US3292067A

US3292067A - Electrical apparatus

Info

Publication number: US3292067A
Application number: US425787A
Authority: US
Inventors: Harry F Clark
Original assignee: Motors Liquidation Co
Current assignee: Motors Liquidation Co
Priority date: 1962-10-30
Filing date: 1965-01-15
Publication date: 1966-12-13
Anticipated expiration: 1983-12-13
Also published as: GB1018685A

Description

Dec. 13, 1966 H. F. CLARK 7 ELECTRICAL APPARATUS Original Filed Oct. 30, 1962 United States Patent 4 Claims. (Cl. 318-221) This application is a division of my copending application Serial No. 234,093, filed October 30, 1962.

This invention relates to electrical apparatus and more particularly to controls for sealed, internally springmounted, electric motor-compressor units and other electric motor applications requiring better overload protection.

Noise and vibrations are minimized by sealed internally spring-mounted, electric motor-compressor units. However, the danger of excessive motor temperatures is increased in such units since a less effective heat transfer between the motor and the sealed casing for the dissipation of heat is inherent in this construction. Consequently, to properly protect the motor under overload conditions, it is necessary to provide an overload protector which will trip quicker and reset more slowly to decrease the heating periods and to increase the cooling periods of the motor during overloads so as to reduce the average temperature and the average ON time.

It is therefore an object of this invention to provide a control for an electric motor which will trip quicker under stalling and starting conditions and yet permit the motor to carry the full rated load under normal conditions.

It is another object of this invention to provide a control for electric motors which, upon an overload, energize a supplementary heater in heat transfer relation with the thermal overload protector to cause the overload protector to trip quicker and for supplying heat to the thermal overload protector during and after tripping to delay the resetting thereof so as to provide a longer cooling period be fore subsequent resetting.

These and other objects are attained in the form shown in the drawings in which the thermal overload protector is provided with a supplemental heater which is located adjacent to the operating bimetal of the protector. The magnetic starting relay is provided with -a bimetal arrangement in which the current to both the main and starting windings flows through a bimetal which is arranged to open the starting contacts in the event that the closed period of the starting contacts is too long due to low voltage or other possible causes. This bimetal is also arranged to effect the opening of a set of contacts which are arranged in shunt with the supplemental heater so that, upon an excessive current flow through this bimetal, the shunting contacts will be opened to cause the current to flow through the supplemental heater to cause the quicker tripping of the overload protector and, also, the heat stored in the supplemental heater will prolong the resetting time of the thermal overload protector. The shuntingcontacts are also opened when the armature of the electromagnetic starting control is energized so that the supplemental heater is also energized during the starting period of the motor so asto provide a quicker trip and a longer reset in the event that the motor stalls or is over loaded during the starting period. These two arrangernents provide adequate protection for an internally spring-mounted, sealed, motor-compressor unit by the provision of the quicker tripping and longer resetting under overload and starting conditions. During normal operation, the-shunting contacts remain closed thereby full load upon the motor and prorating of the overload protector.

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 embodiment of the present invention is clearly shown.

In the drawings:

FIGURE 1 is a plan view of an electric motor starting 0 control and overload protector embodying one form of deenergizing the. supplemental heater and allowing a J my invention shown in the deenergized position;

FIGURE 2 is a plan view of the same control showing the control during the starting period with the armature attracted by the electromagnet and the supplemental heater energized;

FIGURE 3 is a plan view of the control similar to FIG- URE 1 but showing the control immediately after the tripping of the overload protector due to an overload during the running period;

FIGURE 4 is a fragmentary sectional view showing the bimetal overload actuator of the shunt contacts; and

FIGURE 5 is a wiring diagram of the control connected to a split phase electric motor.

Referring now more particularly to the wiring diagram, FIGURE 5, there is shown a supply conductor 20 connected to the junction 22 connecting to one terminal of the main winding 24 and one terminal of the phase winding 26 of the electric motor 28. The second terminal of the main winding 24 connects to the main winding terminal 30 of the starting and overload control 32. The second terminal of the phase winding 26 connects to the phase or starting terminal 34 of the control 32. The second supply conductor 36 is connected through some type of normal control switch 38, such as a thermostat switch, to the line terminal 40 of the starting and overload control 32. As shown in FIGURES l to 3, the terminal 46 rivets the L-shaped contact 42 to the rectangular base 44 of electrical insulating material. The cantilever bimetal 46 carries a contact which is normally held in engagement with the L-shaped contact 42 by a C-shaped toggle spring 48. TheC-shaped toggle spring has a second connection with an inverted L-shaped cantilever bimetal compensating strip 50 having its lower end anchored to an irregular frame 52 of heavy metal which is riveted to the base 44.

The cantilever bimetal 46 has an L-shaped extension 54 which is fastened to the frame 52 at the point 60. It is adjusted to vary its tripping point by the adjusting screw 56. The adjusting screw 56 is frictionally held by the spring clip 58 to prevent undesired or accidental adjustment. Beyond the fastening point 60, the bimetal extension 54 continues as a narrow bimetal leg 62 (see FIG- URE 4) substantially parallel to the bimetal leg 46. At the extreme end of the bimetal leg 62, there is fastened a wide compensating bimetal leg 64 extending in the opposite direction providing ambient temperature compensation for the leg 62. Fastened to the opposite end of the compensating leg 64 is a spring contact member 66 of thin spring metal provided with a U-shaped portion carrying a contact which is adapted to be inherently sprung against the L-shaped contact 68 riveted to the base 44 by the starting or phase winding terminal 34. This spring contact are 66 has an extension 70 which is adapted to exert a spring thrust against the lead weighted end 72 of the armature 74 mounted as a cantilever upon a leaf spring 76 fastened to an extension 78 of the frame 79 which also serves as a core for the electromagnet 80. The armature 74 is also provided with a felt cushion 82 to prevent chattering and noise because of the AC. power source supplied to the electromagnet 80.

When the electromagnet 80 attracts the armature 74 as shown in FIGURE 2, the armature 74 moves out of engagement with the spring contact member 66 so that the contact member 66 is not affected by any chattering of the armature 74 and the contact with the starting contact 68 is made through the spring bias of the spring contact member 66. The extension 70 of the spring contact arm 66 serves to provide spring force to assist the magnetic force provided by the electromagnet 80 in moving the armature 74 out of the unattracted position shown in FIGURES 1 and 3 to the attracted position shown in FIGURE 2. This assists in making the control operate upon relatively low line voltages under which the magnetic attraction is so weak as to require the assistance of the cont-act arm 66 and its extension 70 to complete its movement. The contact 68 connects through the terminal 34 to energize the phase winding 26 during the starting period. Both the starting or phase winding current and the main winding current normally flow through the

bimetal legs

62 and 64 except during the starting period of the motor or after an overload sufficient to affect the bimetal leg 62. As shown in FIGURE 2, the starting or phase winding current flows from the leg 64 through the long spring contact arm 66 to the starting or phase contact 68 and the terminal 34 to the phase winding 26.

Also fastened to the bottom of the bimetal compensating leg 64 is a short spring contact arm 84 carrying at its upper end a contact 85 which is adapted to cooperate with a contact 86 provided on the armature 74. The armature 74 is connected through its biased spring mounting strip to the frame 78 constituting the core of the magnet 80. The spring mounting strip 76 lightly biases the armature 74 to its unattracted position as shown in FIGURES 1 and 3. It also carries the current from the contact 86 and the armature 74 to the frame 78 to which is attached by welding the terminal 88 of the magnet 80. The opposite terminal 90 of the electromagnet 80 is connected to the main winding terminal 30. This main winding terminal 80, of course, connects to one end of the main winding 24.

According to my invention, the frame 52 is provided with an irregular arm terminating in an upwardly extending stop projection 94 on the opposite side of the cantilever bimetal arm 46 from the L-shaped contact 42. This stop projection 94 serves to limit the opening movement of the bimetal 46 and serves as a resetting control in connection with the C-shaped toggle spring 48 and the compensating bimetal 50 to determine the resetting time of the overload bimetal cantilever arm 46. However, the mechanics of the toggle arrangement is such that there is some limit to this open setting in order to provide a reliable resetting point. Consequently, in addition to this stop projection 94, I provide a supplementary heater in the form of a U-shaped strip heater 96 of Nichrorne or similar electrical heater material connected at one end to the projection 94 and connected through the conductor 98 to an unattracted position, limit stop 121 for the contact arm 66 and the armature 74, as shown in FIGURES 1 and 3. This L-shaped stop 121 is welded to the adjacent portion of the armature frame 78 through which the current passing through the heater 96 flows until it meets the connection at the weld point 88 with the terminal of the electromagnet 80.

In operation, the starting control and overload protector normally assume the positions shown in FIGURE 1 during the idle period of the motor which is normally occasioned by the opening of the control switch 38. The armature 74 is unattracted and is biased by the spring hinge '76 to, engage the spring extension 70 to move the contact arm 66 away from the cooperating contact 68 to deenergize the starting or phase winding 26. The contact 86 is in engagement with the contact 85 at the upper end of the short spring contact arm 84 to close a shunt circuit for shunting and deenergizing the supplementary heater 96- Whfln the switch 38 closes, current flows from the supply conductor 36 through the terminal 40, the contact 42, the overload cantilever bimetal arm 46 to the irregular frame 52, thence through the narrow bimetal 62 (see FIGURE 4), the compensating bimetal 64, the spring contact arm 84 through the contact 85, through the contact 86 and through the armature 74, the spring member 76 and the electromagnet frame 78 to the terminal 86 of the electromagnet through which the current flows. After flowing through electromagnet 80, the current flows through the terminal conductor to the main winding terminal 30 from which the current flows through the main winding 24 to the junction 22 connecting with the second supply conductor 20.

This control is designed to operate effectively on normal voltages as well as extremely low voltages. This low voltage operation is provided through the arrangement by which the spring contact arm 66 is biased to closed position, thereby aiding the weakly energized electromagnet 80 in magnetically attracting the armature 74 against the bias .of its spring mounting 76. When the spring contact arm 66 engages the contact 68, the projecting end 70 continues to assist the armature 74 in its movement for a short distance until the armature 74 is close enough to the electromagnet 80 to be sufficiently attracted thereby and pulled to the attracted position shown in FIGURE 2 under low voltage conditions. The attraction provided by the electromagnet 80 pulls the armature 74 away from the extension 70 of the contact arm 66 so that the full bias of the contact arm 66 against the contact 68 maintains full contact pressure without any interruption during the entire starting period of the motor. This prevents damage to the starting contacts.

The attraction of the armature 74 also pulls the contact 86 away from the contact at the upper end of the contact arm 84. This forces the main winding current to flow through an alternate shunt path through the frame 52, the arm 92, the stop 94, the electric heater 96 supplementing the self-heating bimetal arm 46, through the conductor 98, the L-shaped stop member 121 and the major portion of the frame 79 of the electromagnet 80 to the terminal 88. The supplementary heater 96 there fore, during this period, adds to the self-heating provided by the flow of the line current through the cantilever bimetal arm 46 to provide quicker tripping during the starting period of the electric motor 28. During this period, heat is also stored in the heater 96. Should there be a stall or an unusually heavy starting load, sufficient in amount to overload the motor 28 and its

windings

24 and 26, as a result of the heat provided by the heavier current flow through it and the heat added by the heater 46, the cantilever bimetal 96 will snap away from the line contact 42 to the open circuit position shown in FIG- URE 3 against the stop 94, thereby deenergizing all circuits. The heater 96, however, will have stored up a certain amount of heat at the time of tripping upon such an overload which will continue to provide heat at a diminishing rate to the bimetal 46 for a period'of time to prolong the enforced idle period after the separation of the

overload protector contacts

46, 42 to allow further cooling of the electric motor 28 before an attempt is made to restart. This prevents the motor 28 from becoming too hot due to a premature subsequent attempt to restart following an overload.

If there is no overload during the starting period, the reduced current flow through the main winding 24 and the electromagnet coil 80 as a result of the increase of the speed of the motor beyond the balancing speed will sufficiently reduce the magnetic attraction upon the armature 74 to allow it to return to the position shown in FIGURE 1, thereby separating the starting

contacts

68, 66 to deenergize the phase winding 26. In addition, the

contacts

86, 84 will reclose to shunt the supplementary heater 96 and thereby substantially deenergize the heater 96 so as to discontinue its heating effect upon the cantilever bimetal arm 46. This will adjust the tripping point of the cantilever bimetal arm 46 so that full load and full current flow will be permitted through the

overload protector contacts

42, 46 without causing tripping.

However, should there be an overload during this period, the self-heating provided by the increased flow of current through the bimetal leg 62 beyond the full load current will cause it to bow to the right to cause the contact arm 84 to be moved away from the contact 86 to open the shunt for the heater 96 and thereby to reenergize the heater 96 to assist the cantilever arm 46 to open quickly to protect the motor 28 from the overload. The self-heating of the bimetal leg 62 during a prolonged starting period also assists in moving the spring contact member 66 to the open circuit position if this contact member remains in closed position for an excessively long period of time such as may occur under low voltage conditions. The leg 62, therefore, assists in better protecting both the phase winding 26 and the main winding 24 during both the starting and the running periods. It makes the supplementary heater 96 effective even if there should be a defective capacitor or a broken wire or a failure to close the phase winding

circuit contacts

42, 46 upon an attempt to start. During the starting period, the current in the main winding falls to reduce the amount of heating of the leg 62 to minimize nuisance tripping due to heat provided by the supplementary heater 96.

While the embodiment of the present invention, as herein disclosed, constitutes a preferred form, it is to be understood that other forms might be adopted.

What is claimed is as follows:

1. A control for an electric motor having main and phase windings, said control including a self-resetting thermal overload protector for deenergizing said motor upon an overload, an electric heater adapted to be connected in series with the main winding for accelerating the operation of said overload protector and for delaying the resetting thereof, a starting relay having normally open contacts adapted to be connected in series with said phase Winding for energizing said phase winding, and means including normally closed contact means operated by said starting relay to open position during the energization of the phase winding for energizing said heater during the starting period and connected in shunt circuit with only said electric heater for shunting said electric heater to substantially deenergize said heater during the remainder of the running period of the motor.

2. A control for an electric motor having main and phase windings, said control including a self-resetting thermal overload protector for deenergizing sai-d motor upon an overload, an electric heater adapted to be connected in series with the main winding for accelerating the operation of said overload protector and for delaying the resetting thereof, a starting relay having a magnet coil adapted to be connected in series with said main Winding and an armature and normally open starting contacts adapted to be connected in series with said phase winding, thermal means in series circuit relation with said starting contacts provided with means for assisting the opening thereof, means including a normally closed switch for connecting said thermal means in series circuit with the main Winding and for shunting said heater, said thermal means including means responsive to abnormal current flow through it for opening said normally closed switch to energize said heater.

3. A control as defined in claim 2 in which said armature has means for opening said normally closed switch and for closing said normally open contacts.

4. A control as defined in claim 1 having thermal current means adapted to be connected in series circuit with one of said windings and responsive to abnormal current flow for opening said normally closed contacts to energize said electric heater.

References Cited by the Examiner UNITED STATES PATENTS 2,255,437 9/ 1941 Pearce 318-221 2,374,967 5/ 1945 Alexander 318-221 2,521,120 9/1950 Harrold 3l8221 2,722,644 11/ 1955 Clark 318-221 ORIS L. RADER, Primary Examiner. G. A. FREIDBERG, Assistant Examiner.

Claims

1. A CONTROL FOR AN ELECTRIC MOTOR HAVING MAIN AND PHASE WINDINGS, SAID CONTROL INCLUDING A SELF-RESETTING THERMAL OVERLOAD PROTECTOR FOR DEENERGIZING SAID MOTOR UPON AN OVERLOAD, AN ELECTRIC HEATER ADAPTED TO BE CONNECTED IN SERIES WITH THE MAIN WINDING FOR ACCELERATING THE OPERATION OF SAID OVERLOAD PROTECTOR AND FOR DELAYING THE RESETTING THEREOF, A STARTING RELAY HAVING NORMALLY OPEN CONTACTS ADAPTED TO BE CONNECTED IN SERIES WITH SAID PHASE WINDING FOR ENERGIZING SAID PHASE WINDING, AND MEANS INCLUDING NORMALLY CLOSED CONTACT MEANS OPERATED BY SAID STARTING RELAY TO OPEN POSITION DURING THE ENERGIZATION OF THE PHASE WINDING FOR ENERGIZING SAID HEATER DURING THE STARTING PERIOD AND CONNECTED IN SHUNT CIRCUIT WHEN ONLY SAID ELECTRIC HEATER FOR SHUNTING SAID ELECTRIC HEATER TO SUBSTANTIALLY DEENERGIZE SAID HEATER DURING THE REMAINDER OF THE RUNNING PERIOD OF THE MOTOR.