Axial flux motor assembly

[0001] The present application is a continuation-in-part of co-pending U.S. patent application Ser. No. 10/116,974, filed on Apr. 5, 2002, from which priority is claimed.

[0002] Not Applicable.

[0003] The present invention relates generally to a vehicle driveline support assembly and, more particularly, to a vehicle driveline support assembly incorporating a pair of electric motors wherein the driveline support, the pair of electric motors, and a pair of speed reduction transmissions are combined into a single compact power unit with two independent co-axial output shafts which may be independently controlled for speed and torque.

[0004] A variety of driveline support assemblies are known in the art that utilize electric motors to power a driveline or vehicle wheel when accelerating or maintaining driveline motion, or to generate electricity from the driveline's kinetic energy when decelerating. In the past, these systems have used separate bearings for the electric motor, the driveline support and the speed reduction transmission. However, using separate bearings only adds the cost and weight of the assembly and causes the assembly to be less compact. The present invention solves this problem by reducing the number of bearings required in order to make the driveline support assembly lighter, more compact and less expensive to manufacture.

[0005] Briefly stated, the present invention provides an assembly comprising a pair of electric motors and a pair of speed reduction transmissions within a single electric motor case and a driveline support. Each electric motor comprises a stator and a rotor, wherein the rotor is connected to a rotor shaft. A rotor support bearing rotatingly supports each rotor shaft. A driveline support supports a pair of hubs rotatably attached to the housing by a bearing. A case is attached to the housing and supports each stator and an associated speed reduction transmission. Each speed reduction transmission comprises a sun element, at least two planetary elements and an outer ring element attached to the case. Each rotor shaft is attached to a hub through an associated speed reduction transmission. Finally, each rotor shaft, speed reduction transmission, and hub are supported solely by the rotor support bearing, the driveline support bearing, and the outer ring element of the case. A shoulder portion of each rotor shaft abuts an end of the rotor support bearing such that a desired air gap is maintained between each rotor and associated stators.

[0006] The foregoing and other objects, features, and advantages of the invention as well as presently preferred embodiments thereof will become more apparent from the reading of the following description in connection with the accompanying drawings.

[0007] In the accompanying drawings which form part of the specification:

[0008] FIG. 1 is a section view of an integral wheel bearing and axial flux motor having one stator;

[0009] FIG. 2 is a perspective view of a rotor of an axial flux electric motor shown in FIG. 1;

[0010] FIG. 3 is a section view of the rotor of FIG. 2 along line A-A;

[0011] FIG. 4 is a perspective view of a stator of an axial flux electric motor shown in FIG. 1;

[0012] FIG. 5A is a front plan view of the stator of FIG. 4, including windings and an attached case;

[0013] FIG. 5B is a front plan view of the stator of FIG. 4, including an alternate simplified winding arrangement;

[0014] FIG. 6 is a section view of an integral wheel bearing and axial flux motor having two stators;

[0015] FIG. 7A is a section view of a pair of combined axial flux motors, each having one stator according to an embodiment of the present invention;

[0016] FIG. 7B is an enlargement of section 7B, shown in FIG. 7A;

[0017] FIG. 8A is a section view of a pair of combined axial flux motors, each having two stators according to an embodiment of the present invention; and

[0018] FIG. 8B is an enlargement of section 8B, shown in FIG. 8A;

[0019] Corresponding reference numerals indicate corresponding parts throughout the several figures of the drawings.

[0020] The following detailed description illustrates the invention by way of example and not by way of limitation. The description clearly enables one skilled in the art to make and use the invention, describes several embodiments, adaptations, variations, alternatives, and uses of the invention, including what is presently believed to be the best mode of carrying out the invention.

[0021] The present invention comprises an integral wheel support, planetary transmission and electric motor assembly requiring only two support bearings: a wheel support bearing and a rotor support bearing. Referring to FIG. 1, the assembly 10 comprises a wheel bearing 12 of conventional design. The wheel bearing 12 comprises a housing 14 and a hub 16. Located between the housing 14 and the hub 16 are two rows of tapered rollers 18 that allow the hub 16 to rotate within the housing 14. While tapered rollers are shown and preferred, other types of rollers may be used without departing from the scope of the present invention. The hub 16 may be attached to a wheel (not shown) with lugs 20. The bearing is a package wheel bearing that has all clearances preset upon assembly.

[0022] The hub 16 further defines a splined interior bore 22 for accepting a splined shaft 24. The splined shaft 24 extends from a planetary carrier 26 of a conventional gear drive planetary transmission. The planetary carrier 26 is rotatingly attached to three planetary gears 28 by bearings 38. The planetary gears 28 mesh with a stationary outer ring gear 32 formed on an inner surface of a planetary transmission case 30. The planetary transmission case 30 is attached to the wheel bearing 12 by fasteners 34. The planetary transmission case 30 further defines a vent bore 36.

[0023] A sun gear 40 meshes with all three planetary gears 28. The sun gear 40 defines a center bore 42 for receiving a rotor shaft 44. A key 46 prevents relative rotation of the sun gear 40 and the rotor shaft 44. The rotor shaft 44 is rotatingly supported within a motor case 47 by a rotor bearing 48. The rotor bearing 48 comprises two rows of tapered rollers 50 between inner races disposed on the rotor shaft 44. Between a first shoulder 52 of the rotor shaft 44 and the sun gear 40 is located a sun gear spacer 54 which locates the sun gear 40 within the planetary gears. Between a second shoulder 56 of the rotor shaft 44 and the rotor bearing 48, is an air gap washer 58. By controlling the thickness of the air gap washer 58, the axial position of the rotor shaft is manipulated and thus an air gap between a rotor 60 and stator 62 is adjusted. The stator 62 is attached to the motor case 47, and the rotor 60 is attached to the rotor shaft 44.

[0024] Referring to FIG. 2 and FIG. 3, the rotor may be made from low carbon steel. The rotor 60 has several permanent magnets 72 attached by an acrylic adhesive, such as Loctite Multibond acrylic adhesive available from the Loctite Corporation, Rocky Hill, Conn. The magnets 72 are spaced apart by nonmetallic spacers 74. The magnets 34 are preferably neodymium-iron-boron (NdFeB) type permanent magnets and the number of magnets determines the number of poles of the motor (i.e. if twelve magnets are adhered to the rotor, the motor has twelve poles). The magnets 72 are attached to the rotor 60 with their north-seeking faces and south-seeking faces outwardly arranged in an alternating sequence.

[0025] Referring to FIG. 4, the stator 62 comprises a plurality of laminations. More specifically, the stator 62 comprises laminations of ferrous material, preferably iron, that are separated by non-conducting, non-ferrous layers to minimize losses due to eddy currents of magnetic flux within the stator 62. The stator 40 further comprises thirty-six slides 76 defined by thirty-six grooves 78. As shown in FIG. 5A, conductive windings 80 comprising loops of insulated copper wire are placed within the grooves 78 and around the slides 76 such that each winding 80 forms a loop surrounding two intervening grooves 78. Another winding 80 is placed within a groove 78 a portion of which surrounded by the first winding 80 and a groove 78 adjacent the first winding 80. In this manner, windings 80 are placed within the grooves 78 of the stator 80 until every groove 78 has been fitted with a winding 80. FIG. 5B illustrates an alternative simplified winding pattern using a reduced quantity of material.

[0026] Referring back to FIG. 1, the rotor shaft 44 further comprises a rotor shaft extension 66 that extends within a bore of a resolver 68. An end plate 64 is attached to the motor case 47 and supports the resolver 68. A cover plate 70 covers a bore within the end plate 64 that allows access to the resolver 68 without removing the end plate 64.

[0027] The motor operates in a conventional manner for a brushless axial flux induction motor, and changing the thickness of the air gap washer 58 changes the air gap of the axial flux electric motor. The motor is controlled by a known electronic controller that adjusts the pulse width and frequency of current traveling through the wire loops of the stator in order to control the torque and speed of the motor and maintain current within motor limitations.

[0028] An alternate embodiment 100 shown in FIG. 6 includes a rotor 132 having magnets 134 affixed to opposite sides of the rotor 132 by an adhesive. Adjacent magnets 134 on opposite sides of the rotor are aligned so that their opposite poles face outwardly from the rotor 132. In addition to the stator 40 and the windings 44 is a second stator 140 and a second plurality of windings 144 wound within the second stator 140. By adding the second stator 140 and windings 144, the output of the axial flux motor is nearly doubled.

[0029] In a compact power unit embodiment 200, shown in FIGS. 7A and 8A, a pair of axial flux motor assemblies 10 or axial flux motor assemblies 100, as described in detail above, are coupled together in mirrored or back-to-back alignment with a common end plate 202. The common end plate 202 includes an axial bore 204, shown in FIGS. 7B and 8B for supporting a pair of resolvers 68 and for receiving the rotor shaft extension 66 from each rotor shaft 44 in the compact power unit 200. Stator cooling connections 206 are secured to each motor case 47 to carry out heat generated by the windings 80 during heavy duty cycles.

[0030] The compact power unit 200 provides two identical independent output hubs 16, having a common axis of rotation A-A, onto which a pair of drive axles or wheels (not shown) may be secured. The compact power unit 200 is suitable for mounting at an axle centerline of a vehicle to drive either directly or indirectly, a pair of vehicle wheels on opposite sides of the vehicle. Each assembly 10, 10 or 100, 100 in the compact power unit 200 is independently controllable as described above, to regulate speed and torque at each independent output hub 16.

[0031] Independent speed and torque control for opposite wheels is desirable when road surface variations at each wheel produce different coefficients of friction, as the lower wheel driving torque of the two wheels limits the effective driving torque to twice the lowest wheel torque. The application of torque in excess of the lowest wheel torque level results in spinning of the vehicle wheel. Accordingly, when driving in uneven terrain having varied surface coefficients of friction, it is highly desirable to match the driving power supplied to each individual driven wheel to different driving requirements. Driving the driven wheels of a vehicle at different speeds and individually controlling the driving torque when traveling on a slippery surface or around a curve has the distinct advantages of avoiding vehicle deformation, reducing tire wear, attaining improved traction, and enhancing vehicle dynamic stability.

[0032] In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results are obtained. As various changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.