The present invention relates to a refrigerant dehydrating filter according to the preamble of claim 1 and to a method of manufacturing such a filter.
It is well known that refrigeration systems need a filter to separate contaminating water from refrigerant and to trap various particles and other impurities. Dehydrating filters are known and are designed primarily to remove water from the refrigerant. As used herein, the term "refrigeration system" includes air conditioning systems and heat pumps etc and the term "refrigerant' should be understood to extend to fluids used in all these types of equipment.
Compact filters are also known in which an inlet hole into the filter and an outlet hole from the filter are found on a common base in order to present a compact design and to suit preferred applications. Alternatively, filters are known in which the inlet and outlet holes are arranged in different orientations due to their specific intended application.
European Patent Application No. 0 915 308 discloses such a filter, in which the refrigerant flows from an inlet up through desiccating material before the flow is reversed to send it down a tube to an outlet coaxial with the inlet that ends beyond the inlet. When the filter is screwed into a base connected to a condenser unit the inlet and outlet make connections with pipes defined in the base.
This design, and others in which the inlet and outlet are arranged in a different manner due to their specific type of application, make the filter easy to fit. However, this type of filter is structurally complex with a number of components, which must all be located correctly during the assembly process. This leads to assembly problems such that a filter can take a long time to construct. Additionally the various components may not be located securely, which can cause faulty seals.
European patent application 0 838 642 discloses a removable reservoir connected to a header of a condenser for a refrigeration circuit through which refrigeration fluid is passed. The reservoir is produced in the form of a replaceable cartridge provided with a connection able to cooperate with a base of conjugate shape which is fixed to the header and connected to the latter by an inlet manifold and an outlet manifold for the refrigeration fluid.
Swiss Patent No. 342,589 discloses a dehydrating filter characterised by a cylindrical reservoir, a fitting detachably installed in the top part of the reservoir and provided with inlet and outlet ports, an adapter secured in the fitting, two strainers each arranged at a distance from the top and bottom ends of the reservoir, a desiccating agent located between the two strainers, the strainers being provided with coaxial bores, and a vertical tube extending through said bores, the lower end of the tube terminating in the base of the reservoir while the upper end of the tube extends into the adapter and is tightly connected thereto. The adapter has an opening connecting a line for refrigeration fluid to the inside of the vertical tube via an inlet in the fitting, and the fitting having an outlet connected to a further line for the fluid, the whole assembly being so arranged that the fluid is able to flow through the inlet in the fitting, the opening in the adapter and down through the vertical tube, then up through the desiccating agent and finally out through the outlet in the fitting.
European patent application 0 915 307 discloses a fluid tank for an air conditioning condenser. The tank is screwed axially into a connecting base which is in turn brazed to a header box of the condenser. It contains an interchangeable axial cartridge and communicates with the header box through ducts provided in the connecting base.
According to an aspect of the present invention there is provided a refrigerant dehydration filter, comprising an external tube sealed at one end to define a return cavity; an internal tube coaxial with said external tube; a first external connection to said external tube and a second external connection to said internal tube to facilitate a transfer of refrigerant between said tubes, wherein said external tube contains desiccating material, characterised in that: said filter further comprises a filter capsule containing said desiccating material, said filter capsule being fitted within said external tube and having a coaxial tubular section through which said internal tube passes. According to another aspect of the present invention, a method for manufacturing a filter of this type is provided.
The present invention will now be described by way of example only, with reference to the accompanying drawings, of which:
A dehydrating filter embodying the present invention is illustrated in Figure 1. The filter has a hollow external casing 11, 12 of a cylindrical shape, in two interconnecting sections. The first of said sections 11 is substantially cup-shaped and is formed from an aluminium extrusion with a relatively thick base portion 13. Section 11 acts as a cover for a second section 12, constituting a major portion of the device.
The second section 12 also has a cylindrical body, open at one end and designed to couple up with the first section 11 by means of soldered joint 14. The other end of the second section 12 is restricted by a pair of coaxial sleeve sections 15, 16 that terminate in a hole 17. The second section 12 houses a filter capsule within its cylindrical volume. This capsule comprises a cup section 18 of cylindrical shape with an external diameter that can fit within the internal diameter of the section of the hollow external casing 12. The cup 18 has a coaxial tubular section 19 through which a tubular insert 20 passes.
A free annular space is provided between the external surface of the coaxial tubular section 19 and the internal surface of the cup section 18. This annular space is filled with a desiccating material 21 located between two annular felt discs, in the form of a cylindrical sandwich but having a hole down its middle. On the other side of the felt washers there is provided at one end a drilled stopper 23, turned towards the centre of the casing, while at the other end is the drilled base 24 of the cup section 18.
The tubular insert 20 passes into the coaxial tubular section 19 of the cup 18 starting off as a plain tubular section and then becoming a toothed or splined section 25 that extends towards the second sleeve 16 of the second part 12 of the casing, passing into it. The outward facing spline end 25 on the tubular insert 20 has an expanded section 26 which abuts the end of the sleeve section 16 preventing the tubular insert 20 from dropping inside the second part of the casing. The end of the tubular insert 20 has an enlarged diameter 27 onto which a gasket 28 is positioned. The gasket 28 prevents the input fluid from mixing with the output fluid from the filter when it is positioned within the base 29 of a condenser in line with a fluid input channel 30 and fluid output channel 31, as shown in Figure 2. A seal is also ensured due to the provision of two O-ring seals 32 mounted beyond the sleeve section 16.
The end of the tubular insert 20 facing the inside of the casing has a locating ring or similar 33 that keeps the capsule in position with respect to the tubular insert 20. The filter has input channels between the internal surfaces of the sleeve section 16 and the splines 25 on the tubular insert 20. These channels lead into sleeves 15 before passing through the drilled base 24 of the bucket section 18. Subsequently, the input fluid is admitted into the first felt washer 22, passing through the desiccating material 21 before reaching the second felt washer 22 followed by the drilled stopper 23 and escapes into the casing 11, 12. The fluid moves unimpeded into the open free end of the tubular insert 20 and passing through it escapes at the other coaxial end through the seal 27. It can be seen that the input and output channels are coaxial and therefore the filter is particularly compact and straightforward.
Locating ring 33 enables the very rapid assembly of the components of the filter. For example, the casing 11, 12 is formed in aluminium, while tubular insert 20 is fabricated in a plastic material, such as polyamide and is relatively straightforward to manufacture, The gasket is in hydrogenated nitrile to create a seal.
During manufacture, the external cylindrical casing is obtained by extrusion with a similar process being used to produce a second section 12 that completes the casing for the filter. Next, the felt washer 22 is inserted into the cup section 18 up against the drilled base 24. The annular space is then filled with the desiccating material 21 and the second felt washer 22 is positioned in the cup section 18 to contain the desiccating material. Finally, the drilled stopper 23 is put in place by pressing it into the cup section 18. The capsule is therefore ready to be assembled into the complete filter.
The second section of the extruded cylindrical casing forms sleeve sections 15, 16 in an extruded body in aluminium. External threading of this sleeve section 18 is then carried out thereby allowing the filter to be positioned into the hole 29.
This is then followed by a greasing stage then the tubular insert 20 is located into hole 17 of the second section 12 of the casing until the widened part 26 of the splines 25 is up against the end of the sleeve section 16 which prevents the tubular insert from entering the second section 12 of the casing.
The constructed capsule is inserted into the tubular insert 20 and held in place with locating ring 33. The casing is then assembled by soldering the two sections once they have been brought together at 14. This is done by fitting the two sections 11, 12 together and creating an annular solder joint.
The two O-ring seals are fitted on the external surface of the sleeve section 16. A ring type gasket 28 is fitted on the large diameter end section 27 of the tubular insert 20. Once the assembly is completed, an air-tightness test is performed to ensure that performance can be guaranteed in use.