Abstract:
A tank arrangement for a vehicle, particularly a truck, includes at least a first fuel tank and a second fuel tank which are connected by a balancing pipe, a suction pipe for feeding fuel to an engine and a return pipe for feeding fuel from the engine to at least one of the fuel tanks. The balancing pipe is provided with a first end to supply fuel to the first tank and a second end to suck fuel from the second tan, wherein a check valve is arranged upstream of the return pipe in the balancing pipe between the at least two tanks allowing a flow direction from the second tank to the first tank and blocking a flow in the reverse direction. Suction of fuel to the engine is from the first tank only. The check valve provides an automatic purging of the system.

Description:
BACKGROUND AND SUMMARY 
     The invention relates to a tank arrangement and a vehicle with a tank arrangement. 
     U.S. Pat. No. 4,930,537 discloses a fuel utilization system for a truck having multiple tanks, an above-tank crossover pipe coupling the two tanks. A suction pipe is coupled to a primary tank only. A return pipe is coupled to the crossover pipe. 
     As an alternative the return pipe can be coupled directly to the primary tank. This method of transferring liquid between the tanks used in this system is commonly known as siphoning. A Venturi device is arranged inside the tank which is flushed when the tank is completely filled. 
     It is known in the art to use dual tanks for supplying fuel to an engine of a truck. On one hand customers are desirous to have a big tank volume available, on the other hand construction space is very restricted particularly in trucks. As space restrictions do not allow to install one big tank, the tank volume is split in two tanks, e.g. a big master tank and a small slave tank, mounted e.g. on both sides of the frame. The piping between the tanks and the connections to the engine are complex and costly. Often, at least one of the tanks cannot be completely depleted, and refilling of the tanks has to be done in a certain order, i.e. one specific tank has to be filled before the other tank can be filled. 
     It is desirable to provide a tank arrangement which allows for a better fuel use up and an economic piping between the tanks and the engine. It is also desirable to provide a vehicle with a tank arrangement with a robust level balancing system. 
     According to a first aspect of the invention, a tank arrangement for a vehicle, particularly a truck, is proposed, comprising at least a first fuel tank and a second fuel tank which are connected by a balancing pipe, a suction pipe for feeding fuel to an engine and a return pipe for feeding fuel from the engine to at least one of the fuel tanks. The balancing pipe is provided with a first end to supply fuel to the first tank and a second end to suck fuel out of the second tank, wherein a check valve is arranged upstream of the return pipe in the balancing pipe between the at least two tanks allowing a flow direction from the second tank to the first tank and blocking a flow in the reverse direction. 
     Advantageously, the check valve provides an automatic purging function to remove air from the balancing pipe between the first and the second tank. Preferably, the check valve exhibits a low opening pressure corresponding to not more than 100 mm fuel height difference, particularly not more than 500 Pa. 
     Favourably, the tank arrangement allows for complete emptying of both the master and the slave tank. Of course, more than two tanks can be provided, e.g. one master tank with two or more slave tanks. The suction point of the slave tank can be lowered to the tank bottom which provides a better fuel use up. A specific refilling order is not required. The piping between the tanks and the engine is simplified and cost efficient. Additional interfaces on the tanks can be avoided. Existing tank configurations can be used. The second tank can have a smaller volume as the first tank. Particularly, the tank arrangement provides a robust behaviour for different sizes of return flow from the engine to the tank arrangement. 
     Particularly, the fuel return pipe can be of smaller diameter than the balancing pipe. Advantageously, the dimensions of the fuel return pipe and the balancing pipe can be adapted to each other to maintain a siphon effect during driving. A skilled person will do this based on parameters influencing the behaviour, such as an injection strength of the return fuel in an ejector pump, flow rate of return fuel and the like. 
     Further, the connection between the fuel return pipe and the balancing pipe can beneficially be designed such that the fuel entering the balancing pipe flows towards the first tank in which the suction pipe (driven by a fuel pump coupled to the engine) is arranged, thereby maintaining the siphon effect during driving. Most favourably, the system can be designed in a way to ensure that all air is removed from the balancing pipe by means of using the return fuel velocity in the return pipe, an ejector device and the check valve. The system is purging itself automatically also after one of the tanks has been emptied completely. As soon as the tank is refilled, the system can start up automatically again. 
     The direct fuel pipe connection (balancing pipe) between the second and the first tank can be integrated in a return piping provided for removing fuel from the engine to the tank arrangement by integrating the check valve into the piping and arranging the return pipe accordingly with respect to the check valve. The balancing pipe between the tanks can be increased in diameter compared to a usual return pipe. 
     According to a favourable development of the invention, the return pipe and the balancing pipe can be merged in an ejector device supporting fuel transport from the second tank to the first tank, wherein the return pipe can be attached to a high pressure side and the balancing pipe can be attached to a suction side of the ejector device. Advantageously, the ejector device sucks the fuel out of the second tank. No fuel can flow back from the engine or the first tank to the second tank. The ejector device allows to keep the fuel level in the second tank slightly lower than in the first tank. This allows to empty the second tank completely without introducing air from the second tank into the first tank. The ejector device can be designed accordingly for keeping a desired level difference in the tanks. 
     According to a further favourable development of the invention, the check valve can be arranged in a balancing pipe leg inside the second tank. This provides a compact arrangement of the valve. Alternatively, the check valve can be arranged in a balancing pipe portion outside the second tank. The skilled person will choose the proper arrangement according to the actual conditions of the tank arrangement. 
     According to a further favourable development of the invention, the balancing pipe can have a first portion inside the first tank, a second portion inside the second tank and a third portion connected at a first side to a geodetic top portion of the first tank and at a second side to a geodetic top portion of the second tank. 
     Advantageously, a standard tank geometry can be used with connection ports at the top of the tank vessel. 
     According to a further favourable development of the invention, the first tank can provide a suction pipe from the first tank to the engine. Preferably, the engine can be supplied with fuel only by the suction pipe connected to the first tank. As suction of fuel from tank to engine occurs only from the first tank, the second tank can be simplified. The first tank is used as master tank whereas the second tank is used as slave tank. 
     According to a further favourable development of the invention, the first tank can provide a fuel level sensor for sensing the fuel level in the first tank. Favourably, as suction is only made from the first tank, all return fuel from the engine can be guided into the first tank by the check valve. 
     According to a further favourable development of the invention, each of the first and second tanks can provide individual air pipes supplying each tank with air independent from the other tank. The tank arrangement becomes more robust as an air connection between the two tanks can be removed. Freezing problems caused by condensed water in a common air connection can be avoided. Alternatively, the first and second tanks can be connected with one common air connection. In this case, only one air filter is necessary. 
     According to a further favourable development of the invention, the second end of the balancing pipe can have a clearance of not more than 4 cm, preferably not more than 2 cm, to the second tank bottom. Thus, the second tank can be virtually completely emptied thus improving the fuel use up of the tank arrangement. 
     According to a further favourable development of the invention, the return pipe can join the balancing pipe in a valve unit comprising an ejector device supporting fuel transport from the second tank to the first tank, wherein the check valve and the injector valve can be integrated in the valve unit. Advantageously, at least one of the check valve and/or ejector device can provide quick connections with a snap-in function for attaching and detaching the balancing pipe and/or the return pipe. 
     According to another aspect of the invention, a vehicle is proposed comprising a tank arrangement for supplying fuel to an engine. A balancing pipe between at least a first tank and a second tank is attached to geodetic upper half portions of the first tank and second tank. The tanks can be of different volumes or exhibit the same volume. 
     According to a favourable development of the invention, the balancing pipe can be arranged within a web of a vehicle frame. 
     According to a further favourable development of the invention, only the first tank can be supplied with a suction pipe for providing fuel to the engine. A fuel pump can be installed in the first tank. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention together with the above-mentioned and other objects and advantages may best be understood from the following detailed description of the embodiments, but not restricted to the embodiments, wherein is shown schematically: 
         FIG. 1  a sketch of a preferred embodiment of a tank arrangement according to the invention; 
         FIG. 2   a ,  2   b  a cut through a preferred valve unit with a check valve and a ejector device ( FIG. 2   a ), a preferred valve unit displaying quick connectors ( FIG. 2   b ), an alternative kind of a check valve of the butterfly type ( FIG. 2   c ), an alternative kind of a check valve of the mushroom type ( FIG. 2   d ) and an alternative kind of a check valve of the mouth type ( FIG. 2   e ); 
         FIG. 3  preferred arrangement of a balancing pipe between two tanks according to the invention; 
         FIG. 4  a preferred vehicle comprising a tank arrangement according to the invention; and 
         FIG. 5   a ,  5   b  test results with different tank volume combinations with tanks of equal volume ( FIG. 5   a ) and tanks with dissimilar volumes ( FIG. 5   b ). 
     
    
    
     DETAILED DESCRIPTION 
     In the drawings, equal or similar elements are referred to by equal reference numerals. The drawings are merely schematic representations, not intended to portray specific parameters of the invention. Moreover, the drawings are intended to depict only typical embodiments of the invention and therefore should not be considered as limiting the scope of the invention. 
       FIG. 1  depicts schematically a sketch of a preferred embodiment of a tank arrangement  110  according to the invention. The tank arrangement  110  is preferably employable in a vehicle  200  ( FIG. 4 ), particularly a truck. 
     The tank arrangement  110  comprises by way of example a first fuel tank  10  as a master tank with a big volume and a second fuel tank  50  as a slave tank with a smaller volume which are connected by a balancing pipe  70 . The balancing pipe  70  extends with one leg  72  into the first tank  10  and with one leg  76  into the second tank  50 . Fuel from the second tank  50  is transported through the balancing pipe  70  to the first tank  10 . 
     The first tank  10  is connected to an engine  100  by a suction pipe  82  with a filter  74  at its suction end. A clearance  10   a  is established above a bottom  10   b  of the first tank  10  and the suction pipe  82 , i.e. the filter  74 . 
     An air connection pipe  16  feeds air to the first tank  10  through an air filter  20  and an air vent valve  18 , e.g. a ball valve of the normally-open type. A leg  72  of the balancing pipe  70  extends into the first tank  10 . A level of fuel  42  in the inner space  14  of the first tank  10  is sensed by a level sensor  40 . 
     A return pipe  80  feeds surplus fuel from the engine  100  to the first tank  10 . Preferably, the balancing pipe  70  is integrated in the return pipe  80 , indicated by a pipe portion  80   a . Optionally, the outlet of the balancing pipe  70  (or the pipe portion  80   a , respectively) in the first tank  10  can be guided away from the suction point of the first tank  10 . This can be achieved for instance by an L-shaped end piece where the cross leg of the L-shaped end piece is directed crosswise away from the suction point of the suction pipe  82 . The advantage is that if the second tank  50  is emptied and air is sucked in through the balancing pipe  70  the suction pipe  82  does not suck in the air from the balancing pipe  70 . 
     Optionally, a cab heater pipe  32  can be arranged between the first tank  10  and a cab heater pump  30 . A filter  34  is arranged in the cab heater pipe  34 . The cab heater pump  30  feeds fuel to a heating unit for the vehicle&#39;s cab (not shown). 
     The balancing pipe  70 , the return pipe  80 , the suction pipe  82  and the air connection pipe  16  are preferably arranged to enter the tank  10  at its top  12 . The balancing pipe  70 , particularly its leg  72 , the return pipe  80 , and the suction pipe  82  can be combined in a pipe unit  86   a  which can be introduced into the first tank  10  through one common feedthrough  12   a.    
     A unit  86  can be coupled to the level sensor  40  and the air vent valve  18 , preferably by attaching the unit  86 , to the upper portion  12  of the first tank  10  close to the feedthrough  12   a . The unit  86  is also called “fuel sender head” and can be coupled to a control unit (not shown) supplying e.g. fuel level data to the control unit. 
     The second tank  50  is connected to the first tank  10  by the balancing pipe  70 . A clearance  50   a  is established above a bottom  50   b  of the second tank  50  and the balancing pipe  70 , i.e. a filter  78  at the suction end  76   a  of the leg  76  of the balancing pipe  70 . The clearance to the second tank bottom  76   b  can be 4 cm or less so that the second tank  50  can be virtually completely emptied. 
     An air connection pipe  56  feeds air to the second tank  50  through an air filter  60  and an air vent valve  58 , e.g. a ball valve of the normally-open type. A leg  76  of the balancing pipe  70  extends into the second tank  50 . A level sensor for sensing the level of fuel in the inner space  54  of the second tank  50  is not necessary. Preferably, the level of the fuel in the second tank  50  is equal or slightly lower than the fuel level in the first tank  10 . This is indicated in the drawing by a level difference δh between the fuel level in the first tank  10  and the fuel level in the second tank  50 . 
     The balancing pipe  70  and the air connection pipe  56  are preferably arranged to enter the second tank  50  at its top  52 . The balancing pipe  70 , particularly its leg  76 , can be arranged in a pipe unit  84   a  which can be introduced into the second tank  50  through one feedthrough  52   a.    
     A unit  84 , again a so called “fuel sender head”, can be coupled to the air vent valve  58 , preferably by attaching the unit  84  to the upper portion  52  of the second tank  50  close to the feedthrough  52   a.    
     In a portion  70   a  between the legs  72 ,  76  of the balancing pipe  70  a check valve  92  is arranged which enables a flow direction  46  from the second tank  50  to the first tank  10  and blocks a flow in the reverse direction. The check valve  92  is arranged upstream of the conjunction  80   b  of the return pipe  80  to the balancing pipe  70 . Preferably, the balancing pipe  70  is integrated in the return pipe  80 , indicated by a pipe portion  80   a  which feeds the fuel returning from the engine  100  and fuel sucked out of the second tank  50  to the first tank  10 . 
     Suction of fuel to the engine  100  is performed with a fuel pump (not shown) preferably arranged at the engine  100 . Fuel is directly sucked to the engine  100  only from the first tank  10 , where the fuel level is monitored by the level sensor  40 . Thus, the tank arrangement is simplified as the second tank  50  does not need a level sensor or a suction pipe to the engine  100 . 
     The tank arrangement  110  is robust during operation. If the air filter  60  of the second tank  50  is clogged, a slight underpressure is built up and emptying the tank  50  is accomplished a little bit harder. If the air filter  20  of the first tank  10  is clogged, the second tank  50  will be emptied faster than usual. When completely emptied, air will flow through the second tank  50  to the first tank  10  and the big tank  10  will be emptied in a normal way. 
     If the check valve  92  ( FIG. 2   a - 2   f ) breaks, the valve is always open and provides no effect as long as the balancing pipe  70  is free of air. If air is in the balancing pipe  70 , fuel will be returned to the second tank  50 , and the fuel level sinks fast in the first tank  10 . A driver alert is issued as the level sensor  40  detects the low fuel level. 
     If the check valve  92  should be clogged, fuel in the second tank  50  is not used up. 
     If the ejector device  94  should break, all fuel will be returned to the first tank  10 . A lesser amount of fuel is sucked out of the second tank  50 . The fuel level in the second tank  50  will become higher than in the first tank  10 . The second tank  50  cannot be emptied completely. If air enters the leg  76  of the balancing pipe  70  in the second tank  50 , e.g. when the unit  84  is removed, then air will stay in the leg  76  and the second tank  50  will not be emptied at all. 
     Typical inner diameters can be by way of example 9 mm for the fuel suction pipe  82 , 6 mm for the fuel return pipe  80  as well as for the air connection pipes 16, 56 and 12 mm for the direct balancing pipe  70  integrated in the return pipe  80 . It is to be understood that the dimensions can be chosen differently depending on an actual vehicle in which the tank arrangement  110  is provided. 
       FIGS. 2   a  and  2   b  illustrate a preferred valve unit  90  by a cut through the preferred valve unit  90  and a side view of the valve unit  90 . 
     The return pipe  80  joins the balancing pipe  70  in operational interaction with an ejector device  94  in a valve unit  90 . A flow of return fuel returning from the engine  100  to the ejector device  94  sucks fuel from the second tank  50  into the first tank  10 . Upstream of the ejector device port for the return pipe  80  a check valve  92  is arranged which enables flow from the second tank  50  to the first tank  10  and blocks a flow in the reverse direction. The ejector device  94  can by way of example be designed as a Venturi valve or the like. 
     Preferably, quick fittings can be provided at the pipe ports for an easy connection of the balancing pipe  70  and the return pipe  80  to the valve unit  90 . Particularly, the quick fittings provide a snap in function as indicated in  FIG. 2   b  which allows easy plugging in and releasing of the pipes. 
     The check valve  92  has a low opening pressure, e.g. corresponding to 100 mm fuel height difference. The check valve  92  can be a ball type valve as illustrated in  FIG. 2   a . Alternatively, the check valve  92  can be a butterfly type valve as illustrated in  FIG. 2   c . Alternatively, the check valve  92  can be a mushroom type valve as illustrated in  FIG. 2   d . Alternatively, the check valve  92  can be a mouth type valve as illustrated in  FIG. 2   e . The allowed flow direction is indicated as a bold arrow. 
     Referring now to  FIG. 3  and  FIG. 4 , a preferred arrangement of a tank arrangement  110  on a vehicle is shown. The tank arrangement  110  comprising e.g. two tanks  10 ,  50  connected by a balancing pipe  70  according to the invention is depicted in  FIG. 3 . An example embodiment of the vehicle  200  is shown in  FIG. 4 . 
     The tanks  10 ,  50  are each attached to one longitudinal frame beam  210   a ,  210   b  at each side of a vehicle frame  210 . The middle portion of the balancing pipe  70  combined with the return pipe  80  is arranged within a web  212  between the longitudinal beams  210   a ,  210   b  of the vehicle. The valve unit  90  can be arranged inside or outside the second tank  50 . 
     Test results with different tank volume combinations are presented in  FIGS. 5   a  and  5   b , featuring a dual tank arrangement with tanks of equal volume in  FIG. 5   a  and with tanks with dissimilar volumes in  FIG. 5   b . The dual tank arrangement is embodied as described in the preceding drawings. 
     As suction of fuel to the engine  100  ( FIG. 1 ) is performed only from the first tank  10 , the levelling of the fuel levels in both tanks  10 ,  50  ( FIG. 1 ), where the fuel level is monitored by the level sensor  40 . Thus, the tank arrangement is simplified as the second tank  50  does not need a level sensor or a suction pipe to the engine  100 . 
     The noisy-appearing signal V 200  represents the engine speed, and stepwise descending signals A and B represent the fuel level balancing in one of the tanks (signal A) and the other of the tanks (signal B) as a function of time. 
     In  FIG. 5   a , the tank volumes are equal and by way of example comprise 150 litre fuel each. The fuel volume in the tanks drops from 85% at the start of the test phase to about 30% at the end of the test phase, wherein signal B follows nicely signal A. 
     In  FIG. 5   b , the tank volumes are dissimilar and by way of example comprise 150 litre fuel in a small tank and 870 litre fuel in a big tank of the preferred dual tank arrangement. The fuel volume in the tanks drops from 85% at the start of the test phase to about 65% during the test phase, wherein signal B follows nicely signal A. 
     The invention provides a tank arrangement with at least two tanks which permits a complete emptying of the one or more slave tanks which feed fuel to a master tank, while fuel is transferred from the master tank to an engine. The arrangement provides an improved fuel use up and permits a virtually complete emptying of the one or more slave tanks. The suction point of the balancing pipe to the master tank can be lowered to the tank bottom. No specific refilling order of the tanks is required. Particularly, it is possible to drive with the master tank filled and empty slave tanks. The routing of the pipes is simplified and cost efficient.