Field of the Invention

This invention relates to poppet valves assemblies for use in internal combustion engines.

Background of the Invention

The majority of internal combustion engines use a poppet valve system in which a valve element includes a valve stem and a valve head. The valve head engages in a seat at the top of its respective cylinder and is moved on and off that seat by axial movement of its stem. This movement is typically induced by a camshaft acting directly upon a cam follower provided at the end of the valve stem or through a rocker arm. The valve stem is usually spring loaded to return the valve head to its seat.

Currently, there are two main types of cylinder head. The pentroof has a pentroof combustion chamber cylinder head and the radial cylinder head has a hemispherical combustion chamber. Each type of cylinder head has its own advantages and disadvantages.

The 4 valve pentroof cylinder head excels with the durable mechanics of its valve train. However, the configuration of the components in the valve train have a knock-on effect which hinders the design and shape of the combustion chamber. The style and design of the combustion chamber is crucial to an internal combustion engine in regards to its fuel efficiency and performance. The four valve radial cylinder head has the ideal hemispherical shaped combustion chamber but it comes at a price.

The shape of the hemispherical combustion chamber puts limitations on the type of design of valve train to be used which in turn limits the size of the valve heads.

The reason why the valves are smaller on radial cylinder head is that when the valves open the valve heads, they open and start to converge in on each other and only have limited amount of travel before the valve heads collide into each other, instead of opening parallel to each as they do in the pentroof design.

There is, thus, a desire to provide a cylinder head arrangement which combines the durable mechanics of a pentroof design with the advantages of the radial head cylinder.

Embodiments of the invention seek to provide an improved cylinder head. The result being an increase in fuel efficiency of an engine, the reduction of exhaust emissions and the increase in power and performance of any type of four stroke engine, which run on hydrocarbon fuels, i.e. petrol diesel, etc., including race engines.

In particular, embodiments of the invention may effectively allow the valve train from the pentroof to be incorporated into a radial style of cylinder head without any of the restrictions and limitations caused by the mechanics of the designs.

Thus, embodiments may allow the provision of a four valve hemispherical combustion chamber style of cylinder head with large valves which was not possible with prior art designs. The larger valves increase the volumetric flow and they also have a unique feature which allows the valve to have the directional and deflection capabilities for mixing and directing the gases perfectly in the cylinder.

Further, it would be advantageous to provide a poppet valve and/or inlet arrangement for an internal combustion engine which enables the flow into the cylinder to be optimised and/or which may provide the engine designer with extra design freedom in controlling the flow in the cylinder. Such a poppet valve and/or inlet may be provided by embodiments of the invention.

Summary of the Invention

According to one aspect the invention there is provided a poppet valve assembly for use in an internal combustion engine including: a valve stem having an axis and a valve head mounted at one end thereof, wherein the stem is inclined to the front face of the valve head; and a valve guide for receiving the stem for axial movement of the stem wherein the stem and the guide have cooperating formations for causing rotational movement of the stem and hence the head during axial movement of the stem. Preferably the movement is such that the valve head moves at least part laterally with respect to the axis.

At least one of the stem and the guide may be provided with a helical formation. For example, the cooperating formations may comprise cooperating helical formations.

The poppet valve assembly of embodiments of the invention may be particularly suitable for use in a radial cylinder head (i.e. a head which has a hemispherical roof profile and may also be known as a "hemispherical combustion chamber").

The new helical valve may, for example, make it possible to have an engine with a four valve cylinder head complete with a hemispherical combustion chamber also incorporating the larger valves and having the correct valve train fitted i.e. camshaft, cam follower, etc. This has not been possible without the new valve technology. Therefore, embodiments may provide a more fuel efficient engine, with an increase in Brake Horse Power and the reduction of the exhaust emissions.

Accordingly, another aspect of the invention provides a cylinder for an internal combustion engine comprising a poppet valve assembly according to embodiments and in which the cylinder has a radial cylinder head. In particular, by allowing the valve head to lift and rotate away from the valve seat embodiments of the invention may enable better use of the space available in the cylinder and avoid clashing issues of conventional valves in radial and pent cylinder heads. The inclined stem of embodiments of the invention may also help to reduce the splay of the valve stems in a radial head cylinder, in particular in multiport cylinder arrangements, which may otherwise be a practical limitation to the shape of the cylinder head. More particularly, the valve arrangement of embodiments of the invention may enable the valves of a radial chamber to be arranged in parallel pairs in the manner of those of a pent cylinder head.

Furthermore, embodiments of the invention may be arranged to allow the valve to tilt away from the valve seat at the top of a pent or radial cylinder head with minimal valve lift at the lower extent of the valve, thereby enabling the valve opening earlier in the stroke of the piston without risk of clashing. For example, the upper extent of the valve head may move at least partially into the combustion chamber while the lower extent may move a minimal amount so as to avoid clash with the piston.

Embodiments of the invention may provide a pent or radial cylinder head with an increased valve and port size in comparison to a conventional arrangement.

The Applicants have also appreciated that if the valve head moves, at least in part laterally with respect to the axis, then it will move, at least in part, out of the path for the air or gas and hence reduce any obstruction to the airflow in to or the gas flow out of the cylinder. Advantageously, embodiments of the invention retain the simple and robust functionality of a poppet valve while providing greater control of the opening of the valve. For example, embodiments may be utilised with a substantially conventional engine configuration (for example a conventional camshaft).

The valve head may be generally circular or elliptical. The the head may be mounted off centre of the stem but care must be taken to balance the loads on the valve and, therefore, a centrally mounted stem is generally preferred. A circular head valve may enable the poppet valve according to embodiments to be used in a substantially standard cylinder arrangement.

The valve stem may further comprise a sealing surface, for example a plain cylindrical stem section. The sealing surface may be disposed between the formations and the valve head. The valve guide may be provided with a seal for engaging the sealing surface of the valve stem. The provision of a sealing surface between the formations and the valve head avoids complex sealing arrangements on the formations, for example helical formations, and may enable the formations to be lubricated.

The stem and valve may be arranged such that a portion of the movement of the valve is without rotation. The valve may, for example, be arranged to move between 0.05 to 0.1 mm prior to any rotation. For example, the cooperating helical formations may be brought into contact after an initial axial movement of the stem. This may be advantageous in allowing the valve to lift slightly from its seat prior to any rotation and to ensure that the movement the final movement during closing of the valve is purely axial. Such an arrangement may help prevent scuffing of the valve which may otherwise cause premature wearing of the valve and/or seat. Additionally or alternatively, the non-rotational movement of the valve may ensure a good tolerance of valve closing and ensure a good pinch seal is provided around the valve.

Setting the rotational position of the valve head within an appropriate range of angles after an appropriately sensed rotation enables the valve head to be used to deflect the inlet air or gas into the chamber so that, for example, it can be caused to flow against the cylinder wall causing it to spiral down the cylinder.

In a multi-port arrangement, various scenarios can be achieved. Thus the inlet flows for the valves may be all deflected in the same sense or they may be deflected in senses selected for the particular valve. Further, where the deflection is in the same sense, the cylinder facing side of the valve head, which is downstream from another inlet port may be used to deflect the gas stream of that inlet port so that it spirals in a laminar fashion with respect to the gas stream emitted from the first-mentioned downstream port.

As well as enhancing mixing, this deflection arrangement helps to reduce the dead spot which may occur between inlet valves with conventional systems.

Accordingly the invention also includes a method of operating a piston engine in which the valve members are effectively rotated to form deflection barriers to deflect the direction of flow of gas in a chosen direction.

The gas flow direction may be towards the cylinder wall and may be in a sense which is generally tangential to an imaginary circle co-axial with the axis of the piston cylinder.

From another aspect the invention includes an internal combustion engine including a poppet valve as defined above and a valve seat where axial movement of the stem in a valve opening sense causes the valve head to lift and rotate away from the seat. The combined axial rotational movement may cause the valve head to move substantially laterally to the valve seat or as if rotated about an axis line generally orthogonal to the stem axis. Advantageously, this rotating action may provide an additional degree of freedom to the opening action of the valve such that the flow path of gases may be optimised as desired (for example the extent or angle of the inlet may be optimised).

The valve head and valve seat may have cooperating seating surfaces wherein the seating surfaces are substantially parallel or diverged towards the periphery of the valve head.

In some arrangements, the opening of the valves in a cylinder may further be optimised by arranging the valves to rotate in opposing directions. For example one valve may have a left handed helical formation while another has a right handed helical formation. This may allow the valves head to be moved in opposing lateral directions.

According to a further aspect of the invention there is provided a cylinder for an internal combustion engine including a poppet valve according to embodiments and a cylinder head having an inlet port and an air inlet pipe connected thereto where the disposition and/or orientation of the port and/or pipe is selected for creating generally circumferential air flow within the cylinder.

In one embodiment the cylinder head may have two inlet ports and two outlet ports, where the inlet ports are diametrically opposed to each other and the outlet ports are diametrically opposed to each other. In this arrangement it is particularly preferred that the inlet ports are disposed or orientated such that the air will flow in the same direction from each port.

This arrangement is considered novel and inventive in its own right and as such a further aspect of the invention comprises a cylinder for an internal combustion engine including a cylinder head having an inlet port and an air inlet pipe connected thereto and an exhaust port and an exhaust pipe connected thereto, wherein the exhaust pipe is generally orthogonal to the inlet pipe. The cylinder may include two diametrically opposed inlet ports and an inlet pipe connected to each inlet port and two diametrically opposed outlet ports and an exhaust pipe connected to each outlet port and wherein the exhaust pipes are generally orthogonal to the inlet pipes. In a specific embodiment of this construction one inlet port may be orientated so that its air flow is directed to circulate within the cylinder generally within the airflow of the other inlet port.

In any of the embodiments at least one inlet pipe may have an axis tending to the horizontal. The greater the horizontal component of the momentum of the air flowing into the cylinder, the more likely that the initial flow will be generally circumferential. This arrangement can be enhanced or improved wherein the respective plane in which the, or each, inlet port lies is inclined towards the axis of the cylinder.

It will be understood that with a conventional poppet valve, the valve may detract from achieving a generally circumferential flow, because it tends to sit in the intended air path. This problem can be removed or mitigated by using poppet valve assemblies in accordance with embodiments of the invention.

Whilst the invention has been described above it is to be understood that it includes any inventive combination of the features set out above or in the following description or drawings.

Brief Description of the Figures

The invention may be performed in various ways and specific embodiments will now be described, by way of example only, and with reference to the accompanying drawings, in which:

Figure 1 is a schematic view of a valve assembly of a conventional internal combustion engine;

Figure 2 illustrates one embodiment of the valve of the present invention; Figure 3 illustrates a further embodiment;

Figure 4a illustrates the assembly of a helical valve and a helical valve guide;

Figure 4b illustrates the degrees of design freedom in the valve;

Figure 5a is a sectional view through a valve guide and Figure 5b is a view on one end;

Figure 6 is a view from above of a cylinder;

Figure 7 is a partial side view of the cylinder of Figure 1 ;

Figure 8 is a perspective view of the cylinder head of the cylinder of Figure 6, with the head inverted;

Figure 9 is a side view of a helical valve assembly according to an embodiment of the invention;

Figure 10 is a side view of the valve and guide of Figure 9 with other features omitted for clarity;

Figure 1 1 A-C shows the different valve opening provided by a conventional, stepped back and stepped back helical valve;

Figure 12A-C show the arrangement of valves in a radial cylinder head and pent roof cylinder head;

Figure 13 shows the valve layout for a radial cylinder head in accordance with an embodiment of the invention;

Figure 14 shows a close-up of the valve seat and valve opening in an embodiment of the invention;

Figure 15 shows a stepped valve (15A) and a stepped helical valve (15B) according to an embodiment of the invention; and Figure 16 shows a close-up cross-section of a valve guide for use in embodiments of the invention.

Detailed Description of Embodiments

The differences between a pent roof and radial cylinder head will now be explained.

A pent roof design of cylinder head, as the name suggests, revolves around the shape of the pent roof, i.e. the inlet bank of valves is on one side pent roof and the exhaust bank of valves the opposite side of the pent roof. Such an arrangement is shown in Figure 12B.

The inlet valves are situated parallel to each on one side of the pent roof and the exhaust valves are situated parallel to each other on the opposite side.

There are normally two cam shafts driving each bank of valves, one cam shaft driving the inlet bank and other camshaft driving the exhaust bank. The camshaft pushes the valves open in one direction and the valve springs returning them in the other direction pulling the valve back to the valve seat. This is also happening on the other bank but at different times, hence valve timing.

If you were to look at a four valve pent roof cylinder head, it has a pent roof shaped combustion chamber this is due to its mechanical design and it cannot be changed into a hemispherical combustion chamber.

The design of a radial cylinder head is totally different and, as the name suggests, revolves around the four valves radiating out from a central focal point with each valve stem splays outwards from that central point radiating outwards. Then the ends of the valve stems are spaced roughly at an equal distance apart. Such an arrangement is shown in Figure 12A.

This type of configuration is the best for creating the perfect hemispherical style of combustion chamber. One of the problems with this type of design is that it is difficult to drive the radiating valves. This is because the valves are radiating outwards at different angles. To drive the valves a configuration of rocker arms is typically needed which involves some complex geometry and a lot of moving parts.

A key factor in engine design is to have as few moving parts as possible since more moving parts have potential to cause more problems, i.e. reciprocating weight causes huge amount loss in the form of energy and a lot of wear and tear.

Further, a radial cylinder design requires the reduction in size of valve heads unlike the pent roof style of design of combustion chamber which has larger valve heads.

The pent roof cylinder head does not have the ideal type of combustion chamber which is provided by the radial cylinder. Unfortunately, the radial cylinder head has smaller valves and typically requires a more complex rocker system. The helical valve system of embodiments seeks to bridge the gap between the two different types of cylinder head and creates a new type of hybrid engine and cylinder head.

Embodiments of the invention may be incorporated into a pent roof cylinder head which will now be explained in further detail. The pent roof cylinder head can have several combinations of types of valves to be fitted depending on the intended use of the engine. For example, a full race engine may require stepped back valves, the stepped back valve increases the valve aperture considerably more than any other poppet valve and is ideal to increase the Brake Horse Power of a Formula 1 Engine.

A different type valve may apply if the engine was designed for fuel efficiency and low exhaust emissions, for example, the helix valve.

The helical valve opens differently to the stepped back valve because it has a helical valve stem and valve guide.

The helical valve design opens up as much, if not more, than the stepped back valve, but helical valve has a unique feature when the valve opens it can also deflect and direct the incoming gases and mix the air and fuel together and create a more homogenous fuel mixture which is mentioned in detail herein.

A diesel engine could benefit even more with the application of the correct valve configuration especially if the helix valve was fitted with its deflectional and directional capabilities.

The helix valve can have either a right-handed helical drive or a left- handed helical drive. For deflecting and directing the incoming gases to the left or the right or in any part of the cylinder, both types of valve can also have different angled valve heads, this means there are too many combinations to list. For example, there are: different helix angles; different valve head angles; left and right-handed helix; valve stem located at different angles in the cylinder head; different amounts of camshaft travel which, in turn, alter the angle of the valve head and open or close the valve heads more or less. Also, the embodiments may be combined with a diagonally opposed or opposing inlet and exhaust design, with tangential porting.

When all of these factors are taken into consideration, it will be appreciated that embodiments of the invention provide a great range of design freedom to optimise the particular combinations and configurations for any particular engine.

For example, the following basic configurations for both types of cylinder head, the pent roof and the cylinder head with the hemispherical combustion chamber, could be provided:

(i) two stepped back valves on the intake and two standard poppet valves on the exhaust;

(ii) two stepped back valves on the intake and two stepped back on the exhaust;

(iii) two helix valves on the intake and two standard poppet valves on the exhaust;

(iv) two helix valves on the intake and two stepped back valve on the exhaust;

(v) two helix valves on the intake and two helix valves on the exhaust.

The benefits of embodiments for the internal combustion engine by enhancing the gas flow, valve timing and inertia will now be explained.

This valve according to embodiments can be made with different helix angles and head angle combinations to suit different types of applications.

One of these combinations has a reduced helical angle so much so the valve barely twists. If the helix angle is reduced any less it will not turn at all and become a stepped back valve which could have advantages in a Formula 1 cross flow race engine. This is because a race engine is a type of design that utilises a valve system that reduces the restriction the flow gases going in and out of the cylinder head of the engine this creates a cross flow hence the name.

The incorporation of a stepped back valve into the cylinder head of a race engine would increase the flow because the valve opens more with the same amount of lift. (It will be appreciated that the lift cannot be increased because the valves will hit the pistons.)

The helical valve is different to the stepped back valve. The helical valve has more than one function:

i. The helical valve lets in more fuel and air into the cylinder similar to the stepped back valve but they can open earlier.

ii. The helical valve can open up earlier and more and close later whilst the piston is approaching travelling through and past TDC (top dead centre).

This will be explained more below.

iii. When the helical valve opens the helical movement tips the valve heads such that the front leading edges move towards the piston which is coming up to TDC into the combustion chamber and then follows the piston as it descends from TDC.

At TDC the valve heads are very close to the piston, so much so that the manufacturers of the engines profile and reshape the tops of the pistons with what they call cutaways. These cutaways allow for the valves to open a certain amount while the piston is passing through TDC.

They put these cutaways in a piston because it is conducive with the valve timing, gas flowing and fuel mixture which is critical in relationship to the fuel efficiency, exhaust emissions and performance of the complete engine.

It will be appreciated that the interaction of the valves, piston and combustion gases is complex. However, some of the methods car manufacturers use to improve on an engine's fuel efficiency and performance will be described below. The degree of overlap will vary from engine type to engine type. On some Formula 1 engines it may be as much as 80° around TDC. It will be understood that different overlaps require different cam profiles.

Overlapping valve opening of the inlet valve and exhaust valve may be used such that the momentum of the exhaust gases (inertia) utilise the flow to clean out all of the spent exhaust gases out of the combustion chamber. This is called scavenging or purging.

To do this timing of the valves has to be very accurate but reaps dividends because by using the speeding exhaust gases which are now travelling out of the exhaust port at high speed, the inertia of these gases can be used to help the engine run better.

By opening the inlet valve slightly before the piston has got to the top of its stroke (TDC) momentum (inertia) of the exhaust gases may be used for beneficial effect. The speed of the exhaust gases may as they speed out of the exhaust port as they exit at such a rate the gases pull in the clean fresh gases through slightly open inlet valve and across the top of the combustion chamber which cleans out any spent gases from the previous cycle which then insures a better of air and fuel mixture for the next cycle.

A similar method is used to get more air and fuel into the cylinder during the intake stroke. When the piston gets to the bottom of stroke the gases are going so fast and because of momentum (inertia) the high speed gases carry on travelling into the cylinder with the piston coming back up. Then just before the incoming gases lose momentum and start to turn back the valve closes and traps an extra amount of fuel and air in the cylinder that is why a Formula 1 engine revs so much inertia.

When the helix valve is opening it twists slightly and does several things.

The helical valve opens up as much and more with a twist than a stepped back valve.

The helical valve design can be used to utilise the area in the combustion chamber to its advantage, the valve can open easier and better earlier and also have a piston without large cutaways in the tops and still retain the high compression ratio.

The helix valve has deflectional and directional capabilities for mixing the air and fuel together to create a more homogenous fuel mixture and directing the mixed gases into the correct part of the cylinder and combustion chamber.

All these attributes would result in a more efficient internal combustion engine and the reduction in fuel emissions.

Once the correct combination of valve angle and port design is achieved, further refinements could be made to the cylinder head by having a camshaft with a constantly variable adjustment of the amount of lift. The precise adjustment of amount of lift could then change the style of pattern of the swirl and tumble to suit the engines various output speeds creating the best fuel mixture possible in every part of the spectrum of the speed range.

With the new design of helix valve, as the engine speed increases the camshaft travel could automatically adjust one or both inlet valves in conjunction with each other or separately, which in turn would increase or decrease the one or both valve head angles together or separately. This would then alter the direction of the gases utilising both valve heads either singly or together to operate in unison with each other to create the correct type or style of the swirl and tumble required for all the different engine speeds. This variable camshaft adjustment would enable a more homogenous fuel mixture through an even broader band of the engines of speed range increasing fuel efficiency and reducing fuel emissions still further.

The application of a helical valve according to embodiments of the invention to advanced scavenging and purging will now be described in further detail.

As mentioned above, to improve performance there is a method known as scavenging or purging which involves a system called valve overlap.

This valve overlap utilises the exhaust gases and the velocity and inertia which are speeding out of the exhaust port at quite a rate. This inertia then can be used to pull in extra air and fuel into the cylinder and combustion chamber.

This is done by opening the inlet valve early at between 10 and 40 degrees before top dead centre (BTDC).

When the inlet valve is opened early (before top dead centre) several things have to be taken into consideration, for example: how early the valve can start to open in the amount of degrees (BTDC) without the valves hitting the piston; how far the valves can open with the piston at top dead centre (TDC) without them touching the piston; and how deep the cutaways are to be in the piston. These cutaways are in the pistons to relieve the valves and if they were not there, the valves would hit the piston at TDC.

Cutaways in the piston ensure it has a high compression ratio and uses the periphery of the outer piston edge to compress the gases from the outside to the middle of the combustion chamber. Thus, the air and fuel mixture is compressed into the correct area of the combustion chamber from outside the middle using part of the piston and cylinder head called the squish area.

Once the piston is at TDC, the outer edge of the piston is very close to the cylinder head. However, the combustion chamber starts to get deeper as you go towards the middle of the chamber where the spark plug is.

This is where the valve according to embodiments may provide further advantages. It utilises the area in the combustion chamber to its advantage. With a mechanical equation which is like a double-edged sword; the conventional poppet valve cannot do this. In particular, the new valve opens in a different way; the valve heads can open in part of the combustion chamber.

This feature of the embodiment gives you the ability to advance the inlet valve timing on the cam shaft considerably further and opens the valve a lot earlier due to the shape of the combustion chamber. Further, the size of the valve aperture also increases considerably whilst still allowing the piston to travel through TDC without any interference from the valves which have been opened to make a certain sized aperture for scavenging and purging effect.

In embodiments of the invention the pistons may not need cutaways in them for the valves to sit in, which means the compression ratio is higher than it was before. This is advantageous for the design because of the mechanics of the combustion chamber, i.e. there is a limit, and a maximum level of compression ratio that you can have before pre-ignition occurs.

If pre-ignition occurs, an engine will lose power, but the embodiments of the invention may have a further advantage of having too much compression. It would mean that the combustion chamber would have to be larger in order to accommodate the extra amount of fuel and air mixture going into it.

This would be advantageous because of the higher compression ratio which was created due to the pistons not having cutaways in them. A larger, deeper combustion chamber would have to be created which would be beneficial because it means that the valves can open up even more than they would otherwise, which magnifies the earlier equation of the already advanced valve timing and larger valve apertures.

Thus, it will be understood that the resulting cylinder head may have an increased level of valve overlap with valves that open a lot earlier and with a greater valve aperture than before without losing any of the compression ratio, which is needed to enhance the design of the combustion chamber.

Embodiments may therefore be utilised to create an engine with a novel advanced scavenging and purging system which would provide a significant increase in an engine's performance.

A poppet valve assembly 10 is generally indicated in Figure 1 and 9. The assembly comprises a valve element 1 1 including a stem 12 and a head 13. The stem 12 is received in a valve guide 14. Axial downward movement of the stem 12 lifts the valve head 13 from the seat 15 opening an inlet air path generally indicated at 16. The stem 12 carries a valve spring retainer 17 at its end remote from the valve head 13 to receive springs 18 that act to return the valve head 13 to its seat 15.

A rocker arm 19, which is mounted on an axel 20, can be rotated by means of a cam follower 21 , which is engaged on a cam shaft 22. Lifting off the cam follower 21 causes the end 23 of the rocker arm 19 to move the stem 12 axially downwardly and hence displace the valve head 13 from its seat 15. It will be appreciated that many engines omit the rocker arm and, instead, are provided with a cam follower at the end of the stem 12 on which the cam directly acts (as shown in Figure 9).

This construction and operation of the conventional poppet valve assembly for an internal combustion engine is well known to those skilled in the art. It will be observed that if the head 13 is displaced by axial movement of the stem 12 from the seat 15 then it will open up an annular gap through which air can enter into the cylinder space 24 so that however smooth the air path 16 has been made up to that point, the valve head 13 is acting as a restriction and turbulence will arise around its periphery. As can be seen in Figure 2 the Applicant's novel and inventive approach is to cause the valve head 13 to move laterally as well as axially when opening in response to axial movement of the stem whereby the valve head can be significantly moved away from the air path 16 thus removing the problems set out above. As will be explained in more detail below, the Applicant's invention allows for a wide range of different movements and an alternative movement can be seen in Figure 3. It is indeed possible to achieve a substantially lateral movement, once the valve is lifted off the seat, in the manner of a slide valve or the equivalent of the valve head rotating through an axis which is orthogonal to the axis of the stem. For example, such an axis could pass through the centre or the edge of the valve head. Thus, the skilled person will appreciate that the movement of each valve within a cylinder may be carefully tailored by the engine designer to achieve the desired inlet arrangement and flow within the cylinder.

One way of achieving this functionality is best illustrated in Figures 4A, 10 and 1 1 B. It will first be noted that both the valve guide 14 and the stem 12 have cooperating helical formations 25, 26. The helical formations 26 of the guide, can be even better seen in Figures 5a, 5b and 16.

It will be understood that as the stem 12 moves axially within the guide it will also be rotated hence also causing rotation of the valve head.

The resultant movement is dependant in part on the degree of offset of the connection between the stem and valve head 13 from the centre point of the valve head and in part the angle of inclination of the stem 12 relative to the front face of the valve head 13. This point of connection is illustrated at 27 in Figure 4a and Figure 4b illustrates how there are considerable numbers of degrees of freedom for the designer in using various points of connection and various angles of stem inclination. Figures 2 and 3 for example illustrate the difference in movement which can occur. In Figure 2 the movement is substantially a lateral panning movement, whereas in Figure 3 the valve head appears more to be tipping about its edge. Figure 14 shows an example of a valve head 13 lifting and rotating from the valve seat 15.

The valve stem 12 is provided with a sealing surface 15 between the helical formations 25 and the valve head 13. The sealing surface 15 is a plain cylindrical section of the stem 12. The valve guide 14 is provided with an oil seal 30 at its forward end (i.e. the end closest to the valve head 13) for sealingly engaging the seal surface 15. An oil feed 32 may be provided above the seal.

If the valve is being used in a racing or development engine, it is possible for tuning purposes at least, to vary the angle of connection between the valve stem and valve head so that a range of different movements can be tested and a valve then made up in accordance with the preferred option. Alternatively, the valve and/or cylinder may be modelled in a CAD system and the flow the flow may be modelled using Computational Fluid Dynamics to optimise the valve opening position. This would allow both the degree of rotation and the stem inclination to be varied until a desired configuration is found.

Figure 1 1 provides an example of how embodiments of the invention may allow the valve opening to be improved. Three valve arrangements are shown each having the same example valve lift of 1 1 .5mm. With the standard poppet valve of Figure 1 1 B (having a stem which is perpendicular to the valve head) this provides an inlet opening of 9.9mm. With an angled or stepped-back poppet valve of figure 1 1 A (in which example the valve is set back to an angle of 60°) the valve opening is 13.2 mm. With a helix valve in accordance with embodiments of the invention of Figure 1 1 C the valve may be rotated such that the opening is, for example 18.5mm (dependent upon the amount of rotation chosen by the designer. Additionally, it will be noted that the helix valve of figure 1 1 C acts to direct the inlet gases in a chosen direction.

Embodiments of the present invention could be combined with any such systems to further optimise the operation of the engine and may, for example be useful in fine tuning the engine performance in one particular operating condition or to improve performance across a range of conditions. The poppet valve assembly according to embodiments of the invention could be particularly beneficial in engines with a variable valve timing or variable valve actuation system.

Embodiments of the invention are considered to be particularly applicable to a radial cylinder head 300 as shown in Figure 12A. In conventional radial cylinder heads, the stems of the valves are splayed as they generally extend in a radial direction which is generally perpendicular to the valve seat 15. However, by using the valve assembly of embodiments of the invention, it is possible to provide a valve stem 12 which extends at an angle to the valve head 13 such that a more convenient valve assembly may be provided. As shown in Figure 13, the valves may be arranged in pairs on either side of the cylinder (i.e. one pair for the inlet and one pair for the outlet) in a similar arrangement to that which is normally found on a pent roof cylinder head 310. It will be noted that the angle of head 13 relative to the stem 12 on each valve is carefully chosen such that the two inlet stems 12A and 12B have a linear actuation path which is parallel and the two outlet stems 12C and 12D also have parallel actuation paths. A skilled person will understand that this advantageously enables a conventional overhead cam arrangement to be used with a radial head cylinder. Further, as best seen in Figure 12C, the rotation of the valve in accordance with embodiments of the invention allows the direction of valve opening to be tailored within the radial cylinder head 300. In this Figure, two of the valves 13A and 13B have been opened with a similar amount of valve lift but differing rotations such that one valve 13A demonstrates how gases (whether inlet or outlet) can be directed to some extent across the cylinder while the other valve 13B has been rotated such that gases would be directed to some extent along the axial length of the cylinder. Thus, it will be appreciated that the angle of the valve head may easily be varied for a particular engine. It will further be noted in this example that the lower shoulder of valve 13A has moved a lesser distance into the cylinder than the lower shoulder of valve 13B despite the valve lift being approximately equal. This demonstrates the ability of the valve assembly according to embodiments of the invention to utilise an early opening of the valve 13A into the combustion chamber with minimal opening towards the piston.

The applicant has also designed an alternative cylinder head arrangement which can also utilise advantages of the new poppet valves. A cylinder according to one such embodiment, and generally indicated at 210, is shown in figure 6 to 8. The cylinder 210 includes a cylinder head 21 1 and a cylinder body 212, which defines an internal cylinder chamber 213. The cylinder head 21 1 has a pair of diametrically inlet ports 214 with respective inlet pipes 215 and corresponding outlet ports 216 and outlet pipes 217. It will be noted that the inlet pipes 215 and ports 214 are disposed and orientated such that the air flow into the chamber 213 will be generally directed towards the wall 18 of the cylinder body 212 causing a generally circumferential flow to be set up. The circumferential nature of this flow can be enhanced by having the direction of flow of the air into the chamber 213 with a substantial horizontal component.

It will be noted that in the particular embodiment shown in Figure 8 the ports 214 and 216 are inclined towards the axis 219 of the chamber 213, which enables the inlet pipe to lie at a more horizontal orientation than exists in existing engines.

The relative orientations of the inlet pipes 215 and outlet pipes 217 can be adjusted in accordance with the design characteristics of the particular engine in which the cylinder is to be used. In some embodiments the inlet pipes 215 and/or their respective ports may have slightly different orientations so that the airflow of one is directed to lie within the majority of flow of the other. This may enhance the level of flow within the full cross section of the cylinder.

It will be understood that when in the specification we speak of generally circumferential flow, this refers to the initial input of the airflow. As in well known in the art air is drawn in as the piston descends under the influence of atmospheric pressure and so there will always be an axial component to the inflow into the chamber 213 resulting in a spiral until the point at which the inlet stroke of the piston is complete.

It will be understood that the outcome will remove much of the flow shadowing of existing arrangements and may also enhance mixing because of the twisting flow.

This later cylinder arrangement may be beneficial in two senses. First it may enhance the power output of a high performance engine, such as a Formula 1 engine. In that case smoothness of flow, when balanced with good mixing, will be the priority. Alternatively designers may wish to seek for particular high fuel efficiency in which the mixing capabilities of the Applicant's arrangements may be given higher priority. In that case it may be desirable to place a spin on the incoming airflow, for example by providing internal rifling on one or more of the inlet pipes. It will be understood that many designs will seek to balance these benefits, as has been achieved in the hemispherical cylinder head of Figures 12A and 12C.

The cylinder inlet design of this embodiment can be usefully combined with the poppet valve assembly as described herein such that the engine designer may optimise the conditions within the cylinder for a desired performance and/or economy at particular engine loads.

Embodiments of the invention may provide one or more of the following advantages:

• More air and fuel into the cylinder.

• The enhanced porting achievable due to the unique valve design.

• An increased in gas flow achievable by alleviating the friction of the gases on the back side of the valve head.

• The use of the same technology on the exhaust port.

• Having a more direct and inline inlet and exhaust port with less obstructions.

• The design is also used to induce a more laminar air flow into the cylinder elevating dead spots etc. • The unique scavenging and swirling motion that will maximise the flow and give a more homogenous fuel mixture which will in turn give a better flame path and therefore an increase in the engines BHP, fuel efficiency and reduce the exhaust emissions.

• An increased level of fuel mixture dispersal throughout the cylinder and combustion chamber thus utilising the areas which otherwise would not be accessible to enhance performance.

• A level of resilience to wear comparable to a poppet valve.

• Two different approaches in port design (a) increased BHP of an engine (b) to increase fuel efficiency.

• Designed to withstand the high levels of load and stress found in top level race engines.

• Applicable with turbo charged engines and super chargers.

• The cylinder head and valves are suitable for all types of four stroke engines which run on petrol, diesel, gas or any other combustible fuel including bio and alcohol fuels.

Although the invention has been described above with reference to one or more preferred embodiments, it will be appreciated that various changes or modifications may be made without departing from the scope of the invention as defined in the appended claims.

The skilled person will appreciate that the ideal cylinder flow for an engine is dependent upon multiple factors and, therefore, the particular implementation of the invention will be dependent upon the particular of engine in which the invention is being embodied. Through routine design optimisation the skilled person would be able to implement embodiments of the inventions to provide the required flow of any particular engine. For example, the ideal cylinder flow may differ depending upon whether the engine is a normally or forced aspiration (for example turbo charged and/or super charged) engine. Additionally direct injection engines may require a different cylinder flow (for example a stratified fuel charge may be used under certain loads). Further, engines may be arranged to operate in different fuel burn modes (e.g. lean burn, stoichiometric and full power) depending upon the power required during operation.

The skilled person will further appreciate that the variations in stem angle, rotation angle and valve opening, etc, required in practice may be very small to achieve the desired aerodynamic effect on the flow into the cylinder. As such, it will be understood that the figures in the present application may be considered to be somewhat exaggerated for clarity.