Abstract:
A filter device, in particular a reflux vacuum filter, has at least one filter housing ( 7 ) in which at least one filter element ( 3 ) can be accommodated. The filter element defines a longitudinal axis ( 25 ), and has at least two valve units in the form of a bypass valve (V 2 ) and of a pre-pressurizing valve (V 1 ). The valve units are arranged concentric to and along the longitudinal axis ( 25 ) of each filter element ( 3 ).

Description:
FIELD OF THE INVENTION 
     The invention relates to a filter device, particularly a reflux vacuum filter, with at least one filter housing receiving at least one filter element defining a longitudinal axis. At least two valve units, particularly in the form of a bypass valve and a back pressure valve are provided. Moreover, the invention relates to a filter element for such a filter device. 
     BACKGROUND OF THE INVENTION 
     Reflux vacuum filters of the aforementioned type are known. One device of this type is marketed by the company ARGO-HYTOS GmbH and is commercially available under the type designation E084. Reflux vacuum filters are used in hydraulic systems having both an open hydraulic circuit (such as working hydraulics) and a closed hydrostatic system (for example, a traveling mechanism). Reflux vacuum filters can assume both the function of the reflux filter of the open circuit and the function of the vacuum filter of the closed circuit (mechanism), assuming that the reflux flow of the open hydraulic system is not smaller than the volumetric flow of the feed pump for the hydrostatic system. 
     In the operation of these devices, the reflux amount, for example, of the working hydraulics, is supplied to the filter and is purified by the filter medium of the filter element, and full-flow extremely fine filtration can take place. In the filtered fluid available to the feed pump of the hydrostatic system, a preload pressure is maintained by the back pressure valve and ensures that the amount of filtered reflux required by the feed pump of the compensator can be removed. Excess amounts travel via the back pressure valve to the tank connection and are drained towards the tank. At high dynamic pressures caused, for example, by fouling at the filter element, a pressure decrease takes place by triggering of the bypass valve. 
     SUMMARY OF THE INVENTION 
     An object of this invention is to provide a reflux vacuum filter device whose construction enables easy installation in the pertinent hydraulic systems, especially with restricted space conditions where only limited installation space is available. 
     According to the invention, this object is basically achieved by a filter device having all the main components arranged concentrically to the longitudinal axis of the filter element. The overall device can form a slender, uniform body, for example, in an extended cylindrical shape without assemblies protruding laterally on the body or offset to the longitudinal axis, for example, in the form of a bypass valve located laterally to the cylindrical body. 
     In advantageous exemplary embodiments, a third valve unit, specifically in the form of a replenishing valve, is concentric to the longitudinal axis of the filter element. Without departing from the in-line construction, this arrangement ensures that when the reflux pressure fails, an amount of fluid can travel via the replenishing valve from the tank to the intake side of the feed pump of the hydrostatic circuit in an emergency function, so that, for example, the connected traveling mechanism does not fail. 
     In especially advantageous exemplary embodiments in which the filter housing has a head-side cover part with fluid guides bordering the upper end region of the inserted filter element as well as at least one filter input for reflux fluid and at least one filter output for cleaned fluid, the bypass valve is located in the region of the cover part and is in a fluid connection to the fluid guide at the filter input. Compared to the conventional positional arrangement provided for bypass valves, the bypass valve is offset away from the filter sump towards the head side, i.e., into the immediate region of the filter input. At high dynamic pressures, the pressure decrease then takes place directly at the filter input. In this way, operating reliability, especially during cold starting phases, is increased. 
     Preferably, the filter housing has a bottom-side tank connection for the discharge of excess reflux amounts to the tank. The back pressure valve in the bottom region of the filter housing adjacent to the tank connection for blocking or clearing a fluid connection is located between the filter output and tank connection. 
     Exemplary embodiments in which the replenishing valve is located underneath the back pressure valve, nearer the tank connection, in the bottom region of the filter housing, are especially suitable for tank installation of the device since separate feed lines to the replenishing valve are not necessary. 
     The device can be advantageously designed such that the filter medium of the filter element, through which flow can take place from outside to inside during filtration, surrounds a coaxial, fluid-permeable support pipe. Within and at a distance from the support pipe, a concentric interior pipe is provided. The cleaned fluid located on its exterior on the end of the interior pipe is fluid-connected to the units located in the bottom region of the filter housing in the form of the back pressure valve and of the replenishing valve. In this way, within the filter element a pipe-in-pipe system is formed in which the interior pipe exterior borders the clean side during filtration and forms the fluid connection to the bottom-side valve units. This pipe-in-pipe construction leads to an especially compact, slender body of the device with high inherent stability, even when potential pressure fluctuations occur during operation. 
     In these exemplary embodiments, preferably, the bottom region of the filter housing can have a pipe body continuing the interior pipe of the inserted filter element. The valve bodies of the back pressure valve and replenishing valve are guided on the pipe body for opening and closing movements opposite one another. These valve units then form a direct coaxial extension on the bottom of the filter element. 
     In especially advantageous exemplary embodiments, the bypass valve is integrated into the head-side end cap of the filter element. In the cap, at least one bypass channel is formed which with the filter element inserted connects the filter input of the cover part of the filter housing to the input side of the bypass valve. 
     Preferably, the bypass valve is a spring-loaded spool valve whose spool is guided in a hollow-cylindrical valve housing concentric to the longitudinal axis. During opening dictated by the dynamic pressure, this valve forms the fluid connection between the bypass channel and interior of the valve housing. 
     An especially compact construction is produced when the interior pipe of the filter element is a bypass pipe forming on the inside at least part of the fluid connection between the interior of the valve housing of the bypass valve and the tank connection located in the bottom region. In this respect, the valve housing of the bypass valve can form a direct fluid connection to the facing end of the interior pipe. With the bypass valve opened, the pressure decrease out of the valve housing then takes place directly through the interior pipe used as the bypass pipe to the tank connection. 
     The invention offers an especially advantageous option for changing the hydraulic circuit as desired. While when using the interior pipe as the open bypass pipe when the bypass valve is triggered, the pressure drop takes place directly to the tank by way of the interior pipe. The circuit can also be made such that the fluid flowing away when the bypass valve opens does not travel to the tank, but rather flows out of the valve housing directly to the clean side of the filter element, i.e., to the filter output of the device. In this case, the interior pipe of the filter element is closed, and the valve housing has an outflow region with the bypass valve open forming the fluid connection from the interior of the valve housing to the filter output in the cover part. 
     In this connection, the outflow region of the bypass valve can be formed by openings in the valve housing cover. As a head-side, round plug, the housing cover forms the support of the closing spring of the bypass valve. For the fluid flowing off by way of the openings in the valve housing cover, the flow conditions are especially favorable when the openings in the valve housing cover are made in an arrangement distributed in a star shape and with a trapezoidal opening surface. 
     In particular, in cases where the interior pipe is closed and the fluid is flowing directly to the filter output when the bypass valve has been triggered, a protective bypass screen is preferably integrated into the pertinent fluid guide in the cover part. The fluid traveling to the clean side is then free of at least coarser dirt. 
     To prevent the danger of dirt being able to travel by way of replenished fluid to the clean side and to the connection of the feed pump of the downstream hydrostatic circuit when the replenishing valve is opened, preferably a replenishment screen arrangement is inserted into the fluid path between the replenishment openings of the replenishing valve and the tank connection. 
     The subject matter of the invention is also a filter element for a filter device. 
     Other objects, advantages and salient features of the present invention will become apparent from the following detailed description, which, taken in conjunction with the annexed drawings, discloses preferred embodiments of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Referring to the drawings which form a part of this disclosure: 
         FIGS. 1 to 3  are schematic diagrams of circuits of the components of a first exemplary embodiment, a second exemplary embodiment and a third exemplary embodiment of the filter device according to the invention, respectively; 
         FIG. 4  is a partial side elevational view in section of only the upper, cover-side portion of the filter device of the first embodiment of  FIG. 1 , but with a protective bypass screen additionally provided; 
         FIG. 5  is a partial side elevational view in section of only the bottom-side, lower partial portion of the first embodiment of the device shown in  FIG. 4 ; 
         FIG. 6  is a partial front elevational view in section of the head-side partial portion turned by 90 degrees compared to  FIG. 4 ; 
         FIG. 7  is a side elevational view in section of a filter device drawn on a smaller scale compared to  FIGS. 4 to 6  according to the circuit of the third embodiment of  FIG. 3 ; 
         FIG. 8  is a side elevational view in section of only the filter element of the first exemplary embodiment of the filter device corresponding to the circuit of  FIG. 1 ; and 
         FIG. 9  is a perspective view of the valve housing cover of the bypass valve of the exemplary embodiment of  FIG. 7 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the circuit examples shown in  FIGS. 1 to 3 , a connection A is supplied with a fluid reflux amount from working hydraulics (not shown). By way of a connection B, the feed pump of a compensator (not shown), for example a hydrostatic traveling mechanism (not shown), is supplied with the amount of fluid required as the fill amount. This amount of fluid is removed on the clean side  1  of a filter element  3 , i.e., from the reflux flow filtered in full flow and exceeding the filling flow required by the feed pump of the downstream compensator. The clean side  1  of the filter element  3  is connected by way of a back pressure valve V 1  to the tank connection T. The back pressure valve V 1  can be opened by pressure actuation and is set to an opening pressure ensuring that on the clean side  1  and thus on the connection B a pressure level is maintained at which the feed pump of the downstream compensator can remove the required amount by way of the connection B. On a standard basis, the back pressure valve V 1  is set to an opening pressure of 0.5 bar. 
     Downstream of the back pressure valve V I , a replenishing valve V 3  openable likewise by pressure actuation is connected and is set to a low opening pressure of roughly 0.05 bar. Replenishing valve V 3  opens when the pressure of the reflux amount has dropped on the clean side  1 . For operation of the suction pump connected downstream of the connection B, fluid then needs to be replenished via the replenishing valve V 3  from the tank as an emergency function. When the dynamic pressure prevailing on the filter element  3  exceeds a threshold value, recognized, for example, by a fouling indicator VA connected to the dirty side at the connection A, a bypass valve V 2 , can be actuated by pressure to open for a pressure reduction from connection A, and for the circuit from  FIG. 1 , towards the tank. Conventionally, a dynamic pressure of roughly 2 bar prevailing on the filter element  3  is the opening pressure for the bypass valve V 2 . In  FIG. 1  with the back pressure valve V 1  set to an opening pressure of 0.5 bar, the bypass valve V 2  would accordingly be set to an opening pressure of 2.5 bar. 
     The versions of  FIGS. 2 and 3  differ from  FIG. 1  in that the pressure drop from connection A does not take place by way of the bypass valve V 2  towards the tank, but by way of the clean side  1  of the filter element  3  and by way of the back pressure valve V 1  to the tank connection T. The bypass valve V 2  can then be set to an opening pressure of 2.0 bar on a standard basis. 
     The circuit version shown in  FIG. 3  corresponds to that from  FIG. 2 , except that a protective bypass screen  5 , also in the from of a filter element, is located in the flow path of the fluid flowing through the bypass valve V 2  so that the connection B is protected from fouling even when the bypass valve has been opened. The circuit version of  FIG. 2  in which the filter element  3  can be directly bypassed by the opened bypass valve V 2 , without the fluid flowing away via the bypass valve having to flow through a protective screen or protective filter, is advantageous in those cases in which the fluid is an oil of high viscosity for example, during cold starting phases. As is detailed below, the invention makes switching the circuit between the operating modes shown in  FIG. 1  or those in  FIGS. 2 and 3 . 
       FIGS. 4 and 6  each show the head-side end region of a filter housing  7  of the device in an embodiment in which a protective bypass screen  5  or a bypass filter element is present. In these figures the head-side cover part  9  of the filter housing  7  has an upper end termination  11  screwed to the cover part  9 . After the end termination  11  is unscrewed, the filter element  3  of a largely circular cylindrical shape can be placed in the hollow cylinder-shaped main body  15 . The bottom region  17  of main body  15  (see  FIG. 5 ) forms an element receiver  19  holding a ring body  21  of the filter element  3  to form a seal. The ring body  21  forms an extension of the bottom-side end cap  23  of the filter element  13 . This extension is coaxial to the longitudinal axis  25  of the filter element  13 . The end cap  23  forms an enclosure for the lower end of the filter medium  27  of the filter element  3 . The ring body  21  surrounds the opening region  29  of the end cap  23 . This region  29  is fluid-connected to or in fluid communication with the inner filter cavity  31  of the filter element  3  forming the clean side during filtration. 
       FIG. 4  shows the upper region of the device in a position in which the filter output  33  corresponding to the connection B in  FIGS. 1 to 3  is visible. Conversely,  FIG. 6  shows this section of the device in the rotary position in which the filter input  35  can be seen. With the filter element  3  inserted, the filter input  35  is fluid-connected or in fluid communication by way of fluid guides  51  to the exterior  37  of the filter medium  27 . The filter medium exterior forms the dirty side during filtration. Fluid medium flow takes place during filtration from the filter medium exterior to the inner filter cavity  31  forming the clean side. The upper, head-side end cap  39  of the filter element  3  forms not only the enclosure for the upper end of the filter medium  27 , but a hollow cylinder-shaped valve housing  41  for a bypass valve and a support for an interior pipe  43 . Interior pipe  43  is concentric to the longitudinal axis  25  and extends, leaving open the filter cavity  31  forming the clean side, at a distance from the support pipe  45  on whose exterior the filter medium  27  rests. The filter cavity  31  forming the clean side is connected via passages  47  in the end cap  39 , of which  FIG. 4  shows one, to a fluid guide  49  in the cover part  9  leading to the filter output  33 , i.e., to the connection B. The exterior  37  of the filter medium  27  forming the dirty side is in turn connected in the cover part  9  to the fluid guide  51  connected in the cover part  9  to the filter input  35 , i.e., the connection A. As is apparent from  FIG. 6 , bypass channels  53  extend from the fluid guide  51  to the interior of the valve housing  41 . In the valve housing  41 , the valve spool of the bypass valve V 2 , made as a spool valve is movably guided. The valve housing  41  forms a hollow cylinder concentric to the longitudinal axis  25 . On the valve housing inside wall, the valve spool  55  is guided and has an end-side closing edge  57 . When the valve spool  55  has been pushed into the open position, closing edges  57  clears the fluid path from the bypass channels  53  into the interior of the valve housing  41  and thus into the interior pipe  43 . In the exemplary embodiments in which, as shown in  FIGS. 4 to 6 , the interior pipe  43  is open, i.e., is passable, when the bypass valve V 2  has been opened, the pressure can drop by the fluid flowing away through the interior pipe  43  to the tank connection T. The valve spool  55  is pretensioned into the closed position by a compression spring  59  clamped between the valve spool  55  and a cover  61  forming the end-side termination of the valve housing  41 . In the exemplary embodiments with the through interior pipe  43  ( FIGS. 4 to 6  and  8 ), the valve housing cover  61  is a round plug in the form of a closed cap. 
     As already mentioned, the circuitry of the device can be easily changed such that the fluid flowing away via the bypass valve V 2  does not travel directly to the tank, as is the case in the circuit of  FIG. 1 . According to the circuits from  FIGS. 2 and 3  with the bypass valve V 2  opened, the fluid flowing away travels to the clean side  1  of the filter element  3  and can travel from there via the back pressure valve V 1  to the tank connection T. To execute the circuit in this way, i.e., to shift the device into the state shown in  FIG. 7 , only two measures are necessary. First the closure of the interior pipe  43  is accomplished, for example, by the crosspiece  63  in  FIG. 7 . Second, instead of the housing cover  61  in the form of a closed cap, a housing cover  65  open on the top is used, as is shown separately in  FIG. 9 . As shown in  FIG. 9 , the housing cover has outflow openings  67  of a trapezoidal opening surface. Openings  67  are arranged in a star shape through which fluid can flow out of the valve housing  41 , without stronger flow resistance having to be overcome, to the fluid guide  49  and thus to the filter output  33  when the valve spool  55  against the force of the spring  59  executes an opening motion in which the closing edge  57  forms an opening gap so that fluid flows into the valve housing  41  out of the bypass channels  53 . 
     For viscous fluids, for example oil with high viscosity prevailing during cold starting phases, the direct flow connection between the filter input  35  and filter output  33  formed in this way with the bypass valve V 2  opened is advantageous, especially when the protective bypass screen  5  or filter is not connected upstream of the bypass channels  53 . On the other hand, using a protective bypass screen or filter avoids the danger that with the bypass valve V 2  opened dirt can travel to the filter output  33 . In the exemplary embodiments shown in  FIGS. 4 to 7 , a protective bypass screen  5  each is arranged within a bell-shaped intermediate body  69  such that it is located in the fluid path between the fluid guides  51  and the bypass channels  53 . 
     The bell-shaped intermediate body  69  within the cover part  9  separates the fluid guides  49  and  51  from one another and at the same time forms or supports the seal  71  for the upper end cap  39  of the filter element  3 . 
       FIGS. 5 and 7  show the lower bottom region  17  which is connected to the element receiver  19 ; its details are shown most clearly in  FIG. 5 . As illustrated, the interior pipe  43  of the filter element  3  is extended down towards the tank connection T. The filter cavity  31  of the filter element  3  forming the clean side is connected to a pipe body  73  by way of the opening regions  29  in the end cap  23  of the filter element. To form a spring housing, the pipe body is surrounded by a hollow cylindrical spring housing  75  concentric to the longitudinal axis. This spring housing receives a closing spring  77  for the back pressure valve V 1  and a spring  79  for the replenishing valve V 3 . The two compression springs surround the pipe body  73 . The back pressure valve V 1  has an axially movable valve body  81  guided on the exterior of the pipe body  73  with a hollow cylindrical extension  83  on the inside of the spring housing  75 . The spring housing  75  has a cup bottom  85  through which the pipe body  73  extends, and has several replenishment openings  87 . This cup bottom  85  forms the valve seat for the valve body  86  of the replenishing valve V 3 , which body is made as a ring plate. 
     The valve body  81  of the back pressure valve V 1  interacts with the ring body  21  on the end cap  23  of the inserted filter element  3  as a valve seat, against which the valve body  81  is pressed by the closing spring  77 . When the valve body  81  is raised against the force of the closing spring  77 , fluid flows out of the interior  31 , i.e., the clean side of the filter element  3 , via the open region  29  of the end cap  23  along the exterior of the spring housing  75  directly to the tank connection T. When no filter element  3  has been inserted into the device, the valve body  81  with a radially outlying valve disk edge  89  forms the seal of the device relative to the tank connection side by the valve disk edge  89  sealing against the element receiver  19  of the main housing part  15 . 
     The interior of the spring housing  75  is connected by fluid to the filter interior  31 , i.e., to the clean side, by the fluid passages  91  made in the valve body  81  and by the opening regions  29  of the end cap  23 . Towards this clean side, when the valve body  86  made as a ring plate is raised against the force of the closing spring  79  away from the replenishment openings  87 , fluid can be replenished from the side of the tank connection T to travel by the fluid passages  91  of the valve body  81  to the cavity  31  and thus to the clean side and to the connection B. 
     As likewise shown in  FIG. 5 , the underside of the body  85  of the spring housing  75  is connected to a screen housing  93  whose interior  95  borders the replenishment openings  87 . Between the interior  95  and its exterior, i.e., the tank connection T, a replenishment screen  97  or replenishment filter is provided so that in the replenishment process direct unfiltered replenishment of fluid from the tank connection T does not take place. 
     As can be taken from  FIGS. 5 and 7 , the bottom region  17  of the main housing body  15  is connected to an extension pipe  99  made as a submersible pipe of the desired length, for example in tank installation, depending on installation conditions. 
       FIG. 8  shows a filter element  3  separately. It has a continuously open interior pipe  43  and accordingly a valve housing cover  61  in the form of a closed cap. The upper end cap  39  forms a pipe socket  98  projecting appropriately into the end of the interior pipe  43 . Opening edge  100  of pipe socket  98  interacts with the closing edge  57  of the valve spool  55 . When the closing edge  57  is raised off the edge  100 , the fluid path is cleared from the bypass channels  53  into the interior of the valve housing  41  and into the interior of the interior pipe  43  now acting as a bypass pipe towards the tank side. 
     With the filter device according to the invention, a novel pipe-in-pipe system is formed in which the bypass pipe is centrally guided through the filter element support pipe. The position of the bypass valve changes from the “filter sump” upward. By closing the bypass pipe and another bypass closing cover, the switching logic of the filter device can be easily changed, i.e., the bypass goes directly to the intake side. This change is possible among other things by using the novel, internally hollow bypass valve in a spool construction. Furthermore, with the filter device according to the invention without the filter element inserted no buildup of feed pressure is ensured to indicate a missing filter element. Due to the special trapezoidal shape of the cross channels, the novel bypass cap in a cross flow construction prevents the cross section of the filtered oil from being constricted so that energy losses are avoided in filter operation. 
     While one embodiment has been chosen to illustrate the invention, it will be understood by those skilled in the art that various changes and modifications can be made therein without departing from the scope of the invention as defined in the appended claims.