BACKGROUND OF THE INVENTION
The invention relates to a exchangeable filter cartridge for a liquid filter with an annularly constructed filter medium arranged on a support element. The invention further relates to a liquid filter in which such a filter cartridge is installed.
Filter cartridges of the initially described type are known, for instance, from U.S. Pat. No. 5,413,712. This document describes a filter cartridge comprising a support tube holding the filter medium whose end faces are provided with end disks. This filter cartridge can be replaced by removing a cover from the filter housing. A spring in the cover pushes the installed filter cartridge axially against a centrally arranged outlet port. A sealing membrane provides an axial seal between the outlet port and the end disk of the filter cartridge. The sealing membrane is simultaneously configured as a return flow barrier or check valve.
The disadvantage of the described prior art is the use of a spring to produce an axial force to act against the seal. This spring is an additional component in the filter unit and thus reduces the economic efficiency of the solution. Moreover, the axial force that can be applied by the spring to provide a seal is limited. Increasing the axial force by making the spring stiffer has the disadvantage of increasing the closing forces that have to be applied to the cover, which makes it more difficult to replace the filter element.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a cost effective filter cartridge.
Another object of the invention is to provide a filter cartridge which is easily mountable in a filter.
A further object of the invention is to provide a filter unit including a cost effective, easily mountable filter cartridge.
These and other objects are achieved in accordance with the present invention by providing an exchangeable filter cartridge assembly for a liquid filter comprising an annular filter medium with sealed end faces; a support element mounted interiorly of the annular filter medium for supporting the filter medium, the support element having a seat in an end area for a sealing membrane which serves as a return flow barrier, the sealing membrane having a sealing edge for support inside the liquid filter and for sealing a filter inlet, and an additional sealing surface to provide a radial seal between the support element and a filter housing.
In accordance with a further aspect of the invention, the objects are achieved by providing a liquid filter comprising an openable housing with an inlet and an outlet, and an annular filter cartridge disposed on a central support element in the housing, an elastic sealing membrane connected to a seat provided on one end of the support element, the sealing membrane having a sealing edge which is supported inside the housing in such a way that it forms a return flow barrier over the inlet.
The filter cartridge according to the invention has a support element, which is surrounded by an annular filter medium. The support element may have a circular or elliptical cross section. It must have openings through which the liquid from the filter medium can flow into the interior of the support element. The filter medium is mounted on the support element in such a way that the support element prevents it from being deformed or collapsing. The filter medium is preferably made of a pleated or star-folded filter paper. Alternatively, rolls of a nonwoven material or multi-layered filter media of any shape may be used, all of which have in common that they annularly surround the support element.
The invention is characterized by a seat that is formed in the support element to receive a sealing membrane, which may integrate two functions. On the one hand the sealing membrane has a sealing edge, which is supported inside the housing in such a way that the inlet is sealed. When there is no flow through the filter, this creates a return flow barrier or check valve for liquid residues that may remain in the housing, for instance, when the filter is removed. When liquid flows into the inlet of the filter, the sealing edge of the sealing membrane is lifted, so that the liquid can flow into the unfiltered side of the housing volume of the filter.
The second function of the sealing membrane is to provide a direct radial seal between the support element and any housing part. This makes it possible, for instance, to tightly separate the unfiltered side from the filtered side. It is particularly advantageous that the support element may be sealed with respect to an outlet port that connects the interior of the support element with the outlet. The interior of the filter simultaneously forms the filtered side of the filter. This results in a particularly compact embodiment of the liquid filter of the invention.
The configuration of the seat on the support element facilitates mounting of the filter cartridge during initial installation or in any subsequent filter replacement. The filter cartridge and the sealing membrane can be preassembled and then inserted into the housing. The filter cartridge unit, as a whole, is simple to handle, which minimizes possible installation errors. At the same time, the radial seal between center tube and housing assures that the filter functions reliably, since axial tolerances are not critical to the functioning of the seal. An additional spring to produce the axial pressure of the filter cartridge against the housing is not necessary and can be omitted. This simultaneously reduces the mounting forces required to screw on the cover and consequently simplifies the mounting process.
In accordance with a further embodiment of the invention, the sealing membrane is permanently connected to the end area of the support element. This may be accomplished, for instance, by producing the support element using a two-component molding technique. For instance, the support element can be injection-molded from plastic and the sealing membrane from an elastomer that adheres to the plastic. Another option is to adhesively bond the sealing membrane to the support element. In either case, the reliability of the seal between support element and sealing membrane is enhanced, which increases the reliability of the filter unit.
In a further embodiment of the invention, the end area of the support element is provided with a safety interlock to create a form-fit connection between sealing membrane and support element. This assures that the sealing membrane will remain securely on the filter cartridge when the cartridge is removed. This can be accomplished, in particular, in that the form-fit connection acts in the direction of the radial seal between support element and housing. As long as there is increased friction during removal between these two components as a result of the sealing effect, the form-fit connection between the sealing membrane and the support element is simultaneously assured.
When the filter cartridge is removed, however, the sealing membrane can be easily replaced since it is made of an elastomer, so that it can be stretched to overcome the interlocking connection and remove the sealing membrane.
A further embodiment of the invention provides that the support element protrude axially beyond the filter medium. This creates sufficient clearance for the sealing membrane, so that the functional reliability of the filter is further enhanced.
In accordance with one specific embodiment of the invention, the filter cartridge is constructed in such a way that the filter medium is replaceably arranged on the support element. This can be achieved particularly in that the end faces of the filter medium are provided with end disks or foils, which simultaneously seal the end faces of the filter medium and provide a radial seal with respect to the support element. The end disks may advantageously be made of nitrile butadiene rubber. This is an elastomeric mixture that remains sufficiently resilient after a curing process to provide a seal with respect to the support element. The curing process simultaneously produces a tight connection with respect to the end faces of the filter medium.
The described embodiment of the filter cartridge has the advantage that a minimum amount of material has to be discarded when the filter medium is replaced. Both the support tube and the sealing membrane can be reused. The filter medium and the end disks are completely free of metal, which facilitates their disposal, for instance by incineration.
If the sealing membrane is permanently connected to the support element, the filter medium on the support element can be replaced via the opposite end. The support element is inserted into the new filter medium so that a new seal is produced between the end disks and the support element.
The support element is advantageously made in one piece. This is preferably accomplished by plastic injection molding and further optimizes filter cartridge production with respect to costs.
A particularly advantageous embodiment of the liquid filter unit is obtained if the housing has a substantially cylindrical shape and the inlet and outlet are accommodated in the base plate of the housing. The base plate furthermore has a threaded socket to attach the liquid filter at the installation site. Thus the configuration essentially corresponds to that of conventional disposable filters, so that the housing of the exchangeable filter can be installed instead of a throwaway filter.
When the filter is due to be replaced, the liquid filter as a whole is unscrewed from the installation site. The sealing membrane prevents any liquid residues from flowing out of the filter housing. The filter housing is then opened to its optimal position so that the residual oil remains in the housing while the filter cartridge is being replaced. After the housing is mounted, the liquid filter can be remounted at the installation site.
These and other features of preferred embodiments of the invention, in addition to being set forth in the claims, are also disclosed in the specification and/or in the drawings, and the individual features each may be implemented in embodiments of the invention either individually or in the form of subcombinations of two or more features and can be applied to other fields of use and may constitute advantageous, separately protectable constructions for which protection is also claimed.