GB2247917A

GB2247917A - I.c.engine fuel and air intake system

Info

Publication number: GB2247917A
Application number: GB9020158A
Authority: GB
Inventors: Thomas Tsoi-Hei Ma
Original assignee: Ford Motor Co
Current assignee: Ford Motor Co
Priority date: 1990-09-14
Filing date: 1990-09-14
Publication date: 1992-03-18
Also published as: WO1992005361A1; GB9020158D0

Abstract

An intake system for an internal combustion engine is described which comprises an intake duct (16) leading to an intake port (20) of each engine cylinder and a turbulence enhancing unit (50) for increasing turbulence within each intake duct (16). The unit (50) comprises a flow path (22) connected in parallel with each intake duct (16) and an impeller (24) arranged within the parallel flow path (22), the parallel flow path (22) forming in conjunction with a section of the intake duct (16) a closed loop in which the charge is recirculated by the action of the impeller (24).

Description

Title ENGINE INTAKE SYSTEM Field of the invention The present invention relates to an intake system for an internal combustion engine having an intake duct leading to an intake port of each engine cylinder.

Backaround of the invention The importance of mixture preparation to combustion quality is well known and it is desirable to achieve under all conditions a charge with high turbulence in which the fuel is as evenly mixed as possible.

A carburetted engine achieves good fuel preparation but has the well known disadvantage of creating a wet manifold and for this reason, fuel injection is generally to be preferred. With multi-point fuel injection, the fuel quantity can be controlled more accurately under all conditions but the mixture preparation is inadequate.

Even with a well constructed fuel injector, a spray is produced which tends to form a pool of fuel next to the intake valve and this tends to lead to a stratified charge in the combustion chamber.

While the problem of mixture preparation is present in a conventional fuel injection engine, it is not very severe and can generally be tolerated. However, in engines proposed more recently which vary the valve operation and rely on a change in valve timing, event duration or valve lift, to control engine output, the problems of mixture preparation become even more acute because the manifold vacuum and the air flow velocities in the manifold are reduced.

Object of the invention The invention therefore seeks to provide an intake system which improves mixture preparation and is suited for use in an engine with variable valve operation.

Summarv of the invention According to the present invention, there is provided an intake system for an internal combustion engine, comprising an intake duct leading to an intake port of each engine cylinder and means for increasing turbulence within each intake duct, the latter means comprising a flow path connected in parallel with each intake duct and an impeller arranged within the parallel flow path, the parallel flow path forming in conjunction with a section of the intake duct a closed loop in which the charge is recirculated by the action of the impeller.

The invention relies on air circulation which is not derived from manifold vacuum nor naturally occurring air flow in the intake manifold to ensure turbulence in the intake air stream. The energy required to generate the turbulence is instead derived from an external power source driving the impeller. The latter is conveniently powered by an electric motor, but it could conceivably be engine driven.

The invention does not rely on pressure across the intake throttle and does not in any way affect the metering of the air or the fuel. It ensures only that such air as is drawn into the intake manifold is properly agitated, regardless of the air flow conditions within the manifold.

To avoid an accumulation of fuel vapour in the parallel flow path and reduce response time, it is desirable to maintain a small volume in the parallel path and to pump it at a high rate by means of the impeller.

Preferred features of the invention It is often desirable to be able to heat the intake air and with this aim in mind, the parallel flow path should preferably include means for heating the recirculated intake charge.

If fuel is present in the recirculated charge then the heating of the charge will vaporise the fuel and thereby provide an excellent mixing of the fuel and air. Such heating may be carried out either by means of a heat exchanger or an electric heater in the parallel flow path.

Heating of the air is highly desirable at low and part loads because it reduces charge density and therefore reduces pumping losses since less air throttling is required at a given load. However, at full load, such heating reduces maximum performance by reducing the mass of the intake charge and it is preferred therefore to prevent heating of the intake air under high load. If an electric heater is used, this can be achieved by cutting off the electrical supply to the heater but because of thermal inertia, such an approach will not allow rapid response to changes in engine load.

It is preferred instead to provide means for reducing or preventing the charge recirculation in the parallel flow path. This may conveniently be achieved either by including a throttle in the parallel flow path or by regulating the operation of the impeller.

Various geometries are possible for the parallel flow path in that one may be provided unique to each intake tract of the manifold or a single flow path may be connected in parallel to all the intake tracts. The latter is easier to construct and ensures that a more even mixture strength reaches all the cylinders.

Because of the high flow rate of air in the parallel flow path, the high pressure side of the flow path introduces a high velocity hot air stream into the duct which is ideal for vaporising any pool of fuel in the duct.

It is preferred for this reason in a multi-point fuel injected engine to arrange the connections between the parallel flow path and the intake duct one on each side of the fuel spray or fuel jet from the fuel injector so that any accumulation of fuel in the intake duct is scrubbed by the recirculating air stream.

If desired, a fuel injector may be arranged within the parallel flow path to spray fuel directly onto its heat exchanger or electric heater.

Various possibilities also present themselves for positioning the high pressure connection between the parallel flow path and the intake duct to improve mixture preparation. For example, the air stream can be directed tangentially so as to set up a swirl or it may be aimed into the combustion chamber when the intake valve is open to assist the in-cylinder mixing.

In an engine having exhaust gas recirculation, a problem is presented by the need to mix the exhaust gases very thoroughly in the intake charge. The invention can assist in mitigating this problem if the exhaust gases are introduced into the parallel flow path or any part of the loop in which gases are circulated by the action of the impeller.

Brief description of the drawings The invention will now be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic diagram of an intake system in accordance with a first embodiment of the invention, and Figure 2 is a schematic diagram of an intake system in accordance with a second embodiment of the invention.

Detailed description of the preferred embodiments In Figure 1, an intake system is shown schematically which comprises an air filter 10, an intake throttle 12 and a plenum chamber 14 all of which are common to the engine cylinders. A duct 16 connects each individual intake port 20 to the plenum chamber 14 and has mounted within it a fuel injector 18 which directs its spray or jet towards the inlet valve located in the intake port 20. As so far described, this intake system is entirely conventional and the same components will also be found in the embodiment of Figure 2 which is described below.

Even in a conventional engine, fuel preparation is not particularly good when a fuel injection system is used and problems are noticeable at idle, during cold start and during engine transients when the load on the engine is changing and the fueling requirements need to be varied rapidly. More severe difficulties are encountered in an engine having variable valve operation. Here, the control of the valves can be used in a variety of ways depending on the control strategy and some of these strategies, which need not be discussed within the context of the present application have an adverse effect on the mixture preparation because they reduce the charge velocity and manifold vacuum. Indeed, with some control strategies, the throttle 12 can be dispensed with, and while this is very desirable from the point of view of reducing air pumping losses, it is highly undesirable from the mixture preparation viewpoint.

To overcome these problems and achieve good mixture preparation under all conditions, even when valve timing is variable, the invention proposes the addition of a turbulence enhancement unit which is generally designated 50 in the drawings.

The unit 50 includes a parallel flow path 22 connected to the ducts 16 on each side of the fuel injectors 18 by pipes 32 and 34. This flow path 22 includes a throttle 30, a heat exchanger 28 through which exhaust gases or engine coolant flows and an impeller or fan 24 driven by an electric motor 26.

When the impeller 24 is in operation, gas recirculation takes place and air is drawn in through the pipe 34, heated by the heat exchanger 28 and blown out at high velocity through the pipe 32 onto any pool of fuel tending to collect in the intake port 20 near the base of the intake valve (not shown. This recirculation not only created turbulence in the charge of air but vaporises the fuel by scrubbing the walls on which the fuel tends to collect.

The heating of the air and fuel vaporisation are needed at low and part load but tend to reduce maximum performance at full load, because of the reduced charge density.

Because mixture preparation at full load is in any event not in need of enhancement (the high air flow rate is adequate to ensure good mixing), it is desirable to shut off the parallel flow path 22 at high load and this is achieved by the throttle 30. The latter may be electronically controlled if no vacuum is available, but if some vacuum still remains then this may be used to operate the throttle 30 mechanically, for example by means of a bellows unit. Vacuum is relied upon to open the throttle 30 at part load and under high load the throttle is allowed to close by a return spring acting on the bellows.

Inasmuch as the air flow rate created by the impeller is not related to the volume of the air intake charge drawn by the engine, one can create as high an air flow rate as required by suitable design of the impeller. The higher the air speed, the more the air turbulence and the faster the response of the fueling system to changes in engine load.

One could provide a unit 50 for each intake duct 16 but this increases expense. In the embodiment of Figure 1, the unit 50 is common to all the cylinders in that a single unit 50 is connected across two air rails 36, 38 and these are in turn connected to each of the individual tracts 16 by a respective pair of pipes 32, 34.

The embodiment of Figure 2 differs from that of Figure 1 in the position along the intake ducts of the inlet pipe 34' of the parallel flow path 22' (to avoid unnecessary repetition, the same numerals have been used to designate components serving the same function as described by reference to Figure 1 but a prime has been added to the numerals). Instead of the parallel path 22' drawing in air immediately upstream of each fuel injector 18, it does so from a point downstream of the intake throttle 12 common to all the ducts. This simplifies the design by eliminating the need for the rail 38 and the four pipes 34.

Figure 2 also shows that a unit 50 can be used to enhance mixture preparation in a fueling system using centre-point fuel injection or a hybrid system with both centre-point and multi-point injection. The injector 40 sprays fuel onto the intake duct upstream of the throttle 12 but a groove 42 in the wall of the duct ensures that the wetting is confined to the region of the duct between fuel injector 40 and the groove 42. This region falls within the recirculation path of the unit 50, which is generally similar to that shown in Figure 1, and this ensures that the fuel is vaporised before reaching the intake ducts 16.

In a further alternative embodiment of the invention, it is possible to include a fuel injector within the turbulence enhancement unit 50 itself, the spray or jet of the injector being preferably directed in this case onto the heater or heat exchanger so as to be vaporised.

Because the fuel is now vaporised directly, it suffices to produce a jet rather than a fine mist from the injector and indeed it is desirable not to produce a fine mist to avoid the fuel from being carried away by the air stream before it is vaporised. Such an embodiment thus offers the advantage of simplifying and reducing the cost of the fuel injector.

As earlier mentioned, it is desirable during high load operation not to heat the air flow in order not to reduce the charge density. Because of the thermal inertia, removing the heat supply to the parallel flow path sufficiently rapidly and it is for this reason that the throttle 30 has been provided to shut off the parallel flow path 22. This however also means that there is no turbulence enhancement under these conditions. If turbulence enhancement is required without heating of the intake charge this may be achieved by providing a passage which by-passes only the heated section of the parallel flow path, access to this by-pass passage being controlled by a change-over valve replacing the throttle 30. In this case flow always takes place through the turbulence enhancement unit but is directed through a heated or an unheated section depending upon engine load.

Claims

1. An intake system for an internal combustion engine, comprising an intake duct leading to an intake port of each engine cylinder and means for increasing turbulence within each intake duct, the latter means comprising a flow path connected in parallel with each intake duct and an impeller arranged within the parallel flow path, the parallel flow path forming in conjunction with a section of the intake duct a closed loop in which the charge is recirculated by the action of the impeller.

2. An intake system as claimed in claim 1, in which the parallel flow path includes means for heating the charge.

3. An intake system as claimed in claim 2, in which the heating means is a heat exchanger deriving heat from the engine exhaust gases or the engine coolant circuit.

4. An intake system as claimed in claim 2, in which the heating means is an electric heating element.

5. An intake system as claimed in any preceding claim, further comprising means for reducing or preventing the charge recirculation.

6. An intake system as claimed in claim 5, wherein a throttle is included in the parallel flow path to enable recirculation to be reduced or prevented.

7. An intake system as claimed in claim 5, wherein means are provided to control the operation of the impeller so as to enable recirculation to be reduced or prevented.

8. An intake system as claimed in any of claims 2 to 4, comprising a passage for by-passing the heating means and a valve for diverting the recirculating charge flow around the heating means during high load operation.

9. An intake system as claimed in any preceding claim for use in an engine having a plurality of cylinders, wherein a respective parallel flow path is provided for each individual duct leading to a cylinder of the engine, the parallel flow paths of the different cylinders being separate from one another.

10. An intake system as claimed in any of claims 1 to 8, for use in an engine having a plurality of cylinders, wherein a single parallel flow path is provided common to all the ducts leading to cylinders of the engine.

11. An intake system as claimed in claim 10, in which the parallel flow path is separately connected by a first rail at one end to each intake duct at a point near the cylinder intake port and is separately connected by a second rail at its other end to a point in each intake duct upstream from the intake port.

12. An intake system as claimed in claim 10, in which the parallel flow path is separately connected by a first rail at one end to each intake duct at a point near the cylinder intake port and is connected at its other end to a point in the intake manifold common to all the engine cylinders.

13. An intake system as claimed in any preceding claim, wherein a fuel injector is provided to inject fuel into each duct leading to an engine cylinder and in which the connections between the parallel flow path and the intake duct are arranged one on each side of the fuel spray or fuel jet from the fuel injector.

14. An intake system as claimed in any of claims 1 to 12, wherein a fuel injector is arranged within the parallel flow path.

15. An intake system as claimed in any preceding claim, wherein means are provided for introducing exhaust gases to be mixed with the intake charge into the parallel flow path or the part of the intake duct through which gases are circulated by the action of the impeller.

16. An intake system for an internal combustion engine constructed, arranged and adapted to operate substantially as herein described with reference to and as illustrated in accompanying drawings.

17. An internal combustion engine in which the operation of the valves is controlled to vary valve timing, valve event duration or valve lift and having an intake system as claimed in any preceding claim.