US2781484A - Thermally controlled automatic switches - Google Patents

Description

Feb. 12, 1957 Filed June '7, 1952.

C. W. SLOCUM THERMALLY CONTROLLED AUTOMATIC SWITCHES 5 Shets-Sheet l INVEN TOR.

CHARLES W SlocuM 47 7 0ENEY5.

Feb. 12, 1957 c. w. SLOCUM 2,731,484

THERMALLY CONTROLLED AUTOMATIC SWITCHES Filed June 7, 1952 5 Sheets-Sheet 2 INVENTOR. CHAR/.53 1 SL cU ATTORNEWG.

Feb. 12, 1957 c. w. SLOCUM 2,731,484

THERMALLY CONTROLLED AUTOMATIC SWITCHES Filed June 7. 1952 5 Sheets-Sheet 3 NVENTOR. CHARLES SLacu/w 76M; mswm aa flwu u ATTORNEYS. g

United States Patent THERMALLY CONTROLLED AUTOMATIC SWITCHES Charles W. Slocum, Adrian, Mich., assignor to Stubnitz- Greene Spring Corporation, Adrian, IVliclL, a corporation of Michigan Application June 7, 1952, Serial No. 292,260

4 Claims. (Cl. 318-221) This invention relates to thermally con-trolled automatic switches for controlling a main circuit and a subsidiary circuit, particularly the starting and running circuits in a split phase motor such as commonly used in domestic appliances, electric refrigerators, washing machines, blower fans, and etc. In the motors used in these appliances it is customary to use a starting circuit and a running circuit. As soon as the motor attains full speed, it is desirable to cut out the starting circuit. My invention provides a simple automatic heat actuated switch for this purpose. It is desirable to have certain space and force relationship between the starting contacts of the switch at all times substantially constant so that the starting switch will open and close in the same time and under the same conditions regardless of the ambient temperature of the room, the heat generated by the motor winding, and the heat emanating from the other parts of the switch.

I employ a compensating bimetallic arm which carries one contact and is caused to follow up the movable contact in accordance with the internal temperature conditions in the switch box. It is desirable, with a switch to break the starting circuit, to have switch operating conditions that are constant regardless of the internal temperature of the switch box. It is also desirable to provide a constant spacing between the contacts so that the contacts return to their original relative position on cooling in approximately the same time interval under all temperature conditions in the switch box.

Another feature of the invention is the employment of a line switch for breaking the current in the line when there is an overload in the circuit due, for instance, to the stalling of the motor or increasing the load on the motor beyond safe limits. This line switch is affected by means of the internal temperature of the switch box which in turn is affected by the heat of the motor shell, the heat of the motor windings, the heat generated in the switch box by the current passing through the various elements of the automatic switch, and the ambient or room temperature. It is desirable to have all these factors enter into the operation of the line or overload switch because it is the heat both obtaining in the motor and that generated by the amount of current going through the motor which burns out its insulation.

Referring to the drawings:

Fig. 1 is a side elevation of the switch, some of the parts being in section.

Fig. 2 is a schematic drawing of the circuits showing the starting switch and the overload switch.

Fig. 3 is a section taken on the line 3--3 of Fig. 1.

Fig. 4 is an end elevation of the switch viewed on the line 44 of Fig. 1.

Fig. 5 is an exploded view of the starting switch.

Fig. 6 is a plan view of the starting switch bimetallic member.

Fig. 7 is an exploded view, partly broken away, of the overload switch.

1 designates the base of the switch housing which is 'ice the stack 4. This arm carries a contact 5 adapted to engage the contact 6 on the end of the overload switch contact arm 7. A bimetallic line switch arm 8 is secured at the bottom of the stack 4 just above the contact arm 7. When current passes through the bimetallic arm 8 and heats this arm, the free end of the arm curls up, and when it curls up beyond the center line, the U spring 9 throws over this center line and the contact arm 7 is thrown down against the stop screw 10. This opens the line switch in the main circuit passing to both windings.

This circuit will be presently traced. The adjusting screw 11 can be turned to regulate the height of the arm 3 and determine at what heat condition the overload switch will open. The adjusting stop screw 10 also can adjust the position of the contact arm 7 so as to determine what heat condition of the bimetallic member is necessary to close the switch.

The starting or subsidiary circuit switch has two contacts, 12 and 13. Contact 12 is carried on the J bar or straddling member'lS. This J bar is secured by the screw 16 to the compensating bimetallic arm 17 (see Fig. 5). for the starting circuit. These strips are in electrical series, not in parallel. On the end of this strip is an insulating bar 19 (Fig. 5) which contacts with the U spring 20. This U spring 20 engages in the notch 21 in the insulating bar and the notch 22 in the contact arm 23 of the starting switch. The con-tact 13 is secured to the contact arm 23. Arm 23, with ear 23a, contacts post 60 (Fig. 3) which is connected with binding post, connected to the starting winding of the motor.

Now refer to Figs. 2 and 3, and it will be seen how the current courses through the switch and how the two switches operate. The current comes in through the binding post 35 which contacts the starting or subsidiary switch bimetallic arm 18 by means of connector 24. It passes through this arm around the strips which form a grid (Fig. 6) and then, by means of the jumper 25, it passe up to the main arm 3 of the line switch. Now refer to Fig. 1 and it will be seen that the current passes through the main arm 3, the contacts 5 and 6, to the contact arm 7. Thence it passes to the line switch bimetallic arm 8 by reason of the two arms being stacked together in the stack 4. Refer again to Fig. 3. The current passes around in this bimetallic arm 8 from one side of the stack to the other with the insulation 26 intervening Current then passes up through the two conducting spacers 27 and 28, then through spacer 29 to the bimetallic compensating arm 17. This bimetallic compensating arm 17 is a one loop arm as shown in Fig. 5. This is shown as a two strip grid. The current passes from the left hand side of the stack to the right hand side by reason of this loop arm, thence through spacer 31 to the bar 32 and from the bar 32 to the post 33 and the binding post 34 on the bottom of the switch box to the motor running winding.

The current enters the switch box by means of the binding post 35 which contacts with the post 24. The operation is as follows: The current coming infir'st through the multi-strip starting bimetallic member heats this strip 18 quickly and to a high temperature because of the high resistance of the bimetallic metal and also the multi-strip path for the current through the narrow strips. The heat up or the rise in temperature of the-bimetallic arm 18 is considerably greater than the rise in tempera- Patented Feb. 12 1957 18 is a multi-strip (Fig. 6) bimetallic start arm and consequently the resistance is much less than through the narrow strips in the bimetallic arm 18. Very shortly after the motor is started up, the disparity in the temperature of the two arms is sufiicient for the upper bimetallic arm 18 to bend or curl up faster than the lower bimetallic arm 17. This draws the U spring20 out and shortly puts enough stress on the spring to cause the toggle to throw toggle arms 18 and 23 over center and cause the starting switch to open. The running winding current still passes through the bimetallic'arm 18, thus keeping the starting switch open.

It is not necessary for the current to pass through the compensating bimetallic arm 17, but the way the switch is laid out it does so, and this is advantageous. As soon as the bimetallic control arm 18 reaches a temperature say'25 more than the compensating bimetallic arm, the starting switch will open. It does not make any diiferen-ce whether the two temperatures are 100 and 125, or the temperatures are 200 and 225. The purpose of the compensating arm is to maintain a fixed time of opening and closing of the contacts independent either of the ambient or internal temperature of the switch box.

The motor now is running on the current passing only through the running winding. If too great a flux of current for a given ambient or internal temperature condition goes through the main line of the running winding, then the bimetallic arm 8 curls up and the U spring 9 throws the toggle arms 7 and 8 over center and the contacts and 6 separate thereby causing the motor to stop. When the bimetallic member 8 is cooled, the circuit is again reestablished and the motor is again started with the aid of current passing thorugh the starting switch and thence to the starting winding. If the motor is stalled for any reason, the overload of current will again open the overload switch and out 01f all the current.

-It is advantageous to have the current flow through the compensating bimetallic arm 17 for the reason that that keep the temperature of the compensating arm closer to the temperature of the bimetallic control arm 18 and consequently on cooling the starting switch will close much quicker. This is highly desirable because the starting switch must always close before the line or overload switch, otherwise the current would be thrown into the motor in attempting to start it without the aid of the starting winding, which would be disadvantageous.

It is advantageous to have the line switch operated by both the heat generated by the motor current and the internal temperature in the switch box. If the motor overheats due to the windings of the motor overheating, this is conducted through the metal frame and the motor shell to the switch box and this, plus the heating by the current going through the bimetallic arms will open the line switch when the temperature has reached a predetermined point. That point is determined by the adjustment of the screw 11. This determines how great an arc the bimetallicarm 8 must curve through before the U spring 9 throws over center. The screw 10 is adjustable and determines how soon the switch in cooling will throw over center and close again.

The adjusting screw 36 passes through the J bar 15, adjusts the position of the stationary contact 12 and consequently determines how far the start bimetallic arm 18 has to curl before the spring '20 throws the toggle over the center line and causes the movable contact 13 of the starting switch to assume the open position. The adjustingscrew 37 screw into the insulating block 38 onthe end of the bimetallic compensating arm 17. This determines the position of the contact arm 23, when contacts 12 and 13 are open.

The stack is held together by'means 'of bolts 39and 41) which pass through the base and then up through the insulating strips- 26, 4 1, 42, 43, 44, and'4 5, and then through the cap plate46. The nuts 47 and'48'screW on the threaded ends-' ofthe bolts 39 and 40 respectively and thereby clamp the whole stack together. The bolt 40 passe through an insulating sleeve 49 and bolt 39 through an insulating sleeve 50.

I have shown, in Fig. 5, a bimetallic starting switch arm which has four narrow arms through which the current flows in series. The compensating arm 17 i shown as having two wider arms through which the current flows in series. This is only one Way that the difierential in resistance can be carried out. It could be accomplished by bimetallic arms equal in number and width but of different bimetallic metal or any of the methods known to those skilled in the art.

What I claim is:

1. A thermally and electrically controlled apparatus for controllinga main electric circuit and a subsidiary electric circuit, having in combination a base of electric insulating material, a main switch circuit, a bimetallic compensating arm, a subsidiary switch circuit operatively coupleo with the main circuit when the subsidiary circuit is closed and including a switch having a flexible spring arm provided with a contact on the free end, a straddling member on the free end of the compensating arm which straddles the free end of the said spring arm and carries a contact to engage with the contact on the free end of the spring arm to close the subsidiary circuit, a stop for the free end of the spring arm located on the free end of the compensating arm but on the other side of the spring arm from the contact carried by said straddling member, a bimetallic switch arm, a spring connecting the free end of this bimetallic switch arm with the free end of the spring arm, said two arms and spring arranged to form a toggle which can throw over center in the closing and opening of the subsidiary switch, said main circuit including a main line switch having a fixed arm carrying a contact on its free end, a flexible spring arm carrying a contact on its free end and a bimetallic arm having at its free end a spring connecting with the free end of the main switch spring arm of the main line switch, the spring, the spring arm and the bimetallic member of this main switch arranged in a toggle, to throw over center in open ing and closing of the main switch, the main circuit having an electrical resistance portion producing heat for the main switch bimetallic arm during overload, said main circuit passing through the spring arm and the fixed arm of the main line switch, and said main circuit having another electrical resistance portion producing heat for the bimetallic arm of the subsidiary circuit switch during the period the main circuit is closed.

2. For use in a switching system an ambient temperature responsive switch device comprising two switch contacts movable relative to each other, one contact being carried by a first cantilever spring arm for movement into and out of engagement with the other contact, a first cantilever bimetal control having a toggle connection with said spring arm for controlling the movement thereof, a second cantilever bimetal arm carrying said other contact for movement toward and away from saidone contact, said contacts, said first bimetal control, and said second bimetal arm being electrically connected in series, said bimetal control and said bimetal arm being movable in response to the heat generated by the conduction of current therethrough for controlling the opening and closing of said contacts and further being arranged to move both contacts in a common direction in response to a given change in ambient temperature, said first bimetal control having a greater degree of movement than said second bimetal arm in response to a predetermined current through both whereby said first bimetal control dominates the opening and closing of said switch contacts.

3. A switch having in combination, a bar provided with a fixed contact, a spring contact arm with a movable contact on the free end which engages said fixed contact, a bimetallic arm, a spring uniting the free end of said bimetallic arm with the free end of the contact arm to form a toggle, a compensating bimetallic arm carrying the free end of the bar, a main switch circuit splitting at the bar and having a branch circuit through said contacts and the contact arm, said main circuit being in heatproducing relation to the first-mentioned bimetallic arm to cause this to bear against the spring arm and separate the contacts to open the branch circuit when the firstmentioned bimetallic arm is heated by current passing in the main circuit, and means for clamping the arms together in a stack at the ends opposite their free ends.

4. For use in a switching system an ambient temperature responsive switch device comprising two switch contacts movable relative to each other, one contact being carried by a thermally operated control which serves to move said one contact in response to a temperature change, the other contact being carried by another thermally operated control which serves to move said other contact in response to a temperature change, both said controls having a movement relationship in response to a common temperature change which tends to move both contacts substantially equally in the same direction, said References Cited in the file of this patent UNITED STATES PATENTS 2,169,989 Pearce Aug. 15, 1939 2,304,018 Raney Dec. 1, 1942 2,379,602 Stickel July 3, 1945 2,618,721 Clark Nov. 18, 1952

Images