INTERNALLY COOLED VALVE FOR INTERNAL COMBUSTION ENGINES, AS WELL AS METHOD AND DEVICE FOR THE PRODUCTION THEREOF

Abstract

A method and a device for the production of an internally cooled inlet or outlet valve for internal combustion engines, together with the resultant valve includes provision of a workpiece, which has a cylindrical stem and a cylindrical hole and, extends in the axial direction from one end of the valve stem. The method includes reshaping the end of the valve stern by form rolling of the cylindrical stem to a smaller diameter, wherein a diameter of the cylindrical hole is reduced, wherein the cylindrical hole remains. The method further includes reshaping by form rolling the section of the workpiece that is adjacent to the valve stem to form the valve head.

Description

The present invention relates to cooled valves for internal combustion engines. More particularly, the present invention relates to a sodium-cooled intake or exhaust valve for an internal combustion engine, and in particular to its method of production, and to a device for the production of the valve by a rolling process.

Internally cooled, or more particularly, sodium-cooled exhaust valves have been of known art since 1935 at the latest.

Sodium cooling and its effects are well known in the prior art, and the technical advancements of recent years have mainly concerned an increased volume of coolant in the area of the valve disk and simplified production processes, so as to be able to produce sodium-cooled valves more cost-effectively.

However, there continues to be a need for cost-effective and rapid production of internally cooled valves, as well as for an improvement of the cooling properties of existing intake and exhaust valves. A need also exists to have available a cavity valve with maximum cooling performance, which continues to function reliably even at the highest exhaust gas temperatures. It is further intended to reduce the number of components and joint lines of internally cooled valves for reasons of robustness and cost.

In accordance with the present invention, a method is provided for the production of an internally cooled intake or exhaust valve for internal combustion engines, which, instead of being based on the metal-cutting methods of known art, is based on the reshaping of a workpiece, or a semi-finished product. The method comprises the provision of a workpiece, which comprises a stem and a cylindrical hole, which extends in the axial direction from one end of the valve stem. The valve stem end of the workpiece later forms the part that is located at the valve stem end of the finished valve. The valve stem end is reshaped by form rolling of the stem to a smaller diameter, wherein the diameter of the cylindrical hole is reduced, wherein the hole remains. The hole later forms the cavity for a coolant that can move in the cavity in order to transfer heat from an uncooled valve disk in the direction of a cooled valve stem. The method further comprises the reshaping by form rolling of a section of the workpiece that is adjacent to the valve stem to form a valve head. Here the valve head is also reshaped by form rolling. In this basic embodiment of the method at least the valve stem, with a bore located therein, is rolled to a smaller diameter. The method can also be applied to tubular workpieces so as to produce the stem and upper part of a valve disk, wherein a lower part of a valve disk can be formed by a cover, which is bonded to the upper part of the valve disk.

In a basic embodiment the method is based on the reshaping of a workpiece that comprises a cylindrical stem and a cylindrical hole located therein, extending in the axial direction from one end of the valve stem. The valve stem end is reshaped to a smaller diameter by form rolling of the cylindrical stem, wherein a diameter of the cylindrical hole is reduced, wherein the cylindrical hole remains, but can lose its cylindrical shape, since the workpiece is less strongly reshaped in the area of the valve disk than in the area of the valve stem end. The initially cylindrical hole later forms the cavity for a coolant.

Throughout the text, the term “workpiece” is used in the meanings of workpiece and semi-finished product, in order to avoid any unnecessary repetition of the corresponding terms, and any unnecessary prolongation of the text. The terms “workplace” and “semi-finished product” are here used synonymously.

The method comprises a reduction of the diameter of the stem and the bore located therein, together with a shaping of at least the rear face of the valve disk by form rolling. In the basic embodiment of the method, the nature of the formation of the valve disk face is not yet considered.

In an exemplary embodiment of the method, prior to form rolling, the workpiece comprises a diameter that is at least equal to that of the valve disk of the finished valve, and the method further comprises form rolling of a transition section between the valve head and the valve stem to form a concave fillet. By this means, the rear face of the valve disk is produced by form rolling. It is also envisaged that the chamfer for the valve seat and/or the disk rim will be generated by form rolling.

In a further exemplary embodiment of the method, the workplace is cup-shaped. The cup-shaped workpiece has a diameter at the base of the workpiece that corresponds at least to that of the valve disk. The cylindrical hole is designed as a blind hole, which extends from one end of the valve stem in the direction of the base of the cup-shaped workpiece, wherein the form rolling comprises a reshaping of the stem and a shaping of the valve head with at least the valve disk upper face. In this embodiment of the method, the chamfer of the valve seat and a valve edge are in particular also to be produced by form rolling. The base of the workpiece forms the valve disk face and can be brought into its final shape already before the form rolling process. However, it is also possible to provide a stub axle on the valve disk face in order to be better able to guide the valve during the rolling process.

In a further exemplary embodiment of the method for the production of an internally cooled valve for internal combustion engines, an outer base surface of the workpiece already has the shape of the valve disk. With a workpiece of this kind, only the rear face of the valve disk has to be processed by rolling and not the valve disk face.

In an additional exemplary embodiment of the method for the production of an internally cooled valve for internal combustion engines, the workpiece is cup-shaped and has a larger diameter at its base than in the area of the cylindrical stem. By this means, a thinner stem can be used for the workpiece, which enables easier processing in the form rolling process. Here the stem does not have to be rolled from a valve disk diameter to the valve stem diameter; instead a smaller amount of reshaping can be sufficient in order to be able to produce the valve with a cavity in the valve disk.

In a further exemplary embodiment of the method for the production of an internally cooled valve for internal combustion engines, the workpiece is held between the rollers by guides. The guides can comprise individual rollers that abut against an outer surface of the valve stem or valve disk. It is also envisaged that guides will be used, which are in sliding contact with an outer peripheral surface of the valve or workpiece, and hold the valve or workpiece centrally between the rollers. The rollers or sliders can be tracked so as to keep the axis of the valve or workpiece in the plane or surface that is spanned by the two axes of the rollers.

A further exemplary embodiment of the method for the production of an internally cooled valve for internal combustion engines includes hot rolling of the workpiece.

The method can also include heating of the workplace by heaters, such as induction heaters or gas burners, in order to enable a recrystallisation of the material of the workplace, and to counteract the effects of strain hardening.

In an additional exemplary embodiment of the method for the production of an internally cooled valve for internal combustion engines, the latter further comprises an axial movement of the workpiece in the direction towards the stem end during the rolling process. In this manner only a part of the stem can be rolled to a smaller diameter, which should reduce the mechanical load on the rollers and the rolling device considerably.

A further exemplary embodiment of the method for the production of an internally cooled valve for internal combustion engines further comprises a rotation of the workpiece during the rolling process. This does not relate to a machining process on a lathe; instead the workpiece is driven during the rolling process. This step can be advantageous if, as a result of profile turning, sections with different radii make necessary a variable slippage between the workpiece or valve and the rollers. By means of a drive, or active rotation, of the workpiece, adjustments can be made as to which slippage arises on which diameters or radii, and which radii are rolled without slippage during the form rolling process.

Provision can also be to reduce the outer diameter of the stem by turning, after a desired inner diameter has been achieved by rolling. In this case the rolling process merely serves to achieve the inner diameter of the cavity within the valve stem. Here the wall thickness of the material can be selected to be higher than the rolling process alone would require.

The method is based on a basic embodiment involving the reshaping of a workpiece that comprises a cylindrical stem and a cylindrical hole located therein, extending in the axial direction from one end of the valve stem. The valve stem end is reshaped to a smaller diameter by form rolling of the cylindrical stem, wherein a diameter of the cylindrical hole is reduced, wherein the hole remains, but can lose its cylindrical shape, since the workpiece is less strongly reshaped in the area of the valve disk than in the area of the valve stem end. The initially cylindrical hole later forms the cavity for a coolant. Here the cavity for the coolant has a larger diameter in the area of the valve disk, as a result of which the heat transfer from the valve disk to the coolant can be markedly improved.

In accordance with a further aspect of the present invention, a device is provided for the production of an internally cooled valve for internal combustion engines from a workpiece, or semi-finished product. The device comprises a rolling mill for round cross rolling or for skewed rolling, wherein at least two rollers have the profile of an outlet valve. Here the rollers comprise at least surfaces so as to reshape a stem and the rear face of a valve disk by form rolling. The device for the production of an internally cooled valve thus comprises forming rollers, which can roll a valve stem and the rear of the valve disk from a workpiece. In particular, the rolling mill is designed for the purpose of processing a hollow workpiece so as to produce a cavity in an internally cooled valve. Here the rolling mill is intended to reshape an essentially cylindrical hole or blind hole such that the largest possible cavity of an internally cooled inlet or outlet valve can be achieved. In one embodiment the device comprises only rollers, wherein additional guide rollers can be provided so as to guide the workpiece between the rollers. Owing to the large difference in diameter between the valve stem and the valve disk diameter, it is not possible to roll the valve with a rolling device that comprises three interacting rollers.

In an exemplary embodiment of the device for the production of an internally cooled valve, the device further comprises a mandrel that can be inserted into a hole of a workpiece, so as to guide the workpiece during the rolling process. On the one hand, the mandrel can serve as a guide, and on the other hand can serve as a gauge so as to indicate when an inner diameter of a rolled workpiece has achieved a prescribed diameter.

In a further exemplary embodiment of the device for the production of an internally cooled valve, the device further comprises at least one guide so as to hold and guide the workpiece between the rollers, wherein the at least one guide comprises a sliding element and/or one or a plurality of rollers, which abut against an outer surface of the workpiece. These guides hold the stem and/or the disk between the rollers so as to be able to exert a maximum rolling force on the workpiece.

In a further exemplary embodiment of the device for the production of an internally cooled valve, the at least one guide comprises a plurality of rollers, at least one sliding element, which abuts against an outer surface of the workpiece, and/or a mandrel extending into the bore of the workpiece. In this manner, the workpiece can be assigned a defined inner diameter in the area of the stem. Furthermore, a mandrel that can be lubricated or provided with a release agent can also be used for the purpose of achieving a reduction in the thickness of the wall of the valve stem, with an elongation of the valve stem. A polished mandrel can be pulled out of the cavity after the rolling process. The mandrel can also be tapered so as to facilitate extraction of the latter.

In an exemplary embodiment of the device for the production of an internally cooled valve, the at least one guide comprises a sliding element, or one or a plurality of rollers, that abut against an outer surface of the workpiece. The sliding element can be lubricated from an external source so as to reduce the friction and wear on the sliding element. Furthermore, the plurality of rollers can be matched to the contour of the valve so as to exert a uniform pressure on the workpiece during the rolling process. The guides can be arranged on both sides of the workpiece, or only on one side. The individual rollers of the at least one guide can also be arranged such that they can be displaced in the axial direction so as to avoid the rollers rolling in on the stem. The sliding element can have a contour that corresponds to the negative of the contour of the valve, so as to allow the most uniform possible transmission of force onto the workpiece.

In another exemplary embodiment of the device for the production of an internally cooled valve, the latter comprises at least one load cell on the at least one guide, together with individually driven rollers, and a controller that controls the rotational speed of the rollers such that the force on the guides is minimised. Here the workpiece is held centrally between the two rollers by means of a differential activation of the rollers, such that the load and the wear on the guides can be minimised. By means of an appropriate controller, the service life of the rolling device can also be increased, since the intervals at which the guides must be replaced can be extended.

In an additional exemplary embodiment of the device for the production of an internally cooled valve, the at least one guide comprises a plurality of rollers, at least one sliding member, which in each case abut against an outer surface of the workpiece, and/or a mandrel extending into the bore of the workpiece.

In a further exemplary embodiment of the device for the production of an internally cooled valve, the axes of the rollers are arranged skewed relative to one another at an angle of 1° to 12°, preferably of 2° to 10°, and more preferably of 3° to 8°. This embodiment relates to a skewed rolling method, in which the rollers are arranged separated at a distance from one another and not parallel to one another. Depending on the rolling direction and the separation distance between the rollers, a workpiece can be conveyed in the axial direction during the rolling process. This effect is particularly strongly pronounced if the (least) separation distance between the axes of the rollers is located near one end of the rollers. In this configuration, it has not yet been defined how the axis of the workpiece is aligned. It is possible to use an axis of the workpiece that runs parallel to an axis of the rollers. In this case, the workpiece is rolled adjacent to one roller, while the other roller is either in contact with only part of the surface of the workpiece, or has a surface that allows the whole surface to be rolled simultaneously.

In another exemplary embodiment of the device for the production of an internally cooled valve, the axis of the workpiece and the axes of each of the rollers are arranged skewed relative to one another at an angle of 0.5° to 6°, preferably of 1° to 5°, and more preferably of 1.5° to 4°. In this case the rolling device is a so-called skewed rolling device. In the case of skewed rolling, the roller axes are arranged crossed, or skewed, relative to one another. This generates a longitudinal feed in the workpiece as it rotates about its longitudinal axis. The workpiece is held in the nip by means of support blades or guide rollers. The roller gauge can be configured such that the nip narrows. Skewed rolling can also be carried out with correspondingly shaped rollers, such that overall a nip is formed with a constant separation distance. In the present case, however, the nip ideally has the contour of an intake or exhaust valve.

In an additional exemplary embodiment of the device for the production of an internally cooled valve, at least one of the rollers, preferably both rollers, has a hyperboloidal, or rotationally hyperboloidal, outer surface. For lack of a more appropriate name the term hyperboloidal, or rotationally hyperboloidal, outer surface here relates to a hyperboloidal shape that is not formed from straight lines or sections, but from the profile lines of an inlet or outlet valve, in particular of the stem and the rear face of the valve disk. The term hyperboloid here relates to a single-shell hyperboloid, which has the familiar waisted shape and forms circles sectioned, at right angles to the axis of rotational symmetry. The degree of skew of the shapes that generate the rotational hyperboloid is here intended to correspond exactly to the respective skew of the axes of the workpiece and the roller, since under these conditions (in the case in which straight lines generate the hyperboloid), a cylindrical workpiece can be rolled. If the hyperboloidal roller is produced with the profiles of a valve stern/disk, waisted rollers ensue, which can generate a valve with a straight valve stem using the skewed rolling process. This embodiment requires the greatest costs for the means of production, but at the present time can be expected to provide the best results.

In a further exemplary embodiment of the device for the production of an internally cooled valve, the device further comprises an axial guide or clamping chuck so as to guide and/or hold the workpiece, starting from the disk face. With the axial guide the workpiece can be pressed against the rollers in the axial direction so as to be able to form the concave fillet of the rear face of the valve disk. In a basic embodiment the axial guide just prevents the workpiece from moving axially out of the rollers in the direction of the valve disk during the rolling process. If a clamping chuck is used, the workpiece must also have a shoulder, on which the clamping chuck can grip the workpiece. The axial guide provides increased process assurance for the reshaping of the rear face of the valve disk.

In an additional exemplary embodiment of the device for the production of an internally cooled valve, the device further comprises an actuator that can move the workpiece axially away from the base in the direction of the valve stem end. The said actuator can act directly on the above-cited axial guide or the clamping chuck. By means of the actuator, the valve stem can be slowly rolled from the end of the valve stem in the direction of the valve disk, which can significantly reduce the load on the rollers. It is also possible to monitor and execute more precisely the process of reshaping the rear face of the valve disk.

In another exemplary embodiment of the device for the production of an internally cooled valve, the device further comprises a drive that rotates the workpiece during rolling at a predetermined and possibly variable rotational speed. Due to the large difference in diameter between the valve stem and the valve disk, strong torsional forces arise during rolling, which can destroy the workpiece during the reshaping process. It can therefore be necessary, during the profile turning of sections with different radii, to ensure a variable slippage between the workpiece or valve and the rollers. This can be achieved here by driving or actively rotating the workpiece, in particular the valve disk, in order to keep the torsional forces of the workpiece as low as possible, in particular at the transition section between valve disk and valve stem. The rolling device can also be provided with lubrication so as to maintain wear of the rollers as low as possible in sections in which slippage is present.

In another exemplary embodiment of the device for the production of an internally cooled valve, the device further comprises a heating element so as to heat the workpiece during the rolling process. Thus, a relatively small workpiece can be hot rolled even with relatively large rollers, without the need to fear too severe a cooling of the workpiece during the rolling process.

In addition, during the reshaping further energy can be introduced into the workpiece by means of inductive or autogenous heating, or gas heating.

The invention relates to a method in which, starting from a tubular or cup-shaped workpiece, a hollow valve head section and a hollow valve stem are generated by hot rolling. The valve that is generated can be produced without any joint lines, if the starting point is a cup-shaped workpiece. The valve that is generated can have an enlarged cavity in the area of the valve disk, so as to accommodate an increased volume of sodium in the valve as the coolant. A special feature comprises the reshaping by two rollers and a guide, wherein at least one roller is arranged at an angle relative to the workpiece axis and the second axis. Here each of the rollers also has, at the end face facing the workpiece axis, a negative shape or concave geometry of the valve head blank.

Both rollers are able to move towards each other during reshaping, wherein one roller can also be rigidly held in position and only the other roller (and the workpiece) can be moved. Here the workpiece during the reshaping process can rest on a base or guide, and is pressed by the movement of the rollers against the guide and thereby rotated. In addition, the workpiece can also be moved axially against the rollers, wherein the negative shape on the end faces of the rollers forms the concave geometry of the valve head blank. Here the position of a central axis of the workpiece can be located below the central axes of the rollers. So as to reduce the friction on the workpiece, the guide can be mounted on rollers.

In another exemplary embodiment of the device for the production of an internally cooled valve, at least one of the rollers has a surface structure that causes transport of the material of the workpiece in the axial direction. In this embodiment, a fine thread pattern or another roughened surface structure is applied onto at least one surface of one of the rollers. The thread pattern or other roughened surface structure can or should be primarily located on the inclined axis. Here the rollers can be produced from a metal alloy or a ceramic composite material, or in each case can comprise the latter.

By virtue of the angle of the roller(s) relative to the workpiece, and the thread pattern or other roughened surface structure on at least one of the rollers, a central tensile force is exerted on the workpiece, as a result of which an elongation of the blank can be achieved in addition to the diameter reduction.

In accordance with a further aspect of the present invention, an internally cooled valve for internal combustion engines is provided that has been reshaped and produced with one of the methods as described above, or with the device as described above. The valve is characterised in that, before reshaping, the workpiece comprises a stem and also a cylindrical hole that runs from one end of the valve stem in the axial direction. At least the stem of the valve has thereby been reshaped by form rolling of the stem to a smaller diameter, wherein the hole has been maintained and wherein the workpiece before the form rolling process comprises a diameter of at least that of the later valve disk, and wherein a valve head with a concave fillet is produced by form rolling,

In a basic embodiment the valve is reshaped from a workpiece that comprises a cylindrical stem and a cylindrical hole located therein, which extends from one end of the valve stem in the axial direction. The valve stem end has been reshaped to a smaller diameter by form rolling of the cylindrical stem, wherein a diameter of the cylindrical hole is reduced, wherein the cylindrical hole remains as a hole, but can lose its cylindrical shape, since the workpiece is less strongly reshaped in the area of the valve disk than in the area of the valve stem end. The initially cylindrical hole later forms the cavity for a coolant. With non-uniform reshaping, it is thus possible to produce a cavity with a larger diameter, and thus a larger surface area, in the area of the valve disk, which significantly improves the heat transfer between the valve disk and the coolant.

The valve is thus an internally cooled valve, and the stem and at least the rear face of the valve disk have been at least partially produced by the reshaping process. Here further machining process steps can follow in order to achieve the desired surface properties of the stem and/or the rear face of the valve disk. In a basic embodiment, the valve can also be reshaped from a tubular workpiece, wherein an opening on the valve disk can later be closed by means of a cover.

In another exemplary embodiment of the internally cooled valve, the workpiece is cup-shaped, wherein the cup-shaped workpiece has a diameter at a base of the workpiece that corresponds at least to that of the valve disk, wherein the cylindrical hole is a blind hole that extends from one end of the valve stem in the direction of the base of the cup-shaped workpiece. In this embodiment, a larger cavity can be generated in the area of the valve disk than was previously possible with a one-piece valve.

In a further exemplary embodiment of the internally cooled valve for internal combustion engines, the workpiece is cup-shaped and the cup-shaped workpiece has a larger diameter at its base than in the area of the cylindrical stem. Here it is intended that the inner diameter of the blind hole should essentially determine the diameter of the cavity in the area of the valve disk. By virtue of the smaller diameter of the cylindrical stem, the reshaping work and thus the residence time of the workpiece in the rolling device can be reduced. Furthermore, the wall thickness of the cylindrical stem can be increased, which in turn will have a positive effect on the reshaping process.

In a further exemplary embodiment of the internally cooled valve, after the reshaping process the cylindrical hole forms a cavity that extends within the valve stem and the valve disk, and which is partially filled with sodium and sealed.

In yet another exemplary embodiment of the internally cooled valve, this has been produced from a workpiece with a non-cylindrical stem with an outer contour and a cylindrical hole. By a reshaping process of the valve stem end by means of form rolling to form an essentially cylindrical valve stem, the outer contour is transferred at least in part to the non-cylindrical hole after the reshaping process. After the reshaping process the non-cylindrical hole has an inner contour that corresponds to the outer contour. This can be achieved with or without an elongation of the stem, during the rolling process. The dimensions of the outer contour that are required in order to achieve a desired inner contour can be determined relatively easily by means of experiments.

In what follows the present invention will be explained by way of illustrations of exemplary embodiments. The figures represent purely schematic illustrations.

FIGS. 1A to 1D illustrate an embodiment of an inventive device for the production of an internally cooled valve from a tubular workpiece, and the associated production method.

FIGS. 2A to 2C show a further embodiment of an inventive device for the production of an internally cooled valve from a cup-shaped workpiece, and the associated method.

FIGS. 3A to 3C illustrate a further embodiment of an inventive device for the production of an internally cooled valve from a short cup-shaped workpiece, and the associated method.

FIGS. 4A to 4B show an additional embodiment of an inventive device for the production of an internally cooled valve from a short cup-shaped workpiece by means of skewed rolling.

FIGS. 5A and 5B illustrate a further additional embodiment of an inventive device for the production of an internally cooled valve from a short cup-shaped workpiece, and the associated method.

FIGS. 6A and 6B illustrate a further additional embodiment of a workpiece and an internally cooled valve

In both the description and the figures, the same or similar reference symbols are used to refer to the same or similar components and elements. In order to avoid a description of unnecessary length, elements that have already been described in one figure are not separately mentioned in further figures.

In order not to make the drawings unnecessarily complicated, the parts of the rolling device that serve to carry, mount, or drive the rollers, or to move them at right angles to a roller axis, or in the direction of a workpiece axis, have not been illustrated. Any mountings or suspensions of guides and axial guides have also been omitted from the illustrations.

FIG. 1A shows an inventive rolling device with two forming rollers 42. The forming rollers are provided with stub axles 64, with which they can be accommodated in a housing of a rolling device. The forming rollers 42 can also be driven together or individually via the stub axles.

At the top of FIG. 1A, the axes are shown in a plan view, wherein the plane of the drawing extends essentially through the axes 48 of the rollers 42, and the axis 46 of the workpiece 14. The outer contour of the forming rollers 42 corresponds to the negative profile of an inlet or outlet valve that is to be rolled. Between the forming rollers 42 is arranged a tubular workpiece 14 with a through-opening or through-hole 28. The axis 46 of the workpiece 14 and the axes 46 of the rollers 42 are aligned in parallel. At the bottom of FIG. 1A the rollers 42 and the workpiece 14 are shown in a view in the axial direction. In FIGS. 1A and 1B the rollers are designed for a round cross rolling process. The rollers are designed as forming rollers 42. The respective directions of rotation of the rollers and the workpiece are indicated by the arrows 60. In round cross rolling, the workpiece 14 rotates about the axis 46 of the workpiece 14 in the opposite direction to the forming rollers 42 between two forming rollers rotating in the same direction. By the infeed of at least one tool, that is to say, one forming roller 42, the work piece 14 is reshaped. Here it is shown that both rollers are moved towards the workpiece 14 in the direction of movement and force application 62. However, it is also possible to move just one of the rollers 42 in the direction of the workpiece 14, i.e. to move it towards the other roller, wherein the axis of rotation of the workpiece 14 is displaced. Here the workpiece 14 is held in the axial direction by a clamping chuck 56, whose clamping jaws are shown. Here the clamping chuck 56 serves as an axial guide 54 so as to prevent the workpiece 14 from moving during the rolling process in the direction of what will later be the valve disk; such movement is brought about by the axial component of the rolling forces in the area of the rear face of the valve disk.

The form rolling process has, inter alia, the advantage that the molecular chain structure in the workpiece 14 is retained, which generates an undisturbed orientation of the fibres. As a result it can also be established on the basis of the crystal structure using metallurgical methods on the finished valve as to whether it has been produced, that is to say, formed, by forming rollers.

The axes 48 of the forming rollers 42 define a plane, and while the axis of the workpiece 14 lies parallel to this plane, it is not in this plane; instead in the drawing it is below this plane. In a rolling process, the workpiece 14 would be pushed downwards as soon as the forming rollers 42 initiate the rolling process. The workpiece 14 is therefore supported in the figure from below by a guide, more particularly, a radial guide 52, which serves as a radial guide. From an application of the force parallelogram it becomes clear that the force acting on the guide can be much lower than the rolling forces that arise as the forming rollers 42 move towards one another. A sliding friction can therefore be generated in the area of the support, even if strong rolling forces are generated by the rollers in the movement/rolling pressure direction.

It is also possible to lubricate the surface of the radial guide 52 so as to reduce the wear of the contact surface with the radial guide 52. During the rolling process, the guide can be tracked upward in the direction of the axis 46 of the workpiece 14, so as to reduce the load on the radial guide 52. It is also envisaged chat a multi-part guide can be used, which can adapt to the various stages of the reshaping process, in particular in the area of the valve head. It is also envisaged that instead of a rigid guide, a series of rollers can be used, which can be operated with less wear. The rollers can be moved in the axial direction in order to avoid local deformation of the workpiece by the guide rollers.

Above the workpiece, a heating element can be mounted opposite the radial guide 52, which heats the workpiece 14 by flame, radiation or induction, so as to ensure that hot rolling occurs throughout the whole of the reshaping process.

In the rolling method used, the workpiece 14, before the rolling process in the axial direction, can be displaced upwards until it is flush with the upper edge of the forming rollers. However, it is also possible to move the workpiece 14 upwards in the direction of the valve stem end during the rolling process, until the valve stem end is flush with the upper edge of the forming rollers.

Provision can also be made to drive the workpiece 14 by means of the clamping chuck, so as to achieve a slippage between the forming rollers 42 and the workpiece 14, in particular in the area of the valve disk, more particularly, the rear face of the valve disk. Since the rear face of the valve disk has a smaller surface area than the outer surface area of the valve stem, it seems advisable to generate a slippage between the rear face of the valve disk and the corresponding sections of the forming rollers 42, since otherwise the valve could be destroyed as a result of the torsional forces between the rear face of the valve disk and the valve stem. The angular velocity ratios between stem and valve disk are here at least as large as the corresponding radii ratios between valve stem and valve disk. With a ratio of the valve disk to valve stem diameter of about 5, in each case a ratio of the angular velocities for the average diameter of the valve disk to the stem diameter of about 2.5 ensues, which in a normal rolling process would be sufficient to turn or tear off the valve disk from the stem. Therefore, provision can be made to drive the workpiece 14 during form rolling at a higher speed in order to produce a slippage in the area of the valve disk, which significantly offloads the transition section from the valve disk to the valve stem and can thus prevent destruction of the workpiece 14 during form rolling. For this purpose the clamping chuck can set into rotation by a separate drive, not shown, if the latter is provided.

Furthermore, the rolling device can be provided with a single-roller rotational speed control, which is shown in detail in FIG. 1B, so as to reduce the wear on the radial guide 52. This is shown in detail in FIG. 1B. In order not to make FIG. 1A too confusing, the controller is not shown in the latter.

FIG. 1B shows the same elements as FIG. 1A, namely the forming rollers 42 and a finished form-rolled workpiece 14A, wherein the forming rollers 42 are shown in a position at the end of the rolling process. The depiction is purely schematic. The forming rollers 42 have reshaped the workpiece 14 into a reshaped workpiece 14A. The reshaped workpiece 14A still has a through-hole 28, which extends through the whole of the valve stem.

The form rolling device of FIG. 1B is provided with a load cell 66 for at least one radial guide 52, so as to measure the force with which the workpiece is pressed by the forming rollers 42 against the radial guide 52. The form rolling device of FIG. 1B is also provided with individually driven forming rollers 42 which can be activated individually at a selected rotational speed. The load cell or force sensor 66 is connected to a controller 68, which controls at least the rotational speed, that is to say, the drive, of one of the forming rollers 42, so as to limit the force that the workpiece 14/14A exerts on the radial guide 52 during the rolling process. Provision can also be made for the controller to control a rotational speed, more particularly, that of the workpiece, in order to reduce or at least limit the load on the radial guide 52.

Here the workpiece is held centrally between the two rollers by means of a differential activation of the forming rollers, or in another position, such that the load and the wear on the guides 52 can be minimised. The system can also be used in the case of rolling devices with two guides. By means of an appropriate controller, the service life of the rolling device can also be increased, since the intervals at which the guides must be replaced can be extended.

Although the controller for limiting the load on the radial guide 52 is described only in conjunction with FIG. 1B, it is explicitly emphasised here that the said controller should also be regarded as disclosed in the case of the other embodiments that are shown in the figures. The controller has been described only in FIG. 1B, as redundant repetition would only have increased the length of the description unnecessarily.

FIG. 1C shows the finished reshaped workpiece 14A, which comprises a part that essentially forms a valve body. The valve body has a valve stem 8, which at a lower end runs out into a valve disk 6, more particularly, the rear face 24 of a valve disk. The valve body does not yet comprise a valve disk face. The upper part of the valve stem 8 terminates in the stern end 36, with which the valve can later be activated. As illustrated, the stem end can be produced in the course of the form rolling process; however, it is also possible to shape the stem end 36 at a later stage.

The through-hole 28 has been reshaped into the cavity 10 in the valve disk 6 and the valve stem 8. It is also possible to produce just the cavity 10 by reshaping and later to bring the valve stem to a final diameter by a machining process, should it not be possible to achieve the parameters of the diameter of the through-hole 28, or blind hole, and the wall thickness of the workpiece, before and after the form rolling process.

The workpiece can be separated from the tubular remnant along the dotted line that forms the separation line 30. On the valve disk face there is still an opening 18, which can be closed at a later stage with a cover so as to form a finished valve.

FIG. 1D shows the finished valve 4 produced by means of reshaping. The valve body has a valve stem 8, which at a lower end runs out into a valve disk 6, more particularly, the rear face 24 of a valve disk. The opening 18 on the valve disk face 22 is closed by a cover 20, which has been bonded to the valve by friction welding, resistance welding, electron beam welding, or laser welding on a joint line 32.

The cavity 10 is filled with a sodium coolant 12. The coolant used is usually sodium, which is in a liquid state at the operating temperatures of the internal combustion engine. Usually it is not the entire cavity 10, but only ¼, ⅓, ½, ⅔ to ¾ of the cavity of the valve that is filled with sodium. In operation, the sodium in the valve stem 8, that is to say, in the cavity 10 of the valve stem 8, moves up and down and thereby transports heat from the valve disk 6 in the direction of the cooled valve stem S (shaker cooling). The sodium moves within the valve 2 during each opening and closing operation. The cavity 10 has been produced in the valve 2 in that the valve disk 6 has been provided on the valve disk face 22 with an opening 18.

FIG. 2A corresponds essentially to FIG. 1A. A description of reference symbols and elements that have already been described in connection with FIG. 1A will not be repeated here. Instead of a tubular workpiece 14, a cup-shaped workpiece 16 is now used, in which a base already forms the valve disk 6, that is to say, the valve disk face 22. Instead of a through-hole a blind hole 26 is used.

The diameter of the workpiece 16 is larger in the area of what is later the valve disk than in the area of what is later the valve stem 8. The workpiece already has, either essentially or precisely, the height of the later valve. Here the valve stem is formed essentially by form rolling. The valve disk can already be shaped to a large extent by a machining process. The cup-shaped workpiece 16 is held in the axial direction by an axial guide 54 so as to be able to form the rear face of the valve disk. Provision is also made to provide the cup-shaped workpiece 16 with a shoulder on which a clamping chuck can engage, so as to be able to rotate the cup-shaped workpiece during form rolling at a speed that can be selected. This was already explained in the description of FIGS. 1A and 1B. With a shoulder that is held in a clamping chuck, a slippage between the valve disk and the forming rollers can be achieved. The shoulder can be removed after the form rolling by a machining process.

In contrast to the embodiment of FIG. 1A, the wall thickness of that part of the cup-shaped workpiece 16, which later forms the valve stem, can be made thinner, which at a later stage results in a smaller wall thickness for the valve stem. Furthermore, in this design, the cup-shaped workpiece 15 is less strongly reshaped than the workpiece of FIGS. 1A/1B.

In FIG. 2B, the valve is already finished to a large extent after the form rolling. The cavity 10 has a large diameter in the area of the valve disk, which can be expected to result in improved cooling properties. The stem has a smaller wall thickness than in the case of FIG. 1B. By virtue of the lower degree of reshaping it is possible to roll the stem without it becoming necessary to reduce the outer diameter of the valve stem in a further machining process step.

FIG. 2C illustrates an internally cooled valve 4 in accordance with the invention, which has a valve stem that terminates at its lower end in a valve disk. The upper part of the valve stem 8 terminates in a stem end 36. Internally the valve is provided with a cavity 10, which is filled with a coolant 12. The cavity can, for example, be filled with the coolant through an opening or bore in the valve stem. In the area of the valve disk the inventive valve has a cavity with a large diameter, which can exceed the diameter of the valve stem. Here the valve disk, with the valve disk face 22, the rear of the valve disk 24, and the valve stem, are formed from one piece. The finished valve therefore has no joint lines, either in the area of the valve disk or in the area of the lower valve stem. It is possible to close the cavity 10 by means of a valve stem end attached, for example, by means of friction welding, after it has been filled with coolant.

FIG. 3A illustrates essentially the form rolling device of FIG. 2A. A description of reference symbols and elements that have already been described in connection with FIGS. 1A or 2A will not be repeated here. In contrast to the forming rollers of FIG. 2A, the forming rollers of FIGS. 3A are provided with a surface structure 58, which, during the forming rolling process, causes a transport of the workpiece material in the axial direction. The surface structure 58, which causes a transport of the workpiece material in the axial direction, is designed here as a thread pattern, which, with the rotation of the forming rollers 42, generates an axial force in the direction of what is later a valve stem end. With the surface structure, it is possible to use a shorter cup-shaped workpiece 16. In the form rolling process, a force is also exerted in the axial direction onto the cup-shaped workpiece, as a result of which the material during the rolling process can spread not only in the radial direction but also in the axial direction.

Here the surface structure 58 is embodied as a thread pattern. The thread pattern is designed with a small flank height and a small pitch, which only exerts forces, and does not roll a screw thread into the valve stem.

When the forming rollers exert a pressure on the cup-shaped workpiece 16, the material can flow not only in the circumferential and radial directions, but also, as a result of the axial forces, is able to flow, that is to say, to deform, in the axial direction. In overall terms this effect results in an ability to start with a cup-shaped workpiece with a larger wall thickness, which can significantly increase the process reliability of the method.

It is, of course, also possible to provide only one of the forming rollers with the surface structure 58, which causes transport of the workpiece material in the axial direction, or generates an axial force in the workpiece.

FIG. 3B illustrates the rolling process for the cup-shaped workpiece 16 in the direction of the valve stem end, wherein the material displacement is indicated by thin arrows.

FIGS. 3A and 3B can operate without an axial guide if the surface structure 58 generates a sufficiently large axial force to deform the rear of the valve disk face 24 by form rolling.

FIG. 3C shows a valve 4 that has been produced with the form rolling device of FIGS. 3A and 3B. It differs from the valve of FIG. 2C only in terms of the crystal structure of the material.

FIG. 4A corresponds essentially to FIGS. 1A to 3A. A description of reference symbols and elements that have already been described in connection with FIGS. 1A to 3A will not be repeated here.

FIG. 4A utilises the same short cup-shaped workpiece 16 as is shown in FIGS. 3A and 3B. Instead of cylindrical rollers, the axes of which are aligned parallel to one another, the embodiment of FIG. 4A and FIG. 4B uses hyperboloidal forming rollers 44, whose axes are skewed relative to one another. The rolling method represents an skewed rolling method, because the axis of at least one of the forming rollers is inclined with respect to the axis of the cup-shaped workpiece. Technically, the axes of the rollers are skewed relative to one another, wherein an angle between the axes can be specified as the angle in an orthogonal projection of the axes. Here the axes 48 of the forming rollers are each inclined at the same angle to the axis 46 of the cup-shaped workpiece 16. As a result of the inclination and rotation an axial force is generated in the direction of what is later the valve stem end during the rolling process. Thus a similar effect, can be produced as with the surface structure 58 in FIGS. 3A and 3B. It is also possible, of course, to equip the forming rollers of FIGS. 4A and 4B with an appropriate surface structure 58, such as was disclosed in FIGS. 3A and 3B. The forming rollers 44 form single-shell rotational hyperboloids, whose generators are not straight lines, but the profile of an inlet or outlet valve. Cylindrical rollers would not produce a cylindrical product, but rather a single-shell hyperboloid, since the separation distance between the axes of the rollers increases with the distance from the smallest separation distance. To compensate for this effect, the rollers themselves must have the shape of a single-shell hyperboloid. In skewed form rolling the rollers must also have the profiling of the final product, and thus form profiled single-shell hyperboloidal surfaces.

In contrast to the embodiments of FIGS. 1A to 3B, the workpiece is here guided by two opposing radial guides 52, which guide the cup-shaped workpiece 16 between the hyperboloidal skewed rollers 44. The guides must also be tracked during the form rolling process. Here it is also in particular possible to use the single-roller controller of FIG. 4B in the rolling device of FIGS. 4A and 4B.

The workpiece can be guided by an axial guide 54, but can also be held, guided and/or rotated, by a clamping chuck via a shoulder.

As in FIG. 1B, both radial guides 52 can each be provided with at least one load cell 66, each of which is connected to a controller 68, which in turn controls the rotational speed, that is to say, the drive, of at least one of the forming rollers 44. Here again, the controller can be used for the purpose of holding the workpiece 16 accurately between the rollers 44 and/or reducing the wear on the radial guides 52.

FIG. 4A illustrates the hyperboloidal forming rollers 44 in a final position after the form rolling process. When using hyperbolic forming rollers, torsional forces are generated in the stem, which are smaller at lower roller axis angles.

The larger the angle between the roller axes 48, the greater is the axial force generated.

The embodiment of FIGS. 4A and 5B can also operate without an axial guide, since a sufficiently large axial force is generated by the skewed rollers. It is also possible to deploy the surface structure 58 of FIGS. 3A and 3B in order to increase further the axial force generated during the rolling process.

FIG. 5A illustrates a combination of FIGS. 1A, 2A, 3A and 4A. As in FIG. 1A, the cup-shaped workpiece is only guided from one side by means of a radial guide 52. The left-hand forming roller 42 has the same shape as in FIGS. 1A and 2A, and the axis of the left-hand forming roller 42 is aligned parallel with the axis of the cup-shaped workpiece 16. The left-hand forming roller is designed as a hyperbolic forming roller 44, as in FIG. 4A. The hyperbolic forming roller 44 is also provided with the surface structure 58 of FIGS. 3A and 3B. The axis 50 of the hyperbolic forming roller 44 is inclined relative to the axis 48 of the left-hand forming roller 42 and the axis 46 of the cup-shaped workpiece. Thus, during the form rolling process the right-hand hyperbolic forming roller 44 generates a strong axial force in the direction of what is later the valve stem end. With a suitable design this axial force is sufficient to elongate a short cup-shaped workpiece 16 in the axial direction during the form rolling process.

FIG. 5B illustrates the rolling device at the end of the rolling process. In FIG. 5B the hyperboloidal forming rollers 44 are located in a final position after the form rolling process. As a result of the shape of the rollers, the left-hand hyperbolic forming roller 44 covers the upper valve stem end of the rolled valve. The shape of the rollers also causes the valve disk to cover the lower part of the left-hand hyperbolic forming roller 44. Likewise the right-hand hyperbolic forming roller 44 partially covers the valve disk of the reshaped workpiece 16A. The valve stem end covers the upper part of the line of contact of the right-hand hyperbolic forming roller 44 with the valve stem end.

With the one-sided guidance by the radial guide 52, the possibility arises of installing a heater opposite the radial guide 52, which heats the cup-shaped workpiece by way of, for example, an induction heater or a gas heater, so as to hold the workpiece 16 within a temperature range in which hot rolling, more particularly, hot skewed form rolling, is possible.

FIGS. 6A and 6B illustrate a further additional embodiment of a workpiece and an internally cooled valve. The workpiece that is shown in FIG. 6A corresponds essentially to the workpiece of FIG. 2A. In contrast to the workpiece of FIG. 2A the workpiece of FIG. 6A is provided with an outer contour 70. As in FIG. 2A, the blind hole 26 is designed as a cylindrical hole. The outer contour 70 together with the cylindrical blind hole 26 produces a thickness variation of the stem.

As a result of the reshaping process the outer surface of the stem is reshaped so as to be essentially cylindrical. Here the outer contour 70 is flattened and transferred inwards to the inner face of the blind hole 26, wherein an inner contour is formed internally in the blind hole. The thickness variation of the stem is essentially maintained, wherein the contour after the reshaping process is now formed on the inner face, i.e. in the cavity 10, as an inner contour 72. Here the inner contour is designed such that it forms a Laval nozzle at the transition section between the valve disk 6 and the valve stem 8. It should be understood that other inner contours can be generated using this method. It should likewise be understood that this principle can also be applied to the embodiments in which an elongation of the shank is also achieved during the reshaping process, as for example in FIGS. 3, 4 and 5. A to C respectively. At the same time just a broadening and flattening of the contour in the axial direction must also be considered. By this method it is easily possible to achieve shaped cavities 10 with good flow characteristics, which allow a conical transition between the stem and the valve disk. It can also be desirable to generate nozzle shapes, such as the Laval nozzle illustrated in the cavity 10. With this method, it is possible using very simple technical measures to generate almost any smooth or continuous inner contours 70.

It should be noted that all combinations of features of FIGS. 1A and 1B, to 5A and 5B, should also be considered as disclosed, inasmuch as they can be technically implemented. This relates in particular to the control or regulation of the individual roller speeds as a function of forces that have been measured on at least one radial guide. Furthermore, configurations are planned with one-sided and two-sided support by means of radial guides for all embodiments.

REFERENCE LIST

• 4 Inventive internally cooled valve
• 6 Valve disk
• 8 Valve stem
• 10 Cavity
• 12 Coolant
• 14 Tubular workpiece
• 14A Reshaped tubular workpiece
• 16 Cup-shaped workpiece
• 16A Reshaped cup-shaped workpiece
• 18 Opening
• 20 Cover
• 22 Valve disk face
• 24 Rear of the valve disk
• 26 Blind hole
• 28 Through-hole
• 30 Separation line
• 32 Joint line
• 36 Stem end
• 42 Forming roller
• 44 Hyperbolic forming roller
• 46 Workpiece axis
• 48 Forming roller axis
• 50 Hyperbolic forming roller axis
• 52 Guide/radial guide
• 54 Axial guide
• 56 Clamping chuck
• 58 Surface structure that causes a transport of the workpiece material in the axial direction
• 60 Direction of rotation
• 62 Direction of movement/roller pressure
• 64 Stub axle
• 66 Load cell
• 68 Control of the forming rollers rotational speeds
• 70 Outer contour
• 72 Inner contour

Claims

1. A method for the production of an internally cooled valve (4) for internal combustion engines, comprising:

2. The method for the production of an internally cooled valve (4) for internal combustion engines, in accordance with claim 1, wherein prior to the form rolling process the workpiece (14, 16) comprises a diameter of at least that of the valve disk (6) of the finished valve, and further comprising: form rolling of a transition section between the valve head and the valve stem (8) to form a concave fillet.

3. The method for the production of an internally cooled valve (4) for internal combustion engines, in accordance with claim 1 or 2, wherein the workpiece (16) is cup-shaped, wherein the cup-shaped workpiece (14, 16) has a diameter at a base of the workpiece (16) that corresponds at least to that of the valve disk (6),wherein the cylindrical hole is a blind hole (26), which extends from one end of the valve stem (36) in the direction of the base of the cup-shaped workpiece (16), andwherein the form rolling process comprises a reshaping of the stem and a shaping of the valve body.

4. The method for the production of an internally cooled valve (4) for internal combustion engines, in accordance with claim 3, wherein an outer surface of the base of the workpiece (16) already has the shape of the valve disk (6).

5. The method for the production of an internally cooled valve (4) for internal combustion engines, in accordance with claim 3 or 4, wherein the workpiece (16) is cup-shaped, and wherein the cup-shaped workpiece (16) has a larger diameter at a base of the workpiece (16) than in the area of the cylindrical stem.

6. The method for the production of an internally cooled valve (4) for internal combustion engines, in accordance with one of the preceding claims, wherein the workpiece (14, 16) is held between the rollers by means of guides.

7. The method for the production of an internally cooled valve (4) for internal combustion engines, in accordance with one of the preceding claims, wherein the workpiece (14, 16) is hot rolled.

8. The method for the production of an internally cooled valve (4) for internal combustion engines, in accordance with one of the preceding claims, further comprising: axial movement of the workpiece (14, 16) in the direction of the stem end (36) during the rolling process.

9. The method for the production of an internally cooled valve (4) for internal combustion engines, in accordance with one of the preceding claims, further comprising: rotation of the workpiece (14, 16) during the rolling process.

10. The method for the production of an internally cooled valve (4) for internal combustion engines, in accordance with one of the preceding claims, further comprising: turning of the valve stem (8) to a desired outer diameter, after a desired inner diameter of the valve stem (8) has been achieved by rolling.

11. The method for the production of an internally cooled valve (4) for internal combustion engines, in accordance with one of the preceding claims, wherein the provision of the workpiece (14, 16) comprises a provision of the workpiece (14, 16) with a non-cylindrical stem with an outer contour (70) and the cylindrical hole (26, 28),wherein the reshaping of the valve stem end (36) by form rolling comprises areshaping of the valve stem end (36) by form rolling of the stem to a smaller diameter, wherein a diameter of the cylindrical hole is reduced, and a non-cylindrical hole with an inner contour (72) remains.

12. A device for the production of an internally cooled valve (4) for internal combustion engines, from a workpiece (14, 16), comprising: a rolling mill for purposes of round cross rolling or skewed rolling, wherein at least two forming rollers (42, 44) have a profile of an outlet valve.

13. The device for the production of an internally cooled valve (4) in accordance with claim 12, further comprising: a mandrel, which can be inserted into a hole (26, 28) of a workpiece (14, 16) so as to guide the workpiece (14, 16) during the rolling process.

14. The device for the production of an internally cooled valve (4) in accordance with claim 12, further comprising: at least one guide so as to hold and guide the workpiece (14, 16) between the rollers, wherein the at least one guide comprises a sliding member, or one or a plurality of rollers, which abut against an outer surface of the workpiece (14, 16).

15. The device for the production of an internally cooled valve (4) in accordance with claim 11, 12, 13, or 14, further comprising: at least one load cell on the at lease one guide, together with individually driven forming rollers (42, 44),and a controller that controls the rotational speed of the forming rollers (42, 44) such that the force on the guides is minimised.

16. The device for the production of an internally cooled valve (4) in accordance with one of the claims 12 to 15, characterised in that the axes of the rollers are arranged skewed relative to one another at an angle of 1° to 12°, preferably of 2° to 10°, and more preferably of 3° to 8°.

17. The device for the production of an internally cooled valve (4) in accordance with claim 16, characterised in that the axis of the workpiece (14, 16) and the axes of the forming rollers (42, 44) are in each case arranged skewed relative to one another at an angle of 0.5° to 6°, preferably of 1° to 5°, and more preferably of 1.5° to 4°.

18. The device for the production of an internally cooled valve (4) in accordance with one of the claims 16 or 17, wherein at least one of the forming rollers (44) has a hyperboloidal outer surface.

19. The device for the production of an internally cooled valve (4) in accordance with one of the claims 12 to 18, wherein at least one of the forming rollers (42, 44) has a surface structure, which causes a transport of the material of the workpiece in the axial direction.

20. The device for the production of an internally cooled valve (4) in accordance with one of the claims 12 to 19, further comprising: an axial guide or a clamping chuck, so as to guide and/or hold the workpiece (14, 16) from the disk face.

21. The device for the production of an internally cooled valve (4) in accordance with one of the claims 12 to 20, further comprising: an actuator, so as to move the workpiece (14, 16) axially, from the base in the direction of the valve stem end (36).

22. The device for the production of an internally cooled valve (4) in accordance with one of the claims 12 to 21, further comprising: a drive, so as to rotate the workpiece (14, 16) during the rolling process at a predetermined rotational speed.

23. The device for the production of an internally cooled valve (4) in accordance with one of the claims 12 to 22, further comprising: a heating element, so as to heat the workpiece (14, 16) during the rolling process.

24. An internally cooled valve (4) for internal combustion engines, characterised in that it has been reshaped from a workpiece (14, 16) using one of the methods of claims 1 to 10, or using a device according to any one of claims 12 to 23,wherein the workpiece (14, 16) comprises a stem, wherein the workpiece (14, 16) also comprises a cylindrical hole, which extends from one end of the valve stem (36) in the axial direction, wherein at least one stem has been reshaped by form rolling of the stem to a smaller diameter.

25. An internally cooled valve (4) for internal combustion engines in accordance with claim 24, characterised in that prior to the form rolling process the workpiece (14, 16) comprises a diameter of at least that of the valve disk (6), and in that a valve head is produced with a concave fillet by means of form rolling.

26. An internally cooled valve (4) for internal combustion engines in accordance with claim 24 or 25, characterised in that the workpiece (16) is cup-shaped, whereinthe cup-shaped workpiece (16) has a diameter at a base of the workpiece (16) that corresponds at least to that of the valve disk (6), whereinthe cylindrical hole is a blind hole (26), which extends from one end of the valve stem (36) in the direction of the base of the cup-shaped workpiece (16).

27. An internally cooled valve (4) for internal combustion engines in accordance with claim 26, characterised in that the workpiece (16) is cup-shaped, whereinthe cup-shaped workpiece (16) has a larger diameter at a base of the workpiece (16) than in the area of the cylindrical stem.

28. An internally cooled valve (4) for internal combustion engines in accordance with one of the claims 24 to 27, characterised in that after the reshaping process the cylindrical hole (26, 28) forms a cavity (10) that extends within the valve stem (8) and the valve disk (6), which cavity is partially filled with sodium (12) and sealed.

29. An internally cooled valve (4) for internal combustion engines in accordance with one of the claims 24 to 28, characterised in that prior to the rolling process the workpiece (14, 16) has a non-cylindrical stem with an outer contour (70) and with a cylindrical hole (26, 28),wherein as a result of the reshaping of the valve stem end (36) by form rolling the valve has a cylindrical valve stem and a non-cylindrical hole with an inner contour (72).