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A helical screw rotary compressor for a closed loop refrigeration system such as an air conditioning system for a bus or like vehicle is connected in series with a condenser and an evaporator, in that order, with the evaporator at a raised position relative to the compressor and utilizes a vaporizab

A helical screw rotary compressor for a closed loop refrigeration system such as an air conditioning system for a bus or like vehicle is connected in series with a condenser and an evaporator, in that order, with the evaporator at a raised position relative to the compressor and utilizes a vaporizable refrigerant which is miscible with a lubricating oil employed to lubricate the moving components of the screw compressor. The bus engine driven, clutch operated, helical screw rotors are mounted within parallel intersecting bores within the compressor housing. A slide valve underlies the intermeshed rotors and forms a portion of the screw compressor envelope, the rotors opening to a suction port connected to the outlet side of the evaporator above the rotors. A high pressure discharge port at one end of the intermeshed rotors leads to an auxiliary chamber bearing an unload cylinder which drives the slide valve and which opens at the top to a housing discharge port leading to the condenser. An oil separator is interposed within the auxiliary chamber above the unload cylinder. An oil drain passage leads from the auxiliary chamber to an oversized oil sump within the housing beneath the rotors. The slide valve slides in a recess within the casing underlying the rotors. On the suction port side of the recess, a further drain passage leads through a drainage check valve to the sump. This structural arrangement permits all condensed refrigerant and the oil to return by gravity flow to the oil sump whose capacity is at least 1.5 times the volume of the normal oil charge for the system. Condensed refrigerant miscible in the oil and the oil entraining the refrigerant, upon compressor shut down, accumulates in the sump but does not reach the intermeshed rotors and thus prevents clutch burnout by liquid locking during initiation of compressor operation with the clutch mechanically connecting the engine to the intermeshed helical screw rotors.

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In combination, a closed loop refrigeration system for an engine driven motor vehicle, said closed loop refrigeration system comprising: a helical screw rotary compressor, a condenser, an evaporator, conduit means connecting said compressor, said condenser and said evaporator in a closed loop series

In combination, a closed loop refrigeration system for an engine driven motor vehicle, said closed loop refrigeration system comprising: a helical screw rotary compressor, a condenser, an evaporator, conduit means connecting said compressor, said condenser and said evaporator in a closed loop series refrigeration circuit, in that order, and an expansion valve means within said conduit means upstream of said evaporator, said compressor comprising a housing including intersecting parallel bores, intermeshed helical screw rotors mounted for rotation within said bores, said rotors including integral shafts, anti friction bearing pack assemblies carried by said housing, about said shafts for rotatably supporting said intermeshed helical screw rotors for rotation about the shaft axes, a recess underlying said rotors and open to said rotors, a slide valve slidably mounted in said recess, said housing defining a low pressure suction port open to said intermeshed helical screw rotors at one end of said rotors and a high pressure discharge port at the opposite end of said rotors, said slide valve being slidably mounted in said recess for selectively closing off the recess at an end proximate to said suction port, a mass of refrigerant provided within said closed loop system, an oil sump bearing a mass of oil, and defined by said housing underlying the intermeshed helical screw rotors and the slide valve. means for supplying oil under pressure to said bearings for lubrication of the bearing, such that oil lubricating the bearings adjacent to the suction port tends to move into the compressor area under pressure differential between the discharge port and the suction port, said vehicle comprising an internal combustion engine, clutch means mechanically connecting said engine to one of said rotor shafts for driving said intermeshed helical screw rotors about their axes, the improvement comprising: said sump being of a capacity of at least the volume of the oil required for lubrication of the compressor and the mass of refrigerant when in liquid form, said compressor further comprising first gravity flow oil drain passage means operatively connecting the discharge port to the sump for causing said sump to be at discharge pressure during normal operation of the compressor, and second oil drain passage means leading from the recess to the sump, and a ball check valve within said second oil drain passage means for permitting oil and liquid refrigerant draining back to the compressor upon shut down of the refrigeration system from said evaporator to drain from the recess into the oil sump but preventing reverse flow; whereby, during compressor shut down, the refrigerant may freely condense and be totally absorbed in the oil and fill said sump without liquid flooding of the intermeshed helical screw rotors and hydraulic locking of the rotors to prevent damage to the clutch means or engine upon compressor start up, and wherein, during start up, the slide valve recess is cut off from the oil sump to prevent refrigerant blow by from the discharge port side of the compressor through the first oil drain passage means to the sump and from the sump via said second oil drain passage means to the suction port of said compressor.