EP4004350A1

EP4004350A1 - Variable valve train for an engine braking mode

Info

Publication number: EP4004350A1
Application number: EP20743649.4A
Authority: EP
Inventors: Thomas Malischewski; Steffen Hirschmann; Andreas Bug
Original assignee: MAN Truck and Bus SE
Current assignee: MAN Truck and Bus SE
Priority date: 2019-07-23
Filing date: 2020-07-17
Publication date: 2022-06-01
Also published as: BR112022000636A2; CN114096743A; US20220251978A1; DE102019119870A1; WO2021013718A1; US12060815B2

Abstract

The invention relates to a variable valve train (10) for switching an outlet valve (22) of an internal combustion engine to an engine braking mode. The variable valve train (10) has a camshaft (12) with a first cam (34), which is designed as a normal operation cam, and a second cam (36), which is designed as an engine braking cam. A first rocking lever (14) has a first stroke device (38) which is designed for selectively making or breaking a first operative connection between the first cam (34) and the outlet valve (22) by means of the first rocking lever (14). A second rocking lever (16) has a second stroke device (40) which is designed for selectively making or breaking a second operative connection between the second cam (36) and the outlet valve (22) by means of the second rocking lever (16). A valve device (60) selectively connects the first stroke device (38) or the second stroke device (40) to a fluid feed line (66).

Description

Variable valve train for an engine braking mode Description

The invention relates to a variable valve drive for switching an exhaust valve of an internal combustion engine into an engine braking mode.

It is known to use variable valve drives for changing switching times and valve lifts of gas exchange valves of an internal combustion engine during operation of the internal combustion engine. A large number of variable valve trains are known in the prior art.

Variable valve trains can be used, for example, to operate exhaust valves of the cylinders of an internal combustion engine in an engine braking mode in which a valve control curve of the exhaust valves deviates from normal operation.

DE 4025 569 C1 discloses a valve control of an internal combustion engine that can be switched as a drive or brake with exhaust valves controlled differently from a camshaft via control rocker arms in drive and braking function, on which in braking function in addition to the cam acting in drive function, another auxiliary cam (Brake cam) acts. In each case coaxially to a control rocker arm of an exhaust valve, a brake rocker arm guided by a brake cam and resiliently abutting it is mounted, which can be locked on the control rocker arm during braking operation.

DE 10 2017 1 18 852 A1 discloses a power transmission device for a variable valve drive of an internal combustion engine. The power transmission device has a first lever device. The first lever device has a first cam follower and a first receptacle for the first cam follower. The first cam follower can be moved and locked in the first receptacle. The power transmission device has a second Hebelvor direction. The second lever device has a second cam follower and a second receptacle for the second cam follower. The second cam follower can be moved and locked in the second acquisition.

The invention is based on the object of creating an alternative and / or improved variable valve drive for an engine braking mode.

The object is achieved by the features of independent claim 1. Advantageous further developments are given in the dependent claims and the description. The invention provides a variable valve train for switching a (cylinder) exhaust valve of an internal combustion engine into an engine braking mode. The variable valve drive has a camshaft with a first cam, which is designed as a normal operation cam, and a second cam, which is designed as an engine brake cam. The variable valve drive has a first rocker arm with a first idle travel device which is designed to selectively (selectively) create or disconnect a first operative connection between the first cam and the exhaust valve by means of the first rocker arm. The variable valve drive has a second rocker arm with a second idle travel device which is designed to optionally create or separate a second operative connection between the second cam and the exhaust valve by means of the second rocker arm. The variable valve drive has a (z. B. hydraulic) fluid supply line and a valve device which is designed to selectively (selectively) (z. B. only) the first idle travel device or (z. B. only) the second idle travel -Device to connect to the fluid supply line.

The variable valve drive can be activated (or deactivated) by combining two idle travel devices, which either activate (or deactivate) a cam contour of a normal operating cam and an engine brake cam, with an upstream valve device, by means of which either the first idle travel device or the second idle travel device can be activated is to provide an engine braking system in a structurally simple and reliable way. The engine braking function can be carried out appropriately by means of a dual hydraulic actuation system. The switching functionality of the valve device (switching between the idle travel devices) can be implemented in a simple manner. Such a built-up variable valve train can also make it possible to easily implement other features such. B. a hydraulic valve lash adjuster.

The rocker arms can expediently be arranged rigidly on one another or can be pivoted relative to one another.

It is possible that the rocker arms form a common lever body.

In one embodiment, the variable valve train also has a (e.g. hydraulic) fluid drain line. The valve device is designed to optionally (for example only) connect the first free travel device or (for example only) the second free travel device to the fluid drain line. The valve device is preferably designed to connect the first idle travel device to the fluid supply line in a (first) position and to connect the second idle travel device to the fluid outlet line. Alternatively or additionally, the Valve device further designed to connect the first free travel device to the fluid discharge line in a (second) position and to connect the second free travel device to the fluid supply line. Thus, by selecting the position of the valve device, the respective desired free travel device can be activated very easily.

A control and / or regulating unit of the internal combustion engine can expediently effect an adjustment of the valve device. The valve device can, for example, be actuated electrically, pneumatically, hydraulically, by motor and / or magnetically.

In a further exemplary embodiment, the variable valve drive has a first backflow preventer, which is preferably arranged in fluid connection between the valve device and the first idle travel device. Alternatively or additionally, the variable valve drive has a second backflow preventer, which is preferably arranged in fluid connection between the valve device and the second idle travel device.

The first and / or second backflow preventer can expediently be accommodated in the respective tilting lever or arranged outside the respective tilting lever.

The first and / or second backflow preventer can preferably be provided separately from the valve device.

In a further exemplary embodiment, the first backflow preventer is designed to act as a hydraulic valve clearance compensation device for the first operative connection, preferably in a position of the first backflow preventer in which backflow from the first idle travel device is blocked. Alternatively or additionally, the second backflow preventer is designed to act as a hydraulic valve lash adjuster for the second operative connection, preferably in a position of the second backflow preventer in which backflow from the second idle travel device is blocked. If, for example, the first and second idle travel devices are only hydraulically locked in the activated position (e.g. without mechanical locking elements), the hydraulic valve lash adjuster can be based on the functionality of the backflow preventer itself. This can considerably increase the practical suitability of the variable valve drive.

In one embodiment, the first backflow preventer is designed to enable a backflow of fluid from the first free travel device to the valve device and / or the fluid drain line in a first position (e.g. to deactivate the first free travel device for Compensate the cam contour of the first cam / to separate the first operative connection). In a second position, an inflow of fluid from the valve device to the first free travel device can be enabled (for example to activate the first free travel device to create the first working connection). In a third position, a backflow of fluid from the first free travel device to the valve device can be blocked (e.g. to maintain the activation of the first free travel device in order to maintain the first operative connection).

In a further embodiment, the second backflow preventer is designed to enable a backflow of fluid from the second free travel device to the valve device and / or the fluid drain line in a first position (e.g. to deactivate the second free travel device to compensate for the Cam contour of the second cam / to separate the second working connection). In a second position, an inflow of fluid from the valve device to the second free travel device can be enabled (for example to activate the second free travel device to create the second working connection). In a third position, a backflow of fluid from the second free travel device to the valve device can be blocked (for example to maintain the activation of the second free travel device in order to maintain the second operative connection).

In a further embodiment, the first position, the second position and / or the third position of the first backflow preventer and / or the second backflow preventer are set automatically as a function of a fluid supply pressure and a fluid counterpressure on the first backflow preventer and / or on the second backflow preventer.

In one embodiment, the first idle travel device creates the first working connection when fluid is applied, and / or the second idle travel device creates the second operative connection when fluid is applied.

In an alternative embodiment variant, the first idle travel device separates the first working connection when fluid is applied, and / or the second idle travel device separates the second operative connection when fluid is applied.

In one embodiment, the first idle travel device and the second idle travel device are structurally identical and / or functionally identical. For example, the same parts can be used, manufacturing costs can be reduced and incorrect assembly can be prevented.

It is also possible that the first rocker arm and the second rocker arm are structurally identical. In a further embodiment, the first free travel device and / or the second free travel device can only be locked hydraulically and / or free of mechanical locking. The assigned backflow preventer can thus act as a hydraulic valve clearance compensation device. The structure of the idle travel device is simplified.

In one embodiment, the first free travel device and / or the second free travel device has a receiving chamber, a piston which is arranged displaceably in the receiving chamber, a cam follower which is connected to the piston for displacement, a fluid space that is connected to the piston is limited and / or an elastic element which is arranged for tensioning the piston before. The fluid space can preferably be formed in the receiving chamber. For example, the elastic element can be received in the receiving chamber.

It is possible for the variable valve drive to be constructed in such a way that the first idle travel device and the second idle travel device (for example always) are fluidically separated. For example, a fluid line which opens into the fluid chamber of the first free travel device can be fluidically separated from a fluid line which opens into the fluid chamber of the second free travel device.

In a further embodiment, the valve device is designed as a directional valve, preferably as a 4-2-way valve or a 4-3-way valve.

In a further embodiment, the valve device, preferably for keeping the exhaust valve closed (e.g. in a cylinder deactivation mode (e.g. with inlet valve (s) also closed and without fuel supply)), is also designed to be in a (third ) Position to connect the first free travel device and the second free travel device with a fluid drain line. Both the first operative connection and the second operative connection can thus be separated. The outlet valve remains closed throughout the cycle.

In one embodiment variant, the first operative connection and the second operative connection act on the outlet valve and a further outlet valve. Alternatively, the first operative connection can act on the outlet valve and a further outlet valve, and the second operative connection can only act on the outlet valve. For example, only one of two exhaust valves of a cylinder can be operated in engine braking mode and the other exhaust valve can be kept closed. In a further embodiment, the second cam is designed to initially keep the exhaust valve closed in the compression cycle and / or in the exhaust cycle and to open it before a piston movement reaches a top dead center, preferably between 100 ° CA and 60 ° CA before reaching the upper one Dead center. The outlet valve can, for example, be kept open in the expansion stroke, closed at the end of the expansion stroke and / or closed at the end of the outlet stroke.

In a further embodiment variant, the first cam is designed in such a way that the outlet valve is open in the exhaust stroke and is essentially closed in the intake stroke, in the compression stroke and in the expansion stroke.

The invention also relates to a motor vehicle, preferably a utility vehicle (for example a truck or bus), with a variable valve drive as disclosed herein.

It is also possible to use the device as disclosed herein for passenger cars, large engines, all-terrain vehicles, marine engines and the like.

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:

FIG. 1 is a perspective view of a variable valve drive according to an exemplary embodiment of the present disclosure;

FIG. 2 shows a sectional view through the exemplary variable valve drive;

Figure 3 shows a further sectional view through a rocker arm of the exemplary variable

Valvetrain;

FIG. 4 shows an exemplary valve control curve;

FIG. 5 shows a schematic view of the exemplary variable valve drive;

FIG. 6 shows a schematic view of a further exemplary variable valve drive;

FIG. 7 shows a schematic view of a backflow preventer of the exemplary variable valve drive; FIG. 8 is a schematic view of the backflow preventer in a further position; and

Figure 9 is a schematic view of the backflow preventer in a further different

Position.

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

In Figure 1, a variable valve train 10 is shown. The variable valve drive 10 can be part of a (reciprocating piston) internal combustion engine. The internal combustion engine can preferably be included as a driving force source in a motor vehicle, preferably a utility vehicle (e.g. truck or bus). The variable valve train 10 is used to enable one or more exhaust valves of the internal combustion engine to be switched into an engine braking mode.

The variable valve train 10 has a camshaft 12, a first rocker arm 14 and a second rocker arm 16. The rocker arms 14 and 16 are pivotable about a rocker arm axis 18 bar. The variable valve drive 10 also has a valve bridge 20 and two (cylinder) exhaust valves 22 of the same cylinder of the internal combustion engine. The outlet valves 22 can be operated (opened and closed) either by the first rocker arm 14 or the second rocker arm 16 by means of the valve bridge 20. If both outlet valves 22 can be actuated by both rocker arms 14, 16, the valve bridge 20 does not need to be guided. The outlet valves 22 are preferably designed as poppet valves, which are arranged, for example, in a cylinder head of the internal combustion engine.

The first rocker arm 14 is connected via a first adjustment screw 24 to the valve bridge 20 for actuating the outlet valves 22. A valve clearance can be set and readjusted via the adjusting screw 24.

The second rocker arm 16 is rigidly connected to the first rocker arm 14 via an adjusting screw 26. In detail, the adjusting screw 26 sits on a projection (a tab) 28 of the first rocker arm 14. The projection 28 can extend, starting from a main body area of the first rocker arm 14, in a direction parallel to the rocker arm axis 18. With the adjusting screw 26, a game, which, for example, due to manufacturing or assembly tolerances between the first rocker arm 14 and the second rocker arm 16 can be set.

It is also possible for the rocker arms 14, 16 to be rigidly connected to one another as a common body or for the rocker arms 14, 16 to be pivotable relative to one another.

It is also possible that no valve bridge is provided and, for example, only one outlet valve can be actuated directly by the rocker arms 14, 16. Alternatively, it is, for example, also possible that the first rocker arm 14 actuates both outlet valves 22 by means of the valve bridge 20 and the second rocker arm 16 actuates only one of the two outlet valves 22, e.g. B. by means of a through hole in the valve bridge 20.

FIG. 2 shows that the first rocker arm 14 has a cam follower 30 and the second rocker arm 16 has a cam follower 32. The cam follower 30 follows a cam contour of a first cam 34 of the camshaft 12. The cam follower 32 follows a cam contour of a second cam 36 of the camshaft 12. The cam followers 30, 32 can, as illustrated, be designed as rotatable rollers.

The cam followers 30, 32 are each connected to the rocker arms 14, 16 by means of a free travel device (lost motion device) 38, 40. Preferably, the idle travel devices 38, 40 can be constructed identically, as shown. The idle travel devices 38 enable the cam contour of the first cam 34 or of the second cam 36 to be used by means of the rocker arms 14, 16 to actuate the outlet valves 22.

In a locked or activated position, the first free travel device 38 creates an operative connection between the first cam 34 and the outlet valves 22 by means of the first rocker arm 14 (with the interposition of the valve bridge 20). In a non-locked or deactivated position, the first idle travel device 38 separates this operative connection. Instead, the cam contour of the first cam 34 only leads to an up and down movement of the cam follower 30 without moving the first rocker arm 14.

In a comparable manner, the second idle travel device 40 creates an operative connection between the second cam 36 and the exhaust valves 22 in a locked or activated position by means of the first rocker arm 16 (with the interposition of the first rocker arm 14 and the valve bridge 20). In a non-locked or deactivated position, the second idle travel device 40 separates this operative connection. Instead, the cam contour of the second cam 36 merely to move the cam follower 32 up and down without moving the second rocker arm 16.

The first idle travel device 38 and the second idle travel device 40 thus create the respectively associated operative connection when fluid is applied or fluid is supplied. However, it is also possible for the first idle travel device and the second idle travel device to be designed to create the respectively assigned operative connection without the application of fluid and to separate this operative connection when the fluid is applied.

The idle travel devices 38, 40 are controlled in such a way that at most one of the two idle travel devices 38, 40 is in the respectively locked or activated position. This succeeds in that a fluid is supplied either only to the first free travel device 38 or only to the second free travel device 40. In other words, either only the first idle travel device 38 or only the second idle travel device 40 is subjected to a fluid.

The idle travel devices 38, 40 are expediently identical in construction. Only the structure of the idle travel device 38 shown in FIG. 2 is described below.

The free travel device 38 has a receiving chamber 42, a piston 44 and an elastic element 46.

The piston 44 is movably received in the receiving chamber 42. The elastic element 46 elastically supports the piston 44 on a bottom surface of the receiving chamber 42. The elastic element 46 is expediently a spring, preferably a helical spring. The piston 44 rotatably supports the cam follower 30. A fluid space 48 is formed between the bottom surface of the receiving chamber 42 and the piston 44. A fluid, preferably a hydraulic fluid, can be conducted into and out of the fluid space 48 via a fluid line 50. If a fluid is passed into the fluid space 48 and a backflow of the fluid is blocked, the piston 44 is rigidly supported on the receiving chamber 42 via the fluid in the fluid space 48. The cam contour of the first cam 34 is rigidly transferred to the first rocker arm 14 via the idle travel device 38. If no fluid is passed into the fluid space 48 or a return flow of the fluid is not blocked, the piston 44 is movable in the receiving chamber 42. The cam contour of the first cam 34 is compensated by the idle travel device 38 and not transferred to the first rocker arm 14 . ok

FIG. 3 also shows that the piston 44 is secured against falling out of the receiving chamber 42 by a safety device 52. The securing device 52 can, for example, engage in a longitudinal groove or an elongated hole 54 of the piston 44 and thus additionally represent an anti-twist device for the piston 44.

In the illustrated embodiment, the idle travel devices 38, 40 are arranged with respect to the rocker arms 14, 16 on the cam follower or cam side. Alternative arrangements are also possible, for example an arrangement of idle travel devices on the valve side with respect to the rocker arm. In addition, the illustrated structure of the idle travel devices 38, 40 is preferred, but not restrictive for the present disclosure. Deviating or modified configurations are also conceivable, as long as the assigned functionality (i.e. partial creation or separation of the respective operative connection) can be fulfilled.

By means of the first cam 34, the outlet valves 22 can be operated in a normal operating mode of the internal combustion engine. The outlet valves 22 can be opened in the area of the lower dead center at the beginning of the exhaust stroke and closed at the end of the Auslasstak tes in the area of the upper dead center. In the remaining cycles, the outlet valves 22 are closed. The first cam 34 is thus designed as a normal exhaust cam.

The outlet valves 22 (or, for example, only one of them) can be operated in an engine braking mode of the internal combustion engine by means of the second cam 36. The second cam 36 is thus designed as an engine brake cam.

FIG. 4 shows a particularly preferred, non-limiting valve control curve for the exhaust valves 22 in the engine braking mode, which can be brought about by the second cam 36.

In FIG. 4, the abscissa (x-axis) relates to a crankshaft angle and the ordinate (y-axis) relates to a valve lift in mm. A complete four-stroke cycle consisting of compression, expansion, exhaust and intake is shown.

The valve control curve for the engine braking mode shows that the exhaust valve is opened slightly at the end of the compression stroke in the area of top dead center at around 60 ° CA to 100 ° CA before top dead center. At the top dead center, the exhaust valve is opened further and closes at approximately the bottom dead center at the end of the expansion stroke. Opening the exhaust valve at the end of the compression stroke causes the compressed air in the Cylinder is pushed through the opened exhaust valve into the exhaust system by the piston moving to top dead center. The previously performed compression work brakes the crankshaft and thus the internal combustion engine. The cylinder pressure initially rises in the compression stroke, but then falls before top dead center as a result of the opening of the exhaust valve. The open exhaust valve during the expansion stroke causes air to be drawn from the exhaust pipes back into the cylinder. At the end of the expansion stroke, the cylinder is essentially filled with air from the exhaust system.

The valve control curve also shows that the exhaust valve initially remains closed after reaching bottom dead center at the end of the expansion stroke. At the end of the push-out stroke, the exhaust valve opens in the area of the top dead center. The opening takes place again at around 60 ° CA to 100 ° CA before top dead center. The closed outlet valve during the first section of the expulsion stroke has the effect that the air sucked in in the expansion stroke is compressed while doing work. The cylinder pressure increases. The compression work brakes the crankshaft and thus the combustion engine. The opening of the exhaust valve at the end of the exhaust stroke results in the air being pushed through the opened exhaust valve into the exhaust system. In the intake stroke, the cylinder is filled with air again through the open inlet valve or valves. The cycle starts again.

As explained above, the use of the second cam 36 results in a double compression with subsequent decompression, so that an effective engine braking functionality is ensured.

FIG. 5 shows schematically how fluid is supplied to the idle travel devices 38, 40 and removed from them.

The variable valve drive 10 has a (hydraulic) fluid system with a pressurized fluid source 56, a fluid reservoir 58, a valve device 60 and two backflow preventer 62, 64.

The pressurized fluid source 56 can supply pressurized fluid to the valve device 60 by means of a fluid supply line 66. For example, the pressure fluid source 56 can be designed as a fluid or hydraulic pump. The pressurized fluid source 56 can be connected to the fluid reservoir 58. Fluid can be conducted from the valve device 60 to the fluid reservoir 58 via a fluid discharge line (fluid discharge line) 68. The fluid reservoir 58 can be designed as an oil pan, for example. The valve device 60 can assume (at least) two different positions. In the (first) position shown, the pressurized fluid source 56 is connected to the first idle travel device 38. The second idle travel device 40 is connected to the fluid reservoir 58 in the first position of the valve device 60. In a second position, the pressure fluid source 56 is connected to the second idle travel device 40. The first idle travel device 38 is connected to the fluid reservoir 58 in the second position of the valve device 60. It is thus possible to switch back and forth between the rocker arms 14 and 16 and thus the cams 34 and 36 in a particularly simple manner. The valve device 60 can be useful as a 4/2-way valve (directional valve with four connections and two positions) leads out. A series and / or parallel connection of several valves is also possible.

The valve device 60 is in the first position during normal operation of the internal combustion engine. The valve device 60 is in the engine braking mode of the internal combustion engine in the second position. In the first position, the first idle travel device 38 is rigid and the second idle travel device 40 is switched to be movable. The first rocker arm 14 is activated, and the second rocker arm 16 is deactivated. In the second position, the first free travel device 38 is movable and the second free travel device 40 is switched to be rigid. The first rocker arm 14 is deactivated and the second rocker arm 16 is activated.

The backflow preventer 62, 64 can be designed as control or control valves. The backflow preventer 62, 64 are designed to prevent undesired backflow from the respective idle travel device 38, 40, as is described by way of example in detail with reference to FIGS. 7 to 9. In addition, the backflow preventer 62, 64 can enable a backflow from the idle travel devices 38, 40 when the valve device 60 connects the corresponding idle travel device 38, 40 with the fluid drain line 68 or no pressure fluid from the pressure fluid source 56 is connected to the respective backflow prevention device rer 62, 64 is applied.

FIG. 6 shows a fluid system that is modified compared to FIG.

The fluid system of FIG. 6 differs from the fluid system of FIG. 5 in that the valve device 60 can assume a third position. The Ventilein device 60 here can expediently be designed as a 4/3-way valve (directional valve with 4 connections and 3 positions). A series and / or parallel connection of several valves is also possible. In the third position, both idle travel devices 38, 40 are connected to the fluid reservoir 58 a related party. Thus none of the idle travel devices 38, 40 is activated. None of the assigned rocker arms 14, 16 is pivoted during a camshaft revolution. The outlet valves 22 remain closed. In this way, cylinder deactivation can be effected in a simple manner with regard to the outlet valves 22. In addition, the inlet valves can be kept closed and the fuel supply can be stopped in order to switch off the corresponding cylinder.

FIGS. 7 to 9 show an exemplary embodiment for the backflow preventer 62. The backflow preventer 64 can be constructed identically or at least functionally as the backflow preventer 62.

The backflow preventer 62 has a pressurized fluid supply 70, a fluid line 72 and a fluid outlet 74. The pressure fluid supply 70 is used to supply pressure fluid from the valve device 60 to the backflow preventer 62. The fluid line 72 is used to supply pressure fluid from the backflow preventer 62 to the idle travel device 38 and to drain fluid from the idle travel device 38 to the backflow preventer 62. The fluid drain 74 is used to drain fluid from the backflow preventer 62 to the valve device 60 and / or the fluid drain line 68.

The backflow preventer 62 has a movable piston 76. In a rest position (FIG. 7), the piston 76 blocks the pressure fluid supply 70 and creates a fluid connection between the fluid line 72 and the fluid outlet 74 for draining fluid from the idle travel device 38. The piston 76 is elastically pretensioned in the direction of the rest position preferably spring-loaded.

The backflow preventer 62 has a check valve 78 with a movable locking element 80, for. B. a ball. The locking element 80 is elastically pre-tensioned, preferably spring-pre-tensioned, in the direction of a closed position. The check valve 78 is received in ben 76 Kol.

FIG. 8 shows that when pressurized fluid is supplied to the backflow preventer 62 via the pressurized fluid supply 70, the piston 76 can first be moved in such a way that the fluid outlet 74 is blocked. In addition, the blocking element 80 can be moved against the elastic bias, lift off the valve seat and establish a fluid connection between the pressure fluid supply 70 and the fluid line 72 create. Pressurized fluid can be supplied to the idle travel device 38 for activating the idle travel device 38.

If the first cam 34 (see FIG. 2) causes a valve lift in the activated idle travel device 38, the pressure in the fluid line 72 rises suddenly. The check valve 78 closes by moving the blocking element 80 into the valve seat, see FIG. 9. The fluid from the idle travel device 38 cannot escape. The rocker arm 14 is pivoted ge. The backflow preventer 62 thus also acts as a hydraulic valve play compensation device, in particular in combination with the idle travel device 38, which is only hydraulically locked in the activated position, i.e. in particular provided without a mechanical locking device (e.g. no locking piston) is.

The invention is not restricted to the preferred exemplary embodiments described above. Rather, a large number of variants and modifications are possible which also make use of the inventive concept and therefore fall within the scope of protection. In particular, the invention also claims protection for the subject matter and the features of the subclaims independently of the claims referred to. In particular, the individual features of independent claim 1 are disclosed independently of one another. In addition, the features of the dependent claims are independent of all the features of independent claim 1 and, for example, independent of the Merkma len with regard to the presence and / or configuration of the camshaft, the first rocker arm, the second rocker arm, the fluid supply line and / or the valve device of the independent Claim 1 disclosed. All range specifications herein are to be understood as disclosed in such a way that all values falling within the respective range are disclosed individually, e.g. B. also as the respectively preferred narrower outer boundaries of the respective area.

List of reference symbols

10 Variable valve train

12 camshaft

14 First rocker arm

16 Second rocker arm

18 rocker arm axis

20 valve bridge

22 exhaust valve

24 adjusting screw

26 adjusting screw

28 advantage

30 cam followers

32 cam followers

34 First cam

36 Second cam

38 First free travel facility

40 Second free travel device

42 receiving chamber

44 pistons

46 elastic element

48 fluid space

50 fluid line

52 Backup

54 elongated hole

56 source of pressurized fluid

58 fluid reservoir

60 valve device

62 First backflow preventer

64 Second backflow preventer

66 Fluid supply line

68 Fluid Drain Line

70 pressure fluid supply

72 fluid line

74 fluid drain piston

Check valve blocking element

Claims

1. Variable valve train (10) for switching an exhaust valve (22) of an internal combustion engine into an engine braking mode, the variable valve train (10) having:

a camshaft (12) with a first cam (34), which is designed as a normalbetriebsno cken, and a second cam (36), which is designed as an engine brake cam;

a first rocker arm (14) with a first free travel device (38) which is designed to selectively create or separate a first operative connection between the first cam (34) and the outlet valve (22) by means of the first rocker arm (14);

a second rocker arm (16) with a second idle travel device (40) which is designed for the selective creation or separation of a second working connection between the second cam (36) and the outlet valve (22) by means of the second rocker arm (16);

a fluid supply line (66); and

a valve device (60) which is designed to optionally connect the first free travel device (38) or the second free travel device (40) to the fluid supply line (66).

2. The variable valve train (10) of claim 1, further comprising:

a fluid drain line (68),

wherein the valve device (60) is designed to optionally connect the first free travel device (38) or the second free travel device (40) to the fluid drain line (68),

where preferably:

the valve device (60) is designed to:

in a first position to connect the first idle travel device (38) to the fluid feed line (66) and to connect the second idle travel device (40) to the fluid drain line (68); and

in a second position to connect the first free travel device (38) to the fluid drain line (68) and to connect the second free travel device (40) to the fluid supply line (66).

3. Variable valve train (10) according to claim 1 or claim 2, further comprising:

a first backflow preventer (62) which is arranged in fluid communication between the Ven tileinrichtung (60) and the first idle travel device (38); and / or a second backflow preventer (64) which is arranged in fluid connection between the valve device (60) and the second free travel device (40).

4. The variable valve train (10) of claim 3, wherein:

the first backflow preventer (62) is designed to act as a hydraulic valve lash adjuster for the first operative connection, preferably in a position of the first backflow preventer (62) in which backflow from the first idle travel device (38) is blocked; and or

the second backflow preventer (64) is designed to act as a hydraulic valve lash adjuster for the second working connection, preferably in a position of the second backflow preventer (64) in which a backflow from the second idle travel device (40) is blocked.

5. The variable valve train (10) of claim 3 or claim 4, wherein:

the first backflow preventer (62) is designed to:

in a first position to enable a return flow of fluid from the first idle travel device (38) to the valve device (60) and / or the fluid drain line (68);

in a second position to allow an inflow of fluid from the valve device (60) to the first idle travel device (38);

in a third position, to block a return flow of fluid from the first idle travel device (38) to the valve device (60); and / or the second backflow preventer (64) is designed to:

in a first position to enable a return flow of fluid from the second idle travel device (40) to the valve device (60) and / or the fluid drain line (68);

in a second position to allow an inflow of fluid from the valve device (60) to the second idle travel device (40); and in a third position to block a backflow of fluid from the second idle travel device (40) to the valve device (60).

6. The variable valve train (10) of claim 5, wherein:

the first position, the second position and the third position of the first backflow preventer (62) and / or the second backflow preventer (64) are automatically dependent on a fluid supply pressure and a fluid counterpressure on the first backflow preventer (62) and / or on the second backflow preventer (64).

7. Variable valve train (10) according to one of the preceding claims, wherein:

the first free travel device (38) creates the first active connection when fluid is applied and the second free travel device (40) creates the second active connection when fluid is applied; or

the first idle travel device (38) separates the first working connection when fluid is applied and the second idle travel device (40) separates the second working connection when fluid is applied.

8. Variable valve train (10) according to one of the preceding claims, wherein:

the first idle travel device (38) and the second idle travel device (40) are identical and / or functionally identical.

9. Variable valve train (10) according to one of the preceding claims, wherein:

the first free travel device (38) and / or the second free travel device (40) can only be locked hydraulically and / or is free of mechanical locking.

10. Variable valve train (10) according to one of the preceding claims, wherein:

the first idle travel device (38) and / or the second idle travel device (40) comprises:

a receiving chamber (42);

a piston (44) slidably disposed in the receiving chamber (42);

a cam follower (30, 32) which is ver for sliding with the piston (44) connected;

a fluid space (48) delimited by the piston (44); and an elastic member (46) which is arranged for biasing the piston (44).

11. Variable valve train (10) according to one of the preceding claims, wherein:

the valve device (60) is designed as a directional valve, preferably as a 4-2-way valve or a 4-3-way valve.

12. Variable valve train (10) according to one of the preceding claims, wherein:

the valve device (60), preferably for keeping the outlet valve (22) closed, is also designed to:

in a third position to connect the first idle travel device (38) and the second idle travel device (40) to a fluid drain line (68).

13. Variable valve train (10) according to one of the preceding claims, wherein:

the first operative connection and the second operative connection act on the outlet valve (22) and a further outlet valve (22); or

the first operative connection acts on the outlet valve (22) and a further outlet valve (22) and the second operative connection acts only on the outlet valve (22).

14. Variable valve train (10) according to one of the preceding claims, wherein:

the second cam (36) is designed to initially keep the exhaust valve (22) closed in the compression cycle and / or in the exhaust cycle and open before reaching a top dead center of a piston movement, preferably between 100 ° CA and 60 ° CA before Reaching top dead center; and or

the first cam (34) is designed so that the exhaust valve (22) is open in the exhaust stroke and is essentially closed in the intake stroke, in the compression stroke and in the expansion stroke.

15. Motor vehicle, preferably commercial vehicle, with a variable valve train (10) according to one of the preceding claims.