GB578031A - Improvements relating to overload protector devices for electric refrigerator motors - Google Patents

Abstract

578,031. Refrigerating systems. CONSTANTINE, W. W. (General Motors Corporation). June 20, 1944, No. 11694. [Class 29] [Also in Group XXXVII] A thermal overload switch for protecting refrigerator motors of the sealed motor compressor unit type has means for increasing the permissible overload when the refrigerant pressure in the sealed unit rises and for increasing the time delay between successive abortive attempts at starting. In Fig. 1, the sealed unit 20 is connected by a tube 30 to the low pressure evaporator tube 40 and the pump feeds an expansion valve 38 through a condenser tube 36. The bimetallic strip 42 which is heated bv an element 44 in series with the motor, is attached at its free end by a pair of springs 48 to two ears on a rigid arm 50, the other end of which is riveted by the moving contact 52 to a flexible strip fixed to a post 56 at its other end. The arm 50 is moved up or down according to whether the pull of the springs is above or below the centre-line position. On a rise of temperature the arm is pulled down and the flexible strip is bent up to open the contact. The bimetallic strip 42 is carried on a rigid bar 72, flexibly mounted at one end on a post 75 and actuated at its free end between adjustable stops 88, 90, against an adjustable spring 84, by a bellows 80 connected through a tube 82 to the sealed unit. As the vapour pressure rises its cooling properties improve and the expansion of the bellows raises the bar 72 and increases the protector rating. To protect the motor against too frequent automatic attempts at restarting, the resetting adjusting screw 92, limiting the opening motion of the contact, is mounted on a bimetallic strip 94 heated by an element 70 in series with the starting winding 28 of the motor. Successive attempts to start heat the bimetallic strip and so raise the screw 92 to produce a longer delay before contact is restored. A modification is described, Fig. 2 (not shown), in which the sealed unit is connected to the high-pressure side of the expansion valve and the heater giving protection against successive restarting attempts is connected in parallel with the starting winding of the motor.