Abstract:
The invention pertains to a fuel system for internal combustion engines in which the unburned, heated fuel which is permitted to flow back to the tank from the fuel metering assembly is deaerated via an apparatus in order to prevent gases from re-entering the fuel supply pump when the fuel is reinduced thereto. By the inclusion of a jet pump between the fuel return line and the induction line, the degree of efficiency of the fuel supply pump is substantially increased.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a fuel system for internal combustion engines having a fuel tank, a fuel pump connected thereto by a conduit, a fuel metering assembly associated with said pump for feeding fuel to said engine and a return conduit extending from said fuel metering assembly to said tank to discharge excess fuel thereto. The unused quantity of fuel flowing back to the fuel tank can become overly heated because of temperatures either within the system or also outside of it. This leads to a breakdown of the fuel into gaseous and more viscous liquid components. Gas bubbles that result from this breakdown of the fuel are a constant problem and can lead to a failure of the fuel being supplied by the pump. However, it is also important that the fuel that contains entrained air be pumped away while still warm, so as not to cause difficulties later when it is cold. 
     In known fuel systems of this type, the excess fuel quantity is returned without treatment to the supply tank, so that when the quantity of fuel in the tank is at a low level, gas bubbles are easily entrained and fed back into the fuel supply pump. 
     An apparatus is in fact known, in which the returning fuel flows obliquely into a perpendicularly disposed container from which the induction line of the fuel supply branches off. By means of this return flow into the tank it is possible that the fuel can be virtually entirely consumed. However, in this container no deaeration takes place, since on the contrary, given the high rate of flow into the tank and there being little fuel in the tank, air is additionally carried along by the fuel and mixed therewith. 
     OBJECT AND SUMMARY OF THE INVENTION 
     The fuel system according to the invention has the advantage that a substantially complete deaeration of the fuel takes place before the fuel is once again induced by the fuel supply pump. When the return line in addition ends directly before the induction line of the fuel supply pump, particularly in the manner of a jet pump, then even excess fuel quantities in which air is entrained can be taken up directly by the fuel supply pump, and the fuel pump operates at a greater degree of efficiency by exploiting the flow or kinetic energy of the fuel which is being discharged from the return line. 
     The invention will be better understood as well as further objects and advantages thereof become more apparant from the ensuing detailed description of preferred embodiments taken in conjunction with the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a first exemplary embodiment of the fuel system according to the invention with a float-type controlled deaeration line; 
     FIG. 2 shows a further embodiment of a float-type valve which differs from that revealed in FIG. 1; 
     FIG. 3 shows a second exemplary embodiment of the fuel system according to the invention with gas separation accomplished by means of a foraminous element; and 
     FIG. 4 shows further the embodiment shown in FIG. 3. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Turning now to FIG. 1, the fuel system according to the invention comprises a fuel tank 1, which includes an upper inlet 1a, normally closed by a cap 1b through which fuel is periodically admitted to replenish the fuel stored within the fuel tank 1. A fuel supply pump 2 induces fuel 4 via an induction line 3, in order to deliver the fuel 4 via a pressure line 5 to a fuel metering assembly 6. From this fuel metering assembly 6, lines 7 branch off toward the internal combustion engine, leading, for example, to injection nozzles disposed within the intake manifold. A return line 8 also branches off from this fuel metering assembly 6 and empties back into the fuel tank 1. There is a self-contained deaeration container 9 disposed within the fuel tank 1, from the bottom wall 10 of which container a further conduit 11 of the return line 8 branches off and leads to the induction line 3. At the end of the conduit 11 a nozzle 12 is provided which projects into an induction funnel 13 of the induction line 3. The deaeration container 9 is disposed as close as possible to the top of the fuel tank 1, preferably directly beneath the top wall of the tank 1. 
     As soon as the fuel supply pump 2, which is preferably driven electrically, induces fuel from the fuel tank 1 via the funnel 13, and as soon as fuel then exits via the nozzle 12, a jet pump effect is created which causes the fuel that flows from the deaeration container 9 to carry along with it fuel from the fuel tank 1. The geodetic head prevailing from the deaeration container 9 toward the nozzle 12, augmented if possible by a certain overpressure in this container, effects a flow or kinetic energy at the nozzle 12 which is exploited to improve the output of the fuel supply pump 2. 
     The deaeration container 9 has a ventilation line 14 which is controllable by means of a movable valve element 15. This movable valve part 15 is connected with a float-type member 16 which, depending on the height of the fuel level 17 in the deaeration container 9, either presses the valve part 15 against its seat, blocking the deaeration line, or else opens the deaeration line, all of which is believed to be clear from the drawing. The valve element 15 and the float 16 are located within a substantially perpendicularly disposed guidance tube 18. The lowermost position of the float 16 is determined by means of a stop 19. 
     The cross section of the nozzle 12 is adapted in this fuel system to the minimum excess quantity which flows into the deaeration container 9, in order to prevent the container 9 from becoming dry during operation. Should the quantity of fuel greatly increase, for example at low engine rpm and with a corresponding low fuel consumption, then the fuel level in the container 9 rises and the valve element 15 closes. The higher pressure which then establishes itself within the container causes an energy increase at the nozzle 12, which in turn brings about a reduction of the electrical power requirement of the fuel supply pump 2. The pressure in the container 9 is limited by a maximum pressure valve 20. 
     In the view shown in FIG. 2 and in contrast to the system described in the first embodiment, the return line 11&#39; is controllable by another valve element 21, which is also disposed on the float 16&#39;. By this means when the fuel level 17 reaches a critical lower limit in the container 9, the flow from this container is blocked and prevented from reaching the nozzle 12. Thus, in this way the container 9 is prevented from running dry and the possible entry of air or gases into the line 11&#39; and thus into the supply pump 2 is prevented. 
     The disposition and embodiment of the valve, as well as its actuation, are given purely by way of example. The control of such valves naturally can also be accomplished by electrical, mechanical, or other means, as is known in other fuel systems. 
     Relative to the embodiments of this invention shown in FIGS. 3 and 4, a container 22 is provided adjacent to the bottom of the fuel tank 1&#39;, into which the return line 8&#39; discharges and from which the induction line 3&#39; branches off. The inlet and discharge portions of this container 22&#39; are separated by a foraminous element 23 for the purpose of filtering out gas bubbles. The bubbles of fuel which collect above the screen-like member 23 out of the returning fuel flow into the upper region of the container 22. 
     In the embodiment of the invention shown in FIG. 3, air 24 escapes in the form of bubbles via a mushroom-type valve 25 into the fuel tank 1&#39;. The bubbles then reach the upper surface of the fuel, and there dissipate. A plurality of apertures 26 are provided in the bottom of the container 22. In this way make-up fuel is permitted to flow from the fuel tank 1&#39; and replaces the quantity of fuel diverted by the fuel metering assembly 6. A filter or screen element 27 is disposed on the bottom of the container in front of the openings 26. As soon as the fuel level in the fuel tank 1&#39; drops below the height of the top of the container 22, the escaping gas bubbles enter the air space above the fuel surface. In an advantageous manner, however, the container 22 is constantly refilled with fuel through the return line 8&#39;, so that the fuel in the tank 1&#39; can be virtually entirely consumed, without gases entering the fuel supply pump 2. 
     In another embodiment shown in FIG. 4, the gases are directed from the container 22&#39; through a deaeration tube 28 to the air space above the fuel surface 29. In order to attain a corresponding collection of the gas in the region where the tube 28 branches off, the top wall 30 of the container 22 is canted upwardly toward the tube 28, as shown. The subsequent flow of used fuel takes place via bores 31 in the induction line 3&#34;, which are also covered by a screen element 27&#39;. The induction line 3&#34; is embodied, over its course within the fuel tank 1&#34;, as a cooling coil 32. With such a coil 32 it is possible to pre-treat the fuel so that the lower temperatures which prevail in the bottom of the fuel tank effect an additional cooling of the fuel and cause the resulting condensation to take place before the fuel enters the fuel supply pump 2. 
     In this last embodiment of the invention, further modifications are conceivable, for example the return line 8&#39; might discharge upwardly at an angle into the container 22 or that the induction line might branch off from the bottom of the container 22, and the like. 
     The foregoing relates to preferred embodiments of the invention, it being understood that other embodiments and variants thereof are possible within the spirit and scope of the invention, the latter being defined by the appended claims.