GB2219344A

GB2219344A - I.C. engine charge supply system

Info

Publication number: GB2219344A
Application number: GB8813238A
Authority: GB
Inventors: Timothy James Bowman
Original assignee: Ford Motor Co
Current assignee: Ford Motor Co
Priority date: 1988-06-04
Filing date: 1988-06-04
Publication date: 1989-12-06
Also published as: GB8813238D0

Abstract

One of the two manifolds 16 and 18 supplying charge to respective valve ports 12a, 12b or a single valved inlet port of each cylinder is fed with fuel by a carburettor 24. A diaphragm-operated metering needle or a pulsed solenoid valve controls fuel flow in the carburettor 24 in response to air flow in both manifolds controlled by respective throttle valves 20 and 22. The air flow in the manifold 18 is indicated by the vacuum or an air flow sensor 32 and regulates the carburettor 24. <IMAGE>

Description

ENGINE FUELLING The present invention is cor-erned with the fuelling of spark ignited internal combustion engines having more than one inlet port associated with each cylinder.

According to the present invention, a fuelling syste: for an internal conbustion engine having two inlet ports per cylinder comprises two manifolds each having a respective throttle any a plurality branches leading to respective ports of the different cylinders, and a carburettor for metering into only one manifold a quantity of fuel determined by the air flow rate in both manifolds.

Engines having two inlet valves per cylinder and engines having twin tract porting, i.e. two ports ,eadin3 to each inlet valve, have previously been proposed. Eath fuel injection and carburettors have bee sugceed for metering fuel to such enines.

Because of the sophistication cf engines with multiple inlet ports, economy is not a prime cons deration in selection of a fuellinc system and mGre comnonly injection systems have been adopted. For economy, a single injection nozzle pe::- cylinder cc':.ld be derived to suffice but it has been ::c-jn preferable for fuel to be injected into both ports.

The present invention, hovever, is predicated on the discovery that, in carburetted engines, improved cor.bustion occurs if only one port is fuelled and only air is drawn in through the other port.

The reason for this apparent anoraly is believed to be that o:hen fuel is injected, it tends to be poorly dispersed and separate injection into both ports will tend to improve combustion. In a carburetted engine, on the other hand, air atomisation is not a problem and by introducing air through only one port, the charge is stratifie= permitting a richer mixture to be achieved near the spark plug than in other parts of the combustion charber. Thus, contrary to the teaching to be gleaned from injection systems, the more convenient option of fuelling only one set of ports is the more efficient in operation.

The option of only fuelling one manifold is the more convenient not only because a single carburettor will suffice, but because all the expected problems associated with one of the wet manifolds are avoided.

Thus there is no need for an acceleration pump for the manifold nor is there any fuel wastage caused by the drying of the manifold under low load conditions.

Since only one wet manifold is ne~essary, it may be assumed that a single conventional carburettor associated with the wet manifold may be celibrated to run rich to allow for the air passing through the dry manifold. This however would lead to significa.-.t inaccuracy in detering, especially under low load conditions. When the air flow rate through the carburettor is small, only a small error in the assumed air flow rate in the dry manifold will cause significant errors in the mixture strength.

To avoid this problem, the invention proposes the monitoring of the air flow rate in both manifolds but to set the fuel flow rate accordingly, the fuel being fed to only one of the manifolds. In any conventional carburettor, the fuel flow rate is varied as a function of the air flow rate through the venturi of the carburettor. However, other influences can be brought to bear on the flow rate in a variety of ways and in the invention one further parameter used in determining the fuel flow rate is the air flow rate in the dry manifold.

Many possibilities present themselves for modifying the fuel metering in the carburettor in dependence upon the air flow in the dry manifold.

In a mechanical approach to the problem, the metering jet may be associated with G tapering needle, the body of the jet being moved by a mechanical, pneumatic or hydraulic linkage sensitive to the air flow rate in the dry manifold.

As an alternative, one may adopt an electrical approach of modifying the fuelling in dependerce upon the flow rate in the dry manifold. FOr example, the flow rate may be sensed and used to vary the pressure in the fuel line leading to the metering jet or an on/off solenoid valve in series with the entering jet may be pulsed with a varying mark to space ratio to vary the proportion cf time that fuel is allowed to flow through the metering jet.

The invention will now be described further, b) way of example, with reference to the accompanying drawing which is a scher tic representation of a fuelling system of the invent on.

The engine shown in the drawing has four cylinders 10 eah with two inlet valves 12a and 12b end two exha ,t valves 14a and 14b. The ports cf the valves 12a of the different cylinders are connected to a first manifold 16 while the ports 12b are conr.-=cted to a second manifold 18. The two manifolds have ganged butterfly throttle valves 20 and 22 and are connected to a common air filter 26.

A carburettor 24 is arrans upstream of the butterfly valve 20 to supply fuel through the manifold 16 only to the ports 12a of the cylinders. Thus the manifold 16 is a wet manifold but the manifold 18 is dry.

The carburettor 24 is not conventional as it is not sufficiently accurate to monitor the air flow in only one of the two manifolds, especially under part throttle operation. In addition to the fuel line 28 leading to the float chamber of the carburettor 24, a control line 30 is shown in the drawing to represent a control input to the carburettor 24 from a sensor 32 associated with the dry manifold.

In one embodiment of the invention, the control line 32 is a vacuum line which acts on a diaphragm associated with the main jet of the carburettor 4 to vary the mixture strength in the wet manifold in dependence upon the vacuum in the dry me-. fold.

In an alternative embodiment, the sensor 32 is an electrical pressure or air flow sensor and supplies an electrical sianal to the carburettor. This signal may for example be used to control the opening and closing of a fuel valve in the carburettor to vary the proportion of the time in any operating cycle that the fuel valve remains open.

It will be appreciated that many further designs are possible for controlling the mixture strength in the wet manifold to take into account the air flowing through both the dry manifold 18 and the wet manifold 16.

Though described by reference to an engine with four valves per cylinders, the invention is eaually applicable to engines having dual tract porting, that is to say engines where each cylinder has only one intake valve but two intake ports leading to that valve.

Claims

1. A fuelling system for an iT. ternal combustion engine having two inlet ports per cylinder comprises two manifolds each having a reflective throttle and a plurality branches leading to res.zec-ive ports of the different cylinders, and a carburettor for metering into only one manifold a quantity of fuel determined by the air flow rate in both manifolds.

2. A fuelling system as claimed in claim 1, wherein the carburettor has a mete-ing jet associated with a tapering needle, the body of the jet being movable by a mechanical, pneumatic or hydraulic linkage sensitive to the air flow rate in the dry manifold.

3. A fuelling system as claimed in claim 1, wherein the flow rate is sensed in the dry ranifold and the pressure in the fuel line leading to the retering jet is varied in accordance with the flow rate of air in the dry manifold.

4. A fuelling system as claimed in claim 1, wherein the flow rate is sensed in the dry manifold and an on/off solenoid valve in series witn the metering jet Is pulsed with a varying mark to space ratio to vary the proportion of tine that fuel 5 allowed to flow through the metering jet.

5. A fuelling system constructed, arranged and adapted to operate substantially as herein described with reference to and as illustrated in the accompanying drawings.