GB2202901A

GB2202901A - I.C. engine cylinder charge intake arrangement

Info

Publication number: GB2202901A
Application number: GB08707472A
Authority: GB
Inventors: Derek Frost
Original assignee: Ford Motor Co
Current assignee: Ford Motor Co
Priority date: 1987-03-28
Filing date: 1987-03-28
Publication date: 1988-10-05
Also published as: GB8707472D0

Abstract

The intake valve 12 is provided with two intake passages 22, 24 so as to promote toroidal flow in the combustion chamber. To improve lean burn capability, the port geometry is variable by means, e.g. vanes 30, 32, associated with the passages and disposed in close proximity to the intake valve, the through flow cross section of the individual passages being varied to increase the charge velocity at low air flow masses. The valve guide 18 may be moved axially or angularly to regulate the deflection of the vanes 30, 32. <IMAGE>

Description

INTERNAL COMBUSTION ENGINE The present invention relates to internal combustion engines and is particularly concerned with improving the induction of air into the combustion chamber.

According to the present invention, there is provided an internal combustion engine having separate intake and exhaust valves, wherein an intake valve is provided with two diametrically opposed ports whereby to promote toroidal flow in the combustion chamber, and means associated with the ports and disposed in close proximity to the intake valve for varying the through flow cross section of the individual ports whereby to increase the charge velocity at low air flow masses.

The toroidal flow mentioned above results from gases curling off the edge of the inlet valve and breaking away from the valve when it reaches a certain size.

After breaking away, the toroid moves into the cylinder.

The gas flow resembles that of smoke rings blown by cigarette smokers in which the rotation of the gases is such that particles in the gas stream thread in and out of the ring defined by the toroid. By the nature of this flow, gases can remain localised in one region and this can be used to advantage to obtain a stratified charge.

Thus, in a preferred embodiment of the invention, the fuel is injected into one of the ports, the point of injection being selected such that the richness of the mixture will not be uniform in the combustion chamber but will be greater in the vicinity of the spark plug after compression. In this way, it is possible to achieve easier ignition of mixtures which overall are lean but which in the vicinity of the spark are rich enough to ignite readily.

In an alternative embodiment, lean burn capability is improved by increasing the energy stored in the charge by means for varying the cross section of the ports in such a manner as to vary the direction of flow of the air charge so as to promote swirl in the intake charge.

Advantageously, the valve guide of an intake valve constructed as a poppet valve may be used to modify the flow conditions in the intake ports. The lower end of an axially displaceable or rotatable valve guide may act as an obstruction to the air flow and may act upon pivoted or resilient vanes disposed in the individual intake ports to alter the direction of flow of the charge.

The invention will now be described further, by way of example, with reference to the accompanying drawings, in which Figure 1 is a partly sectioned perspective view of a cylinder head for implementing the invention, and Figure 2 is a similar view of an alternative construction of the cylinder head intended to promote swirl in the intake charge.

Figure 1 shows a section through a cylinder head 10 passing through the inlet valve 12. The cylinder head 10 is for an overhead camshaft engine, one bearing seat being shown at 14. The camshaft acts on the inlet valve 12 through a follower or bucket (not shown) which is guided in a cylindrical bore 16. The valve 12 passes through a valve guide 18 which terminates above the valve seat 17.

Air can reach the inlet valve through two intake ports 22 and 24 situated on opposite sides of the valve 12.

This is type of porting though unconventional is known and is believed to improve volumetric efficiency by making better use of the entire skirt area of the valve 12.

In the embodiment of Figure 1, resilient vanes 30 and 32 are arranged in the respective ports 22 and 24 for the purpose of varying the port geometry in dependence upon the prevailing operating conditions of the engine. Each of these vanes is represented as a resilient tongue extending from a retaining ring. The method of retention of the rings is not shown in detail but they may for example be located in a cast recess in the induction ports, relying upon their own resilience.

It has been found with dual porting that not only does the high speed engine improve as a result of increased volumetric efficiency but that lower speed torque is also improved. The lean burn performance of the engine can however be increased still further by increasing the charge velocity under low engine load by reducing the effective cross section of the intake ports in the immediate vicinity of the inlet valve. The fact that the restriction takes place near the valve means that there are less pumpimg losses.

The vanes 30 and 32 are deflected in a vertical plane in the embodiment of Figure 1 with the result that the air speed is increased without any tendency to create swirl about the axis of the valve 12. Swirl in the air flow does however occur as the air spills over the edge of the valve 12 and this creates a toroidal flow as previously described. Such toroidal flow does not occur, or at least not to the same extent, in a single port engine as the flow rate is not even about the circumference of the valve skirt. The faster the air flow rate, the greater will be the stored energy in the incoming charge and this is reflected in greater turbulence after the charge has been compressed. It is well accepted that the greater the charge turbulence, the leaner the minimum mixture strength necessary for complete combustion.

In this case, because of the absence of swirl, it is possible there is a degree of correlation between the point of fuel injection and the position of maximum mixture strength after compression and this may be used to obtain still further lean burn capability by selecting the injection point to maximize mixture strength in the vicinity of the spark plug.

The mechanism for deflecting the vanes 30, 32 is not shown in the drawings, which are intended more to explain the principle of the invention than to illustrate a practical embodiment of the invention.

As one example, it is conceivable that the valve guide 18 may be axially displaceable by means of a rack and pinion arrangement, the pinions for the different cylinders being mounted on a common shaft extending over the length of the cylinder head. The lower end of the valve guide 18 may rest upon the ends of the tongues of the vanes and act as the means for deflecting the vanes.

As drawn, there is of course insufficient room for the rack and pinions but this is merely a packaging problem which may be overcome by raising the height of the cylinder head. As an alternative, rods may pass through the cylinder head above the tongues to act as deflecting means and these may be operated mechanically, electrically or hydraulically.

The embodiment of Figure 2 differs from that of Figure 1 only in that the vanes 30' and 32' are arranged to promote swirl about the axis of the valve 12 by virtue of their being in a plane at right angles to the axis of the valve 12.

Here, the possibility of stratifying the charge does not arise but the stored energy in the charge is still increased by virtue of the swirl and the toroidal flow over the valve skirt and this is reflected in improved lean burn capability. As before, the mechanism for altering the position of the vanes is not shown but may be analogous to that previously described. For example, the valve guide may have extensions in contact with the tongues and may be rotatable by a rack extending over the length of the engine. Alternatively, independent control mechanisms may be provided for actuating the individual vanes.

The port geometry at high engine load is virtually unaltered by virtue of the fact that under these conditions the tongues, which are part cylindrical will rest flush against the walls of the intake ports. At lower engine loads, the port cross sections are progressively reduced to increase charge turbulence after compression to promote lean burn.

The fuelling may be by carburettor or by fuel injection and may be on one or both of the intake ports. In the case of a carburettor, due allowance must of course be made for the pressure drop across the vanes and if only one port is fuelled then allowance must also be made for the air entering the combustion chamber by way of the other port.

Claims

1. An internal combustion engine having separate intake and exhaust valves, wherein an intake valve is provided with two diametrically opposed ports whereby to promote toroidal flow in the combustion chamber, and means associated with the ports and disposed in close proximity to the intake valve for varying the through flow cross section of the individual ports whereby to increase the charge velocity at low air flow masses.

2. An engine as claimed in claim 1, wherein the fuel is injected into one of the ports, the point of injection being selected such that the richness of the mixture will not be uniform in the combustion chamber but will be greater in the vicinity of the spark plug after compression.

3. An engine as claimed in claim 1, wherein lean burn capability is improved by increasing the energy stored in the charge by means for varying the cross section of the ports in such a manner as to vary the direction of flow of the air charge so as to promote swirl in the intake charge.

4. An engine as claimed in any preceding claim, wherein the valve guide of an intake valve constructed as a poppet valve is used to modify the flow conditions in the intake ports.

5. An engine as claimed in claim 4, wherein the lower end of an axially displaceable or rotatable valve guide acts as an obstruction to the air flow.

6. An engine as claimed in claim 4, wherein the lower end of an axially displaceable or rotatable valve guide acts upon pivoted or resilient vanes disposed in the individual intake ports to alter the direction of flow of the charge.

7. An engine constructed and adapted to operate substantially as herein described with reference to and as illustrated in the accompanying drawings.