Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2000-03-16
2001-03-13
Mullins, Burton (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C200S08000A
Reexamination Certificate
active
06201325
ABSTRACT:
BACKGROUND OF THE PRESENT INVENTION
This invention relates to a centrifugal actuator for controlling a switch unit and particularly a starting switch unit of an electric motor for disconnecting the start winding when the motor reaches a desired speed.
Centrifugal actuators for motor starting and other applications are well known. A particularly satisfactory centrifugal actuator for AC induction motors is disclosed in U.S. Pat. No. 4,386,290 entitled “Centrifugal Actuator For AC Induction Motors” which issued May 31, 1983 and is assigned to the assignee of the present invention. Generally, known centrifugal actuator units have a common construction consisting of oppositely located and spring loaded levers or arms, each having a general U-shaped configuration. The switching levers have a relatively heavy outer weight connected to the arms which project inwardly from a hinge support member on a base and are interconnected to an axially movable hub member which responds to the pivotal movement of the weight arms. The hub member is aligned with and actuates the switch. The weighted levers respond to the centrifugal forces which rise as the speed of the motor increases. This results in the movement of the switching levers which establish a positive and fast movement of the hub or other switching device which moves relative to the switch. Generally, the force to create the disconnect movement must be somewhat greater than that to maintain the actuator in the run position. Reversely, on deceleration of the motor a return snap action should be created at a designed speed. Generally the cut-out speed and the cut-in speeds will be different. This difference is highly significant in order to conform the switching operation with the pull-up and full load characteristics as well as the break down performance characteristic of the motor.
The centrifugal actuator is required to operate each time the motor is started, slows down or stops. Sliding motions therefor are minimized within the mechanism to reduce wear and to maintain the desired operation. The switch and the interacting switch actuator desirably provides a movement which is not adversely affected over time by any wear characteristic between the switch and the moving part of the actuator. Structures which minimize sliding action and provides pivotal interaction between the parts with minimal wear interaction wherever possible is therefore desired.
Motors can be mounted both horizontally and vertically. A vertically mounted motor is subject to gravitational forces and may effect the operation of the switch actuator if there are significant differences in the hub and the actuating weight structure.
The cost and life of the parts are always of significance in connection with the normal high speed operation of AC motors. Additionally, the pivotal mounting of the weights requires special consideration with respect to maintaining the integrity of the actuator in the event of excessive speed which tend to cause the weights to actually disengage from the switching mechanism.
SUMMARY OF THE PRESENT INVENTION
The present invention is directed to a centrifugal actuator particularly adapted for induction AC motors and an actuator which can be constructed as a highly cost effective and reliable product. The actuator is precisely and firmly secured to the rotating shaft to avoid weight creep or deflection of the loaded portion of the actuator parts due to extreme forces as well as to further minimize sliding contact between the components and minimizing the load on sliding parts where sliding is required. Precise location of the centrifugal actuator to the shaft to establish and maintain the proper distance between the actuator and the switch as well as maintaining of the actuator in the preset position on the shaft and further preventing any rotation of the shaft is an important consideration. Securing the assembly together at all speeds is a significant requirement. In the present invention, the heavy metal weights are pivotally mounted within a special pivot unit of the centrifugal actuator which prevents the weights from coming off the actuator at speed beyond cut-out speed. The actuator is readily produced from known materials with known production processes to maintain a cost effective centrifugal actuator.
Generally in accordance with the present invention, the centrifugal actuator includes a base member which is firmly secured to the shaft and maintains a preset position. In the preferred construction, the base is firmly secured to the shaft to form a shoulder for the bearing on the adjacent end of the motor. The base of the actuator is secured to the shaft by formation of ribs within the base member to securely grip the shaft, and further is preferably formed with a connector secured to the shaft at one end of actuator to lock the actuator abutting the motor shaft bearing. This construction will automatically preset the proper distance between the actuator and a stationary control switch. The bearing interengagement maintains a clamping load on the actuator base which further minimizes any rotation of the centrifugal actuator on the shaft. In a preferred construction, a sliding hub includes a tubular portion which has a somewhat larger diameter than the base member and is mounted for axial movement thereon. An end flange on one end of the hub's tubular portion is aligned with the switch to actuate the same. Interconnecting recesses and guides support the sliding hub for axial movement on the base.
The weight members are pivotally secured to special pivot units on respective opposite sides of the base and are similarly pivotally mounted. Each weight is formed of an L-shaped configuration including an outer weight leg and a positioning portion including a pair of pivot levers projecting from the weight leg. Each weight further has an inwardly projecting pivot member which is fitted within a corresponding pivot unit on the base. The pivot unit includes a restricted opening permitting the assembly of the weight. The pivot levers of the pivot weights project inwardly to a pivotal connection within pivot bracket or units on the opposite side of the hub. At cut-out speed, the weights pivot arms in the pivot units and the lever pivots in the pivot brackets to move the hub and flange outwardly of the switch. The hub movement is terminated with the switch structure in open position and with the lever arms positively held with a reset moment position to prevent locking of the unit in the open position while further holding the weights locked within the pivot units.
A significant feature of the present invention is the pivoted mounting of the weights to the base member such that the weights are held in place under all conditions. In this aspect, the weights include a pivot rod secured within a hook-like member in the pivot unit of the base member. The rod and the hook-like member are formed with pivot components which pivot the rod in such an orientation as to positively prevent the pivot rod and, therefore, the weights from leaving the base member under all conditions.
The mounting of the hub with the guide members minimizes the sliding contact surfaces between the hub and the shaft. The more heavily loaded areas associated with the pivoted weight and the legs to the hub are essentially and primarily pivot actions rather than sliding actions. When areas of sliding is unavoidable, as between the motion of the hub on the base, the sliding surfaces are minimized as well as the loading therebetween.
The weights, hub and base are constructed such that the gravitational forces do not significantly influence the operation of the actuator. The result is obtained by positioning the pivot point of the weights at or near the center of the mass of the weights, giving due consideration to the mass of the hub.
Both the base and the hub are readily formed as molded plastic members with minimal sliding contact as a result of the construction and support therebetween. The interconnection between the weights and the hub are made essentially totally of pivotal m
Logsdon Michael A.
Nolte Duane R.
Andrus Sceales, Starke & Sawall
Marathon Electric Manufacturing Corportion
Mullins Burton
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