GB2028921A

GB2028921A - Fuel-supply Arrangement

Info

Publication number: GB2028921A
Application number: GB7929322A
Authority: GB
Original assignee: Daimler Benz AG
Current assignee: Daimler Benz AG
Priority date: 1978-08-25
Filing date: 1979-08-23
Publication date: 1980-03-12
Also published as: FR2434276A1; IT7950091A0; DE2837208A1; GB2028921B

Abstract

A feed pump 1 draws fuel from a tank 2 and is also connected to the tank 2 by a line 3 leading via an inlet chamber 4 of a filter 5 and a throttling device 6 adjoining the filter, from whose outlet chamber 7 the fuel is fed to an injection pump 8 which is also connected through an overflow valve 9 to the line 3. A non-return valve 22 may be provided in the line 3 downstream of the throttling device 6. The feed pump 1 may include a hand- operated pump, the dead spaces of which and passages to which contain filling means. In a piston-type feed pump for use in an aforesaid arrangement the inlet connection, delivery valve, suction valve and piston of the said pump and a cam-actuated tappet may be arranged coaxially while the output connection extends at right angles. <IMAGE>

Description

SPECIFICATION Fuel-supply Arrangement The invention relates to a fuel supply arrangement, particularly but not exclusively for an internal combustion engine of a motor vehicle, of the kind comprising a feed pump which draws the fuel from a tank and is also connected to the tank by a bypass by way of an inlet chamber of a filter and a throttling device adjoining the filter, from whose outlet chamber the fuel is fed to an injection pump which is also connected to the bypass through an overflow valve Such arrangements have heretofore been provided with a hand-operated pump connected to the feed pump. It is necessary for reliable starting of a diesel engine, for instance, that fuel injection should commence immediately and with fuel free of air bubbles.After repairs or after the fuel tank has been run dry, however, air accumulates in the injection pump and pipes adjoining it, obstructing immediate fuel injection.

It is therefore necessary for air which may be present in suction pipes, in the filter, in the injection pump suction chamber and in the feed pump to be removed from these spaces as quickly as possible. With feed pumps currently in use in conjunction with injection pumps, the suction with which the air can be removed from the pipes and spaces is inadequate. Consequently too low a delivery rate is obtained to bleed the injection system in an acceptable time solely by actuation of the starter, if it is possible by this means at all.

Consequently, a hand feed pump, with which the entire system was supposed to be bled, has hitherto been provided in addition on ail mechanically actuated piston feed pumps.

However, these hand pumps created several additional, excessively large cavities, so that additional dead volume resulted which was too large for a desirable suction and delivery stroke.

The present invention seeks to reduce the excessively large dead space created by the use of a hand pump and to make the feed pump of smaller and simpler construction altogether, so that delivery will commence immediately when the starter is actuated and rapid bleeding of the system is ensured. This reduction of the dead space may be carried so far that actuation of the hand pump may possibly be no longer necessary at all.

According to the invention, in a fuel-supply arrangement of the aforesaid kind, a non-return valve is provided in the bypass downstream of the throttling device and all the passages leading to a hand pump arranged on the feed pump and spaces pertaining to the hand pump are made smaller than hitherto by filling means, for example by the use of filling pieces. The use of filling pieces is particularly convenient when existing feed pumps already in use are to be converted for the purposes of the invention, so that actuation of the hand pump for bleeding purposes may no longer be necessary. With this embodiment of the invention, an additional non-return valve is essential because air which had entered when, say, the fuel tank ran empty could not immediately escape through the filter.When the feed pump was set in operation, the fuel pumped by it would be returned through the throttling device to the tank, because air compressed in the filter and in the injection pump would offer higher resistance than the bypass. With the non-return valve, on the other hand, not so much fuel will be able to flow away through the throttling device and the rest of the quantity of fuel delivered will be sufficient to displace the air from the filter and injection pump and to convey it by way of the overflow valve and the tank to the atmosphere.

The non-return valve may be a spring-loaded valve or a float valve.

In accordance with a further development of the invention, the hand pump may be completely eliminated or all the passages leading to it and spaces in it may be completely filled with filling pieces. Alternatively, filling may be made integral, from the outset, with remaining associated parts of the feed pump.

In the case of a filter whose outlet chamber comprises a cup-shaped upwardly open cylinder into the base of which a pipe leading to the injection pump opens, the bypass connected to the outlet chamber of the filter may have no nonreturn valve.

If, in view of the above considerations, a fuelsupply arrangement is made from the outset without a hand pump on the feed pump, the latter pump may be so constructed that the inlet connection, the delivery and suction valves and the piston of the pump and a tappet reciprocated by a cam through a roller may be arranged coaxially with the longitudinal axis of the pump, while the outlet connection is disposed at right angles to that axis.

Embodiments of the invention by way of example will now be more fully described with reference to the accompanying drawings in which: Fig. 1 is a diagrammatic illustration of a fuelsupply arrangement comprising a feed pump, filter, injection pump and fuel tank with associated pipes, Figs. 2 and 3 are diagrammatic views of a known feed pump with a hand pump, Figs. 4 to 6 are sectional views of parts of known feed pumps with inserted filling pieces to reduce dead spaces, Fig. 7 is a view, similar to Fig. 1, of an arrangement comprising a filter, whose outlet chamber comprises a cup-shaped upwardly open cylinder, and Fig. 8 is a longitudinal section through a fuel feed pump in accordance with the invention with no hand pump.

Fig. 1 illustrates a fuel supply arrangement, for the engine of a mdtor vehicle, comprising a feed pump 1 which draws liquid fuel through a suction connection from a tank 2 and delivers it into the inlet chamber 4 of a fuel filter 3. There is also a connection to the tank 2 through a bypass pipe 3 from the inlet chamber 4 and a throttling device 6 adjoining the latter. From the outlet chamber 7 of the filter 5, fuel is fed through a pipe 10 to a fuelinjection pump 8 which is connected to the cylinders of the engine and is also connected to the by-pass pipe 3 through an overflow or relief valve 9 ion a pipe 11.

Figs. 2 and 3 illustrate sections through a feed pump 1 of known construction, Fig. 2 showing the pump in a position between strokes of its piston 12 and Fig. 3 in a position during a delivery and suction stroke thereof. The piston 12, of inverted cup shape, was driven by a cam 1 3 acting against a spring 14 extending into the piston. The pump 1 was provided with a handoperated feed pump 1 5 intended for pumping air out of the system when necessary for instance after the tank has been run dry or after repairs. It may be seen from Figs. 2 and 3 to what a large extent dead spaces are present by reason of the hand pump 1 5, the cup shape of the piston 12, into which the spring 14 extends, and the large cross-sections of the valve space.These large dead spaces in known feed pumps aiready installed can be obviated by inserting filling or packing pieces in the manner illustrated in Figs. 4 to 6. In Fig. 4, filling pieces 1 6 and 1 7 are inserted in the suction-valve and delivery valve ports. Fig.

5 shows how dead space in the piston 12 can be reduced by a filling piece 1 8. The piston 12 is shown in its one extreme position in one half of the figure and in its other extreme position in the other half thereof. Fig. 6 illustrates how dead spaces can be totally eliminated by the use of fillings 19 and 21 after the hand pump 1 5 has been removed or rendered inoperative.

However, elimination of dead spaces is not alone sufficient if the hand pump 1 5 of the feed pump 1 is omitted or rendered inoperative, because air which has penetrated into the system, after the tank has been run dry or after repairs, cannot immediately be pumped out again when the feed pump, even if modified or manufactured to have little dead space, is set into operation. It is further necessary to introduce a non-return valve 22 into the bypass pipe 3 downstream of the throttling device 6 because, without this, the fuel delivered by the feed pump 1 would flow away through the device 6 into the tank 2 and air would still remain in the filter 5 and in the injection pump 8.With the non-return valve 22, which opens at an overpressure of only 0.3 bar, the air can be forced out of the filter 5, the injection pump 8 and associated pipes simply by starting up the feed pump 1.

Fig. 7 illustrates another system in which a cup-shaped cylinder 23 is provided in the filter 5.

In this case, part of the air which has penetrated into the injection pump can escape through the pipe 30 and upwardly out of the filter and be pumped immediately through the bypass pipe 3 into the tank 2 when the feed pump 1 is started up. From the tank. it can escape into the atmosphere. Consequently, in this case no nonreturn valve 22 is necessary. The arrow above the pipe 30 indicates the direction of the fuel flow and the lower arrow that of air flow.

Fig. 8 illustrates how a feed pump may be constructed which has been designed from the outset without a hand pump and with very small dead space. The inlet connection 25, suction valve 26, delivery valve 27, piston 38 and a tappet 32 reciprocated by a cam 29 through a roller 31 are arranged coaxially with the longitudinal axis 24 of the pump. The outlet connection 33 on the other hand is perpendicular to the said axis 24.

Claims

1. A fuel-supply arrangement comprising a feed pump which draws fuel from a tank and is also connected to the tank by a bypass through an inlet chamber of a filter and throttling device adjoining the filter, from whose outlet chamber the fuel is fed to an injection pump which is also connected to the bypass through an overflow valve, a non-return valve being provided in the bypass downstream of the throttling device and a hand pump disposed on the feed pump, all of the passages leading to and spaces belonging to the hand pump being made smaller in comparison with earlier constructions, by filling means.

2. An arrangement according to Claim 1, but without a hand pump or with a hand pump in which all of the passages leading to and spaces belonging to the hand pump are completely filled with filling means.

3. An arrangement according to Claim 1 or 2, wherein the outlet chamber of the filter is a cupshaped upwardly open cylinder whose base is penetrated by the passage leading to the injection pump and the bypass is connected to the said outlet chamber without a non-return valve.

4. A piston-type feed pump for use in an arrangement according to Claim 2 or 3, wherein the inlet connection, delivery valve, suction valve and the piston of the feed pump and a tappet reciprocated by a cam through a roller are arranged coaxially with the longitudinal axis of the pump, while the outlet connection is at right angles to that axis.

5. A fuel supply arrangement substantially as hereinbefore described with reference to the accompanying drawings.