Safety control for a motor driven compressor

Claim 2

In a refrigeration system including a compressor, a motor for driving the compressor and means for controlling operation of said motor, a safety control functioning as a circuit interrupt safety switch for controlling said motor operating control means, said compressor during operation generating high pressure of refrigerant at its outlet side and a relatively low pressure at its inlet side, and including lubricating mechanism for said compressor for pumping lubricating oil at an output pressure for said compressor, said safety control comprising; a first pressure sensor responsive to the output pressure of said lubricating mechanism, a second pressure sensor responsive to said pressure at said inlet side of said compressor, electrothermomechanical timer mechanism for timing a trial period, said timer mechanism during such period causing said motor operating control means to run said motor and at the expiration of which period said timer mechanism causes said motor operating means to stop said motor, pressure-responsive means responsive to a selected one of said pressure sensors for disabling said timer mechanism preventing stopping of the said motor under conditions where the pressure sensed attains a certain predetermined level before expiration of said trial period, and characterized in that, cycling means are provided responsive. to said timer mechanism for causing a predetermined number of reoperations of said motor operating control means for consecutive timed trial periods by said timer mechanism.

Claim 3

The system of claim 1, wherein said cycling means includes an electromagnetic stepper relay having four step positions, and said timer mechanism includes a thermal expansion timer having a first pair of normally opened contacts in an energizing circuit for said stepper relay and a second pair of normally closed contacts in an energizing circuit for said motor operating control means.

Claim 4

The system of claim 2, wherein said stepper relay includes contacts operable at its third step for disabling said timer mechanism and motor operating control means for stopping said cycling.

Claim 5

The system set forth in claim 3, wherein manual reset means are provided operable for selectively energizing said stepper relay for stepping said relay back to its first position.

Claim 6

The system of claim 3, wherein said pressure responsive means is a net differential pressure means responsive to the net differential of said pressures sensed by said first sensor at said lubricating mechanism output and said second sensor at said inlet for causing termination of said timing only under conditions where the net differential of said sensed pressures exceeds at least a predetermined amount.

Claim 7

The system of claim 3, wherein said pressure responsive means is a low pressure control responsive to said pressure sensed at the inlet side of said compressor by said second sensor for actuation to the condition terminating said timed period under conditions where said low pressure sensed exceeds at least a predetermined minimum.

Claim 8

The system of claim 3, wherein said pressure-responsive means includes low-pressure circuit interrupting means responsive to pressure sensed at said inlet side by said second sensor for actuation to a second condition under conditions where said inlet pressure sensed exceeds at least a predetermined minimum, and also includes differential pressure circuit interrupt means responsive to the net differential pressure between said sensed inlet pressure side and that sensed at the output of said lubricating mechanism by said first pressure sensor for actuation to a second condition under conditions where said net differential pressure exceeds at least a certain amount, characterized in that, said low pressure and net differeNtial pressure interrupt means are interconnected in the energizing circuit of said stepper relay and timer mechanism for terminating said timed period only under conditions where both said low pressure and differential pressure controls are in their said second actuated conditions, and under all other conditions cause said cycling control to effect said predetermined number of cycles.

Claim 9

The refrigeration system of claim 4, wherein said timer mechanism includes a thermal timer having a heater and a pair of normally closed contacts and a pair of normally opened contacts, and wherein said cycling control is a stepper relay having an energizing coil subject to the closing of said normally open pair of timer contacts, said stepper relay having four positions and four pairs of contacts, a first stepper pair of contacts opening with each energization of the stepper relay and closing with each deenergization thereof, second and third pairs of normally closed stepper contacts responsive to the third deenergization of said stepper relay coil for being actuated open and remaining open until a fourth deenergization and return to zero position of said stepper relay, said stepper relay having a fourth pair of contacts normally open which contacts are closed by upon the first step of said relay to its first position and remain closed until said relay steps to its fourth and zero position, and wherein said first and fourth pair of stepper contacts are connected in series circuit with said stepper relay coil and with the series circuit of a normally open pair of contacts of said pressure responsive means and said normally closed pair of contacts of said timer, and wherein said reset means includes a normally closed pair of contacts in series circuit with said second pair of normally closed stepper contacts, said motor control and said normally closed contacts of the timer, and wherein, said third pair of normally closed stepper relay contacts are connected in series with said timer heater, said normally closed contacts of said pressure-responsive means, and the normally closed contacts of said timer for providing a timed three cycles of operation of said motor-operating control means, said pressure responsive means upon actuation during any of said timed intervals terminating the timing of said timer and maintaining said motor operating control means in run condition, while effecting stepping of said stepper relay automatically to reset condition through said first set of normally closed stepper contacts and said fourth of stepper contacts.

Claim 10

The system of claim 8, wherein said manual reset means when actuated provides a shunt circuit path about said pressure responsive control for causing sequential cycling operating of said stepper relay to its said zero position.