ORIFICE TUBE FOR AN AUTOMOTIVE AIR CONDITIONING SYSTEM

Abstract: An orifice tube for use as an expansion valve in an auto­ motive air conditioning system includes a cylindrical annular mass of porous material (32) having a cavity (31) extending coaxially through it. The orifice tube provides a variable vol­ ume of refrigerant to the refrigeration circuit, controlled acc­ ording to the load on the air conditioning system.

Description: ORIFICE TUBE FOR AN AUTOMOTIVE AIR CONDITIONING SYSTEM The invention relates to an orifice tube for use as an expansion valve within an automotive air conditioning system. A typical, known refrigeration circuit for an automotive air conditioning system includes a compressor driven by an automobile engine, a condenser, an orifice tube used as an expansion valve and an evaporator. In standard operating fashion, the refrigerant is discharged from the compressor and passes, respectively, through the condenser, the orifice tube and the evaporator, and returns to the inlet port of the compressor. The refrigerant causes the evaporator to absord surrounding heat from the inside of a car or other vehicle, It is difficult to control the volume of the refrigerant flowing through the refrigerant circuit of an automotive air conditioning system with a typical orifice tube used as an expansion valve because such an orifice tube has a fixed volume. In particular, when the air conditioning load is low, the volume of the refrigerant flowing through the circuit is too much; and, when the air conditioning system must refrigerate or cool quickly, it is impossible to increase the volume of the flowing refrigerant according to the increase of the air conditioning load. According to the present invention, an orifice tube for use in an automotive air conditioning system as an expansion valve for expanding refrigerant circulating in a refrigeration circuit from its high pressure side to its low pressure side and into an evaporator, includes a housing and means within the housing for providing a variable volume of refrigerant for circulation in the circuit dependent upon the load on the air conditioning system. An air conditioning system incorporating an orifice tube in accordance with the invention is illustrated in the accompanying drawings, in which: Figure 1 shows a refrigeration circuit; Figure 2 is an axial section of the orifice tube; Figure 3 is a graph illustrating the relation between the air conditioning load and the weight of the refrigerant circulating within the circuit; and, Figure 4 is a graph illustrating the relation between the air conditioning load and the pressure loss across the orifice tube. Referring to Figure 1, the illustrated refrigeration circuit for an automotive air conditioning system includes a compressor 1, a condenser 2, an orifice tube 3, an evaporator 4 and an accumulator 5. The refrigerant discharged from the outlet port of the compressor 1 goes through the condenser 2, orifice tube 3, evaporator 4 and accumulator 5, and returns to the inlet port of compressor 1. As shown in Figure 2, the orifice tube 3 comprises a cylindrical housing 33 and an annular cylindrical mass of porous plastics or metallic material 32. The porous material 32 extends axially through the housing 33 and has a cavity 31 extending coaxially through it. When the air conditioning load is low, and the volume of the required refrigerant is low, the refrigerant mainly flows through the cavity 31 which has a relatively low flow resistance. When the air conditioning load is high, and the volume of the required refrigerant is greater, the refrigerant is pumped at a higher pressure and rate and overcomes the greater resistance to flow in the porous material 32, so that the volume of the refrigerant which passes through the porous material 32 increases. The volume and, hence, the weight of the refrigerant flowing through the refrigeration circuit is thus controlled and increases because the volume of refrigerant present in the porous material 321, which did not flow during the low load conditions, enters the circulating flow during the high load condition. Figure 3 shows the relationship between the air conditioning load in kcal/hr and the weight per hour in kg/hr of the refrigerant circulating through the circuit, referred to as the circulating refrigerant weight. The circulating refrigerant weight in an automotive air conditioning system in accordance with the present invention utilizing an orifice tube having a cavity diameter of 1.5 mm and a porous material outer diameter of 4.0 mm is illustrated in solid line; and the circulating refrigerant weight in an automotive air conditioning system using a typical existing orifice tube having an open interior, for example, with an inner diameter of 1.9 to 2.0 mm, is illustrated in broken line. The circulating refrigerant weight using the orifice tube of the present invention is less than the circulating refrigerant weight in the existing autbmotive air conditioning system when the air conditioning load is low, for example, in the 1000 to 2000 kcal/hr range. Also, the circulating refrigerant weight in the automotive air conditioning system in accordance with the present invention is more than that in the existing automotive air conditioning system when the air conditioming load is high, for example, above 3000 kcal/hr. The orifice tube of the present invention thus provides a variable volume of refrigerant according to the load requirements of the air conditioning system. Figure 4 shows the relationship between the air conditioning load in kcal/hr and the pressure loss 2 across the orifice tube in kg/cm2. The pressure loss illustrated in solid line is for an automotive air conditioning system in accordance with the present invention utilizing an orifice tube with a cavity diameter of 1.5 mm and a porous material outer diamter of 4.0 mm; and the pressure loss illustrated in broken line is for a typical existing automotive air conditioning system using an orifice tube with an open interior having an inner diameter of 1.9 to 2.0 mm. The pressure loss using the orifice tube of the present invention is less than that in the existing automotive air conditioning system; particularly, when the air conditioning load is high, the pressure loss in the automotive air conditioner in accordance with the present invention is much less than that in the existing automotive air conditioner, for example, approximately 3 kg/cm2 less (11 to 13 kg/cm2) at an air conditioning load of 5000 kcal/hr. Operating the air conditioning system at such lower pressure losses across the orifice tube enhances the efficiency of the system. As mentioned above, since the area through which the refrigerant flows in orifice tube 3 in accordance with the present invention comprises both the cavity portion 31 and the porous material 32, the volume of the refrigerant which cirulates through to the circuit provided by the porous material 32, and hence the volume of the refrigerant can be properly controlled according to the air conditioning load, particularly during low air conditioning load or high air conditioning load.

Claims: CLAIMS 1. An orifice tube for use in an automotive air conditioning system as an expansion valve for expanding refrigerant circulating in a refrigeration circuit from its high pressure side to its low pressure side and into an evaporator, characterised in that the orifice tube includes a housing (33) and means (32) within the housing for providing a variable volume of refrigerant for circulation in the circuit dependant upon the load on the air conditioning system. 2. An orifice tube according to claim 1, wherein the means for providing a variable volume of refrigerant includes a mass (32) of porous material carried in the housing and providing a first resistance to the flow of the refrigerant through the orifice tube, and a flow area (31) through the housing providing a second resistance to the flow of the refrigerant through the orifice tube, the second resistance being less than the first resistance whereby the volume of the refrigerant circulating in the refrigeration circuit increases as the load on the air conditioning system increases. 3. An orifice tube according to claim 2, wherein the flow area comprises a cavity (31) formed through the porous material (32). 4. An orifice tube according to claim 2 or claim 3, wherein the housing (33) is cylindrical and the porous material (32) is cylindrical and extends coaxially within the tube. 5. An orifice tube according to claim 2 and 3, wherein the cavity (31) extends coaxially through the porous material (32). 6. An orifice tube according to any one of claims 2 to 5, wherein the porous material is plastics. 7. An orifice tube according to any one of claims 2 to 5, wherein the porous material is metallic. 8. An automotive air conditioning system having a refrigeration circuit incorporating an expansion valve in the form of an orifice tube in accordance with any one of the preceding claims.

Inventors: SATO, MOTOHARU
Applicants: SANDEN CORPORATION
Application year: 1985
Main classification: F25B41
IPC codes: B60H1, F25B41