Pump mechanism

Abstract

Provided is a pump mechanism in which a sufficient fluid gap can be ensured and passive control is used. A magnetic-levitation-type pump mechanism (1) is provided with at least: a housing (10) having a blood flow path formed therein; and an impeller (20) that is rotatably housed in the housing (10). The housing (10) has a torque transmission member (11) and a housing-side magnet (12). The impeller (20) has a torque reception member (21) and an impeller-side magnet (22). The impeller (20) is rotated by actions of the torque transmission member (11) and the torque reception member (21). Since the housing-side magnet (12) and the impeller-side magnet (22) are disposed such that thrust force generated by rotation of the impeller (20) and magnetic force of each magnet is balanced, the impeller (20) stays at a predetermined position in a state of being levitated in the housing (10).

Description

[Technical Field]

[0001] The present invention relates to a magnetically levitated pump mechanism. This application claims priority from Japanese Patent Application No. 2020-86132, filed in Japan on May 15, 2020, which is incorporated herein by reference. [Background technology]

[0002] Heart transplantation is the most effective treatment for severe heart failure caused by conditions such as dilated cardiomyopathy. However, the shortage of donors has become a serious problem, resulting in longer waiting times between transplant eligibility and transplant surgery. Therefore, a ventricular assist device (VAD), which pumps blood by rotating an impeller, is used as a bridge until a heart transplant is possible.

[0003] In order for patients to move freely, an artificial heart needs to be implanted in the body, and a small implantable VAD is required. Furthermore, in recent years, there has been a trend toward improved mechanical durability and reduced blood damage. To reduce this, artificial hearts that use non-contact bearings to levitate the impeller have become mainstream. Non-contact bearings are mainly classified into hydrodynamic bearings and magnetic bearings. Hydrodynamic bearings levitate the impeller by utilizing the wedge effect that occurs when the flow path is narrowed in the direction of fluid flow (for example, Non-Patent Document 1). In this case, since a restraining force is generated passively, sensors and the like are not required, which is advantageous for miniaturization.

[0004] However, in this method, the fluid gap between the impeller and the housing must be narrowed to a few tens of micrometers to obtain sufficient rigidity for levitation, and high shear stress acts on the blood, raising concerns about blood damage.

[0005] On the other hand, magnetic bearings levitate the impeller using magnetic force, but according to Earnshaw's theorem, it is impossible to support all five degrees of freedom of motion other than rotation without contact using only a static magnetic field. To achieve impeller levitation, at least one degree of freedom of motion must be controlled using an electromagnet or an external force other than magnetic force. Therefore, magnetic bearings levitate the impeller using feedback control using an electromagnet and a displacement sensor (for example, Non-Patent Document 2). In this case, a fluid gap of several hundred microns can be secured, which reduces blood damage compared to hydrodynamic bearings.

[0006] However, the above method requires sensors and a control system, which makes it difficult to reduce the size of the system and raises concerns about a decrease in system reliability. [Prior art documents] [Non-patent literature]

[0007] [Non-Patent Document 1] Hirohito Sumikura, Kazuyoshi Fukunaga, Akio Funakubo, and Yasuhiro Fukui, "Proposal of an Enclosed Impeller for Axial-Flow Blood Pumps and Its Engineering Verification Using CFD," Life Support, Vol. 20, No. 1 (2008), pp. 9-16. [Non-patent document 2] Hideo Hoshi, Tadahiko Shinshi, Setsuo Takatani. The Third Generation Blood Pumps: Mechanical Non-contact with Magnetic Levitation, Artificial Organs, Vol. 30, No. 5, pp. 324-338, May. 2006. Summary of the Invention [Problem to be solved by the invention]

[0008] Thus, in the development of a small artificial heart, it is important to achieve both miniaturization of the device and reduction of blood damage, and improvements in the levitation method are required.

[0009] The present invention has been made in consideration of the above-mentioned problems, and aims to provide a pump mechanism that can ensure a sufficient fluid gap and uses passive control (no external energy supply is required for control). [Means for solving the problem]

[0010] One aspect of the present invention is a magnetically levitated pump mechanism comprising at least a housing that forms a flow path, and an impeller rotatably accommodated within the housing, the housing having a torque transmission member and a housing-side magnet, the impeller having a torque receiving member and an impeller-side magnet, the impeller rotates due to the action of the torque transmission member and the torque receiving member, and of the five degrees of freedom consisting of three degrees of freedom in the direction of the impeller's rotation axis and the directions of two axes perpendicular to the rotation axis, and the degrees of freedom in the tilt direction around the two axes excluding the impeller's rotation axis, three to four degrees of freedom are controlled only by the balance of magnetic forces of the housing-side magnet and the impeller-side magnet, and the housing-side magnet and the impeller-side magnet are arranged so that for the remaining degrees of freedom, only magnetic force acts in the direction opposite to the direction of displacement due to thrust based on the rotation of the impeller. If we define the stiffness as positive when a force opposite to the displacement acts on the impeller when the impeller is displaced, then the stiffness of the resultant force of thrust and magnetic force in the remaining degrees of freedom will be positive. By having an expanded portion with a different inner diameter at the position where the impeller is located, a passive levitation mechanism that does not require active control can be achieved. The impeller remains suspended in place within the housing.

[0011] According to one aspect of the present invention, by designing the impeller so that the thrust force generated by the rotation of the impeller and the magnetic force of the magnets provided on the housing and the impeller are balanced, a sufficient fluid gap can be secured, Passive levitation mechanism that does not require active control It is possible to provide a pump mechanism using the above. Furthermore, by providing an expanded diameter portion and changing the flow passage diameter, the thrust of the impeller can be changed, and the balance between the thrust and the magnetic force can be adjusted.

[0012] In this case, in one embodiment of the present invention, the four degrees of freedom excluding the degree of freedom in the direction of the impeller's rotational axis are controlled only by the balance of magnetic forces between the housing-side magnets and the impeller-side magnets, and for the degree of freedom in the direction of the rotational axis, the housing-side magnets and the impeller-side magnets are arranged so that a magnetic force acts in the opposite direction to the direction of displacement due to the thrust based on the rotation of the impeller.

[0013] In this case, a sufficient fluid gap can be secured as a pump mechanism in which fluid flows in the direction of the rotation axis, and a pump mechanism using passive control can be realized.

[0016] In one aspect of the present invention, the enlarged diameter portion may be tapered so that the inner diameter gradually increases.

[0017] In this way, the change in thrust can be finely adjusted.

[0018] In one aspect of the present invention, the rotary vanes provided on the impeller may be unevenly distributed at a position corresponding to the expanded diameter portion of the housing.

[0019] This allows the change in thrust force that accompanies the axial displacement of the impeller to be more accurately reflected.

[0020] In one aspect of the present invention, two of each of the housing-side magnets and the impeller-side magnets may be provided at positions straddling the expanded diameter portion.

[0021] By doing so, it is possible to balance out displacements in the radial direction and in the tilt direction.

[0022] In addition, one aspect of the present invention may be a blood pump that pumps blood in an auxiliary artificial heart.

[0023] The pump mechanism according to the present invention can be preferably applied as a blood pump. [Effects of the Invention]

[0024] As described above, according to the present invention, a sufficient fluid gap can be ensured and a pump mechanism using passive control can be provided. [Brief explanation of the drawings]

[0025] [Figure 1]FIG. 1(A) is a partially sectional perspective view showing the configuration of a pump mechanism according to one embodiment of the present invention, and FIG. 1(B) is a side sectional view. [Figure 2] FIG. 2 is a schematic diagram showing the forces acting on an impeller and the direction of displacement of the impeller in a pump mechanism according to one embodiment of the present invention. [Figure 3] FIG. 3 is a schematic diagram illustrating forces acting during axial displacement of an impeller in a pump mechanism according to an embodiment of the present invention. [Figure 4] FIG. 4 is a diagram showing the relationship between the axial displacement of the impeller and the axial force acting on the impeller in a pump mechanism according to one embodiment of the present invention. [Figure 5] FIG. 5 is a schematic diagram illustrating forces acting during radial displacement of an impeller in a pump mechanism according to an embodiment of the present invention. [Figure 6] FIG. 6 is a schematic diagram showing forces acting when the impeller of a pump mechanism according to one embodiment of the present invention is displaced in an inclined direction. [Figure 7] Figures 7(A) and 7(B) are cross-sectional views showing the configuration of a pump mechanism according to another embodiment of the present invention, where Figure 7(A) is a cross-sectional view showing the internal impeller located near the bottom of the housing, and Figure 7(B) is a cross-sectional view showing the internal impeller located near the top of the housing. [Figure 8] FIG. 8 is a diagram showing one form of a housing in an embodiment according to the present invention. [Figure 9] FIG. 9 is a diagram showing the configuration of an impeller A in an embodiment according to the present invention. [Figure 10] FIG. 10 is a diagram showing the relationship between axial displacement and thrust force when impeller A is used in the embodiment according to the present invention. [Figure 11] FIG. 11 is a diagram showing the configuration of an impeller B in an embodiment according to the present invention. [Figure 12] FIG. 12 is a diagram showing the relationship between axial displacement and thrust force when impeller B is used in the embodiment according to the present invention. [Figure 13]FIG. 13 is a diagram showing one form of a magnetic bearing in an embodiment according to the present invention. [Figure 14] FIG. 14 is a diagram showing the relationship between the axial displacement and the axial force of the magnetic bearing in the embodiment according to the present invention. [Figure 15] FIG. 15 is a diagram showing the relationship between radial displacement and radial force of a magnetic bearing in an embodiment according to the present invention. [Figure 16] FIG. 16 is a diagram showing the relationship between the torque and the inclination direction displacement of the magnetic bearing in the embodiment according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0026] A preferred embodiment of the present invention will be described in detail below. Note that the embodiment described below does not unduly limit the content of the present invention as defined in the claims, and not all of the configurations described in the embodiment are necessarily essential as means for solving the problems of the present invention.

[0027] In the following explanation, a blood pump that pumps blood will be described as an example of a pump mechanism according to the present invention. However, the pump mechanism according to the present invention is not limited to this form and can also be applied to, for example, high-purity pumps used in semiconductor manufacturing, pumps for food, and in some cases, pumps that pump gas (fans or blowers).

[0028] 1(A) and 1(B) are a partially cross-sectional perspective view (FIG. 1(A)) and a side cross-sectional view (FIG. 1(B)) showing the configuration of a pump mechanism according to one embodiment of the present invention. One aspect of the present invention is a magnetically levitated pump mechanism 1, which includes at least a housing 10 forming a flow path and an impeller 20 rotatably housed within the housing 10. The housing 10 has a torque transmission member 11 and a housing-side magnet 12, and the impeller 20 has a torque receiving member 21 and an impeller-side magnet 22. The impeller 20 rotates due to the action of the torque transmission member 11 and the torque receiving member 21, and the housing-side magnet 12 and the impeller-side magnet 22 are arranged so that the thrust caused by the rotation of the impeller 20 balances the magnetic force of the magnet, thereby causing the impeller 20 to remain levitated in a predetermined position within the housing 10. The pump mechanism 1 according to one embodiment of the present invention also includes a straightener 30 and a diffuser 40, respectively, upstream and downstream of the impeller 20.

[0029] In one aspect of the present invention, of the five degrees of freedom, including three degrees of freedom in the direction of the rotation axis of impeller 20 and the directions of two axes perpendicular to the rotation axis, and the degree of freedom in the tilt direction around the two axes excluding the rotation axis of impeller 20, three to four degrees of freedom are controlled solely by the balance of magnetic forces between housing-side magnets 12 and impeller-side magnets 22, and the remaining degree of freedom is designed so that only the magnetic force acts in the direction opposite to the direction of displacement due to thrust based on the rotation of impeller 20. Therefore, in one aspect of the present invention, there is no need to use a hydrodynamic bearing as in Patent Document 1, so a wide fluid gap (e.g., several hundred μm) can be ensured, reducing blood damage. Furthermore, no sensors or control systems are required.

[0030] As a combination of torque transmission member 11 and torque receiving member 21, for example, a stator coil is used as torque transmission member 11 and a rotor magnet is used as torque receiving member 21, and current is supplied to the stator coil to generate rotational torque in impeller 20. Alternatively, a permanent magnet that can be rotated by an external motor may be placed in place of the stator coil, and rotational torque may be transmitted to the impeller side in a non-contact manner by magnetic attraction with the rotor magnet. Of course, other methods are also possible.

[0031] In one aspect of the present invention, the housing-side magnets 12 and the impeller-side magnets 22 are arranged in the axial direction of the pump mechanism 1 (the direction of blood flow) so that the thrust caused by the rotation of the impeller 20 and the magnetic force of the magnets are balanced. For example, as shown in FIGS. 1(A) and 1(B), the housing-side magnets 12 and the impeller-side magnets 22 are arranged along the outer periphery of the housing 10 and the inner periphery of the impeller 20, respectively. Note that the arrows shown in the illustration of each magnet in FIG. 1(B) indicate an example of the magnetization direction (the same applies to subsequent figures). Furthermore, the housing-side magnets 12 and the impeller-side magnets 22 are not limited to this arrangement; the housing-side magnets 12 may be arranged on the inner periphery of the housing 10 or on the side of the straightener 30 and diffuser 40, or the impeller-side magnets 22 may be arranged on the outer periphery or at the axial end of the impeller 20.

[0032] In one embodiment of the present invention, in order to adjust the magnitude of the thrust, the housing 10 can be provided with an expanded diameter section 13 with a different inner diameter at the position where the impeller 20 is located. In this way, when the impeller 20 is displaced in the axial direction, the magnitude of the thrust acting on the impeller 20 can be changed, and the magnetic force acting on the impeller 20 can be adjusted to balance with the thrust. The expanded diameter section 13 may have an inner diameter that changes suddenly at a certain point, as shown in FIG. 1(B), or may have a tapered shape so that the inner diameter gradually increases.

[0033] In one aspect of the present invention, in Fig. 1(B), two housing-side magnets 12 (12a, 12b) and two impeller-side magnets 22 (22a, 22b) are provided at positions straddling the expanded diameter portion 13, but the number and arrangement are not limited to this example. Below, the conditions of the levitation mechanism in the pump mechanism 1 according to one embodiment of the present invention will be described in detail.

[0034] The levitation principle of the pump mechanism according to the present invention will be outlined below. In a pump mechanism according to one embodiment of the present invention, the rotation of the impeller applies an axial force to blood, generating blood flow. At this time, a force in the opposite direction to the blood flow acts on the impeller as a reaction, which is called thrust. In this invention, the forces acting on the impeller and the impeller's displacement are considered to be divided into three directions: the axial direction, the radial direction, and the angular direction, as shown in FIG. 2. In the axial direction, two forces act: the magnetic force of the permanent magnets (housing-side magnets and impeller-side magnets) and the thrust force due to the rotation of the impeller. Levitation is achieved by appropriately combining these forces. In the radial and angular directions, only the magnetic force of the permanent magnets (housing-side magnets and impeller-side magnets) is considered to act, and levitation is achieved by this magnetic force.

[0035] Ultimately, this invention proposes a pump mechanism equipped with a passive levitation mechanism that combines magnetic force and thrust, which constrains the five degrees of freedom of the impeller except for rotation, by satisfying all of the following levitation conditions: Note that in this specification, stiffness is defined as positive when, when the impeller is displaced, a force acts on it in the opposite direction to the displacement. <Axial direction> There exists a point of balance where the stiffness of the resultant force of the thrust and magnetic forces is positive and the resultant force is zero. <Radial direction> There exists a point where the magnetic stiffness is positive and the magnetic force is zero. <Tilt direction> There exists a point where the stiffness of the torque due to magnetic force is positive and the torque is zero.

[0036] (1) Axial levitation principle Figure 3 shows the axial force acting on the impeller in a pump mechanism according to one embodiment of the present invention. As mentioned above, according to Earnshaw's theorem, it is impossible to levitate an impeller using only two pairs of levitation magnets (impeller-side magnets and housing-side magnets), and an external force other than electromagnets or magnetic force must be used for at least one degree of freedom. Therefore, in this invention, levitation is achieved by using thrust in the axial direction. Instead of making the axial direction negative stiffness due to the magnetic force between the levitation magnets, the stiffness in the radial and tilt directions is made positive. Levitation is achieved by making the thrust act as positive stiffness in the axial direction. Here, the thrust F generated on the impeller in an axial pump is T [N] is calculated based on the theoretically determined flow velocity distribution inside the pump and is expressed by the following formula (1).

[0037]

number

[0038] In the above formula (1), γ is the unit volume weight of the fluid (kgf / m 3 ), S is the impeller outlet area (m 2 ), H is the total head of the pump (m), μ is the ratio of the impeller boss to the outer diameter of the blade, and g is the gravitational acceleration (m / s 2 ), H th is the theoretical head (m), and u2 is the circumferential flow velocity at the impeller outlet (m / s). The total head of the pump, H (m), takes into account the energy loss within the pump. th (m) is the head calculated ignoring the energy loss within the pump. Also, the impeller boss refers to the shaft excluding the impeller blades.

[0039] According to formula (1), thrust depends on the outlet area and head of the impeller. It has also been reported that head decreases as the gap between the housing wall and the impeller blades increases. This is because backflow is more likely to occur in the gap. The levitation mechanism in the pump mechanism according to one embodiment of the present invention utilizes these characteristics and is designed so that thrust changes with axial displacement of the impeller and its stiffness is positive.

[0040] Therefore, in a pump mechanism according to one embodiment of the present invention, by using a housing shape in which the flow path diameter changes as shown in Fig. 3 as an example, it is thought that when the impeller is displaced, the impeller outlet area, head, and gap between the housing and the impeller blades change, and the thrust changes accordingly. By utilizing this, even when the rigidity of the magnetic force of the permanent magnet is negative in the axial direction, as shown in Fig. 4, it is thought that it is possible to realize a condition in which the resultant force in the axial direction is positive and a point of equilibrium exists, as long as the rigidity of the thrust exceeds it.

[0041] (2) Radial and tilt levitation principles Figure 5 shows the state of the impeller inside the pump when it is displaced radially. At this time, the repulsive force between the impeller-side magnets inside the impeller and the housing-side magnets outside the housing acts as a restoring force on the impeller. Similarly, when it is displaced in the tilt direction, as shown in Figure 6, the repulsive force between the magnets acts as a restoring force. From this, it is thought that the rigidity in the radial and tilt directions becomes positive, causing the impeller to levitate. Note that the magnetic force generated during radial and tilt displacement acts as a restoring force only when the relative axial displacement between the housing-side magnets and the impeller-side magnets is small. It is known that when the relative displacement becomes large, the rigidity in the axial and radial directions reverses, making levitation impossible. Therefore, it is necessary to confirm that the rigidity in the radial and tilt directions is positive at the relative positions of the impeller-side magnets and the housing-side magnets at the axial balance point mentioned above.

[0042] (Other Aspects of the Pump Mechanism) The explanations and drawings up to this point have been based mainly on the assumption of an axial flow pump in which the direction of the flow emitted from the pump mechanism is the same as the direction of the rotation axis of the impeller. However, the pump mechanism according to one embodiment of the present invention is not limited to axial flow pumps, and can also be applied to centrifugal pumps in which the direction of the flow emitted from the pump mechanism is perpendicular to the direction of the rotation axis of the impeller.

[0043] 7(A) and 7(B) are cross-sectional views showing the configuration of a pump mechanism 1 according to another embodiment of the present invention. FIG. 7(A) is a cross-sectional view showing the internal impeller 20 located near the bottom of the housing 10, and FIG. 7(B) is a cross-sectional view showing the internal impeller 20 located near the top of the housing 10. The pump mechanism 1 (centrifugal pump) shown in FIGS. 7(A) and 7(B) also achieves stable levitation in the radial and tilt directions due to positive stiffness caused by the magnetic force between the magnets. However, the axial direction results in negative stiffness due to the magnetic force between the magnets alone. Therefore, in one aspect of the present invention, a step (expanded diameter portion 13) is provided in the housing 10 so that the flow path width changes with axial displacement of the impeller. This results in positive stiffness for the axial thrust. By ensuring that the positive stiffness of the thrust sufficiently exceeds the negative stiffness of the magnetic force, the resultant force becomes positive stiffness. This balance between the thrust and magnetic force enables the impeller 20 to be levitated. [Example]

[0044] The present invention will be described in more detail below using examples, but the present invention is not limited to the following examples in any way.

[0045] <Example 1. Thrust design using computational fluid dynamics analysis> To realize a levitation mechanism for a pump mechanism according to one embodiment of the present invention, the thrust must change with the displacement of the impeller and its stiffness must be positive. Therefore, in Example 1, the thrust was designed using computational fluid dynamics (CFD) analysis. ANSYS Fluent (ver. 19.0, ANSYS Japan, Tokyo) was used for all analyses. The rotation speed was 10,000 rpm, and the Realizable k-ε model was used as the turbulence model. The boundary conditions were a flow rate of 1.5 L / min at the inlet and a gauge pressure of 0 Pa at the outlet. The working fluid was assumed to be an incompressible Newtonian fluid, with a density of 1,060 kg / m 3 and viscosity was 3.6 mPa·s.

[0046] Impeller A shown in Figure 9 was installed inside the housing with the straightener and diffuser shown in Figure 8. The thrust when the impeller was displaced in the axial direction was calculated using CFD analysis, and the impeller shape was improved based on the results. Ultimately, an impeller shape was determined in which the thrust changes with axial displacement of the impeller and the rigidity becomes positive.

[0047] Figure 10 shows the results of calculating the thrust when impeller A (Fig. 9) is displaced in the axial direction. The position where the impeller contacts the end face of the straightener is determined by the axial displacement z imp = 0. Figure 10 The results showed that there was almost no change in thrust due to impeller displacement. The reason for this is thought to be that the impeller displacement was only a few mm compared to the total length of the impeller blades of 27 mm, so the effect of the change in flow path diameter was not noticeable. Therefore, the blade shape was modified and Impeller B shown in Figure 11 was designed. The total length of the impeller blades was reduced to 6 mm so that the majority of the blades would be affected by the change in flow path diameter with a displacement of a few mm. At this time, it was predicted that the reduction in the total length of the blades would result in a decrease in pump head, so as a countermeasure, the number of blades was increased from 2 to 5. The relationship between axial displacement and thrust was investigated using this Impeller B (Figure 11), and the results are shown in Figure 12. It was confirmed that thrust changes with the axial displacement of the impeller, and it was found that 1.5≦z imp ≦3mm, the positive stiffness was 0.32N / mm. From the above, the thrust becomes positive stiffness. The impeller design was completed.

[0048] <Example 2. Design of passive magnetic bearing using magnetic field analysis> To realize a levitation mechanism for a pump mechanism according to one embodiment of the present invention, all of the levitation conditions in each direction described above must be satisfied. Therefore, in Example 2, a passive magnetic bearing was designed that took into account balance with the thrust force. Three-dimensional magnetic field analysis was performed using ANSYS Maxwell (ANSYS Japan, Inc., Tokyo), and it was confirmed that the levitation conditions were satisfied in the axial, radial, and tilt directions. To consider the effect of the motor's rotor magnet on the magnetic bearing, magnetic field analysis was performed with the motor in place as well as the magnetic bearing. Furthermore, an air-core coil was used for the motor stator to avoid attraction with the permanent magnet.

[0049] In the levitation mechanism of the pump mechanism according to one embodiment of the present invention, it is preferable to position the impeller so that it straddles the expanded diameter section (the section where the diameter of the housing changes). Furthermore, considering that the motor (the stator coil on the housing side and the rotor magnet on the impeller side) will be placed in the center, it is preferable that one of the two external levitation magnets (housing-side magnets) be placed in the section with the large flow path diameter (φ20) and the other in the section with the small flow path diameter (φ14) (see Figures 1 and 8).

[0050] Therefore, if the housing wall thickness is 0.5 mm, the external magnets on the inlet side can be placed with an inner diameter of 21 mm or more, and the external magnets on the outlet side can be placed with an inner diameter of 15 mm or more. Furthermore, the magnets embedded inside the impeller (impeller-side magnets) must have an outer diameter of 9 mm or less. Here, it is known that radial rigidity decreases as the distance between the magnets inside and outside the impeller increases, so it is desirable to keep the distance between the magnets inside and outside the impeller as small as possible. Therefore, we designed the inner diameter of the external magnet to be as small as possible, and the outer diameter of the internal magnet to be as large as possible within the range that can be accommodated inside the impeller.

[0051] Next, consider the balance with the thrust force. In the levitation mechanism of the pump mechanism according to one embodiment of the present invention, if the magnetic force is too strong or too weak relative to the thrust, the axial balance point between the thrust and magnetic force will not exist within the impeller's range of motion. Therefore, magnet size, which determines the magnitude of the magnetic force, is important. Parameters that determine magnet size include radial and axial thicknesses. Here, in the levitation mechanism of the pump mechanism according to one embodiment of the present invention, levitation is achieved solely by magnetic force in the radial and tilt directions, so the stiffness of the magnetic force must be positive. Therefore, according to Earnshaw's theorem, the magnetic force has negative stiffness in the axial direction, as shown in Figure 4. However, the positive stiffness of the thrust force sufficiently exceeds the negative stiffness of the magnetic force, making the resultant force positive stiffness.

[0052] Previous research has shown that when adjusting the magnet size of a magnetic bearing, increasing the axial thickness rather than increasing the radial thickness reduces axial negative stiffness. Therefore, in order to reduce axial negative stiffness, we designed the magnet size by keeping the radial thickness of the magnetic bearing thin and constant and increasing the axial thickness. We confirmed the levitation of the designed magnetic bearing using a model that included a motor. The dimensions of the designed magnetic bearing are shown in Fig. 13.

[0053] The procedure for magnetic field analysis in Example 2 is as follows. (1) First, we calculated the magnetic force acting when the impeller was displaced in the axial direction, and confirmed whether the resultant force of that magnetic force and the thrust calculated by fluid analysis had positive stiffness and a point of equilibrium. (2) Next, we calculated the magnetic force acting when the impeller was displaced radially at the axial balance point, and confirmed radial levitation. Since the gap between the impeller blades and the housing wall was 0.5 mm, we calculated the radial displacement from -0.5 to 0.5 mm in 0.1 mm increments. (3) Furthermore, we calculated the magnetic force acting when the impeller is displaced in the tilt direction at the axial balance point, and confirmed levitation in the tilt direction. Geometrically, the impeller will collide with the wall when tilted at approximately 3°, so we calculated the axial displacement in 0.5° increments from -3° to 3°.

[0054] (Results and Discussion) (1) The position where the end face of the external magnet of the magnetic bearing coincides with the end face of the internal magnet is displaced in the axial direction z mag =0 and The result of the magnetic field analysis and the resultant force of the thrust force obtained by CFD analysis are shown in Fig. 14. When the magnetic force is applied, the balance point between the thrust and magnetic force is created. mag When z = 0 imp The magnetic bearings were placed in the housing so that the resultant force of the thrust and magnetic force was z mag = Around 2 There is a balance point at z, and the positive stiffness is 0.19N / mm. This satisfies the axial levitation condition, and z mag It is thought that the impeller will float around =2. (2) Axial balance point z mag At =2, the impeller is displaced radially to calculate the magnetic force. The results are shown in Figure 15. A linear approximation using the least squares method resulted in a positive stiffness of 0.066 N / mm, which indicated radial impeller lift at the axial balance point. (3) Axial balance point z mag At =2, the impeller is displaced in the tilt direction to measure the magnetic force. The calculation results are shown in Figure 16. Linear approximation using the least squares method resulted in a positive stiffness of 0.40 mNm / deg, which indicated radial impeller lift.

[0055] From the above, it was confirmed that the levitation conditions were satisfied for all directions, including axial, radial, and tilt directions. Therefore, it was demonstrated that passive levitation of an impeller is possible by using thrust and magnetic forces.

[0056] Although one embodiment of the present invention has been described in detail above, it will be readily apparent to those skilled in the art that many modifications are possible without substantially departing from the novel features and effects of the present invention. Therefore, all such modifications are intended to be included within the scope of the present invention.

[0057] For example, a term described at least once in the specification or drawings together with a different term having a broader or similar meaning can be replaced with that different term anywhere in the specification or drawings. Furthermore, the configuration and operation of the pump mechanism are not limited to those described in one embodiment of the present invention, and various modifications are possible. [Explanation of symbols]

[0058] 1 pump mechanism, 10 housing, 11 torque transmission member, 12 (12a, 12b) housing side magnet, 13 enlarged diameter portion, 20 impeller, 21 torque receiving member, 22 (22a, 22b) impeller side magnet

Claims

1. A magnetic levitation pump mechanism, at least, a housing forming a flow path; an impeller rotatably accommodated within the housing; the housing has a torque transmission member and a housing-side magnet; the impeller has a torque receiving member and an impeller-side magnet, The impeller rotates due to the action of the torque transmission member and the torque receiving member, Of the five degrees of freedom in total, including three degrees of freedom in the direction of the rotation axis of the impeller and the directions of two axes perpendicular to the rotation axis, and degrees of freedom in the tilt direction around two axes excluding the rotation axis of the impeller, A pump mechanism characterized in that the third and fourth degrees of freedom are controlled only by the balance of magnetic forces between the housing-side magnets and the impeller-side magnets, and the remaining degrees of freedom are controlled such that only magnetic force acts in the opposite direction to the direction of displacement due to thrust based on the rotation of the impeller, and if stiffness is defined as positive when a force in the opposite direction to the displacement acts on the impeller when the impeller is displaced, the housing has an expanded portion with a different inner diameter at the position where the impeller is located so that the stiffness of the resultant force of the thrust and the magnetic force is positive for the remaining degrees of freedom, thereby allowing the impeller to remain levitated in a predetermined position within the housing by a passive levitation mechanism that does not require active control.

2. 2. The pump mechanism according to claim 1, wherein four degrees of freedom excluding the degree of freedom in the direction of the rotational axis of the impeller are controlled only by the balance of magnetic forces between the housing-side magnets and the impeller-side magnets, and the housing-side magnets and the impeller-side magnets are arranged so that, for the degree of freedom in the direction of the rotational axis, a magnetic force acts in a direction opposite to the direction of displacement due to thrust based on the rotation of the impeller.

3. 2. The pump mechanism according to claim 1, wherein the enlarged diameter portion is tapered so that the inner diameter thereof gradually increases.

4. 2. The pump mechanism according to claim 1, wherein the rotary vanes provided on the impeller are located at a position corresponding to the enlarged diameter portion of the housing.

5. The pump mechanism according to claim 1, wherein two of the housing-side magnets and two of the impeller-side magnets are provided at positions straddling the enlarged diameter portion.

6. 6. The pump mechanism according to claim 1, which is a blood pump for pumping blood in an auxiliary artificial heart.

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