Abstract:
A valve lift mechanism, in particular for internal combustion engines of motor vehicles, has a driven cam element, a valve control member which can be driven (translational movement or pivot rotation) by the cam element, and a flexible enveloping element, wherein the cam element is rotationally mounted. The enveloping element may be formed of an open loop with two ends connected by a holder of said valve actuator, and it is movably connected to the valve control member in the plane perpendicular to the axis of rotation of the cam element.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This is a divisional application of my application Ser. No. 10/706,830, filed Nov. 12, 2003, now U.S. Pat. No. 6,796,277; which was a division of application Ser. No. 10/074,811, filed Feb. 12, 2002, now U.S. Pat. No. 6,705,262; which was a continuing application, under 35 U.S.C. § 120, of international application PCT/AT99/00198, filed Aug. 12, 1999, which designated the United States. The prior applications are herewith incorporated by reference in their entirety. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention relates to a valve mechanism, in particular for internal combustion engines of motor vehicles, with a driven cam element and with a valve actuator displaceable or pivotable by the cam element. 
   Valve mechanisms for the valve control of internal combustion engines, in particular for motor vehicles, conventionally have a device (spring, hydraulic element, etc.) by means of which the valve is acted upon in the closing position. At least during the open phase, therefore, the valve actuator (valve tappet, drag lever, rocker arm or the like) is pressed against part of the closed valve control surface, the part being eccentric to the shaft axis. During the closing of the valve, care must be taken to ensure that the valve disk does not strike the valve seat too quickly, since it otherwise rebounds. This requires relatively complicated coordination between the masses to be moved, the forces arising, the material properties, etc. 
   There has therefore been no lack of proposals for guiding the valve actuator positively on the cam element, various embodiments having been developed, which are each based on two eccentric valve control surfaces instead of the return spring. 
   Actual versions may be gathered, for example, from GB patent specification 19,193 (1913) and GB patent specification 434,247, wherein the cam element has, on at least one end face, a groove, the two side walls of which form the valve control surfaces. A roller or the like arranged at the end of the valve actuator engages into the groove from the side. A cam element having a surrounding web is known, for example, from European patent publication EP 429,277. 
   Further examples of positive guides make use, instead of valve control surfaces parallel to the axis of rotation of the camshaft, of two valve control surfaces which are arranged axially one behind the other and are formed on two differently shaped camshaft elements, for example European patent publications EP 355 659 B, and EP 384 361 A. etc. 
   Both the first version of the positive guides with end-face grooves and the lateral engagement of the sensing element and the second version with two earn elements and two sensing elements for each valve have, as compared with the first-mentioned valve mechanism with a return spring, an increased axial extent and a greater number of components which present either structural, spatial or economic problems. 
   SUMMARY OF THE INVENTION 
   It is accordingly an object of the invention to provide a desmodromic valve mechanism of the type mentioned above, which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which appreciably reduces the prior art problems and constitutes a space-saving, lightweight and cost-effective design. 
   With the foregoing and other objects in view there is provided, in accordance with the invention, a valve mechanism, comprising:
         at least one driven cam element having an axis of rotation;   a valve actuator moved by said cam element in a plane perpendicular to said axis of rotation; and   a flexible surround element formed by an open loop with two ends connected by a holder of said valve actuator, said cam element being rotatably disposed in said flexible surround element about said axis of rotation.       

   The surround element surrounds the circumference of the cam element without appreciable play, so that it is matched to the cam shape, and, because of the nature of the surround element, the cam element can rotate in the latter. Since the surround element connected to the valve actuator cannot co-rotate with the cam element, the travel of the cam region about the axis of rotation of the cam element is converted into a lifting or to-and-fro movement of the valve actuator mounted displaceably or pivotably in the cylinder head. The valve actuator does not execute any movement as long as the region of connection of the surround element to the valve actuator comes to bear against the base-circle region of the rotating cam element, is then moved radially away from the axis of rotation of the cam element and is finally led back again, while the cam region of the earn element passes the region of connection of the surround element to the valve actuator. 
   Since the surround element comes to bear, essentially free of play, against the circumferential surface of the cam element, a valve actuator freely projecting from the surround element would always be oriented perpendicularly to the tangent to the circumferential surface of the cam element and at the same time deviate from radial orientation to the axis of rotation of the cam element, on the one hand, in the rising cam region and, on the other hand, in the falling cam region. The movable connection of the surround element to the valve actuator permits the pivoting or tilting movement of the surround element in the cam region, so that the necessary freedom of movement of the valve actuator in its sliding or pivot bearing remains preserved. The surround element is therefore arranged, in particular, pivotably about an axis on the valve actuator or on a holder for the valve actuator. 
   Open loops may be formed from a strip or band consisting of a sheetlike material, wherein threads or fibers are provided in a textile weave, from a band spring which is manufactured, for example, from a titanium alloy and surrounds the circumferential surface of the cam region, or from a roller chain, wherein a fitting joint pin forms the holder of the valve actuator. 
   A woven loop preferably contains, as weft threads, in peripheral direction of the cam element aramid fibers which have high length constancy and temperature resistance. 
   The ends of an open loop element, fabric band or band spring, may be clamped on the valve actuator or its holder, be provided with insertion orifices for receiving a connecting pin or cotter or else be designed for fastening in another way. The insertion orifices may be formed by folding round and, depending on the material of the loop, is stitching, adhesive bonding, welding or the like of the folded-round end. 
   When the two ends of the open loop pass through one another or touching one another, project from the cam element, then, because of the flexibility of the material of the surround element, a physical axis may be unnecessary, since the two ends can be jointly bent on both sides to the required extent. 
   In a particularly advantageous version, the open loop consists of a band closed on itself which is led to and fro around the cam element and the reversals of which form the insertion orifices. 
   If the surround element consists of a material with a low-friction, if appropriate low-frictionally coated surface, then, if appropriate, lubrication of the sliding surfaces, that is to say of the circumferential surface of the cam element and of the coming-to-bear inner surface of the surround element is not necessary. If lubrication is desired or required, there is preferably provision for the cam element to have, radially to the axis of rotation, at least one oil bore which issues on the circumference of the cam element within the flexible surround element. Since the surround element does not rotate, an external oil supply through the surround element via a flexible line may also be envisaged. 
   An oil supply which, under some circumstances, is not necessary at all for maintaining the sliding properties may also be used in order to solve a serious problem in previous positive controls when the valve is pressed down faultily during the closing phase, indeed a slightly open valve also not being pressed reliably into the valve seat because of excess pressure in the cylinder. To be precise, an oil film may be built up in the slight gap between the cam element and the surround element, the oil or the oil pressure centering the surround element in relation to the cam element. 
   Under the action of force from outside (mass inertia forces, etc.), the surround element is pressed out of this force equilibrium, with the result that the oil gap becomes thinner at a specific point. At this point, more oil pressure builds up, which presses the surround element back into the approximately central position again, so that the system is stabilized. 
   This effect not only is helpful in the rotation of the cam element in the surround element, but may also be used in order to generate a valve closing force, thereby also dispensing, on the valve actuator, with a hydraulic element which, in conventional valves, brings about play compensation in the base-circle region. The oil film also has a damping function, so that the mass forces caused by the acceleration and deceleration of the valve also do not act directly on the cam element, and the engine noises are reduced. 
   Instead of a sliding oil film, an air cushion surrounding the cam element may also be built up by means of compressed air. This may be advantageous particularly in the case of a surround element consisting of plastic or of a plastic fabric. 
   In the valve mechanism according to the invention, owing to the omission of the valve spring and spring plate and to the substantially lighter form of construction of the valve tappet or rocker arm, the masses to be accelerated are reduced. The use of light metals, ceramics or plastic for the valve and/or the valve actuator allows a reduction in the masses to be accelerated and decelerated of 50% to 80% of the value of a valve tappet with a return spring and with hydraulic play compensation. The high values occur particularly in the part-load range, since the valve springs have to be designed for full-load safety. Furthermore, the valve can be made shorter, since the space-consuming valve spring is dispensed with. Moreover, the oil supply gives rise not only to linear contact, but also to surface contact. 
   The cam element can also be made smaller. The production of plastic cam elements or camshafts produced completely from plastic, for example by injection molding, can also likewise be implemented. The use of other lightweight construction materials for the production of the camshafts or cam elements, for example aluminum, also becomes possible. On account of the reduction in mass and of sliding lubrication, fuel savings of 5% and more are to be expected. 
   Particularly when valve actuators are actuated jointly, a weak spring may be provided for acting upon each closed valve. 
   Other features which are considered as characteristic for the invention are set forth in the appended claims. 
   Although the invention is illustrated and described herein as embodied in a valve mechanism, in particular for internal combustion engines of motor vehicles, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. 
   The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows integral parts of a first version of a valve mechanism in an oblique view, 
       FIGS. 2  to  4  show various angular positions of the first version of the valve mechanism in cross section, 
       FIGS. 5 and 6  show longitudinal sections through the first version, 
       FIG. 7  shows a longitudinal section through a second version of a valve mechanism, 
       FIG. 8  shows integral parts of a third version of a valve mechanism in an oblique view, 
       FIG. 9  shows a longitudinal section through the third version, 
       FIG. 10  shows a side view of the third version, 
       FIG. 11  shows integral parts of a further version of a valve mechanism in an oblique view, 
       FIG. 12  shows a side view of the fourth version, 
       FIG. 13  shows a cross section through the fourth version, 
       FIG. 14  shows integral parts of a fifth version in an oblique view, 
       FIG. 15  shows a longitudinal section through the fifth version, 
       FIG. 16  shows a cross section through the fifth version, 
       FIG. 17  shows an enlarged illustration of a detail from  FIG. 14 , 
       FIG. 18  shows integral parts of a sixth version in an oblique view, 
       FIG. 19  shows a longitudinal section through the sixth version, 
       FIG. 20  shows an end view of the sixth version, 
       FIG. 21  shows integral parts of a seventh version in an oblique view. 
       FIG. 22  shows a longitudinal section through the seventh version, 
       FIG. 23  shows integral parts of an eighth version in an oblique view, 
       FIG. 24  shows a longitudinal section through the eighth version, 
       FIG. 25  shows an end view of the eighth version, 
       FIG. 26  shows integral parts of a ninth version in an oblique view, 
       FIG. 27  shows a longitudinal section through the ninth version, 
       FIG. 28  shows an end view of the ninth version, 
       FIGS. 29 and 30  show longitudinal sections through a tenth version in two different positions, 
       FIG. 31  shows integral parts of an eleventh version in an oblique view, 
       FIG. 32  shows an oblique view of the eleventh version, 
       FIG. 33  shows a longitudinal section through the eleventh version, 
       FIG. 34  shows integral parts of a twelfth version in an oblique view, 
       FIG. 35  shows a cross section through the twelfth version, 
       FIG. 36  shows an enlarged illustration of a detail from  FIG. 35 , 
       FIG. 37  shows an oblique view of the twelfth version, 
       FIG. 38  shows integral parts of a thirteenth version in an oblique view, 
       FIG. 39  shows a longitudinal section of the thirteenth version, 
       FIG. 40  shows integral parts of a fourteenth version in an oblique view, 
       FIG. 41  shows a cross section through the fourteenth version, 
       FIG. 42  shows integral parts of a fifteenth version in an oblique view, 
       FIG. 43  shows an oblique view of the fifteenth version, 
       FIG. 44  shows integral parts of a sixteenth version in an oblique view, 
       FIG. 45  shows a cross section through the sixteenth version, 
       FIG. 46  shows an enlarged illustration of a detail from  FIG. 45 , 
       FIG. 47  shows integral parts of a seventeenth version in an oblique view, 
       FIG. 48  shows a longitudinal section through the seventeenth version, and 
       FIG. 49  shows an enlarged illustration of a detail from the seventeenth version. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The drawings each show only one valve mechanism, a valve mechanism used for an internal combustion engine of a motor vehicle having, on the carrier shaft  1 , the number of cam elements  2  which is required for the valves. An oil supply to build up an oil film or a supply of compressed air to build up an air cushion on the circumferential surface of the cam element  2  can take place via a hollow carrier shaft, radial orifices  30  in the carrier shaft  1  and via bores  3  in the cam element  2 . As shown in  FIGS. 8  to  10 , the furniture of orifices  30  and bores  3  may in this case also be used for fastening the cam element  2  on the carrier shaft  1  when a fixing pin  20  is inserted. 
   The cam element  2  is surrounded by a surround element  4  which comes to bear essentially on the circumferential surface and which consists of a flexible, resilient and, if appropriate, also elastic material, so that the cam element  2  can rotate about its axis of rotation  8  in the surround element  4  along with the continuous pulsating deformation of the surround element  4 . The cross-sectional shape of the surround element  4  is illustrated in the figures as being matched in each case to the cam element  2 , since the valve mechanism is shown in an exploded illustration here. As an individual element, the surround element  4  is in the shape of a ring solely when the material has sufficient elasticity and thickness, whereas it otherwise forms a collapsed oval or the like. The surround element  4  is prevented from rotation by connection to a valve actuator  10  which, in the case of the valve tappet, is mounted displaceably in a sliding bearing  41  ( FIG. 30 ) and, in the case of a rocker arm or drag lever, is mounted pivotably in a pivot bearing. This also permits a version wherein a sliding medium or lubricant is supplied through the stationary surround element  4 . The surround element  4  is connected to the valve actuator  10  tiltably or pivotably about an axis  15 , so that, when the cam of the cam element  2  passes through the region of connection of the valve actuator  10 , a pivoting of the surround element  4  in relation to the valve actuator  10  becomes possible. This is necessary since, as shown in  FIGS. 2  to  4 , the sliding bearing of the valve shank  11  does not allow any lateral deflection, and the valve shank  11  has to stand in a radial orientation to the axis of rotation  8 . The valve stroke is also evident from a comparison of  FIGS. 2  to  4 . 
   In the first version according to  FIGS. 1  to  6 , the surround element  4  is formed by a ring which consists of a flexible and, if appropriate, slightly elastic plastic and which has only low deformation resistance. 
   The ring contains, at one point, an aperture  5 , wherein a bearing pin  14  running parallel to the axis of rotation  8  of the cam element  2  passes through the valve shank  11 . On the ring inner surface surrounding the cam element  2  is provided a closed thin loop of a band  22  of metal, a low-friction, if appropriate fiber-reinforced plastic, a fabric or the like, wherein the cam element  2  rotates. As shown in  FIGS. 5 and 6 , a small gap  31 , wherein an oil film can be formed for sliding lubrication, remains, generally simply as a consequence of assembly, between the band  22  and the circumferential surface of the cam element  2 . Furthermore, the oil film also has an impact- and noise-damping effect and, as may be gathered from a comparison of  FIGS. 5 and 6 , may also be used for acting upon the closed valve disk when, in the valve closing position, the surround element  4  lies eccentrically to a minimal extent, so that the thickness  31 ,  31 ″ of the gap is smaller in the cam region and larger in the base-circle region, and the oil pressure attempts to compensate the thickness difference which corresponds to the difference between the axis of rotation  8  and the corresponding axis  8  of the surround element  4 . 
     FIG. 7  shows a version wherein the surround element  4  has a plurality of turns  7  of a band which may consist, for example, of a number of closed loops (similar to that of the band  22  in  FIG. 1 ) lying one in the other and made of spring steel, or a strip composed of threads in a textile weave or the like, or which is wound spirally and may likewise consist of a metal band, a fabric band or the like. In this version, a bearing pin  18  of a preferably two-part holder  12 , which carries two valve actuators  10  of identically switched valves, engages between two turns  7  of the surround element  4 . Also illustrated here is action with the aid of a spring  26  which takes effect not for returning the valve actuators  10  into the base-circle region, but only for acting upon the closed valve. 
     FIGS. 8  to  10  show a version wherein the holder  12  is designed in the form of a “smoothing iron”, the bearing pin  18  being arranged between a band  22  and a surrounding body  4  made of plastic or the like, similar to  FIG. 1 , and forming the axis  15 . The end portion of the bearing pin  18  widens slightly, in order to prevent slipping out of place axially in the surround element  4 , the opposite region of the holding body  12  being beveled so that the holding body  12  can be pushed in laterally. The holding body  12  has a threaded bore, into which the valve shank  11  having a thread  28  can be screwed and can be fixed adjustably by means of a lock nut  27 . As mentioned,  FIGS. 8  to  10  also show a possible fixing of the cam element  2  on the carrier shaft  1  by means of a pin  20  which is inserted through bores  30  of the shaft  1  and bores  3  of the cam element  2 . 
     FIGS. 11  to  13  show a version wherein the surround element  4  is formed by a closed rope loop which is arranged slideably in a groove  16  in the circumferential surface of the cam element. The cam element is divided into two cam regions  43  spaced axially from one another, the groove  16 , wherein the oil bores  3  of the cam element  2  issue, forming the middle region. The valve shank  11  of the valve actuator  10  is provided with an, in particular, laterally open hook-like lug  17 , wherein the rope loop is suspended, and is rounded, parallel to the axis  15 , on the top side, in order to allow pivoting, as is evident, above all, from FIG.  13 . The lug  17  may also be designed closed, if a piece of a rope is closed to form the rope loop only after being slipped into the lug  17 . The rope may be a wire rope, a plastic rope, etc. 
     FIGS. 14  to  17  show a version wherein the surround element  4  is formed from a band or strip composed of a titanium-alloyed spring steel, a sheetlike structure produced from aramid fibers and having a textile weave, in particular a fabric or the like. For connection to the valve actuator  10 , a protuberance  6  of the surround element  4  is performed, which can be inserted into a slot  29  of the valve shank  11 . The connection is made by means of a cotter  19  which passes through bores  25  of the valve shank  11  and the protuberance  6  (FIG.  17 ). The surround element  4  may be a single closed loop or turn with a protuberance  6  pressed flat. The single loop or turn may also be formed by combining the two ends  13  of a band which, lying against one another, produce the protuberance  6  and are inserted jointly into the slot  29 . However, as shown in detail in  FIG. 17 , the surround element may also have two turns  17  and be wound “spirally” from one piece. In this version, too, the two ends  13  preferably terminate in the protuberance  6 . In this version, the axis  15  is not implemented physically, but is obtained by the bending region between the protuberance  6  and that part of the surround element  4  which surrounds the circumferential surface of the cam element  2 . 
     FIGS. 18  to  20  show a similar version, wherein the surround element  4 , again formed by a band spring, a fabric band or the like, is designed as an open loop, has a single turn  7  and is connected with its free ends  13  to the holder  12  of the valve actuator  10 . The two ends  13  are cut in or cut out so as to form tongues which are capable of being inserted one into the other and wherein bores  25  are again provided. The ends  13  are bent relative to one another and are led on both sides round the holder  12 . A cotter or pin  19  passes through the two ends  13 , the holder  12  and the end of the valve shank  11  inserted into the holder  12 . The holder  12  is curved on the top side, as can best be seen from  FIG. 20 , so that the relative pivoting of the surround element in relation to the valve actuator  12  is possible during the passage of the cam region. The axis  15  is again not produced physically, but lies in the penetration of the ends  13 , the large radii of curvature ensuring a long useful life. The ends  13  could also each have a laterally open incision extending from one edge to halfway and be inserted one into the other from the side. 
     FIGS. 21 and 22  show a version wherein the surround element  4  (in a similar way to  FIG. 7 ) consists of a relatively large number of turns  7  formed by individual closed loops which can be inserted one into the other and therefore have increasing sizes. The innermost loop, which is illustrated on the left in  FIG. 21 , surrounds the circumferential surface of the cam element  2 . The further loops each have an orifice  9 , the diameter of the orifices  9  decreasing from the inside outward, that is to say from the second smallest to the outermost largest loop. The orifices  9  brought into congruence with one another thereby supplement one another to form a frustoconical, outwardly narrowing receiving orifice for the frustoconical holder  12  of the valve actuator  10 . The holder consists of two parts  12 ′ which supplement one another and between them hold the head  34  of the valve actuator  10 , said head being of spherical design and allowing a movement of the surround element  4  about the axis  15 . The set of turns  7  of the surround element  4  is held on the cam element  2  by two axially adjacent closing disks  33 , and in each case a slight gap, wherein an oil film can likewise form, remains between the surround element  4  and the closing disks  33 . The closing disks  33  may be connected to the cam element  2  or else, as illustrated, be secured axially by sleeves  32  which in each case are pushed onto the carrier shaft  1  in the interspace with an adjacent cam element or bearing element. 
   In the version according to  FIGS. 23  to  25 , the surround element  4  likewise has a plurality of turns  7  which, however, are formed not by individual closed loops, but by a spiral winding of a single piece of band, here, too, the outer turns having bores of different diameter which, according to  FIG. 24 , supplement one another to form the conically narrowing receiving orifice for the holders  12 . The two parts  12 ′ of the holder receive the head  36  of the valve actuator  10 , said head, in this version, being curved part-cylindrically about the axis  15 . In this version, in the surround element  4  a rolling bearing is formed, having rollers  35  which are lined up with one another and roll on the circumferential surface of the cam element  2 . Although not illustrated, in this version, too, an oil supply through bores  30 ,  3  from the carrier shaft  1  or through the surround element  4  from outside is preferably provided. The rollers  35  are held axially by the closing disks  33 , the closing disk  33  having been omitted in the end view of  FIG. 25  for the sake of clarity. 
   A further version is shown in  FIGS. 26  to  28 . In this, the surround element  4  is formed by a roller chain, the joint pins  23  of which laterally connect plates  24  which also have the effect of axial guidance on the cam element  2  engaging between the plates  24 . One joint pin is lengthened and forms the bearing pin  14  for the fork-shaped holder  12  of the valve actuator  10 , the valve shank  11  being screwed adjustably in said holder and being fastened by means of the counternut  27 . 
     FIGS. 29 and 30  illustrate a version which corresponds essentially to  FIGS. 21 and 22 , but wherein the valve actuator  10  in the form of a valve tappet is not arranged perpendicularly to the axis of rotation  8 , but has an inclination to the latter. In this version, too, the axis  15  about which the surround element  4  pivots on the valve actuator  10  is parallel to the axis of rotation  8 . The linear movement of the valve shank  11  in a sliding bearing  41  fixed to the housing or placed in a fixed location generates, in the region of connection to the surround element  4 , a movement component in the direction of the axis of rotation  8 . The surround element  4  is therefore displaceable on the cam element  2  in the direction of the axis of rotation  8  by the amount of the distance  40 . If appropriate, the holder  12  may also be arranged displaceably on the surround element  4 . 
   In the version according to  FIGS. 31  to  33 , the cam element  2  is provided with a circumferential groove  16 , the bottom of which is concentric to the carrier shaft  1 . The cam element  2  is thereby subdivided into two cam regions  43  which are connected via a material-saving middle region. The surround element  4 , which, in this version, is formed by a closed loop of a band or strip, has at one point an adhesively bonded or stitched tab  45  which defines an insertion orifice  47 . The loop and the tab  45  are provided in the middle region with an aperture  5 . The valve actuator  10  has a bore  46  in the fastening region, so that, after insertion into the aperture  5 , a connecting element  48  in the form of a pin or cotter can be pushed through the insertion orifice  47  and the bore  46 . The pin again forms the axis  15  which extends parallel to the carrier shaft  1 . The free end of the valve shank  11  in this case projects into the circumferential groove  16 , with the result that axial guidance is also provided. The band of the surround element  4 , said band being produced preferably by a textile circular technique (circular weaving, circular knitting or the like), contains, above all, aramid threads or fibers and is preferably a seamless fabric ring or the like wherein at least the weft threads consist of an aramid. The fabric may also have a low-friction coating. 
     FIGS. 34  to  37  show a similar version, wherein a circular-worked band, in particular circular-woven or such like band, is again likewise used for producing the surround element  4 . The band circumference corresponds essentially to double the circumference of the cam element  2  and is folded together to form a two-ply open loop. The reversal points of the band at the ends  13  of the open loop even form the insertion orifices  47  for the hollow connecting element  48  which, in this version, is bent in a U-shaped manner. The two ends  13  are cut out in the middle region  52 , and the two cutouts supplement one another to form the aperture  5 , through which the end of the valve shank  11  projects into the circumferential groove  16  of the cam element. The mounting position of the valve actuator  11  can thereby lie, offset laterally, parallel to the axial plane, as is evident from  FIG. 35 , as a result of which advantages in terms of a variation in the roll and contact lines may be afforded. The valve shank  11  may, of course, also lie in the axial plane, as a consequence of which the two insertion orifices  47  are not symmetric. A second part  53  bent in a U-shaped manner is inserted into the hollow connecting element  48  and, for example, adhesively bonded, so that the connection between the surround element  4  and the valve actuator  10  is secured. 
   Instead of by means of the U-shaped connecting element  48 , the two ends  13  of the open loop could also be connected by means of a buckle-like element having one or two slots, through which the ends  13  are guided and are fixed by means of pins inserted into their insertion orifices  47 . The buckle-like element constitutes the holder  12  for the valve actuator, into which holder the latter is screwed or latched. 
   In the version according to  FIGS. 38 and 39 , a sleeve  55  provided with a pair of connecting tabs  56  is inserted into the aperture  5  of the surround element  4  formed by a closed loop and projects inward into the circumferential groove  16 . The connecting tabs  56  are adhesively bonded, welded or the like to the surrounding region of the aperture  5 . The valve shank  11  has a thread  28  at the free end and can be screwed to an adjustable depth into a thread of the sleeve  55  and braced by means of a counternut  27 . The cam element  2  consists, in this version, of two cam regions  43  which are not connected to one another, but are fixed separately on the carrier shaft. Instead of the screw connection, a latching or snapping connection could be made between the sleeve  55  and the valve shank  11 , so that rotation about the axis of the valve shank  11  is possible. In this version, the surround element  4  may be a fabric band in a similar way to  FIG. 31  or a band spring in a similar way to FIG.  21 . The axis  15 , about which the surround element  4  has to pivot to and fro to a limited extent in relation to the valve actuator  10 , runs between the connecting tabs  56  by virtue of the flexibility of the material used. 
   In the versions according to  FIGS. 40  to  46 , the surround element  4  is in each case produced in a closed loop with a protuberance  6  which is divided off from the cam element  2  by an adhesively bonded, stitched or clamped constriction and which receives an insert  54  serving as a holder  12  of the valve actuator  10 . 
     FIGS. 40 and 41  show a version wherein the constriction of the surround element  4  is obtained by means of a flat lug  50 , through which the protuberance  6  pressed flat is slipped. The insert  54  pushed into the protuberance  6  has a latching or threaded bore  57 , into which the latchable or threaded end  28  of the valve shank  11  can be pushed or screwed. In the latter case, a counternut  27  again serves for adjusting or fixing the length of the valve actuator  10 . 
     FIGS. 42 and 43  show an identical connection to the surround element  4  and the valve actuator  10 , wherein connection the constriction of the protuberance  6  is obtained by means of two clamping jaws  49  capable of being braced relative to one another. The two clamping jaws  49  may also be designed identically, so that, in each case, a connecting screw is inserted into a clamping jaw  49 . 
   Instead of the lug  50  or the clamping jaws  49  in the versions of  FIGS. 40  to  43 , a latchable constricting device may also be envisaged, for example by two identically designed parts provided with latching hooks and latching orifices being snapped together with one another. 
     FIGS. 44 and 45  show one possibility for a latching connection between the valve shank  11  and the holder  12 , allowing the valve shank  11  to rotate about its axis. The end of the valve shank  11  is provided with an angular, conical or rounded annular groove  59 , and the insert  54  is provided with two webs which are resilient by virtue of a slot  51  and on which angular, conical or rounded ribs  60  are formed. The valve shank is pushed into the bore  57 , the insert  54  widening at the same time, until the ribs  60  latch into the annular groove  59 . The connecting element  48  causing the constriction and taking the form of a U-shaped hollow shackle is subsequently pushed on and secured by means of the U-shaped counterpiece  53  which is adhesively bonded in or pinched. In each of  FIGS. 40  to  46 , the constriction forms a bendable connection wherein the axis  15  is implemented. 
     FIGS. 47  to  49  show a version wherein, in a similar way to the version according to  FIGS. 34  to  37 , the surround element  4  consists of a band closed on itself which is made of fabric, spring steel or the like and is folded together to form an open two-ply loop and the reversals of which again form insertion orifices  47 . The ends  13  of the open loop are cut out in such a way that they can be inserted one into the other in a similar way to  FIGS. 18  to  20 . In this version, the holder  12  is composed of two parts  12 ′, each of which has a pin-shaped portion  48 ′ of the connecting element  48 , a receptacle and a threaded sleeve for a threaded screw  61 . Two ribs  60  project into the likewise divided orifice  57  and engage into a circumferential groove  59  of the again rotatably held valve shank  11 . The two pin-shaped portions  48 ′ engage into the mutually aligned insertion orifices  47  of the ends  18  engaging one into the other and touch one another in the middle, as is evident from FIG.  48 . In this version, the cam element  2  is not shown as an individually mountable part, but, instead, the camshaft is produced in one piece in a conventional method. Since the positive guidance of the valve actuator makes it possible to have a very lightweight form of construction of the valve mechanism, the entire camshaft may also be produced in a very lightweight form of construction. Said camshaft can therefore also be produced in one piece from an, if appropriate, reinforced plastic or other lightweight construction materials. 
   If a flat fabric strip is used for the surround element  4 , its ends can either be stitched, adhesively bonded or welded to form a closed loop or be folded over and stitched, adhesively bonded or welded, in order to form insertion orifices  47  of the open loop. The apertures  5  or edge and middle cutouts  52  can readily be formed in fabric treated in this way. 
   The valve mechanism is shown, in all the versions, with a valve tappet as the valve actuator  10 . The valve actuator  10  may, however, also comprise a pivotably mounted rocker arm or drag lever, on one end of which the surround element  4  is arranged pivotably about the axis  15 . A camshaft for use with internal combustion engines conventionally has a plurality of valve mechanisms of this type, the cam elements being arranged so as to be angularly offset.