Axial Flow Rotary Valve for an Engine

Abstract

An axial flow rotary valve (1) for an engine, the valve rotatable about an axis (12). The valve having an inlet port (2) extending from an axial opening (5) and terminating as a peripheral opening (7). The port having a throat (22), with a cross sectional area at least 2% less than the axial opening, at a distance of at least 0.2 times the length of the peripheral opening from the end of the peripheral opening closest to the axial opening, and a port floor (19) extending from the first end to the axial opening. The port having a port floor profile (37) generated by the intersection of the port floor with any plane coincident with the axis intersecting the port floor wherein the angle (α) between the tangent to the profile and the axis is less than 60 degrees over at least 75% of the length of the profile.

Description

TECHNICAL FIELD

The present invention relates to an axial flow rotary valve internal combustion engine, and in particular to a structural arrangement of an axial flow rotary valve that improves the breathing capability of the engine.

BACKGROUND

The present invention is concerned with axial flow rotary valves that have both an inlet port and exhaust port in the same valve. In particular it applies to rotary valves that have an outside diameter less than 85% of the cylinder bore diameter and to rotary valve engines where there is one valve per cylinder. An axial flow rotary valve is defined as one in which the axis of rotation of the valve is substantially perpendicular to the cylinder axis and the flow into and out of the valve is approximately parallel to the valve axis.

In multicylinder in-line engines using axial flow rotary valves with both inlet and exhaust ports in the same valve, there are two distinct types of axial flow rotary valves. The first type has one valve per cylinder and the second type has one valve for many cylinders.

The present invention applies to axial flow rotary valves which have one valve per cylinder. In general these multicylinder arrangements have the valve axis perpendicular to the crankshaft axis. However, this does not necessarily have to be the case. In some layouts there may be reasons for having the valve axis angled to a plane that is perpendicular to the crankshaft axis.

In the second type there is one valve for all cylinders in the bank and consequently the valve axis must be parallel to the crankshaft axis. This arrangement is basically flawed as the inlet and exhaust tract length is different for every cylinder. As a consequence the engine cannot use tuned inlet and exhaust tract lengths to optimise performance, a basic feature that is required on all modem engines.

The distinction between these two types applies only to multi cylinder in-line engines only, as on single cylinder engines there must be at least one valve per cylinder. Furthermore because there is no adjacent cylinder imposing geometric constraints on a single cylinder engine, there are no constraints on the orientation of the valve axis relative to the crankshaft axis.

Axial flow rotary valve arrangements of both these types have been proposed for many years. Despite this none have been successfully commercialised. This is partly due to prior art arrangements which have poor breathing and low turbulence. To be competitive, a modem internal combustion engine must have adequate breathing capacity to achieve high volumetric efficiency at high speed. Furthermore, a competitive engine must be capable of generating suitable in-cylinder motion of the air fuel mixture during the intake stroke and breaking this down into small scale turbulence late in the compression stroke to maximise the speed at which the flame travels through the combustion chamber.

The arrangements required to optimise these three parameters in poppet valve engines have evolved over the last hundred years and today there is general consensus on how these parameters are optimised. The axial flow rotary valve introduces many physical constraints not found on the poppet valve, which means the solutions established for the poppet valve internal combustion engine are not readily transferable to the rotary valve.

Contrary to widely held belief, breathing capability in axial flow rotary valves is often found to be poor, particularly when compared to modern four valve engines, where the valve opening rates are very high. The source of this problem lies in the fact that the valve axis is perpendicular to the cylinder axis. This requires the gas flow to turn through 90° when it enters the cylinder from the inlet port or leaves the cylinder and enters the exhaust port. By way of comparison all modern poppet valve engines arrange the inlet port to intersect the poppet valve axis at a very low angle (certainly less than 40°). In addition the poppet valves are inclined to the cylinder axis at a very low angle. Consequently the angle through which the incoming air must be bent when it enters the cylinder from the inlet port is very low thus minimising the flow losses that inevitably arise when fluid flows are turned through a large angle.

Breathing issues on axial flow rotary valve engines and the gas sealing system are interconnected. The shape and size of the window are determined by the nature of gas sealing arrangement. Many gas sealing arrangements dictate the use of small windows. In these arrangements it is essential that the flow through these windows is normal to the window in order to maximise the discharge coefficient of the window.

Turning the flow adjacent the roof of the inlet port through 90° does not present a problem as the effective radius about which the flow is turning is large and the flow is against the roof. Turning the flow adjacent the port floor through 90° does however create considerable difficulties. In general the radius through which the flow must turn is small and the flow is away from the port floor. Inevitably the flow will become separated from the port floor generating shedding vortices and consequent large flow losses. All prior art rotary valves have either ignored this issue or attempted to turn the flow adjacent the port floor through 90° such that the flow through the window is perpendicular to the window.

The problem of flow separation has been addressed by increasing the radius on the floor of the inlet port. A typical example is U.S. Pat. 4,404,934 (Asaka et al). This detail requires the valve outer diameter to be larger than would otherwise be required. The consequence is valves that have a diameter close to that of the cylinder bore diameter which creates problems with the placement of the spark plug with resultant poor thermal efficiency as discussed below.

A large valve diameter helps increase the breathing capacity of the valve as the rate at which the flow area opens is a function of the valve's peripheral velocity. Despite this, the arrangement of U.S. Pat. 4,404,934 (Asaka et al) has very poor breathing capacity. This is a result of the very small diameter of the inlet and exhaust ports compared to the diameter of the valve (less than 40% of valve diameter) and a window constrained by the gas sealing mechanism to have very small length, say less than 40% of the cylinder diameter.

The present invention is preferably intended for use with an array of floating seals positioned around the outside of a rectangular window to affect the gas sealing. U.S. Pat. No. 4,852,532 (Bishop) shows a typical example. This gas sealing arrangement has the advantage that the window can be made very long (up to 90% of the cylinder bore) which results in very high area opening and closing rates and large flow areas with consequent potentially excellent breathing. Prior art valves have however failed to fully exploit this potential and window lengths have been relatively modest.

Furthermore, previous arrangements using the array of floating seals have difficulty exploiting their window openings as a result of the large fluid flow losses associated with turning the flow through 90° and small port areas. The arrangement shown in U.S. Pat. No. 4,852,532 (Bishop) is typical. Although larger than many previous proposals the inlet port has a diameter that is still only 60% of the valve diameter. The very small radius on the port floor makes it impossible for the flow to be turned through 90° without the flow separating from the wall and creating large shedding vortices adjacent the wall. This particular problem is better addressed in U.S. Pat. No. 5,509,386 (Wallis et al) where the port floor rises towards the centre of the valve adjacent the window such that the radius on the floor can be increased with consequent decrease in the flow losses for the fluid flowing adjacent the port floor. However the flow must still be turned through 90°, particularly as the window has relatively low axial length, and the radius is still relatively small. As a result there are still significant losses associated with this arrangement. This particular problem cannot be addressed by increasing the radius of the port floor as this would drive the port floor closer to the valve axis with consequent reduction in the throat area of the valve.

Despite the fact the window flow areas are potentially very large compared to the equivalent poppet valve flow areas no arrangements have been developed that exploit this potential. Most if not all of these arrangements have lower breathing capacity than the equivalent poppet valve engines despite the large potential flow area advantage.

High breathing capacity on its own is not sufficient to guarantee satisfactory engine performance. It is well known from extensive studies of poppet valve engines that the presence of small scale turbulence in the charge gases during combustion dramatically increases the flame speed through the gases. An important source of this small scale turbulence is the flow fields that are established in the cylinder during the induction stroke. It is important to have an inlet port geometry that together with the cylinder geometry allows the establishment of suitable in-cylinder flow fields.

Turbulence is very important in all engines but particularly so in rotary valve engines where the presence of small scale turbulence could potentially greatly increase combustion speeds and help ameliorate the effects of the inevitable non optimum spark plug locations found in rotary valve engines. There is no known literature that addresses the issue of in-cylinder flows and the generation of small scale turbulence in rotary valve engines.

Several methods have been devised in conventional poppet valve engines to generate small scale turbulence late in the compression stroke. The three main existing methods of doing this are known as “swirl”, “tumble” and “squish”. In the case of swirl and tumble this is done by creating a bulk flow field in the cylinder during the intake stroke which decays to small scale turbulence during the compression stroke.

Tumble is defined as a flow vortex in the cylinder rotating about an axis perpendicular to the cylinder axis. In an engine designed for tumble a single major vortex is established during the inlet stroke. As the piston rises on the following compression stroke the vortex is compressed until it reaches a critical aspect ratio where it breaks into smaller vortices. As the piston continues to rise these smaller vortices continue to break up over and over again until they become small scale turbulence.

Aspect ratio is defined as the width divided by the height of an object, except for when this is less than one, when the reciprocal (height divided by width) is used. When the piston is at bottom dead centre (bdc) the aspect ratio for oversquare engines is given by the bore divided by the stroke.

In one aspect, the present invention is concerned with methods for generating tumble in rotary valve engines. When considering tumble two types of engine must be considered. Firstly those with conventional bore stroke ratios of approximately 1:1 and secondly those with high bore stroke ratios. There is no known prior art teaching on how to generate tumble in axial flow rotary valve engines with either conventional bore stroke ratio or high bore stroke ratio.

Most commercially available engines have bore stroke ratios around 1:1. In these engines the aspect ratio when the piston is at bottom dead centre is 1, which is conducive to the formation of a single major tumble vortex.

High speed engines however use oversquare engines (ie where the bore is greater than the stroke) in order to reduce the acceleration the piston and rods are subjected to at maximum engine speed. They are said to have high bore stroke ratios. For the purpose of this application an engine with a high bore stroke ratio is defined as one that has a bore stroke ratio greater than 1.4:1.

Engines using rotary valves of the type disclosed in this application potentially have very high breathing capacity and are particularly well suited to use in high speed engines. However, the aspect ratio when the piston is at bottom dead centre is greater than 1.4 and this is not conducive to the formation of a single tumble vortex. As discussed above, rotary valve engines require higher than normal levels of small scale turbulence than typically found in poppet valve engines. Absence of this higher level of turbulence will result in low flame speed and poor thermal efficiency.

The present invention seeks to overcome one or more of the disadvantages associated with the breathing capability of the above mentioned prior art rotary valves.

SUMMARY OF INVENTION

In a first aspect, the present invention consists of an axial flow rotary valve for an internal combustion engine, said valve comprising an axis about which said valve is adapted to rotate, and at least one port extending from a substantially circular axial opening at one end of said valve, terminating as a peripheral opening on the periphery of said valve, said peripheral opening having a first end proximate to said axial opening and a second end remote from said axial opening, said port having a throat at a first distance axially from said first end, a port floor extending from said first end to said axial opening, the distance between said port floor and said axis progressively increasing as said port floor extends away from said throat to said first end, and the distance between said port floor and said axis progressively increasing as said port floor extends away from said throat to said axial opening such that the cross sectional area of said throat is at least 2% less than the cross sectional area of said axial opening, and a port floor profile generated by the intersection of said port floor with any plane coincident with said axis intersecting said port floor, characterised in that said first distance is at least 0.2 times the axial length of said peripheral opening and the angle between the tangent to said profile and said axis is less than 60 degrees over at least 75% of the length of said profile between said first end and said throat.

Preferably, said plane is coincident with the centre of said peripheral opening. Preferably, said port is an inlet port. Preferably, the normal area of said peripheral opening is at least 20% greater than the cross sectional area of said throat.

Preferably said valve is adapted to rotate within a bore of a cylinder head of said engine, a window in said bore communicating with a combustion chamber, said peripheral opening periodically communicating with said window as said valve rotates, and an array of floating seals surrounding said window to affect gas sealing.

In a second aspect, the present invention consists of a rotary valve engine comprising a rotary valve rotatable about an axis within a bore in a cylinder head, a window in said bore communicating with a combustion chamber, said valve comprising at least one port extending from a substantially circular axial opening at one end of said valve, terminating as a peripheral opening on the periphery of said valve, said peripheral opening periodically communicating with said window as said valve rotates, and an array of floating seals surrounding said window to affect gas sealing, said peripheral opening having a first end proximate to said axial opening and a second end remote from said axial opening, said port having a throat at a first distance axially from said first end, a port floor extending from said first end to said axial opening, the distance between said port floor and said axis progressively increasing as said port floor extends away from said throat to said first end, and the distance between said port floor and said axis progressively increasing as said port floor extends away from said throat to said axial opening such that the cross sectional area of said throat is at least 2% less than the cross sectional area of said axial opening, and a port floor profile generated by the intersection of said port floor with any plane coincident with said axis intersecting said port floor, characterised in that said first distance is at least 0.2 times the axial length of said peripheral opening and the angle between the tangent to said profile and said axis is less than 60 degrees over at least 75% of the length of said profile between said first end and said throat.

In a third aspect, the present invention consists of an axial flow rotary valve for an internal combustion engine, said valve comprising an axis about which said valve is adapted to rotate, and at least one port extending from an axial opening at one end of said valve, terminating as a peripheral opening on the periphery of said valve, said peripheral opening having a first end proximate to said axial opening and a second end remote from said axial opening, said port having a throat and a port floor extending from said first end to said axial opening, the distance between said port floor and said axis progressively increasing as said port floor extends away from said throat to said first end, and the distance between said port floor and said axis progressively increasing as said port floor extends away from said throat to said axial opening, characterised in that the shape of said port floor between said throat and said first end is adapted to direct air flowing adjacent said port floor through said peripheral opening at an angle of less than 60 degrees to said axis.

Preferably, the cross sectional area of said throat is at least 2% less than the cross sectional area of said axial opening. Preferably, said axial opening is substantially circular. Preferably, the axial distance from said first end to said throat is at least 0.2 times the axial length of said peripheral opening.

Preferably, said port floor has a port floor profile generated by the intersection of said port floor with any plane coincident with said axis intersecting said port floor, the angle between the tangent to said profile and said axis being less than 60 degrees over at least 75% of the length of said profile between said first end and said throat. Preferably, said plane is coincident with the centre of said peripheral opening.

Preferably, said port is an inlet port. Preferably, the normal area of said peripheral opening is at least 20% greater than the cross sectional area of said throat.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view of an internal combustion engine with a conventional 1:1 bore stroke ratio with a rotary valve in accordance with the present invention

FIG. 2 is a cross-sectional view of the rotary valve depicted in FIG. 1 on a plane perpendicular to the axis of the rotary valve and passing through the midpoint of the axial extremities of the valve opening as indicated by line II-II

FIG. 3 is a cross-sectional view of the rotary valve depicted in FIG. 1 on a plane perpendicular to the axis of the rotary valve and passing through the throat as indicated by line III-III.

FIG. 4 is a cross-section view of the rotary valve of FIG. 2 through a plane coincident with the valve axis and centre of the inlet opening as indicated by line IV-IV.

FIG. 5 shows an alternative embodiment of a rotary valve in accordance with the present invention viewed in the same manner as FIG. 4.

FIG. 6 is the same cross-sectional view as FIG. 1 but showing a schematic of the flow streamlines in the valve and the cylinder with the piston at bottom dead centre;

FIG. 7 is an isometric sectional view through an alternative embodiment of a rotary valve internal combustion engine in accordance with the present invention having a high bore stroke ratio and schematically showing the dual cross flow tumble regime generated during the induction stroke with the piston at bottom dead centre;

FIG. 8 is a transverse cross-sectional view through VIII-VIII of the same internal combustion engine shown in FIG. 7 schematically showing the dual cross tumble flow;

FIG. 9 is a sectional view of a prior art rotary valve.

BEST MODE OF CARRYING OUT THE INVENTION

The rotary valve assembly shown in FIG. 1 comprises a valve 1 and a cylinder head 10. Valve 1 has an inlet port 2 and an exhaust port 3. Valve 1 has a cylindrical centre portion 4 of constant diameter. Inlet port 2 extends from inlet axial opening 5 and terminates at inlet peripheral opening 7 in the periphery of centre portion 4. Exhaust port 3 extends from exhaust axial opening 6 at the opposite end of valve 1 and terminates at exhaust peripheral opening 8 in the periphery of centre portion 4. Exhaust peripheral opening 8 axially overlaps inlet peripheral opening 7 and is circumferentially offset to inlet peripheral opening 7. Inlet peripheral opening 7 and exhaust peripheral opening 8 are approximately rectangular. Inlet peripheral opening 7 has a first end 20 proximate to inlet axial opening 5 and a second end 21 remote from inlet axial opening 5. Valve 1 is supported by bearings 9 to rotate about axis 12 in cylinder head 10. Axis 12 is perpendicular to cylinder axis 18. Bearings 9 allow valve 1 to rotate about axis 12 whilst maintaining a small running clearance between periphery of centre portion 4 and bore 11 of cylinder head 10.

Cylinder head 10 is mounted on the top of cylinder block 14. Piston 15 reciprocates in cylinder 13 formed in cylinder block 14. As valve 1 rotates, inlet peripheral opening 7 and exhaust peripheral opening 8 periodically communicate with window 16 in cylinder head 10, allowing the passage of fluids between combustion chamber 17 and valve 1.

Window 16 is approximately rectangular in shape and has a first window end 23 proximate to inlet axial opening 5, a second window end 24 remote from inlet axial opening 5. A window lip 28 is formed at first window end 23.

An array of floating seals 41 surround window 16, to affect gas sealing between valve 1 and cylinder head 10. The seals 41 shown in FIG. 1 are circumferential seals located at opposite ends of window 16. However, the array also comprises axial seals (not shown in FIG. 1) substantially parallel to axis 12 and adjacent opposite sides of window 16. The array of floating seals 41, may for example be of the type disclosed in any of U.S. Pat. No. 4,852,532 (Bishop) or U.S. Pat. No. 5,509,386 (Wallis et al) or U.S. Pat. No. 5,526,780 (Wallis).

In FIG. 2, Φ is the angle subtended by lines passing through axis 12 and leading edge 34 and trailing edge 35 respectively of inlet peripheral opening 7, at an axial location midway between the axial extremities of inlet peripheral opening 7. FIG. 3 is a cross section through throat 22 of inlet port 2. Port floor 19 is defined as the portion of the wall of inlet port 2 subtended by angle Φ where angle Φ is defined above.

FIG. 4 is a cross-section view of a rotary valve 1 through a plane coincident with axis 12 and the centre of inlet peripheral opening 7. Although peripheral opening 7 is described as substantially rectangular with edges 34, 35 being approximately parallel to axis 12, there are applications where it is beneficial to incline one or both of edges 34,35 to axis 12 by a small amount, typically less than 10°. Similar issues arise with window 16. This creates issues with the definition of the centre of inlet peripheral opening 7 or the centre of window 16 that are addressed by defining their centre as follows:

The centre of inlet peripheral opening 7 is defined as the midpoint between edges 34 and 35 of inlet peripheral opening 7 at an axial location midway between the axial extremities of inlet peripheral opening 7. The centre of window 16 is defined as the midpoint between the sides of window 16 at an axial location midway between the axial extremities of window 16.

Throat 22 of inlet port 2 is defined as the section normal to axis 12 and lying between first end 20 and inlet axial opening 5 where the smallest cross-sectional port area occurs. In the event the smallest cross-sectional port area occurs at more than one section normal to axis 12 throat 22 is defined as that section axially closest to first end 20. In this application all cross-sectional port areas are measured in a plane normal to axis 12.

Throat 22 of inlet port 2 is located an axial distance A from first end 20 of inlet peripheral opening 7 where A is greater than 0.2 times the axial length L of inlet peripheral opening 7. The axial length L of inlet peripheral opening 7 is defined as the axial length between the axial extremities of inlet peripheral opening 7.

For the purposes of this application the shape of the surface that forms inlet port floor 19 is limited to a description of the two-dimensional profiles generated by the intersection of port floor 19 by planes coincident with axis 12. FIG. 4 shows a typical example of such a port floor profile 37. Port floor profile 37 is defined as the two dimensional profile generated by the intersection of port floor 19 by a plane coincident with valve axis 12.

Upstream of throat 22 the radial distance between port floor 19 and axis 12 progressively increases as port floor 19 extends away from throat 22 towards axial opening 5. Downstream of throat 22, the radial distance between port floor 19 and axis 12 progressively increases as port floor 19 extends away from throat 22 towards first end 20. As a result the cross sectional area of throat 22 is smaller than the cross sectional area of the substantially circular inlet axial opening 5. Preferably the cross sectional area of throat 22 is at least 2% less than the cross sectional area of inlet opening 5.

At the throat the tangent to port floor 19 is typically parallel to axis 12. At first end 20 of inlet peripheral opening 7 the tangent to port floor profile 37 intersects axis 12 at an angle α. Axially outward of first end 20 the tangent to port floor profile 37 intersects axis 12 at a varying angle α₁. In this embodiment, in the region between first end 20 and throat 22 α₁ is always less than 60°. For the purposes of this application tangent angle is defined as the angle at which the tangent to port floor profile 37 intersects axis 12

As a result of the underlying valve geometry the size of the tangent angle α will vary depending on the angular orientation of the intersecting plane. However the largest tangent angles α for any particular valve will typically occur when the intersecting plane passes through the centre of inlet peripheral opening 7.

The shape of port floor 19 thus effectively has a large radius about which the flow adjacent to port floor 19 can be turned without danger of the flow becoming separated from port floor 19. After being turned, the flow adjacent port floor 19 is then directed through inlet peripheral opening 7 at angle a to axis 12 into window 16. An important feature of port floor 19 is that it only turns the incoming flow adjacent port floor 19 through the angle α (refer to FIG. 4) where α is less than 60° and typically may be as low as 30°. As a consequence, separation of flow from port floor 19 is avoided.

Port floor 19 of the alternative embodiment shown in FIG. 5, is different in its detail adjacent first end 20. The small radius R adjacent first end 20 will have little effect on the performance of port floor 19, and as such flow adjacent port floor 19 will still be directed through inlet opening 7 at an angle α of less than 60°. Similarly, the performance of port floor 19 is not affected in the event the small radius R adjacent first end 20 is replaced by a small chamfer.

The functional requirement of this invention is achieved if the greater portion of port floor 19 surfaces, between throat 22 and first end 20, have small tangent angles. Small portions of port floor 19 where the tangent angle is large will have little effect on the direction of the flow adjacent port floor 19 when the rest of port floor 19 has small tangent angles. This particularly applies to any rapid changes in port floor shape immediately adjacent first end 20 that may be required to blend inlet peripheral opening 7 to port floor 19, such as radius R in FIG. 5, since this localised rapid shape change is not capable of substantially changing the direction of flow through inlet peripheral opening 7. As a consequence port floor profiles 37 are constrained to certain tangent angles over a proportion of the length of port floor profile 37 only. Preferably port floor profile 37 between throat 22 and first end 20 should have tangent angles less than 60 degrees over at least 75% of the length of port floor profile 37.

To illustrate the functional and structural differences between the present invention and the prior art, FIG. 9 shows a sectional view through a rotary valve 1a representative of the prior art having a port floor 19a shaped similarly to that disclosed in U.S. Pat. No. 5,509,386 (Wallis et al). The throat of port 2a is located at a distance C from first end 20 of less than 0.2 times the axial length L of inlet peripheral opening 7a. The port floor between throat 22a and first end 20a is shaped substantially as a constant radius R1 that is designed to direct flow through inlet peripheral opening 7a at an angle β of approximately 90° to valve axis 12. Furthermore, the port floor profile between throat 22a and first end 20a does not have a tangent angle of less than 60 degrees over at least 75% of its length.

In FIG. 1 the surface of window lip 28 is approximately tangent to port floor 19 at intersection of port floor 19 with first end 20 of inlet peripheral opening 7. Window lip 28 provides a surface to which the flow may remain attached as it passes through window 16. By this means the flow adjacent port floor 19 remains attached to a surface until the point it finally enters cylinder 13. Window lip 28 results in a re-entrant zone in combustion chamber 17 which would normally be avoided in combustion camber design. This zone has however been demonstrated not to adversely affect combustion.

Referring to FIG. 6, the port roof 25 provides a surface that turns the air adjacent to this surface through nearly 90°. Port roof 25 has at least one large diameter radius about which the flow is turned. This large radius combined with the fact the flow is impinging onto the wall of port roof 25 ensures the flow near port roof 25 is turned through an angle approaching 90° with very small flow losses. Flow adjacent port roof 25 is thus turned through an angle approaching 90° and flows through window 16 substantially normal to window 16.

Flow adjacent port floor 19 is turned through angle a of less than 60° and flows through window 16 at an angle of (90-α)° to cylinder axis 18. Those flows occurring between port floor 19 and port roof 25 are turned through various angles between 90° and α° and pass through inlet peripheral opening 7 at angles varying between 0° and (90-α)° to cylinder axis 18. The potential difficulty with this approach is that the area of inlet peripheral opening 7 is not efficiently used. Flow through Inlet peripheral opening 7 is maximised when the flow is normal to inlet peripheral opening 7. This particular problem is addressed by making the normal area of inlet peripheral opening 7 substantially greater than the cross sectional area of throat 22. As a consequence the loss of flow efficiency through inlet peripheral opening 7 is compensated by having a larger inlet peripheral opening 7 area than would otherwise be necessary. Typically inlet peripheral opening 7 may have a normal area 50% greater than the cross sectional area of throat 22.

The normal area of inlet peripheral opening 7 is the area contained between ends 20, 21 and edges 34, 35 of inlet peripheral opening 7 projected onto a plane normal to another plane that is coincident with axis 12 and the centre of inlet peripheral opening 7.

FIG. 6 shows flow streamlines for an engine with a conventional bore stroke ratio of 1:1 and with piston 15 at bottom dead centre of the inlet stroke. The flow stream lines indicate the path of particular gas particles through cylinder 13 and schematically illustrate the strong tumble gas motion generated in such an arrangement.

During the induction stroke the flow occurring adjacent port roof 25 passes through inlet peripheral opening 7 approximately normal to inlet peripheral opening 7 and flows down adjacent cylinder wall 26. Flow occurring adjacent port floor 19 passes through inlet peripheral opening 7 at α° to inlet peripheral opening 7, then passes through window 16 attached to window lip 28 into combustion chamber 17 where it flows towards far cylinder wall 26 where it converges with the flow from port roof 25. As port floor 19 flow approaches cylinder wall 26, down which the port roof flow is flowing, the port floor flow is turned through (90-α)° and flows down the bore of cylinder 13 close to cylinder wall 26.

By this process the inlet air is forced against cylinder wall 26 remote from inlet axial opening 5 creating ideal conditions for the formation of tumble flow. The downward air flow concentrated against one side of cylinder 13 hits the crown of piston 15 which turns the air through 180 deg after which it travels up opposite cylinder wall 27 where it becomes entrained by the inlet air from valve 1 and is turned again to flow down cylinder wall 26.

Axial flow rotary valves using this principle have excellent breathing capacity together with extremely high tumble. Rotary valves of this type generate high tumble flows irrespective of the location of the valve relative to the centre of cylinder 13 provided that the engine has a bore stroke ratio of approximately 1:1. Consequently, valve 1 can be offset to cylinder axis 18 in order to provide an appropriate location for the spark plug near the centre of cylinder 13 without adversely affecting the generation of tumble flow. Engines of this type have outstanding combustion even in the event the spark plugs are somewhat offset from the cylinder centre.

Whilst this solution satisfactorily addresses the issue of tumble generation on rotary valve engines with conventional bore stroke ratios it does not address the issue on engines with high bore stroke ratios that have an unfavourable (from a tumble perspective) aspect ratio when the engine is at bottom dead centre. Further this solution relies on an offset valve arrangement that introduces other difficulties in the construction of multicylinder in-line engines.

FIG. 8 shows an internal combustion engine with a high bore stroke ratio (2:1) typical of that found on many high speed engines. Axis 12 intersects cylinder axis 18. Spark plugs 29 each have a nose 40 which faces combustion chamber 17. Nose 40 is defined as that portion of spark plug 29 that is exposed to combustion chamber 17. Spark plugs 29 are located either side of valve 1 and are inclined inward towards cylinder axis 18. Valve 1 has a small outside diameter which allows spark plugs 29 to be inserted beside valve 1 whilst still each having spark plug nose 40 located inboard of the wall of cylinder 13.

In rotary valve arrangements with high bore stroke ratios, the incoming air stream is prevented from forming a strong tumble vortex of the type previous described by the unfavourable geometry of cylinder 13 when piston 15 is at bottom dead centre. Referring to FIG. 7 the incoming air stream enters cylinder 13 as previously described. It travels towards the crown of piston 15 as a gas jet in cylinder 13. Unable to roll back under itself as previously described, the gas jet impinges on surfaces formed by the crown of piston 15 and cylinder wall 26 where the jet flow splits into two. After splitting the jet curves back on itself and runs around the wall of cylinder 13 towards combustion chamber 17 in the process forming two approximately symmetrical vortices. The vortices shown in FIG. 7 are inclined to cylinder axis 18. As this flow is three dimensional the projection of this flow onto a plane perpendicular to axis 12 will produce two counter rotating vortices 31 as shown in FIG. 8. These counter rotating vortices form a “dual cross tumble” vortex. The tumble is referred to as “cross tumble” as the plane of the tumble is perpendicular to that previously described in engines of conventional bore stroke ratio.

The aspect ratio of these vortices at bdc is given by the cylinder radius (cylinder bore/2) divided by the stroke. In the case of an engine with a bore stroke ratio of 2:1 the aspect ratio of these vortices at bdc is 1, the optimum ratio for tumble generation.

The strongest dual tumble vortices will be generated when both vortices are symmetrical and of equal magnitude. If the vortices have significantly different magnitudes the stronger one tends to destroy the weaker one. Symmetrical vortices are generated by centring window 16 on cylinder axis 18.

The term “comprising” as used herein is used in the inclusive sense of “including” or “having” and not in the exclusive sense of “consisting only of”.

Claims

1. An axial flow rotary valve for an internal combustion engine, said valve comprising an axis about which said valve is adapted to rotate, and at least one port extending from a substantially circular axial opening at one end of said valve, terminating as a peripheral opening on the periphery of said valve, said peripheral opening having a first end proximate to said axial opening and a second end remote from said axial opening, said port having a throat at a first distance axially from said first end, a port floor extending from said first end to said axial opening, the distance between said port floor and said axis progressively increasing as said port floor extends away from said throat to said first end, and the distance between said port floor and said axis progressively increasing as said port floor extends away from said throat to said axial opening such that the cross sectional area of said throat is at least 2% less than the cross sectional area of said axial opening, and a port floor profile generated by the intersection of said port floor with any plane coincident with said axis intersecting said port floor, characterised in that said first distance is at least 0.2 times the axial length of said peripheral opening and the angle between the tangent to said profile and said axis is less than 60 degrees over at least 75% of the length of said profile between said first end and said throat.

2. A rotary valve as claimed in claim 1 wherein said plane is coincident with the centre of said peripheral opening.

3. A rotary valve as claimed in claim 1 wherein said port is an inlet port.

4. A rotary valve as claimed in claim 1 wherein the normal area of said peripheral opening is at least 20% greater than the cross sectional area of said throat.

5. A rotary valve as claimed in claim 1 wherein said valve is adapted to rotate within a bore of a cylinder head of said engine, a window in said bore communicating with a combustion chamber, said peripheral opening periodically communicating with said window as said valve rotates, and an array of floating seals surrounding said window to affect gas sealing.

6. A rotary valve engine comprising a rotary valve rotatable about an axis within a bore in a cylinder head, a window in said bore communicating with a combustion chamber, said valve comprising at least one port extending from a substantially circular axial opening at one end of said valve, terminating as a peripheral opening on the periphery of said valve, said peripheral opening periodically communicating with said window as said valve rotates, and an array of floating seals surrounding said window to affect gas sealing, said peripheral opening having a first end proximate to said axial opening and a second end remote from said axial opening, said port having a throat at a first distance axially from said first end, a port floor extending from said first end to said axial opening, the distance between said port floor and said axis progressively increasing as said port floor extends away from said throat to said first end, and the distance between said port floor and said axis progressively increasing as said port floor extends away from said throat to said axial opening such that the cross sectional area of said throat is at least 2% less than the cross sectional area of said axial opening, and a port floor profile generated by the intersection of said port floor with any plane coincident with said axis intersecting said port floor, characterised in that said first distance is at least 0.2 times the axial length of said peripheral opening and the angle between the tangent to said profile and said axis is less than 60 degrees over at least 75% of the length of said profile between said first end and said throat.

7. An axial flow rotary valve for an internal combustion engine, said valve comprising an axis about which said valve is adapted to rotate, and at least one port extending from an axial opening at one end of said valve, terminating as a peripheral opening on the periphery of said valve, said peripheral opening having a first end proximate to said axial opening and a second end remote from said axial opening, said port having a throat and a port floor extending from said first end to said axial opening, the distance between said port floor and said axis progressively increasing as said port floor extends away from said throat to said first end, and the distance between said port floor and said axis progressively increasing as said port floor extends away from said throat to said axial opening, characterised in that the shape of said port floor between said throat and said first end is adapted to direct air flowing adjacent said port floor through said peripheral opening at an angle of less than 60 degrees to said axis.

8. A rotary valve as claimed in claim 7 wherein the cross sectional area of said throat is at least 2% less than the cross sectional area of said axial opening.

9. A rotary valve as claimed in claim 7 wherein said axial opening is substantially circular.

10. A rotary valve as claimed in claim 7 wherein the axial distance from said first end to said throat is at least 0.2 times the axial length of said peripheral opening.

11. A rotary valve as claimed in claim 7 wherein said port floor has a port floor profile generated by the intersection of said port floor with any plane coincident with said axis intersecting said port floor, the angle between the tangent to said profile and said axis being less than 60 degrees over at least 75% of the length of said profile between said first end and said throat.

12. A rotary valve as claimed in claim 11 wherein said plane is coincident with the centre of said peripheral opening.

13. A rotary valve as claimed in claim 7 wherein said port is an inlet port.

14. A rotary valve as claimed in claim 7 wherein the normal area of said peripheral opening is at least 20% greater than the cross sectional area of said throat.