Abstract:
The invention relates to a valve drive of an internal combustion engine, comprising at least one camshaft whereon at least one cam carrier is arranged in a rotationally fixed and axially displaceable manner. Means for applying axial tension are formed between the at least one camshaft and the at least one cam support, thereby enabling the at least one cam support to be fixed in an axial manner.

Description:
This application is a § 371 application of PCT/EP2004/002758, which claims priority from DE 10312581.7, filed Mar. 21, 2003, and DE 10312582.5, filed Mar. 21, 2003. 
   BACKGROUND 
   This invention relates to a valve drive of an internal combustion engine comprising a cylinder head. 
   Mechanical devices designed to improve the thermodynamic properties of internal combustion engines have been disclosed, devices which affect the operating cycle of the valve drive and, for example, affect the timing of the valve drive and, for example, enable speed-dependent variation of the opening times or the lift of charge-cycle valves. 
   SUMMARY OF THE INVENTION 
   Publication DE 42 30 877 discloses such a device, one in which a cam carrier is mounted on a base camshaft so as to be nonrotatable and axially displaceable. The cam carrier consists of a tubular material on which at least one cam is mounted, such that a plurality of cam paths proceeds axially displaced from a common base circle. A charge-cycle valve may be actuated by the axial displacement of the cam piece on the base camshaft by the variously configured cam paths, the cam paths differing in lift and/or phase relationship. 
   One advantageous device for axial displacement of a cam carrier has been disclosed in publication EP 0 798 45 1, a device in which a worm gear drive is configured on both sides of the cam carrier and has as recess a curved path into which a final control element may be introduced for axial displacement of the cam carrier. 
   In order for a cam carrier to remain on the base camshaft in the position in which it had been displaced by fitting of the final control element into the worm gear drive, a detent device is provided which consists of detent means mounted in the base camshaft and fitted into detent grooves made in the cam carrier. Three detent grooves corresponding to the three cam paths are configured on one cam. 
   The essential disadvantage of this camshaft-centered configuration of the detent device is that the base camshafts and the cylinder head are often made of different materials having different thermal expansion coefficients. As a result, the camshaft-centered detent device will not lock with precision either in an unwarmed internal combustion engine or one warmed-up for operation. This effect may be intensified by inaccuracies in manufacture and assembly or ones determined by operation to the extent that reliable operation of the internal combustion engine is not possible. 
   A cylinder-head-centered detent device for a base camshaft with axially displaceable cam carriers has been disclosed in publication DE 101 48 243, mounting of the base camshaft in the cylinder head of the internal combustion engine being effected by means of at least one camshaft bearing including the cam carrier. 
   The detent device consists of detent means mounted in the camshaft bearing and fitted into detent grooves made in the cam carrier. In a cam carrier with two cams each having two cam paths, there must be two axially adjacent detent grooves in which the detent means is engaged. 
   The essential disadvantage of this cylinder-head-centered detent device is represented by the extensive wear occurring in the camshaft bearing, since an appreciable portion of the sliding surfaces is employed for the detent grooves. In addition, the base camshaft and the cam carrier are displaced to one side of the camshaft bearing by the detent means. This detent device also requires a good supply of lubricant, something which cannot be guaranteed over the precision-fitted and often polished gliding surfaces of the bearings. 
   The object of the invention is to create a valve drive in which the cam carrier is reliably held in its position after displacement, irrespective of thermal effects. 
   In one embodiment of the invention a first axial position of the cam carrier is defined in that a first contact surface rigidly mounted on a cam carrier is in contact with a first contact surface rigidly mounted on a cylinder head. 
   A second axial position of the cam carrier is accordingly defined in that a second contact surface rigidly mounted on a cam carrier is in contact with a second contact surface rigidly mounted on a cylinder head. 
   Provision is made such that means are configured for application of an axial tensioning force between the base camshaft and at least one cam carrier. This tensioning force is oriented so that the cam carrier when in the first axial position is also displaced in the direction of this first axial position. Similarly, the cam carrier in the second axial position is also displaced in the direction of this second axial position. This tensioning force exerts its effect independently of thermally determined expansion effects of the valve drive. 
   Provision is made such that the first axial contact surface rigidly mounted on a cam carrier and the second contact surface rigidly mounted on a cam carrier are side surfaces of the carrier of at least one cam. 
   The first contact surface rigidly mounted on a cylinder head and the second contact surface rigidly mounted on a cylinder head are side surfaces of the camshaft bearing comprising the cam carrier. 
   In one advantageous development of the invention provision is made such that the means for application of an axial tensioning force from the base camshaft to the cam carrier is configured as a detent device. 
   The detent device has detent means mounted in the camshaft and movable in the radial direction, the detent means being pressed by a force directed radially preferably against the interior surface of the cam carrier. At least two circumferential detent grooves spaced an axial distance from each other are configured on the inside of the cam carrier, the detent grooves being configured to be approximately v-shaped in the cam carrier, so that the two sides of the detent groove form a ramp for the detent means. The detent grooves conceivably might also be configured in the base camshaft, in which case the detent device would be configured in the cam carrier. 
   In another advantageous development of the invention provision is made such that the radially oriented force is the restoring force of a spring element. 
   Provision is made in another advantageous development of the invention such that the detent means is a detent bolt, the side of the detent facing the detent grooves being rounded. 
   In an alternative advantageous development of the invention provision is made such that the detent means is a detent ball. 
   In a last advantageous development of the invention provision is made such that a cam carrier is mounted on the at least one base camshaft for each cylinder of the internal combustion engine. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The valve drive of an internal combustion engine claimed for the invention is described in what follows on the basis of an exemplary embodiment with reference to seven figures, of which 
       FIG. 1  presents a side view of a four-cylinder internal combustion engine as claimed for the invention; 
       FIG. 2  a view of the internal combustion engine shown in  FIG. 1  along line II-II; 
       FIG. 3  a perspective view of the camshafts installed in the internal combustion engine shown in  FIGS. 1 and 2 , with the cylinder head cover removed; 
       FIG. 4  a view of one of the two camshafts, disassembled; 
       FIG. 5  a section of the camshaft shown in  FIG. 3  with a cam carrier enclosed in a bearing block; 
       FIG. 6  a section of the cam carrier shown in  FIG. 5 , in the first valve lift control position; 
       FIG. 7  a section of the cam carrier shown in  FIG. 5 , in the second valve lift control position. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIGS. 1 to 3  illustrate an example of an external-ignition four-cylinder in-line internal combustion engine having a crankcase  30  with a cylinder head  31  and cylinder head cover  33  of conventional design. Two intake and two outlet valves (not shown) are installed per cylinder, the intake valves being operated by an intake-valve camshaft and the outlet valves by an outlet-valve camshaft  16  controlled by conventional means. For this purpose the intake camshafts and the outlet camshafts  16  are mounted so as to be in parallel with the longitudinal axis of the engine and are mounted on the two sides of the row of cylinders in the cylinder head  31  so as to be rotatable. 
   The outlet camshaft  16  and the intake camshaft, which consists of a base camshaft  1  and four cam carriers  2 , are driven by conventional means not shown. 
     FIG. 4  shows the intake camshaft, on the base camshaft  1  of which the four cam carriers  2  configured as hollow shafts are mounted spaced axially at a distance from each other. The cam pieces  2  are mounted on the base camshaft  1  so as to be axially displaceable but non-rotatable. As is shown in  FIGS. 3 ,  4 ,  5 ,  6 , and  7 , a worm-wheel drive with an axial curve  10  or  11  configured as a recess which winds spirally around the cam carrier axis is mounted on both ends of each cam carrier  2 . 
   Two cams are mounted on each cam carrier  2 , two different cam paths  6 ,  7  and  8 ,  9 , axially displaced, proceeding from the same basic circle for each cam. The cylindrical area of the covering surface of each cam piece  2  located between the two cams is designed as bearing surface for a camshaft bearing  3 . 
   As is shown in  FIGS. 3 ,  5 ,  6 , and  7 , each cam carrier  2  with this cylindrical bearing surface is mounted in a camshaft bearing block  3  of the cylinder head  31  so as to be rotatable and axially displaceable. 
   The two front surfaces of the cams facing the camshaft bearing block  3  are configured as bearing surfaces  18  and  19 . The front surfaces of the camshaft bearing block  3  facing the cams are correspondingly configured as bearing surfaces  17  and  20 . The spacing between the two bearing surfaces  17  and  18  of the cams is greater than the spacing of the bearing surfaces  19  and  20  of the camshaft bearing block  3 . 
   The maximum distance which may separate the bearing surfaces  17 ,  19  from the bearing surfaces  18 ,  20  corresponds to the width of the cam paths  6 ,  7 ,  8 ,  9  and to the distance to which a cam carrier may be displaced by the axial curves  10  and  11  of the worm drives. 
   The charge-cycle valves  27 ,  28  of the internal combustion engine are actuated by the cams by way of drag levers  21 , which are configured with a roller  23  in order to reduce friction. 
   A play equalization element  25 ,  26  mounted in the cylinder head is conventionally associated with the drag levers  21 ,  22 . 
   As is shown in  FIGS. 6 and 7 , the interior of the cam carriers  2  has two mutually parallel axially spaced detent grooves  34 ,  35  extending over the entire interior circumference of the cam carrier. The detent grooves are in approximation v-shaped, the edges of the v-shaped detent groove being rounded. 
   The two detent grooves  34 ,  35  are designed with groove walls extending diagonally from radially outward to radially inward which form tapered surfaces  36 ,  37 , the tapered surface  36  forming with the groove  34  an angle of inclination α to the axis of rotation of the camshaft  1  and the surface  37  forming with the groove  35  an angle of inclination β to the axis of rotation of the camshaft  1 . 
   As seen in  FIGS. 5 ,  6 , and  7 , a stop ball  40  of conventional design is mounted so as to be movable in a radial pocket bore  38 . The stop ball  40  is pretensioned by a spiral pressure spring  39  one end of which rests on the bottom of the pocket bore  38  configured as opposing bearing and the other end of which rests on the ball  40 , in such a way that the stop ball  40  is pretensioned to press against the radially interior surface of the cam carrier  2 . 
   The distance between the tapered surfaces  36  and  37  and the two grooves  35  and  36  and the axial position of the pocket bore  38  are coordinated so that, when the bearing surface  18  of the cam  8  rests on the bearing surface  20  of the bearing block  3 , the stop ball  40  is in contact with the tapered surface  37  (as illustrated in  FIG. 7 ) and, when the bearing surface  19  of the cam  7  is in contact with the bearing surface  17  of cam bearing block  3 , the stop ball  40  is in contact with the tapered surface  36  of the groove  34  (as illustrated in  FIG. 5  and  FIG. 6 ). 
   Thus, when the cam carrier  2  is in the position illustrated in  FIGS. 5 and 6 , in which the bearing surface  19  of the cam  7  is in contact with the bearing surface  17  of the bearing block  3 , there is introduced into the cam carrier  2 , by way of the stop ball  40  and the tapered surface  36  of the circumferential groove  34 , an axial force from the camshaft  1  into the cam carrier  2  which is oriented in the direction opposite that of the axial force acting from the bearing block  3  by way of the bearing  17  on the bearing  19  of the cam  9 . Thus, the cam carrier  2  is fixed in position for both axial directions. 
   When the cam carrier  2  is in the position illustrated in  FIG. 7 , in which the bearing surface  18  of the cam  8  is in contact with the bearing surface  20  of the bearing block  3 , the stop ball  40  is in contact with the tapered surface  37  of the second circumferential groove  35 , as a result of which an axial force is introduced by the camshaft  1  into the cam carrier  2 , a force the direction of action of which is opposite the direction of action of the axial force acting from the bearing surface  20  of the bearing block  3  by way of the bearing surface  18  of the cam  8 . In this operating position as well the cam carrier  2  is fixed in position in both directions. 
   Varying extension of the base camshaft in relation to the cylinder head effects only slight displacement of the point of contact of ball  40  and the tapered surface  36  (first position as illustrated in  FIG. 6 ) or the tapered surface  37  (second position as illustrated in  FIG. 7 ). In addition, the axial force required is introduced by the ball  40  as a function of the inclination α or β of the tapered surfaces  36 ,  37 . 
   Displacement of the lift valve control from the operating state illustrated in  FIGS. 5 and 6  to the operating state illustrated in  FIG. 7  is effected in that, as illustrated in  FIG. 6 , the carrier pin  14  of an electric actuator mounted in the cylinder head  31  and associated with the axial curve  10  is engaged in the axial curve  10  configured as a recess. As a result of rotation of the camshaft  1  and the cam carrier  2 , contact between the carrier pin  14  and the groove walls of the axial curve  10  causes the cam carrier  2  to be displaced axially to the left until the ball  40  pretensioned by the spring  39  rolls into the groove  35  of the cam carrier  2 . 
   As the ball  40  rolls over the tapered surface  37  as the cam carrier  2  undergoes further axial displacement, the bearing surface  18  of the cam  8  moves toward the bearing surface  20  of the bearing block  3  and comes into axial contact with it. The ball  40  remains in axial contact with the bearing surface  37 . The cam carrier  2  is fixed in axial position. The carrier pin  14  is again removed by conventional means by the electric actuator  12  from the axial curve  10  configured as a circumferential groove. 
   The carrier pin  15  of one of the electric actuators  13  associated with the axial curve  11  and mounted in the cylinder head  31  is introduced by the actuator into the axial curve  11  configured as a recess in order to displace the lift valve control from the operating state illustrated in  FIG. 7  to the operating state illustrated in  FIG. 5  and  FIG. 6 . As a result of rotation of the camshaft  1 , the cam carrier  2  in  FIG. 7  is displaced axially to the right by the contact between the groove walls of the axial curve  11  and the carrier pin  15 , so that the stop ball  40  first rolls out of the groove  35  along the outline of the tapered surface  37  against the force of the spring  39 , along the outline of the tapered surface  36 , until the ball  40  is forced by the restoring force of the spring  39  into the groove  34  and the bearing surface  17  of the cam  7  comes into contact with the bearing surface  19  of the bearing block  3 . Contact is maintained between carrier ball  40  and tapered surface  36 . The cam carrier  2  is fixed in position axially in both directions by the contact between bearing surface  17  of the cam  7  and the bearing surface  19  of the bearing block  3  on one side and by the contact between cone  36  and stop ball  40  on the other side. The carrier pin  15  is removed by a conventional method from the circumferential groove of the axial curve  11  by means of the electric actuator  13 . 
   Operation of the electric actuators is controlled by conventional means (not shown) by the engine control equipment (not shown). 
   The values of angles α and β are determined on the basis of individual requirements, so that the axial force of fixing in the operating positions is ensured for the lift valve control and so that removal of the detent connection after engagement of the carrier pins  14  and  15  in the circumferential grooves  10  and  11  when rotation of the camshaft  1  in the direction of its operation is made certain. For example, the values selected for angles α and β, between 15° and 45°, are the same, 30° for example. 
   Even if each of the tapered surfaces  36  and  37  has a constant angle of inclination α and β over its axial extent in the exemplary embodiments illustrated, it is also conceivable, if a dynamic axial force process is practical, that the inclination of one or both tapered surfaces  36  and  37  could be configured to have a constantly variable angle of inclination α or β in the axial direction. 
   The four cam carriers  2  of the camshaft  1  illustrated in  FIGS. 3 and 4  may thus be displaced individually by the associated actuators  12  and  13  between their two operating positions for the purpose of lift valve control. 
   A configuration such as this of displacement of the lift valve control is possible both for an intake camshaft controlling intake valves only and for an outlet camshaft  16  controlling outlet valves only. It is also possible to provide a configuration such as this on a camshaft which controls both intake valves and outlet valves. 
   In an internal combustion engine which has two camshafts  1  and  16  as illustrated in  FIGS. 1 to 3 , one of which is designed exclusively to control the intake valves and the other exclusively to control the outlet valves, the displacement of the lift valve control may be designed to take place only on one of the two camshafts or on both camshafts. 
   A configuration such as this of controlled displacement of the lift valve control is also possible on internal combustion engines with a larger or smaller number of cylinders than the four cylinders indicated in the exemplary embodiment. A configuration such as this of controlled displacement of the lift valve control is also possible with different cylinder configurations of engines, such as in engines with cylinders in line, V engines, or VR or W engines. Lift valve control displacement is possible both on spark-ignition and on spontaneous-ignition internal combustion engines.