Patent Publication Number: US-2013228039-A1

Title: Sliding cam system havnig slide grooves and locking means

Description:
BACKGROUND 
     The invention relates to a sliding cam system with sliding cams that are arranged on a main shaft, advantageously on a shaft that is used as a camshaft of a reciprocating piston internal combustion engine in a rotationally locked but axially displaceable manner, with a device that can be actuated advantageously electromagnetically and has a movable actuator pin for adjusting the sliding cams into different axial positions by means of displacement grooves that interact with the actuator pin on the periphery of the sliding cams, wherein the adjustment device is arranged fixed in position on a component of the internal combustion engine, and with a device for locking the sliding cams in the different axial positions, wherein the locking device has at least one recess allocated to each of the axial positions. 
     Such a sliding cam system is known from EP 0 798 451 A1. The sliding cams of this system are displaced by means of displacement grooves on the shaft, so that cam disks that have different travels and are positioned one next to the other control the gas-exchange valves by means of actuation elements accordingly. For locking the sliding cam in the different axial positions corresponding to the alignment of the cam disks relative to the actuation element, locking devices are provided between the shaft and the sliding cams. These locking devices consist of holes in the shaft with springs and locking bodies arranged in these holes and associated recesses on the inner periphery of the sliding cams. 
     These holes weaken the shaft in each area of the sliding cams, resulting in a not insignificant risk of damage to the shaft that is loaded by strong alternating forces. 
     In addition, such sliding cam systems have the problem that the tolerance accumulation between the actuator and/or actuator pin and the displacement groove is relatively large. This leads to large run-in areas for the actuator pin and thus to wide sliding cams. 
     In addition, a not insignificant axial force is required between the actuator pin and the displacement groove, in order to move the sliding cams out of the locking devices, wherein the locking body must be moved over the flank of the recess against the force of the spring. 
     SUMMARY 
     The object of the invention is therefore to improve a sliding cam system of the described type so that the spring-loaded locking device can be eliminated and the sliding cam system can be used for small distances of the cylinders or the gas-exchange valves of the reciprocating piston internal combustion engine. These measures should be achieved with simple, economical means. 
     The objective of the invention is met in that the recesses are formed as locking grooves on the periphery of the sliding cams and the run-in and run-out areas of the displacement grooves lie in the planes of two adjacent locking grooves. Therefore, both the locking of the sliding cam and also the displacement of this cam are performed on the shaft with the adjustment device. In order to initiate the axial displacement of the sliding cam, when it reaches the run-in area of the sliding cams, the actuator pin moves into the displacement grooves that lie deeper than the locking grooves, so that the sliding cam is then displaced. The displacement groove here passes through the area between the two adjacent locking grooves. This crossing takes place twice for the back and forth movement of the sliding cam between two adjacent cam disks. At this location is then also a side opening of the flanks of the locking grooves and a short section without lateral guidance in the locking groove. During this phase, however, the displacement cam is located in the reference circle of the cam travel, i.e., the actuation element and the gas-exchange valves are not actuated in this area. Therefore, at this point in time, the lowest axial forces act on the displacement cams, so that the guiding gap for the locking of the sliding cam is not harmful. 
     Thus, because the locking device, which has a spring, locking element, recesses, and, above, all, holes, is eliminated, the transverse forces that act on the actuator pin and the displacement groove flanks are also smaller. In addition, a longer displacement area can be selected, in order to likewise reduce the forces on the actuator pin and the displacement groove. 
     Advantageously, the width of the displacement groove and the width of the locking groove are the same, so that both grooves can be contacted by means of the same actuator pin. 
     The actuator pin is advantageously arranged in the adjustment device so that it is in active engagement with the locking grooves or their flanks in the base position that normally corresponds to the de-energized state of the adjustment device and so that the adjustment device contacts the displacement grooves in a run-out stage. Therefore, only simple activation of the actuator pin is required. 
     In order to keep the material expense for the sliding cams and thus the weight low, the locking grooves are formed by disk-shaped guiding contours that are arranged on an essentially circular cylindrical peripheral area of the displacement cam. 
     In one alternative construction of the invention it is provided that the adjustment device has locking elements that are in active engagement with the locking grooves. The locking elements are here advantageously formed as sleeves that surround the actuator pins. These sleeves guide the sliding cam in the locking grooves. Therefore it is possible that the width of the locking grooves is larger in this case than the width of the displacement grooves, because the sleeves can have a certain wall thickness around the actuator pins. 
     However, the sleeves can also have, in the area of the locking grooves, lateral flattened sections that extend up to the periphery of the actuator pins. Then the grooves can have the same width. 
     Because the sleeves have flattened sections, that is, guiding surfaces, in front of and behind the actuator pins, the guidance of the sliding cams is improved, because a longer guidance of the sleeves in the locking grooves is given in the peripheral direction. 
     Due to the construction according to the invention, i.e., positioning of the sliding cams over the flanks of the locking grooves, the position and production tolerances are reduced so that the displacement groove can also have an optimum acceleration for the axial movement. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For further explanation of the invention, reference is made to the drawings in which embodiments of the invention are shown simplified. Shown are: 
         FIG. 1 : a perspective view of a section of a sliding cam with two locking grooves and one displacement groove; 
         FIG. 2 : a perspective view similar to  FIG. 1  with a displacement groove in the opposite direction; 
         FIG. 3 : a side view of a cutout similar to  FIG. 2  with an actuator pin and a part of an adjustment device; 
         FIG. 4 : a view corresponding to  FIG. 3  with extended actuator pin; 
         FIG. 5 : a view corresponding to  FIGS. 1 and 2  in different rotational position; 
         FIG. 6 : a section through  FIG. 5  according to line A-A; 
         FIG. 7 : a view of a sliding cam with adjustment device and two actuator pins; 
         FIG. 8 : a view corresponding to  FIG. 7  at an enlarged scale, and 
         FIG. 9 : a perspective view of a part of the adjustment device with actuator pins and sleeves. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In  FIGS. 1 to 9 , as far as shown in detail, a sliding cam is marked with  1  that has cam disks with different travel, but identical reference circles, on both sides of the adjustment and locking areas, as shown, in particular, in  FIGS. 7  and  8 . The sliding cam  1  also has locking grooves  2  and displacement grooves  3  between the cam disks. The locking grooves  2  are limited by guide contours  4  that project from a cylindrical area of the sliding cam  1 . The displacement grooves  3  are formed between two adjacent locking grooves  2 , in order to cause a displacement of the sliding cams  1  on a not-shown shaft, so that the cam disks can be brought individually into active engagement with not-shown actuation elements, in order to initiate raising movements to the corresponding gas-exchange valves. The displacement grooves  3  are formed, as can be seen, in particular, in  FIGS. 4 and 5 , on a peripheral area of the sliding cams  1  lying deeper relative to the locking grooves. 
     Furthermore, an adjustment device is marked with  5  (see, in particular,  FIG. 7 ) that has electromagnetically activated actuator pins  6  that extend permanently into the locking grooves and can also engage in the displacement grooves  3  in another run-out stage. In  FIGS. 3 and 4 , an actuator pin  6  is shown for illustrating the inventive proposal, while the adjustment device  5  has two actuator pins  6  according to  FIGS. 7 to 9 . As shown in  FIGS. 7 to 9 , sleeves  7  enclose the actuator pins  6  and project into the locking grooves  2 . In the embodiment according to  FIGS. 7 to 9 , the sleeves  7  have lateral flattened sections  8  that extend up to the periphery of the actuator pins  6 . 
     As can be seen in  FIGS. 1 to 8 , the guide grooves  4  have breaks that allow the passage of the displacement groove  3  from a locking groove  2  into the other locking groove  2  and a passage of the base area of an actuator pin  6  or a sleeve  7 . 
     Because the sliding cam  1  is displaced when the not-shown actuation element is located in the reference circle of the cam disk and the sliding cam  1 , the breaks are also allocated to this peripheral area. In this peripheral area, however, is the lowest axial load of the sliding cam, so that the break of the guide contours is problem-free. Furthermore, the sliding cam  1  is guided in this area exactly over the displacement groove  3 . In addition, the flattened sections  8  of the sleeves  7  produce an extended guide area on the guide contours  4 , so that even when the internal combustion engine is stopped, due to the thermal displacements there are no problems that cannot be compensated with the run-out bevels  9  on the guide contours  4 . 
     It should still be noted that the use of two actuator pins with and without locking elements can lead to a reduction of the width of the locking groove area, because a single guide contour  4  (see, e.g.,  FIG. 8 ) that is enclosed by locking elements, e.g., the sleeves  7 , or the actuator pins  6 , is sufficient for guiding the sliding cam  1  in the axial direction. 
     List of Reference Numbers 
       1  Sliding cams 
       2  Locking grooves 
       3  Displacement grooves 
       4  Guide contours 
       5  Adjustment device 
       6  Actuator pins 
       7  Sleeves 
       8  Flattened sections 
       9  Run-out bevels