WO1999049912A1

WO1999049912A1 - Sealed motor stator assembly for implantable blood pump

Info

Publication number: WO1999049912A1
Application number: PCT/US1999/006122
Authority: WO
Inventors: Tracy V. Petersen; Douglas C. Thomas; Pieter W. C. J. Le Blanc
Original assignee: Nimbus, Inc.
Priority date: 1998-03-30
Filing date: 1999-03-26
Publication date: 1999-10-07
Also published as: AU3105899A

Abstract

A motor stator assembly for use in an implantable blood pump incorporates a number of features capable of improving the reliability and longevity of the motor, and facilitates convenient manufacture, testing, and installation. To prevent motor failure due to environmental factors such as humidity, heat, and salinity, the assembly may include a sealed housing that protects the motor stator from contaminants. Openings in the housing for external electrical conductors can be provided with matched or compression seals formed, for example, from glass or ceramic materials. The motor assembly reduces the possibility of electrical shorts by displacing groups of windings apart from one another. Also, the stator housing can be evacuated during assembly and filled with a multi-purpose material capable of dampling vibration generated by the windings, electrically isolating the windings from the housing and from one another, and thermally conducting heat away from the windings to the housing. A motor stator assembly constructed according to the present invention also enables convenient manufacture, testing, and installation without significant risk of damage. The entire motor stator assembly can be sealed prior to installation in the blood pump, and may form a discrete component that can be added to or removed from the blood pump with ease. The assembly thereby enables separate manufacture and shipment from a remote location. In addition, the assembly can be separately tested prior to installation. For convenient installation, the motor stator assembly may incorporate a two-part, annular housing that defines a central conduit to receive a portion of the blood flow channel of the pump.

Description

1 -

SEALED MOTOR STATOR ASSEMBLY FOR IMPLANTABLE BLOOD PUMP

STATEMENT AS TO FEDERALLY SPONSORED RESEARCH The U.S. Government has a paid-up license in this invention and the right in limited circumstances to require the patent owner to license others on reasonable terms as provided for by the terms of NO1-HV58155 awarded by the National Heart, Lung, and Blood Institute.

TECHNICAL FIELD The present invention relates to electric motor assemblies and, more particularly, to motor stator assemblies useful with axial-flow implantable blood pumps.

BACKGROUND INFORMATION A number of axial flow implantable blood pumps presently are under development for application as either artificial hearts or cardiac assist devices. An axial flow blood pump 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 blades can be 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 motor stator typically includes three or more groups of windings. Each group is formed from a conductive wire and wound around a stack of metallic stampings. The rotor carries a permanent magnet. The motor stator and - 2 - rotor, in effect, form a brushless dc motor. The windings associated with the stator poles are sequentially energized to create a rotating electric field that drives the rotor about its longitudinal axis. For this rotating field, the windings must be disposed around the rotor. Thus, the stator is annular in shape, forming a ring-like structure that extends around the rotor. In some cases, the annular stator is embedded in the wall of the pump housing, around the blood flow channel and rotor.

In view of its application as an artificial heart or cardiac assist device, reliability and longevity are critical performance factors of an implantable blood pump. Among the most critical components of the pump is the motor. In the event the motor fails, the pump fails, leaving the residual function of the heart as the only means for continued cardiac operation and survival. In artificial heart applications, motor failure is catastrophic.

SUMMARY

The present invention is directed to a motor stator assembly for use in an implantable blood pump. In accordance with the present invention, this motor stator assembly may incorporate one or more features capable of significantly improving the reliability and longevity of the motor. As another advantage, the motor stator assembly can be constructed to facilitate convenient manufacture, testing, and installation without damaging the assembly or otherwise compromising motor performance.

A motor stator can be susceptible to environmentally-induced failure. The motor stator includes a stack of metallic stampings that are wound precisely with coated conductive wire. The stampings and windings are extremely susceptible to corrosion in the presence of high levels of humidity, temperature, and salinity. Each of the above is an environmental factor that is typically present in a blood pump upon implantation. Excessive corrosion can result in loss of electrical continuity or at least decreased electromagnetic efficiency, leading to - 3 - excessive heat generation and power consumption. Thus, a barrier to corrosion is highly desirable to ensure extended and reliable operation.

The motor stator assembly of the present invention provides an effective barrier against corrosion. In particular, the assembly includes a sealed housing that protects the motor stator from contaminants. The housing can be formed from titanium components and welded to form a barrier between the stator components and the outside environment. Also, openings in the housing for external electrical conductors can be provided with matched or compression seals formed, for example, from glass or ceramic materials. The seals protect the motor stator from outside contaminants and also act as electrical insulators between the electrical conductor and the housing at the openings.

The housing and seals provide the stator components with a substantially hermetic enclosure. The term 'substantially hermetic," as used herein, means generally air and fluid tight, but not necessarily evacuated. The isolation and containment provided by the sealed housing simplifies the problem of sterilizing the stator components, which may have geometries that make sterilization difficult. Specifically, the stator components are sealed within the housing, generally protecting the outside environment from contaminants that could be borne by such components. The reliability and longevity of a motor stator also may suffer from certain operational factors. For example, electrical shorts can occur between adjacent winding groups or between windings and the pump housing, rendering the motor inoperable. In addition, the stator windings can generate vibration during use due to high frequency coil oscillation. In this case, excessive vibration can cause abrasion of the insulative coating on the windings, resulting in less efficient performance or motor failure. The stator windings also can generate excessive heat, potentially leading to overheating and motor failure.

The motor stator assembly of the present invention also is capable of alleviating such operationally-induced problems. For example, the stator windings can be atypically configured such that adjacent groups of windings are displaced - 4 - and insulated from one another to prevent group-to-group short circuits. In addition, the stator housing can be evacuated during assembly, if desired, and filled with a multi-purpose material capable of damping the vibration generated by the windings, electrically isolating the windings from the housing and from one another, and thermally conducting heat away from the windings to the housing. In this manner, the housing is electrically insulated from the windings but still is capable of serving as a heat sink. Further, the stator housing has an annular design that enables the stator to be positioned for enhanced thermal dissipation by blood moving through the flow channel. A motor stator assembly constructed according to the present invention also enables convenient manufacture, testing, and installation without significant risk of stator damage. In particular, the entire motor stator assembly can be sealed prior to installation in the blood pump. The motor stator assembly may form a discrete component that can be added to or removed from the blood pump with ease, enabling separate manufacture and shipment from a remote location. In addition, the motor stator assembly can be separately tested prior to installation. For convenient installation, the motor stator assembly may incorporate a two-part, annular housing that defines a junction to receive a portion of the blood flow channel. In one embodiment, the present invention provides a motor stator assembly for use in an implantable blood pump, the motor stator assembly comprising a motor stator, a housing enclosing the motor stator, an opening formed in the housing to receive an electrical conductor for connection with the motor stator, and a seal mountable within the opening and around the electrical conductor, wherein the seal substantially hermetically seals the motor stator within the housing.

In another embodiment, the present invention provides a motor stator assembly for use in an implantable blood pump, the motor stator assembly comprising a motor stator, the motor stator being substantially annular in shape and thereby defining a ring-like portion and a conduit, a first housing member that - 5 - encloses an outer surface of the ring-like portion of the motor stator, a second housing member, coupled to the first housing member, that encloses an inner surface of the ring-like portion of the motor stator adjacent the conduit, an electrical conductor for providing electrical current to the motor stator, an opening, formed in one of the first and second housing members, that receives the electrical conductor for connection with the motor stator, and a seal mounted within the opening and around the electrical conductor to protect the motor stator from external contaminants, wherein the first and second housing members, in combination with the seal, substantially hermetically seal the motor stator. In a third embodiment, the present invention provides a motor stator assembly for use in an implantable blood pump, the motor stator assembly comprising a motor stator, a housing enclosing the motor stator, the housing being sealed to protect the motor stator from external contaminants, a mechanical damping material disposed within the housing to dampen vibration generated by the motor stator during operation, an opening formed in the housing to receive an electrical conductor for connection with the motor stator, and a seal mountable within the opening and around the electrical conductor to protect the motor stator from external contaminants.

In a fourth embodiment, the present invention provides a motor stator assembly for use in an implantable blood pump, the motor stator assembly comprising a motor stator having a plurality of windings arranged in groups within the motor stator, wherein the groups of windings are displaced from one another to electrically isolate adjacent groups of windings, and a housing enclosing the motor stator, the housing defining a central conduit for receiving a portion of a blood flow channel of the implantable blood pump.

In a fifth embodiment, the present invention provides a motor stator assembly for use in an implantable blood pump, the motor stator assembly comprising a motor stator, wherein the motor stator is substantially annular in shape, thereby defining a ring-like portion and a conduit, a plurality of windings arranged in groups within the motor stator, wherein the groups of windings are displaced from one another to electrically isolate adjacent groups of windings, a first housing member enclosing an outer surface of the ring-like portion of the motor stator, a second housing member enclosing an inner surface of the ring-like portion of the motor stator adjacent the conduit, the second housing member including a tube member that receives at least a portion of a blood flow channel of the implantable blood pump, a material disposed within the housing to dampen vibration generated during operation of the motor stator, the material being substantially electrically insulative to electrically isolate the motor stator from the housing and substantially thermally conductive to conduct heat away from the motor stator, an opening formed in the housing to receive an electrical conductor for connection with the motor stator, and a glass seal mountable within the opening and around the electrical conductor, wherein the first and second housing members are joined together to enclose the motor stator and, together with the seal, form a substantially hermetic barrier between the motor stator and the environment outside of the housing members.

In a sixth embodiment, the present invention provides an implantable blood pump comprising a pump housing defining a blood flow path, a rotor disposed within the blood flow path, an annular motor stator for actuating the rotor, the stator defining an outer surface and a conduit, a first housing member substantially enclosing the outer surface of the motor stator, a second housing member substantially enclosing the inner conduit of the motor stator sub-assembly, the second housing member having a tube member that extends through the conduit and forms a portion of the blood flow path.

Other advantages, features, and embodiments of the present invention will become apparent from the following detailed description and claims.

DESCRIPTION OF DRAWINGS FIG. 1 is a longitudinal cross-sectional diagram of an implantable blood pump incorporating a motor stator assembly in accordance with the present invention: - 7 -

FIG. 2 is an end view of the motor stator assembly shown in FIG. 1 from an outflow side;

FIG. 3 is an end view of the motor stator assembly shown in FIG. 1 from an inflow side; FIG. 4 is cross-sectional side view of the motor stator assembly shown in FIG. 1 taken along line 1-1' of FIG. 2;

FIG. 5 is an exploded side cross-sectional view of the motor stator assembly shown in FIG. 1 illustrating assembly; and

FIG. 6 is a cross-sectional end view of the motor stator of the stator assembly shown in FIG. 1;

FIG. 7 is a side view of the motor stator shown in FIG. 6;

FIG. 8 is cross-sectional side view of the motor stator shown in FIG. 6 taken along line 3-3'; and

FIG. 9 is a perspective view of the motor stator of FIG. 6. Like reference numbers and designations in the various drawings indicate like elements.

DETAILED DESCRIPTION FIG. 1 is a longitudinal cross-sectional diagram of an implantable blood pump 10 incorporating a motor stator assembly 12 in accordance with an embodiment of the present invention. Pump 10 can be implanted within a human to provide the function of an artificial heart or a cardiac assist device. As shown in FIG. 1, pump 10 includes a two-part pump housing 14 having an inflow portion 16 and an outflow portion 18. The interior of pump housing 10 defines a generally cylindrical blood flow channel 20. Inflow portion 16 has an inflow opening 22 through which blood enters flow channel 20. Outflow portion 18 has an outflow opening 24 through which blood exits flow channel 20. An elongated rotor 26 is disposed within pump housing 14 and extends axially along blood flow channel 20. Rotor 26 is mounted, at opposite ends, for rotation within inflow and outflow bearing blocks 28, 30, respectively. Impeller blades 32, 34 are mounted on rotor - 8 -

26 and oriented to impart axial pumping energy to the blood flow upon actuation of the rotor. In FIG. 1, only two impeller blades 32, 34 are visible. However, rotor 26 may carry three or more impeller blades, each arranged, for example, in a spiral-like pattern. Motor stator assembly 12 is disposed within pump housing 14 and is generally annular in shape, defining a central conduit 29 that is coextensive with a portion of blood flow channel 20.

With further reference to FIG. 1, inflow and outflow portions 16, 18 of pump housing 14 are reciprocally threaded, as indicated by reference numeral 36, such that one can be screwed into the other to couple both portions and enclose motor stator assembly 12 and rotor 26. An o-ring 38 may be incorporated to ensure a snug fit. As indicated by reference numerals 35, 37, inflow and outflow portions 16, 18 are also threaded at opposite ends adjacent inflow and outflow openings 22, 24, respectively, for connection with additional conduit hardware (not shown) designed to be joined with the cardiovascular system for operation. Motor stator assembly 12 includes a motor stator housing 40 that encloses a motor stator 42. Housing 40 includes a first housing member 44 and a second housing member 46. Motor stator 42 has three or more separate groups of windings, two of which are illustrated in FIG. 1. In particular, FIG. 1 shows a first winding group 48 having a first metal stamping portion 50 and a set of windings 52 wound about the stamping portion. Similarly, a second winding group 54 has a second metal stamping portion 56 and a set of windings 58. An electrical conduit 60 is coupled to outflow portion 18 of pump 10 via a redundantly sealed connection 62 realized by two or more o-rings. Electrical conduit 60 carries an electrical cable 64 to motor stator assembly 12 for connection of electrical conductors with respective winding groups.

FIGS. 2 and 3 are end views of motor stator assembly 12 taken from outflow and inflow sides, respectively, of pump 10. FIG. 4 is cross-sectional side view of motor stator assembly 12 taken along line 1-1' of FIG. 2. As shown in FIG. 2, the annular shape of motor stator 42 defines a ring-like portion 65 and central conduit 29. With reference to FIGS. 2 and 4, second housing member 46 - 9 - includes a first radial flange 66. First radial flange 66 caps ring-like portion 65, as shown in FIG. 2, at an outflow end of stator assembly 12. First radial flange 66 extends radially outward from central conduit 29. Second housing member 46 also may include a recessed circular lip 68 that defines an inner diameter of central conduit 29. As shown in FIGS. 2 and 4, lip 68 has a diameter that is slightly smaller than the inner diameter of first radial flange 66. Lip 68 is configured for abutment with a first channel section 70 (shown in FIG. 1) that is received for fluid communication with central conduit 29 upon installation of motor stator assembly 12 in pump 10. As further shown in FIG. 4, first radial flange 66 is coupled to a circular side wall 72 of first housing member 44, thereby closing stator assembly 12 at the outflow end. In particular, the outer diameter of first radial flange 66 is selected such that an outer periphery is sized for attachment to an exposed end of circular side wall 72. With reference to FIG. 3, first housing member 44 includes a second radial flange 74 that caps ring-like portion 65 at an inflow end of stator assembly 12. Second radial flange 74 extends radially inward from wall 72 to the outer wall of a tube member 76 of second housing member 46. Second radial flange 74 of first housing member 44 and tube member 76 of second housing member 46 are coupled together, thereby closing stator assembly 12 at the inflow end. In particular, an inner diameter of second radial flange 74 is sized for close fit with the outer diameter defined by the outer wall of tube member 76. First housing member 44 encloses an outer surface of ring- like portion 65 of motor stator 42. Second housing member 46 encloses an inner surface of ring-like portion 65 of motor stator 42 adjacent central conduit 29. In this manner, the inner surface of second housing member 46 forms an integral part of flow channel 20 of pump 10. With further reference to FIGS. 2-4, motor stator assembly 12 includes openings to receive electrical conductors for transmission of electrical current to motor stator 42. Specifically, as shown in FIG. 2, first radial flange 66 of second housing member 46 includes three or more openings 78, 80, 82 to receive three or more separate conductors 84, 86, 88. Opening 80 is shown in FIG. 4. Conductors - 10 -

84, 86, 88 may be formed, for example, from Kovar, Invar, or stainless steel materials. Kovar is a trademark of Carpenter Technology Corporation. The above materials are generally characterized by minimal thermal expansion over the maximum range of temperatures likely to be encountered by pump 10. Each conductor 84, 86, 88 carries electrical current for one of the motor stator winding groups, and can be coupled to terminals associated with the respective windings. As illustrated by conductor 86 in FIG. 4, each of conductors 84, 86, 88 may comprise a terminal pin with external and internal terminals 85, 87, respectively. Terminals 85, 87 are configured for connection to leads extending from electrical conduit 60 and stator 42, respectively, e.g., by soldering, welding, or crimping. As shown in FIG. 1, for example, electrical cable 64 may include three of more wire leads, generally designated by reference numeral 89, for connection with respective terminal pins. Thus, each conductor 84, 86, 88 corresponds to one of three phases for energization of the windings of motor stator 42. The electrical current carried by each conductor 84, 86, 88 energizes the respective windings of motor stator 42 to generate electromagnetic field energy for actuation of rotor 26. The phases are controlled in a well known manner such that the stator windings are energized sequentially to create a rotating field. Rotor 26 carries a permanent magnet that interacts with the rotating field to move the rotor. The moving rotor thereby actuates impeller blades 32, 34 to impart axial pumping energy to the blood flowing through channel 20.

First and second housing members 44, 46 are coupled to one another in a manner sufficient to substantially hermetically seal housing 40 against external contaminants that could damage motor stator 42. First and second housing members 44, 46 preferably are formed from a biocompatible metal material such as titanium. Metal materials, in general, prevent diffusion of contaminants across the barrier created by housing 40. To seal motor stator housing 40 against external contaminants, first and second housing members 44, 46 can be coupled together using a variety of techniques including laser welding, inertia welding, and electron welding. Titanium is desirable for the fabrication of housing 40 on the basis of - 11 - proven biocompatibility and ease of manufacture including suitability for use with welded bonds. This material also facilitates the formation of substantially hermetic seals in openings 78, 80, 82. In particular, this material bonds well with a variety of desired seal materials, as will be explained. In addition to the seal provided by coupling housing members 44, 46, it is necessary to seal openings 78, 80, 82. With reference to FIG. 2, to protect motor stator 42 from external contaminants, seals 90, 92, 94 are formed in openings 78, 80, 82 and around conductors 84, 86, 88, respectively. Seals 90, 92, 94 can be formed from a variety of materials including glass and ceramics. Such materials are fused and hardened within openings 78, 80, 82 to form either matched or compressive seals. For a matched seal, the coefficients of thermal expansion for housing 40, conductors 84, 86, 88, and seals 90, 92, 94 are closely matched. For a compression seal, the coefficients of thermal expansion are intentionally mismatched such that seals 90, 92, 94 compressively bear against the inner surfaces of openings 78, 80, 82 and conductors 84, 86, 88 upon fusion and hardening. In either case, the seal material completely fills the gap between the inner surface of openings 78, 80, 82 and conductors 84, 86, 88, providing a barrier against diffusion or other transfer of contaminants. The seal material also is electrically insulative, thereby electrically isolating conductors 84, 86, 88 from the inner surfaces of openings 78, 80, 82. Further, the seal material hardens and adheres to the metal components, generally anchoring conductors 84, 86, 88 within openings 78, 80, 82. In this manner, seals 90, 92, 94 are capable of preventing movement of conductors 84, 86, 88 during testing, handling, and use. Such movement could lead to abrasion or other conductor damage. Examples of suitable materials for fabrication of seals 90, 92, 94 include borosilicate, alumina, quartz, silicon carbide, sapphire, zirconia, and fused silica. An example of a suitable borosilicate compound is the material commercially marketed under the Super Seal tradename by Hermetic Seal Corporation of Temple City, California. Seals 90, 92, 94 can be obtained in a preformed condition as a finished part. Specifically, seals 90, 92, 94 can be preformed as cylindrical - 12 - feedthrough rings, with appropriate diameters, that can be mounted in openings 78, 80, 82 to receive conductors 84, 86, 88. Alternatively, this material is available in a powder form that is readily susceptible to custom molding in a desired configuration. In either case, the resulting seals 90, 92, 94 are mounted within openings 78, 80, 82 and subjected to fusion and curing to seal against the inner surface of the openings and the outer surface of conductors 84, 86, 88. Such seals have been observed to bond well with a variety of metals that could be used to form housing 40 and conductors 84, 86, 88. For example, this borosilicate material bonds particularly well with titanium, Kovar, Invar, and stainless steel materials. Also, for a matched seal, this material has a thermal coefficient that enables seals 90, 92, 94 to be approximately thermally matched with the material of housing 40, e.g., titanium. Consequently, the expansion and contraction profiles of seals 90, 92, 94 and housing 40 can be selected to ensure a robust seal under a wide range of temperature conditions. As an alternative, the use of a ceramic material for seals 90, 92, 94 allows for the seal to be brazed both to conductors 84, 86, 88 and to the walls of openings 78, 80, 82. As with glass seals, performed cylindrical shapes such as feedthrough rings can be fabricated from a variety of ceramic materials, including alumina and zirconia. Such preforms can be impregnated with a thin metallic film at the surfaces that contact conductors 84, 86, 88 and openings 78, 80, 82. The metallic film can be applied via chemical vapor deposition, plasma deposition, or sputtering, and can have thicknesses on the order of 0.0001 mm to 0.1 mm. Once metallized, seals 90, 92, 94 can be fixtured together with the respective conductors 84, 86, 88. The annular space between seals 90, 92, 94 and conductors 84, 86, 88 then can be filled with a nonferrous metal brazing alloy. Suitable brazing alloys are commercially available, for example, from Wesgo, Inc. of Belmont, California. The braze joints between seals 90, 92, 94 and conductors 84, 86, 88 are effected by heating the fixtured components in a furnace to a temperature above 450 degrees Celsius, but below the melting point of the conductor material and metallic film. The braze alloy is distributed throughout the annular space by capillary action. The - 13 - braze joints between seals 90, 92, 94 and the inner walls of openings 78, 80, 82 can be created in a similar manner, either simultaneously with or subsequent to fabrication of the seal-conductor braze joints. In the event the seal-wall joint is made later, the seal-conductor braze joints can be made as discrete sub-assemblies of the overal stator housing. Once brazing is completed, conductors 84, 86, 88 can be plated with gold, if desired, for improved solderability and electrical conductivity. Complete brazing operations and the fabrication of sub-assemblies as described above can be carried out, for example, by Hittman Materials and Medical Components, Inc. of Columbia, Maryland. The formation of seals 90, 92, 94 and the welding of first housing member 44 and second housing member 46 combine to provide a substantially hermetic seal for motor stator assembly 12. Also, following the bonding of first and second housing members 44, 46 and formation of seals 90, 92, 94, stator housing 40 can be evacuated of air. As shown in FIG. 2 and 4, for example, motor stator assembly 12 may include a tap 96 through which air can be evacuated.

Following evacuation, a stop 98 can mounted within the opening defined by tap 96, and welded in place or otherwise fixed to seal housing stator assembly 12. The hermetically sealed housing 40 is effective in protecting motor stator 42 from the outside environment. In particular, housing 40 provides a barrier against external contaminants that could cause corrosion or shorting. For example, housing 40 and seals 90, 92, 94 protect the metal stampings and windings of stator 42 from the humidity and salinity to which pump 10 is exposed upon implantation. Such elements, in combination with temperatures generated during stator operation, could otherwise cause corrosion leading to failure or at least inefficient performance. Also, the isolation and containment afforded by housing 40 simplifies the problem of sterilization of motor stator 42. Sterilization of motor stator 42 is ordinarily difficult due to its geometry, but is generally unnecessary with the hermetic seal provided by housing 40. The hermetic seal protects the outside environment from exposure to contaminants that could be borne by motor stator 42. In summary, - 14 - housing 40 and seals 90, 92, 94 provide a barrier to corrosion and ensure sterilization, thereby contributing to extended and reliable operation of pump 10.

Prior to or in conjunction with evacuation, stator housing 40 can be filled with a mechanical damping material 100. The damping material fills the voids between motor stator housing 40 and motor stator 42, and serves to dampen vibration generated by high frequency oscillation of stator windings 52, 58 during operation. Damping material 100 thereby prevents abrasion of windings 52, 58 and associated stamping portions 50, 56 due to such vibration, improving the reliability and long-term performance and efficiency of stator 42. This material may comprise a liquid that is introduced into housing 40 and either hardens or remains in liquid state. For more effective damping performance, material 100 preferably hardens to a solid but compliant state. Damping material 100 also may be selected to be substantially electrically insulative. In this case, damping material 100 further serves to electrically isolate windings 52, 58 from one another, thereby reducing the possibility of short circuits. As another advantage, damping material 100 can be selected to be substantially thermally conductive. With this characteristic, damping material 100 is effective in thermally conducting heat away from windings 52, 58 to stator housing 40. In this manner, first housing member 44 of stator housing 40 is electrically insulated from windings 52, 58 but is capable of serving as a heat sink. Consequently, damping material 100 can be effective in reducing the possibility of thermally-induced stator failure.

A variety of materials may be appropriate to yield the damping, insulative, and thermal characteristics desirable for damping material 100. An example of a suitable material is Epoxylite #210 stator potting compound, commercially available from Epoxylite Corporation, of Irvine, California.

According to specifications published by Expoxylite, this particular material is generally characterized by a hardness of Shore D 70-75, a dielectric strength of 375 volts/mil (15000 volts/mm) and a thermal conductivity of 5.9 x 10^"4 cal/cm³/s/^°C. This material is available in a liquid form with an accompanying hardening compound. The damping material 100 is injected into stator assembly 12 via tap - 15 -

96 in an amount sufficient to fill the interior of housing 40 and any voids between winding groups 48, 54. Once material 100 hardens, it electrically isolates windings from one another and from housing 40, provides a thermal conduction path between the windings and housing 40, and dampens vibratory energy that may be generated during operation. Stop 98 is fixed with tap 96 to seal housing 40.

The thermal conductivity of material 100 complements the enhanced thermal conductivity provided by the design of housing 40. Specifically, as shown in FIG. 2, stamping portions 50, 56 and windings 52, 58 of motor stator 42 are positioned adjacent central conduit 29 of second housing member 46, which forms part of blood flow channel 20. Thus, the heat generated by motor stator 42 is not only dissipated by the thermal mass of first housing member 44, but also by second housing member 46 and, more particularly, the blood flowing through channel 20. Damping material 100 facilitates such heat dissipation, providing a thermal conduction path to housing 40. Thermal energy is thereby dissipated by housing 40 via central conduit 29 and via the junction of stator assembly 12 with inflow and outflow portions 16, 18 of pump 10. The blood flow in central conduit 29, in particular, assists in carrying heat away from stator assembly 12. In summary, the design of housing 40 and the incorporation of damping material 100 serve to more effectively couple the heat-generating elements and heat-dissipating elements of pump 10, enhancing the reliability and operating life of pump 10.

FIG. 5 is an exploded side cross-sectional view of motor stator assembly 12 taken along line 1-1' of FIG. 2. FIG. 5 illustrates the various components of motor stator assembly 12 and the manner in which they are assembled for installation in pump 10. In particular, as shown in FIG. 5, tube member 76 of second housing member 46 is inserted into aperture 101 defined by the annular motor stator 42. Second housing member 46 and motor stator 42 then are inserted within first housing member 44. Tube member 76 of second housing member 46 extends through the central opening 102 defined by second radial flange 74. The first radial flange 66 of second housing member 46 abuts against the end of circular side wall 72 of first housing member 44. Also, tube member 76 includes steps - 16 -

101, 103. As shown in FIG. 5, step 103 abuts with stamping portions 50, 56 of stator 42, thereby limiting the extent of tube member 76 beyond second radial flange 74 of first housing member 44. First and second housing members 44, 46 can be welded together at the junction of side wall 72 and first radial flange 66, and at the junction of second radial flange 74 and tube member 76. Following welding of first and second housing members 44, 46, fabrication of seals 90, 92, 94, and injection of damping material 100, if desired, motor stator housing 40 is complete and is hermetically sealed against the flow of contaminants into or out of the housing. For installation of motor stator assembly 12 within pump 10, tube member 76 has a tube segment 104 and recessed circular lip 68. Tube segment 104 extends outward through central opening 102 defined by second radial flange 74 of first housing member 44. With reference to FIG. 1, upon installation in pump housing 14, tube member 76 serves as a junction for first channel section 70 and a second channel section 106 of outflow portion 18 and inflow portion 16, respectively. Specifically, at the outflow side of pump 10, first channel section 70 is inserted into the central opening 108 defined by first radial flange 66, and abuts with circular lip 68. First channel section 70 and opening 108 are sized for a tight fit upon insertion. To enhance the sealing pressure between first channel section 70 and the inner surface of opening 108, however, one or more elastomeric o-rings may be added. At the inflow side, tube segment 104 is received for abutment within a recessed area 110 formed in second channel section 106. Again, one or more o-rings may be added to enhance sealing pressure between tube segment 104 and second channel section 106. Following connection of channel sections 70, 106 with central conduit 29, inflow portion 16 and outflow portion 18 are screwed together via threads 36 to close the pump housing 14 with motor stator assembly 12 inside.

As illustrated by FIG. 5, motor stator assembly 12 can be manufactured separately from pump 10. In other words, motor stator assembly 12 forms a discrete component of pump 10 and does not require integral fabrication with the - 17 - other pump hardware. Following manufacture, motor stator assembly 12 is sealed, facilitating separate shipment and handling from a remote manufacturing facility with minimal risk of stator damage. Also, the discrete, sealed assembly 12 facilitates independent testing of motor stator 42 prior to installation within pump 10. In this manner, a motor stator assembly 12 that does not pass applicable electrical or hermetic specifications can be detected in advance of installation in pump 10. This modularity also allows ready repair and replacement.

FIGS. 6-9 are various views of a motor stator 42 illustrating the orientation of stator winding groups. For ease of illustration, FIGS. 6-9 show only a small number of windings relative to the many windings that would be wrapped about the metal stampings in practice. As a further measure toward improved reliability and longevity, the stator windings are atypically configured such that adjacent groups of windings 48, 54, 112 are displaced from one another to prevent group-to-group short circuits. In typical applications involving brushless dc motors, the radial distance, or "air gap," between the stator stampings and the rotor is relatively small. In the motor stator 42 shown in FIGS. 6-9, however, the air gap is substantially larger than in other stators. In a typical dc stator sized for axial flow implantable applications, for example, the air gap is on the order of 0.125 to 0.25 mm. The air gap for motor stator 42, in contrast, may be on the order of 1 to 2 mm. This larger air gap allows for more clearance between the permanent magnets carried by rotor 26 and stator 42, thereby allowing more room for the rotor and impeller blades 32, 34. In addition, the stator teeth, i.e., those portions of the stator stampings around which the insulated wire is wound, are fewer in number than in a typical stator. For example, motor stator 42 need only include three stator teeth 114, 116, 118. As illustrated by FIGS. 6-9, the stampings are laminated to form a common stator ring 120.

With the increased air gap and smaller number of teeth, motor stator 42 further provides a greater volume to accommodate winding groups 48, 54, 112. Consequently, the windings need not be wound around stator teeth 114, 116, 118 in an overlapping or interleaved manner with adjacent winding groups. Instead, - 18 - winding groups 48, 54, 112 can be displaced from one another and generally avoid contact. In addition, the space between winding groups 48, 54, 112 can be filled with additional insulating materials such as damping material 100, described above with reference to FIG. 4. The spaces between adjacent winding groups 48, 54, 112 and the insulating material filling those spaces virtually eliminates the possibility of phase-to-phase short circuits in motor stator 42. Therefore, motor stator 42 offers greatly increased reliability. The increased air gap and lesser number of teeth present in the motor stator design illustrated by FIGS. 6-9 have been observed to provide acceptable operation in terms of both power consumption and heat generation.

The foregoing detailed description has been provided for a better understanding of the invention and is for exemplary purposes only. Modifications may be apparent to those skilled in the art without deviating from the spirit and scope of the appended claims.

Claims

- 19 - WHAT IS CLAIMED IS:

1. A motor stator assembly for use in an implantable blood pump, the motor stator assembly comprising: a motor stator; a housing enclosing the motor stator; an opening formed in the housing to receive an electrical conductor for connection with the motor stator; and a seal mountable within the opening and around the electrical conductor, wherein the seal substantially hermetically seals the motor stator within the housing.

2. The motor stator assembly of claim 1, wherein the seal comprises a material selected from the group consisting of glass and ceramic.

3. The motor stator assembly of claim 2, wherein the seal is a matched seal.

4. The motor stator assembly of claim 2, wherein the seal is a compression seal.

5. The motor stator assembly of claim 1, wherein the seal is electrically insulative, thereby insulating the housing from the electrical conductor at the opening.

6. The motor stator assembly of claim 1, wherein the seal comprises borosilicate. - 20 -

7. The motor stator assembly of claim 1, further comprising a mechanical damping material disposed within the housing to dampen vibration generated during operation of the motor stator.

8. The motor stator assembly of claim 7, wherein the damping material is substantially electrically insulative, thereby electrically isolating the stator windings from the housing.

9. The motor stator assembly of claim 8, wherein the damping material is substantially thermally conductive, thereby conducting heat away from the motor stator.

10. The motor stator assembly of claim 7, wherein the damping material is substantially thermally conductive, thereby conducting heat away from the motor stator.

11. The motor stator assembly of claim 1, wherein the motor stator includes stator windings, the motor stator assembly further comprising a substantially electrically insulative material disposed within the housing to electrically isolate the stator windings from the housing.

12. The motor stator assembly of claim 1, further comprising a substantially thermally conductive material disposed within the housing to conduct heat from the motor stator.

13. The motor stator assembly of claim 1, wherein the motor stator is substantially annular in shape, the motor stator thereby defining a ring-like portion and a conduit, and wherein the housing includes a first housing member and a second housing member, the first housing member enclosing an outer surface of the - 21 - ring-like portion of the motor stator, and the second housing member enclosing an inner surface of the ring- like portion of the motor stator adjacent the conduit.

14. The motor stator assembly of claim 13, wherein the first housing member and second housing member are coupled together and, in combination with the seal, serve to substantially hermetically seal the housing.

15. The motor stator assembly of claim 13, wherein the second housing member includes a tube member with a first radial flange at one end, and the first housing member includes a first opening, a second opening, and a second radial flange that defines the second opening, the first radial flange being coupled to the first housing member adjacent the first opening, and the tube member being coupled to the second radial flange of the first housing member adjacent the second opening, thereby enclosing the motor stator and, in combination with the seal, substantially hermetically sealing the housing.

16. The motor stator assembly of claim 13, wherein the second housing member includes a tube member that defines a central conduit forming a portion of a blood flow channel of the implantable blood pump.

17. The motor stator assembly of claim 1, wherein the housing is substantially annular in shape and is configured to receive at least a portion of a blood flow channel of the implantable blood pump.

18. The motor stator assembly of claim 1, wherein the motor stator includes windings, the windings being arranged in groups, wherein the groups of windings are displaced from one another to electrically isolate adjacent groups of windings. - 22 -

19. The motor stator assembly of claim 1, wherein the housing comprises titanium.

20. The motor stator assembly of claim 1, wherein the opening comprises a plurality of openings, each of the openings being formed in the housing to receive an electrical conductor for connection with the motor stator, and wherein the seal comprises a plurality of seals, each of the seals being mountable within one of the openings and around one of the electrical conductors, wherein the seals substantially hermetically seal the motor stator within the housing.

21. A motor stator assembly for use in an implantable blood pump, the motor stator assembly comprising: a motor stator, the motor stator being substantially annular in shape and thereby defining a ring-like portion and a conduit; a first housing member that encloses an outer surface of the ring-like portion of the motor stator; a second housing member, coupled to the first housing member, that encloses an inner surface of the ring-like portion of the motor stator adjacent the conduit; an electrical conductor for providing electrical current to the motor stator; an opening, formed in one of the first and second housing members, that receives the electrical conductor for connection with the motor stator; and a seal mounted within the opening and around the electrical conductor to protect the motor stator from external contaminants, wherein the first and second housing members, in combination with the seal, substantially hermetically seal the motor stator.

22. The motor stator assembly of claim 21, wherein the first housing member forms a portion of a blood flow channel of the implantable blood pump. - 23 -

23. The motor stator assembly of claim 21, wherein the seal comprises a material selected from the group consisting of glass and ceramic.

24. The motor stator assembly of claim 21, further comprising a mechanical damping material disposed within the housing to dampen vibration generated during operation of the motor stator.

25. The motor stator assembly of claim 21, wherein the motor stator includes stator windings, the motor stator assembly further comprising a substantially electrically insulative material disposed within the housing to electrically isolate the stator windings from the housing.

26. The motor stator assembly of claim 21, further comprising a substantially thermally conductive material disposed within the housing to conduct heat from the motor stator.

27. The motor stator assembly of claim 21, wherein the motor stator includes windings, the windings being arranged in groups, wherein the groups of windings are displaced from one another to electrically isolate adjacent groups of windings.

28. A motor stator assembly for use in an implantable blood pump, the motor stator assembly comprising: a motor stator; a housing enclosing the motor stator, the housing being sealed to protect the motor stator from external contaminants; a mechanical damping material disposed within the housing to dampen vibration generated by the motor stator during operation; an opening formed in the housing to receive an electrical conductor for connection with the motor stator; and - 24 - a seal mountable within the opening and around the electrical conductor to protect the motor stator from external contaminants.

29. The motor stator assembly of claim 28, wherein the seal comprises a material selected from the group consisting of glass and ceramic.

30. The motor stator assembly of claim 28, wherein the damping material is substantially electrically insulative to electrically isolate the motor stator from the housing and substantially thermally conductive to conduct heat away from the motor stator.

31. The motor stator assembly of claim 28, wherein the motor stator is substantially annular in shape, the motor stator thereby defining a ring-like portion and a conduit, and wherein the housing includes a first housing member that encloses an outer surface of the ring-like portion of the motor stator, and a second housing member that encloses an inner surface of the ring-like portion of the motor stator adjacent the conduit, the second housing member including a tube member that receives a portion of a blood flow channel of the implantable blood pump.

32. The motor stator assembly of claim 28, wherein the motor stator includes windings, the windings being arranged in groups, wherein the groups of windings are displaced from one another to electrically isolate adjacent groups of windings.

33. A motor stator assembly for use in an implantable blood pump, the motor stator assembly comprising: a motor stator having a plurality of windings arranged in groups within the motor stator, wherein the groups of windings are displaced from one another to electrically isolate adjacent groups of windings; and - 25 - a housing enclosing the motor stator, the housing defining a central conduit for receiving a portion of a blood flow channel of the implantable blood pump.

34. A motor stator assembly for use in an implantable blood pump, the motor stator assembly comprising: a motor stator, wherein the motor stator is substantially annular in shape, thereby defining a ring-like portion and a conduit; a plurality of windings arranged in groups within the motor stator, wherein the groups of windings are displaced from one another to electrically isolate adjacent groups of windings; a first housing member enclosing an outer surface of the ring-like portion of the motor stator; a second housing member enclosing an inner surface of the ring-like portion of the motor stator adjacent the conduit, the second housing member including a tube member that receives at least a portion of a blood flow channel of the implantable blood pump; a material disposed within the housing to dampen vibration generated during operation of the motor stator, the material being substantially electrically insulative to electrically isolate the motor stator from the housing and substantially thermally conductive to conduct heat away from the motor stator; an opening formed in the housing to receive an electrical conductor for connection with the motor stator; and a glass seal mountable within the opening and around the electrical conductor, wherein the first and second housing members are joined together to enclose the motor stator and, together with the seal, form a substantially hermetic barrier between the motor stator and the environment outside of the housing members. - 26 -

35. An implantable blood pump comprising: a pump housing defining a blood flow path; a rotor disposed within the blood flow path; an annular motor stator for actuating the rotor, the stator defining an outer surface and a conduit; a first housing member substantially enclosing the outer surface of the motor stator; a second housing member substantially enclosing the inner conduit of the motor stator sub-assembly, the second housing member having a tube member that extends through the conduit and forms a portion of the blood flow path.