Abstract:
A hydromechanical driving device generates forward-pushing movements of a band-shaped filter material according to the pressure prevailing in the fluid to be filtered to operate band filter devices. The hydromechanical driving device includes a hydraulic accumulator ( 29 ) provided with a movable element ( 31 ) separating a first storage space ( 33 ) from a second storage space ( 35 ). The side of the separating element ( 31 ) bordering the first storage space ( 33 ) is impinged upon by the pressure generated the first storage space by the fluid to be filtered. A mechanical device ( 17 ) translates a movement of the separating element ( 31 ) into a forward pushing movement. A pressure control unit ( 47, 49, 51 ) generates lower pressure in the second storage space ( 35 ) than the pressure generated by the fluid to be filtered according to the amount of pressure and/or the degree of impurity of the fluid to be filtered. The lower pressure causes the separating element to be displaced.

Description:
FIELD OF THE INVENTION 
   The present invention relates to a hydromechanical driving device of a strip-filter mechanism for generation of feed movements of the strip-like filter material of the strip-filter mechanism as a function of the pressure prevailing in the fluid to be filtered. 
   BACKGROUND OF THE INVENTION 
   Strip-filter mechanisms in which a strip-like filter material is used as separating medium are disclosed, for example, in DE 43 11 297 A1 or DE 93 01.154 U1. In the operation of such mechanisms, the filter material is advanced as a function of the extent of fouling of the respective strip area through which the filter material flows so as to make fresh filter material available for the filtration process as required. Since the differential pressure between the fouled side and the clean side of the strip-filter mechanism grows with increase in the extent of fouling of the filter material, the value of this differential pressure or the level of the pressure prevailing in the space containing the fluid to be filtered may serve as a criterion for initiation of a filter material feed movement. 
   The advance of the strip-like filter material may be effected by conventional means by winding the filter material. As is shown, for example, in German Patent Application 101 26 443.7, not of the state of the art, a fouled strip from a roll containing the supply of filter material is subsequently rolled onto a roll connected to the drive shaft of the drive device. In such strip-filter mechanisms, the fluid to be filtered flows from the exterior inward through the unused filter material, so that fouling of the filter material always occurs during the filtration process on the outermost layers of the roll. The outermost layers of the roll are wound from the feed roll when the degree of fouling is sufficiently great, and onto the roll connected to the drive shaft of the drive device. 
   The electromotive drive devices usually provided for generation of the feed movement by rotation of the corresponding winding shaft result in relatively high structural complexity and correspondingly high costs. 
   SUMMARY OF THE INVENTION 
   An object of the present invention is to provide a drive device characterized by an especially simple design and correspondingly low production costs. 
   The object of the present invention is basically attained by a hydromechanical drive device used to generate feed movements of the strip-like material for operation of strip-filter mechanisms as a function of the pressure prevailing in the fluid to be filtered. The drive has a hydraulic accumulator with a movable separating element separating a first accumulator space and a second accumulator space. The movable separating element has a side adjoining the accumulator space against which the pressure of the fluid to be filtered prevailing in this space is applied. A mechanism converts movement of the separating element to feed movement. A pressure control mechanism performs the function of generating in the second accumulator space a lower pressure effecting movement of the separating element as a function of the pressure level and/or the extent of fouling of the fluid to be filtered. 
   For the present invention, a hydromechanical drive is provided to replace the electromotive drive systems provided in the state of the art, and to thereby obtain significant simplification. Neither an external power supply nor a corresponding electronic control unit is required. In the present invention, the pressure of the fluid to be filtered functions, because of the movement of the separating element of the hydraulic accumulator it effects, both as energy source for the drive and as an actuating variable determining initiation of the feed movement. Fouling of the section of the strip participating in the filtration process results in corresponding increase in pressure in the space of the strip-filter mechanism containing the fouled fluid to be filtered. The process in question is self-regulating, so that conversion of pressure to an electric signal may be dispensed with. 
   In one preferred embodiment, the pressure control mechanism generates in one of the accumulator spaces of the hydraulic accumulator a pressure which is lower than the pressure of the fluid to be filtered. A movement of the separating element of the hydraulic accumulator and accordingly movement feeding the filter material are then generated. A control valve may be provided and actuated by the movement of the separating element. 
   The configuration devised may be such that two fluid connections to the respective accumulator space are provided. By the first connection to this accumulator space, pressure lower than that prevailing in the first hydraulic accumulator may be generated. The pressure equaling that prevailing in the first accumulator space is generated by the second fluid connection, since it is connected to the fluid to be filtered. 
   In this configuration, the control valve is designed so that it is actuated by the movement of the separating element. The first fluid connection is opened when the separating element is in one end position and the second fluid connection is closed. When the separating element is in the other end position, the second fluid connection is opened and the first fluid connection is closed. 
   To generate by the first fluid connection pressure in the second accumulator space lower than that of the fluid to be filtered, a pressure control valve may be provided at this connection. The pressure control valve may be set for a pressure value which is lower than the pressure of the fluid to be filtered prevailing at the second fluid connection. As an alternative, this fluid connection may also be connected to the space of the strip-filter mechanism containing the filtered fluid, which space has a pressure lower than that of the fluid to be filtered. 
   The drive device may be integrated with the respective strip-filter mechanism on the basis of the hydrodynamic principle of operation of the drive device of the present invention, in which no external energy supply or external control is required. For example, the drive device is installed in its entirety in the respective strip-filter mechanism so that the hydraulic accumulator is positioned in or on the space containing the fluid to be filtered. The fluid may enter the first accumulator space of the hydraulic accumulator through suitable passages. Preferably, a diaphragm accumulator is used as the hydraulic accumulator. The mechanism for generation of the feed movement on the basis of the reciprocating movement of the separating element, for example, the diaphragm of the diaphragm accumulator, may have an actuating rod moving back and forth and connected to the separating element. As a component of a ratchet drive, the actuating rod converts the reciprocating movement to rotary movement in one direction of rotation (take-up direction) by a ratchet wheel and a detent operating in conjunction with this wheel to rotate the winding shaft to take up the roll with the fouled filter material. Another ratchet drive, such as a free-wheel drive (not shown), might also be used in place of the ratchet wheel. 
   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 a preferred embodiment of the present invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Referring to the drawings which form a part of this disclosure: 
       FIG. 1  shows a greatly simplified, diagrammatic side elevational view in section of the diaphragm accumulator according to an embodiment of the drive device of the present invention; 
       FIG. 2  is a diagrammatic view of the operation of the illustrated embodiment of the drive device of the present invention; and 
       FIG. 3  is a diagrammatic top plan view showing the operation of the part of a strip-filter mechanism in which are mounted a feed roll of filter material in strip form and a roll for take-up of used filter material to be wound by the drive device according to the illustrated embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 3  shows a greatly simplified diagram of a space  3  inside a housing  1 . This space contains a fouled fluid to be filtered. A feed roll  5  with strip-like filter material is mounted to rotate freely on a fluid-permeable core  7  in the space  3 . The space  9  situated inside the core  7  receives the filtered fluid which flows through the roll  5  from the exterior to the interior, that is, from the space  3 . The filtration process is effected by filtration in depth. The fouling particles filtered out are deposited on the outermost layers of the feed roll  5 . 
   The increase in the differential pressure between the space  3  containing the fluid to be filtered and the space  9  containing the filtered fluid resulting from the increase in the extent of fouling of the outer layers of the feed roll  5  performs the function of an actuating variable for initiation of a process of feeding the strip-like filter material. In that process, this filter material is wound off the feed roll  5  and onto a take-up roll  11 . The directions of rotation of feed roll  5  and take-up roll  11  occurring during this feed process are indicated by curved arrows. The take-up roll  11  is set in rotation by a winding shaft  13  (also see  FIG. 2 ) of the drive device of the present invention. 
     FIG. 2  shows a simplified diagram of the ratchet drive  15 , which generates the rotary movement of the winding shaft  13  on the basis of the reciprocating movements of an actuating rod  17 . The reciprocating movements of the rod  17  in the direction of the double arrow  19  result in reciprocating pivoting about the winding shaft  13  of a freely pivoting ratchet lever  21  to which a spring-loaded ratchet  25  is hinge-connected. Ratchet  25  engages the sawtooth gearing  27  of a ratchet wheel  23 . This ratchet  25  interacts with the sawtooth gearing  27  so that rotary movement of the ratchet wheel  23  counterclockwise occurs only when the actuating rod  17  moves to the left (in  FIG. 2 ). 
   The mechanism for generating the reciprocating movement of the rod  17  is illustrated in detail in  FIG. 1 . This mechanism has a hydraulic accumulator in the form of a diaphragm accumulator  29 . The diaphragm  31  of accumulator  29  forms a movable separating element between a first accumulator space  33  and a second accumulator space  35 . A pressure plate  37  is applied to the diaphragm  31  on its side facing the second accumulator space  35 , and is rigidly connected to the actuating rod  17 . Actuating rod  17  is centrally positioned in and extends in the longitudinal direction of the housing of the diaphragm accumulator  29 , and may be moved back and forth in this longitudinal direction (double arrow  19 ) as the diaphragm  31  is moved. The cover  39  on the end side and positioned on the accumulator space  33  not only forms a guide for the actuating rod  17 , but also has ports  41  by which the accumulator space  33  is connected to the space  3  containing the fluid to be filtered (see  FIG. 3 ) of the strip-filter mechanism. The pressure of the fluid to be filtered then prevails in the accumulator space  33  during operation. A pressure spring  45  is supported by the cover  39  and a stop plate  43  of the actuating rod  17  so that the diaphragm  31  and actuating rod  17  are pretensioned for movement to the right, as shown in the drawing, into an end position illustrated in  FIG. 1 . 
   The space  35  positioned on the left in  FIG. 1  is closed up to a first fluid connection  47  and a second fluid connection  49 . A control valve situated in the space  35  has a movable valve body  51 . The valve body  51 , which is indicated only in highly simplified diagrammatic form in  FIG. 1 , forms part of a seat valve by which one of the fluid connections  47 ,  49  may be opened while the other connection  47 ,  49  may be closed, depending on the position of the valve body  51 . The valve body  51  may be controlled by the movement of the diaphragm  31 . When the diaphragm  31  is situated in the end position, shown in  FIG. 1  to be on the right side, the valve body  51  is in a position in which the first fluid connection  47  is open and the second fluid connection  49  is closed. The valve body  51  is actuated by an above-center or over-center tilting mechanism connecting this element  51  to the diaphragm  31 . The valve body  51  is switched more or less instantly only in the two end positions of the diaphragm  31 . This tilting mechanism has an actuating rod  55  which is hinge-connected or pivoted to the valve body  51  at one end, and is slidable in a sleeve  53  and guided in movement against the force of a spring. The sleeve is hinge-connected or pivotally by a forked connecting rod  57  to the facing end  59  of the actuating rod  17 . A roll  61 , which rolls on the inside of the diaphragm accumulator housing, is positioned at the free end of the sleeve  53 . 
   When the diaphragm  31  moves to the left from the end position shown in  FIG. 1 , the sleeve  53  is moved. The roll  61  rolls on the inner wall of the accumulator in the direction of an arrow  63 . The rod  55  enters the sleeve  53  a short distance against the force of the spring. When the above-center position of the sleeve  53  is reached, such being the case when the left-side end position of the diaphragm  31  is reached, the rod  55 , under the force of the spring, reverses the valve body  51  about its fulcrum  65 , in a tilting movement indicated by a broken-line arrow  67  into the other valve position. The fluid connection  49  is then instantly opened, and the fluid connection  47  is instantly closed. 
   The method of operation of the drive device is as follows. The pressure of the fluid to be filtered prevails in the accumulator space  33  in the position illustrated in  FIG. 1 . The pressure prevailing in the other accumulator space  35  is set at a correspondingly lower pressure by the pressure control valve  69  mounted on the fluid connection  47 . If, during the operation of the strip-filter mechanism, the pressure of the fluid to be filtered and so the pressure in the accumulator space  33  increases as a result of increase in the extent of fouling of the filter material to a value at which the action of the reset spring  45  tends to retain the diaphragm  31  in the end position on the right shown in  FIG. 1  is overcome, the diaphragm  31  and accordingly the actuating rod  17  are moved to the left as shown in  FIG. 1 . The winding shaft  13  (see  FIG. 2 ) is rotated by the ratchet drive  15  so that used filter material is wound off the feed roll  5  and onto the take-up roll  11  by the winding shaft  13 . 
   When the end position of the diaphragm  31  on the left-side end is reached (this position is not illustrated), the tilting mechanism instantly reverses the valve body, so that the fluid connection  49  is opened and the fluid connection  47  closed as a result of the pivoting indicated by the arrow  67  ( FIG. 1 ). The fluid connection  49  is connected to the fluid to be filtered (space  3  in  FIG. 3 ), so that the same pressure now prevails in the accumulator space  35  as in the accumulator space  33 . As a result of the equal pressure, the diaphragm  31  is moved by the force of the reset of the spring  45  back to the right into the end position shown in  FIG. 1 . The tilting mechanism moves the valve body  51  in turn into the valve position illustrated in  FIG. 1 , so that the initial state is again reached, that is, the operating cycle is completed. 
   In place of the connection of an adjustable pressure control valve to the fluid connection  47 , the fluid connection  47  could be connected directly to the space  9  ( FIG. 3 ) containing the filtered fluid, in which the pressure level is lower than that in the space  3 . When a pressure control valve  69  is used, the resulting controlled amount is discharged into the tank (not shown) upstream from the strip-filter mechanism. 
     FIGS. 2 and 3  show that the entire drive device is installed in the housing  1  of an appropriate strip-filter mechanism. As is to be seen in  FIG. 3 , as the operation progresses in which filter material is in succession wound off the feed roll  5  and onto the take-up roll  11 , the take-up roll  11  becomes greater in diameter, while the diameter of the feed roll  5  becomes smaller. As  FIGS. 2 and 3  show, in keeping with this circumstance, the winding shaft  13  and the take-up roll  11  are mounted on a pivoted rocker  71 . As  FIG. 2  shows, all components of the drive device are mounted on this rocker  71 , that is, both the diaphragm accumulator  29  with the actuating rod  17  and the ratchet drive  15  for the winding shaft  13 , which may be actuated by this rod. Consequently, as the diameter of the take-up roll  11  increases, the entire drive device may be moved by the rocker  71  to adjust to the diameter of the increased roll  11   a , so that the axis of rotation of the winding shaft  13  may be displaced, as is illustrated by broken lines in  FIG. 3 . 
   The diaphragm accumulator  29  provided in the exemplary embodiment may be replaced by a hydraulic accumulator of another type with a movable separating element to actuate the actuating rod  17  of the drive device in reciprocating movement. The hydraulic accumulator is not to be understood in the classic sense as performing the function of storing hydraulic energy, but is rather to be viewed more as a medium separating element, one separating element  31  separating two media accumulator spaces  33 ,  35 . 
   The differential pressure measured could also be represented by the dynamic pressure, which increases with increase in the extent of fouling. In this instance, the accumulator space  35  preferably is connected to the tank by the valve  69 . The amount of the differential pressure or of the dynamic pressure may be adjusted by the force of the spring of the respective valve  69 . In addition, the tilting mechanism  53 ,  55  performs a safety function in that it initiates a discharge process, for example, when the pressure peaks in the respective accumulator space are impermissibly high. Since the fluid connection  49  of the accumulator space  35  may be connected to the fouled side of the device, a suitable filter device (not shown) may be provided upstream from the connection  49 . 
   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.