Abstract:
A device for changing the rotational position of a rotating, driven control shaft that controls the opening and closing of gas exchange valves of an internal combustion engine and is displaced via an electric motor and an interposed toggle lever arrangement having a downstream diagonal toothing arrangement for simplified displacement with minimal force and energy expenditures. The result is a simple, accessible, easy to maintain economical displacement drive for changing the rotational position of the control shaft in order to change the control times of gas-exchange valves in an internal combustion engine.

Description:
The invention is based on a device for changing a rotational position, as defined hereinafter. 
     BACKGROUND OF THE INVENTION 
     In such a device, which is known from German Patent Disclosure DE-A1 31 46 613, a driving toothed wheel for driving two control shafts disposed parallel to one another is provided for each shaft. These driving toothed wheels have a parallel diagonal teeth with which the wheels engage a corresponding parallel, diagonal front toothing of a transmission element. This element is embodied as a toothed wheel having a hub whose bore has a spline shaft toothing on the casing surface, the toothing being slid on an outer spline shaft toothing of the end of the control shaft and axially displaceable there without torsion. For displacing the transmission element, the element is coupled with a sleeve having a rack-and-pinion toothing at its outer circumference that is engaged by a corresponding pinion of an adjusting shaft, which in turn is coupled with an electric motor via a worm gearing. The toothed wheel of the transmission element in this instance is embodied to be essentially wider than the driving toothed wheel so that the element remains in engagement with the driving toothed wheel, despite being longitudinally displaced on the spline shaft end of the control shaft. During this displacement the rotational position of the transmission element, together with the rotational position of the control shaft, changes with respect to the rotational position of the driving toothed wheel. 
     This device requires an electric motor for each control shaft. This makes the device for changing a rotational position very costly to construct, and requires a drive that is integrated into the engine block and is located between the engine block and the driving toothed wheel, which is located on the outside and driven by the crankshaft. The driving toothed wheel, and again a toothed wheel driving the driving toothed wheel, both require a diagonal toothing, so that in this case as well operation is more costly with respect to the toothed wheels to be used. 
     OBJECT AND SUMMARY OF THE INVENTION 
     In contrast, the device of the invention has the advantage that the rotational position of the control shaft can be changed in a simple manner with few transmission elements. A small electric motor having less driving power can be used in this device. In a modification in accordance with the invention, a desired transmission of force or direction can be achieved with the aid of the transmission lever, and an influence can be established on the rate of adjustment and initial position. The subject matter can be attained in a simple manner by the selection of the lever arm ratio of the two-armed lever. By means of interposing the support lever between the stationary support and the pivoting pin, a greater output adjustment variable can be achieved with respect to the input adjustment variable, in the form of the adjustment of the screw socket on the threaded spindle, and with the use of small adjustment forces. 
     In this case the electric motor, along with a threaded spindle, can advantageously be compact and disposed transversely to the ends of the control to be easily accessible. In an advantageous manner, a simple connection by adjustable contact that can be realized with commercial machine elements is produced between the transmission lever and the driving element. This embodiment is designed to be simple, accessible and compact, as ensues from the subject herein. In an advantageous manner, a plurality of control shafts can also be adjusted at low cost with an electric motor. In this instance, the lever transmission also has a positive effect on the power needs of the electric motor. In a further advantageous manner, a second electric motor can be provided for emergency operations; this motor is activated when the first electric motor fails. Finally, the embodiment offers the option of guiding the cam shaft back into an end position when the electric motor is turned off. 
    
    
     The invention will be better understood and further objects and advantages thereof will become more apparent from the ensuing detailed description of exemplary embodiments taken in conjunction with the drawing. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a first exemplary embodiment that includes a device for operating a single control shaft; 
     FIG. 2 shows a second exemplary embodiment for operating two parallel control shafts; and 
     FIG. 3 is a section along line III--III in FIG. 1. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The section in FIG. 1 shows the end of a control shaft, in this case a camshaft 1, of an internal combustion engine not shown in detail. By means of this camshaft, gas exchange valves of the engine are operated in a standard, known manner. The camshaft 1 is seated in housing 2 of the engine in a manner not shown in detail. For driving the camshaft, the camshaft has a front flange 3, from whose outwardly-pointing face end 4 a stepped bore 5, 6 extends coaxially to the axis of the camshaft. The part 5 of the stepped bore, which is larger in diameter and leads away directly from the face end, forms a level shoulder 7 at the transition to a part 6 of the bore, which is smaller in diameter, where a hub 8 of a driving toothed wheel 9 acting as a driving element comes into contact with the shoulder on the front side. At its circumference, the driving toothed wheel has a chain wheel 10, which engages a driving chain, not shown, during operation of the engine. The driving chain in this case is driven either directly or indirectly by the crankshaft of the associated engine, so that the driving toothed wheel rotates in synchronization with the rpm of the engine. Disposed in the disk 11 of the chain wheel are a plurality of oblong holes 12 extending in the direction of the circumference and through each of which a guide sleeve 13 extends; the guide sleeve rests on one end against the front face 4 of the front flange 3, and on the other end against a holding ring 14 after passing through the disk 11. A screw pin is pulled through this ring and the guide sleeve 13 and is screwed into the front flange 3 and serves in axially securing the driving toothed wheel, which is, however, rotatable corresponding to the oblong hole 12. 
     The driving toothed wheel further has an inner diagonal toothing 16 on the casing surface of the inner passage bore. This toothing engages an outer diagonal toothing 17 of a power take-off element 18. The driving element has a trunnion 20 that has an outer spline shaft toothing 21, via which the trunnion engages an inner spline shaft toothing 22 on the casing surface of the stepped bore part 6 that has the smaller diameter and is displaceable without torsion along this spline shaft toothing, axially to the camshaft 1. Contiguous to the trunnion 20, the power take-off element has a pot-shaped part 24, which has a cylindrical circumferential surface with the said outer diagonal toothing and, at its transition to the trunnion 20 having the smaller diameter, has a flat annular surface 25 with which it can come into contact with the shoulder 7 as an end stop. 
     The bottom 27 of the pot-shaped part is embodied as a level running surface for a needle bearing 28, on which a level plate 29 is seated in the axial direction of the camshaft. On the side remote from the camshaft, the plate 29 has a connecting trunnion 30, which is coaxial to the camshaft and extends through a central opening of a threaded ring 31 screwed into an inside thread 32 in the inside casing surface of the pot-shaped part 24. Again, a needle bearing 33 is disposed between the pot-shaped part 24 and the plate 29. By means of this arrangement, the connecting trunnion 30 is connected to the power take-off part 18 to be rotatable and with frictional lockup in the axial direction. The power take-off part 18 is now displaceable inside the hub 8 of the driving toothed wheel with the aid of the connecting part formed from the connecting trunnion 30 and the plate 29. Because the rotational position of the driving part is fixed in the spline shaft toothing 21 and 22 with respect to the camshaft 1, when the driving part is displaced, the driving toothed wheel is twisted relative to the camshaft because of the diagonal toothing. When the driving toothed wheel is held securely, the camshaft twists relative to the rotational position of its drive. 
     A shaft 34 is secured to the connecting trunnion in order to displace it; the end of a two-armed transmission lever 35 can pivot around this shaft. This lever is part of a toggle lever arrangement 36 comprising two lever parts, the transmission lever 35 and a one-armed support lever 37, which is seated with its one end on a pivot shaft 38 located between the lever ends of the two-armed transmission lever 35, and whose other end has a bearing 39 secured to the housing. The other end of the transmission lever 35 is pivotably seated in a bearing 47 on a screw socket 40 disposed on a threaded spindle 41 which in turn is part of an electric motor 42, as its outwardly protruding motor shaft, or is coupled to a motor shaft of the electric motor 42. The electric motor is flanged to the outside of the housing 2 of the engine and protrudes with the threaded spindle 41 through an opening 43 into the housing, with the threaded spindle lying essentially perpendicular to the axis of the camshaft. The seating of the transmission lever 35 on the screw socket 40, and the bearing 39 of the support lever 37, which are attached to the housing, are preferably disposed one behind the other and aligned in the axial direction of the threaded spindle, and are located in a common plane with the axis of the threaded spindle. Moreover, the bearing 39 is preferably also in a plane that passes through the axis of the camshaft and is perpendicular to the axis of the threaded spindle 41. 
     When the electric motor is driven, the screw socket 40, which is secured against rotation by the lever arrangement 36, is moved axially on the threaded spindle 41, and in the process displaces the two-armed transmission lever 35 together with the support lever 37 in such a way that a great displacement is achieved with little force because of the toggle lever principle, and transmitted onto the connecting trunnion 30. In this way a great output displacement can be produced with little displacement force and input displacement, and the relative rotational position of the camshaft to its drive can be adapted quickly. The lever arrangement is practically a double toggle lever comprising the one-armed lever 37, which forms a toggle lever together with the lever arm of the two-armed transmission lever 35 disposed between pivot axis 38 and socket 40; the one-armed lever also forms a toggle lever with the lever arm disposed between the pivot shaft 38 and the shaft 34 of the transmission lever 35. 
     The lever arm ratio must always be 1:1! (number 38 in the middle between 47 and 34) so that points 47 and 34 move on the spindle shaft or camshaft axis. The transmission of motion can be set by means of the initial position of the motion of the screw socket 40 within specific limits. The total length of the lever 35 has an effect on the transmission of motion. 
     The direction of displacement of connecting part 29, 30 can be changed by means of the initial position of the screw socket 40 to the left or, seen from the bearing 39, to the right in the top view of FIG. 1. Finally, even a reversal of the motion of the connecting part in the displacement region can be achieved when the screw socket is displaced in the displacement region, in appropriate adaptation of the lever lengths, by means of the projection of the bearing 39 from a position to the left of the bearing 39 into a position to the right of the bearing 39. The threaded spindle 41 is then correspondingly embodied to be longer than shown in FIG. 1. Thus numerous setting options result that can also be adapted to the conditions of the associated engine. To make possible the passage of the screw socket 40 through the geometrical axis of the bearing 39, support levers and transmission levers are preferably embodied in duplicate on both sides of the threaded spindle, and the support levers are seated inside the housing in trunnions inserted from the outside. 
     To complete the arrangement, as shown in dashed lines in FIG. 1, the motor shaft of the electric motor can be secured to the outside end of the motor shaft 45, for example, by a flat spiral spring, the other end of which is fixedly secured to the housing of the electric motor, as also shown in a top view in FIG. 3. With the aid of this flat spiral spring 46, the motor shaft 45 is prestressed such that with a lack motor ignition, with the lifting of the self-locking of the threaded spindle, the motor shaft is reversed into an initial position, thus bringing the camshaft into a desired end position. In this regard, FIG. 3 shows the position of the flat spiral spring 46 with respect to the motor shaft 45, along section III--III. 
     In operation, when a set, relative camshaft position must be maintained, the electric motor is partly excited in such a manner that the driving forces of the electric motor from the partial excitation maintain the balance with the sum of the reversing forces from the cam drive and flat spiral spring. In the initial end position in the retarded position, emergency service of the engine, including starting of the engine, is possible. 
     While in the exemplary embodiment of FIG. 1 only a single camshaft was displaced by means of the electric motor 42, it is possible in the embodiment of FIG. 2 to simultaneously adjust two camshafts disposed, for example, adjacent and parallel to one another. In such a case a second screw socket 140 is disposed on the threaded spindle 41, along with the screw socket 40 already shown in FIG. 1, the screw socket 140 being connected to a toggle lever arrangement 136 of the same type as toggle lever arrangement 36. By means of this arrangement, a second camshaft 101 is twisted analogously to the first camshaft 1. The threaded spindle can be seated at one end in a bearing 50 such that it is secured to the housing, which is necessary because of the length of the spindle, or it is also simultaneously connected at its seating position to a second electric motor 142, which is first currentless when the first electric motor 42 is in operation, and then serves solely in the seating of the spindle 41. However, should the operating ability of the first electric motor 42 fail for some reason, the second electric motor 42 can be used as a replacement to drive the spindle 41. In this way good operating reliability is achieved. 
     As can be taken from FIG. 2, the initial position of screw sockets 40 and 140 varies, that is, to the left or right of the bearing 39, so that opposed displacement motions are achieved when the electric motor is driven. Moreover, the initial position of the driving part 18 is accordingly variable with respect to the driving toothed wheel 9. The lever length of the respective lever pair 36 and 136, respectively, is selected variably so that different adjustment rates can be achieved with adaptation to the conditions of the engine. In this case as well a reversal of motion can be realized as needed. 
     In a simplified embodiment the camshaft adjustment is also possible with only one lever between the screw socket and the connecting part when the stationary support of the transmission lever is displaceable inside the lever, for example when it is embodied in a crank, or when the connection to the screw socket is embodied to be displaceable inside such a crank. If this is the case, the lever can also be seated stationarily at its end as a one-armed lever on which the screw socket and the connecting part engage different points. Moreover, the lever can also be embodied as a bell crank. 
     The foregoing relates to preferred exemplary embodiments of the invention,it being understood that other variants and embodiments thereof are possible within the spirit and scope of the invention, the latter being defined by the appended claims.