Bearings – Rotary bearing – Plain bearing
Reexamination Certificate
1999-01-26
2001-02-13
Footland, Lenard A. (Department: 3682)
Bearings
Rotary bearing
Plain bearing
C417S356000, C417S423120
Reexamination Certificate
active
06186665
ABSTRACT:
TECHNICAL FIELD
The present invention relates to bearing assemblies and, more particularly, to bearing assemblies for securing a motor rotor useful in a rotary blood pump.
BACKGROUND
A number of rotary blood pumps presently are under development for application as either artificial hearts or cardiac assist devices. An axial flow blood pump, for example, typically includes a pump housing that defines a blood flow channel, an impeller mechanism mounted within the blood flow channel, an electric motor rotor coupled to actuate the impeller mechanism for blood pumping action, and an electric motor stator for actuating the rotor by electromagnetic force. The impeller mechanism may take the form of blades that are mechanically coupled to the rotor via a transmission shaft. Alternatively, the impeller blades can be mounted directly on the rotor. In this case, the rotor may form an elongated member that extends axially along the blood flow path. The impeller blades may be mounted about the rotor, for example, in a spiral-like pattern. The rotor is mounted in a bearing assembly.
Performance, reliability and longevity are critical performance factors for blood pumps due to their use as artificial hearts and/or cardiac assist devices. Among the most critical components of the pump is the motor. When the motor fails, the pump fails, leaving the residual function of the heart as the only means for continued cardiac operation and survival. Motor performance is highly dependent on the operation of the motor rotor and bearing assembly. The bearing assembly can be susceptible to seizure due to thrombosis at the bearing interface that restricts rotor movement. Excessive heat and/or inadequate heat removal near the bearing assembly can also lead to bearing seizure. To minimize the incidence of seizure and reduce wear, the bearing assembly ordinarily must be constructed to aggressive tolerances that drive up the cost and complexity of manufacture. In artificial heart applications, notwithstanding cost and complexity of manufacture, bearing failure can be catastrophic. Accordingly, bearing design improvements remain a constant focus for the blood pump industry.
SUMMARY
The present invention is directed to a motor rotor assembly for use in a blood pump. The motor rotor assembly may be useful in pumps configured for implantable or extracorporeal applications. Also, such pumps may take the form of rotary pumps, such as axial flow or centrifugal flow pumps. Axial flow pumps will be described herein for purposes of illustration.
The motor rotor assembly can include an inflow bearing disposed within the blood flow conduit proximal to an inflow port of the blood flow conduit, an outflow bearing disposed within the blood flow conduit proximal to an outflow port of the blood flow conduit, and a motor rotor disposed within a blood flow conduit and rotatably mounted between the inflow bearing and the outflow bearing. An inflow end of the rotor forms an inflow ball-and-cup bearing interface with the inflow bearing, and an outflow end of the rotor forms an outflow ball-and-cup bearing interface with the outflow bearing.
In accordance with an embodiment of the present invention, the outer diameter of the outflow ball-and cup bearing interface is larger than an outer diameter of the inflow ball-and-cup bearing interface. For example, the diameter of the outflow ball-and-cup bearing interface can be made at least two times larger and, in some embodiments, at least three times larger than the diameter of the inflow ball-and-cup bearing interface. Also, the diameter of the outflow ball-and-cup bearing interface can be less than or about equal to the largest diameter of the motor rotor.
Each of the ball-and-cup bearing interfaces can include a ball portion and a cup portion, the ball portion being disposed against the cup portion to form a ball-and-cup bearing interface therebetween. The resulting bearing interface may be substantially hemispherical in shape. The ball portions of each ball-and-cup bearing interfaces can be oriented to face the inflow port. For example, the ball portion of the inflow ball-and-cup bearing interface can be disposed on the inflow end of the rotor with the ball portion being oriented to face the inflow port. In this case, the inflow bearing defines a cup-like area for receipt of the ball portion of the rotor. Similarly, the ball portion of the outflow ball-and-cup bearing interface can be disposed on the outflow bearing for receipt in a cup-like portion disposed at the outflow end of the rotor.
The motor rotor assembly can also include inflow and outflow stator hubs disposed within the blood flow conduit to support inflow and outflow stator blades, respectively. The outflow stator hub, for example, can have an inflow end proximal to the motor rotor, and an outflow end proximal to the outflow port. Further, the outflow stator hub can be smaller at an end of the outflow stator hub that is more proximal to the outflow port than a diameter of the outflow stator hub that is more proximal to the motor rotor.
The outflow bearing may be secured to the outflow stator hub. In such embodiments, the ball portion of the outflow ball-and-cup bearing interface can be disposed on the inflow end of the outflow stator hub and oriented to face the inflow port. Also, the inflow bearing may be secured to the inflow stator hub, with the cup-like area of the inflow bearing being disposed at the outflow end of the inflow stator hub. Alternative orientations are conceivable, e.g., orientations in which the ball portions of both the inflow ball-and-cup bearing interface and the outflow ball-and-cup bearing interface are oriented to face the outflow port.
One or more flow stator blades can be secured to the outflow stator hub. For example, each stator blade can extend radially outward from the stator hub and toward an inner wall of the blood flow conduit. Each stator blade can have a leading edge and a trailing edge with the trailing edge being more proximal to the outflow port than the leading edge. In such an arrangement, the outflow ball-and-cup bearing interface can be disposed at a point that is more proximal to the inflow port than the leading edge of the stator blade. Alternatively, the stator blade can be extended such that the leading edge is disposed at a point that is more proximal to the inflow port than the outflow bearing interface.
A bearing assembly, in accordance with an embodiment of the present invention, can provide a number of advantages. For example, a motor rotor assembly or blood pump incorporating aspects of the invention may be constructed from fewer parts. In particular, integration of the stator hubs and bearings can reduce the number of discrete components and assembly steps. Using fewer parts can facilitate reduced manufacturing costs and complexity, and improve pump reliability. Reducing blood pump complexity can improve pump performance and lower the risk of thrombogenesis. For example, outflow stator blades can be attached to a stator hub along their entire longitudinal length. Further, larger bearings are easier to manufacture due to reduced tolerances. Fewer parts also decrease the number of tolerances that must be monitored.
A larger bearing assembly can obviate the need for a diffuser cone required by some designs, as well as the associated close-running clearances between the diffuser cone and the stator blades. Larger bearing sizes can reduce the incidence of bearing fracture during manufacture and/or handling, due to greater structural integrity and robustness. Further, fewer parts can translate into fewer thrombosis initiation points. In summary, a motor rotor assembly or blood pump in accordance with the present invention may significantly improve the performance, reliability, and longevity of the motor rotor assembly.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.
Butler Kenneth C.
le Blanc Pieter W. C. J.
Maher Timothy R.
Petersen Tracy V.
Fish & Richardson P.C. P.A.
Footland Lenard A.
Nimbus Inc.
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