GB2248087A

GB2248087A - Engine fuelling system including a fuel vaporiser

Info

Publication number: GB2248087A
Application number: GB9019304A
Authority: GB
Inventors: Thomas Tsoi-Hei Ma
Original assignee: Ford Motor Co
Current assignee: Ford Motor Co
Priority date: 1990-09-04
Filing date: 1990-09-04
Publication date: 1992-03-25
Anticipated expiration: 2010-09-04
Also published as: GB9019304D0; GB2248087B

Abstract

A fuel injector 34 for each engine cylinder injects fuel directly into the combustion chamber or into an intake port 18 of the cylinder and a central fuel injection and vaporising unit 40 supplies metered quantities of vaporised fuel to a plenum chamber 14 of the intake manifold 10 common to all the cylinders. An electronic control unit 30 controls the injectors and the injection and vaporising unit in dependence upon sensed engine operating parameters. The unit 40 operates alone at idling with gradual transition to operation of the injectors 34 alone at high load. The system may be used with intake valve control of the charge intake. <IMAGE>

Description

Title ENGINE FUELLING SYSTEM Field of the invention The present invention relates to a fuelling system for an internal combustion spark ignited engine.

Description of the known prior art The classical system for fuelling a spark ignited engine is the use of a single carburettor. The intake air for all the cylinders is passed over a metering jet and atomises a quantity of fuel related to the mass air flow. Apart from inaccurate fuel metering, inadequate fuel preparation and uneven mixture distribution, a carburettor suffers from the serious problem of wetting of the intake manifold.

This wetting creates a pool of fuel which is a cause of such problems as hesitation during acceleration and over rich mixtures during overrun. Of course, the principle of operation of a carburettor and its disadvantages are all well known and they need not therefore be analysed further in the present context.

Various improvements have been proposed to carburettors to overcome some of the problems outline above. Acceleration pumps have been used to avoid the hesitation caused by the wet manifold. Deceleration valves have been used to introduce limited amounts of air during overrun to weaken the over rich mixture in order to ensure proper combustion. Heated manifolds and vaporisers have been suggested to reduce wall wetting and improve mixture preparation.

The use of vaporisers in the intake manifold to reduce wall wetting has certain attendant problems. To vaporise the fuel a heater is used which also heats the intake air and reduces its density. Furthermore, the air mass is reduced still further by the volume occupied by the fuel vapour. As a result of this, maximum performance of the engine under full load is limited. Transient response is also poor in such fuelling systems because of the time required to vaporise the fuel and the hysteresis effect of the volume of mixture in the intake manifold.

An inexpensive improvement over the carburettor has been the centre point fuel injection system in which fuel is metered centrally instead of being aspirated but a manifold is still used to distribute air/fuel mixture to the individual cylinders. This improves the accuracy of control of the metered fuel quantity, but does nothing to reduce the problems caused by wall wetting.

The current state of the art in fuelling systems is multipoint fuel injection systems. Such systems are known of varying degrees of sophistication ranging from untimed injection into each intake port to timed injection under high pressure directly into the combustion chamber. All multi-point fuel injection systems enjoy the benefit good transient response, that is because they have an unheated dry manifold which permits the air/fuel ratio to be controlled rapidly and accurately in response to changes in operating conditions. Even with port injection, the hysteresis effect of a wet manifold is significantly reduced.

The disadvantage of multi-point fuel injection systems lies in the poor mixture preparation. A concentrated spray of fuel is injected over a very short time period and, despite attempts at atomising the spray, reliance is placed on the charge being mixed by turbulence within the combustion chamber. At full load, there is a long pulse and the effect is not too serious but under idle and light load conditions, there is only a short burst of fuel, which is not accurately controlled because the injector is near the limit of its mio\mrm n opening time, and the air turbulence is at a minimum and insufficient to mix the fuel uniformly. The resulting inhomogeneous charge can cause instability in combustion.

Many of the fuelling problems associated with multi-point fuel injection are now being aggravated by concepts which are being proposed and researched for improving engine efficiency under idle and part load conditions. These proposals have included changing valve timing, event duration and valve lift in order to control the intake charge without incurring pumping losses, but a consequence of such changes is reduced manifold vacuum and reduced mixing of the charge within the manifold.

It will be seen from the above that all known fuelling systems have their strengths and weaknesses and that air/fuel ratio control accuracy and mixture preparation have presented conflicting requirements which have yet to be overcome satisfactorily even for conventional engines.

For these reason, no known system optimises performance under all operating conditions more especially so in engines using variable valve timing and valve lift.

Object of the invention The invention seeks to provide a fuelling system suitable for an engine having variable valve timing load control, which system offers the advantages of improved mixture preparation under idle and part load operation, rapid transient response and good performance under full load conditions.

Summarv of the invention According to the present invention, there is provided a fuelling system for a multi-cylinder spark ignited internal combustion engine, comprising an air intake manifold, a fuel i.nXc-,er for each engine cylinder to inject fuel directly into the combustion chamber or into an intake port of the cylinder, a central fuel injection and vaporising unit for supplying metered quantities of vaporised fuel to a plenum chamber of the intake manifold common to all the cylinders, and an electronic control unit for controlling the injectors and the injection and vaporising unit in dependence upon sensed engine operating parameters.

The invention thus provides a multi-point fuel injection system with the addition of a centre-point vaporised fuel injection capability, the multi-point system, depending on operating conditions being used instead of, or to supplement, the centre-point fuelling system.

Preferably, the electronic control unit is such that the engine is fuelled by centre-point vaporised injection alone during idle and part load operation and is fuelled by multi-point injection alone under high load operation.

Under part load and idle conditions, a vaporised centre point injection system will provide good mixture preparation and distribution and suffers only from a sluggish response to transients. This can however be overcome by supplementing the centre-point vaporised fuel by multi-point injection.

Under full load, the multi-point fuelling alone gives the desired advantage of maximising the charge density and the vaporised fuel supply need play no part in the fuelling.

Because it allows centre-point vaporised fuelling during idle and part load, the fuelling of the invention is particularly suitable for an engine using variable valve timing to control the intake charge. Under these conditions, the problems of poor fuel preparation associated with multi-point fuelling are circumvented.

Nevertheless, the performance of the engine under full load will not be impaired by low charge density.

It is advantageous, for the change-over Ctorcl the centrepoint fuelling mode to the multi-point fuelling mode to be progressive, fuel being provided by all injectors over part of the operating range.

Brief description of the drawing The invention will now be described further, by way of example, with reference to the accompanying drawing which is a block diagram of a fuelling system in accordance with the invention.

Detailed descrintion of the preferred embodiment The single figure shows an air intake manifold 10 having an intake duct 12 leading to a plenum chamber 14 and runners 16 leading from the plenum chamber 14 to individual intake ports 18 of the engine cylinders. A butterfly valve 20 is arranged in the intake duct 12 to control the air intake quantity but in an engine in which the intake charge is controlled by valve timing, this valve 20 may not be present.

The fuelling system comprises an electronic control unit (ECU) 30 with output lines 32 (only one is shown) leading to injectors 34 arranged near the individual intake ports 18. The ECU 30 receives a signal over a line 38 from a mass air flow meter (MAF) 36 and is connected (in a manner not shown) to receive other data pertaining to engine operation such as engine speed, throttle pedal position, engine temperature, manifold vacuum and so on as in known fuel injection systems.

As so far described, the fuelling system does not differ materially from conventional multi-point fuel injection systems and more detailed description is not therefore deemed necessary.

In contrast to known multL-etint injection systems, the fuelling system in the drawing includes an injection and vaporising unit 40 supplying metered quantities of vaporised fuel to the intake duct 12 for distribution through the manifold 10 to the individual cylinders. The unit 40, as its name implies, includes an injector 42 and a vaporiser 44 which are controlled by way of respective lines 46, 48 by the ECU 30.

The ECU 30, based on the sensed operating parameters, determines the instantaneous quantity of fuel required by the engine. Depending on the load conditions, this fuel is metered to the engine either exclusively through the unit 40, or exclusively through the injectors 34, or through a combination of both.

Under idle and part load conditions, fuel is supplied predominantly through the unit 40 to achieve good mixture preparation. The injectors 34 can be used under these conditions to effect correction of the mixture strength during sharp acceleration to improve transient response.

Under full load, the injectors 34 are used to fuel the engine and because the unit 40 is inoperative only air reaches the intake ports and it is not heated by the vaporiser so that the charge density is maximised.

To avoid harshness in the change-over between injection modes, the ECU 30 progressively brings in the multi-point fuelling as the centre-point fuelling is phase out and vice-versa.

The ECU 30 may be formed by minor modification to existing fuelling computers. The ECU 30 differs from such existing computers only in as much as the fuel to be metered is apportioned between the injectors 34 and the unit 40 in dependence upon engine load and transient conditions as can be determined from the sensed parameters.

Claims

1. A fuelling system for a multi-cylinder spark ignited internal combustion engine, comprising an air intake manifold, a fuel injector for each engine cylinder to inject fuel directly into the combustion chamber or into an intake port of the cylinder, a central fuel injection and vaporising unit for supplying metered quantities of vaporised fuel to a plenum chamber of the intake manifold common to all the cylinders, and an electronic control unit for controlling the injectors and the injection and vaporising unit in dependence upon sensed engine operating parameters.

2. A fuelling system as claimed in claim 1, wherein the electronic control unit is such that the engine is fuelled by centre-point vaporised injection alone during idle and part load operation and is fuelled by multi-point injection alone under high load operation.

3. A fuelling system as claimed in claim 2, wherein during part load and idle operation, the centre-point vaporised injection is supplemented by the multi-point injection during acceleration.

4. A fuelling system as claimed in claim 2 or 3, wherein the change-over from the centre-point fuelling mode to the multi-point fuelling mode is progressive, fuel being provided by all injectors over part of the load operating range.

5. A fuelling system for a multi-cylinder spark ignited internal combustion engine constructed, arranged and adapted to operate substantially as herein described with reference to and as illustrated in the accompanying drawing.

6. A multi-cylinder spark ignited internal combustion engine in which the intake charge is controlled by varying the valve timing, the valve event duration or valve lift in combination with a fuelling system as claimed in any preceding claim.