Electricity: motor control systems – Closed loop speed control system for dc motor with commutator – Armature control by digital or combined analog and digital...
Reexamination Certificate
2000-05-08
2001-11-20
Masih, Karen (Department: 2837)
Electricity: motor control systems
Closed loop speed control system for dc motor with commutator
Armature control by digital or combined analog and digital...
C318S254100, C318S132000, C318S434000, C318S724000
Reexamination Certificate
active
06321032
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to improvements in electric motors and in particular, to an improved brushless repulsion type motor. Conventional repulsion motors are typically constructed with a single phase stator and a DC rotor having an armature winding connected to a commutator.
Diametrically opposed carbon brushes riding on the commutator are shorted together, but are not directly connected to the AC power line. When AC power is applied to the stator winding, currents are induced in the armature to create the rotor field. Important advantages possessed by the repulsion motor are the relatively high value of the starting torque with comparatively low starting current, the ability to sustain high starting torques for long periods of time, such as may exist under conditions of high inertial load, and an adaptability to wide range speed control.
The speed torque curve of a repulsion motor is similar to that of universal series motors or series type DC motors. The no-load speed of the repulsion motor can be many times higher than the synchronous speed. A problem with the conventional repulsion motor is that the brushes and commutator wear out quickly due to arcing and heat generated by the brushes in contact with the commutator. As a result, basic repulsion motors are not commonly used today because of the brush wear problem.
Other motor types have been designed to minimize these problems. For example, a repulsion start, induction run motor is designed with a squirrel cage rotor embedded in the wound armature. Mechanical means are used to lift the brushes from the commutator when the rotor speed reaches a predetermined value, and the motor then runs as an induction motor. This is done to develop a very high starting torque for the induction motor.
Another motor is disclosed in U.S. Pat. No. 5,424,625, incorporated by reference herein. In accordance with that disclosure, electronic switching means is carried on the rotating armature to short individual coils at appropriate times in a cycle of rotation to eliminate the need for brush and commutator elements. Specifically, an electronic switch circuit is provided for replacing the switch and current carrying function of one pair of oppositely disposed commutator segments or bars. Electrical power needed to energize the electronic switching means and any related control circuitry on the armature is produced on the armature by induction from the stator field. The control electronics on the armature include circuitry to sense an enabling signal from stationary signaling means mounted on the stator in order to control the actuation of the electronic switches. Control circuitry is operative when a coil is at a predetermined angular position, relative to the stator. Each switch shorts the ends of an associated coil together. The result of this short is essentially the same as that achieved in the prior art by a pair of opposed shorted brushes.
However, the armature and induction field within such motor housing produce heat which is not easily dissipated and the temperature in the motor rises. Such elevated temperature reduces the power capability, reliability, and life of electronic switches and other components. It is also very difficult to replace or repair the electronic components within the motor housing. This involves complete disassembly of the motor, which is both time consuming and expensive.
SUMMARY OF THE INVENTION
The present invention advantageously provides an improved brushless repulsion motor which provides construction alternatives to the prior art of brushless repulsion motors. In this respect, applicant has placed the electronic switching and control circuitry outside of the motor housing, while maintaining the advantageous utilization of the electronic switches to short individual coils at appropriate times in the cycle of rotation. Therefore, the heat generated by the motor has a much reduced effect on the temperature environment of the electronic parts. In addition, with the placement of the electronic parts exterior to the motor housing, it is much easier to provide maintenance service when required.
More particularly in this respect, a repulsion motor is provided comprising a stator and a rotor rotatably mounted on the stator for rotation about an axis. The stator and rotor are contained within a motor housing, the stator having at least one pair of poles, a field winding on the stator for producing a field in the stator, and a plurality of coils on the rotor adapted to electromagnetically interact with the field of the stator winding. In a preferred embodiment, electronic switches are located on an extension of the rotor shaft outside the motor housing and, preferably within a separate housing or enclosure, to selectively short successive ones of the rotor coils when the coils are in a desired angular position relative to the stator poles. Thus, the alternating stator field induces a current in the coils and produces a resultant relative rotation between the rotor and stator.
In the preferred embodiment, the signaling means and the controls for operating them are also located outside the motor housing and within the second housing. Each of the electronic switches and control circuitry is wired to a signal receiving means located on the armature outside the motor housing. The signal is then transmitted to the control circuitry, which in turn sends a signal to the electronic switches to short the ends of an associated coil together.
The present invention improves brushless repulsion motors significantly. Due to the location of the switches outside the motor housing, the switches are not subject to the same heat to which they are subject inside the motor housing. Placing the electronics outside the motor housing and connecting them to rotor coils inside the motor housing also adds the distinct advantage of easily allowing replacement or repair of the electronic switches and other components as necessary. There is no need to work inside confined, frequently hot spaces of the motor or the necessity to remove the bearing and end bell of the motor to obtain access to the electronic switches. In a preferred embodiment, the entire electronic switch assembly can be connected to the rotor windings by a quick connect plug or other means to allow easy separation for repair or replacement. Finally, heat sinks for the electronic switches are more effective in the cooler environment outside the motor housing.
It is thus an outstanding object of the present invention to provide an improved brushless repulsion motor using electronic switching to short individual coils of a repulsion motor.
It is yet another object of the present invention to provide an improved brushless repulsion motor in which electronic switches are easier to replace if damaged than heretofore known.
Still another object of the present invention is to provide an improved brushless repulsion motor in which the heat generated within the motor housing is diminished as a factor in designing the electronic switching.
Yet still another object of the present invention is to provide an improved brushless repulsion motor which is easy to repair and maintain.
Still another object of the present invention is to provide an improved brushless repulsion motor in which power transistor switches act as vanes of a fan blade for additional cooling of the motor.
These and other objects of the invention will become apparent to those skilled in the art upon reading and understanding the following detailed description of the preferred embodiment.
REFERENCES:
patent: 4761602 (1988-08-01), Leibovich
patent: 5424625 (1995-06-01), Haner
patent: 5677586 (1997-10-01), Horst
patent: 5798591 (1998-08-01), Lillington et al.
patent: 6108488 (2000-08-01), Haner
Haner Lambert
Jones William M.
Dynamotors, Inc.
Masih Karen
Vickers Daniels & Young
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