BRIEF DESCRIPTION OF THE DRAWING
A better understanding of the present invention will be had upon reference to the following detailed description when read in conjunction with the accompanying drawing, wherein like reference characters refer to like parts throughout the several views, and in which:
FIG. 1 is a sectional view illustrating an exemplary electric motor of the type used in an HEV;
FIG. 2 is a plan view illustrating one embodiment of the present invention;
FIG. 3 is a view similar to FIG. 2, but illustrating an embodiment installed in an electric motor;
FIG. 4 is a view similar to FIG. 3, but illustrating a modification thereof;
FIG. 5 is a sectional view illustrating yet a further embodiment of the present invention;
FIG. 6 is a cross-sectional diagrammatic view illustrating yet a further embodiment of the present invention;
FIG. 7 is a sectional view taken substantially along line 7-7 in FIG. 6 and enlarged for clarity; and
FIG. 8 is a diagrammatic view illustrating an HEV vehicle.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE PRESENT INVENTION
With reference first to FIG. 1, a cross-sectional view of an electric motor 10 is shown of the type used in an HEV. The motor 10 includes a stator housing 12 which is grounded to a chassis 14 of an HEV by any conventional means, such as a grounding strap 16, metal bolts and the like. The stator housing 12, furthermore, supports the stator windings 18.
A rotor 20 having a rotor core 22 is rotatably mounted to the stator housing 12 by one or more conventional bearing assemblies 24 which typically include metal bearings such as ball bearings, spindle bearings, sleeve bearings and the like. Such metal bearings 24, however, may produce relatively high impedance at high radio frequencies, i.e. radio frequencies in the range of 500 kilohertz to 110 megahertz, due to bearing lubrication and the like. Such radio frequencies overlap the AM and FM radio bands.
The rotor 20 also includes a rotor output shaft 26 which is typically metal in construction. The rotor output shaft 26 is used to drive the load, such as the drive wheels in an HEV. Since the impedance between the rotor core 22 and the rotor shaft 26 is typically very low at high radio frequencies and then is negligible. It is desirable to reduce the impedance between the rotor core 22 and the stator housing 12 to reduce the emissions of EMI from the rotor output shaft 26.
With reference now to FIGS. 2 and 3, in a first embodiment of the invention, a metallic spring ring 30 is disposed between the rotor 20 and stator housing 12. This resilient ring 30 is dimensioned so that portions 32 of the ring 30 maintain contact with the rotor 20 while other portions 34 of the ring 30 maintain contact with the stator housing 12. In practice, such a ring 30, which may be made of spring metal, presents an electrical conductive path with a very low inductance and capacitance between the rotor 20 and the stator housing 12 at high radio frequencies thus effectively reducing the impedance between the rotor core 22 and the stator housing 12 at these high radio frequencies. In doing so, the ring 30 effectively shunts the radio frequency emissions which may be present on the rotor core 22 to the stator housing 12 and ultimately to the vehicle chassis 14. Thus, the ring 30 effectively reduces the ratio of the rotor core-stator housing impedance divided by the impedance between the rotor core 22 and the rotor output shaft 26.
With reference now to FIG. 4, a different embodiment of the ring 30′ is illustrated having a different shape than the ring 30 illustrated in FIGS. 2 and 3. However, the ring 30′ in FIG. 4 also includes portions 32′ which maintain electrical contact with the rotor 20 as well as outer portions 34′ which maintain electrical contact with the stator housing 12. The ring 30′ is also preferably constructed of spring metal and compressed between the rotor 20 and the stator housing 12. As such, the ring 30′ illustrated in FIG. 4 illustrates in the same fashion as the ring illustrated in FIGS. 2 and 3.
With reference now to FIG. 5, a still further embodiment of the present invention is shown in which at least one, and preferably several circumferentially spaced conductive brushes 40 are mounted within cavities 42 provided in the stator housing 12. Each cavity 42 is open to the rotor 20 while compression springs 44 are disposed between the brushes 40 and the stator housing 12 to urge the brushes 40 radially inwardly and into contact with the rotor 20. These springs 44 thus ensure electrical contact between the brushes 40 and the rotor 20 as well as a low impedance electrically conductive path between the brushes 40 and the rotor 20 at high radio frequencies.
Still referring to FIG. 5, in order to enhance the electrical contact between the brushes 40 and the stator housing 12, one or more spring clips 46 are optionally disposed in each cavity 42 so that the spring clips 46 contact one side of its associated brush 40. The spring clips 46 are preferably constructed of a spring metal material and resiliently urge the opposite side of its associated brush 40 into contact with the stator housing 12. In doing so, the spring clips 46 further reduce the impedance between the brush 40 and the stator housing 12 at high radio frequencies. Consequently, like the spring rings 30 and 30′ in FIGS. 2-4, the brushes 40 effectively reduce the impedance of the electrical path between the rotor core 22 and stator housing 12 at high radio frequencies.
With reference now to FIGS. 6 and 7, a still further embodiment of the present invention is shown in which a dielectric layer 50 is mounted to the stator housing 12 so that the dielectric layer 50 extends annularly around the rotor 20. The dielectric layer 50, furthermore, is dimensioned so that an air gap 52 is provided between the dielectric material 50 and the rotor 12.
The dielectric material which forms the dielectric layer 50 is selected and the air gap 52 is dimensioned such that the dielectric layer together with the rotor 26 and stator housing 12 forms a bypass capacitor at high radio frequencies. As such, the bypass capacitor exhibits a very low impedance at the high radio frequencies thus effectively reducing the impedance between the rotor core and the stator housing through the bypass capacitor.
With reference now particularly to FIG. 7, in order to provide optimum performance of the bypass capacitor, the dielectric layer 50 may have two or even more different thicknesses for the dielectric layer 50, as shown at zone 54 and zone 56. Similarly, the air gap 58 between the zone 54 and the rotor 26 may be different than an air gap 60 between the thicker zone 56 of the dielectric layer 50 and the rotor 20. In this fashion, the bypass capacitor may exhibit the characteristics of two different bypass capacitors, each having a different capacitance so that the bypass capacitor formed by the dielectric layer zone 54 may provide a very low impedance electrically conductive path at one high radio frequency range, e.g. 500 kilohertz to 1.7 megahertz corresponding to the AM radio band while other bypass capacitor formed by the dielectric zone 56 may exhibit low impedance electrically conductive path at a different radio frequency range, e.g. 98 to 109 megahertz or the radio frequency of the FM radio band.
With reference now to FIG. 8, an HEV 60 is illustrated having two drive wheels 62. The motor 10 is drivingly connected to the wheels 62 by the motor output shaft 26 and powers the HEV. A power inverter 64 is carried by the HEV and electrically powers the motor 10. Thus the present invention reduces EMI transmission from the output shaft 26 by providing an electrically conductive path between the rotor and stator housing with low impedance at high radio frequencies.
From the foregoing, it can be seen that the present invention provides a novel electric motor particularly suited for an HEV in which the impedance between the rotor and the stator housing is reduced at high radio frequencies. By doing so, radio frequency emissions which may be present on the rotor windings are shunted to the stator housing rather than transmitted as EMI from the rotor shaft.
Having described our invention, however, many modifications thereto will become apparent to those of skill in the art to which it pertains without deviation from the spirit of the invention as defined by the scope of the appended claims.
Patent Application
20080088187
