer circumferential surface of an erected wall, which is erected in the axial direction inside the pump chamber, swell outward and whose center lies on an axis of the fixed shaft is formed on one of the pump case and the impeller and the spherical surface portion is fitted into a tube hole of the guide tube so as to make sliding contact, and at another end in the axial direction, a spherical surface portion that is produced by having an outer circumferential surface of the guide tube swell outward and whose center lies on the axis of the fixed shaft is formed on the guide tube and the spherical surface portion is fitted into an erected wall of one of the pump case and the impeller.