Conventionally, the shaft of the poppet valve slides in a hole in the cylinder head called valve guide. As many other components of internal combustion engines, the shaft and the head of a poppet valve and the valve guide as well as the valve seat of the cylinder head are subjected to considerable thermal and mechanical load and stress. High thermal and mechanical loads are usually connected with increased wear, it is therefore desirable to have a valve providing decreased wear and improved lubrication characteristics, compared to conventional poppet valves of internal combustion engines.

It is desirable to reduce the wear between a valve shaft and the valve guide of an internal combustion engine.

To reduce wear between the components it has been tried to use e.g. sintered valve guides, or to use coatings of valve shafts that tend to form cracks which in turn may serve to contain a lubricant to act as a kind of oil reservoir to ensure immediate lubrication during operation of an internal combustion engine. However the use of coating being prone to form microscopic cracks has the severe disadvantage that it is on one hand difficult to control the formation of the cracks in size and extension and on the other hand it is tried not to weaken the structure of the coated shaft. According to the present invention a poppet valve is provided having improved sliding characteristics, comprising a valve head, a valve shaft, and a valve shaft end, wherein a sliding surface is provided to extend along said valve shaft between said valve head and said shaft end and wherein said sliding surface is provided with at least one recess. The at least one recess is provided to serve as a kind of lubricant or oil reservoir to improve the lubrication between the valve shaft and a valve shaft guide in a cylinder head of an internal combustion engine. In a basic embodiment the recess may be embodied as a hole or a channel-like recess, that may be embodied as a circumferential ring-shaped recess. In a more complex embodiment a single recess may be embodied as a kind of helix. It is also considered to use a kind of tree- or root-like structure to implement the recess. It may also be possible to implement the recess in a kind of fishbone-shape.

In an example embodiment of the poppet valve, said sliding surface comprises a slide-in portion, a slide-out portion and an intermediate slide portion. The slide-out portion is located close to the head of the valve and is constituted by the part of the slide surface that during operation slides out of a valve guide when the valve opens. The slide-in portion refers to the part of the sliding surface close to the end of the valve shaft that slides into the valve guide when the valve opens. The intermediate slide portion or guide slide portion refers to the part of the sliding surface between said slide out portion and said slide in portion. That is the intermediate sliding portion is the surface of the valve shaft that during operation is always in contact with or inside the valve guide. This definition is important to be able to define different sections of the sliding surface, wherein it is preferred, that the openings or recesses in the sliding surface of the shaft are only located in the intermediate portion or in the intermediate portion and the slide-in portion of the sliding surface, to prevent that oil or lubricant is transported into the intake or exhaust system of an internal combustion engine.

In an additional example embodiment the sliding surface or at least said intermediate slide portion comprises round, square-shaped, rectangular or polygonal recesses. The terms “round, square-shaped, rectangular or polygonal” are to be considered in the wind off state of the surface of the valve shaft. This embodiment refers to recesses basically representing point or dot-like recesses providing punctiform oil / lubricant reservoirs on the sliding surface.

Another example embodiment of the poppet valve is provided with a sliding surface or at least with an intermediate slide portion that comprises linear recesses. In this embodiment the recesses basically represent lines that may be embodied in a circumferential direction or in an axial direction or preferably in a helical direction of the shaft. It is preferred that the recesses form e.g. parallel left- and right-hand helices on the surface of the shaft. In a different example embodiment of the poppet valve the sliding surface or at least said intermediate slide portion comprises arc shaped recesses. The arc- or crescent-shaped recesses are arranged in a scaled like manner. In this embodiment the recesses basically represent circle lines that can be arranged to form a kind of fish-scale like shape or dragon scale line arrangements. The scales may be oriented in a circumferential direction or in an axial direction or preferably in a helical direction of the shank. It is also contemplated to use axial rows or multiple rows of arc- or crescent-shaped recesses that altematingly face to the shaft end side and the valve head side of the valve shaft. Such an embodiment may produce a kind of zig-zag current of lubricant up and down the shaft of a poppet valve during operation.

Another example embodiment of a poppet valve are provided with round, cylindrical or frustum-shaped recesses. This embodiment is directed to the shape of the recesses itself, or rather to the cross section of the recesses, wherein the cross section forms a half circle, nearly a circle or a rectangle or a trapezoid. The shape of the recess effects the collecting and dispersing properties of lubricant in the gap between the valve shaft and the inner surface of the valve guide. Another exemplary embodiment of the poppet valve employs recesses having a pyramid- shape or having a triangular cross section or an inclined half-oval cross section in a plane parallel to an axial direction. Recesses having a pyramidal or triangular shaped cross section may be used to achieve different oil scraping and deploying characteristics. For example a triangular cross section having the shape of a right triangle wherein e.g. one of the legs represents the opening of the triangle shows good oil scratching properties as the leg and good oil deploying properties at the hypotenuse. That is by selecting the angles of a triangular shaped recess it is easily possible to control the lubricating properties of the recesses. An inclined half-oval cross section provides a simple way to implement a linear recess having a pump-effect without significant stress concentration effects. A half-oval cross section also provides the advantage that it it not necessary that the tip of the machining tool has to be too sharp. The half-oval cross section may also be interpreted as a very scalene triangle with a very rounded tip.

In another example embodiment the recesses are arranged on the sliding surface or at least on the intermediate sliding surface in rows. This row may be embodied as a single row in a circular ring shape or in a helical line, but it is also possible to use different rows extending in a circumferential direction. It is also envisaged to use short rows that in turn form a larger pattern of recesses. In yet another example embodiment the recesses are arranged on the sliding surface or at least on the intermediate sliding surface in a rectangular, triangular or hexagonal pattern.

That is the regular pattern may represent triangular, rectangular or honeycomb like patter as the sliding surface of the valve shaft. To improve the operation characteristics the main direction of the grid may be tilted to the axis of the shaft. A tilted grid may reduce the formation of chatter mark- or brinelling- like wear on the shaft or on the surface of the valve guide. It has to be kept in mind that the valve shaft is often rotated by“Tumomat ^tnl ” or “Rotocup ^tm ” devices at each valve opening by a fix angle and that the pattern of recesses should not“lock on” to a rotational or linear movement of the valve shaft to prevent uneven wear of the valve shaft or the valve guide sliding surface. Therefore it is desirable to avoid a movement of the sliding surface that corresponds to the grid of the recesses. The term honeycomb- like arrangement is also considered to encompass a net of recesses leaving only round or hexagonal lands as sliding surface, which is possible, as the depth of the recesses is to be considered small enough to avoid undesirable notching effects or stress concentration effects.

In another example embodiment of the poppet valve said recesses are arranged in a circumferential direction in a non-equidistant pattern. That is, the recesses do not form an even grid but a kind of uneven distribution to avoid that the grid may“lock on” an angle of rotation of a valve turning device or onto the movement of the valves which may result in uneven wear.

In one embodiment the arrangement of recesses has a rotational symmetry of one. A rotational symmetry of one represents, a rotational symmetry of 360° or in other words no such thing as a rotational symmetry. This may be achieved e.g. by an increasing distance of neighboring recesses. It is also possible to arrange the recesses in a helical way, to prevent higher rotational symmetries. For example to avoid a rotational symmetry a pentagonal 72° arrangement around the circumference may be replaced by 70°, 71°, 72°, 73° and 74° succession. This may result in a slightly uneven distribution of the recesses but all in all a rotational symmetry of 1 can easily be achieved.

In another example embodiment the arrangement of said recesses is balanced in a

circumferential direction, in an axial direction or overall. This may be achieved in case of the 70°, 71°, 72°, 73° and 74° rotational symmetry- 1 -distribution e.g. by rearranging the distances to 70°, 74°, 71°, 73° and 72°, to avoid any lack of balance. This may result in asymmetry similar to old engine cooling fans with an uneven distribution of fan blades to avoid any resonance caused by an even vibration of the air in the engine compartment. A similar approach may also be used for the distribution of recesses on the valve shaft.

In another example embodiment of the poppet valve, said at least one recess is produced by needle impact, laser engraving or photoengraving, etching or electrical discharge machining. Needle impact is a simple method to reshape the surface. Due to the impact crater created by the needle impact it may be necessary to post-process the sliding surface after needle impacting. Laser engraving provides a fast and simple method for machining recesses into a surface without or only minimal post-processing. Photoengraving and etching as well as electrical discharge machining, may be used to surface processing without any post processing of the surface at all.

In one embodiment said at least one recess has a radial depth between 3 pm and 100pm preferably between 5pm and 50pm and more preferably between 8pm and 15pm. That is, the size of the recess is less than 1/lOmm. The size of the recesses is intended to be rather small to avoid any interference between the rims of the recesses and the sliding surface of the valve guide. In another example embodiment of the poppet valve said at least one recess has an axial width between 5 pm and 200pm preferably between 10pm and 100pm and more preferably between 20pm and 50pm. This does not define a length of the recess in case of linear or crescent recesses but the width in a cross section in a direction normal to a local longitudinal direction of said recess.

In the following the present invention is described by means of exemplary embodiments.

Figures 1A and IB show a conventional valve in cross sectional views, to define the different portions of the sliding surface of the valve shaft.

Figures 2A to 2C show an embodiment of a valve according to the invention in side view, a developed view of the sliding surface and an enlarged partial cross sectional view of three recesses. Figures 3A and 3 B each show an embodiment of a valve, having slightly differing patterns of recesses, in a side view and in a developed view of the sliding surface.

Figures 4A, 4B, 4C and 4D show different possible patterns of recesses each in a developed view.

Figures 5A to 5B show an embodiment of a valve having a linear spiraling pattern of linear recesses, in a side view and in a developed view of the sliding surface.

Figures 5C to 51 show enlarged partial cross sectional views of linear recesses.

Figures 6 A to 6C show an embodiment of a valve having a crescent shaped recesses arranged in a fish-scale pattern, in a side view and in a developed view of the sliding surface as well as an enlarged partial cross sectional view of three recesses.

In the following the present invention is described by schematic non-scale diagram to visualize the principle of the present invention. In the figures as well as in the specification similar or like reference numbers are used to refer to similar or like components and elements.

Figures 1 A and IB each show a conventional poppet valve 42 in a cross sectional view, and is provided to define the different portions of the sliding surface of the valve shaft. Figure 1 shows a conventional poppet valve 42 inserted in a cylinder head and guided by a valve guide 44. In figure 1 the valve is closed and a conical part of the valve head 4 is in contact with valve seat 36 of a cylinder head 38.

The valve shaft 6 is in contact with an inner surface of the valve guide 44. In the closed position, the sections designated SO and IS are in contact with the inner surface of the valve guide 44. In figure IB the valve is in an open position, wherein the sections designated SI and IS are in contact with the inner surface of the valve guide 44. The section SO is called slide-out portion SO and the section SI is designated slide-in portion SI, while the part of the sliding surface between the slide in portion and the slide out portion is designated

intermediate sliding portion or intermediate sliding surface IS. The slide-in portion SI is located close to the valve shaft end 8. The slide-out portion SO is located close to the valve head 4.

In figure IB the valve is in an open position, where it is clear that the slide out portion SO extends into an intake / exhaust port 46 of the cylinder head 38. That a part of the sliding surface of the valve shaft 6 is exposed to intake / exhaust port 46 leads to a situation in which oil lubricating the valve shaft 6 may get into the combustion chamber or into the exhaust system and may cause harm or damage to a three way catalytic converter, or decrease the effectiveness of the combustion or the effectiveness of the catalytic process. The stroke S of the valve corresponds to the width of the slide in portion SI and the slide out portion SO. The length of sliding surface SL the valve guide corresponds to the sum of the length of the valve guide 44 and the length of the stroke S.

Figures 2 A shows a side view of an embodiment of a poppet valve according to the present invention. As in case of the conventional poppet valve it comprises valve head 4, a valve shaft end 8 and a valve shaft 6. A part of the valve shaft 6 serves as a sliding surface SL- The sliding surface SL comprises a slide out portion SO a slide in portion SI and an intermediate sliding portion IS. The sliding surface is provided at the intermediate portion IS and at the slide-in portion SI with a grid of recesses 10. In the recesses, tiny amounts of lubricant 48 may be stored and can serve as a reservoir to ensure sufficient lubrication during operation valve.

Figure 2B shows the wind of a developed view of the sliding surface SL that is also divided in the slide-in portion IS the slide out potion SO and the intermediate sliding portion IS. In the developed view it becomes apparent that the sliding surface uses a very regular arrangement or pattern of the recesses. It is also shown that the slide-out portion SO is not provided with recesses to avoid the leaking of lubricant 48 into the intake or exhaust port. The line CS shows the line along which the cross sectional view of figure 2C has been taken. It may be preferred that the pattern has a pattern repeat length that corresponds to the length of the stroke S. In case no valve rotator is used the axially aligned rows of recesses may cause an uneven wear of the valve shaft or the valve guide. In case a valve rotator is employed care has to be taken to avoid 51, 42° or 25, 71 ° rotators, as in these cased the valve rotation angle corresponds to the circumferential repeat of the recess pattern, which may in turn lead to a regular wear pattern, when the pattern always moves along the same path on the inside of the valve guide.

In figure 2C the single recesses 10 are depicted in an enlarged cross sectional view. The recesses 10 are embodied as substantial round recesses 12. The recesses serve as small reservoirs for a lubricant 48 such as oil that lubricates the gap between the valve shaft 6 and the valve guide 42. The round punctiform recesses 12 may hold enough oil to lubricate an area that corresponds to the square of the distance to a next recess 12.

Figure 3A and 3B each show an embodiment of valves having slightly different patterns of recesses. Figure 3A corresponds largely to figure 2A, in that a grid of punctiform recesses are arranged in a regular grid pattern 20 on the sliding surface of the shaft. In contrast to figure 2A the pattern of 3A is slightly helical. That is, in case the valve is rotated by a valve rotator each recess covers a slightly different path on the inside of the valve guide. With this amendment it is possible to avoid any wear pattern that corresponds to the pattern of the recesses. In Figure 3 A each axial row of recesses 12 of the grid is slightly displaced in an axial direction with respect to the neighboring row of recesses.

Figure 3B does not fully correspond to the pattern of 3 A, but to the pattern of Figure 2B that has slightly been rotated. That is, in contrast to the pattern of Fig. 3 A the rows of recesses 12 in fig. 3B are no longer parallel to the axial direction but are inclined to the axial direction indicated by the ordinate of the diagram. That is figures 3 A and 3B represent similar but different embodiments of valve shafts provided with pattern of recesses 12.

Figures 4A to 4D show different patterns of recesses or recessed patterns each in a developed view of a respective sliding surface. As figures 2B and 3B, figures 4A to 4D show developed views of different embodiments of sliding surfaces of valve shafts. In figure 4 A, the distances between the recesses have been varied in the circumferential direction in each row, while the distances in the axial direction have not been amended. It is possible to slightly shift some of the recesses in the circumferential direction without shifting the overall balance of the recesses. This has been used by engine cooling fans to avoid the buildup of acoustic resonances in engine compartments, leading to strangely deformed looking radiator fans.

This principle has been applied to each of the circumferential rows resulting in a pattern that has no rotational symmetry. Even though this pattern may seem to be prone to cause also an irregular wear pattern, this is avoided when valve rotators are used that turn the valves for small angles during each opening process. The irregular pattern avoids that the rotational angle and the circumferential repeat of the pattern may be equal. Figure 4B shows a completely irregular pattern of recesses. This pattern is neither regular in the circumferential direction nor in the axial direction. However, it is still possible to avoid any uneven distribution if e.g. the density of the recesses is maintained on a circular area at with a radius in the scale of 3 to 6 average distances between the recesses, to even out the irregularities on a larger scale. It is for example possible to employ the Penrose tiling to generate a nearly equidistant repetition free recess pattern with a very regular distribution of recesses.

Figure 4C shows an embodiment of a hexagonal pattern with linear recesses. As in the case of figure 3B it is also possible to employ a tilted version of this pattern.

Figure 4D shows a hexagonal pattern wherein the sliding surface is provided with a honeycomb structure recess. This embodiment enables a very good lubrication as all the recesses are connected which improves the distribution of the lubricant 48. As in case of figure 4C this pattern may also be tilted with respect to the axial direction. To avoid larger amounts of lubricant getting into the intake / exhaust port, the slide out surface is not provided with any recess, and serves as a kind of lubrication seal. Figures 5 A shows a side view of another embodiment of a poppet valve according to the present invention. The poppet valve corresponds to the one depicted in figure 2A, wherein instead of punctiform recesses linear recesses 14 are employed. The recesses each form helices that are inclined by approximately 45° to the axial direction of the valve 2. The linear recesses may not be limited and are depicted as extending nearly along the whole shaft 6.

The linear recesses may be machined with lower size compared to the punctiform recesses of figures 2A and 3 A as the greater length of the recesses make it possible to carry a similar amount of lubricant event with a smaller cross section i.e. smaller width and smaller depth compared to the punctual recesses. The use of helical recesses may help to ameliorate the notching effect that may occur in case of circumferential recesses.

Figure 5B shows the developed view of the sliding surface SL of the valve of figure 5 A. A slightly irregularly grid of linear recesses is used to improve effectiveness of the recesses. However, it is also possible to use a very regular pattern. In contrast to the depicted embodiment it is also possible to use shorter recesses that only extend for two, one or only a half or a quarter of the circumference resulting in an even more irregularly looking pattern. As in the case of the pattern shown in figure 4D, the pattern may provide a continuous recess from the valve head 4 to the valve shaft end 8. Figure 5C shows the linear recesses that are provided with a triangular cross section. The embodiment has a cross section that forms an isosceles triangle. The recesses serve as small reservoirs for a lubricant 48 such as oil that lubricates the gap between the valve shaft 6 and the valve guide 42. The linear recesses 12 may hold enough oil to lubricate an area that corresponds to a quarter of the distance to the next parallel linear recess 12, as the surface is provided with a grid of crossing recesses.

Figure 5D shows three linear recesses having a pear shaped cross section. The recesses serve as linear reservoirs for a lubricant 48 such as oil. Due to the pear shaped cross section the linear recesses may hold much more oil than the ones with the triangular cross section. In case of a helical recess this recess may cause a slight helical movement of the lubricant during opening and closing of the valve.

Figure 5D shows an embodiment having linear recesses having a half-circular cross section. This embodiment enables an increased oil containing volume compared to the triangular recesses of figure 5C. Additionally the half-circular recesses may be manufactured using conventional machining technology, in contrast to the ones of figure 5D, that may best be manufactured using a laser machining process. Figure 5F shows another embodiment of recesses having a triangular cross section. In contrast to the version of figure 5C, the triangle cross section does not form an isosceles triangle. The cross section of the recess is asymmetric. This results in different oil-scratching or oil-funneling properties on the up- or down stroke of the valve shaft in the valve guide. This feature may be used to improve a desired movement of the lubricant in the gap.

Figure 5G employs recesses having a triangular cross section wherein one leg of the recess is substantially normal to the surface of the valve shaft at least in a local scale. Compared to the non-uniform shape the pumping effect of the recess further increases as compared to the embodiment of figure 5F.

Figure 5H employs recesses having also a triangular cross section. In figure 5H both walls representing the legs of the triangle face in the same direction. Here the neighboring surface of the valve shaft and one wall of the recess a form an acute angle. This angle acts as a wedge and tends to cut a part of the lubricant layer and deflect it towards the recess. In the other movement direction the other wall and the inner surface of the valve guide form a kind of funnel to inject lubricant between the valve guide and the valve shaft. This design of the recesses also improves a pumping effect of the recess when the valve is moving up and down.

Figure 51 represents a kind of combination of figure 5E and figure 5H, wherein the cross section of a curved or half-oval recess is inclined with respect to the surface of the valve shaft. As in case of figure 5H the recess may show significant lubricant pumping effects.

Figures 6 A shows a side view of another embodiment of a poppet valve 2 according to the present invention. The basic features of the poppet valve correspond to the ones depicted in figure 2A. However, instead of round or linear recesses crescent or bend recesses 16 are employed. Additionally, the cross sections of the recesses are no longer symmetrically. The valve shaft is provided with crescent shaped recesses that form on a local basis a fish- or dragon scale like pattern. The shape of the crescent recesses 16 in combination with their arrangement and the cross section is intended to cause a transport of lubricant48 along the valve shaft. In figure 6A the recessed form a scaling that runs from the head 4 to the valve end 8, at the side the direction of the scaling is reversed and runs from the valve shaft end 8 to the valve head 4. The crescent recesses 16 are intended to have a non-symmetric cross sectional shape, so that the recesses itself cause a transport of lubricant when moved back and forth. As in the case of conventional fish scaling, the recesses are provided to move the lubricant in a direction of the apex of the crescent recesses 16. In figure 6A only the intermediate portion is depicted as being provided with the crescent recesses.

Figure 6B shows the fish-scale pattern in a developed view. In contrast to conventional fishes, the scale pattern comprises upward and downward parts. In one part the scale pattern is designed to move the lubricant in one part form the valve shaft end or the slide in portion SI to the vale head or the slide out portion SO. In another part, the scale pattern is reversed to move the lubricant in one part form the valve head or the slide out portion SO to the vale shaft end or the slide in portion SI. With this arrangement it is possible to achieve a very even distribution of lubricant with only a few strokes of the valve.

In figure 6B optionally the slide in portion SI and the slide out portion SO may also be provided with recesses (indicated by thin line crescents) to transport lubricant present in these areas towards the intermediate section or intermediate portion IS of the sliding surface SL.

Figures 6C show an embodiment of a valve having crescent shaped recesses 16 have a cross section in the form of a right triangle, wherein the hypotenuse of the right triangle extends away from the apex of the crescent. With such a recess, the scale pattern resembles the actual fish scale pattern in that it provides a significant directional preferential direction for the transport of lubricant 48. When moved back and forth, the lubricant is scraped by the rectangular leg from the surface of the valve guide while the pointed angle between the hypotenuse and the surface of the valve guide funnels the lubricant into the gap, resulting in a movement of lubricant from left to right during each stroke of the valve.

It may be noted that the shape of the recesses of the embodiment of figure 6A and 6B may also have the shape indicated in figures 5H and 51, to improve the movement of the lubricant. Reference list

2 poppet valve

4 valve head

6 valve shaft

8 valve shaft end

10 recess

12 round recess

14 linear recess

16 crescent recess

18 helical linear recess

20 grid pattern

22 row pattern

24 hexagonal pattern

26 irregular pattern

28 fish scale pattern

30 round cross section

32 triangular cross section

34 right triangular cross section

36 valve seat

38 cylinder head

42 conventional poppet valve

44 valve guide

46 intake / exhaust port

48 lubricant

SL sliding surface

SI slide-in sliding portion / sliding surface

15 intermediate sliding portion / surface SA slide-out sliding portion / surface