MOTOR STARTING DEVICE

Abstract: A motor starting device for de-energising the starting winding when the required motor speed is reached comprising electromagnetic means (3) to urge actuation of the switching means (20, 21) and a latch member (10) controlled by a thermal temperature-balanced bimetallic strip (5) to prevent switching until the bimetallic strip (5) reaches a selected temperature through current flow therethrough.

Description: "MOTOR STARTING DEVICE" FIELD OF THE INVENTION This invention relates to a motor starting device and in particular it relates to a device of the type which controls the energisation of a start winding to run the motor up to speed to be then switched over to continued operation, the start winding being de-energised during the running period of the motor. OBJECT OF THE INVENTION Many forms of such devices have been known in the past, but the object of the present invention is to provide a device which introduces a time element in the switching of the start winding independent of the current draw which is taking place for instance in the electromagnetic coil, the purpose of this being to overcome the difficulty which exists at present when a motor is switched on and then switched off and again switched on without leaving a sufficient time delay for the mechanism to reset itself. SUMMARY OF THE INVENTION The present invention utilises an electromagnetic coil in the normal way in circuit with the motor winding which coil includes a spring loaded pivoted keeper which is pulled down by energisation of the coil, but the motor start winding is controlled indepen- dently of this by a bimetallic strip connected so that there is a current flow through the bimetallic strip to the start winding through contacts under control of a contact blade held in position by a latch member which is arranged to be engaged and held by the bimetallic strip until such time as the bimetallic strip is sufficiently heated to release the latch member and break the hold by allowing the contact blade to return. Thus the invention relates in general to a motor starting device adapted to de-energise the starter winding when the motor has attained the required speed and torque, and according to a preferred form a housing supports an electromagnetic coil arranged to actuate switch means in the housing, the invention being characterised by a latch member connected between the electromagnetic coil and the switching means, and by a bimetallic strip which may be in series with the electromagnetic coil or otherwise energised, the bimetallic strip being connected to hold the latch member against displacement by the electromagnetic coil until the bimetallic strip is heated, the latch * member having means to actuate the switch means. A preferred feature is a keeper fulcrumed to actuate the latch member and spring connected to be returned after pull from the electromagnetic coil, and also spring connected to the latch member to urge the end portion of the latch member against the keeper. A further preferred feature is an arrangement of switch blades to be actuated by displacement of the latch member, but under control of the bimetallic strip which releases the latch member to move only when the bimetallic strip has been heated by current flow to the motor. The device can be summarised as comprising an electromagnetic coil to initiate the switching action by setting a keeper, and a bimetallic strip to prevent actual switching occurring until the bimetallic strip reaches a selected temperature. DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan of the device with the cover removed, FIG. 2 is a section of same on line 2-2 of FIG.l, FIG. 3 is a plan showing particularly the switching blades and contacts but with the case sectioned as on line 3-3 of FIG. 2, and FIG. 4 is a schematic perspective view showing the interconnection between the keeper of the electro¬ magnetic coil and the latch member, showing also how the bimetallic strip latches the keeper until the temperature of the strip reaches a required value. DESCRIPTION OF THE ILLUSTRATED PREFERRED EMBODIMENT The housing 1 has a cover 2 and has at one end an electromagnetic coil 3 and within the housing switch means and a bimetallic strip 5. The electromagnetic coil 3 has a keeper 6 which is hingedly supported on the core 7 of the electro¬ magnetic coil 3, the free end of the keeper 6 being urged away from the core by a return spring 8 when the coil is not energised. Slidable within the housing 1 is a latch member 10 which is located between guides and has one end 11 adjacent the free end of the keeper 6 and has near the other end a notch 12 at the end of a face 13. The end 11 is urged into contact with- the free end of the keeper 6 by a blade spring 14 which is secured at the end 15 to the fulcrumed end part of the keeper 6 and has its other end project through an aperture 16 in the latch member 10. The return blade spring 8 has its end engaged against a part of the housing 1 and is arranged to urge the free end of the keeper 6 away from the core 7 so that when no current flow exists in the coil 3 the free end of the keeper 6 pushes the latch member 10 back to a position where the end of a bimetallic strip 5 engages the notch 12 and, unless the bimetallic strip 5 is heated, the latch member cannot return to its forward position even though the free end of the keeper 6 is pulled against the core 7. If this occurs the blade spring 14 is tensioned in readiness to move the latch member 10 to actuate the switch when the temperature of the strip reaches a sufficient value to disengage from the notch 12. The bimetallic strip 5 is bifurcated as illustrated and held to project from a pair of terminal blades 17 and 18 so that the free end 22 of the latch member 10 is disposed adjacent to the notch 12, the latch member 10 being positioned to have its end engaged in the notch 12 only when not heated. By this arrangement when the strip is heated by the current flowing to the start winding, the bimetallic strip flexes and its end portion is withdrawn from contact with the notch 12 to release the latch member which is then pushed back into contact with the keeper 6 by the flexure of the blade spring 14, at which stage the current flow to the starter winding is terminated. The bimetallic strip 5 will be seen to be made in two parts, A and B, the bifurcated part A being the current carrying part, the expanding part B being a temperature compensating part moving oppositely under ambient temperature to temperature-stabilize the end which engages the notch 12 to always remain in the notch-engaging position excepting when current flow takes place in the bifurcated part A. The device is reset so soon as the motor is switched on, through the magnetic coil 3 drawing the free end of the keeper 6 down, but the bimetallic strip 5 at this stage has cooled and the latch member 10 is held by it to hold the start winding contacts engaged until such time as the current flowing through the bimetallic strip heats it sufficiently to flex it to release the latch member 10. The terminal blades 17 and 18 also support the switch blades 20 and 21 which have contacts 22 at their free ends, these switch blades 20 and 21 being curved inwardly at their intermediate portions to engage a ramp 23 on the latch member 10, the purpose of this ramp 23 being to force the contact ends of the two switch blades outwardly away from the terminal blades 24 and 25 which form power outlets for the motor starting device. The switch blades 20 and 21 are balanced about the latch member 10 which is loosely guided, as shown particularly in FIG. 3, by projections 28 on the body, thus allowing the switch blades to compensate for somewhat different spring characteristics. The bimetallic strip is used to operate contacts, (OPEN), and an electromagnetic coil is used to reset the contacts (CLOSE). The motor start winding is connected to a common terminal via normally closed contacts and the bimetallic strip, and the main winding is connected via the electromagnetic coil. A single switch blade 20 or 21 could be used depending on the function required. The dotted section 30 in FIG. 3 shows how the housing 1 can be extended to provide further connecting terminals. The housing can be mounted by using the mounting legs 31. OPERATION OF THE DEVICE (a) The motor switch is energised to pull in the keeper 6 of the electromagnetic coil 3 but the switch transition does not take place because -the latch member 10 is held by the free end of the bimetallic strip 5 engaging the notch 12. (b) The bimetallic strip 5 heats due to start winding current flow through the bifurcated part of the bimetallic strip 5 and the free end releases the latch member 10 after a predetermined time as set by the bimetallic strip, and switch transition occurs. (c) The bimetallic strip 5 is now allowed to cool down while the motor continues to run, and the free end of the bimetallic strip 5 moves to rest on the face 13 on the latch member adjacent to the notch 12 and remains so while the motor runs. (d) On switching off the motor the electromagnetic coil 3 is de-energised and the keeper spring 8 pushes the keeper and with it the latch member 10 back, and the free end of the bimetallic strip drops into the notch 12 of the latch member, and the motor start winding is now relatched for an immediate start.

Claims: THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS: 1. A motor starting device adapted to de-energise the starter winding, in which a housing supports an electromagnetic coil arranged to actuate switch means in said housing, characterised by a latch member connected between the keeper of the said electromagnetic coil and the said switch means, and by a bimetallic strip connected to hold the said latch member against displace¬ ment by the said electromagnetic coil until the said bi¬ metallic strip is heated by current flow, the said latch member having means to actuate the said switching means. 2. A motor starting device according to claim 1 characterised in that the said bimetallic strip is supported from the said housing to engage a notch in the said latch member when the said bimetallic strip is not heated whereby to hold the said latch member against an urge to be moved by the said keeper until the said bimetallic strip is heated by start current. 3. A motor starting device according to claim 1 or 2 characterised in that the said electromagnetic coil has a keeper fulcrumed near a first end portion and has a second end portion engageable by the said latch member, and by a blade spring attached to the said keeper and engaging the said latch member to urge the said latch member against the said second end portion of the said keeper. 4. A motor starting device according to claim 1 characterised in that at least a switch blade of the said switch means is moved to switch an electrical circuit by engagement with an actuating member on the said latch member. ' OMPI rt CO i rt ro Pi er ro P' H) ro J P. P- ro ti CO ti ?t CO i ro rt P- ui ro α si ) ro Pi ro P P* "-<! •i Pi P rt Hi o Ω ti co Hi P" o ro 3 Ω rt 3 o er ro rt P ro 3 er P- σ 4 ro 0 ) ro CO Pi ti 0) τ> P- Pi ti P. P P' P- P Pi et P» 09 Pi ro rt rt P- 3 Ω P 4 Φ ro er ro Ω Pi rt P 3 CO ti CO ro P o 3 P* 3 rt tr P. Pi o ro 09 ti 7t P P Φ ro •i Pi ro rt 09 09 TJ P- ro i ro Ω P- K rt P Ω er CO rt o ro ft o P « P* CO rt P Pi er ti P- ro 09 P α ro bifurcated bimetallic strip supported by the said housing from a first end portion and having a second end portion engageable on the said latch member to prevent movement of the said latch member toward the said electromagnetic coil when said coil is energised but to release the said latch member when the said bimetallic strip is heated so as to move under the urging of the said first spring means, and means on the said latch member to effect electrical switching. 9. A motor starting device according to claim 1 or 8 characterised in that the said bimetallic strip is formed in two parts, the first part being bifurcated and supported at one end and adapted to carry start current, and a second part projecting from the free end of the bifurcated part to engage the said latch member, the said first and the said second part being arranged to move oppositely under ambient temperature to form ambient temperature stabilising means. 10. A motor starting device according to claim 1 characterised in that the said -means for effecting the electrical switching comprise at least a switch blade supported by said housing to project generally parallel to the said latch member, and by a ramp on the said latch member to actuate the said switch blade when the said latch member is moved. 11. A motor starting device according to claim 8 characterised in that the said means for effecting the electrical switching comprise a pair of spring blades arranged one on each side of the said latch member, one end of each said spring blade being supported from the said housing, the other end of each said spring blade carrying contacts, an intermediate part of each said spring blade engaging a ramp on said latch member whereby longitudinal movement of the said latch member moves the contact ends of the said spring blades to effect switching. 12. A motor starting device according to claim 11 characterised in that the said latch member is loosely guided in the said housing and is positionable laterally to a limited amount by pressure of the said spring blades on the said ramp. 13. A motor starting device according to claim 8 characterised in that the said first spring means and the said second spring means comprise blade springs attached to the said keeper, said first spring means having a free end portion engaging the said latch member and the second said spring member having a free end portion engaging the said housing. - 14. A motor starting device for de-energising the starting winding when the required motor speed is reached comprising an electromagnetic coil to urge actuation of the switching means, and a bimetallic strip to prevent switching until the bimetallic strip reaches a selected temperature. 15. A motor starting device substantially as hereinbefore described with reference to the accompanying drawings. ^JR OM

Inventors: SLACK DOUGLAS JOHN, SLACK, DOUGLAS, JOHN
Applicants: TEXAS INSTRUMENTS AUSTRALIA, TEXAS INSTRUMENTS AUSTRALIA LIMITED
Application year: 1983
Main classification: H01H7
IPC codes: H01H7, H01H50