WO1988001018A1

WO1988001018A1 - Fuel distribution system

Info

Publication number: WO1988001018A1
Application number: PCT/GB1987/000548
Authority: WO
Inventors: Thomas Tsoi-Hei Ma
Original assignee: Ford Motor Company Limited; Ford Werke A.G.; Ford France S.A.; Ford Motor Company
Priority date: 1986-08-04
Filing date: 1987-07-31
Publication date: 1988-02-11
Also published as: GB8619020D0; GB2193536A

Abstract

Fuel metering and distribution system for a spark ignited internal combustion engine. The system comprises a float chamber (10), a plurality of tubes (14) each including a respective metering jet (16) and communicating at one end with the float chamber (10) and at the other end with a chamber (18) connectable to a venturi (21) arranged in the air intake manifold of the engine. The chamber (18) has a plurality of separate compartments each arranged to receive the fuel metered through a respective one of the metering jets (16) and a plurality of fuel supply lines (26) is provided to feed the fuel from each compartment to a respective one of the engine cylinders.

Description

FUEL DISTRIBUTION SYSTEM

The present invention relates to fuel distribution system employing a dry induction manifold, the metered fuel being distributed to the intake ports of the individual cylinders without passing through the induction manifold.

A fuel distribution system employing a dry manifold is described in EP-A-0 138 425. The fuel in the latter application is metered by means of a device which employs the same principle as a carburettor but the metered fuel is directly fed to the individual cylin¬ ders. In this way, a system is provided which benefits from the advantages of a dry manifold, previously only obtained with fuel injection, but retains the low manu- facturing cost associated with a carburettor.

In the above application, the fuel metered through a single jet is introduced into a chamber from which it is sucked by individual fuel supply lines and conducted to the intake ports of the cylinders. Even though the correct amount of fuel may have been metered for all the cylinders, it is possible that one cylinder may draw more fuel from the reservoir than another cylinder. To avoid this problem, the above European application uses an emulsion tube to create a froth above the fuel level and the fuel supply lines terminate above the level of the fuel in the reservoir. This step however does not suffice to overcome the problem fully and under some conditions the fuel distri¬ bution has been found to be uneven. According to the present invention, there is provided a fuel metering and distribution system for a spark ignited internal combustion engine comprising a float chamber, means for metering fuel from the float chamber to a second chamber connectable to a venturi arranged in the air intake manifold of the engine, and a plurality of fuel supply lines for supplying fuel from the second chamber to the respective engine cylinders. wherein the second chamber comprises a plurality of separate compartments each connected to only one engine cylinder through a respective one of the fuel lines and wherein the metering means comprises a plurality of tubes each including a respective metering jet and communicating at one end with the float chamber and at the other end with a respective one of the compartments of the second chamber.

The problem of uneven fuel distribution is thus avoided in the present invention by the use of separate metering jets and separate fuel supply paths for the cylinders. The compartments of the fuel chamber are all connected to the same venturi so that the pressure differences across all the metering jets are equal. As the jets are themselves matched accurately, it is possible to ensure that precisely the same amount of fuel is distributed to all the cylinders.

It is preferred that the mouths of the fuel supply lines be arranged at the bottom of the individual compartments of the fuel chamber so that gravity may assist in feeding the fuel down the supply lines. The mouths may comprise an upstanding slotted portion to act in the manner of an emulsion tube to enable air to be drawn in with the fuel. In order to assist in feeding the fuel down the supply lines, it is also advantageous to ensure that the compart ented fuel chamber is arranged in the engine compartment above the level of the intake ports of the cylinders. It is particularly preferred that cyclone junc¬ tions be employed to connect the other ends of the fuel supply lines to the intake manifold, each cyclone junction comprising a conical cavity connectable at its narrower end to induction manifold in the vicinity of an intake port and at its wider end to a line leading to the intake manifold venturi, the fuel supply lines opening into the conical cavities of the cyclone junctions. The aerodynamic forces within the cyclone junction and the effect of gravity enable the fuel to be supplied reliably through the supply lines under all engine operating conditions.

The invention will now be described further, by way of example, with reference to the accompanying drawings, in which :

Figure 1 is a schematic representation of a fuel metering system of the invention,

Figure 2 shows details of the construction of the block drawn in chain dotted lines in Figure 1, and

Figure 3 shows a partly sectioned perspective view of a cyclone junction.

In Figure 1 , there is illustrated a system for metering and distributing fuel to the individual cylinders of an internal combustion engine. The distribution system is de^'signed such that the induction manifold does not contain fuel and remains dry, thereby permitting better control of the mixture strength under all operating conditions.

The illustrated system comprises a float chamber 10 in which a predetermined head of fuel is maintained in the manner conventionally adopted in carburettors. The fuel passes from the float chamber 10 by way of a fuel metering valve 12 into a reservoir 13 in which there are immersed four tubes 14 each fitted with a respective metering jet 16.

The metering valve 12 is an on/off valve which is operated constantly by a cyclic square waveform having a variable mark to space ratio. When the valve 12 is open, the rate of flow of fuel through each of the tubes 14 is dictated by the pressure across the metering jets 16 and the cross sectional areas of the jets 16. When the valve 12 is closed, on the other hand, there is no flow of fuel through the tubes 14. When the valve is rapidly opened and closed, therefore, the average fuel flow is determined both by the jets 14 and the mark to space ratio of the opening of the valve 12. The valve ΣZ may Ibe. a solenoid valve connected to a circuit which converts: an analogue or digital control signal

5. indicating the desired variation of the mixture strength into a square wave oscillation having a mark to space ratio determined by the control signal.

The ends of the tubes 14 remote from the jets 16 open into a chamber 18 which is connected by way of a

10 vacuum line 20 to a venturi 21 arranged in the intake manifold leading to the intake ports of the cylinders the venturi being positioned upstream of a butterfly throttle valve 23. In this way, the pressure across the jets 16 is determined by the engine air intake and this

15 in turn varies the fuel flow rate as a function of engine load and speed.

The fuel metered by the jets 16 and flowing through the tubes 14, on reaching the chamber 18, spills into the chamber 18 and is fed from there to the

20 intake manifold 22 immediately upstream from the intake ports ' by means of four fuel lines 26. To ensure that the cylinders receive correctly balanced mixtures, the lower end of the chamber 18 is divided into four compartments 24 each of the tubes 14 opening into a

25 respective one of the four compartments 24. In this way it is ensured that the cylinders receive equal quantities of fuel since all the tubes 14 and the jets 1.6 are properly matched and the individual compartments ensure that fuel metered for one cylinder cannot reach

30 any other cylinders, the fuel flow paths for the individual cylinders being totally isolated from one another.

The fuel spilling into the compartments 24 of the chamber 18 is at the same pressure as the vacuum line

35 20. Under some engine conditions, there is sufficient pressure differential across the fuel lines 26 to enable the metered fuel to flow at the required rate through the fuel lines but under other conditions this pressure differential is not sufficient and steps must be taken to assist the flow of the metered fuel through the fuel lines 26.

A first step that is taken is to place the chamber 18 higher in the engine compartment than the intake ports so that the fuel flow in the fuel lines 26 should be assisted by gravity.

In the illustrated embodiment, fuel flow through the fuel lines is further assisted by introducing the fuel from the fuel lines 26 into the manifold 22 by means of cyclone junctions 28 which are connected to one another by a first air rail 30 and to the venturi 21 by way of a further air rail 32. Air flows through the rails 30 and 32 into the manifold 22 by way of the junctions 28.

As best seen in Figure 3, each junction 28 has a conical cavity 29 connected at its larger end to the air rail 30 and at its narrower end to the manifold 22. The fuel lines 26 open tangentially into the conical cavities.

Air entering the manifold 22 through 'the cyclone junctions 28 causes a cyclone within the cavities 29 of the junctions 28 tending to create a pressure drop at the mouth of the fuel lines 26 to assist in causing the fuel flow through the fuel lines 26. The pressure at the ends of the fuel lines 26 is furthermore isolated by the cyclone junctions from the fluctuating pressures in the intake manifold 22 in the vicinity of the intake ports and is instead connected to the same venturi pressure as obtains in the chamber 18. The forces acting to force the fuel through the fuel lines 26 are therefore only gravity and the aerodynamic forces created by the effect of the cyclone in the junctions

28. These are sufficient to ensure proper flow along the fuel lines 26 under all engine operating conditions.

The parts of the metering system lying within the chain-dotted block 40 of Figure 1 are shown in more detail in Figure 2. The reservoir 13 and the chamber 18 are formed as one unit with the reservoir 13 disposed beneath the chamber 18. The reservoir has a fuel supply line 12a which leads to the metering valve 12 and which enters the reservoir 13 from below. The jets 16 are arranged at the upper end of the reservoir 13. The tubes 14 are formed as bores in a cylinder 17 which bores are traversed by cross bores 19 closed at their ends by blanking plugs 50. The cross bores in turn open into four further axial bore 52 which together constitute the compartmented fuel distribution chamber and are connected at their upper end to the venturi line 20.

The fuel supply lines 26 pass through the reservoir 13 (being sealed appropriately for example by means of 0-rings) and open into the bores 52. The ends of the fuel supply lines 26 have a thin slot 54 through which the fuel is drawn, the slot serving to ensure that air is drawn in with the fuel into the supply lines 26.

Claims

1. A fuel metering and distribution system for a spark ignited internal combustion engine comprising a float chamber (10) , means for metering fuel from the float chamber (10) to a second chamber (18) connectable to a venturi (21) arranged in the air intake manifold of the engine, and a plurality of fuel supply lines (26) for supplying fuel from the second chamber (18) to the respective engine cylinders, characterised in that the second chamber (18) comprises a plurality of separate compartments (52) each connected to only one engine cylinder through a respective one of the fuel lines (26) and in that the metering means comprises a plurality of tubes (14) each including a respective metering jet (16) and communicating at one end with the float chamber (10) and at the other end with a respective one of the compartments (52) of the second chamb'er (18) .

2. A system as claimed in claim 1, wherein the mouths of the fuel supply lines (26) are arranged at the bottom of the individual compartments (52) of the second chamber (18) so that gravity may assist in feeding the fuel down the supply lines (26) .

3. A system as claimed in claim 2, wherein the mouths each comprise an upstanding slotted portion (54) to act in the manner of an emulsion tube to enable air to be drawn in with the fuel.

4. A system as claimed in any preceding claim, wherein in order to assist in feeding the fuel down the supply lines (26) , the second chamber (18) is arranged, during use, above the level of the intake ports of the cylinders.

5. A system as claimed in any preceding claim, wherein cyclone junctions (28) serve to connect the ends of the fuel supply lines (26) to the intake manifold (22) , each cyclone junction (28) comprising a conical cavity (29) connectable at its narrower end to the induction manifold in the vicinity of an intake port and at its wider end to a line (30) leading to the intake manifold venturi (21) , the fuel supply lines (26) opening into the conical cavities (29) of the cyclone junctions (28) .

6. A system as claimed in any preceding claim, wherein the metering means comprise an electrically operable valve (12) arranged in series with all the metering jets (16) for periodically interrupting the fuel supply from the float chamber (10) to all the compartments (52) of the second chamber (18) .