US2943171A - Electrical apparatus - Google Patents

Description

June 28, 1960 H. F. CLARK 2,943,171

ELECTRICAL APPARATUS Filed April 8, 1957 64 53 Insular/0n 57 as 40 4o 62 aL| 54 L2 44 76 52 m 2 1 2o 78 g 78 Fig.2 Fig. 3

Fig. 4

INVENTOR.

Harry F Clark 2 Claims. (Cl. 200-88 assignor to General Detroit, Mich., a corporation of This invention relates to electrical apparatus and more particularly to electromagnetic starting controls for electric motors. This application is a continuation-in-part of my copending application Serial No. 361,198, filed June 12, 1953, which on July 30, 1957, issued as Patent 2,801,312.

Electromagnetic starting controls can be inexpensively and readily built forv a specific motor for operation over a relatively narrow range of line voltages. However, the diificulties of design and manufacturing increase greatly as the range of required satisfactory operation is extended over wider ranges of voltages and when extended to operate with more than one specific motor.

. It is an object of this invention to provide an inexpensive electromagnetic starting control with a simple, inexpensive current responsive bimetal arrangement which will enable it to operate over wider ranges of voltages and to control several motors of different characteristics.

It is another object of this invention to extend the bimetal overload control to provide a current responsive bias to open the starting contacts.

' These and other objects are attained in the form shown in the drawings in which a normally closed spring contact mechanism is pushed open by a spring mounted armature bar when an electromagnet cooperating with the bar is deenergized. The spring contact means is provided with a current carrying ambient compensated bimetal arrangement by which, should the starting contacts remain closed for an extraordinarily long time during the starting period of the motor such as often occurs under extremely low voltage conditions, the bimetal will be self-heated sufliciently by the current flowing through it to the contact means to bias and move the contact means to open position to deenergize or change the energization of the starting or phase winding. 7

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings, wherein a preferred form of the present invention is clearly shown.

1 in the drawings: 7

-Figur e l is a plan view of a starting control embodying one form of my invention;

Figure 2 is a left end view of the overload bimetal and its extension for varying the bias ofthe spring contact means;

Figure 3 is aplan view of the overload bimetal and the current actuated extension thereof;

Figure 4 is a plan view of a modified form of starting control; and

Figure 5 is a plan view of a bimetal starting contact means with a compensating bimetal portion of the modified form shown in Figure 4.

Referring now more particularly to Fig. 1, there is shown a flat base 20 of electrical insulating material. An L-shaped member 22 is staked edgewise to the base 20. The horizontal portion of the L-shaped member 22 has fastened to it the overload compensating bimetal 24.

2,943,171 Patented June 28, 1960 This bimetal 24 has an upwardly extending overload protector portion provided with a pivoting edge 28 to which the C-shaped toggle spring 30 is pivotally connected. A hook-shaped compensating bimetal 32 has one end anchored to the vertical portion of the L-shaped member 22. The hook portion pivotally connects to the C-spring 30. The base is provided with a stationary overload contact 34 connected by the conductor 36. and a control switch 38 to supply conductor L The cantilever bimetal 24 is provided with an overload contact 40 arranged to normally remain in contact with the stationary contact 34. However, when an excessive current flows through the contacts 34 and 40 and the bimetal 24, the bimetal 24 will be heated and provides a bias to the left which, when continued to a sufliciently high temperature, will cause the restraining force of the toggle spring 30 to be exceeded, thereby allowing the bimetal 24 to move against the fixed stop 42. When the bimetal 24 cools, a bias will be created to overcome the toggle spring 34 to return the contact 40 into contact with the contact 34.

The current flows from the bimetal 24 through the L-shaped support 22 through the conductor 44 to the electromagnet coil 48 wrapped around the offset portion of the flat bar 50 of soft electrical steel and finally connects to the terminal 74. This core member 50 is staked edgewise to the base and has a downwardly extending projection 52 to which is fastened a wire or flat spring hinge 54. This hinge 54 connects to the fiat bar armature 56 provided with a, lead weight and a felt cushion for minimizing chatter. The spring hinge 54 normally biases the armature 56in a clockwise direction into engagement with the upper projecting spring arm of the contact spring 58. The contact spring 58 has a U-shaped olfset 60 extending around the stationary contact 62 and provided with a movable contact adapted to normally engage the stationary contact 62 because of the counterclockwise bias of the spring contact member 58. This bias of the spring contact member 58 is less than the bias of the spring hinge 54 so that the armature 56 engages the projecting end of the spring contact member 58 to force the spring contact member 58 away from the stationary contact 62 until the upper projection of the spring contact member 58 engages the stop 64. This stop 64 is fastened to the top of the armature core 50 and is of non-magnetic material. The upper projection of the spring contact member 58 assists inthe movement of the armature 56 towards its fully attracted position until after the'contact 62 is engaged.

' The stationary contact 62 is connected by the conductor 66 to one terminal of the phase winding 68. The common terminal of the phase winding 68 and the main winding '70 is connected to the supply conductor L The second terminal of the main winding 70 is connected by the conductor 72 to the terminal 74 connecting with the second end of the electromagnet coil 48. The material thus far described provides an inexpensive and yet very satisfactory starting control for a specific electric motor over a relatively narrow range of line voltages.

According to this invention, in order to extend the v range of voltages over which the control willoperate satisfactorily and also to extend the range of motors over which it will operate satisfactorily, the bimetal 24 is provided with a narrow current carrying actuating extension 76 extended upwardly, which carries the phase winding current. When heated, it tends to curl in a clockwise direction. The upper end of this narrow actuating bimetal portion is connected to a downwardly extending wide compensating bimetal portion 78 which is not substantialy heated by the current flow but is substantially responsive to ambient temperature. It is of the same length as the portion 76 and curls in the same direction a similar amount upon changes of ambient temperature. The bottom of the spring contact member 58 is connected to the bottom of the compensating portion 78 so that the efiect .of ambient temperature upon the actuating portion 76 is compensated for by the efiect o f theambient temperature on the compensatinggpo-rson 78. r

Under high voltage conditions (110-125 Volts), the armature 56 is pulled all the way in to closed magnetic position in which the felt pad 57 engages the coil 48;. The armature 56 drops out or releases when the motor 80 comes up to speed, due to the decrease in the main winding 70 current through the coil 48 to open the starting contacts 58-62. Under low voltage conditions (90 volts), the armature 56 is only pulled tothe left far enough to allow the starting contacts 62 to engage. The engagement of the starting contacts 58-62 terminates the spring assistance of the member 58 to, move the armature 56 toward the attracted position. While the motor 80 is accelerated, the starting current flowing through the bimetal (76-78) heats it and causes it to bow to the right, thereby causing the starting contactsto open at a higher current (5.4-6.4 amps.) than was initially re quired (3.2-4.8 amps.) to close them. 7 r

a The above change in current relationship during the starting period permits the relay to be set for a much lower pull-in current (3.2-4.8 amps.) than the balance speed main winding current (5.4-6.4 amps.) and therefore provides satisfactory operation at extremely low voltages (80-90 volts). In the event of arelay calibration change due to mishandling, mistreatment or other causes such thatthe armature 56 will not release with a normal decreasein main winding current, the bimetal (76-78) will continue to bow to the right because of the continued heating thereof by the current fiow until the starting contacts (58-62) areopened by this thermal bimetal timer action before the overload contacts (40-34) trip open. At extremely low voltages (80-90 volts), where formerly the main winding current washelow the minimum pull-in amperage (5.4), the starting contacts 58-62 were not closed and only the main Winding current was available to trip open the overload contacts 40-34. This delayed the opening of the contacts 40-34 so that the main winding 70, would overheat. With the lower pull-in amperage (3.2-4.8 amps.) the phase winding current is also added to help trip open the overload contacts 40-34 and the overload trip time is greatly reduced, thereby preventing damage to the windings 68-70. It also makes it possible to control motors of various sizes and types such as the simple splitphase motor, the'oapacitor start motor and the capacitor start and run motors. i

In Figs. 4 and S a modified form is shown in which similar parts bear the same reference characters. This form differs from the form shown in Figs. 1-3 in that the spring contact means is arranged as shown in Fig. 5 and formed of a single strip of bimetal designated by the reference character 124. This strip oi bimetal 124 is generally bent into a U-shape with onele'g 125 of the bimetal 124 being provided with a left ofiset 127. ,The opposite leg 129 is provided with a U-shaped oifset 13 1 extending to the right and normally into contact with the offset 127. The interior of the U-shaped ofiset 131 is provided with the movable contact 133 adapted to be normally spring-biased into contact with the stationary p 4 contact 62. The ofiset portions 127 and 131 may be provided with an electrical insulating coating or surface which will substantially prevent current flow between them. Consequently, the phase winding current will normally flow through the leg 129. If the supply voltage should be abnormally low and the armature remain attracted for a prolonged period; the current flow through the bimetal leg 129 will heat the leg sufliciently and cause the leg 129 to curl in a clockwise direction until it moves the contact 133 away from the stationary contact 62 and its extension moves into engagement with the thin metal stop 64. Otherwise, the construction and operation are substantially the same as in Figs. 1-3.

While the form of embodiment of the invention as herein disclosed constitutes .a preferred form, it is to be understood that other forms might be adopted, as may come within the scope of the claims which follow.

What is claimed is as follows: r 1 l. A control including a spring contact means having a spring blade with an inherent, spring force biasing it to closed position, an armature having 21 released position in which it engages said blade and holds open said spring contact means, an electromagnet magnetically associated with said armature to pull said armatureaway from the contact means, a thermal overload control including a bimetal member and a contactoperated'by said bimetal member, said bimetal memberv having an extension operatively connected to said springbladeto bias said spring contact meanstoward the open position upon heating thereof, andmeans for conducting electrical. current through said bimetal member. to said, contact means for heating said bimetal member coincidentally to the closing of the spring contact means. v

2. A control including a normally stationary mounting, a bimetal member provided with a narrow actuating portion having one endpontion fastened tosaid mounting, said member being also provided with a wide am bient temperature compensating portion connected at one end portion .to a second end portion of said actuating portion and extending fromv said connection in the same general direction as said actuating portion, a spring contact means comprising a spring blade connected to the second end portion of said compensating portion and extending in the opposite direction and being electrically connected in series with said actuating portion having an inherent spring force biasing it to closed position, said bimetal member having its bimetal action arranged tov bias said contact means to open position by the heating effect of the electric current flowing through said narrow portion and the contacts, an armature having a leased position in which it engages said spring blade and holds open said spring-contact means, and an electro magnet magnetically associated with said armature to pull said armature away from the contact means.

References Cited in the file of this patent UNITED STATES PATENTS

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