Valve drive device, in particular for an internal combustion engine

A valve train device, in particular for an internal combustion engine, includes at least one camshaft which has at least one cam element with at least one multi-track cam. The cam element is provided to be axially displaced by a maximum displacement path. The valve train device further includes a limiting mechanism which is provided to limit in at least one operating state the displacement path of the cam element to a switching path of the switching operation.

BACKGROUND AND SUMMARY OF THE INVENTION

The invention concerns a valve drive device and an internal combustion engine with a valve drive device.

A valve drive device for an internal combustion engine with at least one camshaft which has at least one cam element with at least one multi-track cam, which is intended to be axially displaced by a maximum displacement path is known from DE 10 2011 050 484. The valve drive device has a latching mechanism which is intended to lock a changeover to a central cam track, but which is unlatched by the cam element at high speeds so that the cam element exceeds the desired axial displacement.

The invention is based, in particular, on the task of providing a valve drive device with which a safe switchover between valve strokes can be achieved at high camshaft speeds.

The invention is based on a valve drive device, in particular for an internal combustion engine with at least one camshaft which has at least one cam element with at least one multi-track cam, which is intended to be axially displaced by a maximum displacement path.

It is proposed that the valve drive device comprises a limiting mechanism intended to limit, in at least one operating condition, the displacement path of the cam element to a switching path for a switching operation, thereby safely limiting axial displacement of the cam element and preventing overshooting of a desired axial displacement, thus achieving safe switching between valve strokes even at high camshaft speeds. In this context, a “multi-track cam element” is understood to mean a cam element with at least two partial cams, each of which forms a cam track for actuating a gas shuttle valve, the partial cams providing different valve lift and/or valve timing. In this context, a “maximum displacement path” is understood to mean a displacement path of the cam element in which the cam element is displaced from an axial position, in which an outermost cam track is provided for actuating the gas exchange valve, to an axial position, in which an opposite outermost cam track is provided for actuating the gas exchange valve. In this context, a “switching path for a switching operation” is understood to mean an axial displacement of the cam element with which the cam element is displaced from an axial position, in which a cam track for actuating the gas exchange valve is provided, to an axial position, in which a directly adjacent cam track for actuating the gas exchange valve is provided. In particular, the switching path for a switching operation is at most equal to the maximum displacement path and, if a cam of the cam element has at least three cam tracks, less than the maximum displacement path. One length of the switching path for a switching operation corresponds in particular to one length of the maximum displacement path divided by a number that is one less than a number of cam tracks.

It is further proposed that the valve drive device comprises a positive locking element at least connected to the cam element and intended for positive connection to the limiting mechanism, thus allowing a simple construction of the valve drive device to be achieved.

It is also proposed that the limiting mechanism should have a stop element with two opposite stop surfaces for the positive locking element, so that the stop element can be used to limit the displacement to one switching path in one axial direction and one opposing axial direction, and a simple design of the valve drive device can be achieved.

Furthermore, it is proposed that the stop surfaces be spaced apart in such a way that any displacement is limited to the value of the distance between adjacent cam tracks, so that a limitation of the displacement path to a switching path for switching between adjacent cam tracks can be limited in a simple way.

It is also proposed that the limitating mechanism should include an auxiliary actuator to displace the stop element so that one switching element can be used to limit the displacement path to one switching path for switching adjacent cam tracks if more than two cam tracks of a multi-track cam are used.

It is also proposed that the valve drive device has a switching actuator for axially displacing at least one cam element, which comprises at least one switching element which is in permanent operative connection with the cam element, and a drive for axially displacing the switching element designed to be decoupled from the switching element so that, after the switching operation has been completed, when the limiting mechanism blocks further displacement of the cam element, the drive can be decoupled from the switching element and thus a precise actuation of the drive in order to limit the displacement of the cam element to the switching path can be dispensed with.

It is also proposed that the switching element be permanently connected to the positive locking element, thus eliminating the need for an additional component to engage with the switching element and simplifying the design of the valve drive device.

It is also proposed that the switching actuator should include a slipping clutch designed to decouple the switching element and the drive from each other, thus providing a simple design for decoupling the switching element from the drive.

It is also proposed that the valve drive device should include a spindle for transmitting a driving force from the drive to the switching element, which is connected to the drive via the slipping clutch, thus providing a simple design for decoupling the switching element from the drive.

It is also proposed that at least one multi-track cam should have at least three cam tracks, allowing the limiting mechanism to be used with particular benefit for safe switching between adjacent cam tracks.

Furthermore, the invention concerns an internal combustion engine with a valve drive device corresponding to the invention, which reliably limits an axial displacement of the cam element and prevents overshooting of a desired axial displacement, thus achieving safe switching between valve strokes even at high camshaft speeds.

Further advantages can be seen in the description of the figures below. The figures show an example of the invention. The figures, the description of the figures and the claims contain numerous features in combination. Experts will also consider the features individually and combine them into other useful combinations.

DETAILED DESCRIPTION OF THE DRAWINGS

FIGS. 1 to 3show a section of an internal combustion engine with a valve drive device10, with a camshaft11, which has an axially displaceable cam element13, which has two multi-track cams14,18, and an axially displaceable positive locking element22, which is connected to the cam element13. The positive locking element22extends along an entire circumference of the camshaft11and forms a circumferential engagement contour. During the displacement process for an axial displacement of the cam element13, switching forces are applied to the engagement contour of the positive locking element22and displace the positive locking element22axially on the camshaft11. The cam element13is axially displaced by connecting the positive locking element22to the cam element13. In the design example shown, the positive locking element22is designed as a single piece with the cam element13. In an alternative design, the positive locking element22can be designed separately from, but connected to, the cam element13and, in the event of axial displacement, can move the cam element13indirectly via the connection with the cam element13. The positive locking element22is designed as a circumferential rib.

The camshaft11consists of a drive shaft12on which the cam element13is located. The drive shaft12has a spur toothing on its outer perimeter. The cam element13has a corresponding spur gearing on its inner perimeter, which meshes with the spur gearing of the drive shaft12. The cam element13is mounted on the drive shaft12, rotationally fixed but displaceable in both axial directions. The drive shaft12comprises a crankshaft connection for connection to an unspecified crankshaft. In alternative designs, the drive shaft12can be dispensed with, for example by assembling the camshaft11from several cam elements13which mesh at their edges.

The valve drive device10comprises a switching actuator23for axial displacement of the cam element13. The two multi-track cams14,18each comprise three partial cams15,16,17,19,20,21with different cam tracks which form different valve lift curves. One partial cam each15,16,17,19,20,21of the cams14,18is in contact with an unspecified cam follower for actuating a gas exchange valve of the internal combustion engine. The switching actuator23moves the cam element13axially in order to switch between the different partial cams15,16,17of the cam14and the partial cams19,20,21of the cam18, which are in contact with the cam follower. The valve drive device10has a permanent active connection between the switching actuator23and the positive locking element22. The switching force for axial displacement of the cam element13is transmitted via the permanent active connection. The permanent operative connection is maintained during the entire operation of the valve drive device10and over a complete revolution of the camshaft11. The cam element13is intended to be moved axially by a maximum displacement path. The maximum displacement corresponds to a distance by which the cam element13has to be moved axially in order to switch from a cam track of an outermost cam15,19to a cam track of an outermost cam17,21.

The switching actuator23is arranged on a schematically illustrated camshaft housing28and fastened there. The switching actuator23consists of a housing which is firmly connected to the camshaft housing28and an axially displaceable switching element26. In the example shown, the switching actuator23also comprises a rotatable spindle24and a drive25which drives the spindle24and is in the form of an electric motor. Switching element26is located on spindle24. Spindle24is designed to transmit a driving force from drive25to switching element26. The switching element26is moved axially by turning the spindle24with the drive25. In alternative designs, the drive25can be used as a hydraulic motor or another drive machine instead of an electric motor. Instead of a spindle24, a running rail or a cable device could, for example, be used to support switching element26.

The positive locking element22forms an interface for applying the switching force acting in the axial direction to the cam element13. The switching force acting in the axial direction is applied only by the switching actuator23and is independent of a rotary movement of the camshaft11. The course of an axial displacement movement is determined solely by the switching actuator23via the drive25, which drives the spindle24and thus displaces the switching element26. The switching element26has an engagement groove27, which is intended for engagement with the positive locking element22. The positive locking element22is designed as a circumferential rib. In alternative designs, the positive locking element22can be designed as a groove and the switching element26as a rib or pin.

The permanent active connection between the switching actuator23and the positive locking element22may have an active surface which is dependent on a rotation angle of the camshaft11and which is adapted in a rotation angle range to the switching forces to be transmitted in the rotation angle range. The active surface, which depends on the angle of rotation of the camshaft11, can be achieved, for example, by different radial extensions of the positive locking element22in the angle of rotation ranges, in which different switching forces occur.

The valve drive device10comprises a limiting mechanism30, which is intended to limit, in at least one operating condition, the displacement path of the cam element13to a switching path for a switching operation, The switching path for a switching operation corresponds to a displacement path of the cam element13, in which a cam track of a partial cam15,16,17,19,20,21is switched over to a cam track of an adjacent partial cam15,16,17,19,20,21. The limiting mechanism30is designed to limit the displacement to avoid overshooting of the adjustable axial position at high speeds.

The valve drive device10comprises a positive locking element29connected to the cam element13, which is intended for a positive connection with the limiting mechanism30. The positive locking element29is designed as a single piece with the positive locking element22, which is in permanent active connection with the switching element26of the switching actuator23. In alternative designs, the positive locking element29can be designed separately from the positive locking element22, which is in permanent active connection with the switching element26of the switching actuator23. The positive connection of the positive locking element29with the limiting mechanism30is intended to block the axial displacement of the cam element13after completion of the switching movement and thus to limit the displacement path to the switching path.

The limiting mechanism30has a stop element31with two opposite stop surfaces32,33for the positive locking element29. The limiting mechanism30limits the displacement path by means of the two opposite stop surfaces32,33when switching between cam tracks in two opposite axial directions, for example a first switching and a second switching, which restores an axial position of the cam element13before the first switching. In alternative designs, it is conceivable that the stop element31may have two stop surfaces32,33facing away from one another for the positive locking element29, which move in opposite axial directions into a blocking position before the displacement is carried out in order to limit the displacement path.

The stop surfaces32,33are spaced at a distance34apart, which limits displacement to the value of the distance between adjacent cam tracks. The limiting mechanism30thus limits the displacement path of the cam element13to a switching path for a switching operation that corresponds to a distance between adjacent cam tracks. The distance34between the stop surfaces32,33is constant. In alternative designs, it is conceivable that the stop element31is designed in such a way that the distance34between the stop surfaces32,33can be changed, e.g., in order to enable switching by one or two cam track widths in one switching operation.

The limiting mechanism30includes an auxiliary actuator35for moving the stop element31. The auxiliary actuator35is designed to move the stop element31by a distance of adjacent cam tracks. A switchover from a cam track of the outermost of the partial cams15,19to a cam track of a respective other outermost partial cam17,21is effected by a displacement of the cam element13, in which switchover to the cam track of the central partial cam16,20is effected and wherein the displacement path is limited by the stop element31of the limiting mechanism30to the switching path required for this purpose (seeFIG. 1andFIG. 2), a subsequent displacement of the stop element31by a distance of the adjacent cam spurs and a subsequent displacement of the cam element13by a further distance of adjacent cam tracks, the displacement path being limited by the stop element31of the limiting mechanism30to the switching path required for this purpose (seeFIG. 3). The auxiliary actuator35moves the stop element31between a first switching position, in which it is possible to switch from a cam track of one of the outermost partial cams15,19to a cam track of the middle part cam16,20and vice versa, and a second switching position, in which it is possible to switch from a cam track of the middle part cam16,20to a cam track of the other outermost part cam17,21and vice versa.

The drive25for axial displacement of the switching element26is intended to be decoupled from switching element26. A decoupling takes place when the stop element31of the limiting mechanism30forms a positive connection with the positive locking element29. It is thus not necessary to stop the drive25precisely when the stop element31is form-fit with the positive locking element29.

The switching actuator23comprises a slipping clutch36, which is intended to decouple the switching element26and the drive25from each other. The spindle24is connected to the drive25via the slipping clutch36. The slipping clutch36releases automatically on reaching a positive locking of the positive locking element29, which is designed as a single piece with the positive locking element22for engagement with the switching element26, and decouples the switching element26and the drive25from each other.

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