Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2002-09-26
2004-08-17
Mullins, Burton (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S06800R, C310S181000, C310S198000, C310S268000
Reexamination Certificate
active
06777838
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to electric motors and, more particularly, to direct current electric motors suitable for reliably and efficiently powering electric vehicles and industrial machinery.
2. Description of Related Art
There are numerous electric motors available for propelling electric automobiles. These include both direct current (DC) motors designed to drive directly off of the batteries and alternating current (AC) motors which require electrical circuitry for converting the DC power in the batteries to AC power. The most efficient of these AC motors requires three or more phase power.
Such motors have a high power-to-weight ratio, can be made to run efficiently, and are inherently reliable because of their brushless design. A disadvantage of such motors is the fact that the battery power must be first converted to AC before it can be used by the motor. This disadvantage shows up in the need for complex circuitry. This is especially true for AC motors having three or more phases. Along with the need for complex circuitry is the fact that the failure of even a single electrical component in the system can result in total failure of the drive circuitry for producing AC power. This results in DC electric power in the batteries, and a motor that requires AC power. This renders the entire drive system useless.
Therefore, such drive systems suffer from the potential of leaving the driver stranded. Despite these obstacles, companies such as AC Propulsion Inc. have made considerable advances in the use of AC motors in electric cars. In particular, high power to weight ratios have been achieved.
In the powering of industrial machinery, in many applications it is desirable to have an electric motor that has considerable amounts of torque and power at relatively low RPM values. This is normally achieved by gearing the motor down, however this practice results in added moving parts, increased mechanical losses, and adds cost and complexity to the overall system. In general DC electric motors have good torque characteristics which make them ideal for use in many industrial applications. In general with DC electric motors, the more mechanical drag on the motor, the more torque is produced. In this respect such motors are ideal for propelling electric cars as well. This is especially true if one wants to drive the wheels of such a vehicle directly by employing a motor in the wheel hub. There are several reasons why DC electric motors are advantageous.
DC electric motors require little circuitry to drive them from batteries. In some cases they can be wired directly with only a switch to turn the system on and off. Another advantage offered by DC electric motors is the fact that such motors do not require starting circuitry in the way that many AC motors do.
The first electric cars were produced at the turn of the century and were powered by DC electric motors. Such motors utilized two sets of electromagnets to produce their torque. One set was mounted to the inside of the motor casing. These electromagnets had one set of poles facing inward, and the other set of poles against the steel casing to magnetically connect them in series. The motor casing with its electromagnets made up the stator portion of the motor. When power was on, these electromagnets maintained the same field. At each end of the motor casing were end caps having holes which were centrally located which supported a bushing or bearing through which the rotational portion (or rotor) was supported. The rotor consisted of a round shaft having a larger diameter set of electromagnet windings wound onto an iron core. The ends of the rotor windings were fixed to conductive copper strips that were insulated from each other and the motor casing using resin or other suitable insulating material. A set of brushes which were usually made of graphite pushed up against the copper strips in the rotor to make electrical contact while also allowing the rotor to rotate. The position of the brushes relative to the stator electromagnet windings was always set so that the proper rotor electromagnets were turned on at the appropriate times by the brushes to always magnetically drive the rotor in the same direction (i.e., by interaction of the stator magnetic field with the magnetic field of the electromagnets in the rotor).
While these motors were suitable for powering both electric cars, as well as industrial equipment, Their efficiency was somewhat limited by the fact that power losses occurred in both sets of electromagnets due to the resistance of their windings.
In the early 1930s, the General Electric Company developed the first permanent magnets that were strong enough to replace one set of electromagnet windings in DC motors. This Permanent magnet material was called Alnico, and soon several grades were made commercially available. Shortly thereafter, the first useful permanent magnet motors began to appear. These motors basically used permanent magnets to replace the stator electromagnets. While these motors had an increased efficiency when compared to their predecessors, they suffered from the possibility of demagnetization of the permanent magnets if the electromagnetic field in the rotor exceeded the “coercive force” (a measure of the resistance to demagnetization of permanent magnets) of the permanent magnets in the stator. To partially alleviate this problem, stronger ceramic permanent magnets were developed, and still stronger magnets called “Rare Earth Magnets” are among the most recent developments.
All DC permanent magnet motors run the risk of demagnetization of their permanent magnets if the electromagnetic field of the windings exceed the coercive force of the permanent magnets. To alleviate this problem, a maximum safe operating voltage for any DC permanent magnet motor is specified which under maximum power conditions (i.e., at stall) the resistance of the electromagnet windings will be high enough to prevent a flow of current through the electromagnet sufficient to cause irreversible damage to the permanent magnets. This current is considerably greater than the normal operating current, and for this reason, normal operating conditions for traditional permanent magnet DC electric motors only utilize a fraction of their true power capabilities based on their permanent magnets. In fact, most of these motors only utilize between 10% and 25% of their true potential.
The wire diameter used in winding an electromagnet core basically determines the magnetization force in ampere-turns for a given cross-sectional core diameter at a given voltage. Increasing the number of turns reduces the number of amperes that will flow through the coil, but increases the number of turns thus, maintaining the same number of ampere-turns. In order to more effectively use the permanent magnets of a permanent magnet motor under normal running conditions (i.e., at 10% to 25% of stall current) electromagnet windings must be activated that are more than capable of demagnetizing the permanent magnets in the motor under the conditions of stall. One way to accomplish this is to wind the electromagnet in layers and using thinner wire successively in the outer layers. On start up, all the layers of wire in the electromagnet are used. The resistance of the thinner outer wire prevents excessive currents in the motor thus preventing demagnetization of the motor permanent magnets. Once the motor RPM value reaches a safe level, the outer layers are shunted, thus increasing ampere turns in the motor and increasing the utilization of the motor permanent magnets. An interlock is also provided that prevents accidental activation of the shunt mechanism under stall or low RPM conditions. Other methods may be employed to wind electromagnet cores providing this type of electromagnet. Also included is twisting two or more strands of a given thickness insulated electromagnet wire together and winding the core. At one end the two strands are connected. This becomes the common. At the other end, the two leads
Mackie Peter W.
Miekka Fred N.
Mullins Burton
Satermo Eric K.
LandOfFree
Methods and apparatus for increasing power of permanent... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Methods and apparatus for increasing power of permanent..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Methods and apparatus for increasing power of permanent... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3296234