US2302050A - Split-phase motor control - Google Patents

Description

1942- G. c. PEARCE 2,302,050

SPLIT'PHASE MOTOR CONTROL Filed Jan. 51, 1939 1 VENTOR. MW

ATTORNEYS MZL Patented Nov. 17, 1942 SPLIT-PHASE MOTOR CONTROL George C. Pearce, Dayton, Ohio, assignor to General Motors Corporation, Dayton, Ohio, a corporation of Delaware Application January 31, 1939, Serial No. 253,828 1 Claim. (Cl. 172-279) This invention relates to refrigerating apparatus and more particularly to control means for controlling single phase, alternating current, electric motors. Q

In refrigerating systems and other installations it is customary to provide a thermostatic switch for starting and stopping the motor which drives the compressor and an electro-thermal or electromagnetic starting relay which controls enererates a tilting mercury tube. This tilting mercury tube has a contact at one end connecting with one end of the starting winding and a pair of contacts at the other end, one of which is connected to a source of power and the other of which is connected'to the common terminal of the starting and running windings. In the middle of the mercury tube, between the contacts'at either end of the tube, there is provided glzation and deenergization of the starting winda dam having an orifice therein. When the mering of the motor. This second control is indecury tube is tilted to the position shown in Fig. 2, pendent of the thermostat control excepting no current flows because none of the sets of conthat it is operated electrically when the thermotacts are bridged. However, when the mercury stat energizes the motor circuit. Thus a dual tube is changed from the position shown in Fig. control has been necessary for such systems. In 2 to the position shown in Fig. 3 all three of the such a system, the snap action provided in the contacts are bridged by the mercury so that both thermostat is somewhat noisy and in addition the the startingand running windings are energized, electromagnetic or the electro-thermal starting However, after the mercury tube remains in the relay are also somewhat noisy. position shown in Fig. 3 for a short time the mer- It is an object of my invention to provide a cury runs to one end of the tube, as shown in simplified control for refrigerating systems and Fig. 4, so that the long contact which connects other installations in which the thermostat dito the starting windings is no longer Contaeted rectly controls the energization of both the starty e mercury a in this y the Startin ing and the running windings, winding is deenergized. The length of time the It is another object of my invention to provide tart g W nd ng is ene gized is determined by a pressure operated control in which the movement provided by the pressure operated means operates the contact means for controlling the energization of both the starting and running windings.

It is another object of my invention to provide a control in which the force provided by the pressure operated-means furnishes the power for closing and opening both the starting and running winding circuits of the electric motor.

It is still another object of my invention to provide a control which is very silent.

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

In the drawing:

Fig. 1 is a view partly diagrammatic showing a refrigerating system and a control therefor embodying my invention;

Fig. 2 is a sectional view of the mercury tube in the ofi position;

Fig. 3 is a sectional View of the mercury tube when tripped to starting position; and

I Fig. 4 is a sectional view of the mercury tube showing conditions prevailing during the running period.

Briefly, I have shown a refrigerating system provided with a thermostat control which opthe size of the orifice.

Referring now to the drawing and more particularly to Fig. 1, there is shown for the purpose of illustrating my invention, a refrigerating system including a compressor 20 for compressing refrigerant and for forwarding the compressed refrigerant to a condenser 22 where the condensed refrigerant is liquefied and collected in a receiver 24. From the receiver the liquid refrigerant is forwarded under the control of a suitable expansion device 26 such as an expansion valve or restrictor to an evaporating means 28 located within the compartment 30 to be cooled, The refrigerant evaporates within the evaporating means 28 under reduced pressure and absorbs heat from the air or fluid within the compartment 30. This evaporated refrigerant is returned to the compressor through the return conduit 32. The compressor 20 is driven by an electric motor 34 shown diagrammatically. This motor 34 is shownas of the split phase type having starting winding 36 and a running winding 38. Instead of the split phase type a capacitor start motor having a capacitor connected in series or parallel with the starting winding 36 may also be used in conjunction with the control herein disclosed.

Heretofore it has been customary to provide a thermostat in series with the running winding 38 and to provide an electrically operated electromagnetic or electrothermal relay which is operated by the current flowing through the .running winding 88 for operating contacts for controlling the energizing of the starting winding 36. There has always been some difliculty with these relays, particularly because of fluctuating voltage conditions and different voltage conditions existing in diiferent communities and even in different portions of the diflerent communities. It has therefore been necessary to provide voltage compensating devices or other protective devices to accommodate the various voltage conditions to which the motor may be subjected. These starting devices require a certain amount of energy for their operation and are also somewhat noisy and troublesome,

In order to overcome these difliculties I have provided a mercury tube type of contact mechanism which not only controls energization of the running winding but also controls the energization of the starting winding. The mercury tube controls are in themselves substantially noiseless and trouble free. They are sealed so that there is practically no contact trouble. By my improved arrangement only one tube is required for controlling both windings.

In my arrangement one of the sources of power is connected by conductor 82 to the contact 88 within the sealed glass mercury tube 88 which forms a part of the thermostat control 88 for the refrigerating system. One end of the running winding 38 and one end of the starting winding 88 are connected together and this connection is in turn connected by the conductor 88 to the other lines of the source of power. The other end of the running winding 88 is connected by the conductor 58 to a winding which is coiled about a ratchet wheel type of solder pot overload as designated by the reference character 52 which, in turn is connected by the conductor 58 to a second contact 58 within the mercury tube 88. a

The contacts 88 and 58 are in one end of the tube while the third contact 58 extends to the opposite end of the tube and has its end portion turned downwardly.

Near the middle of the tube is provided a dam 88 which may be formed of glass or metal fused into the glass walls of the tube. This dam is located between the turned down end of the contact 58 and the contacts 88 and 58. This dam is slanted so as to force the mercury to flow through an orifice 82 in moving from the end where the contact 58 is located to the opposite end where the contacts 88 and 88 are located. This orifice holds some of the mercury in contact with the contact 58 for a brief period of time so that all the contacts are bridged by the mercury as shown in Fig. 3. During this brief period of ment of the mercury tube to the angle shown in Figs. 3 and 4, while the stop 12 limits the movement of the tube to the angle shown in Fig. 2. In order to provide a snap action so that a differential may be provided between starting and stopping, the member 88 is provided with a pin 18 at its upper end to which is connected a light tension toggle spring 18 having its lower end connected to a pin 18 formed on the pivot bracket 88.

The member 88 is also provided with a lever arm 88 having its end portion connected by a link 82 to the end of a primary lever 88 pivotally connected by the threaded pin 88 to an upwardly extending arm 88 of the switch frame. The switch frame is also provided with a base portion 88 upon which is mounted a metal bellows 82 having a pin on its upper end which engages the primary lever 88. This bellows 82 is connected by capillary tubing 88 to a thermostat bulb 88 mounted upon the evaporating means 28. This bulb 88 may be charged with a volatile fluid so that the pressure within the bellows 82 will correspond with the temperature of the evaporating means. However, if desired, the bulb 88 may be placed out of contact with the evaporating means,

but within the compartment 88 so that it will be responsive to the temperature of the fluid in the compartment rather than to the temperature of the evaporating means 28. The expansion of the bellows 82 is opposed by a compression type coil spring 88 which has its tension adjusted by a finger knob III by which the temperature at which the bellows moves the mercury tube from one extreme position to the other may thus be adjusted.

In order to protect the motor 88 and particularly the running winding 88 from overloads and in order to use the mercury contacts for the overload contacts, I pivotally mount the pivot support bracket 88 upon the pin H8 which pivotally connects the bracket 88 to an ear provided upon the base 88. A tension type coil spring In con-- nects a portion of the bracket 88 above the pivot pin H8 to a pin H8 so as to tend to turn the time the motor will start upon both windings and v I clamp at its center portion, which extends from a leverand bracket member 88, pivotally mounted upon the threaded pin 88 which is threaded into the pivot support member 88. The member 88 is provided with stop projections 18 and 12 which engage the sides of the pivot support 88 to limit the tilting movement of the mercury tube 88 in either direction. The stop I8 limitsv the movebracket 88 in a clockwise direction to the pivot pin H8. This will tilt the mercury tube 88 into the position shown in Fig. 2 so as to prevent the energization of the electric motor 88. The ratchet wheel solder pot device 82 normally prevents the movement of the bracket 88 to this position since it holds the pawl I21 provided on pivot support 88 so as to prevent clockwise movement of the pivot support 88 upon the pivot pin I 18. When an overload occurs the heat given 0! by the current flowing in the coil around the solder pot ratchet wheel device 82 will heat the solder to permit the ratchet wheel to rotate and release the pawl i2! and the pivot support 88 to permit the pivot support 88 to rotate about the pivot H8 in order to move the meurcury tube to the position shown in Fig. 2. The pivot support 88 is returned to its normal operating position after the solder congeals and again holds the ratchet wheel. This is done by manually operating the lever I28 which projects from the pivot support 88.

The control as shown in Fig. 1 shows the refrigerating system and its driving motor operating under normal running conditions. The mercury tube 88 is in the position shown in Fig. 8 and only the running winding 88 is energized. When the evaporating means 28 is sumciently cool, the pressure within the bellows 82 will be lowered 'sufliciently to enable the spring 88 to force the primary lever 84 downwardly to throw the lever portion of bracket 64 across its dead center so that the mercury tube is moved to the position shown in Fig. 2, thereby stopping the operation of the motor and'the refrigerating system.

When the evaporator 28 again warms up, the pressure within the bellows 92 will become so!- iiciently great to overcome the tension of the compression spring 98 and the toggle spring 16 to move the mercury tube 46 back to the position shown in Fig. 1. When the mercury tube is moved to the position shown in Fig. l the mercury will be disposed as shown in Fig. 3, with a portion of the mercury being held by the dam in contact with the starting winding contact 58, while another portion is in contact with the other two contacts 44 and 56. The mercury flowing through the orifice 62 will connect the two pools of mercury so that both the main contact 56 and the starting contact 58 will be connected or bridged electrically to the power supply contact 44. This will make it possible for the motor to start. The amount of mercury held behind the dam 62, as shown in Fig. 3, together with the size of orifice determines the length of time the starting winding is energized since this determines the length of time the mercury remains in contact with the contact 58 as shown in' Fig. 3. It is only necessary that the starting winding remain energized a very short length of time allowing the motor to begin to rotate and to attain some speed. The mercury will rather quickly flow through the orifice G2 to the lower end of the mercury tube 48 so that it will then be disside of a source of current for energizing said seen that this control is simple, eflicient and reliable. and it is also exceptionally quiet.

While the form of embodiment of the inventionas herein disclosed, constitutes a preferred form, it is to be understood that other forms might be adopted, all coming within the scope of the claim which follows:

What is claimed is as follows:

Control means for an electric motor having starting and running windings connected to one side of a source of current comprising in combination, a sealed tube partially filled-with electric conducting fluid, said sealed tube being provided with an electrode adapted to be connected to said starting winding, said sealed tube being provided with a second electrode adapted to be connected to the running winding and a third electrode adapted to be connected to the other windings, means for tilting the tube, and means within said tube whereby upon tilting the tube in the one direction the circuit is first closed between said third electrode which is connected to mined time interval.

GEORGE C. PEARCE.

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