Patent Application
20100247229
The present invention generally relates to vehicular electric machines, and more particularly relates to an end ring for a vehicular electric machine.
In recent years, advances in technology have led to substantial changes in the design of automobiles. One of these changes involves the complexity, as well as the power usage of various electrical systems within automobiles, particularly those within alternative fuel vehicles. For example, alternative fuel vehicles such as hybrid vehicles often use electrochemical power sources, such as batteries, ultracapacitors, and fuel cells, to power the electric traction machines (or motors) that drive the wheels, sometimes in addition to another power source, such as an internal combustion engine.
Such electric traction machines typically include an annular rotor assembly that rotates axially on a shaft or hub within a stationary stator assembly. The rotor assemblies are configured to generate magnetic flux either inductively by using electromagnets or, in the case of an internal permanent magnet machine (IPM), by using a multitude of permanent magnets arrayed within a central magnetic core. To retain the permanent magnets axially within the central magnetic core, end rings are mounted on the shaft or hub at the end of the rotor core. To prevent shorting of the magnetic flux from the core region of an IPM, the end rings are fabricated from a low permeability, non magnetic material such as stainless steel or aluminum. Such end rings typically have a planar, annular, disc-like geometry, and are often fabricated from powdered metals using a sintering process or machined from a blank. Prior to installation on the shaft, the rings are machined over a significant portion of their surface area to remove surface roughness and achieve desired features. In addition, because end rings are typically mounted onto shafts using a friction mount, further precise machining of the inner circumference of the ring is also important to ensuring a tight and secure fit suitable for operation at high rates of rotation.
Accordingly, it is desirable to provide an end ring for a vehicular electric machine that requires less finish machining and is fabricated from lower cost, lighter weight materials. It is also desirable if such an end ring has greater stiffness and rigidity and is configured for improved retention of bonded permanent magnets. Further, for hub-mounted rotor assemblies, it is also desirable if the end ring provides increased protection from magnetic flux shorting while enhancing coolant flow between the rotor and the hub without increased ring weight. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.
In accordance with an embodiment, by way of example only, an end ring for a rotor assembly in a vehicular electric machine is provided. The rotor assembly has a first end and is configured to rotate on a shaft. The end ring comprises an annulus circumscribing the shaft and engaging the first end of the rotor assembly, and a sleeve coupled to the annulus and circumferentially coupled to the shaft.
In accordance with another embodiment, by way of example only an end ring of a type suitable for deployment in a vehicular electric machine is provided. The electric machine has a rotor assembly configured to rotate with a hub assembly, the hub assembly including a sleeve portion about which the rotor assembly is circumscribed and including a flange having a first surface and extending radially outward from an end of the sleeve portion. The end ring comprises an annular ring having a second surface configured to reside adjacent the first surface and having a third surface configured to reside adjacent an end of the rotor assembly, and a first protrusion extending from the second surface and configured to engage the first surface so as to separate the first surface from the second surface.
A more complete understanding of the present invention may be derived by referring to the detailed description and claims when considered in conjunction with the following figures, wherein like reference numbers refer to similar elements throughout the figures, and
The various embodiments of the present invention described herein provide an end ring for a rotor assembly of an electric machine suitable for deployment on a vehicle. The electric machine may be, for example, an internal permanent magnet machine and may comprise an electric generator or an electric motor, or a combination of these (motor/generator). The end ring is stamped from a single layer of a low magnetic permeability metal made from rolled metal sheet. The end ring is also configured with features that facilitate assembly procedures and enhance machine performance and efficiency during operation. These features, described in detail below, result in reduced shorting of magnetic flux, increased stiffness, enhanced coolant flow, a more secure retention for permanent magnets during bonding to the rotor core, alignment indexing of the end ring to the rotor core to facilitate assembly, and improved coupling between the end ring and the shaft or hub to enhance reliability when operating at elevated temperatures and high rates of rotation.
The automobile 10 may be any one of a number of different types of automobiles, such as, for example, a sedan, a wagon, a truck, or a sport utility vehicle (SUV), and may be two-wheel drive (2WD) (i.e., rear-wheel drive or front-wheel drive), four-wheel drive (4WD), or all-wheel drive (AWD). The automobile 10 may also incorporate any one of, or combination of, a number of different types of engines (or actuators), such as, for example, a gasoline or diesel fueled combustion engine, a “flex fuel vehicle” (FFV) engine (i.e., using a mixture of gasoline and alcohol), a gaseous compound (e.g., hydrogen and/or natural gas) fueled engine, or a fuel cell, a combustion/electric motor hybrid engine, and an electric motor.
In the exemplary embodiment illustrated in
In one embodiment, first annulus 66 and first sleeve 70 are integrally joined together. As used herein, the term “integrally joined” or “integrally formed” means that a first element, (such as first annulus 66) extends or transitions in a continuous manner from a second element, (such as first sleeve 70) and not as two separate and distinguishable elements. First sleeve 70 is mounted substantially concentrically to the outer surface of shaft 54 by, for example, press/interference fitting. First annulus 66 has an inner face that engages the end of rotor assembly 50 adjacent to an end of magnet array 58. First annulus 66 comprises a low magnetic permeability material and provides axial (along any line substantially parallel to axis A-A′) retention to magnet array 58 containing magnetic flux generated by these magnets within rotor assembly 50, and improving the efficiency of electric machine assembly 32 thereby. Second end ring 38 is also fabricated from a suitable low magnetic permeability metal and is configured similarly to first end ring 34, and includes a second annulus 74 integrally joined to a second sleeve 78. Second annulus 74 is configured to provide axial retention to magnets disposed proximate a second end 82 of rotor assembly 50, and second sleeve 78 mounts by interference fit circumferentially to shaft 54.
During operation, rotor assembly 50 rotates with shaft 54 about axis A-A′ substantially concentrically within stator assembly 46 generating mechanical energy thereby. End rings 34 and 38 rotate with rotor assembly 50, each ring providing axial retention to magnet array 58, and containing magnetic flux generated by these magnets within rotor assembly 50. As will be described in detail below, first and second sleeves 70 and 78 provide end rings 34 and 38, respectively, with secure coupling to shaft 54 even at elevated operating temperatures and high rates of rotation.
First sleeve 70 is press/interference fit circumferentially over the outer cylindrical surface 92 of shaft 54, and is non-planar with first annulus 66. First sleeve 70 may extend away from annulus 66 along shaft 54 by any suitable distance without limitation. In one embodiment, sleeve 70 assumes the form of a flaring of inner circumferential edge 86. In another embodiment, sleeve 70 is tapered having a diameter that decreases with distance away from annulus 66 to facilitate mounting and interference fitting onto shaft 54. Such an interference mount in conjunction with the increased circumferential contact of a sleeve design helps to provide a more secure fit at elevated temperatures and high rotation speeds. In a further embodiment, sleeve 70 also includes a tab 94 configured to engage a keyway or groove 95 machined into surface 92 of shaft 54. Tab 94 provides additional rotational support to end ring 34 preventing sleeve 70 from rotating with respect to shaft 54 including during operation at elevated temperatures.
Referring to
In one embodiment, end ring 166 includes at least a first protrusion 178 on a side adjacent the flange portion end 170, and having a cavity 182 on a side adjacent magnet array 150. Protrusion 178 is configured to separate flange portion end 170 from magnet array 150 and lamination core 146 by creating an air gap 190 that increases the magnetic shielding of end ring 166. In another embodiment, cavity 182 engages with a first magnet 194 of magnet array 150 providing axial (along any line substantially parallel to rotational axis B-B′) retention thereto. While end ring 166 is shown in
The various embodiments of the present invention described herein provide an end ring for a vehicular electric machine. The end ring includes an annular ring (or annulus) configured to retain permanent magnets axially within the magnet array of an IPM. The annular ring may be coupled to a hub assembly or to a motor shaft. In the case of a hub assembly, the annular ring is coupled to a cylindrical mounting surface within the assembly. When shaft-mounted, the annular ring is coupled to a sleeve configured for interference mounting to the outer surface of the shaft. The end ring is fabricated from high mechanical strength, low magnetic permeability rolled sheet metal which reduces the need for surface finishing, thereby reducing material and machining expense. In various embodiments, the annular ring and sleeve (if used) have additional features for enhancing performance and facilitating machine assembly. Features associated with the annular ring include an indexing tab configured to engage with a keyway in the hub core to aid with core/end ring alignment during assembly. The annular ring may also have protrusions/cavities configured for various performance enhancing functions including: 1) providing additional spacing between permanent magnets and the hub end without adding weight to the ring, 2) adding rigidity to the annular ring for enhanced resilient retention of permanent magnets, 3) providing a coolant flow passage between the hub and annular ring. The annular ring may also have integrally formed tabs configured to retain individual permanent magnets during bonding to the rotor core. The sleeve is configured for a more secure mount to the shaft and may include tapering to suit this purpose. The sleeve may also include a tab configured to engage with a shaft keyway to prevent slippage at elevated temperatures and high rates of rotation.
While at least one example embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the example embodiment or embodiments described herein are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing the described embodiment or embodiments. It should be understood that various changes can be made in the function and arrangement of elements without departing from the scope of the invention and the legal equivalents thereof.
