Patent Publication Number: US-2011056875-A1

Title: Filter apparatus and filter element for such a filter apparatus

Description:
The invention relates to a filter apparatus, in particular intended for installation in a fluid reservoir tank. The corresponding engineering solutions are also referred to, according to the professional terminology of the field, as in-tank solutions. Furthermore, the invention relates to a filter element for this kind of filter apparatus. 
     EP 1 419 807 B1 discloses an in-tank filter apparatus, with an exchangeable filter element, which can be accommodated in a reservoir tank for fluids, in particular in the form of hydraulic fluid, and which separates a dirty side from a clean side. Furthermore, the prior art solution is provided with a receptacle, which holds in a removable manner the filter element and which has a passage for the filtered fluid in the direction of the clean side of the tank. In this case there is a retaining element, which inhibits any passage of foreign bodies through the opening of the passage to the clean side of the tank. In the engineering solution known from the prior art, a cone serves as the retaining element. The shell of the cone is perforated so that when the filter element is changed, foreign bodies are prevented from passing to the clean side of the tank, but the fluid in the element can drain, provided that it is exchanged for a new element. The installed filter element has a pleated filter mat, which is supported by a support tube jacket downstream of the specified direction of flow. 
     A comparable in-tank solution is also disclosed in DE 10 2004 014 149 B4, where the prior art filter apparatus has at least one filter element with a pleated filter mat, which can be received in a filter housing, which can be connected to a fluid system, in particular in the form of a hydraulic reservoir tank, through fluid connections by means of a connection system in such a way that a fluid is enabled to circulate. The filter housing can be mounted in a removable manner on said fluid device by means of an attachment mechanism. This attachment mechanism is embodied in the form of a bayonet catch, which can be locked and released by rotating the filter housing. In this context the attachment mechanism has at least one moveable locking element which is configured in the manner of a rotationally mounted rotary disk valve, which in the locking position blocks the respective fluid connection, which can be assigned to said rotary disk valve. When the rotary disk valve moves into an open position, it releases said respective fluid connection for the passage of fluid. 
     During filtration with such in-tank filter apparatus, there is the basic tendency, especially in the event of high working pressure conditions and/or large quantities of fluid, for the fluid that is to be cleaned to splash and produce foam during its passage through the respective filter element. The tendency to produce foam is caused by the gas bubbles, in particular bubbles of air, which are routinely entrained in the fluid, especially in the form of hydraulic oil, in the preceding hydraulic working circuit. This is especially the case when such filter apparatus are used for mobile machines, such as excavators, wheel loaders, or telescopic loaders, etc., that are largely provided with a working hydraulic system, for example, in the form of hydraulic cylinders, which can be supplied and controlled by pumps. In order to improve the prior art solutions in such a way that the fluid that produces foam and splashes out of the filter element is prevented from making direct contact with the rest of the fluid or oil volume in the reservoir tank, the filter elements are confined in suitable enclosing housings inside the tank. Each enclosing housing forms a kind of presettling space or pre-chamber, in which the fluid to be cleaned can become quiescent, and any gas bubbles that may have formed can escape upwards as a function of their buoyancy force. However, the said settling chambers occupy a relatively large amount of design space inside the actual tank volume, so that ultimately the result is a reservoir tank that in its entirety is too large in design. Especially if the working pressure conditions are high and/or the amounts of fluid to be filtered are very large, the volume of the pre-chambers is routinely insufficient to allow the oil to become adequately quiescent before delivery into the actual reservoir tank. 
     Therefore, working on the basis of this prior art, the object of the invention is to further improve the known solutions in such a way that they can also be used unconditionally for mobile applications and that while maintaining the advantages of cleaning the fluid especially well, a space-saving and cost-effective solution is provided, with which it is easy to deliver the fluid to a reservoir tank even in the event of high pressure conditions and/or very large quantities of fluid. 
     This kind of problem is solved by a filter apparatus having the features disclosed in claim  1  in its entirety as well as a filter element having the features disclosed in claim  10 . 
     The filter apparatus according to the invention has at least one preferably exchangeable filter element, through which the fluid flows from the inside to the outside and which is surrounded, in each case maintaining a presettable radial distance and with formation of a fluid flow space, by a housing wall, which has a plurality of passage points, of which some are arranged below the variable fluid level in the reservoir tank and the rest of the passage points are arranged above this fluid level. Owing to this arrangement, the fluid that is cleaned by the respective filter element and that enters into the fluid flow space flows in a laminar manner through the assignable passage points into the reservoir tank in the area of the respective flow level and above the same. As a result, the undesired formation of splashes and foam as the fluid emerges is reliably avoided. Owing to the pressure differential between the inflowing, uncleaned fluid and the outflowing, cleaned fluid, the latter can be raised above the fluid level in the fluid flow space in the tank, with simultaneous distribution along the inside of the housing wall with the passage points, to which end capillary effects may also contribute. Then the resulting uniform fluid film makes it possible for the fluid to emerge without splashing and foaming out of the said passage points at right angles to the housing wall. 
     To the extent that the cleaned fluid in the fluid flow space exhibits any gas bubbles, like air bubbles, they are also delivered to the respective passage point that collects the bubbles for a delivery inside the reservoir tank that is close to the fluid level. To this end the bubbles become larger in their volume preferably for the purpose of an easier delivery. In this way the gas bubbles obtain a higher buoyancy force and separate more easily from the emerging, cleaned fluid volume, in particular in such a manner that there is no formation of either foam or splashes that would otherwise promote the entrainment of gas or air in the emerging fluid volume. To the extent that the fluid volume is substantially degassed inside the reservoir tank, it is possible to reliably avoid any malfunction due to gas bubbles and any damage to the working hydraulic system under normal operating conditions, when the fluid is correspondingly removed and conveyed to the working hydraulic system. Owing to the homogeneous emergence characteristics, the floating particulates that may still be in the tank are not swirled up. Therefore, it is possible to dispense altogether with the presettling chambers that, moreover, occupy design space in the tank. 
     Should the fluid level and, thus, the oil level, drop below the bottommost passage points, a circumstance that could be the case, for example, when switching off the working hydraulic system of the machine, it cannot be ruled out that an air cushion will collect there, a state that is obviously not desired, as already stated above. In order to take active steps against such a risk, an especially preferred embodiment of the filter apparatus according to the invention provides that the housing wall is configured so as to be closed in the direction of its underside and that an additional sleeve is installed in the fluid flow space. This additional sleeve has additional passage points below the assumed lowest fluid level and otherwise forms up to and above this level a closed sleeve surface. 
     As an alternative, it can also be provided in order to remedy this effect that each filter element that is installed exhibits with its outer sleeve, which forms a kind of support tube—in particular, a support cylinder—a non-perforated, closed sleeve component as far as below the minimum oil level (fluid level) expected in the tank. Then below that, there are, accordingly, the additional passage points, preferably in the form of a perforation in the said support tube sleeve, in order to avoid the said air cushion. Thus, there is the possibility of installing the sleeve as a stand-alone add-on component into the fluid flow space or of modifying the outer support tube of the filter element in such a way that the described sleeve function is achieved. 
     Other advantageous embodiments of the filter apparatus according to the invention are the subject matter of the other dependent claims. 
    
    
     
       The solution according to the invention is explained in detail below on the basis of a variety of embodiments with reference to the drawings, which show in principle, but not according to scale 
         FIG. 1  shows a longitudinal sectional view of a first embodiment of the filter apparatus according to the invention; 
         FIG. 1A  shows a graphical rendering corresponding to  FIG. 1 , but depicted in a different sectional plane; 
         FIG. 2  shows a perspective outside view of the filter apparatus according to  FIG. 1 ; and 
         FIG. 3  shows a partially cut open view of a second embodiment of the filter apparatus; 
         FIGS. 4 and 5  shows a third embodiment of the filter apparatus, shown once as a longitudinal sectional view, and once as a side view, where the bottom base member is also shown as a sectional view. 
     
    
    
     The filter apparatus, shown in  FIG. 1 , is intended for installation in a container-like fluid reservoir tank  10 , comparable to the installation situation according to the EP 1 419 807 B1. The drawing according to  FIG. 1  shows only the upper tank wall  12  of the fluid reservoir tank  10  as well as an associated receiving wall  14  for anchoring the filter apparatus. Between these wall sections  12 ,  14  runs an inflow channel  16  for the fouled fluid, coming, for example, from the hydraulic circuit of a working hydraulic system (not depicted in detail) of a construction machine or the like. 
     Furthermore, the filter apparatus has a filter element  18  with a preferably pleated filter mat  20 . Otherwise the filter element  18  is made essentially like a circular cylinder. The filter mat  20  extends between an upper end cap  22  and a bottom end cap  24  as parts of the filter element  18 . The bottom end cap  24  has a conventional bypass valve  28 , which is positioned in the middle and extends coaxially to the longitudinal axis  26  of the filter apparatus. When the filter mat  20  is clogged with contaminants, this bypass valve opens and allows the fluid to bypass the filter mat  20  in the uncleaned state and to drain through a bottom bypass port  30  into the reservoir tank  10 . Since the filter mat  20  is traversed by flow from the inside to the outside, i.e., the flow takes place from the inside  32  of the filter element  18  in the direction of the interior  34  of the fluid reservoir tank, the filter mat  20  is enveloped by a support tube or a support jacket  36  for the purpose of reinforcing towards the outside. This support tube  36  is configured so as to be preferably circularly cylindrical and has corresponding passage openings (not shown in detail) for the passage of fluid that has been cleaned by means of the filter mat  20 . However, a suitably shaped support jacket (not shown) could also conform with the outer contour of the pleated filter mat and, thus, provide the support function in order to enhance the pressure stability of the element towards the outside. Even this kind of support jacket has the corresponding passage openings for the fluid medium. The fluid entry of the uncleaned fluid, coming from the inflow channel  16 , occurs through the upper inflow opening  38  of the filter element in the direction of the said interior  32  of the same. 
     The filter element  18  is received in a housing, all of which is designated with the reference numeral  40 . The upper side of this housing has a flange-like expansion  42 , which supports the filter apparatus in this area on the upper side of the upper tank wall  12 . Adjoining the said expansion  42  in the downward direction is a cylindrical housing wall  44 , which is designed so as to be closed on its underside  46 , save for the said bypass port  30 . Preferably the pertinent underside  46  of the housing wall  44  is made as a stand-alone bottom part; and the housing wall  44  is supported with its respective free end on a shoulder-like step of the underside  46  as well as on the flange-like expansion  42 . In order for the described combined system of the housing  40  to remain in the assembled state, as shown in  FIG. 1 , the outer periphery in the direction of the filter mat  20  with the support tube  36  has retaining rods  48 , of which  FIG. 1  shows only one retaining rod  48  in its entirety. Of the two other retaining rods  48  that are installed for this purpose,  FIG. 1  shows for the sake of simplicity only one additional rod  48  with its bottom connection end, projecting from below the underside of the bottom part  46 . In this area the respective retaining rod  48  is screwed together with a threaded nut  50 ; and the upper end of the respective retaining rod  48  is rotated into the flange-like expansion  42  by means of a corresponding internal thread. As a result, the housing wall  44  between the expansion  42  and the bottom part  46  can be securely anchored under a specified prestress. 
     In order to be able to install the housing  40  into the upper tank wall  12 , this upper tank wall has a corresponding circularly cylindrical recess  52 , the diameter of which is at least greater than the outside diameter in the area of the transition between the flange-like expansion  42  and the outer periphery of the housing wall  44 . Furthermore, there is a lid member  54  as a part of the filter apparatus. This lid member has a handle  56  to make it easier to install the filter apparatus into the illustrated tank  10  and to remove it from the same. The lid member  54  has a shoulder-like expansion  58 , which sits on the upper side of the receiving wall  14 ; and an offset of the expansion  58  reaches into the clear inside diameter of the receiving wall  14  so as to make contact with the same. In order to seal the fluid, this area has an annular sealing element  60  of the conventional design. As shown especially in  FIG. 2 , there are attachment screws  62  that are positioned opposite each other and diametrically to the longitudinal axis  26  of the apparatus. These attachment screws are used to fasten the lid member  54  to the receiving wall  14 . After slackening the screws  62 , the filter apparatus can be removed from the tank  10  and installed again in the reverse sequence of assembly. Such assembly operations are necessary, to the extent that a used filter element  18  is to be exchanged for a new element. 
     A magnetic bar  64  runs concentrically to the longitudinal axis  26 . This magnetic bar has, in particular, the function of a permanent magnet and is securely attached, when viewed in the viewing direction of  FIG. 1 , with its upper end in the lid member  54 , in particular is screwed into said lid member. With its other opposite free end, said magnetic bar extends through the inside  32  of the filter element  18 . Such a magnetic bar  64  makes it possible to separate out the magnetizable metal components in the fluid to be filtered. Both the magnetic bar  64  and the bypass valve  28  are provided optionally and are not mandatory for the function of the filter apparatus as a whole. 
     Furthermore,  FIG. 1  shows that the cylindrical housing wall  44  occupies a presettable radial distance from the outer peripheral surface of the filter element  18 , so that in this respect a fluid flow space  66  is formed. The pertinent fluid flow space  66  extends parallel to the outer peripheral surface of the filter element  18 . In particular, it extends in the axial longitudinal direction parallel to the longitudinal axis  26  of the apparatus between the upper side of the bottom part  46  and the bottom side of the flange-like expansion  42 . Furthermore, the fluid flow space  66  is defined outwards in essence by the housing wall  44  and inwards by the outer peripheral surface of the filter mat  20 . To the extent that a support jacket or a support tube  36  is used for the filter mat  20 , the corresponding outer peripheral surface forms the limiting boundary for the fluid flow space  66 . 
     The embodiment according to  FIG. 1  shows a fluid level  68  inside the reservoir tank  10 ; and the filter element  18  and, thus, the fluid flow space  66  lie partially below the level  68  and partially above the same. As a function of the inflowing fluid volume over the inflow channel  16  or the outflowing volume required for the working hydraulic system, the fluid level  68  varies in relation to the illustrated momentary position in  FIG. 1 . Moreover, the fluid flow space  66  is not impaired as a flow space with the exception of the penetration of the individual retaining rods  48  (cf.  FIG. 1 ). 
       FIG. 1   a  shows a different sectional plane than in  FIG. 1 , but is otherwise intended to relate in essence to the same filter apparatus. In this case the filter apparatus has individual connecting rods  70 , which were omitted in  FIG. 1  for the sake of a better overview.  FIG. 1   a  shows only two of a total of three connecting rods  70 . The ends of the connecting rods  70  are connected to the lid member  54 . Otherwise, the connecting rods rest against the upper end cap  22  of the filter element  18 , in order to hold the latter in the illustrated installation position. In this respect there is the option of removing from the housing  40  only the filter element  18  that is to be exchanged by removing the lid member  54 ; otherwise, said housing remains in its installation position on the upper tank wall  12 . Other approaches to the solution are possible here, for example, in the sense that in the event that the crosspieces  70  are permanently connected to the housing  40 , even the housing together with the filter element  18  can be removed, if desired, by way of the lid member  54 . For the sake of greater simplification in relation to  FIG. 1 ,  FIG. 1   a  no longer shows the walls  12 ,  14  or the attachment screws  62 , which extend through the corresponding recesses  72  in the lid member  54 . As the orientation of the handle  56  shows, the drawing according to  FIG. 1   a  is swiveled by 90 degrees out of the drawing plane according to the drawing from  FIG. 1 . 
     Furthermore, it is clear from  FIG. 2 , which shows an external view of the filter apparatus from  FIG. 1 , that the housing wall  44  has window-like passage openings  74 , which form circumferential groups on the periphery and are positioned one above the other in the manner of a ring. At the same time the two adjacent groups have the same axial distance in relation to each other; and the individual passage openings  74  inside a group also exhibit the same amount of spacing between each other in the radial direction. It is also clear from the drawing in  FIG. 1  that at the given fluid level  68 , the bottom group of passage openings  74  is still covered by the fluid level; and the higher level group of passage openings  74  empties on the level upper side into the interior of the tank  10 . In the present embodiment there is a screen or lattice structure layer  76  inside the housing wall  44  and resting against its interior. This screen or lattice structure layer forms a continuous cylinder jacket and extends over the edge of all of the window-like passage openings  74  that are all the same in design. In order for the structure layer  76  to remain against the inside of the housing wall  44 , it can be suitably fastened by spot welding (not illustrated in detail). 
     However, instead of a single structure layer  76 , it is also possible, in terms of amount, for each window opening  74  to have its own dedicated lattice that then covers from the inside this window opening with its edge-sided projecting length. The structure layer  76  can be embodied by an expanded metal lattice as well as any other kind of thin meshed lattice or network, even in the form of a fabric structure with warp and weft threads. Preferably, the structure layer  76  that is inserted in each case for the plurality of passage points exhibits for each passage point an opening cross section of less than one millimeter. The choice of the clear opening cross sections for the passage points of the structure layer depends on the environmental conditions, like the viscosity of the fluid that is fed in, especially in the form of hydraulic oil, which ultimately also depends on the ambient temperature values. The window openings  74  are configured preferably in the shape of a rectangle, but other opening geometries would be just as possible in this respect. 
     If at this point the filter apparatus according to  FIGS. 1 ,  1 A, and  2  is put into service, then the fluid flows through the filter mat  20  from the inside to the outside and, in so doing, is cleaned. Since some of the fluid that is stored in the tank  10  and is below the level  68  flows into the bottom passage openings  74 , the inflow space  66  that is below the level  68  fills up with fluid, with the consequence that the subsequent fluid that continues to flow in from the inside  32  is pushed upwards, so that the result is a film-like hollow column of fluid in the fluid flow space  66 . This fluid rests against the inside of the housing wall  44  and against the passage points of the screen or lattice structure layer  76  that is perforated for this purpose. The resulting fluid arrangement that rises above the fluid level  68  flows through the passage points into the window-like passage openings  74 , a flow that is largely laminar. At the same time splashing or foaming events during this passage are reliably avoided. As a function of the fluid volume and the fluid pressure, generated by way of the fluid feed into the inflow channel  16 , the resulting laminar flow can emerge in the area of the fluid level  68  or correspondingly above the same. As a function of the size of the volume for the fluid flow space  66  and given a suitably narrow radial layout, i.e., with a negligible degree of radial spacing, a supporting capillary effect may be produced for the upward movement in the direction of the outside of the filter element  18 . 
     As a function of the mesh width for the structure layer  76 , the clear opening cross sections for the passage points may be chosen in such a way that any gas bubbles, such as air bubbles, that are in the cleaned fluid can settle on such a perforated structure layer  76 . In this case if the gas is to be released close to the fluid level, then the bubbles are collected on the structure layer  76  and are increased in volume under the influence of their surface tension for easier release, so that they can rise upwards out of the filter apparatus effortlessly like the CO 2  beads in a carbon dioxide containing beverage, so that the fluid in the tank is effectively degassed. Since the hydraulic working devices are often sensitive to the introduction of gas, this approach effectively rectifies the risk of a malfunction. 
     Instead of the cylindrical peripheral wall  44  that is a component of the apparatus housing and that is closed (as illustrated in  FIGS. 1 ,  1 A and  2 ) with the exception of the window-like openings  74 , said peripheral wall  44  can also be replaced in its entirety or for the most part by a cylindrical structure layer  76  having corresponding passage points (not illustrated). Another alternative is to configure the structure layer  76  as multiple layers, so that the result is a stiffer design for the housing wall  44 , in order to be able to reliably control the resulting pressure differentials in the tank  10 . Instead of the illustrated embodiment that provides for the individual passage points the same opening cross section, it would also be conceivable in a suitably modified design to change the clear opening cross section in the direction of the rising fluid flow in the fluid flow space  66 , in particular, to make the same shape change, in order to achieve in this way an improvement in the fluid rise in the fluid flow space  66 . 
     The following embodiments are described only insofar as it is necessary to show the major distinction with respect to the preceding embodiment. Hence, for the same components with the same function the same reference numerals that were used above are used here; and the resulting designs also apply to the modified design variants. 
     The embodiment according to  FIG. 3  has, instead of the connecting rods  70 , a compression spring  78  that extends between the lid member  54  and the housing  40 . When the lid member  54  is firmly secured, the housing  40  of the filter apparatus pushes against the top side of the upper tank wall  12 . Instead of the previous two groups of window-like passage openings  74 , the engineering solution according to  FIG. 3  has three groups that are positioned one above the other. The fluid level in turn is indicated, as an example, with a triangle under the reference numeral  68 . The essential feature in the modified embodiment according to  FIG. 3  is that below the lowest possible fluid level  68  there are additional passage points  80  in the form of a perforation in the cylindrical sleeve  82 . However, the corresponding sleeve  82  with its closed surface areas empties below the lowest conceivable fluid level  68  and below that point has additional passage points  80 . 
     The said sleeve  82  can be inserted into the fluid flow space  66  as a stand-alone component. However, there is also the possibility that the illustrated sleeve  82  is an essential part of the filter element  18 , especially in the circumference of the additional passage points  80 , and insofar envelops the filter mat  20  of the filter element  18  as a support tube or support jacket. Should the oil level in the form of the fluid level  68  drop below the illustrated window-like passage openings  74 , an air cushion could collect there when the working hydraulic system is switched off. However, this air cushion does not develop, if the outer support cylinder of the filter element  18  has, according to the illustration from  FIG. 3 , a non-perforated section as far as below the minimum possible oil level. According to the drawing from  FIG. 3 , this non-perforated section can also be implemented with a separate sleeve  82  that is made, for example, of a plastic material. 
     In the embodiment according to  FIGS. 4 and 5 , two filter elements  18  are arranged one above the other in a coaxial arrangement in relation to the longitudinal axis  26  of the filter apparatus. In this case the bottom filter element  18 , viewed in the viewing direction of  FIG. 4 , is intended for the fine filtration; and the element that is positioned above is intended for the coarse filtration. If the fine filtration element  18  is clogged with contaminants, then it is still possible to conduct a coarse filtration by way of the upper element  18 . In the present embodiment under discussion the filter apparatus is configured so as to be closed, except for the bypass valve  28  that is now positioned at the very top. At this point the fouled fluid flows through the passage on the bottom side  46  into the respective filter element  18 . The two filter elements  18  are separated from each other in the middle by means of a spacing mechanism  84  that has a fluid passage in the center. Then as a function of the degree of contamination for the bottom fine filter element  18 , a portion of the fluid flows noticeably through the upper coarse filter  18 . Otherwise, the filtered fluid flows from the bottom filter element  18  into the fluid flow space  66  that has already been described above. 
     It is especially clear from  FIG. 5  that this time there are two groups of window-like passage openings  74 , in total, five groups of two that are arranged one above the other. Furthermore,  FIG. 5  shows the two anticipated bottom and upper fluid levels  68  (oil level minimum/oil level maximum).  FIG. 5  also shows that this time the filter apparatus extends between a tank upper side  68  and a bottom tank chamber  88  that for this purpose forms the inflow channel  16  for the fouled fluid. In order to anchor the two filter elements  18  that are positioned one above the other with their respective end caps on the lid member  54 , there is this time a single connecting rod  70  that is arranged in the middle. The filter arrangement can be pulled out of the housing wall  44  by means of a pivotable handle  90 . 
     The inventive filter apparatus according to the illustrated embodiments makes it possible to receive dirt particles in the 10 μm range without further effort. Fouled filter elements  18  can be easily exchanged; and the special housing arrangement makes it possible to actively rectify the risk of recontamination. The magnetic bar  64  that is used in each case and configured as a magnetic core is clearly visible from the outside during maintenance work and, if desired, can be cleaned by hand with a suitable cloth. Moreover, the magnetic bar  64  is configured in such a way that the foreign particles adhere uniformly to it without any accumulation of contaminants in the area of the bypass valve  28 , a state that might have an adverse effect on the operational reliability of the valve. The element is well supported between the wall sections  12  and  14  especially in the event of vehicle movements, so that the result is not an inadvertent removal of the components of the filter apparatus with the consequence of an unintentional bypass flow of the unfiltered fluid to the clean side of the tank arrangement. On the whole, the filter apparatus according to the invention enables a modular concept, a feature that contributes to lowering the production costs. 
     However, it is especially important that the engineering solution according to the invention makes possible a homogeneous laminar flow of the cleaned fluid from the filter apparatus back into a tank without producing any splashing effects or undesired foam. In addition, the inserted structure layers exhibiting the fine mesh passage openings improve the degassing properties and preclude with certainty any deleterious introduction of air into the hydraulic medium.