US2640120A

US2640120A - Centrifugal switch

Info

Publication number: US2640120A
Application number: US219449A
Authority: US
Inventors: Heinzmann Fritz
Original assignee: Individual
Current assignee: Individual
Priority date: 1950-03-17
Filing date: 1951-02-28
Publication date: 1953-05-26
Anticipated expiration: 1970-05-26
Also published as: FR1068619A; GB683668A

Description

May 26, 1953 F. HElNzMANN CENTRIFUGAL swITcH Filed Feb. 28, 1951 Patented May 26, 1953 OFFICE CENTRIFUGAL SWITCH Fritz Heinzmann, Albershausen, Kreis Goeppingen, Wurttemberg, Germany Application February 28, 1951, Serial No. 219,449 In Germany March 17, 1950 1 Claim. l

Induction motors are usually started by the aid of an auxiliary phase in which a current differing in phase from that of the working windings is produced. When the starting process is at an end and a certain speed has been attained, the auxiliary phase must be cut off automatically. This operation is carried out by means of a Centrifugal switch. This switch comprises a centrifugal speed governor and two contacts which are broken and connected respectively by the governor. l

Cutting off the auxiliary phase must take plac instantaneously so that the spark may break olf and the contacts be protected against erosion. Astatic or unstable adjustment is therefore required for the centrifugal governor. Furthermore, switching oif the auxiliary phase must take place at a precisely fixed speed allowing only a small tolerance. If the speed is too low at the moment when the auxiliary phase is switched o if, the motor will slow down and stop. If the speed is `too high, the auxiliary windings will fuse. Small dimensions in length and diameter and absolute reliability in operation are further requirements such a switch has to meet. Furthermore, the rotating masses must be as small as possible; otherwise there will arise, after some time of service, a rattling noise which is not permissible with regard to the use most of the motors in question are designed for. Besides meeting the beforementioned requirements the centrifugal switch must also be simple and inexpensive. Repulsion motors start with a high starting torque. After the motor has heen started. the armature winding is short-circuited by a centrifugal switch, so that the motor continues working as an induction motor. In this case the centrifugal switch has to meet similar operating conditions. The switch must be reliable, operating instantaneously at a precisely xed speed. If the starting time is too long, the motor will heat up toc much and possibly get damaged,

The before-mentioned conditions are not or only partly met by the centrifugal switches used at present for the purpose question. This deficiency will be removed the present invention. According to this invention a centrifugal speed governor' having radially arranged pressure springs-the design of such a governor in itself being knownis mechanically and functionally combined with a conducting ring fixed to the governor sleeve and sliding, while the motor is starting, on two stationary contacts. Besides this ina-in feature there are other new features proving of value for the use in question.

Referring to the accompanying drawings: Fig. la is a perspective view. Fig. l is a longitudinal section, Fig. 2 a side view of such a centrifugal switch, while it is at rest, with closed contacts. Fig. 3 is a longitudinal section of the same centrifugal switch during normal worlr of the motor, the weights being swung out and the contacts separated from each other. Figs. 4, 5, and 5 show a side view, a longitudinal section, and a top view of one of the weights I. Fig. 7 shows a contact mechanism as it has hitherto been most usual. Fig, 8 shouf's centrifugal force diagrams, the governor lift being drawn on the abscissa AB, and the centrifugal forces on the ordinate BC. X-X is the rotation axis of the centrifugal governor. Figs. 9 and l0 show side view and top view of the governor support.

The weights i are pivotally seated in the U- shaped part 2 by means of pivots 3. Part 2 is iirmly connected with tube 4 fitted to the shaft. Parts f2 and 4 form together the governor support. The spring supports 5 supporting the inner ends of pressure spings i5 are movably seated in the weights I. The outer ends of these springs are supported by nuts T screwed on to bolts 8 firmly fixed to tube il. By means of arms il the weights i exert their pivoting action on governor sleeve lil. A conducting ring il is firmly xed tc sleeve lil. While the motor is starting, this ring,r slides on contacts i3 and lll fixed to stationary contact bearer i2, thus conducting the current through these contacts. Conducting bars l5 are connected with the auxiliary phase.

l-litherto centrifugal governors having plate springs have sometimes been employedfor the purpose in question. Such plate springs are exposed to breaking if they are not treated carefully enough. The spring force diagram varies according to but slight diierences in thickness of plate. such differences being unavoidable in manufacturing plate springs. Tension springs, which are also used, are particularly exposed to breaking at their bent suspension loops. The spring force diagram shows rather considerable diiferencies, no uniform initial tension being obtainable. Torsion springs acting on the link bolts, or axially arranged pressure springs are also used for the purpose in question. With such springs work consumed by friction is considerable, because the springs transmit their full load on the lin Is. Hence it follows that the centrifugal switch operates at varying speeds owing tc the varying conditions with regard to friction or lubrication. Plate springs or tension springs or torsion springs allow speed regulation only within a narrow range able for the purpose in question..

.and i4.

and by using conioiicated means. Pressure springs, however, are easily adjustable, so that the characterstic and speed required for the purpose in question is obtainable with all desired accuracy. Furthermore, pressure springs absolutely reliable in operation and resisting to fracture, however rudely they may be treated. Speed control within a comparatively *if e range is possible by simply adjusting the nuts l. s the centrifugal force of the w lits i directly opposes the force of the springs t friction is reduced to the minimum, so that the speed at which the switch required to operate always exactly the'sanie.

Fig. '7 shows a contact device as it has hitherto been most usual. Plate spring I1 fixed `to oontact bearer h3 is stressed by the `governor sleeve while contacts i8 and i3 are inl closed `position, whereas it is released 'ii/'lien the weights move outwards, the contacts being disconnected Aat the same time. The lift of Contact spring il' is liniited. by plate vS shows the Centrifugal force diagram c-b--o t of the centrifugal speed governor having transverse sp `ings `the adjustment of the governor being astatic `it is -necessary for obtaining an instantaneo-1s operation. The centrifugal force dia-grani, which in this case is nearly in accordance with the `diagram of -the transverse springs, intersects the axis of .the abscissa AB in the intersection point with rotation axis. Sometimes unstahle adjustment i the governor is advisable, so that the centrifugal force diagram intersects the axis of the abscissa in a point that is still more f stent from being beyond the rotation axis x Diagram.

a/-b--d respresents the force eidg-ram of the contact spring il. This spring must have acertain minimum power to ensure safe -disconncotion. of the contact i3. L the spring is too weak, the Contact does not break oi', .and the motor will be damaged. a-c representing the Contact .spring force while the weights are in inward position, is longer than b-d representing the contact sp ing torce while .the weights are in outward position, so vthat o-b-e-f is the resultant centrifugal force of the governor combined with contactspring,T l?. Hence it folios/s Vthat the governor -becomes static and thereby unserif'ice- Ir astatic or unstable adjustment of the governor combined with-contact spring I l shall be obtained, buildingin uncommonly heavy rfeghtsis necessary in order t0 `increase the diierenoe between Contact spring force diagram a-b-c-d and centrifuga-l force diagram a-b-g-i. Such Weights `favour a noisy working of the governor and increase its construction dimensions.

The present invention .removes the beforeinentioned difoulty by providing the .conducting ring H passing the current through contacts i3 In .this case no additional spring power influencing the characteristic of the centrifugal governor in an unfavourable oanner., is required. The diagram a-b-c--d is non-existent.

The weights l are made of sheet metal by noncutting shaping, this working process being most simple. They are provided with a radial hole 2 I, an upright edge 22 having a rounded-off outside, and naps 23 having a bent-in inside. The edge 22 and the flaps 23 serve to stiften the weights, and help to increase the governing power. The outside of the edge 22 is rounded off in order to obtain an accordingly smaller outside diameter of the governor. The edge 22 engages in recesses 24 of the U-shaped part 2, which is also made of sheet metal by non-cutting shaping. By this arrangement the construction length is reduced. Fixed in part 2 is a tube :l the bore of which deponds on the diameter of the shaft.

The governor support and the weights may also be cast, die-cast, or pressed.

The conducting ring may also be carried on the governor sleeve in ball bearing seat, so that it does not move when being in Contact with the contacts, whereby wearing down the contacts due to friction .at the conducting will be avoided.

rShe new combination. described in lthis specification and the additional foe-.tures of this invention provide for the construction of a centrifugal switch that is reliable in service easily a retable. instantaneaousl;f switching, working with least possible noise, simplified and shortened in its design, whereby it 'meets the requirements such a deice is desired for, in a manner that has hitherto been striven for by manifold vain efforts. As is apparent from the present specification, only part of these requirements would be achievedy if for example the centrifugal speedgovernor of the described construction were coinbir d with a contact device .of another construction, or the described. contact device with another centrifugal speed governor.

VI claim:

Centrifugal switch comprising .a support fitted to the shaft, two weightspivotally connected with said support, pressure springs adapted to oppose the outward movement of said weights and having their outer ends in contact with nuts and their inner ends in contact with movably seated spring supports, said nuts being screwed on to stay bolt screws i'irnily'iixed to said support, said spring supports being movably lseated iii said weights, a sleeve slidingly seated on the shaft and movably connected vith said Weights, a conducting `ring fixed to said sleeve, a contact bearer fixed to the stationary centrifugal switch casing, two contacts fixed to said contact bearer, conducting bars fixed to said contact `bearer and connected with said contacts.

FRITZ HEINZMANN.

References Cited in .the le of this patent UNITED STATES PATENTS Number Name Date 1,510,263 Defibaugh Sept. 30, 1924 1,552,589 White Sept. 8, 1925 1,580,161 Persons Apr. 13, 1925 '2,318,313 House May 4, 1943