Liquid purification or separation – Flow – fluid pressure or material level – responsive – Fluid pressure responsive by-pass
Reexamination Certificate
2002-05-17
2003-08-12
Drodge, Joseph (Department: 1723)
Liquid purification or separation
Flow, fluid pressure or material level, responsive
Fluid pressure responsive by-pass
C210S132000, C210S167050, C210S232000, C210S333010, C210S323200, C210S340000, C210S416400, C126S197001
Reexamination Certificate
active
06605210
ABSTRACT:
The present disclosure relates to the subject matter disclosed in international application No. PCT/EP00/07654 of Aug. 8, 2000, which is incorporated herein by reference in its entirety and for all purposes.
The invention relates to a filter device for filtering a hydraulic fluid, with a filter housing in which a filter element is disposed.
The invention also relates to a filter element for a filter device of this type and to a hydraulic circuit with a filter device.
Filter devices of the type stated at the beginning have many uses, for example in self-propelled machinery, such as construction or agricultural machinery for example. In such cases, the hydraulic systems have to meet very high requirements concerning the cleanliness of the hydraulic fluid in order for them to operate as intended over long periods without any malfunctions and with little wear. With many hydraulic systems there is already a high risk of damage occurring to the hydraulic pumps being used when they are put into operation for the first time, on account of residues of dirt remaining in the hydraulic fluid tank. In particular in the case of complexly shaped tanks formed as a cast part or welded construction, reliable, thorough cleaning is scarcely possible with a reasonable amount of effort. Therefore, at least one protective filter which holds back dirt particles of a minimum size of about 60 &mgr;m is usually disposed upstream of the hydraulic pumps.
However, protective filters of this type are usually not adequate to ensure the required long-term wear resistance of the highly stressed hydraulic components. To do so, in many cases much smaller dirt particles have to be effectively filtered out from the hydraulic fluid. For this purpose, a separate fine filter, with a fineness of less than 15 &mgr;m, that is to say with which dirt particles of a minimum size of approximately 15 &mgr;m can be removed, may be used in addition to said protective filter. In this case, the protective filter is used in the form of a suction filter, which is disposed in the intake line of the hydraulic pump, and the fine filter is fitted in the return line or pressure line of the hydraulic system. In this case, screening elements are usually used as the suction filter, while filter elements with filter material of nonwoven fabric, which in many cases themselves still filter out dirt particles of a size of around 5 &mgr;m from the hydraulic fluid with an efficiency of at least 50%, can be used in the pressure or return filters. Although the use of two separate filters with different filter fineness makes it possible to achieve a long service life of the hydraulic system, it involves considerable costs both in terms of fitting out a system for the first time and in terms of servicing.
Alternatively, it may also be envisaged to use only a single filter with a fineness of at least about 20 &mgr;m, so that dirt particles of a size of at least 20 &mgr;m are still filtered out from the hydraulic fluid with an efficiency of 99% by means of the single filter used. This not only permits reliable protection of the hydraulic pumps, but also protects the further hydraulic components from contaminants. Since the filter is disposed upstream of the pump, however, and consequently has to be formed as a suction filter, a large overall volume is required for the filter, in order that, in spite of the filter fineness used, a relatively low permissible pressure loss on the suction side of the hydraulic pump is not exceeded. This disadvantage is particularly significant whenever a heavy-bodied oil has to be used as the hydraulic fluid or low temperatures, and consequently high viscosities for the hydraulic fluid, are to be expected when the hydraulic system is put into operation.
It is an object of the present invention to develop a filter device of the type stated at the beginning which ensures reliable protection both of a hydraulic pump and of other highly stressed hydraulic components and has a compact, easy-to-service form of construction.
This object is achieved according to the invention in the case of a filter device of the generic type by the filter element comprising a first and a second subelement, the first subelement having a higher filter fineness than the second subelement and both subelements being insertable through a common insertion opening into the filter housing, and by it being possible for hydraulic fluid to be fed to each subelement via a separate supply inflow in the filter housing and for filtered hydraulic fluid to be discharged from both subelements via a common outflow in the filter housing.
According to the invention, a combination filter element which can be inserted into the filter housing and has two subelements with different fineness is provided for the filter device. The filter housing has at least two access openings, so that different flows of hydraulic fluid can be fed to the two subelements. The filtered hydraulic fluid can then be discharged via a third opening in the filter housing. Such a configuration of the filter device makes it possible to dispose one of the two subelements of the filter element upstream of a hydraulic pump, while the other subelement can be disposed downstream of other hydraulic components. The subelement disposed upstream of the hydraulic pump may in this case have a coarser fineness than the other subelement, so that the pressure loss on the suction side of the hydraulic pump can be kept low, while at the same time even very small dirt particles can be filtered out of the hydraulic fluid by means of the other subelement, in that the subelement is disposed in the return line of the hydraulic system. To do so, separate access openings for the two subelements are provided on the filter housing.
Since the two subelements can be inserted into the filter housing via a common insertion opening, the filter device is also distinguished by being very easy to service, since it is not required to dismantle the filter device completely to allow the two subelements to be exchanged.
The two supply inflows are preferably separated fluid-tightly from each other by means of at least one sealing element. Such a configuration provides the possibility of inserting the two subelements into a common receiving space of the filter housing, into which the two supply inflows open, it then being ensured by at least one sealing element that the supply inflow for the first subelement is separated fluid-tightly from the supply inflow for the second subelement. O-ring seals may be used, for example, as the sealing elements. The sealing elements are preferably held on the subelements and can be inserted together with the filter elements into the filter housing.
In the case of a preferred embodiment, it is provided that at least the first subelement has an associated bypass line with a bypass valve. The first subelement is distinguished by a higher fineness, so that there is the risk, in particular for this subelement of it gradually becoming clogged during its use. This results in an increasing pressure loss. To avoid an impermissible pressure increase at the first subelement, the bypass valve is provided in the form of a pressure-relief valve, which releases the bypass line if a pressure increase beyond fixed normal values takes place on the flow-accepting side of the first subelement. This avoids damage to the first subelement.
It is of advantage if the bypass line connects the supply inflow of the first subelement to the supply inflow of the second subelement. Such a configuration has the advantage that, in the event of an impermissible pressure increase at the first subelement, the hydraulic fluid can continue to be filtered by means of the second subelement even though the first subelement is bypassed, so that, even when the first subelement is clogged, at least relatively coarse dirt particles continue to be filtered out of the hydraulic fluid by means of the second subelement.
Alternatively, it may be provided that the bypass line connects the supply inflow of the first subelement to the common outflow of
Cecil Terry K.
Drodge Joseph
FSP-Holding AG
Lipsitz Barry R.
McAllister Douglas M.
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