Patent Document

BACKGROUND OF THE INVENTION 
     The invention pertains to a filter head, designed to hold at least two filter elements. 
     In an internal combustion engine, the fuel is cleaned by two filter elements. These are installed in a stationary filter head. A shutoff lever is used to determine manually the number of filter elements through which the fuel will flow. During normal operation, for example, the fuel will flow through both elements, whereas, during maintenance work, it will flow through only one filter element, which allows the other filter element to be replaced. 
     A filter head with integrated feed channels and return channels, with two filter elements, and with a shutoff lever is known from U.S. Pat. No. 1,861,805. The lever is connected nonrotatably to a switching drum, so that turning the shutoff lever has the effect of actuating the switching drum, which in turn controls the flow of liquid through the feed and return channels. The switching drum and the filter head are sealed off radially from each other. So that the switching drum is free to rotate inside the filter head, an appropriate annular gap must be present. 
     A critical aspect of a filter head of this type is that, when one of the filter elements is to be replaced and the filter element has therefore been removed from the filter head, fuel escapes from the filter head through the annular gap. The classification societies for marine engines specify that no leakage may occur while the first filter element is active and the second filter element is being replaced. For this reason, this filter head cannot be used without supplemental measures such as the installation of nonreturn valves. Another critical point is that the shutoff lever must be turned against the force caused by the pressure of the fuel. In the case of a common-rail system, the low-pressure pump produces a pressure level of approximately 8 bars, which means that the shutoff lever is difficult to actuate. 
     SUMMARY OF THE INVENTION 
     The invention is based on the task of providing a filter head to hold at least two filter elements which fulfills the requirements of the classification societies and is also easy to operate. 
     The filter head according to the invention comprises a cover, which closes off the housing, and a spring element, which produces an axial force which presses the sealing surfaces of the switching drum against the cover and the housing. The spring element, especially a set of disk springs, presses one of the end surfaces of the switching drum against the cover and the other end surface against the housing. In practice, the spring element is dimensioned in such a way that any separation between the contact surfaces is reliably avoided. This axial seal is much more effective at reducing the amount of leakage than a radial seal. In practice, this means that, when the first filter element is removed and the second filter element is active, no fuel can drip out of the filter head and reach the environment. In addition, the axial seal has the effect that the amount of force required to actuate the shutoff lever is independent of the delivery pressure of the low-pressure pump of the common-rail system. 
     The switching drum has a 2-part design. The spring element; axial transfer bores, which communicate with the feed channels and the return channels in the housing and cover; and a driver pin, which transmits rotational movement between the two parts of the switching drum, are installed in the interior of the switching drum. 
     So that, when one of the filter elements is deactivated, no fuel in the switching drum will be able to leak from an open transfer bore to a closed transfer bore, the distance between two transfer bores is greater than the distance between a transfer bores and the outside diameter of the switching drum. When the pressure cone which forms expands, it will therefore expand not in the direction of the closed transfer bore but rather in the direction of the outer circumference of the switching drum. 
     A first relief space is provided in the interior of the switching drum to collect leaking fuel. In addition, a second relief space is provided on the circumference of the switching drum. Because the surface structure of metallic seals means that such seals can never be absolutely leak-tight, leaking fuel trickling into the two relief spaces is sent to the pressureless fuel feed line leading to the low-pressure pump. 
     Exemplary embodiments of the invention are explained below by reference to the attached drawings 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a perspective view of a filter head with two filter elements; 
         FIG. 2  shows a cross section of  FIG. 1 ; 
         FIG. 3  shows a cross section of the switching drum; 
         FIG. 4  shows a front view of the housing; and 
         FIG. 5  shows part of  FIG. 4  in detail. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a perspective view of a filter head  1  with two filter elements  2 A and  2 B. The filter head  1  comprises the following components: a housing  3 , a cover  7  to close the housing  3 , a switching drum  6  in the interior of the cover and housing, along with a shutoff lever  16 , which is connected nonrotatably to the switching drum  6 , and a locking pin  17  to hold the shutoff lever  16  in position. 
     Feed channels to supply uncleaned fuel and return channels to carry away the cleaned fuel are integrated into the interior of the housing  3  and the cover  7 . The inflow ZU to the filter head (unclean side) and the outflow AB from the filter head (clean side) are indicated in  FIG. 1  by corresponding arrows. The classification societies prescribe for marine engines that it must be possible to replace a filter element while the engine is running, and that, when the first filter element is active, for example, filter element  2 A, no leakage may occur when the second filter element, here filter element  2 B, is being replaced. This means that no fuel may drip out of the filter head and reach the surroundings. The filter head must therefore be leak-tight. 
     The arrangement offers the following functionality: 
     The shutoff lever  16  determines the rotational position of the switching drum  6 . The drum  6  in turn releases or shuts off the flow from the feed channels in the housing  3  to the feed channels in the cover  7 . The same applies correspondingly to the return channels. During normal operation, the shutoff lever  16  is in the center position, as illustrated in  FIG. 1 . In the center position, both filter elements  2 A and  2 B are in operation. In the left position, the filter element  2 A is operating, whereas filter element  2 B is deactivated. In this position, filter element  2 B can be removed from the filter head and the filter insert replaced. In the right position, filter element  2 B is operating, whereas the filter element  2 A is deactivated. Under these conditions, the filter element  2 A can be removed from the filter head  1 . The locking pin  17  is used to hold the shutoff lever in the selected position. 
       FIG. 2  shows a cross-sectional view of the arrangement according to  FIG. 1 , where the reference numbers of  FIG. 1  have been carried over without change. The further explanation provided here applies to both  FIG. 2  and  FIG. 3 .  FIG. 3  shows a magnified cross-sectional view of the switching drum  6 , which has been rotated into a position different from that shown in  FIG. 2 . 
     In  FIG. 2 , the shutoff lever  16  is shown in the middle position, as a result of which fuel is able to flow through both filter elements  2 A and  2 B. The switching drum  6  is supported in the cover  7  and in the housing  3 . The switching drum  6  is made up of two parts,  6 A and  6 B, with an integrated spring element  8 . A stack of disk springs is preferably used as the spring element  8 . The switching drum  6  (part  6 A) is sealed off against the cover  7  in the axial direction by a sealing surface  9 A. The switching drum  6  (part  6 B) is sealed off against the housing  3 , also in the axial direction, by a sealing surface  9 B. The sealing force acting against these sealing surfaces  9 A and  9 B is generated by the spring element  8 , which presses the end surfaces  10 A and  10 B of the switching drum  6  onto the corresponding surfaces of the cover  7  and the housing  3 . See here  FIG. 3 . In contrast to the prior art, in which there is always a small gap present as a result of manufacturing tolerances, in the present design the sealing surfaces rest against each other, metal to metal. Because the surface structure of metallic sealing surfaces means that such seals can never be absolutely leak-tight, additional measures are taken. To collect the fuel which leaks while the filter element is removed, a first relief space  14  is provided in the interior of the switching drum  6  ( FIGS. 3 and 5 ), and a second relief space  15  is provided on the circumference of the switching drum. Leaking fuel trickling through by way of the two relief spaces  14 ,  15  is thus guided to the pressureless fuel feed side of the low-pressure pump of a common-rail system. 
     The switching drum  6  has four axial transfer bores, namely, two feed transfer bores  12  and two return transfer bores  13 . By way of these transfer bores, the channels in the cover  7  are either connected to or separated from the channels in the housing  3 . The transfer bores  12 ,  13  are located on a common reference circle with an overlap, as a result of which, regardless of the position to which the switching drum  6  has been turned, it is always possible for fluid to pass through one filter element or both filter elements  2 . The rotational movement of the first part  6 A of the switching drum  6  is transmitted to the second part  6 B by a driver pin  11 . 
     As shown in  FIG. 2 , the flow path of the fuel to be cleaned is as follows: inflow ZU, feed channels  4  in the housing  3 , feed transfer bores  12  in the switching drum  6 , feed channels  18  in the cover  7 , back into the feed channels of the housing  3  (located outside the plane of the drawing), and from there into the filter elements  2 A and  2 B. The flow path of the cleaned fuel is: from the filter elements  2 A and  2 B to the return channels  5  of the housing  3 , return transfer bores  13  in the switching drum  6 , return channels  19  in the cover  7 , and via return channels in the housing to the outflow AB. 
       FIG. 4  shows a front view of the housing  3  after the cover  7  has been removed. The further explanation provided here also applies to  FIG. 5 , which shows a detail X taken from  FIG. 4 . The two feed transfer bores  12 A and  12 B and the two return transfer bores  13 A and  13 B are located in the switching drum  6 , through which they extend in the axial direction, that is, perpendicular to the plane of the drawing. The distance between a transfer bore and the circumference  20  of the switching drum  6  is smaller than the distance between two adjacent transfer bores. In detail X of  FIG. 5 , therefore, the radial distance “sr” between the return transfer bore  13 A and the circumference  20  of the switching drum  6  is smaller than the distance “sz” to the adjacent return transfer bore  13 B. When the filter element is deactivated, the pressure cone which forms around the return transfer bore  13 A, for example, therefore expands to the circumference  20  of the switching drum  6  and from there to the second relief space  15 . The leaking fuel accumulating in the second relief space  15  is carried away without pressure through a vent channel  21  (see  FIG. 4 ). 
     The following advantages of the invention can be derived from the preceding description: 
     because of the axial seals and the relief spaces, the filter head is leak-tight in correspondence with the rules of the classification societies; 
     the adjusting force required to actuate the shutoff lever is independent of the pressure level of the fuel; 
     tightly sealing shutoff units such as ball valves are not needed, which means that the filter head is less expensive; and 
     the filter head is very compact. 
     Although the present invention has been described in relation to particular embodiments thereof, many other variations and modifications and other uses will become apparent to those skilled in the art. It is preferred, therefore, that the present invention be limited but by the specific disclosure herein, but only by the appended claims.

Technology Category: f