Internal combustion engine valve drive arrangement

In an internal combustion engine valve drive arrangement having cam elements which are supported on a camshaft so as to be axially displaceable and having switch gates which are coupled to the cam elements and have gate tracks with track segments and switching segments for displaceing the cam elements, the track segments and the switching segments are formed, at least in part, in partial areas of the switch gates.

BACKGROUND OF THE INVENTION

The invention relates to an internal combustion engine valve drive arrangement including cam elements supported on a cam shaft so as to be axially displaceable and switch gate mechanisms coupled to the cam elements for axially moving the cam elements.

An internal combustion engine valve drive arrangement having independently axially displaceable cam elements and having a switch gate for displacing the cam elements is already known from DE 10 2004 021 375 A1.

It is the object of the present invention to provide a valve lift switching arrangement for an internal combustion engine having at least three cylinders arranged in a row wherin the three cyliders have different valve activation times.

SUMMARY OF THE INVENTION

In an internal combustion engine valve drive arrangement having cam elements which are supported on a camshaft so as to be axially displaceable and having switch gates which are coupled to the cam element and have gate tracks with track segments and switching segments for displaceing the cam element, the track segments and the switching segments are formed, at least in part, in partial areas of the switch gates.

It is proposed that the track segment and the switching segment are designed in one piece in at least one partial area. An angular range which includes the track segment and the switching segment may thus advantageously be kept small, so that the gate track may advantageously have a large number of switching segments. In particular, a continuous gate track having at least three switching segments may thus be implemented, so that valve lift switching for an internal combustion engine having at least three cylinders arranged in a row, having different valve activation times, may be achieved. A “switch gate” is understood to mean a unit for axially displacing the at least one cam element, and which has at least one gate track that is provided for converting a rotary motion into an axial adjusting force. A “gate track” is understood in particular to mean a track for forced guidance on one or both sides of a switch pin. The gate track is preferably designed in the form of a web, in the form of a slot, and/or in the form of a groove. The switch pin is preferably designed in the form of a shifting shoe which surrounds the web, in the form of a pin which engages in the slot, and/or in the form of a pin which is guided in the groove.

A “track segment” is understood to mean a segment of the gate track which has at least one radial inclination. A “radial inclination” is understood in particular to mean that the gate track in this segment has an inclination by which a progression of the gate track radially deviates from a circular line about a main rotational axis of the at least one cam element, as the result of which a rotary motion of a camshaft may be converted into a radially acting force. The track segment is preferably designed as a meshing segment of the gate track or as a demeshing segment of the gate track. A “meshing segment” is understood in particular to mean a segment in which the radial inclination results in an effective height which increases in the rotational direction. A “demeshing segment” is understood in particular to mean a segment in which the radial inclination results in an effective height which decreases in the rotational direction. A “rotational direction” is understood in particular to mean a direction of rotation along which the cam element is acted on by a rotary motion during a valve activation.

A “switching segment” is understood in particular to mean a segment of the gate track which has at least one axial inclination. An “axial inclination” is understood in particular to mean that the gate track in this segment has an inclination by which a progression of the gate track axially deviates from a circular line about a main rotational axis of the at least three cam elements, as the result of which a rotary motion of the camshaft may be converted into an axially acting force. A “segment” is understood in particular to mean a portion of the gate track with which a defined function, for example switching the at least one cam element, meshing a switch pin, or demeshing a switch pin is associated. In principle, the gate track may have multiple segments of the same type situated one behind the other, for example multiple switching segments having different functions, for example switching of different cam elements. In this context, “in one piece” is understood in particular to mean that the gate track has a double functionality in the partial area, i.e., is simultaneously provided for meshing or demeshing a switch pin and for switching the at least one cam element.

It is further proposed that the at least one track segment includes a partial area which has only a radial inclination. The track segment may thus be partially separate from the switching segment, so that the switch pin may be meshed with the gate track in a particularly secure manner. In this context, “only” is understood in particular to mean that the track segment in the partial area has only one increasing or decreasing effective height. In particular, this term is understood to mean that the gate track in this partial area has no axial inclination.

In addition, it is proposed that the switching segment includes a partial area which has only an axial inclination. The switching segment may thus be provided with a length, necessary for switching the at least one cam element, which keeps forces acting on the switch pin sufficiently small. The switching segment preferably has a length of at least 60 degrees camshaft angle, advantageously at least 80 degrees camshaft angle, and particularly advantageously at least 100 degrees camshaft angle. An “angular range” is understood in particular to mean an extension of the cam element in the peripheral direction. A degree indication in “degrees camshaft angle” is understood in particular to mean the degree indication based on the camshaft; i.e., one revolution of the camshaft corresponds to 360 degrees camshaft angle.

In one particularly advantageous embodiment, it is proposed that the at least one gate track has an axial inclination and a radial inclination in the at least one partial area in which the track segment and the switching segment are designed in one piece. The partial area in which the track segment and the switching segment are designed in one piece may thus have a particularly advantageous design.

In one refinement of the invention, it is proposed that the internal combustion engine valve drive arrangement has at least two gate elements, each of which forms a portion of the at least one track segment. As the result of distributing the track segment over two gate elements, the switching segment may be situated completely on one of the gate elements, while the track segment connected upstream or downstream from the switching segment may be provided with a sufficient angular extent. A “gate element” is understood in particular to mean an element which at least partially forms the gate track. In principle, the gate element may be designed in one piece with the cam element.

The partial area of the track segment, which has only the radial inclination, is preferably situated, at least for the most part, on one of the gate elements. The partial area in which the track segment and the switching segment are designed in one piece may thus advantageously be situated on the second gate element, so that the switching segment may advantageously be provided for switching the second gate element. The term “for the most part” is understood in particular to mean that at least 50 percent, advantageously at least 60 percent, and particularly advantageously at least 75 percent, of the partial area which has only the radial inclination is situated on the first gate element.

In addition, it is advantageous for the switching segment to be situated completely on one of the gate elements. The second gate element may thus advantageously be displaced by means of the switching segment, so that switching capability of a cam element which is associated with the second gate element may advantageously be achieved. In this context, “completely” is understood in particular to mean that the switching segment which is situated on the second gate element is delimited by two partial areas which are situated on the second gate element and which extend in the peripheral direction. One of the partial areas is preferably formed by the track segment, and the second partial area is preferably formed by a transition segment. A “transition segment” is understood in particular to mean a partial area of the gate track which has neither an axial inclination nor a radial inclination. In one advantageous embodiment, all switching segments in each case are completely situated on one of the gate elements.

In addition, it is proposed that the internal combustion engine valve train device has at least one further track segment which has an axial inclination in at least one partial area. Switching capability of at least one further cam element may thus be achieved, so that an internal combustion engine valve train device may be implemented for an internal combustion engine having four or more cylinders.

At least one of the track segments preferably forms a meshing segment, and at least one of the track segments preferably forms a demeshing segment. An advantageous design of the gate track, in particular having a short length, may thus be achieved.

The internal combustion engine valve train device particularly advantageously includes a further switching segment which is designed, at least in part, in one piece with the further track segment. Thus, the meshing segment may be designed in one piece with the one switching segment, and the demeshing segment may be designed in one piece with the further switching segment, so that the length of the gate track may have a particularly advantageous design.

The invention will become more readily apparent from the following description of an exemplary embodiment of the invention with reference to the accompanying drawings. The drawings, the description, and the claims contain numerous features in combination. Those skilled in the art will also advantageously consider the features individually and combine them into further meaningful combinations.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

FIGS. 1 through 14show an internal combustion engine valve drive arrangement according to the invention. The internal combustion engine valve drive arrangement is provided for an internal combustion engine having at least three cylinders arranged in a row which have different valve activation times. The internal combustion engine valve drive arrangement may be used for an internal combustion engine in which only three cylinders are arranged in a row, such as for an in-line engine having three cylinders or a V engine having six cylinders, for example. However, the internal combustion engine valve drive arrangement is also usable for an internal combustion engine in which six cylinders are arranged in a row, each having the same or at least similar valve activation times.

The internal combustion engine valve drive arrangement includes a camshaft33having three cam elements10,11,12. The cam elements10,11,12are in the form of cam supports. At least one cam34, having two partial cams35,36with different valve activation curves, is situated on each of the cam elements10,11,12. The partial cams35,36of each of the cams34are each situated directly adjacent to one another. The cam elements10,11,12are axially displaceable. A switch is made inside the cam34from one partial cam35to the other partial cam36by means of an axial displacement of one of the cam elements10,11,12. Thus, each of the cam elements10,11,12has two discrete switching positions in which a different valve lift is switched for the cylinder(s) associated with the corresponding cam element10,11,12.

The camshaft33has a drive shaft37for mounting of the cam elements10,11,12. The drive shaft37includes a crankshaft connection for connection to a crankshaft, not illustrated in greater detail. The crankshaft connection may be provided via a camshaft adjuster which is provided for setting a phase position between the camshaft33and the crankshaft.

The cam elements10,11,12are axially displaceable on the drive shaft37in a rotationally fixed manner. The drive shaft37has spur toothing on its outer periphery. The cam elements10,11,12have corresponding spur toothing on their inner periphery which engages with the spur toothing of the drive shaft37.

In addition, the internal combustion engine valve train device includes a switch gate13. The switch gate13is provided for sequentially displacing the three cam elements10,11,12one after the other in a switching operation. The switch gate13includes two gate tracks14,15for displacing the cam elements10,11,12. The first gate track14is provided for displacing the cam elements10,11,12along a first switching direction from the first switching position into the second switching position (seeFIGS. 5 through 9). The second gate track15is provided for displacing the cam elements10,11,12along a second switching direction from the second switching position into the first switching position (seeFIGS. 10 through 14).

Furthermore, the internal combustion engine valve drive arrangement includes a switching unit30which has switch pins31,32for engaging with the gate tracks14,15, respectively. The switching unit30has a stator housing38which is fixedly connected to an engine block, not illustrated in greater detail, of the internal combustion engine. The switch pins31,32are situated in the stator housing38so as to be displaceable along their main direction of extension. The gate tracks14,15are in the form of grooves in which the switch pins31,32, respectively, may be forcibly guided on both sides. During a switching operation in the first switching direction, the first switch pin31is brought into engagement with the first gate track14. During a switching operation in the second switching direction, the second switch pin32is brought into engagement with the second gate track15.

The gate tracks14,15have a plurality of switching segments20,21,22,23,24,25. The first gate track14includes the three switching segments20,21,22, which are provided for switching the three cam elements10,11,12in the first switching direction. The switching segments20,21,22are each associated with exactly one of the cam elements10,11,12. The gate track14also includes a track segment16forming a meshing segment and a track segment18forming a demeshing segment. The second gate track15has an analogous design. The second gate track15includes the three switching segments23,24,25, a track segment17designed as a meshing segment, and a track segment19forming a demeshing segment.

The switching segments20,2122,23,24,25each have an axial inclination. Due to the axial inclination, the cam element10,11,12which is associated with the corresponding switching segment20,21,22,23,24,25is displaced when the corresponding switch pin31,32is engaged with the corresponding switching segment20,21,22,23,24,25. The track segments16,17have a radial inclination. The gate tracks14,15, which are designed as grooves, have a continuously increasing depth in a partial area of the track segments16,17forming meshing segments. The corresponding gate track14,15has an essentially constant depth in an area situated between the track segment16,17and the corresponding track segment18,19forming a demeshing segment. The corresponding gate track14,15has a continuously decreasing depth in the area of the track segments18,19.

Each of the two gate tracks14,15is continuous; i.e., the switch pin31,32brought into engagement with the gate track14,15, respectively, via the corresponding track segment18,19runs in succession through the switching segments20,21,22,23,24,25of the corresponding gate track14,15before the switch pin31,32is again released from the gate track14,15by means of the track segment18,19. The cam elements10,11,12are thus sequentially switched one after the other. In a switching operation along the first switching direction, first the axially outer cam element,10, then the axially middle cam element11, and lastly the axially outer cam element12is switched. In a switching operation along the second switching direction, first the axially middle cam element11then the axially outer cam element12, and lastly the axially outer cam element10is displaced. Thus, the two switching operations are not symmetrical with respect to a switching sequence of the cam elements10,11,12.

For forming the two gate tracks14,15, the internal combustion engine valve drive arrangement includes three gate elements26,27,28. The first gate element26is designed in one piece with the first cam element10. The second gate element27and the second cam element11are likewise designed in one piece. The third gate element28is situated at a distance from the third cam element12, and is connected to the third cam element12in a rotationally fixed as well as an axially fixed manner.

The switch gate13is situated in an area of the camshaft33in which the axially outer cam element10and the axially middle cam element11adjoin one another. In this area the two gate elements26,27have only an angular range of 120 degrees camshaft angle in each case. The third gate element28is likewise situated in the area of the camshaft33in which the cam elements10,11adjoin one another. The gate element28likewise has an angular range of 120 degrees camshaft angle. In the area of the switch gate13, the three gate elements26,27,28thus have approximately equal angular ranges. Thus, in a rotation of the camshaft33by 360 degrees camshaft angle, the first gate element26, the second gate element27, and the third gate element28face the switching unit30in succession,

The three gate elements26,27,28form the gate tracks14,15. The gate tracks14,15, which are grooves, are cut directly into the gate elements26,27.28. The three gate elements26,27,28in each case form a portion of the gate track14,15.

The track segment16of the gate track14which is a meshing segment starts on the third gate element28and ends on the first gate element26. The first switching segment20of the gate track14is situated completely on the first gate element26. The second switching segment21of the gate track14is situated completely on the second gate element27. The third switching segment22of the gate track14is situated completely on the third gate element28. The track segment18of the gate track14which is a demeshing segment extends from the third gate element28to the first gate element26. The gate track14thus extends over an angle that is larger than 360 degrees camshaft angle.

The track segment17of the gate track15starts on the first gate element26and ends at the second gate element27. The first switching segment23of the gate track15is situated on the second gate element27. The second switching segment24of the gate track15is situated on the third gate element28. The third switching segment25of the gate track15is situated on the first gate element26. The track segment19of the gate track15extends from the third gate element28to the first gate element26. The gate track15thus likewise extends over an angle that is larger than 360 degrees camshaft angle.

The third gate element28and the axially outer cam element12are coupled to one another for axial movement (seeFIG. 2). The drive shaft37is designed, at least in part, as a hollow shaft. The internal combustion engine valve drive arrangement includes a connecting unit29which couples the third gate element28to the third cam element12. The connecting unit29includes a coupling rod39which is guided in the drive shaft37. The drive shaft37includes a first opening through which the coupling rod39is coupled to the gate element28, and a second opening through which the coupling rod39is coupled to the cam element12. The cam element12is thus coupled to an axial motion of the gate element28in an at least practically rigid manner. The cam element12and the gate element28are connected to one another in a rotationally fixed manner via the drive shaft37.

The first gate track14is provided for an adjustment of the cam elements10,11,12in the first switching direction. The second gate track15is situated in a mirror image with respect to the first gate track14and phase-shifted relative to same. Thus, the structure of the second gate track15corresponds to that of the first gate track14. A difference between the two gate tracks14,15is that the axial inclination of the switching segments23,24,25of the second gate track15is directed oppositely with respect to the axial inclination of the switching segments20,21,22of the first gate track14. In addition, a start of the second gate track15is phase-shifted with respect to a start of the first gate track14. Thus, due to the structural similarities, in particular the first gate track14is described below; a description of the first gate track14, taking into account the phase offset, in principle is analogously applicable to the second gate track15.

The track segment16of the gate track14designed as a meshing segment, the switching segments, and the first switching segment20are partially designed in one piece. The gate track14has an axial inclination and a radial inclination in a partial area in which the track segment16and the switching segment20are designed in one piece. In addition, the track segment18designed as a demeshing segment and the switching segment22are partially designed in one piece. The gate track14likewise has an axial inclination and a radial inclination in a partial area in which the track segment18and the switching segment22are designed in one piece.

The track segment16designed as a meshing segment, the switching segments20,22, and the track segment18designed as a demeshing segment are also partially separate. Originating from a start, the gate track14includes a partial area which has solely a radial inclination. In this partial area, in which the gate track14extends in the peripheral direction and has only an increasing radial depth, the track segment16is separate from the switching segment20. The partial area in which the track segment16and the switching segment20are separate is situated for the most part on the gate element28.

The partial area in which the switching segment20and the track segment16are designed in one piece adjoins the partial area which has solely the radial inclination. The switching segment16, and thus also the partial area in which the track segment16and the switching segment20are designed in one piece, is situated completely on the cam so element10.

A partial area of the gate track14in which the gate track14has solely an axial inclination adjoins this partial area. The switching segment20and the track segment16are once again separate in this partial area. The gate track14has an approximately constant depth in this partial area. The switching segment20is followed by a transition segment40in which the gate track14has neither a radial inclination nor an axial inclination. The transition segment40provides a transition from the cam element10to the cam element11. The transition segment40is formed partly by the cam element10. The transition segment40is situated between the two switching segments20,21.

The portion of the gate track14that is situated on the gate element27has an essentially constant depth. The gate element27forms a further portion of the transition segment40. In addition, the switching segment21is situated completely on the cam element11.

For a transition between the switching segment21and the switching segment22, the gate track14includes a further transition segment41which has neither a radial inclination nor an axial inclination. The further transition segment41adjoins the switching segment21. The transition segment41is formed partly by the cam element11and partly by the gate element28.

The switching segment22associated with the cam element12adjoins the transition segment41. The gate track14initially has solely an axial inclination in a partial area which directly adjoins the transition segment41. The switching segment22is initially separate from the track segment18which is a demeshing segment.

In its further progression, the gate track14once again has a partial area with an axial inclination and a radial inclination. The track segment18and the switching segment22are designed in one piece in this partial area. In the partial area in which the track segment18and the switching segment22are designed in one piece, the gate track14has a decreasing depth. This partial area is adjoined by a partial area in which the track segment18is separate from the switching segment22. In this latter partial area, the gate track14has solely a radial inclination. A majority of the partial area in which the track segment18is separate from the switching segment22is formed by the first gate element26.

The switch pins31,32of the switching unit30are respectively provided for one of the two switching directions in which the cam elements10,11,12may be displaced. The switch pin31provided for the first switching direction is extended in order to displace the cam elements10,11,12in the first direction. The switch pin31is brought into engagement with the track segment16of the first gate track14in the form of a meshing segment due to the rotary motion of the camshaft33(seeFIG. 5). Upon further rotary motion of the camshaft33, the switch pin31initially partially meshes with the gate track14without an axial force being exerted on one of the cam elements10,11,12.

The switch pin31engages with the switching segment20, which is situated on the first gate element26and associated with the first cam element10, due to the further rotary motion of the camshaft33(seeFIG. 6). As a result of one-piece design of the switching segment20and the track segment16designed as a meshing segment, the switch pin31is also engaged with the track segment16. The rotary motion of the camshaft33thus brings about an axial force on the cam element10, while the switch pin31engages further with the gate track14. The cam element10is displaced from the first switching position into the second switching position due to the engagement of the switch pin31with the switching segment20and the rotary motion of the camshaft33.

After the switch pin31has completely passed through the switching segment20, the cam element10is switched into the second switching position. The switch pin31engages with the first transition segment40due to the further rotary motion. As a result of the rotary motion of the camshaft33, the switch pin31is transferred from the portion of the gate track14that is situated on the first gate element26to the portion of the gate track14that is situated on the second gate element27.

Due to the further rotary motion, the switch pin31becomes engaged with the switching segment21which is situated on the second gate element27and associated with the second cam element11(seeFIG. 7). The rotary motion of the camshaft33and the engagement of the switch pin31with the switching segment21bring about an axial force on the cam element11which switches the cam element11from the first switching position into the second switching position. After the switch pin31has completely passed through the switching segment21, the cam element11is switched into the second switching position.

Upon further rotary motion of the camshaft33, the switch pin31is transferred via the transition segment41from the second gate element27to the third gate element28. The switch pin31thus becomes engaged with the switching segment22which is situated on the gate element28and is associated with the cam element12.

Since the switching segment22is partly separate from the track segment18designed as a demeshing segment, the rotary motion of the camshaft33and the engagement of the switch pin31with the gate track14initially bring about only an axial force on the cam element12. Due to the further rotary motion, the switch pin31reaches the partial area in which the switching segment22and the track segment18are designed in one piece (seeFIG. 8). The switch pin31is thus already demeshed, while a force still acts on the cam element12which displaces the cam element12along the first switching direction.

As soon as the switch pin31has passed through the switching segment22, the cam element12is also switched into the second switching position. The switch pin31is further demeshed due to the track segment18designed [as a demeshing segment], which is also separate from the switching segment22(seeFIG. 9). During the demeshing, the switch pin31is pushed into the stator housing38due to the rotary motion of the camshaft33and the radial inclination of the gate track14. As soon as the switch pin31has completely passed through the track segment18which is a demeshing segment, the switching operation of the cam elements10,11,12from the first switching position into the second switching position is fully complete.

A switching operation in the second switching direction by means of the second gate track15is carried out in an analogous manner. After the meshing into the track segment17of the gate track15(seeFIG. 10), the switch pin32passes through the track segment17and the switching segment23(seeFIG. 11). The switch pin32is then transferred to the subsequent switching segment24by means of a transition segment42(seeFIG. 12). The switch pin32is transferred to the switching segment25by means of a transition segment43(seeFIG. 13), and is subsequently again demeshed by means of the track segment19(seeFIG. 14).

The track segments16,17designed as meshing segments each have an angular range of approximately110degrees camshaft angle. The switching segments20,21,22,23,24,25each have an angular range of likewise approximately 110 degrees camshaft angle. The transition segments40,41,42,43each have an angular range of approximately 10 degrees camshaft angle. The track segments18,19designed as demeshing segments each have an angular range of approximately 95 degrees camshaft angle.

The track segment16and the first switching segment20of the first gate track14are designed in one piece over an angular range of approximately 40 degrees camshaft angle. The last switching segment22of the first gate track14and the track segment18are likewise designed in one piece over an angular range of approximately40degrees camshaft angle. The second gate track15has an analogous design. The gate tracks14,15thus each have a length of approximately 475 degrees camshaft angle. Thus, the track segments16,17designed as meshing segments and the track segments18,19of the gate tracks14,15, respectively, designed as demeshing segments are each partly axially situated next to one another.

To prevent improper meshing of the switch pins31,32directly into one of the switching segments20,21,22,23,24,25while skipping the corresponding meshing track segment16,17, the internal combustion engine valve train unit has a cover unit44(seeFIG. 3). The cover unit44is provided for covering unused parts of the gate tracks14,15.

For partially covering the first gate track14, the cover unit44includes a first cover element45which is fixedly connected to the first gate element26, which forms the meshing track segment16. The switching segment21of the second cam element11and the switching segment22of the third gate element28are covered by the cover element45in an operating state in which the cam elements10,11,12are in one of the switching positions. The meshing track segment16and the switching segment20of the first gate element26are open. The cover element45, which is coupled to the first gate element26, releases the switching segment21of the second gate element27and the switching segment22of the third gate element28due to the displacement of the first cam element10by means of the first switching segment20. The switch pin31may thus mesh with the gate track14solely via the portion of the gate track14, situated on the first gate element26, into the switching segments21,22of the gate track14situated on the second gate element27and the third gate element28.

The cover unit44includes a second cover element46for partially covering the second gate track15. The second cover element46has a design that is analogous to the first cover element45. Both cover elements45,46are designed in the form of a sleeve, which in the appropriate switching position encloses parts of the switch gate13, and thus partially covers the gate tracks14,15. The cover elements45,46have an angular range of approximately240degrees camshaft angle. The segments16,17designed as meshing segments are partially introduced into the cover elements45,46.

The switching unit30has a bistable design. The two switch pins31,32may remain in an unactivated state in an extended switching position and also in a retracted switching position. The switch pins31,32have an unstable middle position. If one of the switch pins31,32is in a position between the extended switching position and the middle position, the corresponding switch pin31,32automatically switches into the extended switching position. If one of the switch pins31,32is in a position between the retracted switching position and the middle position, the corresponding switch pin31,32automatically switches into the retracted switching position.

For extending the switch pins31,32, the switching unit30includes an electrical actuator unit by means of which a force for the extension may be exerted on the switch pins31,32. The switch pins31,32are independently extendable. The actuator unit is provided solely for extending the switch pins31,32. The switch gate13is provided for retracting the switch pins31,32. During the demeshing of the switch pins31,32from the corresponding gate track14,15, respectively, the switch pins31,32are moved over the unstable middle position and automatically retract. Thus, the track segments18,19of the gate tracks14,15designed as demeshing segments are provided for retracting the switch pins31,32.

The internal combustion engine valve train device has a locking unit47for locking the cam elements10,11,12in the switching positions. The cam elements10,11,12in each case have two locking positions. The locking unit47includes a plurality of locking recesses48,49,50which are provided at the inner sides of the cam elements10,11,12. In addition, the locking unit47includes a plurality of thrust pieces51,52,53which are fixedly connected to the drive shaft37. The cam elements10,11,12are locked with respect to the drive shaft37by means of the thrust pieces51,52,53.

A sequence in which the switch pins31,32come into engagement with the cam elements10,11and the gate element28while passing through the corresponding gate track14,15may have any given design in principle. For example, it is conceivable for the gate element28to have a track segment designed as a meshing segment, the gate element27subsequently being situated on the gate element28, and the gate element26having a track segment designed as a demeshing segment. A sequence in which the cam elements10,11,12are thus displaced is freely definable in principle.