Electric Drive Unit

Abstract

An electric drive unit 100 comprising an alternating current, AC, motor; and a cover 102 mechanically coupled to the AC motor, the cover comprising an aperture for receiving AC busbars 110 for coupling the motor to an inverter 108, an annular cavity surrounding the aperture, and a common mode choke 106 disposed in the cavity. The choke may comprise a ring of material disposed in the annular cavity and surrounding the aperture. The cover may comprise a bulkhead 104 mechanically coupled to an end of the AC motor where the cover may further comprise an end cover mechanically coupled to the bulkhead, where the end cover comprises the aperture and the annular cavity. The motor may comprise terminals 114 for electrically coupling the motor to the AC busbars, where the terminals are enclosed within the cover and disposed adjacent to the aperture. The annular cavity may be disposed in an exterior surface of the cover. The drive unit may form part of an electric drive system comprising a rotor 112 arranged along a first axis where the AC busbars extend through the aperture in a direction perpendicular to the first axis, and where the drive unit and system may be used in a vehicle.

Description

TECHNICAL FIELD The present disclosure relates to an electric drive unit including a common mode choke. In particular, the present disclosure relates to an electric drive unit including a common mode choke disposed in an annular cavity of a cover of the electric device unit. Aspects of the invention relate to an electric drive unit, an electric drive system, and to a vehicle. BACKGROUND It is known to provide a means of filtering on the outputs of an inverter in an electric drive system in order to suppress electrical noise, or interference, generated in the inverter travelling through conductors coupling the inverter to an electric machine such as an AC motor. One way of providing such filtering is to use an AC common mode choke placed around AC busbars connecting the inverter to the electric machine. In known arrangements, the common mode choke is integrated into the inverter to provide noise suppression close to the source of the noise. The common mode choke is a passive electromagnetic device that may be formed in the shape of a ring arranged around the busbars. However, with improvements in inverter design and packaging, the inclusion of the common mode choke within the inverter may become a significant limit on the size and arrangement of the inverter. It is an aim of the present invention to address one or more of the disadvantages associated with the prior art. BRIEF SUMMARY Aspects and embodiments of the invention provide an electric drive unit, electric drive system and a vehicle as claimed in the appended claims. In one aspect, an electric drive unit includes an alternating current (AC) motor. The electric drive unit also includes a cover mechanically coupled to the AC motor, the cover includes an aperture for receiving a plurality of AC busbars for coupling the AC motor to an inverter, an annular cavity surrounding the aperture, and a common mode choke disposed in the annular cavity. Advantageously, providing a common mode choke as a feature disposed in an annular cavity of a cover / bulkhead attached to an AC motor, such that AC busbars to be connected to the motor are inserted through the common mode choke, facilitates an inverter design not including a common mode choke. This may provide significantly increased design freedom when designing and packaging the inverter, and a system including the inverter and motor, including allowing a more compact inverter design. Optionally, the common mode choke comprises one of a nanocrystalline, ferromagnetic or ferrite material. Advantageously, the position of the common mode choke in an annular cavity on a surface of a cover of the drive unit allows design freedom of material used according to any requirements of a particular use case. Optionally, the common mode choke comprises a ring of material disposed in the annular cavity and surrounding the aperture. Advantageously, the implementation of the common mode choke as a ring of material inserted into the annular cavity allows for easy modification (or even removal) of the common mode choke used depending on noise filtering requirements in a particular drive unit. Different choke specifications can easily be implemented by modifying the ring of material, e.g. through changing the number of layers of a nanocrystalline tape forming the ring of material, and the desired choke inserted into the annular cavity when assembling the electric drive unit. Optionally, the cover comprises a bulkhead, the bulkhead mechanically coupled to an end of the AC motor. Optionally, the cover comprises an end cover mechanically coupled to the bulkhead, wherein the end cover comprises the aperture and the annular cavity. Advantageously, the aperture and annular cavity may be incorporated into a bulkhead structure that may generally be present in electric drive unit designs, this may avoid any increase in part count, other than the choke itself, and further facilitates efficient use of space Optionally, the AC motor comprises a plurality of terminals for electrically coupling the AC motor to the plurality of AC busbars, the plurality of terminals enclosed within the cover and disposed adjacent to the aperture. Advantageously, positioning motor terminals inside the cover and adjacent to the aperture allows the length of the busbars to be minimized while still providing suitable space for the common mode choke, enabling efficient use of space. Optionally, the annular cavity is disposed in an exterior surface of the cover. Advantageously, providing the annular cavity in an exterior surface of the cover facilitates easy assembly of choke to a preassembled motor-cover assembly. This arrangement may allow for a reduction of stock keeping units (SKUs) by matching different chokes to a common motor-cover assembly according to requirements for a particular vehicle on which it is to be used. According to another aspect of the invention, there is provided an electric drive system comprising an electric drive unit as described above, the electronic drive system further comprising an inverter, and a plurality of AC busbars extending through the aperture and electrically coupling an AC output of the inverter to the AC motor. Advantageously, arranging the AC busbars that connect the inverter to the motor such that the busbars pass through the aperture, and therefore through the choke present in the annular cavity surrounding the aperture, allows the choke to filter common mode noise generated in the inverter that would otherwise be passed to the motor. This arrangement has been found to provides compact packaging allowing the common mode choke to be located in what might otherwise be unused space in the electric drive system. Optionally, the AC motor comprises a rotor arranged along a first axis, and wherein the plurality of AC busbars extend through the aperture in a direction perpendicular to the first axis. Optionally, the AC motor is a three-phase AC motor and the plurality of AC busbars comprises three AC busbars. The use of three-phase AC motors is common in electric drive applications. Advantageously, the disclosed arrangement is suitable for filtering common mode noise on three-phase AC busbars used in such applications. Optionally, the inverter is mechanically coupled to the electric drive unit. Advantageously, mechanically coupling the inverter to the electric drive unit may allow for compact packaging of the electric drive system. Optionally, the annular cavity comprises a first portion, the common mode choke disposed in the first portion, and a second portion disposed between the first portion and the exterior surface of the cover, and wherein the inverter comprises a protrusion, the protrusion positioned within the second portion of the annular cavity when the inverter is coupled to the electric drive unit. Advantageously, providing a protrusion on the inverter arranged to fit within a second portion of the annular cavity, and thereby provide an overlap between the inverter casing and the cover of the electric drive unit, may provide shielding of noise present on the busbars between the inverter and the common mode choke. Furthermore, by arranging the protrusion to abut the common mode choke, the choke may be securely held in place within the first portion of the annular cavity without requiring use of any further components. According to another aspect of the invention, there is provided a vehicle including an electric drive unit or an electric drive system as described above. According to another aspect of the invention, there is provided a method of providing a common mode choke to filter common mode noise in an electrical drive system for a vehicle, the method comprising, connecting a cover to an AC motor, the cover comprising an aperture and an annular cavity surrounding the aperture, positioning a common mode choke comprising a ring of material into the annular cavity surrounding the aperture, and electrically coupling an inverter to the AC motor, wherein electrically coupling the inverter to the AC motor comprises inserting a plurality of AC busbars electrically coupled to the inverter through the aperture. Advantageously, in a method of providing a common mode choke as a feature disposed in an annular cavity of a cover or bulkhead attached to an AC motor, and then inserting a plurality of AC busbars to be connected to the motor are through the common mode choke, an inverter design not including a common mode choke may be used. This may provide significantly increased design freedom when designing and packaging the inverter, and a system including the inverter and motor, including allowing a more compact inverter design. Optionally, the method further comprising electrically coupling each of the plurality of AC busbars to a respective one of a plurality of terminals of the AC motor, wherein the plurality of terminals are enclosed within the cover and disposed adjacent to the aperture. Advantageously, positioning motor terminals inside the cover and adjacent to the aperture allows the length of the busbars to be minimized while still providing suitable space for the common mode choke, enabling efficient use of space. Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and / or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and / or features of any embodiment can be combined in any way and / or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and / or incorporate any feature of any other claim although not originally claimed in that manner. BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: FIG. 1 shows an end view of an electric drive unit coupled to an inverter in accordance with an embodiment of the invention; FIG. 2 shows an isometric view of the electric drive unit coupled to the inverter in accordance with an embodiment of the invention; FIG. 3 shows a side view of the electric drive unit in accordance with an embodiment of the invention; FIG. 4 shows a side view of the electric drive unit coupled to the inverter in accordance with an embodiment of the invention; FIG. 5A-C illustrates a steps for assembling an inverter to an electric drive unit including installing a common mode choke in the electric drive unit in accordance with an embodiment of the invention; FIG. 6 shows a vehicle in accordance with an embodiment of the invention; and FIG. 7 illustrates a method of providing common mode choke in an electric drive system for a vehicle in accordance with an embodiment of the invention. DETAILED DESCRIPTION In the following detailed description, reference is made to the accompanying figures that form a part hereof, and in which are shown by way of illustration specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that structural, logical, and electrical changes may be made without departing from the scope of the present invention. The sequence of operations is not limited to that set forth herein and may be changed as will be apparent to those skilled in the art, with the exception of operations necessarily occurring in a certain order. With reference to Figure 1 an electric drive unit 100 is illustrated wherein the electric drive unit comprises an integrated alternating current (AC) common mode choke, or common mode choke, according to an embodiment of the invention. As illustrated, the electric drive unit 100 includes an electric machine, such as an AC motor, including rotor 112. A 4 cover 102 is mechanically coupled to the electric machine, covering one end of the electric machine. A bulkhead 104 may be provided between the cover 102 and the electric machine. As illustrated in Figure 1, the cover 102 includes an aperture for receiving a plurality of AC busbars 110 for coupling the electric machine to an inverter 108. An annular cavity is provided in a surface of the cover 102 surrounding the aperture and a common mode choke 106 is disposed in the annular cavity. While in Figure 1 only a portion of the common mode choke 106 is illustrated for clarity, it will be understood that the common mode choke 106 could be implemented as a ring structure. In an electric drive system, an inverter 108 may be attached to the electric drive unit 100 and electrically coupled to the electric machine via a plurality of AC busbars 110. Each of the AC busbars 110 may be coupled to a corresponding one of a plurality of terminals 114 of the electric machine. The busbars 110 are arranged to pass through the aperture in the cover 102. Thus, the AC busbars 110 may be arranged to pass through a centre of the common mode choke 106, as well as the annular cavity, allowing the AC common mode choke 106 to provide for suppression of at least some common mode noise present on the busbars 110. Thus, a common mode choke 106 can be integrated into a cover 102 of the electric machine, rather than implemented within the inverter 108. This configuration allows the common mode choke 106 to be arranged within otherwise unused space within the electric drive unit 100, while allowing more efficient packaging of the inverter 108. Therefore, this arrangement facilitates more compact packaging of the inverter 108 with the electric drive unit 100 and thereby provides for a more efficient overall use of space in the assembled electric drive system. A common mode choke may be a passive electromagnetic device that is able to filter a high-frequency noise signal present on multiple conducting elements, i.e. a high-frequency noise signal that is common to the signals present on multiple wires or busbars. The frequency range filtered by the common mode choke can be controlled based on the size and configuration of the common mode choke. For example, the common mode choke may be implemented as a ring of material, or core, surrounding the multiple conducting elements, such as the AC busbars 110 illustrated in Figure 1. The common mode choke may comprise a ferromagnetic or ferrite material or may be formed from a nanocrystalline magnetic alloy, for example an FeCuNbSiB alloy. In embodiments, the common mode choke may be manufactured by winding a nanocrystalline tape to form a desired size and shape. In embodiments, the cover may include the bulkhead 104, with the bulkhead 104 mechanically coupled to an end of the electric machine. The cover may further include the end cover 102 mechanically coupled to the bulkhead 104 and with the aperture and annular cavity formed in the end cover 102. In embodiments, rotor 112 has an axis of rotation along a first axis and the plurality of busbars extend through the aperture in a direction perpendicular to the first axis. The electric machine may be an AC motor, more particularly a three-phase AC motor and the plurality of busbars 110 may comprise three AC busbars. Figure 2 provides an isometric view of the electric drive unit 100 coupled with the inverter 108 as illustrated in Figure 1. Figure 3 shows a side view of the electric drive unit 100 prior to coupling of the electric drive unit 100 with the inverter 108. As illustrated in Figure 3, the electric drive unit 100 may be coupled to a main drive unit housing 118 incorporating 5 further components such as one or more gears of a transmission associated with the electric drive unit 100 to allow mechanical power to be transferred to one or more wheels of an electric vehicle. As can be seen in Figure 3, an aperture 116 is provided through the cover 102 of the electric drive unit 100. The aperture 116 is substantially adjacent to the AC motor terminals 114 which are enclosed within the end cover 102. The AC common mode choke 106 is disposed in an annular cavity on an exterior surface of the end cover 102, and surrounds the aperture, such that a space is provided through the cover 102, and through a centre of the AC common mode choke 106, to receive the AC busbars 110 to allow the inverter 108 to be electrically coupled with the electric machine. Figure 4 provides the same side view of the electric drive unit 100 of Figure 3 following mechanical coupling of the inverter 108 to the electric drive unit 100. As illustrated in Figure 4, when the inverter 108 is installed to the electric drive unit 100, the AC busbars 110 coupled to the inverter 108 extend through the aperture 116, and through the centre of the common mode choke 106. The busbars 110 can then be coupled to the electric machine via the plurality of terminals 114. Figure 5A-C illustrates a process of assembling an electric drive system including the electric drive unit 100 and the inverter 108. In a first stage 5A of assembly, the electric machine may be provided mechanically coupled to the end cover 102. The end cover 102 includes the aperture 116 arranged proximate to the plurality of terminals 114 of the electric machine. In an exterior surface of the end cover 102, an annular cavity 120 is provided surrounding the aperture 120. In a second stage 5B of assembly, the common mode choke 106 is inserted into the annular cavity 120. In a third stage 5C of assembly, the inverter 108 is mechanically coupled to the electric drive unit 100. The AC busbars 110 associated with the inverter 108 are inserted through the aperture 116 in the cover 102 and coupled to the terminals 114. In embodiments a protruding portion of an inverter assembly may be provided surrounding the busbars 110, wherein the common mode choke 106 is disposed in a first portion of the annular cavity 120, a second portion of the annular cavity 120 disposed between the first portion and the exterior surface of the cover 102. Upon mating of the inverter 108 to the electric drive unit 100, the protruding portion is inserted into the second portion of the annular cavity. A vehicle 600 in accordance with an embodiment of the present invention is described herein with reference to the accompanying Figure 6. The vehicle 600 includes an electric drive unit 100 in accordance with examples of the present invention. The vehicle 600 in the present embodiment is an automobile, such as a wheeled vehicle, but it will be understood that the electric drive unit 100 may be used in other types of vehicle, such as aircraft, watercraft, etc. as well as in other devices including an electrically powered motor. Figure 7 illustrates a method 700 of providing a common mode choke to filter common mode noise in an electric drive system for a vehicle. According to the method of Figure 7, a cover is provided including an aperture 116 and an annular cavity 120 surrounding the aperture 116 and the cover is connected 710 to an AC motor. A common mode choke 106 is positioned 720 into the annular cavity 120. An inverter 108 is then electrically coupled 730 to the AC motor. Electrical coupling of the inverter 108 to the AC motor is achieved by inserting a plurality of AC busbars 110, coupled to the inverter 108, through the aperture 116 and through a centre of the common mode choke 106. Electrical connection between the inverter 108 and the AC motor can be completed by electrically coupling each of the plurality of AC busbars 110 to a corresponding one of a plurality of terminals 114 of the AC motor. The plurality of terminals 114 may be enclosed within the cover and disposed adjacent to the aperture 116. It will be appreciated that various changes and modifications can be made to the present invention without departing 5 from the scope of the present application.

Claims

1. An electric drive unit comprising:an alternating current, AC, motor; anda cover mechanically coupled to the AC motor, the cover comprising:an aperture for receiving a plurality of AC busbars for coupling the AC motor to an inverter;an annular cavity surrounding the aperture; anda common mode choke disposed in the annular cavity.

2. The electric drive unit of claim 1, wherein the common mode choke comprises a ring of material disposed in the annular cavity and surrounding the aperture.

3. The electric drive unit of claim 1 or 2, wherein the cover comprises a bulkhead, the bulkhead mechanically coupled to an end of the AC motor.

4. The electric drive unit of claim 3, wherein the cover further comprises an end cover mechanically coupled to the bulkhead, wherein the end cover comprises the aperture and the annular cavity.

5. The electric drive unit of any one of claims 1 to 4, wherein the AC motor comprises a plurality of terminals(114) for electrically coupling the AC motor to the plurality of AC busbars, the plurality of terminals enclosed within the cover and disposed adjacent to the aperture.

6. The electric drive unit of claim 5, wherein the annular cavity is disposed in an exterior surface of the cover.

7. An electric drive system comprising the electric drive unit of any one of claims 1 to 6, the electric drive system further comprising:an inverter; anda plurality of AC busbars extending through the aperture and electrically coupling an AC output of the inverter to the AC motor.

8. The electric drive system of claim 7, wherein the AC motor comprises a rotor arranged along a first axis; and wherein the plurality of AC busbars extend through the aperture in a direction perpendicular to the first axis.

9. The electric drive system of claim 7 or 8, wherein the AC motor is a three-phase AC motor and the plurality of AC busbars comprises three AC busbars.

10. The electric drive system of any one of claims 7 to 9, wherein the inverter is mechanically coupled to the electric drive unit.

11. The electric drive system of claim 10, wherein the annular cavity comprises a first portion, the common mode choke disposed in the first portion, and a second portion disposed between the first portion and the exterior surface 5 of the cover; andwherein the inverter comprises a protruding portion, the protruding portion positioned within the second portion of the annular cavity when the inverter is coupled to the electric drive unit.

12. A vehicle comprising the electric drive unit of any one of claims 1 to 6 or the electric drive system of any one of claims 7 to 11.

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