EP3441581B1 - Sliding cam system and method for operating a combustion engine - Google Patents

Description

The invention relates to a sliding cam system for a variable valve train, a variable valve train, a motor vehicle and a method for operating an internal combustion engine.

Valve-controlled internal combustion engines have one or more controllable intake and exhaust valves per cylinder. Variable valve controls allow flexible control of the valves to change the opening time, closing time and / or the valve lift. As a result, engine operation can be adapted to a specific load situation, for example.

From the DE 196 11 641 C1 A valve train is known with which the actuation of a gas exchange valve with several different stroke curves is made possible. For this purpose, a sliding cam with at least one cam section having a plurality of cam tracks is rotatably but axially displaceably mounted on the camshaft and has a stroke contour into which an actuator in the form of a pin is inserted from the outside radially to produce an axial displacement of the sliding cam. Due to the axial displacement of the slide cam, a different valve lift is set for the respective gas exchange valve. After the axial displacement thereof relative to the camshafts, the sliding cam is locked in its axial relative position on the camshaft in that, depending on the axial relative position, at least one spring-loaded locking ball, which is received and supported in the camshaft, engages in at least one locking groove. The axial displacement of the sliding cam to change the valve lift takes place exclusively in the so-called base circle of the or each cam section or the cam tracks of the same. This limits the switching speed of the valve train.

The shorter the matching base circles of the cams are, the less time is available for axially displacing the sliding cam. The less time is available for axially shifting the sliding cam system, the steeper the ramp of the shift gate (engagement track) must be. When the sliding cam is axially displaced, considerable forces can sometimes arise in the contact between the pin of the actuator and the shifting gate. Particularly with steep ramps, particularly large forces can occur which can negatively influence the service life of the sliding cam system and / or limit a maximum switching speed.

From the DE 10 2012 112 482 A1 discloses a method of operating an internal combustion engine with a plurality of cylinders. To operate gas exchange valves, the internal combustion engine has a valve train with at least one rotatably mounted camshaft and with at least one sliding cam that can be axially displaced on the respective camshaft. The respective sliding cam has at least one link section with at least one groove formed on an outer lateral surface of the respective link section, the respective sliding cam having at least one cam section with a plurality of cam tracks for setting different valve lifts. In order to effect an axial displacement of the respective sliding cam, an actuatable pin of an actuator is inserted from radially outside into a groove in the link section. The axial displacement of the respective sliding cam is carried out depending on the axial displacement direction of the same and / or depending on a valve clearance outside a base circle of the or each cam section thereof.

The GB 2 545 257 A discloses an internal combustion engine with a cam shifting system comprising a switch unit that is rotationally fixed and axially movable with respect to a camshaft, the switch unit comprising at least two cams configured to be selectively brought into contact with a cam follower. The cams are provided with a base circle and at least one cam lobe. During an axial displacement of the switching unit, the cam follower contacts at least a part of at least one cam elevation outside the base circle.

The US 8 863 714 B1 , the DE 10 2012 209 860 A1 , the US 2015/075468 A1 and the US 2007/034182 A1 disclose further sliding cam systems.

The invention is based on the object of providing an alternative or improved sliding cam system and method for operating an internal combustion engine in which the forces which occur during the displacement process of the cam carrier are reduced in comparison with conventional systems.

The object is achieved by a sliding cam system and a method according to the independent claims. Advantageous further developments are specified in the dependent claims and the description.

The sliding cam system is designed for a variable valve train of an internal combustion engine of a motor vehicle, in particular a commercial vehicle. The sliding cam system points a camshaft and a cam carrier. The cam carrier is arranged on the camshaft in a rotationally fixed and axially displaceable manner between a first axial position and a second axial position and has a first cam, a second cam and a first engagement track for axially displacing the cam carrier. The sliding cam system has a cam follower that is operatively connected to the first cam in the first axial position of the cam carrier and is operatively connected to the second cam in the second axial position of the cam carrier. The sliding cam system has a first actuator, which has a retractable and extendable element, in particular a pin, for engagement in the first engagement track for axial displacement of the cam carrier. The first cam and the second cam are offset from one another along a longitudinal axis of the camshaft arranged. The first cam has a base circle area and a valve lift area with a boundary section which adjoins the base circle area of the first cam. The second cam has a base circle area and a valve lift area with a boundary section which adjoins the base circle area of the second cam. The boundary section of the first cam and the boundary section of the second cam are of identical design and are arranged at the same circumferential position around the longitudinal axis of the camshaft. The first actuator, the cam follower and the first engagement track are arranged and designed in such a way that the cam carrier can be axially displaced while the cam follower is in operative connection with the boundary section of the first cam and / or the boundary section of the second cam.

The sliding cam system enables an extension of the time available for the axial displacement of the cam carrier by expansion into the limit sections of the cams. Due to the larger switching range, the accelerations and thus the inertial forces can be reduced for the axial shift at the same switching speed. On the one hand, this can be used, for example, to increase functional reliability and service life due to lower forces and pressures. On the other hand, this can be used, for example, to increase the maximum switching speed of the system.

In particular, the first cam can be formed directly adjacent to the second cam.

In a particularly preferred embodiment, the first actuator, the cam follower and the first engagement track are arranged and designed such that an axial displacement of the cam carrier begins and / or ends while the cam follower is in operative connection with the boundary section of the first cam or the boundary section of the second cam . In particular, the beginning and / or the end of the axial displacement of the cam carrier can thus be shifted into the boundary regions. The time available for axially displacing the cam carrier can thus be extended.

In one embodiment, the boundary sections extend over a range greater than or equal to 1 ° camshaft angle.

In a further development, the boundary sections extend over a range between 5 ° and 45 ° camshaft angles, in particular between 15 ° and 30 ° camshaft angles.

In a further embodiment, the boundary sections form a common flat ramp.

In one embodiment variant, the boundary sections are arranged in an outlet area of the first and second cams. Alternatively or additionally, the axial displacement of the cam carrier begins when the cam follower is in operative connection with the boundary section of the first cam or the second cam. The axial displacement preferably ends while the cam follower is in operative connection with the base circle region of the first cam or of the second cam. However, it is also possible for the axial displacement to end only in a further boundary section in an inlet region of the first or second cam, the further boundary sections of the first and second cams in turn being of the same design and arranged at the same circumferential position around the longitudinal axis of the camshaft.

In a further embodiment variant, the boundary sections are arranged in an inlet area of the first and second cams. Alternatively or additionally, the axial displacement of the cam carrier ends when the cam follower is in operative connection with the boundary section of the first cam or the second cam. The axial displacement of the cam carrier preferably begins while the cam follower is in operative connection with the base circle region of the first cam or the second cam. However, it is also possible that the axial displacement already begins in another limit section in a run-out area of the first or second cam, the other limit sections of the first and second cam in turn having the same design and being arranged at the same circumferential position around the longitudinal axis of the camshaft.

In one exemplary embodiment, the cam carrier has a second engagement track for axially displacing the cam carrier in a direction opposite to an axial displacement caused by the first engagement track. The sliding cam system also has a second actuator, which has a retractable and extendable element, in particular a pin, for engagement in the second engagement track for axial displacement of the cam carrier. The second actuator, the cam follower and the second engagement track are arranged and designed such that an axial displacement of the cam carrier can be carried out (in particular begins and / or ends) while the cam follower is in operative connection with the boundary section of the first cam or the boundary section of the second cam .

In particular, the first actuator and the second actuator can be provided separately from one another. However, it is also possible for the first actuator and the second actuator to be provided in a common housing.

The first engagement track and the second engagement track can preferably be provided separately from one another. However, it is also possible for the first engagement track and the second engagement track to be arranged in the same area of the cam carrier. The first engagement track and the second engagement track can preferably intersect.

In a further exemplary embodiment, the first engagement track has a cross-sectional constriction to reduce play between the first engagement track and the retractable and extendable element of the first actuator when engaging (the extended element in the first engagement track). The cross-sectional constriction is arranged such that the play reduction takes place before the cam follower comes into operative connection with the boundary section of the first cam or the second cam. Thus, the section of the engagement track provided for reducing the play does not shorten the section of the engagement track provided for the axial displacement of the cam carrier.

To achieve the same advantages, it is also possible for the second engagement track to have a cross-sectional constriction to reduce play between the second engagement track and the retractable and extendable element of the second actuator when engaging (the extended element in the second engagement track). The cross-sectional constriction is arranged such that the play reduction takes place before the cam follower comes into operative connection with the boundary section of the first cam or the second cam.

In a particularly preferred embodiment, the first engagement track and / or the second engagement track extends spirally around the longitudinal axis of the camshaft.

In a further embodiment, the retractable and extendable element of the first actuator and / or the second actuator can be moved radially with respect to the longitudinal axis of the camshaft.

The invention also relates to a variable valve train for an internal combustion engine. The variable valve train has a slide cam system as disclosed herein. The variable valve train has a gas exchange valve, in particular an inlet valve or an outlet valve, which is operatively connected to the cam follower. The first cam and the second cam cause different valve lifts, opening times and / or closing times of the gas exchange valve.

In one development, the gas exchange valve is an outlet valve. The first cam is designed for normal operation of the internal combustion engine, in which the first cam keeps the exhaust valve open during the exhaust stroke. The second cam is designed for engine braking operation of the internal combustion engine, in which, preferably, the exhaust valve is initially kept closed in the compression stroke and in the extension stroke and is opened before a piston movement reaches top dead center.

In a preferred embodiment, the second cam is designed so that the exhaust valve opens between 100 ° KW and 60 ° KW (crankshaft angle) before reaching top dead center. As an alternative or in addition, the second cam is designed such that the exhaust valve closes in the region between top dead center and 30 ° CA after top dead center after opening in the extension stroke. Alternatively or additionally, the second cam is designed such that the outlet valve closes after opening in the compression stroke in the range between bottom dead center and 30 ° CA after bottom dead center.

The invention also relates to a motor vehicle, in particular a commercial vehicle (for example a truck or bus), comprising the variable valve train as disclosed herein or the sliding cam system as disclosed herein.

The invention also relates to a method for operating an internal combustion engine with a sliding cam system. The sliding cam system has a cam carrier which is arranged on a camshaft in a rotationally fixed manner and is axially displaceable, with a first cam and a second cam. The first cam and the second cam each have a base circle area and a valve lift area with a boundary section which is arranged adjacent to the respective base circle area. The boundary section of the first cam and the boundary section of the second cam are of identical design and are arranged at the same circumferential position about a longitudinal axis of the camshaft. The sliding cam system has a cam follower, which is optionally operatively connected to the first cam or the second cam. The method has the axial displacement of the cam carrier, the axial displacement of the cam carrier being carried out, in particular starting or ending, while the cam follower is in operative connection with the boundary section of the first cam and / or the second cam.

The method offers the same advantages as the slide cam system disclosed herein. In addition, the method has greater flexibility since it is not limited to the axial displacement of the cam carrier by means of the actuators and engagement tracks as disclosed herein.

In particular, the method can use the slide cam system disclosed herein, preferably with elements of actuators that can be moved in and out radially and engage in spiral engagement tracks, for axially displacing the cam carrier. However, it is also possible for the method to use a different displacement system for axially displacing the cam carrier.

In a preferred embodiment, the axial displacement of the cam carrier begins while the cam follower is operatively connected to the boundary section of the first cam or the second cam, and / or ends while the cam follower is operatively connected to the base circle region of the first cam or the second cam.

Alternatively or additionally, the axial displacement of the cam carrier begins and / or ends while the cam follower is in operative connection with the base circle region of the first cam or second cam, and / or ends while the cam follower is in operative connection with the boundary section of the first cam or second cam.

Figur 1

eine perspektivische Ansicht eines beispielhaften variablen Ventiltriebs;

Figur 2

eine weitere perspektivische Ansicht des beispielhaften variablen Ventiltriebs;

Figur 3

eine Draufsicht auf eine Nockenwelle des beispielhaften variablen Ventiltriebs;

Figur 4

eine Längsschnittansicht der Nockenwelle von Figur 3 entlang der Linie A-A;

Figur 5A

eine erste Querschnittansicht der Nockenwelle von Figur 4 entlang der Linie B-B;

Figur 5B

eine zweite Querschnittansicht der Nockenwelle von Figur 4 entlang der Linie C-C;

Figur 6

ein Weg-Nockenwellenwinkel-Diagramm; und

Figur 7

eine Vergrößerung eines Bereichs des Weg-Nockenwellenwinkel-Diagramms von Figur 6.

The preferred embodiments and features of the invention described above can be combined with one another as desired. Further details and advantages of the invention are described below with reference to the accompanying drawings. Show it:

Figure 1

a perspective view of an exemplary variable valve train;

Figure 2

another perspective view of the exemplary variable valve train;

Figure 3

a plan view of a camshaft of the exemplary variable valve train;

Figure 4

a longitudinal sectional view of the camshaft of Figure 3 along the line AA;

Figure 5A

a first cross-sectional view of the camshaft of Figure 4 along the line BB;

Figure 5B

a second cross-sectional view of the camshaft of Figure 4 along line CC;

Figure 6

a displacement camshaft angle diagram; and

Figure 7

an enlargement of a range of the displacement-camshaft angle diagram of Figure 6 .

The embodiments shown in the figures correspond at least partially, so that similar or identical parts are provided with the same reference numerals and for their explanation reference is also made to the description of the other embodiments or figures in order to avoid repetitions.

The following is with reference to Figure 1 to Figure 4 First, a variable valve train with a sliding cam system is described. The sliding cam system enables switching between different valve control curves of the actuated gas exchange valves. The system disclosed by way of example relates to the actuation of exhaust valves of an internal combustion engine. However, the principles disclosed herein are also applicable to a variable valve train for one or more intake valves.

In the Figures 1 and 2nd A variable valve train 10 is shown. The variable valve train 10 has a camshaft 12 and a cam carrier 14. In addition, the variable valve train 10 has first and second transmission devices 16 and 18 and first and second exhaust valves 20 and 22. In addition, the variable valve train 10 has a first actuator 24 and a second actuator 26. The cam carrier 14, the transmission devices 16 and 18 and the actuators 24 and 26 form a sliding cam system 11.

The camshaft 12 is designed as an output camshaft, which actuates the output valves 20 and 22. The camshaft 12 is part of a double camshaft system (not shown in detail) which additionally has an intake camshaft (not shown) for actuating one or more intake valves. The camshaft 12 is arranged together with the intake camshaft as an overhead camshaft. The camshaft 12 and the intake camshaft thus form a so-called DOHC system (double overhead camshaft). Alternatively, the camshaft 12 could also form a so-called SOHC system (single overhead camshaft). In other embodiments, the camshaft 12 can also be arranged as an underlying camshaft.

The cam carrier 14 is arranged in a rotationally fixed manner on the camshaft 12. The cam carrier 14 is additionally arranged axially displaceably along a longitudinal axis of the camshaft 12. The cam carrier 14 can be axially displaceable between a first stop 28 and a second stop 30.

With reference to the Figures 1 to 4 cam carrier 14 is described below. The cam carrier 14 has three cams 32, 34 and 36 which are offset from one another in a longitudinal direction of the cam carrier 14 and the camshaft 12. The first cam 32 is arranged at a first end of the cam carrier 14 and is designed for normal operation, as will be described in detail later by way of example. The second cam 34 is arranged adjacent to the first cam 32 and is designed for engine braking operation, as will also be described later in detail by way of example. The third cam 36 is spaced apart from the second cam 34 and the second end of the cam carrier 14. The third cam 36 is designed for normal operation. The third cam 36 is shaped like the first cam 32.

The cam carrier 14 also has a first cam-free section 38 and a second cam-free section 40. The first cam-free section 38 is arranged at the second end of the cam carrier 14. The second cam-free section 40 is arranged between the second cam 34 and the third cam 36. In the first cam-free section 38, a first engagement track (shift link) 42 extends spirally around a longitudinal axis of the cam carrier 14. In the second cam-free section 40, a second engagement track (shift link) 44 extends spirally around the longitudinal axis of the cam carrier 14.

To move the cam carrier 14 between the stops 28 and 30, the actuators 24 and 26 ( Figures 1 and 2nd ) selectively engage (engage) with extendable elements (e.g. pin or pin; not shown in detail) in the engagement tracks 42, 44. Specifically, the first actuator 24 can selectively engage the first engagement track 42 to shift the cam carrier 14 from one axial position to another axial position. In a first axial position, the cam carrier 14 bears against the second stop 30. In a second axial position, the cam carrier 14 bears against the first stop 28. In the Figures 1 to 4 the cam carrier is shown in the first axial position. The second actuator 26 can in turn selectively engage the second engagement track 44. Then the cam carrier 14 is shifted from the first axial position to the second axial position. The first actuator 24 and the second actuator 26 are controlled by a schematically represented control unit 27 ( Figures 1 and 2nd ) controlled.

The shift is triggered in that the extended pin of the respective actuator 24, 26 is stationary with respect to an axial direction of the camshaft 12. As a result, the slidable cam carrier 14 is displaced in a longitudinal direction of the camshaft 12 due to the spiral shape of the engagement tracks 42, 44 when the extended pin is in the respective engagement track 42, 44 engages. At the end of the displacement process, the pin of the respective actuator 24, 26 is guided by the respective engagement track 42, 44 opposite to the extension direction and thus retracted. The pin of the respective actuator 24, 26 comes out of engagement with the respective engagement track 42, 44.

The first transmission device 16 and the second transmission device 18 ( Figures 1 and 2nd ) establish an operative connection between the cam carrier 14 and the exhaust valves 20, 22. The first exhaust valve 20 is operated (opened) when the first cam 32 or the second cam 34 presses the first transmission device 16 down. The second exhaust valve 22 is operated (opened) when the third cam 36 pushes the second transmission device 18 down.

The cam carrier 14 is in the first axial position (as in FIGS Figures 1 to 4 ), the first transmission device 16 is operatively connected between the first cam 32 and the first exhaust valve 20 via a cam follower 16A. In other words, the first transmission device 16 is not operatively connected between the second cam 34 in the first axial position of the cam carrier 14 and the first exhaust valve 20. The first exhaust valve 20 is actuated according to a contour of the first cam 32. In the second axial position of the cam carrier 14, the first transmission device 16 is operatively connected via the cam follower 16A between the second cam 34 and the first exhaust valve 20. The first exhaust valve 20 is actuated according to a contour of the second cam 34.

In the first axial position of the cam carrier 14, the second transmission device 18 is operatively connected between the third cam 36 and the second exhaust valve 22 via a cam follower 18A. The second exhaust valve 22 is actuated according to a contour of the third cam 36. In the second axial position of the cam carrier 14, the second transmission device 18 does not actuate the second exhaust valve 22. In the second axial position of the cam carrier 14, the cam follower 18A of the second transmission device 18 lies at the same axial position with respect to the camshaft 12 as the first cam-free section 38. The first cam-free section 38 has no elevation for actuating the second transmission device 18. If the cam carrier 14 is in the second axial position, the second exhaust valve 22 is not actuated.

The first cam-free section 38 thus has two functions. On the one hand, the first cam-free section 38 receives the first engagement track 42. On the other hand, the first serves cam-free Section 38 that no actuation of the second exhaust valve 22 takes place in the second axial position of the cam carrier 14. This functional integration is inexpensive for reasons of installation space.

In the illustrated embodiment, the first transmission device 16 and the second transmission device 18 are each designed as a rocker arm. In other embodiments, the transmission devices 16 and 18 can be designed as rocker arms or tappets. In some embodiments, the transmission devices 16 and 18 can have rotatably mounted rollers, for example, as cam followers 16A, 18A.

With reference to Figure 4 A locking device 46 is shown. The locking device 46 has an elastic element 48 and a locking body 50. The elastic element 48 is arranged in a blind hole in the camshaft 12. The elastic element 48 prestresses the locking body 50 against the cam carrier 14. First and second recesses 52 and 54 are arranged in an inner peripheral surface of the cam carrier 14. To lock the cam carrier 14, the locking body 50 is pressed into the first recess 52 when the cam carrier 14 is in the first axial position. In the second axial position of the cam carrier 14, the locking body 50 is pressed into the second recess 54.

In Figure 5A is a section through the second cam 34 along the line BB in Figure 4 shown. The second cam 34 has a first base circle region 34A and a second base circle region 34C. The base circle areas 34A, 34C are separated from one another by a first valve lift area 34B and on the other hand by a second valve lift area 34D. The second valve lift area 34D has a boundary portion 34E that is directly adjacent to the first base circle area 34A. The boundary section 34E forms a trailing edge (ramp) of the second cam 34.

In Figure 5B is a section through the first cam 32 along the line CC in Figure 4 shown. The first cam 32 has a base circle area 32A and a valve lift area 32B. The valve lift area 32B has a boundary portion 32C that is directly adjacent to the base circle area 32A. The boundary section 32C forms a trailing edge (ramp) of the first cam 32.

The boundary portion 32C of the first cam 32 and the boundary portion 34E of the second cam 34 are the same. The boundary portion 32C of the first cam 32 and the Boundary portions 34E of the second cam 34 are arranged at a same circumferential position with respect to a longitudinal axis of the camshaft 12. The boundary sections 32C, 34E form a common flat ramp. The boundary sections 32C, 34E thus enable the cam carrier 14 to be axially displaced not only in the base circle region 32A, 34A, but also in the boundary section 32C, 34E.

In the Figure 6 Various curves A to E are shown in a path-camshaft angle diagram. In Figure 7 is an enlargement of a portion of the graph of Figure 6 in which in particular the boundary sections 32C, 34E are shown.

A dotted curve A indicates a valve lift of the exhaust valve 20 according to a normal operation, as caused by the first cam 32. The curve A thus corresponds to a rolled-up cam profile of the first cam 32. In normal operation, the exhaust valve 20 is opened during the exhaust stroke (push-out stroke) for pushing out exhaust gas through the valve lift area 32B. Otherwise, the exhaust valve 20 remains closed due to the base circle area 32A of the first cam 32.

A solid curve B indicates a valve lift of the exhaust valve 20 according to an engine braking operation, as caused by the second cam 34. The curve B thus corresponds to a rolled-up cam profile of the second cam 34. In the engine braking mode, the exhaust valve 20 is slightly opened at the end of the compression stroke in the area of the top dead center at around 60 ° KW to 100 ° KW before the top dead center by the first valve lift area 34B. This is in Figure 6 each shown at around -225 ° NW (camshaft angle) and at around 135 ° NW. At top dead center, exhaust valve 20 is further opened by valve lift region 34B and closes at about bottom dead center at the end of the expansion stroke. Opening the exhaust valve 20 at the end of the compression stroke causes the compressed air in the cylinder to be pushed through the opened exhaust valve 20 into the exhaust system by the piston moving to top dead center. The compression work previously performed brakes the crankshaft and thus the internal combustion engine. The open exhaust valve 20 during the expansion stroke causes air to be drawn back into the cylinder from the exhaust pipes. At the end of the expansion stroke, the cylinder is essentially filled with air from the exhaust system.

In engine braking operation, the exhaust valve 20 can first be closed by the second base circle region 34C after reaching the bottom dead center at the end of the expansion cycle being held. At the end of the extension stroke (exhaust stroke), the outlet valve 20 opens in the area of the top dead center through the second valve lift area 34D. The opening again takes place at around 60 ° KW to 100 ° KW before top dead center. This is in Figure 6 each shown at around -45 ° NW and at around 315 ° NW. The closed exhaust valve 20 during the first portion of the extension stroke causes the air drawn in the expansion stroke to be compressed while doing work. The cylinder pressure rises. The compression work brakes the crankshaft and thus the internal combustion engine. The opening of the exhaust valve 20 at the end of the push-out cycle results in the air being pushed into the exhaust system through the opened exhaust valve 20. In the intake stroke, the cylinder is filled with air again through the open intake valve or valves. The cycle starts again.

As explained above, the use of the second cam 34 to control the exhaust valve 20 results in double compression with subsequent decompression, so that engine brake functionality is guaranteed.

Like especially the Figure 7 As can be seen, the first cam 32 and the second cam 34 are matched to one another such that the boundary section 32C of the first cam 32 and the boundary section 34E of the second cam 34 are of identical (identical) design. This enables an axial displacement of the cam carrier 14 not only within the base circle areas 32A, 34A. Instead, the axial displacement can additionally take place while the cam follower 16A is operatively connected to one of the limit sections 32C, 34E. This means that the axial displacement can begin earlier. This can be seen from the curves C, D and E.

The dash-dotted curve C relates to a movement of the movable pin from one of the actuators 24 or 26 with respect to the cam carrier 14. The dashed curve D relates to a movement of the respective engagement track 42 or 44 and thus of the cam carrier 14 along the longitudinal axis of the camshaft 12 The colon-dash curve E shows a course of a depth contour of the respective engagement track 42 or 44 (only in Figure 6 shown). An axial displacement of the cam carrier 14 in the first axial position to the second axial position is described below. Axial displacement of the cam carrier 14 from the second axial position to the first axial position takes place analogously.

First of all, the movable pin of the first actuator 24 is extended in the direction of the first engagement track 42 and thereby tracks into the first engagement track 42. The tracking is done by the trained depth contour of the first engagement track 42 enables (see curve E). After the engagement, a cross-sectional narrowing of the first engagement track 42 leads to a play reduction between the pin of the first actuator 24 and the first engagement track 24. The play reduction takes place in an area S (see Figure 7 ). The area S is reached and traversed by the pin of the first actuator 24 before the cam follower 16A reaches the limit section 32C of the first cam 32. When the cam follower 16A finally reaches the limit section 32C of the first cam 32, the spiral shape begins in the first engagement track 42, which causes an axial displacement of the cam carrier 14. Thus, the cam carrier 14 is already displaced in a first displacement region V1, while the cam follower 16A is in contact with the limit section 32C. This starts the axial displacement of the cam carrier 14 before the cam follower 16A reaches the base circle region 32A. In the base circle region 32A, 34A, the axial displacement of the cam follower 16A is carried out further (displacement region V2) and finally ended before the cam follower 16A reaches the first valve lift region 34B.

The axial displacement of the cam carrier 14 thus also takes place outside the base circle regions 32A, 34A in the boundary section 32C of the first cam 32 and the boundary section 34E of the second cam 34. This increases the time range for the axial displacement of the cam carrier 14. Because of the increased displacement range, the accelerations and thus the inertial forces can be reduced for the axial displacement of the cam carrier 14 at the same switching speed. On the one hand, this can be used to increase functional reliability and service life due to lower forces and pressures. On the other hand, this can be used to increase the maximum switching speed of the system.

In the example shown, the additional displacement range V1, which is made possible by the identically configured limit sections 32C, 34E, extends over approximately 22 ° camshaft angles.

In order to enable an axial displacement of the cam carrier 14 shown in the figures, it may be necessary to design the cam-free section 38, which serves both as a zero cam and is provided with the second engagement track 42, with an additional axial tolerance range (clearance range). The adjacent cam 36 is made correspondingly narrower. Then, during the axial displacement within the boundary portions 32C, 34E from the second axial position to the first axial position, the cam follower 18A axially shifted within this additional tolerance range. A collision of the cam follower 18A with a cam runout of the third cam 36 is prevented.

However, those skilled in the art will recognize that the slide cam system described herein is not limited to the application described herein. For example, as an alternative or in addition to the same design of the outlet areas (outlet areas), an identical design of the startup areas (inlet areas) of the cams can be provided in order to implement the boundary sections of the same design. It is also possible to use the principles described herein with variable valve trains for intake valves of an internal combustion engine. For example, a start-up area of a first cam for normal operation can be designed identically to a start-up area of a second cam for mill operation and can be positioned at the same circumferential position with respect to the longitudinal axis of the camshaft. It should also be emphasized that the displacement device (first actuator, second actuator, first engagement track, second engagement track) disclosed here does not necessarily have to be used to extend the switching range for axially displacing the cam carrier. Rather, for example, a method for operating an internal combustion engine with any displacement device for the cam carrier can comprise displacing the cam carrier while the cam follower is in contact with the boundary region or regions. In particular, an axial displacement can begin and / or end when the cam follower is in contact with a limit area.

Reference list

10th

Variable valve train

11

Sliding cam system

12th

camshaft

14

Cam carrier

16

First transmission device (first rocker arm)

16A

Cam follower

18th

Second transmission device (second rocker arm)

18A

Cam follower

20th

First exhaust valve

22

Second exhaust valve

24th

First actuator

26

Second actuator

27

Control unit

28

First stop

30th

Second attack

32

First cam

32A

Base circle area

32B

Valve lift range

32C

Boundary portion of the valve lift area 32B

34

Second cam

34A

First base circle area

34B

First valve lift range

34C

Second base circle area

34D

Second valve lift range

34E

Boundary portion of the second valve lift range 34D

36

Third cam

38

First cam-free section

40

Second cam-free section

42

First engagement trace

44

Second engagement lane

46

Locking device

48

Elastic element

50

Blocking body

52

First recess

54

Second recess

A

Valve control curve according to cam 32

B

Valve control curve according to cam 34

C.

Pen movement

D

Engagement track / cam carrier movement

E

Depth contour of the engagement track

S

Game reduction area

V1

First (axial) displacement range

V2

Second (axial) displacement range

Claims (15)

1. A sliding cam system (11) for a variable valve train (10) of an internal combustion engine of a motor vehicle, in particular a commercial vehicle, comprising:

   a camshaft (12);

   a cam carrier (14) which is arranged on the camshaft (12) fixedly so as to rotate with it and axially displaceably between a first axial position and a second axial position, and comprises a first cam (32), a second cam (34) and a first engagement track (42) for the axial displacement of the cam carrier (14) ;

   a cam follower (16A) which is operatively connected to the first cam (32) in the first axial position of the cam carrier (14) and is operatively connected to the second cam (34) in the second axial position of the cam carrier (14); and

   a first actuator (24) which comprises an element which can be retracted and extended, in particular a pin, for engaging into the first engagement track (42) for the axial displacement of the cam carrier (14) ;

   the first cam (32) and the second cam (34) being arranged offset with respect to one another along a longitudinal axis of the camshaft (12);

   the first cam (32) comprising a base circle region (32A) and a valve lift region (32B) with a limiting section (32C) which adjoins the base circle region (32A) of the first cam (32);

   the second cam (34) comprising a base circle region (34A) and a valve lift region (34D) with a limiting section (34E) which adjoins the base circle region (34A) of the second cam (34);

   the limiting section (32C) of the first cam (32) and the limiting section (34E) of the second cam (34) being of identical configuration and being arranged at an identical circumferential position about the longitudinal axis of the camshaft (12); and

   the first actuator (24), the cam follower (16A) and the first engagement track (42) being arranged and configured in such a way that an axial displacement of the cam carrier (14) can be carried out while the cam follower (16A) is operatively connected to the limiting section (32C) of the first cam (32) and/or the limiting section (34E) of the second cam (34)

   characterized in that
   the first engagement track (42) comprises a cross-sectional constriction for the reduction of the play between the first engagement track (42) and that element of the first actuator (24) which can be retracted and extended during the engagement, which cross-sectional constriction is arranged in such a way that the reduction of the play takes place before the cam follower (16A) passes into an operative connection with the limiting section (32C) of the first cam (32) or the limiting section (34E) of the second cam (34).
2. The sliding cam system (11) according to Claim 1, the first actuator (24), the cam follower (16A) and the first engagement track (42) being arranged and configured in such a way that an axial displacement of the cam carrier (14) begins or ends while the cam follower (16A) is operatively connected to the limiting section (32C) of the first cam (32) or the limiting section (34E) of the second cam (34).
3. The sliding cam system (11) according to Claim 1 or Claim 2:

   the limiting section (32C) of the first cam (32) and the limiting section (34E) of the second cam (34) extending over a region of greater than or equal to 1° camshaft angle; and/or

   the limiting section (32C) of the first cam (32) and the limiting section (34E) of the second cam (34) extending over a region of between 5° and 45° camshaft angle, in particular between 15° and 30° camshaft angle.
4. The sliding cam system (11) according to one of the preceding claims, the limiting section (32C) of the first cam (32) and the limiting section (34E) of the second cam (34) forming a common flat ramp.
5. The sliding cam system (11) according to one of the preceding claims:

   the limiting section (32C) of the first cam (32) being arranged in a run-out region of the first cam (32) and the limiting section (34E) of the second cam (34) being arranged in a run-out region of the second cam (34); and/or

   the axial displacement of the cam carrier (14) beginning when the cam follower (16A) is operatively connected to the limiting section (32C) of the first cam (32) or the limiting section (34E) of the second cam (34), and preferably ending while the cam follower (16A) is operatively connected to the base circle region (32A) of the first cam (32) or the base circle region (34A) of the second cam (34).
6. The sliding cam system (11) according to one of the preceding claims:

   the limiting section (32C) of the first cam (32) being arranged in a run-in region of the first cam (32) and the limiting section (34E) of the second cam (34) being arranged in a run-in region of the second cam (34); and/or

   the axial displacement of the cam carrier (14) ending when the cam follower (16A) is operatively connected to the limiting section (32C) of the first cam (32) or the limiting section (34E) of the second cam (34), and preferably beginning while the cam follower (16A) is operatively connected to the base circle region (32A) of the first cam (32) or the base circle region (34A) of the second cam (34).
7. The sliding cam system (11) according to one of the preceding claims, the cam carrier (14) comprising a second engagement track (44) for the axial displacement of the cam carrier (14) in an opposed direction with respect to an axial displacement which is brought about by the first engagement track (42), and the sliding cam system (11) comprising, furthermore:

   a second actuator (26) which comprises an element which can be retracted and extended, in particular a pin, for engaging into the second engagement track (44) for the axial displacement of the cam carrier (14) ;

   the second actuator (26), the cam follower (16A) and the second engagement track (44) being arranged and configured in such a way that an axial displacement of the cam carrier (14) can be carried out while the cam follower (16A) is operatively connected to the limiting section (32C) of the first cam (32) or the limiting section (34E) of the second cam (34).
8. The sliding cam system (11) according to Claim 7:
   the second engagement track (44) comprising a cross-sectional constriction for the reduction of the play between the second engagement track (44) and that element of the second actuator (26) which can be retracted and extended during the engagement, which cross-sectional constriction is arranged in such a way that the reduction of the play takes place before the cam follower (16A) passes into an operative connection with the limiting section (32C) of the first cam (32) or the limiting section (34E) of the second cam (34).
9. The sliding cam system (11) according to one of the preceding claims:

   the first engagement track (42) and/or the second engagement track (44) extending spirally about the longitudinal axis of the camshaft (12); and/or

   it being possible for that element of the first actuator (24) and/or the second actuator (26) which can be retracted and extended to be moved radially with regard to the longitudinal axis of the camshaft (12) .
10. A variable valve train (10) for an internal combustion engine, having:

    a sliding cam system (11) according to one of the preceding claims; and

    a gas exchange valve (20), in particular an inlet valve or an outlet valve, which is operatively connected to the cam follower (16A),

    the first cam (32) and the second cam (34) bringing about different valve lifts, opening times and/or closing times of the gas exchange valve (20).
11. The variable valve train (10) according to Claim 10:

    the gas exchange valve (20) being an outlet valve;

    the first cam (32) being configured for a normal operation mode of the internal combustion engine, in the case of which the first cam (32) holds the outlet valve open in the exhaust stroke; and

    the second cam (34) being configured for an engine braking operation mode of the internal combustion engine, in the case of which the outlet valve is first of all held closed in the compression stroke and in the exhaust stroke, and is opened before a top dead centre of a piston movement is reached.
12. The variable valve train (10) according to Claim 10 or Claim 11, the second cam (34) being configured in such a way that:

    the outlet valve opens between 100° crank angle and 60° crank angle before the top dead centre is reached; and/or,

    after opening in the exhaust stroke, the outlet valve closes in the region between the top dead centre and 30° crank angle after the top dead centre; and/or,

    after opening in the compression stroke, the outlet valve closes in the region between the bottom dead centre and 30° crank angle after the bottom dead centre.
13. A motor vehicle, in particular a commercial vehicle, comprising the variable valve train (10) according to one of Claims 10 to 12 or the sliding cam system (11) according to one of Claims 1 to 9.
14. A method for operating an internal combustion engine having a sliding cam system (11) according to one of Claims 1 to 9, the method comprising:
    axial displacement of the cam carrier (14), the axial displacement of the cam carrier (14) being carried out, in particular beginning or ending, while the cam follower (16A) is operatively connected to the limiting section (32C) of the first cam (32) and/or the limiting section (34E) of the second cam (34).
15. The method according to Claim 14:

    the axial displacement of the cam carrier (14) beginning while the cam follower (16A) is operatively connected to the limiting section (32C) of the first cam (32) or the limiting section (34E) of the second cam (34), and/or ending while the cam follower (16A) is operatively connected to the base circle region (32A) of the first cam (32) or the base circle region (34A) of the second cam (34); and/or

    the axial displacement of the cam carrier (14) beginning while the cam follower (16A) is operatively connected to the base circle region (32A) of the first cam (32) or the base circle region (34A) of the second cam (34), and/or ending while the cam follower (16A) is operatively connected to the limiting section (32C) of the first cam (32) or the limiting section (34E) of the second cam (34) .

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