EP2839122B1 - Valve train of an internal combustion engine, and internal combustion engine - Google Patents

Description

The invention relates to a valve train of an internal combustion engine, with at least one base camshaft on the rotationally fixed and axially displaceable between at least two axial positions at least one Ventilbetätigungsnocken exhibiting cam carrier is provided, wherein the cam carrier for axial displacement by means of an actuator associated with a shift gate, which on its circumference has two opposing in the axial direction, intersecting slide tracks, each having a reversal point. The invention further relates to an internal combustion engine with a valve train.

Valve trains of the type mentioned are known from the prior art. They are used for internal combustion engines, in which the cycle of gas exchange valves of individual cylinders of the internal combustion engine can be influenced to improve the thermodynamic properties. The at least one cam carrier, which may also be referred to as a cam piece, is arranged rotationally fixed and axially displaceable on the base camshaft. The cam carrier is usually associated with a plurality, that is to say at least two, valve actuation cams. Each of these valve actuation cams has an eccentricity, which serves to actuate one of the gas exchange valves of the internal combustion engine at a specific angle of rotation of the basic camshaft. Accordingly, the valve actuating cam run together with the base camshaft so that the respective gas exchange valve of the internal combustion engine is actuated by the associated valve actuating cam or its eccentricity at least once per revolution of the basic camshaft. The valve actuating cam cooperates preferably with a roller rocker arm of the gas exchange valve by coming into abutting contact with this.

Preferably, a plurality of valve actuation cams are provided, which may be assigned to different cam groups. The valve actuation cams of a cam group now differ, for example, with regard to the angular position of their eccentricity or the extent of the same in the radial direction (height) and / or in the circumferential direction (length). By the axial displacement of the cam carrier this can be brought into at least two, for example in a first and a second, axial position. In the first axial position, the gas exchange valve becomes a first of the valve actuation cams and, in the second axial position, a second of the valve actuation cams operated, which are assigned to the same cam group. As a result of the displacement of the cam carrier, in particular the opening time, the opening duration and / or the lift of the gas exchange valve, in particular as a function of an operating state of the internal combustion engine, can be selected.

The displacement or displacement of the cam carrier in the axial direction takes place with the aid of an adjusting device, which comprises a shift gate on the cam carrier and a stationarily arranged actuator, usually in a cylinder head of the internal combustion engine. The actuator has an extendable driver, which can be brought into engagement with an example helical or spiral slide track of the shift gate. The slide tracks are provided on the shift gate, which is assigned to the cam carrier. For example, the shift gate is formed on the cam carrier or operatively connected thereto for axial displacement. The slide tracks are each along a course of a preferably, but not necessarily continuous curved path and have a certain width, which is preferably adapted to the width of the driver of the actuator. Usually, the slide track is slightly wider than the driver, so that a smooth passage through the slide track is possible by the driver. The slide tracks are, for example, as radial grooves, which pass through the circumference of the shift gate, so are formed open-edge in this.

The curved path, for example, is centrally located in the slide track and is a line in the mathematical sense. This line can be composed of several line sections. If in the following from a point of the slide track is mentioned, so is always a point on the slide track underlying cam track meant. The slide tracks run at least partially in the axial direction in opposite directions and intersect at a crossing point. Each of the slide tracks has a turning point. In accordance with the above explanations, this reversal point is to be understood as meaning a point on the curved path, the latter describing the course of the slide track. The reversal point corresponds, for example, to a point of the slide track, when it is reached by the driver of the actuator, the cam carrier is present exactly between two axial positions of the cam carrier, in particular in a dead center between the axial positions. Usually, the curved path runs straight in a section around the turning point, ie it has a constant pitch in the axial direction, but not a bend. In this case, the turning point coincides, for example, with the center of this straight section (seen in the longitudinal direction of the section). In a specific embodiment corresponds the turning point is a turning point of the curved path, ie a point at which the curved path changes its curvature behavior. In the reversal point, it changes in this case either from a right-hander to a left-hander or vice versa. Such a change can also be referred to as a bow change. In known from the prior art valve trains usually fall the reversal points of the slide tracks with the intersection of the intersecting slide tracks together.

In the design of the internal combustion engine, numerous parameters are often fixed, for example, a distance between the individual cylinders of the internal combustion engine. In addition, it is desirable to reduce the installation space of the internal combustion engine. From both conditions it follows that the valve train of the internal combustion engine must be realized with a constant and limited space, which can be problematic if the cam carrier is to be axially displaceable, in particular multi-stage displaceable. For this reason, the above-described, intersecting course of the slide tracks is often used in such a valve train. In this context, for example, describes the DE 10 2009 053 116 A1 a valve train of an internal combustion engine, comprising a carrier shaft and a rotationally fixed between two axial displaceable arranged cam piece having at least one cam group immediately adjacent cam with different cam lobes and designed as a groove Axialkulisse with outer guide walls for specifying two intersecting slide tracks , And with an engageable in the Axialkulisse actuating pin for moving the cam piece in the direction of both slide tracks.

From the prior art are still the DE 20 2009 011 804 U1 as well as the DE 10 2009 007 819 A1 known. The first document shows a device for camshaft adjustment of an internal combustion engine, in which a ram unit has a constant outer diameter at the first engagement depth and at a second penetration depth and is driven along the direction of movement by an electromagnetic actuator which has a first stable positioning position for the first penetration depth, a second stable parking position for the second penetration depth and a third parking position for a disengaged state of the ram unit in a first and second control drive controllably offers. The latter document shows a valve train of an internal combustion engine, in which guide vanes are provided with journals which are rotatably received in both sides of the crossing region of the slide tracks on the groove bottom of the axial slide bearing points. In addition, the guide has a guide vanes coupling steering linkage, which is hinged to the bearing pin and synchronized the opposite direction of rotation of the guide vanes.

In such a valvetrain, however, the problem arises that the driver of the actuator during the passage at least one of the slide tracks - usually in the region of the intersection - without lateral guidance, because the guide wall of the slide track, from which the driver is guided in the axial direction, is interrupted by the crossing of the other gate track. The cam carrier must therefore, in order to complete the axial displacement, move with the help of the kinetic energy already impressed on the cam carrier by the driver, at least over a short distance due to its inertia. However, this requires the application of a sufficient amount of kinetic energy. The applied kinetic energy increases with the speed of the internal combustion engine, because the basic camshaft is usually fixedly coupled to a crankshaft of the internal combustion engine. This still means that the internal combustion engine must be operated at a minimum speed to allow a successful axial displacement of the cam carrier by means of the actuator. However, this is not desirable because it may also be necessary in operating ranges of the internal combustion engine with a lying below the minimum speed for compliance with emission limits and / or to achieve optimal efficiency of the internal combustion engine, the cycle of the gas exchange valves by the axial displacement of the cam carrier influence.

It is therefore an object of the invention to propose a valve train of an internal combustion engine, which does not have the disadvantages mentioned above, but in particular allows a reliable axial displacement of the cam carrier even at low speeds of the internal combustion engine.

This is achieved according to the invention with a valve train having the features of claim 1. It is provided that the reversal points are offset in the circumferential direction to each other. These should therefore not, as known from the prior art, in particular in the crossing point coincide. Rather, they are offset from each other so that they are spaced apart at least in the circumferential direction. Usually, they continue to lie in a common longitudinal section plane of the shift gate; a plane perpendicular to the longitudinal axis thus comprises both reversal points and the point of intersection. Thus, in particular, there is a displacement of at least one of the reversal points exclusively in the circumferential direction, but not in axial direction. By moving the reversal points in the circumferential direction to each other, the driver is in contact with at least one of the slide tracks - seen in the circumferential direction - longer with the respective guide wall of the slide track. In this way, the cam carrier is displaced over a greater axial distance than known from the prior art, before the driver gets out of engagement with the guide wall. Accordingly, the cam carrier must travel a smaller remaining distance due to the kinetic energy impressed on it. Accordingly, the reliability of the axial displacement of the cam carrier is significantly increased, because there is no risk that the cam carrier, especially at too low speed of the internal combustion engine, the axial displacement can not complete, so does not reach the desired axial position. In this way, it is possible to perform the axial displacement of the cam carrier even at speeds which are significantly lower than those required in known from the prior art valve trains speeds.

A further development of the invention provides that each guide track in each case has an inlet region, an outlet region and a reversal region connecting them to one another, the inlet region and the outlet region being aligned in the circumferential direction and arranged in the axial direction on opposite sides of the switching element. The inlet region, the reversal region and the outlet region are arranged one behind the other in this order in the circumferential direction or in the direction of rotation of the shifting gate. Engages the driver of the actuator in the slide track, it passes through accordingly first the inlet area, then passes into the reversal area and exits via the outlet area again from the slide track. Preferably, in this case, the outlet region has a ramp which pushes out the driver in the radial direction to the outside, so that the driver is again disengaged from this after a single passage through the slide track. This means that the driver can not intervene again in one of the slide tracks in a subsequent revolution of the basic camshaft or the shift gate, but rather that the axial displacement of the cam carrier is completed after the single passage of the slide track. If the cam carrier is to be displaced again, the driver of the actuator must therefore be relocated inwardly in the radial direction so that it engages with one of the slide tracks, in particular the respective inlet area.

Each of the slide tracks, consisting of the inlet region, the reverse region and the outlet region, preferably extends over almost the entire circumference of the cam carrier. In particular, it can also be provided that the inlet area - seen in the circumferential direction - immediately adjoins the outlet area. Preferably, however, the inlet region is arranged spaced from the outlet region in the circumferential direction. The inlet region and the outlet region are aligned in the circumferential direction, that is not curved in the axial direction. Rather, they run only in the circumferential direction. The reverse region, however, has a course (also) in the axial direction, wherein the reverse regions of the two slide tracks are provided in opposite directions in the axial direction and intersect. The reversal areas accordingly each comprise the intersection point of the slide tracks. Accordingly, the reversal point is also present in each of them. The inlet area and the outlet area are - seen in the axial direction - provided on opposite sides of the shift gate. In this case, the inlet region is connected to the outlet region via the reversal region, so that the reversal region or the part of the reversal region underlying cam track extends both in the circumferential direction and in the axial direction of the shift gate.

A development of the invention provides that the reversal region connects the inlet region and the outlet region with a continuous course, in the center of which the reversal point lies. The part of the curved path, which is encompassed by the reversal region, runs continuously, thus connecting the respective inlet region to the respective outlet region without cracks. In particular, the reversal area is continuously connected to both the inlet area and the outlet area. That is, at a point where the lead-in area encounters the turn area, the turn area corresponds to the orientation of the turn area, the orientation of the lead-in area, and the orientation of the lead-out area, respectively. The pitch in the axial direction coincides in these points between the inlet region and the reversal region or the reversal region and the outlet region in this respect. The reverse region accordingly has a substantially S-shaped profile. The continuous course of the reversal region should now have a midpoint (seen in the longitudinal direction of the course), in which the reversal point of the respective slide track lies. The center of the course, if the reversing area has a straight section, lies in the middle of this straight section. Alternatively, the center may also correspond to the aforementioned inflection point, in which the course changes its curvature behavior from a right-hander to a left-hander, or vice versa.

A development of the invention provides that the inlet area and the reversal area in a starting point and the reversal area and the outlet area collide in an end point, wherein the starting point and / or the end point of one of the slide tracks in the circumferential direction relative to the starting point or the end of the other Sliding coasters are offset. Under the starting point or the end point is first to understand a point in which the curved path passes from the inlet region in the reversal region or from the reversal region in the outlet region. Because the slide track has the specific width, a start line and, under the end point, an end line can be understood correspondingly below the starting point, which are each defined by a specific circumferential position.

In order to offset the reversal points of the slide tracks in the circumferential direction to each other, it is now provided to offset the starting points or end points of the slide tracks against each other. It may be provided only to offset the starting point of one of the slide tracks opposite the starting point of the other of the slide tracks or alternatively the end point of one of the slide tracks opposite the end point of the other of the slide tracks. Preferably, however, both the starting point and the end point of the one of the slide tracks are each arranged offset by the same distance to the starting point and end point of the other of the slide tracks. In this way changes - seen in the circumferential direction - the length of the inlet region and / or the outlet region of the slide track whose starting point or end point is offset, while the length of the reversal region preferably remains the same. If only the starting point or only the end point is displaced, in particular the extent of the reversal area in the circumferential direction changes.

A development of the invention provides that the slide tracks have groove bases, which are at least partially provided, offset in height in the radial direction to each other, whereby the slide tracks with the underlying groove in the radial direction, in particular in the region of the intersection of slide tracks, having a guide wall formed by the height offset. The slide tracks are in the form of grooves formed in the cam carrier. They therefore have groove bases, which form a base or bottom of the grooves, ie a conclusion of the grooves in the radial direction inwards. These groove grounds should be at least partially offset in height for the two slide tracks in the radial direction to each other, ie at the same circumferential position for one of the Sliding linkages have a radial position, which is different from the radial position of the groove base of the other of the slide tracks. In this way, there are guide walls for the slide tracks with the groove base lying deeper in the radial direction, which are formed by the height offset.

The height offset of the groove bottoms is provided in particular in the reversal region or in the region of the intersection of the slide tracks. In such an embodiment, the guide walls formed by the height offset for the actuator or its driver are also in the area of the intersection of the slide tracks, although at least a portion of the guide walls is removed by the intersection of the slide tracks. In that regard, can be realized for the driver of the actuator by the radial offset of the groove bases for at least one of the slide tracks a continuous, also present in the region of the intersection or in the reversal region. The initially described problem of incomplete axial displacement can not occur in an interaction of the actuator with the slide track, which has the guide walls formed by height offset. However, this is still the case for the other of the slide ways.

A development of the invention provides for this reason that the reversal point of the slide track is offset with the groove base lying higher in the radial direction in the direction of rotation of the cam carrier to the front. The direction of rotation is circumferential, but specifies the orientation more accurately. While the circumferential direction points in the direction of rotation as well as in the direction opposite to the direction of rotation, the direction of rotation provides an orientation for the displacement of the reversal points in the circumferential direction relative to one another. Because a continuous guiding is achieved by the actuator or its driver for the slide track with the groove base which lies deeper in the radial direction, the incomplete axial displacement of the cam carrier can not occur for this slide. For this reason, the respective reversing point must be adapted for the respective other slide track, so the slide track with the groove base lying higher in the radial direction, that here better guidance of the cam carrier is achieved by the driver in the axial direction. This is achieved by moving the reversal point in the direction of rotation of the cam carrier forward, ie in the direction of rotation.

A development of the invention provides that the offset is greater than 0 ° and less than or equal to 40 °, in particular at least 10 ° and at most 20 °, preferably exactly 10 ° or 20 °, is. In principle, the offset of the reversal points of the slide tracks can be chosen arbitrarily. The greater the offset, the better the shift gate is guided in the axial displacement by the actuator or its driver in the axial direction. Therefore, at least one offset should be present, which is greater than 0 °, so that the reversal points of the slide tracks do not coincide. At the same time, the offset should be less than or equal to 40 °. Advantageously, the offset is between 10 ° and 20 ° or corresponds to these values. The indication of the offset in degrees is equivalent to the distance on the circumference of the shift gate between two straight lines intersecting the longitudinal axis of the basic camshaft, between which the corresponding angle is present. Basically, the offset can therefore be specified as a distance on the circumference or as an angle with respect to the angle of rotation of the shift gate or the basic camshaft.

A development of the invention provides that the cam carrier is assigned a locking device which has a plurality of locking grooves corresponding to the axial positions, in which a spring-loaded locking element engages in a locking manner for urging the cam carrier into the closest axial position. In order to keep the cam carrier or the shift gate in the current axial position, while the cam carrier is not to be displaced by means of the actuator in the axial direction, the locking device is provided. This has the locking grooves and the locking element. Preferably, a corresponding locking groove is provided for each of the axial positions. If the cam carrier or the shift gate is present in one of the axial positions, then the locking element engages with a detent in the corresponding locking groove. In this way, a moving out of the cam carrier is prevented from the axial position, unless a force is impressed on the shift gate or the cam carrier by means of the actuator, which is sufficient to effect a displacement despite the locking engagement of the locking element in the locking groove. The locking element is spring-loaded and is urged by the spring force in the direction of the locking grooves.

If the cam carrier is in one of the axial positions, then the locking element engages as described in the corresponding locking groove. If, in contrast, the cam carrier lies between the axial positions, for example during axial displacement by means of the actuator, the locking element urges the cam carrier into the closest axial position. The locking device may be formed, for example, as a ball catch with ramps. The locking element is so far as a spherical element and the locking grooves each have in the direction of the nearest locking groove sloping Ramps, so that the locking element can reach in any case in one of the axial positions. Thus, if only an incomplete axial displacement is achieved by means of the actuator, the locking device causes the cam carrier to be brought into the closest axial position.

A development of the invention provides that in each case two of the locking grooves are spaced from a separating element, wherein the separating element has a dead center, via which the locking element is moved by a displacement by means of the actuator. Between the locking grooves, therefore, the separating element is provided which these spaced apart in the axial direction. For example, the ramp described above, which drops in the direction of the nearest locking groove, is present on the separating element. Nevertheless, the separating element usually has a dead center, in particular between two of the ramps. If the locking element is arranged in the region of the dead center, then it can not cause any displacement of the cam carrier in the axial direction. For this reason, the locking element is to be displaced beyond the dead center during displacement by means of the actuator. This can be achieved by the staggered arrangement of the reversal points in the circumferential direction in a simple manner.

The invention further relates to an internal combustion engine having a valve drive, in particular according to the preceding embodiments, wherein the valve train has at least one base camshaft, on the rotationally fixed and axially displaceable between at least two axial positions at least one Ventilbetätigungsnocken exhibiting cam carrier is provided, wherein the cam carrier for axial displacement means an actuator associated with a shift gate, which has at its periphery over two opposing in the axial direction, intersecting slide tracks, each having a reversal point. It is provided that the reversal points are offset in the direction of contact with each other. The valve train of the internal combustion engine can be developed according to the above embodiments.

• Figur 1 einen Längsschnitt durch einen Bereich eines Ventiltriebs einer Brennkraftmaschine, wobei eine Grundnockenwelle mit einem auf dieser axial verschiebbaren Nockenträger und einer dem Nockenträger zugeordneten Schaltkulisse dargestellt ist,

Figur 2

eine Schaltkulisse in einer ersten Ansicht,

Figur 3

die Schaltkulisse in einer zweiten Ansicht,

Figur 4

die Schaltkulisse in einer dritten Ansicht,

Figur 5

eine schematische Ansicht der Schaltkulisse,

Figur 6

eine weitere Schaltkulisse in einer ersten Ansicht,

Figur 7

die weitere Schaltkulisse in einer zweiten Ansicht,

Figur 8

die weitere Schaltkulisse in einer dritten Ansicht, und

Figur 9

eine weitere Ansicht der erfindungsgemäßen Schaltkulisse.

The invention will be described in more detail below with reference to the embodiments illustrated in the drawing, without any limitation of the invention. Showing:

• FIG. 1 a longitudinal section through a portion of a valve train of an internal combustion engine, wherein a base camshaft with an axially displaceable on this Cam carrier and a cam carrier associated with the cam carrier is shown,

FIG. 2

a shift gate in a first view,

FIG. 3

the shift gate in a second view,

FIG. 4

the shift gate in a third view,

FIG. 5

a schematic view of the shift gate,

FIG. 6

another shift gate in a first view,

FIG. 7

the further shift gate in a second view,

FIG. 8

the further shift gate in a third view, and

FIG. 9

another view of the shift gate according to the invention.

The FIG. 1 shows a portion of a valve train 1 of an internal combustion engine, not shown. The valve drive 1 consists of a base camshaft 2 and an axially displaceable on this cam carrier 3. The cam carrier 3 has a central recess 4, which is penetrated by the base camshaft 2. In the region of the recess 4, the cam carrier 3 has an internal toothing, not shown here, which cooperates with a likewise not shown external toothing of the base camshaft 2 to the cam carrier 3 rotatably, but axially displaceable, to keep on the base camshaft 2. The cam carrier 3 has a plurality of valve actuation cams 5, 6, 7 and 8, the valve actuation cams 5 and 6 being assigned to a cam group 9 and the valve actuation cams 7 and 8 to a cam group 10. Furthermore, the cam carrier 3 has a shift gate 11, which is part of an adjusting device not shown here. With the help of the adjusting device of the cam carrier 3 is displaceable on the base camshaft 2 in the axial direction.

The valve actuation cams 5, 6, 7 and 8 serve to actuate gas exchange valves, not shown, of the internal combustion engine. It can be seen that the valve actuating cam 5, 6, 7 and 8 shown here are eccentric, wherein the eccentricities different angular positions or circumferential positions with respect to the cam carrier 3 and / or have different extensions in the radial direction and / or circumferential direction. For actuation of the gas exchange valves, the valve actuating cam 5, 6, 7 and 8, for example, together with Rollenschlepphebeln 12 and 13 of the respective gas exchange valve by contact contact. Each of the roller rocker arms 12 and 13 are assigned the respective valve actuation cams 5 and 6 or 7 and 8 of the corresponding cam group 9 or 10. The roller rocker arm 12 is thus actuated by the valve actuation cams 5 or 6 and the roller rocker arm 13 by the valve actuation cams 7 or 8.

Due to the different design of the valve actuation cams 5 and 6 or 7 and 8 with each other, thus, a corresponding stroke, opening time and / or an opening period of the gas exchange valve is set. By axial displacement of the cam carrier 3, the roller cam followers 12 and 13 can be actuated by the valve operating cam 5 or 6 or 7 or 8 of the respective cam group 9 or 10. The cam carrier 3 is displaced, for example, as a function of an operating state of the internal combustion engine, so that always that valve actuating cam 5 or 6 with the roller cam follower 12 or that valve actuation cam 7 or 8 cooperates with the roller cam follower 13 for its operation, with which, for example, an optimal efficiency or optimum performance the internal combustion engine can be achieved.

In order to keep the cam carrier 3 in its current axial position, if no axial displacement is provided by means of the actuator, it is associated with a locking device 14. The locking device 14 has a plurality of locking grooves 15 and 16 corresponding to the axial positions. In the embodiment shown here, two locking grooves 15 and 16 are provided because the cam carrier 3 should be axially displaceable between two axial positions. However, it can also be a larger number of axial positions and correspondingly a larger number of locking grooves, in particular three or four, may be provided. The locking grooves 15 and 16 are formed on the base camshaft 2 side facing the cam carrier 3, ie in a wall of the recess 4, in the cam carrier 3. You can completely encompass the base camshaft 2 in the circumferential direction, so be present over the entire inner circumference of the cam carrier 3. The locking device 14 further has locking elements 17 which are spring-loaded by means of one or more spring elements 18. The locking elements 17 and the spring element 18 are at least partially arranged in the base camshaft 2 or in a radial direction through this drilled hole 19.

The spring element 18 urges the locking elements 17 in the radial direction outward in the direction of the locking grooves 15 and 16. The locking elements 17 engage when the cam carrier 3 is in one of the intended axial positions, latching in the locking groove 15 and 16 a. A first of the axial positions is assigned, for example, the locking groove 15 and a second of the axial positions of the locking groove 16. In the embodiment shown here, the cam carrier 3 is so far in its first axial position. Between the two locking grooves 15 and 16, a separator 20 is present, which is in particular designed as a divider.

The separator 20 has - seen in longitudinal section - ramps 21, which are each inclined in the direction of the respective nearest locking groove 15 and 16. In this way, the cam carrier 3, should it not be in one of the intended radial positions, urged into the respective nearest axial position because the locking elements 17 cooperate with the corresponding ramp 21 in such a way that the cam carrier 3 is displaced axially in the direction of the closest axial position , Between the two ramps 21, however, there is a dead center 22, in particular in a turning point of the separating element 20 between the ramps 21. In this dead center 22, the separating element 20 is inclined neither in the direction of the locking groove 15 nor the locking groove 16. If the cam carrier 3 is thus arranged in the axial direction such that the locking elements 17 cooperate with the separating element in the area of its dead center 22, then the locking device 14 can not cause a displacement of the cam carrier 3 in the axial direction and thus a displacement in one of the axial positions , It should be noted that, in principle, another embodiment for the locking device 14 may be provided. The embodiment described here is for illustration only.

Based on FIGS. 2 to 9 the shift gate 11 will be described in more detail below. The show FIGS. 2 to 5 a substantially known shift gate 11 and the FIGS. 6 to 9 11. A shift gate 11 according to the invention. Both the essentially known shift gate 11 and the shift gate 11 according to the invention can be used for the valve drive 1 described above, so that reference is also made to the above explanations.

The FIGS. 2, 3 and 4 show various views of the shift gate 11, which is already known substantially. It is clear that the shift gate 11 has on its outer circumference two slide tracks 23 and 24, which are formed as grooves. The slide tracks 23 and 24 extend in accordance with the cam tracks 25 and 26, which are present centrally in the slide track 23 and 24, respectively. The cam tracks 25 and 26 are lines in the mathematical sense, while the slide tracks 23 and 24 extend around the cam tracks 25 and 26 with a certain width. The slide tracks 23 and 24 extend at least partially in the axial direction in opposite directions and therefore intersect at a crossing point 27. Under the crossing point 27 is to be understood in particular a point at which the cam tracks 25 and 26 of the slide tracks 23 and 24 intersect. The area in which the slide tracks 23 and 24 intersect, is - due to their width - naturally not punctiform.

The cam tracks 25 and 26 and thus also the slide tracks 23 and 24 have reversal points 28 and 29. In this case, the reversal point 28 of the slide track 23 and the curved path 25 and the reversal point 29 of the slide track 24 and the curved path 26 is assigned. Among the reversal points 28 and 29 points of the slide tracks 23 and 24 are to be understood, in which centers of the cam tracks 25 and 26 are present. For the sake of simplicity, the reversal points 28 and 29 shown here correspond to inflection points of the cam tracks 25 and 26, in which a curve curved in one direction merges into a curve curved in the opposite direction. Usually, however, the cam tracks 25 and 26 will not have inflection points in the mathematical sense. It becomes clear that in the FIGS. 2 to 4 Shifting gate 11 shown reversing points 28 and 29, which coincide, that is identical. However, as a result, as in the FIG. 3 represented, guide paths a and b of the slide track 24, ie areas in which an actuator, not shown, or a driver of the actuator abuts against guide walls 30, 27 are identical on both sides of the crossing point. For the shift gate 11, in which the reversal points 28 and 29 coincide, a = b applies accordingly.

This means, however, that in an axial displacement of the cam carrier 3 by an interaction of the actuator with the shift gate 11, the driver of the actuator is guided only over the guide path a until it reaches the crossing point 27, in which it no longer rests against the guide wall 30 , Accordingly, a sufficient kinetic energy must be applied to the cam carrier 3 and the switching flows 11 have been to be completed by inertia influence the axial displacement or to carry out the axial displacement at least until the locking device 14 takes over the further displacement in the direction of the desired axial position. Because the kinetic energy in principle depends on the speed of the basic camshaft 2 and thus a crankshaft of the internal combustion engine, the internal combustion engine must be operated at a speed which is greater than a minimum speed to effect a successful axial displacement of the cam carrier 3 on the base camshaft 2.

This circumstance is based on the FIG. 5 seen. In an upper area of this figure, first, the locking device 14 is shown schematically. Indicated here are the positions in which the locking elements 17 may be present in the locking groove 15 and 16 respectively. Also visible is the separating element 20 with its inclined in the direction of the locking grooves 15 and 16 ramps 21 and located between the ramp dead center 22. The locking grooves 15 and 16 and thus the intended axial positions of the cam carrier 3 are spaced in the axial direction with the distance d , Accordingly, the distance between each of the locking grooves 15 and 16 and the dead center is 22 d / 2. The distance by which the cam carrier 3 has to be displaced at least during the axial displacement, so that the locking elements 17 can be displaced beyond the dead center 22 and thus can assume the further displacement in the direction of the desired axial position, is accordingly greater than d / 2.

In the lower area of the FIG. 5 are the shift gate 11 and the slide tracks 23 and 24 and the associated cam tracks 25 and 26 shown schematically. Also shown is a driver 31 of the actuator in two different positions, which he occupies with respect to the cam carrier 3 in an intervention in the slide track 24. The reference numeral 31 denotes the cam carrier in a first direction in the direction of rotation of the cam carrier 3 and the reference numeral 31 'in a second, in the direction of rotation further back. The direction of movement of the driver 31 with respect to the shift gate 11 is indicated by the arrow 32. In this illustration, it is clear that the slide tracks 23 and 24 consist of inlet regions 33 and 34, reverse regions 35 and 36 and outlet regions 37 and 38. In an intervention of the driver 31 in the slide track 23 he passes through the inlet area 33, then the reversal area 35 and finally the outlet area 37. For the slide track 24 he passes through the inlet area 34, the reversing area 36 and the outlet area 38 in the order given. In this case, the inlet regions 33 and 34 as well as the reversal regions 35 and 36 each encounter a starting point 39 or 40 each other. Similarly, the reversing regions 35 and 36 and the outlet regions 37 and 38 abut one another in end points 41 and 42, respectively. The distance between the starting points 39 and 40 and the end points 41 and 42 - in the circumferential direction - is indicated by I ₁ and I ₂ . These sizes thus denote the length of the reverse regions 35 and 36 in the circumferential direction. The reversal regions 35 and 36 are, for example, curved in their progression beginning (which adjoins the starting point 39 or 40, respectively) and their trailing end (which lies before the end point 41 or 42), while an intervening section in which the reversal point 28 or 29 lies , is straight, so having a constant slope in the axial direction. Alternatively, of course, a continuous curved course can be provided, in whose inflection point the respective turning point 28 or 29 is located.

The driver 31 in its first position is in the inlet region 34. In its second position, indicated by the reference numeral 31 ', is in a position in which it is no longer guided by the guide wall 30 in the axial direction. It is clear that the driver 31 has traveled with respect to the shift gate 11 between its two positions a distance from a. This distance a corresponds to the distance in the axial direction, up to which the guide wall 30 extends in the direction of the crossing point 27 and thus ensures the guiding of the driver 31 in the slide track 24. Due to the symmetrical structure of the slide tracks 23 and 24 can be effected with the switching gate 11 presented here only a displacement of the cam carrier 3 in the axial direction by a distance a. However, a is usually smaller than the distance d / 2 described above, so that when the cam carrier 3 has too low a kinetic energy in the axial direction, the locking elements 17 may be in or even before the dead center 22 between the locking grooves 15 and 16 come come. In this case, it may happen that the cam carrier 3 is displaced by the locking device 14 back to its original position. For this reason, it must be ensured when using the shift gate 11 shown here that the kinetic energy of the cam carrier 3 is sufficiently large, which requires a speed of the internal combustion engine, which is above the minimum speed.

This problem can be solved by using the basis of the FIGS. 6 to 9 Be encountered switching gate 11 according to the invention described. Basically, the equivalent of the FIGS. 6 to 9 described construction of the shift gate 11 the basis of FIGS. 2 to 5 so far as to the above statements is referenced. In the following, only the differences will be discussed. It is clear that in the embodiment of the invention, the shift gate 11, the reversal points 28 and 29 no longer fall on each other, but in the circumferential direction of the shift gate 11 are offset from each other. In this case, the turning point 29 of the curved path 24 should be offset in the direction of rotation of the cam carrier 3 and the shift gate 11 forward. This also means that the reversal points 28 and 29 no longer coincide with the point of intersection 27, but are offset relative to this in the circumferential direction to the rear or to the front. The offset of the reversal points 28 and 29 is achieved in particular by displacing the starting points 39 and 40 relative to one another by the distance (on the circumference) or the angle (relative to the angle of rotation of the cam carrier 3) y. This is especially in FIG. 7 seen. The size y can be specified in this respect either as a distance or as an angle.

Since the extension of the reversing regions 35 and 36 is still the same, so that I ₁ = I ₂ , it follows that the reversal points 28 and 29 are also offset by the distance or angle y, as shown in the FIG. 8 is shown. It follows that the driver 31 when passing through the slide track 24 is longer in engagement or contact contact with the guide wall 30, as would be the case when passing through the sliding wall 23. Thus, in this embodiment, the shift gate 11 for the guide paths a '>b', wherein the two values based on the FIGS. 2 to 5 correspond to the values a and b described. Because a 'greater than d / 2 or at least equal, is realized on a displacement of the cam carrier 3 in an axial position, from which the locking device 14 provides for further displacement. Thus, there is no longer the risk that the locking elements 17 stop in the dead center 22 with an engagement of the driver 31 in the slide track 24. This means that the minimum speed of the internal combustion engine, in contrast to the known from the prior art shift gate 11 can be significantly reduced or equal to zero.

In order to achieve a corresponding guide for the slide track 23, this has a groove bottom 43 which is lower in the radial direction than a groove bottom 44 of the guide track 24. The height-offset arrangement of the groove bases 43 and 44 to each other in particular in the reversal areas 35 and 36th or around the crossing point 27 around. However, it can also extend over the entire slide track 23. In this way, in the slide track 23 in the region of the crossing point 27 is always a guide wall 44, which by the height offset is formed and allows for the slide track 23 a continuous guiding of the driver 31 of the actuator. Due to the offset arrangement of the groove bases 43 and 44, a continuous guidance of the driver 31 during the axial displacement of the cam carrier 3 is thus made possible for the slide track 23 with the guide track 45, while due to the staggered arrangement of the reversal points 35 and 36 in the circumferential direction to each other for the Sliding wall 24 at least one lead over the dead center 22 is realized also. With the shift gate 11 according to the invention, a valve drive 1 can be realized so far in which for the axial displacement of the cam carrier 3 no or at least only a smaller minimum speed of the internal combustion engine must be present in order to achieve a reliable displacement.

Claims (10)

1. Valve train (1) of an internal combustion engine, comprising at least one main camshaft (2) on which at least one cam carrier (3), which has valve actuation cams (5, 6, 7, 8), is provided for rotation therewith and axially displaceable between at least two axial positions, wherein, for the axial displacement by means of an actuator (31), a shifting gate (11) is associated with the cam carrier (3), which comprises two guide tracks (23, 24) on the circumference thereof, which run in opposite directions in the axial direction, intersect and each have one reversal point (28, 29), wherein

   - the reversal point (28, 29) corresponds to a point of a respective guide track (23, 24) at which, when reached by a catch (31) of the actuator, the cam carrier (3) is positioned exactly between the two axial positions of the cam carrier (3), and wherein

   - the reversal point (28, 29) coincides with a centre point of a straight section of the respective curved track (23, 24), which extends about the reversal point (28, 29), or wherein

   - the reversal point (28, 29) corresponds to a turn-around point of each curved track (23, 24),

   characterized in that the reversal points (28, 29) are positioned offset from one another in a circumferential direction.
2. Valve train according to claim 1, characterized in that each guide track (28, 29) comprises an inlet area (33, 34), an outlet area (37, 38) and a reversal area (35, 36) connecting these together, which comprises the reversal point (28, 29), wherein the inlet area (33, 34) and the outlet area (37, 38) are oriented in a circumferential direction and are arranged on opposite sides of the shift gate (11) in an axial direction.
3. Valve train according to any of the preceding claims, characterized in that the reversal area (35, 36) connects the inlet area (33, 34) and the outlet area (37, 38) with a steady curve, in the centre of which lies the reversal point (28, 29).
4. Valve train according to any of the preceding claims, characterized in that the inlet area (33, 34) and the reversal area (35, 36) intersect at a starting point (39, 40), and the reversal area (35, 36) and the outlet area (37, 38) intersect at an end point (31, 42), wherein the starting point (39, 40) and/or the end point (41, 42) of one of the guide tracks (23, 24) are positioned offset in a circumferential direction with respect to the starting point (39, 40) and/or the end point (41, 42) of the other guide track (24, 23).
5. Valve train according to any of the preceding claims, characterized in that the guide tracks (23, 24) comprise slot bases (43, 44), which are at least partially provided, in particular in the reversal area (35, 36), vertically offset from each other in a radial direction, whereby the guide track (23, 24) with the slot base (43, 44) arranged in a lower position in a radial direction, and in particular in the area of the intersection (27) of the guide tracks (23, 24), comprises a guide wall (45) formed by the height offset.
6. Valve train according to any of the preceding claims, characterized in that the reversal points (28, 29) of the guide track (23, 24) with the slot base (43, 44) arranged in a higher position in a radial direction is offset forwards in a rotational direction of the cam carrier (3).
7. Valve train according to any of the preceding claims, characterized in that the offset is greater than 0° and less than or equal to 40°, in particular at least 10° and not more than 20°, preferably exactly 10° or 20°.
8. Valve train according to any of the preceding claims, characterized in that a locking device (14) is associated with the cam carrier (3), which comprises a plurality of locking grooves (15, 16) corresponding to the axial positions, into which a spring loaded locking element (17) latchingly engages in order to push the cam carrier (3) into the nearest axial position.
9. Valve train according to any of the preceding claims, characterized in that each
   two of the locking grooves (15, 16) are spaced apart by a dividing element (20), wherein the dividing element (20) comprises a top dead centre (22) beyond which the locking element (17) is moved upon shifting by means of the actuator.
10. Internal combustion engine comprising a valve train according to one or more of the preceding claims.

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