Patent GB-450911-A (GB)
Title: Improvements in and relating to electric circuit controllers
IPC: H01H1/54
Filed: 1935-10-30
Abstract: 450,911. Partly electromagnetic switches and actuating controllers. BRITISH THOMSON-HOUSTON CO., Ltd., Crown House, Aldwych, London. Oct. 30, 1935, No. 29970. Convention date, Oct. 31, 1934. [Classes 38 (iii) and 38 (v)] A circuit-controller comprises a resilientlysupported switch member of magnetic material which is first moved with its support to bring contacts into or out of engagement with cooperatively-arranged fixed contacts electromagnetic means being adapted, in response to the engagement of the first pair of co-operating contacts due to movement of the switch member with its support, to produce a magnetic attraction on this member, whereby it is rocked in relation to the support about the initially-engaged contacts to bring with a snap action a further pair of co-operating contacts into engagement, subsequent disengagement of said further contacts occasioned by movement of the switch member in an opposite direction about the initially-engaged pair being arranged to permit of a sudden decrease in the energization of the electromagnet for enabling the switch member to operate with a snap-action so as to complete the disengaging action of the contacts. As shown in Fig. 1 one or more switches which may form -a motor controller are operated by a shaft 36 with handle 11. On rotation of the handles in an anticlockwise direction an arm 40 stresses a spring 37 and causes a switch arm 29 to rotate, the arm 29 bearing a magnetic contact-carrying member 28 which can have a limited angular rotation relatively to its carrying arm. The member 28 carries three contacts 24 .. 26 and engagement first takes place between the centre contact 25 with the central fixed contact 21 (Fig. 4) these being formed of good contact-making material such as copper or tungsten. This contact engagement completes the circuit of an electromagnet 14 which immediately attracts the member 28 causing it to rock about its centre on the engaged contacts as fulcrum until a pair of high conductivity contacts 24, 20 formed, for example, of silver, are engaged (Fig. 5) acting as a shunt to the relatively higher resistance contacts 25, 21. Thus the switch is maintained in the closed position with the major part of the current passing through the contacts 24, 20. If further switches are mounted on the operating shaft further operating movements of the handle 11 are made, each switching position being defined by a roller 46 on a pivoted spring- controlled arm 47 engaging successive teeth in a ratchet plate 49, the spring reaction between the roller and ratchet teeth also ensuring a snap-action initial engagement of the " make " contacts of successive switches. Switches which have been operated remain closed, the operation of the shaft merely causing greater stresses in their actuating springs. On reverse rotation of the shaft, however, the switches are opened again in reverse order, the opening of each individual switch being as follows. When the arm 40 engages the lateral extension 29<a> of the arm 29, the latter is positively moved in a clockwise direction. The first part of this movement causes a rocking of the member 28 in the opposite direction separating contacts 24, 20 and bringing the arcing contacts 22, 26 into engagement (Fig. 6). This causes a shortcircuiting of a greater part of the coil 14 and also a diversion of the remaining flux, mainly through the left-hand pole-pieces 16b, 17<b>. Further movement of the arm 29 thus draws away contact carrying member 28 away against the diminished attractive force of the electromagnet, contacts 21, 25 separating prior to contact 22, 26 so that the circuit is broken wholly at the latter. The flux between the poles 16b, 17b exerts a blow-out action on the arc at breaking. Where a number of the switches described are utilized as a seriesparallel motor-controller the opening of certain switches at predetermined stages of the operation of the controller may be produced by cams 44 secured to the shaft 36 and adapted to co-operate with arms 42 pivoted at 43 and bearing off-set portions for engaging the switchactuating arms 29.