The present invention relates to a fuel system for an internal combustion engine, in which a fuel pump supplies fuel to the engine via a forward line and is arranged in a fuel chamber which is accommodated in a fuel tank and is designed with side wall and upper wall, to which fuel chamber fuel can be transferred from the fuel tank by means of an ejector which is driven by a fuel flow, produced by the fuel pump, in a return line which opens into the fuel chamber, and which upper wall is designed with an outlet.

In order to ensure that air does not enter the fuel system of a vehicle, it is known to arrange the fuel pump in the fuel tank of the vehicle in a separate fuel chamber which is filled up with fuel from the surrounding fuel tank. In this connection, use has been made of return fuel from the engine in order to drive an ejector which sucks fuel from the fuel tank into the fuel chamber and the fuel pump. A disadvantage of this solution, however, is that the suction capacity of the ejector decreases when the engine load increases and consequently the return flow from the engine decreases. During idle running, when the return flow from the engine is great, a considerably greater suction capacity of the ejector is obtained, however, with an unnecessarily large fuel surplus in the fuel chamber as a result.

The aim of the invention is to eliminate these disadvantages and to bring about a fuel system which better ensures an adequate filling of the fuel chamber at different engine loads.

This aim is achieved according to the invention by the fuel system being designed according to what is indicated in the characterising part of Claim 1.

It is thus achieved that the ejector can supply a greater quantity of fuel to the fuel chamber, the greaterthe load on the engine is. This also results in a relatively small filling of the fuel chamber via the ejector during idle running when the fuel consumption is low.

The invention is explained in greater detail below with the aid of the exemplary embodiment of a fuel system according to the invention, which is shown diagrammatically in the attached drawing.

In a fuel system 1 designed according to the invention for an internal combustion engine 2, a fuel pump 3 supplies fuel to the engine 2 from a fuel tank 5 via a forward line 4. In order to ensure that air does not enter the fuel system, the fuel pump 3 is arranged in a separate fuel chamber 6 which is accommodated in the fuel tank 5 and is designed with a side wall 6' and an upper wall 6". In the fuel chamber 6, the fuel level is kept so high that the fuel pump 3 cannot suck air.

In the fuel chamber 6, there opens on the one hand a return line 7 for unused fuel from the engine 2 and on the other hand a return line 8 which is connected to the forward line 4 and via which a part of the fuel flow from the fuel pump 3 can return to the fuel chamber 6 without passing the engine 2. In the return line 8, there is an ejector 9 which by means of a suction line 10 can suck up fuel from the fuel tank 5 and thus forms a pump. The ejector 9 is driven by the return flow from the fuel pump 3 in the return line 8, the result of which is that both return fuel from the fuel pump and fresh fuel from the fuel tank are supplied to the fuel chamber 6 via the line section 11 of the return line 8, which line section is situated afterthe ejector 9.

At the top of the fuel chamber 6, there is an outlet 12 which is made up of a relatively small opening in the upper wall 6" and via which any surplus fuel in the fuel chamber 6 can flow out into the fuel tank 5. It is desirable that, when the fuel pump is in operation, there is a fuel surplus in the fuel chamber 6 in order to ensure good pump operation, and according to the invention the fuel flows to and from the fuel chamber 6 are to be dimensioned in such a manner that a fuel surplus is obtained.

The suction line 10 expediently opens close to the bottom of the fuel tank 5 in order to ensure good fuel supply. The ejector 9 can advantageously be of the type which is known through Swedish Patent Application 8703319-7, but other embodiments are also possible.

The engine 2 is of the injection type and is provided with a number of injection nozzles 13. To regulate the fuel pressure as a function of the engine load, there is a pressure regulator 14. In the event of increasing engine load, increasing fuel pressure is required.

In a fuel system in which the engine 2 has a fuel consumption of 2 l/h during idle running and 70 l/h during full-load running, it is possible according to the invention to use a fuel pump 3 which during idle running can produce a flow of 130 l/h and during full-load running a flow of 110 l/h, reduced on account of increased fuel pressure. The forward line 4 and the return line 8 can in this connection be dimensioned in such a manner that during idle running the fuel flow from the fuel pump is divided up so that 112 l/h are supplied to the engine while 18 l/h are supplied to the return line 8, whereas on the other hand during full-load running the fuel flow from the uel pump is divided up so that 87 l/h are supplied to the engine and 23 l/h are supplied to the return pipe 8. The ejector 9 will thus suck in via the suction line 10 a flow of 60 l/h during idle running and 150 l/h during full-load running. The result is that the fuel chamber 6 is supplied with a total flow of 188 l/h during idle running, namely 110 l/h via the return line 7 and 78 l/h via the line section 11. Since the pump capacity during idle running is 1301/h, an outflow of 58 l/h is thus obtained via the outlet 12. Correspondingly, the fuel chamber 6 is supplied with a flow of 190 l/h during full-load running, namely 17 l/h via the return line 7 and 173 l/h via the line section 11. The outflow via the outlet 12 is then 80 l/h.

It thus emerges that according to the invention the ejector 9 ensures a considerably greater fuel feed into the fuel chamber 6 from the fuel tank 5 during full-load running than during idle running. This is because during full- load running both flow and pressure in the return line 8 are greater than during idle running. Moreover, a fuel surplus in the fuel chamber 6 is ensured during full-load running, while the fuel surplus in the fuel chamber 6 can be kept at a relatively low level during idle running.

In order to achieve a sufficiently good suction effect in the ejector 9, it has emerged that the flow in the return line 8 connected to the forward line 4 does not need to amount to more than 25% at the most of the flow from the fuel pump.

The dimensioning of the fuel system indicated here is suitable for an engine with the selected fuel consumption, but it is of course possible, according to

requirements, to dimension in another manner within the scope of the invention.

In comparison with a previously customary solution without return line 8 and with the ejector 9 placed in the return line 7, there is achieved according to the invention, with the same capacity of the fuel pump, a better filling of the fuel chamber 6 during full-load running and a considerably reduced fuel surplus in the fuel chamber 6 during idle running.