Patent Description:
Intravascular blood pumps such as the Impella® pump by Abiomed, Inc. of Danvers, MA, are quickly becoming the current standard for ventricular assist devices. The range of Impella® pumps currently comprises the Impella <NUM>® pump, the Impella <NUM>® pump, the Impella CP® pump and the Impella LD® pump. These pumps are inserted into a patient percutaneously through a single access point (e.g. radial access, femoral access, axillary access) such that the pump head can be placed into a desired location within the patient's body via small diameter (<NUM>-7Fr) catheters. Such desired locations include, but are not limited to, the left or right ventricle of the patient's heart. The pump head comprises an electric motor that includes a stator winding configured to magnetically interact with a rotor for rotation thereof resulting in a volumetric flow of blood through the rotor and hence through the heart of the patient. Efficient motors that produce good flow rates are sought. Further prior art can be found in <CIT>.

Currently the Impella® pump is capable of delivering blood at flow rates between about <NUM> to about <NUM> liters per minute (lpm). However, with the use of Impella® in an increasing number of surgical procedures, a greater demand is being placed on the need to increase the blood flow rates produced beyond these levels. This means a higher rotor speed is required from the electric motor. However due to the small geometries involved, increasing the rotor speed has several implications that may affect the operation of such small sized pumps. For example, increasing the rotor speed may involve the increase in generation of heat (joule heating) within the electric motor. As the device is percutaneously inserted into the patient's body, any such increase in heat generation may have disastrous effects on surrounding tissue. Another consideration is the resistive load placed on the device where any modifications to the electrical motor to achieve a higher flow rate may lead to a decrease in motor efficiency due to resistive losses.

Given the shortcomings in the state of the art as identified above, there is significant need for increasing the flow rate produced by electric motors while maintaining or increasing the efficiency of the motor.

According to the invention, an intravascular blood pump comprising the features of claim <NUM> is provided. Disclosed herein are devices for addressing various problems and shortcomings of the state of the art, as identified above. More particularly, disclosed herein are intravascular blood pumps for insertion into a patient's body. Typically, the device will be positioned in the patient's vasculature such as, but not limited to, the patient's heart or aorta. In some aspects a portion of the device (e.g. a motor and rotor of the pump portion of the device) sits outside of the patient's heart (i.e. in the aorta) and another portion of the device (e.g. a cannula) extends into the patient's heart (e.g. the left ventricle). While certain aspects of the invention are described with the pump positioned in the heart, one of ordinary skill will appreciate that the pump may be positioned in other locations of the patient's vasculature. Any descriptions of the pump being positioned in the patient's heart are provided by way of illustration of one possible placement of the device in the patient's vasculature and not by way of limitation. The blood pump comprises an elongate housing having a proximal end connected to a catheter and a distal end connected to the pump, the housing having a longitudinal axis. The blood pump also comprises a slotless permanent magnet motor contained within the housing, the motor having p magnet pole pairs and n phases, where p is an integer greater than zero, and n is an integer ≥ <NUM>. The motor comprises a stator winding having 2np coils wound to form two coils per phase per magnet pole pair such that a coil from each phase is circumferentially arranged next to a coil from a different phase in a sequential order of phase, the arrangement repeated along the stator winding such that each coil of the 2np coils spans <NUM>/(<NUM>np) mechanical degrees about the cross section of the stator winding. The motor also comprises a permanent magnet rotor supported for rotation and configured to generate a magnetic flux for interaction with the stator winding. The blood pump is configured such that the two coils per phase per magnet pole pair of the stator winding are connected in series such that a direction of current flow through a first coil of the two coils is opposite to a direction of current flow in a second coil of the two coils, the current flow in the first coil and the current flow in the second coil interacting with opposite polarities of the magnetic flux of the rotor for producing torque in the same direction, thereby facilitating rotation of the rotor for the flow of blood through the pump.

In another embodiment, there is provided a slotless permanent magnet electric motor having p magnet pole pairs and n phases, where p is an integer greater than zero, and n is an integer ≥ <NUM>, the motor having a longitudinal axis. The motor comprises a stator winding having <NUM>np coils wound to form two coils per phase per magnet pole pair such that a coil from each phase is circumferentially arranged next to a coil from a different phase in a sequential order of phase, the arrangement repeated along the stator winding such that each coil of the <NUM>np coils spans <NUM>/(<NUM>np) mechanical degrees about the cross section of the stator winding. The motor also comprises a permanent magnet rotor supported for rotation and configured to generate a magnetic flux for interaction with the stator winding. The motor is configured such that the two coils per phase per magnet pole pair of the stator winding are connected in series such that a direction of current flow through a first coil of the two coils is opposite to a direction of current flow in a second coil of the two coils, the current flow in the first coil and the current flow in the second coil interacting with opposite polarities of the magnetic flux of the rotor for producing torque in the same direction, thereby facilitating rotation of the rotor.

In some implementations, each of the coils comprise either N/<NUM> turns for even values of N, or (N ± <NUM>)/<NUM> for odd values of N, where N is the number of winding turns in a coil of a conventional stator winding having np coils wound to form one coil per phase per magnet pole pair, where N is an integer ≥ <NUM>. In certain implementations, the resistance of the two coils connected in series per phase is equivalent to the resistance of a single coil of the conventional stator winding. In other implementations, the two coils per phase are connected in series such that their start terminals or their end terminals are connected together.

In certain implementations, the two coils per phase are connected to the coils of the other phases in either a star or a delta configuration. In some implementations, the 2np coils comprise any one of helical windings, rhombic windings, conventional windings and hybrid windings. In other implementations, the stator winding has a coil usage function that defines a vertical component of the coil relative to the longitudinal length of the stator winding that interacts with the magnetic field of the rotor to contribute to the torque generated in the motor. In certain implementations, for helical coil windings, the coil usage function is maximized when the vertical component is two-thirds the longitudinal length of the stator winding. In some implementations, the coil usage function has the same form for all phases but shifted by <NUM>/n electrical degrees for each phase.

In further implementations, the coil usage function defines a vertical component of a coil relative to the longitudinal length of the stator winding that contributes to a torque generated in the motor. In some implementations, the motor comprises a three-phase, two-pole machine. In other implementations, the motor comprises a six-coil two-pole machine, each coil spanning <NUM> mechanical degrees about the cross section of the stator winding. In certain implementations, the motor generates a torque constant that is about <NUM>% greater than the torque constant of a motor having a conventional stator winding with np coils wound to form one coil per phase per magnet pole pair.

In other implementations, the rotor pumps blood at a rate between about <NUM> lpm and about <NUM> lpm. In some implementations, the pump may be inserted into the right ventricle of the patient's heart. In further implementation, the pump may be inserted into the left ventricle of the patient's heart.

The stator windings according to embodiments of the present disclosure employ two coils per phase per magnet pole pair, connected as described above. This provides for a <NUM>% increase in torque constant in electric motors using such stator windings when compared to conventional electric motors having stator windings with one coil per phase per magnet pole pair. Such a stator configuration does not increase the resistive load on the stator, and thus reduces joule heating within the electric motor. In effect the electric motor of the present disclosure provides for a stator coil winding pattern with enhanced motor efficiency.

To provide an overall understanding of the devices described herein, certain illustrative embodiments will be described. Although the embodiments and features described herein are specifically described for use in connection with intravascular blood pumps, it will be understood that all the components and other features outlined below may be combined with one another in any suitable manner and may be adapted and applied to other types of procedures requiring an efficient electric motors with high rotor speeds. The invention as claimed, however, comprises all technical features defined in claim <NUM>.

The devices and methods described herein relate to an intravascular blood pump for insertion into a patient's body (i.e. the patient's vasculature such as the heart, aorta, etc.). The blood pump comprises an elongate housing having a proximal end connected to a catheter and a distal end connected to the pump, the housing having a longitudinal axis. The blood pump also comprises a slotless permanent magnet motor contained within the housing, the motor having p magnet pole pairs and n phases, where p is an integer greater than zero, and n is an integer ≥ <NUM>. The motor comprises a stator winding having 2np coils wound to form two coils per phase per magnet pole pair such that a coil from each phase is circumferentially arranged next to a coil from a different phase in a sequential order of phase, the arrangement repeated along the stator winding such that each coil of the 2np coils spans <NUM>/(<NUM>np) mechanical degrees about the cross section of the stator winding. The motor also comprises a permanent magnet rotor supported for rotation and configured to generate a magnetic flux for interaction with the stator winding. The blood pump is configured such that the two coils per phase per magnet pole pair of the stator winding are connected in series such that a direction of current flow through a first coil of the two coils is opposite to a direction of current flow in a second coil of the two coils, the current flow in the first coil and the current flow in the second coil interacting with opposite polarities of the magnetic flux of the rotor for producing torque in the same direction, thereby facilitating rotation of the rotor for the flow of blood through the pump.

The intravascular blood pump of the present disclosure allows for an increased motor efficiency by incorporating a double helical stator winding. Such a stator winding comprises two coils per phase per magnet pole pair connected in the abovementioned configuration. This provides for a <NUM>% increase in torque constant over conventional blood pumps employing one coil per phase per magnet pole pair. Such a stator configuration does not increase the resistive load on the stator, and thus reduces joule heating within the electric motor. In effect the electric motor of the present disclosure provides for a stator coil winding pattern with enhanced motor efficiency.

<FIG> illustrates an exemplary intravascular blood pump <NUM> for insertion into the body of a patient, according to an embodiment of the present disclosure. Blood pump <NUM> comprises a motor unit <NUM> and a pump unit <NUM> arranged along a longitudinal axis <NUM>. The motor unit <NUM> comprises an electric motor including a stator winding <NUM> and a rotor <NUM> contained within a housing <NUM>. The stator winding <NUM> extends along the length of the motor unit <NUM> from a proximal end <NUM> to a distal end <NUM>, and comprises wires <NUM> wound in a particular pattern, the details of which will be provided below. The stator winding <NUM> defines a central lumen <NUM> in which the rotor <NUM> is positioned. The stator winding <NUM> is slotless such that the wires <NUM> are wound upon themselves and not onto a conventional laminated stator core. Feed lines <NUM>, <NUM> provide the necessary electrical connections externally from the pump <NUM> to the stator winding <NUM> for operation of the motor unit <NUM>. Each of the wires <NUM> may have an insulating coating (not shown), and, optionally, the wound stator wires <NUM> may be encapsulated or over-molded by a synthetic epoxide resin (also not shown).

In <FIG>, the stator winding <NUM> and the housing <NUM> are depicted as separate components, however it will be understood that the stator winding <NUM> may be encapsulated within the housing <NUM> to form a single component. The housing <NUM> comprises a proximal end <NUM> and a distal end <NUM>. The proximal end <NUM> of the housing <NUM> is coupled to a distal end <NUM> of a catheter <NUM> which may comprise a flexible tube. Catheter <NUM> comprises a lumen <NUM> which extends towards the physician for control and operation of the blood pump <NUM>.

The rotor <NUM> comprises a permanent magnet <NUM> that is rotationally supported about a shaft <NUM> within the lumen <NUM> of the stator <NUM>. Magnet <NUM> may comprise a cylindrical permanent magnet that surrounds the shaft <NUM> within the motor unit <NUM>. Shaft <NUM> extends from the motor unit <NUM> into the pump unit <NUM> and facilitates rotation of an impeller <NUM> for the pumping of blood. In certain implementations, the rotor <NUM> may comprise several permanent magnets radially arranged about the shaft <NUM>, or an electromagnetic magnet having its own rotor windings. For example, for a motor having one pole pair, the magnet <NUM> may comprise one north pole N and one south pole S. As a further example, for a motor having two pole pairs, the magnet <NUM> may comprise two north poles N1 and N2, and two south poles, S1 and S2, arranged alternately around the shaft <NUM>.

Further, while <FIG> illustrates the rotor <NUM> as rotatable within the stator <NUM>, the electric motor <NUM> may be configured such that the stator <NUM> is held stationary about the shaft <NUM> and the rotor <NUM> is configured as a cylinder that rotates around the stator <NUM>. Shaft <NUM> extends along the length of the motor unit <NUM> and extends into a cylindrical housing <NUM> of the pump unit <NUM>. In some implementations, the shaft <NUM> may be hollow and comprise a lumen <NUM> for the passage of a guidewire, for example.

The distal end of the shaft <NUM> is coupled to an impeller <NUM> located within the pump housing <NUM>. Interaction between the stator <NUM> and rotor <NUM> of the motor unit <NUM> generates torque in the rotor <NUM> causing the shaft <NUM> to rotate, which, in turn, causes the impeller <NUM> to rotate in the cylindrical pump housing <NUM>. When this occurs, blood is sucked into the pump via an axial intake opening <NUM> for conveyance in the axial direction, the blood issuing laterally from the openings <NUM> and flowing axially along housing <NUM>. In this manner the pump <NUM> generates a flow of blood within the heart of the patient.

<FIG> illustrate exemplary stator winding patterns <NUM>-<NUM> according to an embodiment of the present disclosure. In <FIG> the coil winding patterns for a single wire in a stator are shown, such as wires <NUM> in <FIG>, however it will be understood that the complete stator winding, such as stator winding <NUM> in <FIG>, will be obtained by the axial arrangement of a plurality of similarly wound wires about a longitudinal axis of the motor unit <NUM>, such as the longitudinal axis <NUM> in <FIG>.

<FIG> illustrate exemplary coil winding patterns employed in two-pole electric machines in which one mechanical degree is equal to one electrical degree. The coil winding patterns in <FIG> may be used to form the stator winding <NUM> of the motor unit <NUM> in <FIG>. <FIG> shows a conventional stator winding pattern <NUM> in which each wire <NUM> in the stator extends from a proximal end <NUM>, along the length of the stator <NUM>, to a distal end <NUM>. At the distal end <NUM>, the wire <NUM> follows the external perimeter of the stator for <NUM> mechanical degrees and returns to the proximal end <NUM>. Because the end points of the wire <NUM> both end up at the proximal end <NUM>, conventional coil winding patterns <NUM> may be faced with an end turn stack up issue in which each of the plurality of wire ends at the proximal end <NUM> of the stator winding <NUM> has to be electrically connected to the stator feed line, which, in turn, may cause crowding and connections issues. <FIG> shows a rhombic stator winding pattern <NUM> in which each wire <NUM> is arranged in a bent configuration. Unlike the conventional winding <NUM> in <FIG>, the rhombic winding comprises one continuous wire that is wound several times over, each complete turn shifted axially to form the stator coil. The bent configuration of the rhombic winding may require post-assembly.

<FIG> shows a helical stator winding pattern <NUM> in which each wire <NUM> is arranged in an elliptical configuration around the stator. The helical stator winding pattern <NUM> is similar to the rhombic winding pattern <NUM> in <FIG> but without the bend which simplifies the coil winding process. The helical winding <NUM> is a one-step winding which can be easily formed without the need for any post-assembly steps. <FIG> shows a hybrid stator winding pattern <NUM> that comprises a winding that is a mixture of the conventional windings as shown in <FIG> and the rhombic windings as shown in <FIG>. Such a hybrid stator winding allows for the optimum ratio of torque to resistance by adjusting the vertical length, x, and/or horizontal angular span, y, of the coil.

The following disclosure makes use of the helical winding pattern <NUM> of <FIG> in the respective stator windings. However, it will be understood that the stator windings in the present disclosure may employ any of winding patterns as described in relation to <FIG>. Further, in some implementations of the present disclosure, any other stator winding patterns may be employed.

Embodiments of the present disclosure will be described with reference to a conventional stator winding having one coil per phase per permanent magnet pole pair. <FIG> illustrate cross sections of exemplary stator windings for use in an electric motor, such as stator winding <NUM> of motor unit <NUM> in <FIG>. <FIG> shows a conventional stator winding <NUM> comprising one coil per phase per permanent magnet pole pair for use in a three-phase electric motor having one pole pair (i.e. one north pole N and one south pole S). In the present disclosure, the three phases of the electric motor are referred to as phases A, B and C. In the conventional stator winding <NUM>, each phase comprises one coil - coil <NUM> (labelled 'A') for phase A, coil <NUM> (labelled 'B') for phase B, and coil <NUM> (labeled 'C') for phase C. Each of the coils <NUM>-<NUM> comprises a winding having a plurality of N turns, where N is an integer and N > <NUM>, where each coil has the same number of turns. The windings are formed from wires that have been turned in a specific manner, such as that described in relation to <FIG>, thereby resulting in each coil having a start point and an end point, as indicated by the wire ends <NUM>-<NUM> in <FIG>. Embodiments of the present disclosure will be described with respect stator windings having helical coils; however, it will be understood that any winding type may be employed.

As seen in <FIG>, the lateral distribution of coils <NUM>-<NUM> is such that they are equally distributed about the stator winding <NUM> where each coil spans <NUM> electrical (equal to <NUM> mechanical degrees in a two-pole electrical machine) about the circumference of the cross section of the stator winding <NUM>. While stator winding <NUM> is employed in a three-phase electric motor having one coil per magnet pole pair, for a general electric motor having n phases and p magnet pole pairs, each coil of a conventional stator winding <NUM> having one coil per phase per magnet pole pair would span <NUM>/(np) mechanical degrees about the circumference of the cross section of the stator winding. As for the axial distribution of the coils about the longitudinal axis of the conventional stator winding <NUM>, the windings of the coils <NUM>-<NUM> are configured such that they are each wound from the proximal end of the stator winding <NUM> (such as proximal end <NUM> of stator winding <NUM> in <FIG>), extending longitudinally towards the distal end (such as distal end <NUM> of stator winding <NUM> in <FIG>), and returning back to the proximal end. In this manner, each of the coils <NUM>-<NUM> of the stator winding <NUM> effectively comprises an inner layer and an outer layer, the outer layer overlaid on the inner layer, as shown in the cross section of <FIG>. In this configuration, the lead wires for each of the coils <NUM>-<NUM> are located at the proximal end of the stator winding <NUM> for connectivity with the feed lines to the electric motor, such as lead lines <NUM>, <NUM> as shown in <FIG>.

<FIG> shows a stator winding <NUM> comprising two coils per phase per magnet pole pair for use in a three-phase electric motor having one pole pair, according to an embodiment of the present disclosure. With this arrangement, stator winding <NUM> is a double coil winding, and, when implemented with helical coils as depicted in <FIG>, the stator winding <NUM> is a double helical coil winding. In the stator winding <NUM>, each phase A, B and C of the three-phase electric motor comprises two coils. Thus, phase A comprises coil <NUM> (labelled 'A1') and coil <NUM> (labelled 'A2'), phase B comprises coil <NUM> (labelled 'B1') and coil <NUM> (labelled 'B2'), and phase C comprises coil <NUM> (labelled 'C1') and coil <NUM> (labelled 'C2'). With reference to the conventional stator winding <NUM> in <FIG>, if each coil <NUM>-<NUM> comprises a winding having N turns, where N is an integer and N ≥ <NUM>, each of the coils <NUM>-<NUM> of stator winding <NUM> comprises a winding having either N/<NUM> turns for even values of N, or (N ± <NUM>)/<NUM> for odd values of N, with each coil having the same number of turns. Thus, each coil in the stator winding <NUM> comprises about half the number of turns as the coils in the conventional stator winding <NUM> in <FIG>. For example, if coils <NUM>-<NUM> of the conventional stator winding <NUM> comprises <NUM> turns each, coils <NUM>-<NUM> of the stator winding <NUM> would comprise about <NUM> turns each. The winding turns of each coil <NUM>-<NUM> may comprise any of the aforementioned winding types, such as, for example, a helical winding.

The lateral distribution of coils <NUM>-<NUM> is such that they are equally distributed about the stator winding <NUM> where each coil spans <NUM> mechanical degrees about the circumference of the cross section of the stator winding <NUM>. While stator winding <NUM> is employed in a three-phase electric motor having two coils per phase per magnet pole pair, for a general electric motor having n phases and p magnet pole pairs, each coil of the stator winding <NUM> of the present disclosure having two coils per phase per magnet pole pair would span <NUM>/(<NUM>np) mechanical degrees about the circumference of the cross section of the stator winding. The axial distribution of the coils in stator coil <NUM> is similar to that of the conventional stator coil <NUM>. The axial distribution of the coils about the longitudinal axis of the stator winding <NUM> is such that the windings of the coils <NUM>-<NUM> are each wound from the proximal end of the stator winding <NUM> (such as proximal end <NUM> of stator winding <NUM> in <FIG>), extending longitudinally towards the distal end (such as distal end <NUM> of stator winding <NUM> in <FIG>), and returning back to the proximal end. In this manner, each of the coils <NUM>-<NUM> of the stator winding <NUM> effectively comprises an inner layer and an outer layer, the outer layer overlaid on the inner layer, as shown in the cross section of <FIG>. In this configuration, the lead wires for each of the coils <NUM>-<NUM> are located at the proximal end of the stator winding <NUM> for connectivity with the feed lines to the electric motor, such as lead lines <NUM>, <NUM> as shown in <FIG>.

Coils <NUM>-<NUM> in the conventional stator winding <NUM> and coils <NUM>-<NUM> of the stator winding <NUM> of the present disclosure may be electrically connected in any configuration for electric motors, such as, for example, a star connection or a delta connection. <FIG> shows the coils <NUM>-<NUM> of the stator winding <NUM> in <FIG> connected in an exemplary star configuration <NUM>. Coils <NUM>-<NUM> are represented as their resistive loads RA, RB and RC, respectively. In the star configuration <NUM>, the end point 'Ae' of coil <NUM>, the end point 'Be' of coil <NUM>, and the end point 'Ce' of coil <NUM>, are connected together. The start point 'As' of coil <NUM>, the start point 'Bs' of coil <NUM>, and the start point 'Cs' of coil <NUM>, are connected to a feed line, such as feed lines <NUM>, <NUM> of the blood pump <NUM> in <FIG>. In this manner, each branch of the star configuration <NUM> comprises a single load corresponding to the coils for each phase in the stator winding <NUM>.

<FIG> shows an exemplary electrical connection of the coils in the stator winding <NUM>, according to an embodiment of the present disclosure. Here coils <NUM>-<NUM> are represented as resistive loads RA1 and RA2 for phase A, respectively, coils <NUM>-<NUM> are represented as resistive loads RB1 and RB2 for phase B, respectively, and coils <NUM>-<NUM> are represented as resistive loads RC1 and RC2 for phase C, respectively. As mentioned in the foregoing, coils <NUM>-<NUM> of stator winding <NUM> each comprise half the turns of coils <NUM>-<NUM> of stator winding <NUM>. Thus, the resistive load per phase of the double stator winding <NUM> is the same as the resistive load per phase of the conventional stator winding <NUM>, i.e. RA = RA1 + RA2, RB = RB1 + RB2, and RC = RC1 + RC2. As such, the double coil configuration of stator winding <NUM> does not place an additional resistive load on the electric motor when compared to the load presented by conventional stator winding <NUM>.

As shown in the connection diagram of <FIG>, each branch of the star configuration <NUM> comprises two coils having their like terminals connected, i.e. the two coils are connected back to back. For example, for phase A, coils <NUM>-<NUM> represented by resistive loads RA1 and RA2, respectively, are connected such that the end points 'A1e' and 'A2e' are connected together. Similarly, end points 'B1e' and 'B2e' of coils <NUM>-<NUM> of phase B represented by resistive loads RB1 and RB2, respectively, are connected together, and end points 'C1e' and 'C2e' of coils <NUM>-<NUM> of phase C represented by resistive loads RC1 and RC2, respectively, are connected together. The start point 'A1s' of the resistive load RA1 of coil <NUM> for phase A, the start point 'B1s' of the resistive load RB1 of coil <NUM> for phase B, and the start point 'C1s' of resistive load RC1 of coil <NUM> for phase C, are connected to a feed line, such as feed lined <NUM>, <NUM> of the blood pump <NUM> in <FIG>. Additionally, the start point 'A2s' of the resistive load RA2 of coil <NUM> for phase A, the start point 'B2s' of the resistive load RB2 of coil <NUM> for phase B, and the start point 'C2s' of resistive load RC2 of coil <NUM> for phase C, are connected together.

The manner in which the coils <NUM>-<NUM> of the double stator winding <NUM> of the present disclosure are connected is important as it determines how the coils <NUM>-<NUM> interact with the magnetic flux generated by the rotor during operation of the electric motor. With the star configuration <NUM> as depicted in <FIG>, the direction of current flowing through coil A1 of stator winding <NUM> is opposite to the direction of current flowing through coil A2. Similarly, the direction of current flowing through coil B1 of stator winding <NUM> is opposite to the direction of current flowing through coil B2, and the direction of current flowing through coil C1 of stator winding <NUM> is opposite to the direction of current flowing through coil C2. This means that coil A1 having a first direction of current flowing therethrough interacts with a first pole of the rotor while coil A2 having a second direction of current flowing therethrough, opposite to the first direction of current in coil A1, interacts with a second pole of the rotor opposite the first pole. Additionally, coil B1 having a first direction of current flowing therethrough interacts with a first pole of the rotor while coil B2 having a second direction of current flowing therethrough, opposite to the first direction of current in coil B1, interacts with a second pole of the rotor opposite the first pole. Further, coil C1 having a first direction of current flowing therethrough interacts with a first pole of the rotor while coil C2 having a second direction of current flowing therethrough, opposite to the first direction of current in coil C1, interacts with a second pole of the rotor opposite the first pole. The interaction of the coils of the stator winding <NUM> with the magnetic flux of the rotor during operation will be described in relation to <FIG>.

<FIG> illustrates an exemplary cross-section <NUM> of the blood pump <NUM> of <FIG> employing stator winding <NUM> in a three-phase two-pole electric motor, taken along line X-X' during operation. As previously mentioned, while stator winding <NUM> is suitable for the operation of a three-phase electric motor having two coils per phase per magnet pole pair, a stator winding for an electric motor having any number of phases n and magnet pole pairs p can be used within the scope of the present disclosure, bringing the total number of coils used to 2np. In <FIG>, coils marked with an 'x' indicate current flowing into the page, orthogonal to the plane of the page, while coils marked with a '•' indicate current flowing out of the page, orthogonal to the plane of the page. As illustrated, coils <NUM>-<NUM> for phase A are connected as described in relation to <FIG> such that the direction of current flowing through coil <NUM> is opposite to the direction of current flowing through coil <NUM>. With the physical arrangement and electrical connection of coils <NUM>-<NUM> as described in the foregoing, the polarity of the magnetic field generated from the permanent magnet stator <NUM> that coil <NUM> interacts with is opposite to that which interacts with coil <NUM>.

Similarly, coils <NUM>-<NUM> for phase B of the electric motor are connected such that the direction of current flowing through coil <NUM> is opposite to the direction of current flowing through coil <NUM>. With the physical arrangement and electrical connection of coils <NUM>-<NUM> as described in the foregoing, the polarity of the magnetic field generated from the permanent magnet stator <NUM> that coil <NUM> interacts with is opposite to that which interacts with coil <NUM>. Further, coils <NUM>-<NUM> for phase C of the electric motor are connected such that the direction of current flowing through coil <NUM> is opposite to the direction of current flowing through coil <NUM>. With this arrangement, coils <NUM>-<NUM> each see a different polarity from the magnet pole pair of the stator. With the physical arrangement and electrical connection of coils <NUM>-<NUM> as described in the foregoing, the polarity of the magnetic field generated from the permanent magnet stator <NUM> that coil <NUM> interacts with is opposite to that which interacts with coil <NUM>. The interaction of the coils of the stator winding <NUM> with the magnetic flux of the rotor during operation generates a torque that acts on the rotor causing it to rotate.

<FIG> illustrates another example of a cross-section of a double coil stator winding <NUM> for use in an electric motor having three phases A, B and C, and two permanent magnet pole pairs N1-S1 and N2-S2, according to an embodiment of the present disclosure. According the aforementioned general definitions, the electric motor using stator winding <NUM> has n = <NUM> and p = <NUM>. As discussed in relation to stator winding <NUM> in <FIG>, stator winding <NUM> also comprises two coils per phase per magnet pole pair resulting in <NUM> coils <NUM>-<NUM> in total. In the stator winding <NUM>, due to the presence of two magnet pole pairs in the electric motor, each phase A, B and C of the three-phase electric motor comprises two coils. Thus, phase A comprises coils <NUM>-<NUM> (labelled 'A1,' 'A2,' 'A3' and 'A4' respectively), phase B comprises coils <NUM>-<NUM> (labelled 'B1,' 'B2,' 'B3' and 'B4' respectively), and phase C comprises coils <NUM>-<NUM> (labelled 'C1,' 'C2,' 'C3' and 'C4' respectively). As shown in <FIG>, a coil from each phase is circumferentially arranged next to a coil from a different phase in a sequential order of phase, and that arrangement is repeated along the stator winding such that each coil spans <NUM>°/(<NUM>np) = <NUM>°/(2x3x2) = <NUM>° about the cross-section of the stator winding <NUM>.

As with the coils of stator winding <NUM>, coils <NUM>-<NUM> may be electrically connected in either star or delta configuration in which (i) coils <NUM>-<NUM> for phase A are connected back to back with their like terminals together along the branch for phase A of the star or delta connection, (ii) coils <NUM>-<NUM> for phase B are connected back to back with their like terminals together along the branch for phase B of the star or delta connection, and (iii) coils <NUM>-<NUM> for phase C are connected back to back with their like terminals together along the branch for phase C of the star or delta connection. With such an electrical connection, (i) the direction of current flowing through coils A1 and A3 is opposite to the direction of current flowing through coils A2 and A4, (ii) the direction of current flowing through coils B1 and B3 is opposite to the direction of current flowing through coils B2 and B4, and (iii) the direction of current flowing through coils C1 and C3 is opposite to the direction of current flowing through coils C2 and C4.

In this manner, coil A1 having a first direction of current flowing therethrough interacts with a first pole N1 of the rotor, coil A2 having a second direction of current flowing therethrough, opposite to the first direction of current in coil A1, interacts with a second pole S1 of the rotor opposite the first pole N1, coil A3 having a first direction of current flowing therethrough interacts with a third pole N2 of the rotor, and coil A4 having a second direction of current flowing therethrough, opposite to the first direction of current in coil A3, interacts with a fourth pole S2 of the rotor opposite the third pole N2. Similarly, coil B1 having a first direction of current flowing therethrough interacts with a first pole N1 of the rotor, coil B2 having a second direction of current flowing therethrough, opposite to the first direction of current in coil B1, interacts with a second pole S1 of the rotor opposite the first pole N1, coil B3 having a first direction of current flowing therethrough interacts with a third pole N2 of the rotor, and coil B4 having a second direction of current flowing therethrough, opposite to the first direction of current in coil B3, interacts with a fourth pole S2 of the rotor opposite the third pole N2. Finally, coil C1 having a first direction of current flowing therethrough interacts with a first pole N1 of the rotor, coil C2 having a second direction of current flowing therethrough, opposite to the first direction of current in coil C1, interacts with a second pole S1 of the rotor opposite the first pole N1, coil C3 having a first direction of current flowing therethrough interacts with a third pole N2 of the rotor, and coil C4 having a second direction of current flowing therethrough, opposite to the first direction of current in coil C3, interacts with a fourth pole S2 of the rotor opposite the third pole N2. The interaction of the coils of the stator winding <NUM> with the magnetic flux of the rotor during operation generates a torque that acts on the rotor that causes the rotor to rotate.

<FIG> illustrates a further example of a cross-section of a double coil stator winding <NUM> for use in an electric motor having five phases A, B, C, D and E, and one permanent magnet pole pair N-S, according to an embodiment of the present disclosure. According the aforementioned general definitions, the electric motor using stator winding <NUM> has n = <NUM> and p = <NUM>. As discussed in relation to stator windings <NUM> and <NUM>, stator winding <NUM> also comprises two coils per phase per magnet pole pair resulting in <NUM> coils <NUM>-<NUM> in total. Phase A comprises coils <NUM>-<NUM> (labelled 'A1' and 'A2' respectively), phase B comprises coils <NUM>-<NUM> (labelled 'B1' and 'B2' respectively), phase C comprises coils <NUM>-<NUM> (labelled 'C1' and 'C2' respectively), phase D comprises coils <NUM>-<NUM> (labelled 'D1' and 'D2' respectively), and phase E comprises coils <NUM>-<NUM> (labelled 'E1' and 'E2' respectively). As shown in <FIG>, a coil from each phase is circumferentially arranged next to a coil from a different phase in a sequential order of phase, and that arrangement is repeated along the stator winding <NUM> such that each coil spans <NUM>°/(<NUM>np) = <NUM>°/(2x5x1) = <NUM>° about the cross-section of the stator winding <NUM>.

As with the coils of stator windings <NUM> and <NUM>, coils <NUM>-<NUM> may be electrically connected in either star or delta configuration in which (i) coils <NUM>-<NUM> for phase A are connected back to back with their like terminals together along the branch for phase A of the star or delta connection, (ii) coils <NUM>-<NUM> for phase B are connected back to back with their like terminals together along the branch for phase B of the star or delta connection, (iii) coils <NUM>-<NUM> for phase C are connected back to back with their like terminals together along the branch for phase C of the star or delta connection, (iv) coils <NUM>-<NUM> for phase D are connected back to back with their like terminals together along the branch for phase D of the star or delta connection, and (v) coils <NUM>-<NUM> for phase E are connected back to back with their like terminals together along the branch for phase E of the star or delta connection. With such an electrical connection, (i) the direction of current flowing through coil A1 is opposite to the direction of current flowing through coil A2, (ii) the direction of current flowing through coil B1 is opposite to the direction of current flowing through coil B2, (iii) the direction of current flowing through coil C1 is opposite to the direction of current flowing through coil C2, (iv) the direction of current flowing through coil D1 is opposite to the direction of current flowing through coil D2, and (v) the direction of current flowing through coil E1 is opposite to the direction of current flowing through coil E2.

In this manner, coil A1 having a first direction of current flowing therethrough interacts with a first pole N of the rotor, and coil A2 having a second direction of current flowing therethrough, opposite to the first direction of current in coil A1, interacts with a second pole S of the rotor opposite the first pole N. Similarly, coil B1 having a first direction of current flowing therethrough interacts with a first pole N of the rotor, and coil B2 having a second direction of current flowing therethrough, opposite to the first direction of current in coil B1, interacts with a second pole S of the rotor opposite the first pole N. Further, coil C1 having a first direction of current flowing therethrough interacts with a first pole N of the rotor, and coil C2 having a second direction of current flowing therethrough, opposite to the first direction of current in coil C1, interacts with a second pole S of the rotor opposite the first pole N. Coil D1 having a first direction of current flowing therethrough interacts with a first pole N of the rotor, and coil D2 having a second direction of current flowing therethrough, opposite to the first direction of current in coil D1, interacts with a second pole S of the rotor opposite the first pole N. Finally, coil E1 having a first direction of current flowing therethrough interacts with a first pole N of the rotor, and coil E2 having a second direction of current flowing therethrough, opposite to the first direction of current in coil E1, interacts with a second pole S of the rotor opposite the first pole N. The interaction of the coils of the stator winding <NUM> with the magnetic flux of the rotor during operation generates a torque that acts on the rotor that causes the rotor to rotate.

The interaction of the current flowing in the coils of the stator winding <NUM> with the magnetic flux density of the two-pole rotor during operation will be described by referring back to <FIG>. As described in relation to <FIG>, rotor <NUM> is in constant rotation when in use. <FIG> depicts the position of the rotor <NUM> at an instant when the rotor is radially positioned as shown, and with the direction of current flowing through the coils of the stator winding <NUM> as indicated. In the illustrated position, the permanent magnet rotor <NUM> produces a magnetic flux density B that is represented by a magnetic field pattern comprising magnetic field lines <NUM>. The magnetic field lines <NUM> begin at the north pole N and end at the south pole S of the rotor <NUM>. According to Lenz's law the interaction between the magnetic flux density B and the length of the stator winding L in a direction perpendicular to the magnetic flux density B generates a torque T within the rotor <NUM> for rotation thereof, governed by the equation: <MAT> where ẑ is a direction parallel to the longitudinal axis <NUM> of the rotor <NUM>, Br̂ is a radial component of the magnetic flux density, that is perpendicular to the longitudinal axis <NUM> of the rotor <NUM>, Lẑ is the vertical component of coil winding that is parallel to the longitudinal access of the motor rotor and × denotes the vector cross product. Thus, the flow of current in stator winding <NUM> causes rotation of the rotor <NUM> about the longitudinal axis <NUM>, which, in turn, causes a corresponding rotation of the impeller <NUM> coupled to the distal end of the rotor shaft <NUM>.

<FIG> illustrates the conventional stator winding <NUM> during use in a three-phase two-pole electric motor in which one electrical degree equals to one mechanical degree. The horizontal axis of the plot represents the angular position along the circumference of the stator winding <NUM> and the vertical axis represents the longitudinal length of the stator winding <NUM> moving from the distal end to the proximal end of the stator winding <NUM>. As previously mentioned, each of coils <NUM>-<NUM> comprises a plurality of wires wound in a particular manner, such as, for example the helical winding of <FIG>. In <FIG>, the wires are wound helically and each of the coils <NUM>-<NUM> is shown as a band that is arranged between the proximal end (top end of the plot) and the distal end (bottom end of the plot) of the stator winding <NUM>. Due to the manner in which the helical coils <NUM>-<NUM> are wound, each of bands in <FIG> overlap to form the stator winding <NUM>. For improved visualization, <FIG> illustrate each of the winding patterns of coils <NUM>-<NUM> for phases A, B and C in stator winding <NUM> when viewed separately - when the coils as shown in <FIG> are overlaid, the stator winding <NUM> as shown in <FIG> results. Additionally, it should be noted that while each band representing coils <NUM>-<NUM> comprises a plurality of wires, only nine representative wires are shown per coil in <FIG>. Wire ends or lead lines <NUM>-<NUM> for each of the coils <NUM>-<NUM> are also shown at the proximal end of the stator winding <NUM>. The direction shown on each lead line <NUM>-<NUM> represents the direction of winding the wires forming the respective coils <NUM>-<NUM>. For example, the direction indicated on lead line <NUM> represents the starting point of the wire forming winding <NUM> and lead line <NUM> indicates the end point of the wire forming winding <NUM>. Coils <NUM>-<NUM> are arranged in the stator winding <NUM> in an angular symmetric manner such that a coil from each phase is circumferentially arranged next to a coil from a different phase in a sequentially order of phase, thus resulting in the stator winding pattern as shown in <FIG>. The coil span for each of the coils <NUM>-<NUM> of stator winding <NUM> is <NUM>°/(np) = <NUM>°/(3x1) = <NUM>°.

During operation of the electric motor, electrical current from a motor controller, is passed through the stator winding <NUM> via the feed lines, such as feed lines <NUM>-<NUM> in <FIG>, connected to the wire ends <NUM>-<NUM> such that the magnitude of current flowing through each of the coils <NUM>-<NUM> is the same. As the coils <NUM>-<NUM> overlap in their arrangement within the stator winding <NUM>, the effect of current flow in each of the coils may be influenced by the current flow in an adjacent or overlapping coil. Thus, due to the physical arrangement of the coils <NUM>-<NUM> in the stator winding, the net effect of the current flow through all the coils <NUM>-<NUM> of stator winding <NUM> cancel out. This effect will be further discussed in relation to <FIG>.

<FIG> illustrates only coil <NUM> (coil A) of the stator winding <NUM> during use. Coil A corresponds to phase A. Coil <NUM> is shown comprising only five representative winding wires <NUM>-<NUM>, however it will be understood that coil <NUM> comprises a plurality of wires that form a band (as shown in <FIG>). As can be seen, the path taken by the current in each of the winding wires <NUM>-<NUM> have regions of overlap as the wires are wound between the proximal and distal ends of the stator winding <NUM> (such as proximal end <NUM> and distal end <NUM> as shown in <FIG>). For example, due to the winding direction of the wires <NUM>-<NUM> in the coil <NUM>, the current in the wires <NUM>-<NUM> flows into the triangular region <NUM>, and then turn and leave the triangular region <NUM>. When the wires <NUM>-<NUM> turn and leave the triangular region <NUM>, the longitudinal component of current in the wires changes. This is shown in <FIG>, where the current I flowing in wire <NUM> entering triangular regions <NUM> has directional components Iz and Iθ (longitudinal and angular components, respectively). When leaving triangular region <NUM>, the current I changes direction and has directional components -Iz and Iθ. Thus, longitudinal component of current -Iz leaving triangular region <NUM> is opposite to the longitudinal component of current Iz entering triangular region <NUM>. Similarly, the current in the wires <NUM>-<NUM> flow into the triangular region <NUM>, and then turn and leave the region <NUM>. When the wires <NUM>-<NUM> turn and leave the triangular region <NUM>, the longitudinal component of current in the wires changes and is completely opposite to the longitudinal component of current in the wires entering triangular region <NUM>. Because the magnitudes of the currents in wires <NUM>-<NUM> are the same and the longitudinal component of current flow are in complete opposition to each other entering and leaving the triangular regions <NUM> and <NUM>, the effect of the longitudinal component of currents in wires <NUM>-<NUM> (represented by arrows <NUM>-<NUM> in <FIG>) on the rotor cancel out in triangular regions <NUM> and <NUM>, i.e. Iz - Iz = <NUM> as indicated in <FIG>. Thus, the longitudinal component of current in the wires <NUM>-<NUM> in triangular regions <NUM> and <NUM> does not contribute to the torque developed in the rotor, per equation (<NUM>).

As described in equation (<NUM>), the torque T generated within the rotor <NUM> is dependent on the longitudinal length L of the current carrying wires of the coil in a direction parallel to the longitudinal axis <NUM> of the rotor <NUM>. Thus, only the vertical directional component of wires <NUM>-<NUM> in <FIG> contributes to the generated torque T within the rotor. The vertical component of the wires <NUM>-<NUM> can be easily visualized by drawing a vertical line in <FIG> and determining the direction of the longitudinal component current flowing in the wires <NUM>-<NUM> at the point of intersection of the wires <NUM>-<NUM> and the vertical line.

The contribution of the mechanical arrangement of the wires in the coil to the generated torque T is described by a coil usage function <NUM>, as shown in <FIG>. The vertical component of the wires <NUM>-<NUM> that contributes to the torque T in the rotor can be seen in <FIG> where wires <NUM>-<NUM> carrying current with longitudinal components in opposing directions do not overlap. For example, for coil angular positions θ of <NUM>° to <NUM>° about the stator winding <NUM>, there is no overlap of wires and the currents flowing in wires <NUM>-<NUM> have a longitudinal component that is in the same direction, however at the coil angular position θ of <NUM>° and <NUM>° about the stator winding <NUM>, respectively, the wires overlap and the longitudinal component of current flowing in the overlapped wires <NUM>-<NUM> is in completely opposing directions.

Accordingly, the coil usage function is at its maximum when the longitudinal component of current flowing in wires <NUM>-<NUM> is in the same direction, as can be seen in <FIG> for <NUM>° ≤ θ ≤ <NUM>° and <NUM>° ≤ θ ≤ <NUM>° about the stator winding <NUM>, where there are no overlapping wires carrying currents having longitudinal components that are in opposing directions. This maximum is about <NUM>/<NUM> the full length of the stator winding <NUM> for a three-phase two-pole electric motor, as shown in <FIG> where the coil usage is maximum at about <NUM>%. The coil usage function is zero at θ = <NUM>° and θ = <NUM>° about the stator winding <NUM> where the wires overlap and the longitudinal component of current in the overlapped wires is equal but opposite in direction. For completeness, for <NUM>° < θ < <NUM>°, <NUM>° < θ < <NUM>°, <NUM>° < θ < <NUM>°, and <NUM>° < θ < <NUM>°, the wires <NUM>-<NUM> are partly overlapped with currents having longitudinal components in opposing directions, resulting in some contribution towards the torque T generated in the rotor. This can be seen in <FIG> where the coil usage varies linearly with θ for <NUM>° < θ < <NUM>°, <NUM>° < θ < <NUM>°, <NUM>° < θ < <NUM>°, and <NUM>° < θ < <NUM>°.

<FIG> illustrates the stator winding <NUM> according to an embodiment of the present disclosure during use in a three-phase two-pole electric motor at one instant during operation. As described in the foregoing, coils <NUM>-<NUM> are wound using helical windings, such as the helical winding <NUM> of <FIG>, however any winding type may be used. In <FIG>, the coils <NUM>-<NUM> are shown as bands that are arranged between the proximal end (top end of the plot) and the distal end (bottom end of the plot) of the stator winding <NUM>. Due to the manner in which the helical coils <NUM>-<NUM> are wound, each of bands in <FIG> overlap to form the stator winding <NUM>. As with <FIG>, for improved visualization, <FIG> illustrate each of the winding patterns of coils <NUM>-<NUM> for phases A, B and C in stator winding <NUM> when viewed separately - when the coils as shown in <FIG> are overlaid, the stator winding <NUM> as shown in <FIG> results. Additionally, it should be noted that while each band representing coils <NUM>-<NUM> comprises a plurality of wires, only five representative wires are shown per coil in <FIG>. Wire ends or lead lines for each of the coils <NUM>-<NUM> are also shown at the proximal end of the stator winding <NUM>, with arrows indicating the direction of winding of wires forming the respective coils <NUM>-<NUM>.

Coils <NUM>-<NUM> are arranged in the stator winding <NUM> in an angular symmetric manner such that a coil from each phase A, B and C is circumferentially arranged next to a coil from a different phase in a sequential order of phase, thus resulting in the stator winding pattern as shown in <FIG>. As previously described, the present disclosure relates to a stator winding having two coils per phase per magnet pole pair. Thus in <FIG>, phase A is shown as comprising coils <NUM>-<NUM> in <FIG>, phase B is shown as comprising coils <NUM>-<NUM> in <FIG>, and phase C is shown as comprising coils <NUM>-<NUM> The coils span for each of the coils <NUM>-<NUM> of stator winding <NUM> is <NUM>°/(<NUM>np) = <NUM>°/(2x3x1) = <NUM>°.

During operation of the electric motor, direct current from a six-step direct current controller (not shown) is passed through the stator winding <NUM> via feed lines, such as feed lines <NUM>-<NUM> in <FIG>, connected to the lead lines at the proximal end of the stator winding <NUM> such that the magnitude of current flowing through each of the coils <NUM>-<NUM> is the same. As the coils <NUM>-<NUM> overlap in their arrangement within the stator winding <NUM>, the effect of current flow in each of the coils may be influenced by the current flow in an adjacent or overlapping coil. Unlike the conventional stator winding <NUM> shown in <FIG>, due to the physical arrangement of the coils in stator winding <NUM>, the effect of the current flow through the coils <NUM>-<NUM> does not cancel out.

<FIG> illustrates only coils <NUM>-<NUM> (coils A1 and A2) of the stator winding <NUM> according to an embodiment of the present disclosure, during use. Coils A1 and A2 correspond to phase A. Coils <NUM> is shown comprising five representative winding wires <NUM>-<NUM> and coil <NUM> is shown comprising five representative winding wires <NUM>-<NUM>, however it will be understood that each of coils <NUM>-<NUM> comprise a plurality of wires that form a band (as shown in <FIG>). As can be seen, the path taken by the current in each of the winding wires <NUM>-<NUM> have regions of overlap as the wires are wound between the proximal and distal ends of the stator winding <NUM> (such as proximal end <NUM> and distal end <NUM> as shown in <FIG>). For example, the current in the wires <NUM>-<NUM> flow into triangular regions <NUM> and <NUM>, and then turn and leave the triangular regions <NUM>-<NUM>. Similarly, the current in the wires <NUM>-<NUM> flow into the triangular regions <NUM>-<NUM>, and then turn and leave the triangular regions <NUM>-<NUM>.

As described in relation to <FIG>, when the wires <NUM>-<NUM> turn and leave the triangular regions <NUM>-<NUM>, and when wires <NUM>-<NUM> turn and leave the triangular regions <NUM>-<NUM>, the longitudinal component of current in the respective wires changes. In wires <NUM>-<NUM>, (i) the longitudinal component of current flowing out of triangular region <NUM> is opposite to the longitudinal component of current flowing into the triangle region <NUM>, and (ii) the longitudinal component of current flowing out of triangular region <NUM> is opposite to the longitudinal component of current flowing into the triangle region <NUM>. When the wires <NUM>-<NUM> turn and leave the triangular regions <NUM>-<NUM>, the longitudinal component of current in the wires changes and is completely opposite to the longitudinal component of current flow in the wires entering triangular regions <NUM>-<NUM>.

Similarly, in wires <NUM>-<NUM>, (iii) the longitudinal component of current flowing out of triangular region <NUM> is opposite to the longitudinal component of current flowing into the triangle region <NUM>, and (iv) the longitudinal component of current flowing out of triangular region <NUM> is opposite to the longitudinal component of current flowing into the triangle region <NUM>. When the wires <NUM>-<NUM> turn and leave the triangular regions <NUM>-<NUM>, the longitudinal component of current in the wires changes and is completely opposite to the longitudinal component of current in the wires entering triangular regions <NUM>-<NUM>. Because the magnitudes of the currents in wires <NUM>-<NUM> are the same and the longitudinal component of current flow are in complete opposition to each other entering and leaving the triangular regions <NUM>-<NUM>, the effect of the currents in wires <NUM>-<NUM> (represented by arrows <NUM>-<NUM> in <FIG>) cancel out in regions <NUM>-<NUM>, i.e. Iz - Iz = <NUM> as indicated in <FIG>.

However, as the stator winding <NUM> has two coils per phase per magnet pole pair, i.e. a double winding, coils <NUM>-<NUM> also comprise additional diamond shaped regions of overlap <NUM>-<NUM>. As shown in <FIG>, these diamond shaped regions of overlap occur away from the proximal or distal ends of the coils <NUM>-<NUM>. In effect, these diamond shaped regions are actually back to back triangular regions that result when bands from coils A1 and A2 overlap with each other. In these diamond shaped regions, the longitudinal component of current in the wires <NUM>-<NUM> flows into the regions <NUM>-<NUM> in one direction, and then leave the regions <NUM>-<NUM> in the same direction. Because the magnitudes of the currents in wires <NUM>-<NUM> are the same and the longitudinal component of current flow are the same to each other in regions <NUM>-<NUM>, the effect of the currents in wires <NUM>-<NUM> represented by arrows <NUM>-<NUM> in <FIG>, do not cancel out, but add together in regions <NUM>-<NUM>, i.e. Iz + Iz = <NUM>Iz as indicated in <FIG>. These diamond shaped regions of overlap <NUM>-<NUM> in which the effects of the longitudinal component of current flowing through wires <NUM>-<NUM> do not cancel increases the coil usage for phase A. These regions <NUM>-<NUM> are effectively positive zones which enhance the performance of the stator coil <NUM>. While <FIG> describes the effect of current flow in coils <NUM>-<NUM> for phase A of stator winding <NUM>, a similar effect will be seen from current flow in coils <NUM>-<NUM> for phases B and C of stator winding <NUM>.

It should be noted that in the stator winding <NUM> according to embodiments of the present disclosure, the regions <NUM>-<NUM> are effectively dead zones in which the effect of the currents flowing through the windings cancel out. These dead zones are much smaller compared to regions <NUM> and <NUM> of the conventional stator winding <NUM>. At the same time, due to the manner in which stator winding <NUM> is formed, additional positive zones are formed which improves the performance of the stator winding <NUM>.

As described in relation to equation (<NUM>), the torque T generated within the rotor <NUM> is dependent on the longitudinal length L of the current carrying wires of the coil in a direction parallel to the longitudinal axis <NUM> of the rotor <NUM>. In effect, only the vertical directional component of wires <NUM>-<NUM> in <FIG> contributes to the generated torque T within the rotor. The vertical component of the wires <NUM>-<NUM> can be easily visualized by drawing a vertical line on <FIG> and determining the direction of current flowing in the wires <NUM>-<NUM> that intersect with the vertical line.

The contribution of the mechanical arrangement of the wires in the coil <NUM> to the generated torque T is described by a coil usage function <NUM>, as shown in <FIG>. The vertical component of the wires <NUM>-<NUM> that contributes to the torque T in the rotor <NUM> can be seen in <FIG> where wires <NUM>-<NUM> carrying current with longitudinal components in opposing directions do not overlap. For example, for <NUM>° ≤ θ ≤ <NUM>° about the stator winding <NUM>, the current flowing in wires <NUM>-<NUM> have longitudinal components that are in the same direction (despite the wires overlapping in regions <NUM> and <NUM>), however at the coil angular position θ of <NUM>° and <NUM>° about the stator winding <NUM>, respectively, the wires overlap and the longitudinal component of current flowing in the overlapped wires <NUM>-<NUM> is in completely opposing directions.

Accordingly, the coil usage function is at its maximum when the longitudinal component of current flowing in wires <NUM>-<NUM> is in the same direction, as can be seen in <FIG> for <NUM>° ≤ θ ≤ <NUM>° and <NUM>° ≤ θ ≤ <NUM>° about the stator winding <NUM>, where there are no overlapping wires carrying currents with longitudinal components in opposing directions. As with stator winding <NUM>, this maximum is about <NUM>/<NUM> the full length of the stator winding <NUM> for a three-phase two-pole electric motor, as shown in <FIG> where the coil usage is maximum at about <NUM>%. It should be noted that the maximum coil usage for stator winding <NUM> (for the coil angular range (<NUM>°)) is twice that for stator winding <NUM> (for the coil angular range (<NUM>°)). The coil usage function is zero at θ = <NUM>° and θ = <NUM>° about the stator winding <NUM> where the wires overlap and the longitudinal component of current flow in the overlapped wires is equal but in complete opposite in directions. For completeness, for <NUM>° < θ < <NUM>°, <NUM>° < θ < <NUM>°, <NUM>° < θ < <NUM>°, and <NUM>° < θ < <NUM>°, the wires <NUM>-<NUM> are partly overlapped, resulting in some contribution towards the torque T generated in the rotor. This can be seen in <FIG> where the coil usage varies linearly with θ for <NUM>° < θ < <NUM>°, <NUM>° < θ < <NUM>°, <NUM>° < θ < <NUM>°, and <NUM>° < θ < <NUM>°.

<FIG> illustrates the coil usage functions <NUM>-<NUM> for all three phases A, B and C, respectively, for the conventional stator winding <NUM>. The usage function for each phase in <FIG> is identical to that shown in <FIG>. <FIG> illustrates the coil usage functions <NUM>-<NUM> for all three phases A, B and C, respectively, for the stator winding <NUM> according to an embodiment of the present disclosure. The usage function for each phase in <FIG> is identical to that shown in <FIG>. The usage functions shown in <FIG> are similar in shape for all three phases, and the curves for each phase are shifted by <NUM>° from the previous phase. <FIG> illustrates the variation in magnetic flux density B about the angular position of the stator winding for the electric motor having one magnetic pole pair, at an instant in time. As the magnetic rotor of the electric motor rotates in time, the magnetic flux density curve of <FIG> would be of the same shape but would move along the horizontal axis as the north and south poles rotate about the longitudinal axis <NUM> of the rotor <NUM>.

From <FIG>, and using Lenz's law (equation (<NUM>)), the torque T generated in the conventional stator winding <NUM> and the stator winding <NUM> of the present disclosure can be determined by using the relation: <MAT> which is essentially the area under the magnetic flux density curve in <FIG> multiplied by the respective coil usage functions in <FIG>. By definition, the torque constant kT is the torque T per unit current I, and thus the torque constant can be determined using the relation: <MAT>.

<FIG> shows the resulting torque constant KT generated in the conventional stator winding <NUM> (labelled as '1X Helical') and the stator winding <NUM> according to embodiments of the present disclosure (labelled as '2X Helical') for one complete torque cycle. Using a six-step direct current motor controller, one complete torque cycle spans <NUM>°. As can be seen in <FIG>, the torque constant for the double coil stator winding <NUM> is increased by about <NUM>% from that of the conventional stator winding <NUM> for one torque cycle of the electric motor. By 'about' what is meant is that this value is susceptible to variation by about <NUM>%, i.e. the increase in torque brought about by the double helical 'about' applies to any other recitation in the present disclosure. In some implementations of the present disclosure, the increase in torque may be at least about <NUM>%.

Table <NUM> shows representative data for two blood pumps having three-phase two-pole electric motors with single helical and double helical stator windings. Specifically, the single helical stator winding is similar to the conventional stator winding <NUM> as described in the foregoing, implemented with the helical winding type <NUM> as shown in <FIG>. The double helical stator winding is similar to the stator winding <NUM> as described in the foregoing, also implemented with the helical winding type. As can be seen, the double helical stator winding results in an electric motor with the same coil resistance of <NUM>Ω/phase as that of the conventional single helical winding, and with an increased torque constant of <NUM> × <NUM>-<NUM> N·m/A, i.e. an increase of <NUM>% from that of the conventional single helical winding. Noticeably, the average current in the coils of the double helical stator winding has decreased by about <NUM>%, thus indicating that the heating within the coils of the double helical stator winding has also decreased (as the coils resistance has not changed). The results in Table <NUM> confirm that the double helical stator winding according to embodiments of the present disclosure improves the efficiency of electric motors and hence blood pumps employing such stator windings. The blood pumps employing the above described stator windings comprising two coils per phase per permanent magnet pole pair are configured to operate at a flow rate of about <NUM> lpm and about <NUM> lpm, where 'lpm' indicates liters per minute.

The foregoing is merely illustrative of the principles of the disclosure, and the devices and methods can be practiced by other than the described implementations, which are presented for purposes of illustration and not of limitation. It is to be understood that the devices described herein, while shown in respect of a double helical stator winding of an electric motor for a blood pump, may be applied to other systems in which an electric motor with increased torque and high motor efficiency is desired. The invention as claimed, however, comprises all technical features defined in claim <NUM>.

In the foregoing disclosure, it will be understood that the term 'about' should be taken to mean ± <NUM>% of the stated value. Further, the term electric motor should be taken to be synonymous with the term electric machine, as is widely known in the art. All measure of degrees (with unit °) should be taken as mechanical degrees unless otherwise stated.

Claim 1:
An intravascular blood pump (<NUM>) for insertion into a patient's body, the pump (<NUM>) comprising:
an elongate housing (<NUM>) having a proximal end (<NUM>) connected to a catheter (<NUM>) and a distal end (<NUM>) connected to the pump (<NUM>), the housing (<NUM>) having a longitudinal axis (<NUM>); and
a slotless permanent magnet motor (<NUM>) contained within the housing (<NUM>), the motor (<NUM>) having p magnet pole pairs and n phases, where p is an integer greater than zero, and n is an integer ≥ <NUM>, the motor (<NUM>) comprising:
a stator winding (<NUM>; <NUM>; <NUM>; <NUM>) having 2np coils (<NUM>-<NUM>; <NUM>-<NUM>; <NUM>-<NUM>) wound to form two coils per phase per magnet pole pair such that a coil from each phase is circumferentially arranged next to a coil from a different phase in a sequential order of phase, the arrangement repeated along the stator winding (<NUM>; <NUM>; <NUM>; <NUM>) such that each coil of the 2np coils (<NUM>-<NUM>; <NUM>-<NUM>; <NUM>-<NUM>) spans <NUM>/(<NUM>np) mechanical degrees about a cross section of the stator winding (<NUM>; <NUM>; <NUM>; <NUM>), and
a permanent magnet rotor (<NUM>) supported for rotation and configured to generate a magnetic flux for interaction with the stator winding (<NUM>; <NUM>; <NUM>; <NUM>),
characterized in that the two coils per phase per magnet pole pair of the stator winding (<NUM>; <NUM>; <NUM>; <NUM>) are connected in series such that a direction of current flow through a first coil of the two coils is opposite to a direction of current flow in a second coil of the two coils, the current flow in the first coil and the current flow in the second coil interacting with opposite polarities of the magnetic flux of the rotor (<NUM>) for producing torque in the same direction, thereby facilitating rotation of the rotor (<NUM>) for a flow of blood through the pump (<NUM>).