Abstract:
A filter device for separating water and other impurities from liquid fuel including a housing body ( 11 ), inside which a first filter element ( 12 ) is disposed; a collector vessel ( 17 ) which is disposed underneath the filter element ( 12 ); a pump ( 25 ) which is used to remove water present in the collector vessel ( 17 ), and a detector ( 23 ) which is used to determine whether water has accumulated in the collector vessel ( 17 ).

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a filter device for separating water and other impurities from liquid fuels with a housing body having a first filter element disposed in its interior and a water collecting vessel disposed underneath the filter element. 
     DE 33 06 294 C2 discloses a filter device, which is used to separate water and other impurities from liquid fuels, particularly to separate water and solid particles contained in diesel fuels. The known filter device comprises a housing body in the interior of which a first and a second filter element are arranged. A collector basin is disposed underneath these filter elements. This collector basin has two separate areas for collecting and discharging the impurities and the water. At the lower end, the system is provided with a drain plug. As soon as the removed water has reached a certain amount, the drain plug must be manually opened and the water discharged from the filter device. This is time-consuming; moreover, manual removal of the water is reliable only if an operator checks the entire device at regular intervals. 
     SUMMARY OF THE INVENTION 
     The object of the invention is to avoid the aforementioned disadvantages and to provide a filter device for separating water and other impurities from liquid fuels, which provides reliably purified fuel without requiring manual maintenance. 
     This object is attained by the invention as described and claimed hereinafter. 
     The substantial advantage of the invention is that an automatic water discharge mechanism is provided in the filter device. This ensures nearly maintenance free operation. Only replacing the filter element requires manual intervention in the system. 
     According to one embodiment of the invention, the pump works in suction operation or pressure operation, i.e., for suction operation it is disposed in the water discharge line. For pressure operation it is disposed in the fuel intake line and thus generates a positive pressure in the filter device, which is relieved by opening a valve in the water discharge line. The water flows out due to the positive pressure within the filter device. 
     To prevent problems at extremely low temperatures, the filter device is provided with a heating element. This can be a heat exchanger which is supplied with a heat transfer medium. It is also possible to arrange an electrical heating unit in the system, which is actuated when the temperature falls below a certain level. Instead of a heating element, the fuel return flow may be used to heat the fuel. Due to the heat of the engine, the return flow typically has a higher temperature than the fuel coming from the tank. This heated fuel may be supplied to the filter device via a thermostat valve. 
     The filter device can comprise two filter systems. The first filter is a prefilter, the second a downstream main filter. The two filter systems can be constructed identically and be linked by corresponding adapter elements. 
     To monitor the performance of the filters, it is possible in accordance with a further embodiment of the invention to utilize pressure sensors. A pressure sensor can measure, for instance, the differential pressure between intake line and discharge line and signal that the filter needs maintenance when the differential pressure exceeds a certain threshold value. If the fuel is supplied to the filter device at a defined pressure, a sensor is required only in the discharge line. Based on the measurement signal of the sensor, a pressure difference caused by the filter device can be determined and displayed. 
     If the fuel system has been emptied, the system has to be refilled with a corresponding pump. This pump can for instance be a manually operated pump for venting. 
     Typically, the filter devices according to the invention are used in trucks, construction machines and the like. To prevent the transfer of vibrations and shocks of the machine to the filter system, a further embodiment of the invention provides for vibration decoupling and arrangement of the filter device on a support structure with corresponding decoupling elements. 
     These and other features of further preferred embodiments of the invention are set forth in the claims as well as in the description and the drawings. The individual features may be implemented either alone or in combination in the embodiment of the invention or in other fields of application and may represent advantageous embodiments that are protectable per se, for which protection is hereby claimed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described in greater detail with reference to working embodiments. 
     FIG. 1 shows a schematic representation of a filter system, 
     FIG. 2 shows a further variant of a filter system, 
     FIG. 3 shows a sectional view of a mechanically detailed filter system, 
     FIG. 4 is a variant of the schematic structure shown in FIG. 2, and 
     FIG. 5 is a schematic representation of the venting of the two filters. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The filter system according to FIG. 1 comprises a prefilter  10  with a filter housing  11 . The filter housing contains a filter element  12 . The fluid to be filtered is supplied from a tank  13  via line  14  to a first intake line  15  for prefilter  10 . There the fuel enters the contaminated fluid area  16 . Any water contained therein settles out in water reservoir  17 . The fuel flows through filter element  12  and leaves prefilter  10  purified via clean fluid area  18  and discharge line  19 . Via discharge line  19  the fuel reaches a fluid pump  20  where it is highly compressed and guided through a main filter  21  to the injection valves (not shown) of an internal combustion engine. The excess fuel is returned to the tank via line  22 . 
     In prefilter  10  a water sensor  23  is provided. At an appropriately high water level in the water reservoir  17 , the water sensor generates a signal that causes the water to be pumped away via a two-way valve  24  by means of pump  25  and to be supplied via the two-way valve to a water discharge vessel  27 . To remove the residual water in pump  25  and the various valves  24 ,  26 , the valves are switched. Actuating pump  25  causes fuel to be supplied to the pump via line  28 . Due to the switched valve  26 , this fuel is supplied via a second feed line  29  to the prefilter  10 . 
     FIG. 2 shows a filter system with a prefilter  10  and a main filter  21 . Fuel is supplied to prefilter  10  via line  30  and pump  31  as well as pressure relief valve  32 . In prefilter  10  there is again a sensor  33  to detect any water that has collected on the bottom of the prefilter and a discharge line  34 . If the amount of water exceeds a certain measured value, the sensor causes the two-way valve  35  to be opened. Due to the pump pressure of pump  31  the water flows to the water discharge via discharge line  34  and two-way valve  35 . 
     The filtered fuel passes via line  36  and fluid pump  20  to the main filter  21 , where it is purified and then leaves the main filter and the filter system via line  37 . From there the fuel is conveyed to the individual injector nozzles of an internal combustion engine. The excess fuel is returned via line  38  of fluid pump  20 . 
     To heat the prefilter  10 , the excess fuel, which is supplied via line  38  to fluid pump  20 , can be diverted there and be provided to the prefilter via line  39  and a thermostat valve  40  in order to heat the fuel contained in the prefilter. If the thermostat valve does not switch over toward prefilter  10 , the heated fuel flows via line  41  directly into supply tank  42 . 
     FIG. 3 shows a detailed sectional view of the individual components of a compact system in which both a prefilter and a main filter are provided. As the drawing shows, the two filters are identically constructed. This results in a significant reduction in the manufacturing cost. Both filters comprise a filter housing  11 , each with a filter element  12  therein and a support tube  43 . In the prefilter  10  there is also a water sensor  44 . The filter housings are directly attached to a filter carrier  45  and can be removed to replace the filter element. The filter carrier includes three sensors. Sensor  46  detects the fuel pressure after the prefilter, sensor  47  the fuel pressure in front of the main filter, and sensor  48  the fuel pressure after the main filter. 
     Pump  49  for dewatering the prefilter is disposed at the side of the prefilter. In the area of the pump, water outlet  50  is provided. Also visible on the filter carrier are the fluid inlet  51  and fluid outlet  52 . It is of course also possible to integrate certain mechanical components in the filter carrier through lines in the filter carrier. 
     The filter carrier is provided with vibration-decoupling mounting elements  53 ,  54 . These can, for instance, be rubber elastic elements fixed to a mounting structure by means of a screwed connection. 
     At the prefilter disposed on the right side, the purified fluid is directed outwardly via connection  56  and is supplied via a line (not shown) to the main filter disposed on the left side. The fluid purified in the main filter passes to the fuel injection pump via connection  57 . 
     FIG. 4 shows a variant of the schematic structure depicted in FIG.  2 . The significant difference from the structure of FIG. 2 is that only two pumps are required for filling the entire system, emptying both filters and dewatering the prefilter  10 . These are pumps  31  and  58 . 
     The pump  31  pumps the fuel from tank  42  both into the prefilter and via line  59  also into the main filter  21 . A valve  60  and a non-return valve  61  are installed in line  59 . Above the switching valve  62 , which is a two-way valve, there is a line  63  leading to tank  42  and a line  64  leading to a water collector vessel  65 . Above and below valve  62 , sensors  66 ,  67  are installed in the line. These sensors generate actuating signals for valve  62 . 
     When the system is initially filled, pump  31  is actuated. Pump  31  fills the main filter  21  via line  59  and non-return valve  61  and the prefilter  10  via line  68 . If valve  60  can be opened when main filter  21  is being filled, the non-return valve  61  is not required. It merely represents an alternative embodiment. To remove any water that may have accumulated in the prefilter  10 , pump  58  is actuated. Initially the fluid flows through line  63  into tank  42 . As soon as water impinges on one of the two sensors  66 ,  67 , the corresponding sensor switches valve  62  so that the water is subsequently discharged via line  64  into the water collector vessel  65 . As soon as fuel impinges on sensor  67 , it switches valve  62  back to the position shown. After a certain predefined time, pump  58  is turned off. 
     When the filter elements are replaced, the filters must be emptied. For this purpose, valve  60  is opened. With the aid of pump  58 , both prefilter  10  and main filter  21  can now be emptied via line  63 . 
     Pumps  58  and  31  can advantageously be arranged in a common pump module. This has the advantage that the connections are placed within the module so that no external lines are required. 
     FIG. 5 shows a schematic illustration of the venting of the two filters  10  and  21 . During filling, the air escaping from the enclosed structures flows via line  69  and line  70  into a venting block  71  and from there via a throttle point  72  and line  73  into the fuel tank  42 . The escaping air lifts the non-return valve of filter  21 , which consists of a ball  74 , in upward direction where the ball does not seal an orifice but is merely held. As soon as the system is filled, a suction pump creates a negative pressure in prefilter  21  so that ball  74  moves downwardly and seals the venting opening. In the main filter  21  there is positive pressure. As a result, a small amount of fuel escapes via line  69  and throttle point  72  so that no air cushion can build up in the main filter.