Variable valve train for engine braking mode

Abstract

The invention relates to a variable valve mechanism (10) for switching an exhaust valve (22) of an internal combustion engine to an engine braking mode. The variable valve mechanism (10) comprises a camshaft (12) having a first cam (34) designed as a normal operation cam and a second cam (36) designed as an engine braking cam. A first rocker (14) has a first stroke device (38) designed to selectively establish or disconnect a first effective connection between the first cam (34) and the exhaust valve (22) through the first rocker (14). A second rocker (16) comprises a second stroke device (40) designed to selectively establish or disconnect a second effective connection between the second cam (36) and the exhaust valve (22) through the second rocker (16). A valve device (60) selectively connects the first stroke device (38) or the second stroke device (40) to a fluid supply line (66).

Description

Technical Field

[0001] The invention relates to a variable valve train for switching exhaust valves of an internal combustion engine into an engine braking mode. Background Art

[0002] It is known to use a variable valve train to change the switching time and valve stroke of the 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.

[0003] The variable valve train may be used, for example, to operate the exhaust valves of a cylinder of an internal combustion engine in an engine braking mode, in which the valve control curve of the exhaust valves deviates from normal operation.

[0004] DE 40 25 569 C1 discloses a valve controller for an internal combustion engine that can be switched to a drive or a brake, which has exhaust valves that are controlled differently by a camshaft via a control rocker in the drive function and the brake function, in the brake function, in addition to the cam that acts in the drive function, another auxiliary cam (brake cam) also acts on the exhaust valve. A brake rocker guided by the brake cam and elastically resting on the brake cam is mounted coaxially relative to each control rocker of the exhaust valve, which brake rocker can be locked on the control rocker during the braking operation.

[0005] DE 10 2017 118 852 A1 discloses a power transmission device for a variable valve mechanism of an internal combustion engine. The power transmission device has a first rod device. The first rod device has a first cam follower and a first receiving portion for the first cam follower. The first cam follower can be moved and locked in the first receiving portion. The power transmission device has a second rod device. The second rod device has a second cam follower and a second receiving portion for the second cam follower. The second cam follower can be moved and locked in the second receiving portion. Summary of the invention

[0006] The object of the present invention is to provide an alternative and / or improved variable valve train for engine braking mode.

[0007] The present invention provides a variable valve mechanism for switching the (cylinder) exhaust valve of an internal combustion engine to an engine braking mode. The variable valve mechanism includes a camshaft (Nockenwelle), which has a first cam designed as a normal operating cam and a second cam designed as an engine braking cam. The variable valve mechanism includes a first rocker (Kipphebel) with a first stroke device (Leerweg-Einrichtung), and the first stroke device is designed to selectively (selectively) establish or disconnect a first effective connection between the first cam and the exhaust valve through the first rocker. The variable valve mechanism includes a second rocker with a second stroke device, and the second stroke device is designed to selectively (selectively) establish or disconnect a second effective connection between the second cam and the exhaust valve through the second rocker. The variable valve mechanism includes a (e.g., hydraulic) fluid supply pipeline and a valve device, which is designed to selectively (selectively) (e.g., only) connect the first stroke device or (e.g., only) the second stroke device to the fluid supply pipeline.

[0008] By combining two stroke devices for activating (or deactivating) the cam profiles of the normally operating cam and the engine brake cam with an upstream valve device for activating the first stroke device or the second stroke device, the variable valve mechanism can provide an engine brake system in a structurally simple and at the same time reliable manner. The engine brake function can thus be appropriately performed by the dual hydraulic drive system. The switching function of the valve device (switching between the stroke devices) can be realized in a simple manner. A variable valve mechanism constructed in this way can also simply realize other features, such as a hydraulic valve clearance compensation device.

[0009] The rockers can be arranged rigidly one above the other or can be rotated relative to one another.

[0010] The rockers may form a common rod body.

[0011] In an exemplary embodiment, the variable valve mechanism further comprises a (e.g. hydraulic) fluid discharge line. The valve device is designed to selectively connect (e.g. only) the first stroke device or (e.g. only) the second stroke device to the fluid discharge line. Preferably, the valve device is designed to connect the first stroke device to the fluid supply line and the second stroke device to the fluid discharge line in the (first) position. Alternatively or supplementarily, the valve device is also designed to connect the first stroke device to the fluid discharge line and the second stroke device to the fluid supply line in the (second) position. Therefore, by selecting the position of the valve device, the corresponding desired stroke device can be very easily enabled.

[0012] Expediently, the control and / or regulating unit of the internal combustion engine can realize the regulation of the valve device. The valve device can be driven, for example, electrically, pneumatically, hydraulically, by a motor and / or magnetically.

[0013] In another exemplary embodiment, the variable valve mechanism comprises a first backflow preventer, which is preferably arranged in the fluid connection between the valve device and the first stroke device. Alternatively or in addition, the variable valve mechanism comprises a second backflow preventer, which is preferably arranged in the fluid connection between the valve device and the second stroke device.

[0014] Expediently, the first and / or the second backflow preventer can be accommodated in the respective rocker or arranged outside the respective rocker.

[0015] Preferably, the first and / or second backflow preventer may be provided separately from the valve device.

[0016] In a further exemplary embodiment, the first backflow preventer is designed to act as a hydraulic valve clearance compensation device for the first effective connection, preferably in the position of the first backflow preventer blocking the backflow from the first stroke device. Alternatively or in addition, the second backflow preventer is designed to act as a hydraulic valve clearance compensation device for the second effective connection, preferably in the position of the second backflow preventer blocking the backflow from the second stroke device. For example, if the first and second stroke devices are thus locked in the respective activation positions only hydraulically (e.g. without mechanical locking elements), the hydraulic valve clearance compensation device can be generated by the function of the backflow preventer itself. Thereby, the practical practicality of the variable valve mechanism can be significantly increased.

[0017] In one embodiment, the first backflow preventer is designed to allow the fluid from the first stroke device to flow back to the valve device and / or the fluid discharge line in a first position (e.g., deactivate the first stroke device to compensate for the cam profile of the first cam / to disconnect the first effective connection). In a second position, the fluid can be allowed to flow from the valve device to the first stroke device (e.g., enable the first stroke device to establish the first effective connection). In a third position, the fluid can be blocked from flowing back from the first stroke device to the valve device (e.g., keep the first stroke device enabled to maintain the first effective connection).

[0018] In another embodiment, the second backflow preventer is designed to allow the fluid from the second stroke device to flow back to the valve device and / or the fluid discharge line in the first position (e.g., deactivate the second stroke device to compensate for the cam profile of the second cam / to disconnect the second effective connection). In the second position, the fluid can be allowed to flow from the valve device to the second stroke device (e.g., enable the second stroke device to establish the second effective connection). In the third position, the fluid can be blocked from flowing back from the second stroke device to the valve device (e.g., keep the second stroke device enabled to maintain the second effective connection).

[0019] In another embodiment, the first position, the second position and / or the third position of the first backflow preventer and / or the second backflow preventer are automatically adjusted according to the fluid supply pressure and the fluid backpressure at the first backflow preventer and / or the second backflow preventer.

[0020] In a variant embodiment, the first stroke device establishes a first effective connection when a fluid is applied, and / or the second stroke device establishes a second effective connection when a fluid is applied.

[0021] In an alternative variant embodiment, the first stroke device disconnects the first operative connection when the fluid is applied, and / or the second stroke device disconnects the second operative connection when the fluid is applied.

[0022] In an exemplary embodiment, the first stroke device and the second stroke device have the same structure and / or the same function. Therefore, for example, the same components can be used, the manufacturing cost is reduced and incorrect assembly is prevented.

[0023] The first rocker and the second rocker may also have the same structure.

[0024] In another exemplary embodiment, the first stroke device and / or the second stroke device can only be locked hydraulically and / or have no mechanical locking element. Therefore, the associated backflow preventer can be used as a hydraulic valve clearance compensation device. The structure of the stroke device is simplified.

[0025] In one embodiment, the first stroke device and / or the second stroke device comprises a receiving chamber, a piston movably arranged in the receiving chamber, a cam follower connected to the piston for movement, a fluid chamber defined by the piston and / or an elastic element arranged to pre-tension the piston. Preferably, the fluid chamber may be formed in the receiving chamber. For example, the elastic element may be accommodated in the receiving chamber.

[0026] The variable valve mechanism can be configured so that the first stroke device and the second stroke device are (eg always) fluidly separated. For example, the fluid line leading to the fluid chamber of the first stroke device can be fluidly separated from the fluid line leading to the fluid chamber of the second stroke device.

[0027] In a further embodiment, the valve device is designed as a directional valve, preferably a 4-2-way valve or a 4-3-way valve.

[0028] In another embodiment, the valve device preferably for keeping the exhaust valve closed (e.g. in a cylinder shut-off mode (e.g. the intake valve(s) are also closed and no fuel is supplied)) is also designed to connect the first stroke device and the second stroke device to the fluid discharge line in the (third) position. Thus, not only the first effective connection but also the second effective connection can be disconnected. The exhaust valve remains closed throughout the entire cycle.

[0029] In a variant embodiment, the first operative connection and the second operative connection act on one exhaust valve and the other exhaust valve. Alternatively, the first operative connection may act on the exhaust valve and the other exhaust valve, while the second operative connection may act only on the exhaust valve. Thus, for example, in engine braking mode only one of the two exhaust valves of a cylinder may be operated, while the other exhaust valve may remain closed.

[0030] In another variant embodiment, the second cam is designed to initially keep the exhaust valve closed during the compression stroke and / or the exhaust stroke and to open the exhaust valve before reaching the top dead center of the piston movement, preferably between 100° crankshaft angle (KW: Kurbelwellenwinkel) and 60° crankshaft angle before reaching the top dead center. For example, the exhaust valve can be kept open during the expansion stroke, closed at the end of the expansion stroke and / or closed at the end of the exhaust stroke.

[0031] In another modified embodiment, the first cam is designed so that the exhaust valve is opened in the exhaust stroke and is substantially closed in the intake stroke, the compression stroke, and the expansion stroke.

[0032] The invention also relates to a motor vehicle, preferably a utility vehicle, such as a truck or a bus, having a variable valve train as disclosed herein.

[0033] The devices disclosed herein may also be used in passenger cars, large engines, off-road vehicles, marine engines, and the like. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The above preferred embodiments and features of the present invention can be combined with each other in any way. Other details and advantages of the present invention will be described below with reference to the accompanying drawings.

[0035] Figure 1 A perspective view of a variable valve mechanism according to an exemplary embodiment of the present disclosure is shown.

[0036] Figure 2 A cross-sectional view of an exemplary variable valve mechanism is shown.

[0037] Figure 3 Another cross-sectional view of a rocker of an exemplary variable valve mechanism is shown.

[0038] Figure 4 An exemplary valve control curve is shown.

[0039] Figure 5 A schematic diagram of an exemplary variable valve train is shown.

[0040] Figure 6 A schematic diagram of another exemplary variable valve mechanism is shown.

[0041] Figure 7 A schematic diagram of a backflow preventer of an exemplary variable valve train is shown.

[0042] Figure 8 A schematic diagram showing a backflow preventer in another position.

[0043] Fig. 9 A schematic diagram showing a backflow preventer in a different position. DETAILED DESCRIPTION

[0044] The embodiments shown in the figures are at least partially identical, so that similar or identical parts are provided with the same reference numerals and, in order to avoid repetition, the same reference numerals are also explained with reference to the description of other embodiments or figures.

[0045] Figure 1 A variable valve mechanism 10 is shown. The variable valve mechanism 10 may be part of a (piston reciprocating) internal combustion engine. The internal combustion engine may preferably be included as a driving force source in a motor vehicle, preferably in a multi-purpose vehicle (e.g. a truck or bus). The variable valve mechanism 10 is used to allow one or more exhaust valves of the internal combustion engine to be switched into an engine braking mode.

[0046] The variable valve mechanism 10 includes a camshaft 12, a first rocker 14 and a second rocker 16. The rockers 14 and 16 can rotate around a rocker shaft 18. The variable valve mechanism 10 also includes a valve bridge (Ventilbrücke) 20 and two (cylinder) exhaust valves 22 of the same cylinder of the internal combustion engine. The exhaust valve 22 can be selectively driven (opened and closed) by the first rocker 14 or the second rocker 16 through the valve bridge 20. If the two exhaust valves 22 can be driven by two rockers 14, 16 respectively, the guidance of the valve bridge 20 can be omitted. The exhaust valve 22 is preferably designed as a lift valve, which is arranged, for example, in the cylinder head of the internal combustion engine.

[0047] The first rocker 14 is connected to the valve bridge 20 via a first adjusting bolt 24 to drive the exhaust valve 22. The valve clearance can be adjusted and readjusted via the adjusting bolt 24.

[0048] The second rocker 16 is rigidly connected to the first rocker 14 via an adjusting bolt 26. In detail, the adjusting bolt 26 is seated on a projection (tab) 28 of the first rocker 14. The projection 28 may extend from a main body area of ​​the first rocker 14 in a direction parallel to the rocker axis 18. The adjusting bolt 26 may be used to adjust a clearance that is generated, for example, due to manufacturing or assembly tolerances between the first rocker 14 and the second rocker 16.

[0049] The rockers 14 , 16 can also be rigidly connected to one another as a common body, or the rockers 14 , 16 can be swivelled relative to one another.

[0050] Also can not be provided with valve bridge, and rocker 14,16 for example only directly drives one exhaust valve.Alternatively, for example by through hole in valve bridge 20, first rocker 14 can drive two exhaust valves 22 for example through valve bridge 20, and second rocker 16 drives only one of two exhaust valves 22.

[0051] Figure 2 It is shown that the first rocker 14 has a cam follower 30 and the second rocker 16 has a cam follower 32. The cam follower 30 follows the cam profile of a first cam 34 of the camshaft 12. The cam follower 32 follows the cam profile of a second cam 36 of the camshaft 12. As shown, the cam followers 30, 32 can be designed as rotatable rollers.

[0052] The cam followers 30, 32 are connected via a travel device (lost motion device) 38, 40 of the rocker 14, 16, respectively. Preferably, as shown in the figure, the travel devices 38, 40 can be designed identically. The travel devices 38, 40 allow the cam profile of the first cam 34 or the second cam 36 to be selectively used to drive the exhaust valve 22 via the rocker 14, 16.

[0053] In the locked or activated position, the first lift device 38 establishes an effective connection between the first cam 34 and the exhaust valve 22 via the first rocker 14 (with the valve bridge 20 inserted). In the unlocked or deactivated position, the first lift device 38 disconnects the effective connection. Instead, the cam profile of the first cam 34 only causes the cam follower 30 to move up and down without moving the first rocker 14.

[0054] In a similar manner, in the locked or activated position, the second stroke device 40 establishes an effective connection between the second cam 36 and the exhaust valve 22 via the second rocker 16 (with the first rocker 14 and the valve bridge 20 inserted). In the unlocked or deactivated position, the second stroke device 40 disconnects the effective connection. Instead, the cam profile of the second cam 36 only causes the up and down movement of the cam follower 32 without moving the second rocker 16.

[0055] Therefore, when the fluid is applied or supplied, the first stroke device 38 and the second stroke device 40 establish their respective effective connections. However, the first stroke device and the second stroke device can also be designed to establish their respective effective connections when the fluid is not applied and disconnect the effective connections when the fluid is applied.

[0056] The stroke devices 38, 40 are controlled so that at most one of the two stroke devices 38, 40 is in the respective locked or enabled position. This is achieved by supplying fluid only to the first stroke device 38 or only to the second stroke device 40. In other words, the fluid is applied only to the first stroke device 38 or the second stroke device 40.

[0057] The travel devices 38, 40 are structurally identical. Therefore, only the one shown as an example is described below. Figure 2 The structure of the stroke device 38 in.

[0058] The stroke device 38 includes a receiving chamber 42 , a piston 44 and an elastic element 46 .

[0059] The piston 44 is movably accommodated in the accommodation chamber 42. The elastic element 46 elastically supports the piston 44 on the bottom surface of the accommodation chamber 42. The elastic element 46 is appropriately a spring, preferably a helical spring. The piston 44 rotatably supports the cam follower 30. A fluid chamber 48 is formed between the bottom surface of the accommodation chamber 42 and the piston 44. A fluid, preferably a hydraulic fluid, can be introduced into the fluid chamber 48 and discharged therefrom through a fluid line 50. If the fluid is introduced into the fluid chamber 48 and the fluid backflow is blocked, the piston 44 is rigidly supported on the accommodation chamber 42 by the fluid in the fluid chamber 48. The cam profile of the first cam 34 is rigidly transferred to the first rocking lever 14 via the stroke device 38. If no fluid is introduced into the fluid chamber 48 or if the fluid backflow is not blocked, the piston 44 is movable in the accommodation chamber 42. The cam profile of the first cam 34 is compensated by the stroke device 38 and is not transferred to the first rocking lever 14.

[0060] Figure 3 It is also shown that the piston 44 is secured against falling out of the receiving chamber 42 by a safety mechanism 52. The safety mechanism 52 can, for example, engage in a longitudinal groove or an elongated hole 54 in the piston 44, thereby additionally representing an anti-rotation device for the piston 44.

[0061] In the exemplary embodiment shown, the stroke devices 38, 40 are arranged on the camshaft side or cam side relative to the rocker 14, 16. Alternative arrangements are also possible, for example, the stroke device is arranged on the valve side relative to the rocker. In addition, the structure of the stroke devices 38, 40 shown, although preferred, does not limit the present disclosure. Different or modified configurations are also conceivable as long as the relevant operating mode can be achieved (i.e., partially establishing or disconnecting the corresponding effective connection).

[0062] In the normal operation mode of the internal combustion engine, the exhaust valve 22 can be operated by the first cam 34. The exhaust valve 22 can be opened in the bottom dead center area at the beginning of the exhaust stroke and closed in the top dead center area at the end of the exhaust stroke. In the remaining strokes, the exhaust valve 22 is closed. Therefore, the first cam 34 is designed as a normal exhaust cam.

[0063] In an engine braking mode of the internal combustion engine, the exhaust valve 22 (or for example only one of the exhaust valves) can be actuated by means of the second cam 36. The second cam 36 is therefore designed as an engine braking cam.

[0064] Figure 4 A particularly preferred, non-limiting valve control curve of the exhaust valve 22 in the engine braking mode is shown, which can be generated by the second cam 36 .

[0065] exist Figure 4 In FIG. 1 , the abscissa (x-axis) represents the crankshaft angle, and the ordinate (y-axis) represents the valve stroke in mm. It shows a complete four-stroke cycle consisting of compression, expansion, exhaust and intake.

[0066] The valve control curve for engine braking operation shows that the exhaust valve opens slightly at the end of the compression stroke in the top dead center area of ​​about 60° crankshaft angle (KW) to 100° crankshaft angle before top dead center. The exhaust valve opens further at top dead center and closes at the end of the expansion stroke approximately at bottom dead center. The opening of the exhaust valve at the end of the compression stroke allows the compressed air in the cylinder to be pushed into the exhaust system through the open exhaust valve by the piston moving to top dead center. The compression work previously performed brakes the crankshaft and thus the internal combustion engine. The cylinder pressure initially increases in the compression stroke, but then drops before top dead center due to the opening of the exhaust valve. The opening of the exhaust valve during the expansion stroke allows air to be sucked back into the cylinder from the exhaust line. At the end of the expansion stroke, the cylinder is essentially filled with air from the exhaust system.

[0067] The valve control curve also shows that at the end of the expansion stroke, after reaching the bottom dead center, the exhaust valve initially remains closed. At the end of the exhaust stroke, the exhaust valve opens in the region of the top dead center. This opening again takes place at about 60° crankshaft angle to 100° crankshaft angle before the top dead center. The closing of the exhaust valve during the first part of the exhaust stroke allows the air drawn in during the expansion stroke to be compressed during work. The cylinder pressure increases. The compression work brakes the crankshaft and thus the internal combustion engine. The opening of the exhaust valve at the end of the exhaust stroke causes air to be pushed into the exhaust system through the open exhaust valve. In the intake stroke, the cylinder is filled with air again through one or more open intake valves. The cycle begins again.

[0068] As mentioned above, the use of the second cam 36 results in a double compression and subsequent decompression, thereby ensuring an effective engine braking function.

[0069] Figure 5 It is schematically shown how fluid is supplied to the stroke devices 38 , 40 and how it is discharged from them.

[0070] The variable valve mechanism 10 comprises a (hydraulic) fluid system having a pressurized fluid source 56 , a reservoir 58 , a valve arrangement 60 and two backflow preventers 62 , 64 .

[0071] The pressurized fluid source 56 can supply pressurized fluid to the valve device 60 through a fluid supply line 66. For example, the pressurized fluid source 56 can be designed as a fluid pump or a hydraulic pump. The pressurized fluid source 56 can be connected to a reservoir 58. The fluid can be directed from the valve device 60 to the reservoir 58 via a fluid discharge line (fluid drain line) 68. The reservoir 58 can be designed as an oil pan, for example.

[0072] The valve device 60 can adopt (at least) two different positions. In the (first) position shown, the source of pressurized fluid 56 is connected to the first stroke device 38. In the first position of the valve device 60, the second stroke device 40 is connected to the reservoir 58. In the second position, the source of pressurized fluid 56 is connected to the second stroke device 40. In the second position of the valve device 60, the first stroke device 38 is connected to the reservoir 58. Thus, it is possible to switch back and forth between the rockers 14 and 16 and therefore between the cams 34 and 36 in a particularly simple manner. In this case, the valve device 60 can be appropriately designed as a 4 / 2-way valve (directional valve with four interfaces and two positions). It can also be designed as a series and / or parallel connection of multiple valves.

[0073] In normal operation of the internal combustion engine, the valve device 60 is in the first position. In engine braking operation of the internal combustion engine, the valve device 60 is in the second position. In the first position, the first stroke device 38 is switched to be rigid, while the second stroke device 40 is switched to be movable. The first rocker 14 is activated and the second rocker 16 is deactivated. In the second position, the first stroke device 38 is switched to be movable, while the second stroke device 40 is switched to be rigid. The first rocker 14 is deactivated and the second rocker 16 is activated.

[0074] The backflow preventers 62, 64 can be designed as control valves or regulating valves. The backflow preventers 62, 64 are designed to prevent undesired backflow from the corresponding stroke devices 38, 40 (see reference Figures 7 to 9In addition, if the valve device 60 connects the corresponding stroke device 38, 40 to the fluid discharge pipeline 68 or the pressurized fluid from the pressurized fluid source 56 is not applied to the corresponding backflow preventer 62, 64, the backflow preventer 62, 64 can allow backflow from the stroke device 38, 40.

[0075] Figure 6 Shows relative to Figure 5 Deformed fluid system.

[0076] Figure 6 Fluid system and according to Figure 5 The difference of the fluid system is that the valve device 60 can adopt a third position. In this case, the valve device 60 can be appropriately designed as a 4 / 3-way valve (directional valve with 4 interfaces and 3 positions). It can also be designed as a series and / or parallel connection of multiple valves.

[0077] In the third position, both stroke devices 38, 40 are connected to the reservoir 58. Therefore, the stroke devices 38, 40 are not activated. During the rotation of the camshaft, the associated rocker 14, 16 does not rotate. The exhaust valve 22 remains closed. Thus, cylinder deactivation with respect to the exhaust valve 22 can be achieved in a simple manner. In addition, the intake valve can also remain closed and the oil supply is stopped in order to deactivate the corresponding cylinder.

[0078] Figures 7 to 9 An exemplary embodiment of a backflow preventer 62 is shown. The backflow preventer 64 may have the same construction as the backflow preventer 62 or at least the same function.

[0079] The backflow preventer 62 includes a pressurized fluid supply 70, a fluid line 72, and a fluid drain 74. The pressurized fluid supply 70 is used to supply pressurized fluid from the valve device 60 to the backflow preventer 62. The fluid line 72 is used to supply pressurized fluid from the backflow preventer 62 to the stroke device 38, and to discharge fluid from the stroke device 38 to the backflow preventer 62. The fluid drain 74 is used to discharge fluid from the backflow preventer 62 to the valve device 60 and / or the fluid drain line 68.

[0080] The backflow preventer 62 includes a movable piston 76. In the rest position ( Figure 7 ), the piston 76 blocks the pressurized fluid supply 70 and establishes a fluid connection between the fluid line 72 and the fluid discharge 74 for discharging fluid from the stroke device 38. The piston 76 is elastically prestressed in the direction of the rest position, preferably by a spring.

[0081] The backflow preventer 62 comprises a non-return valve 78 with a movable locking element 80 , for example a ball. The locking element 80 is elastically prestressed, preferably by a spring, in the direction of the closed position. The non-return valve 78 is accommodated in the piston 76 .

[0082] Figure 8 It is shown that when pressurized fluid is supplied to the backflow preventer 62 via the pressurized fluid supply 70, the piston 76 may initially move in a manner that blocks the fluid discharge 74. In addition, the locking element 80 may move against the elastic pretension, lift off the valve seat and establish a fluid connection between the pressurized fluid supply 70 and the fluid line 72. Pressurized fluid may be supplied to the stroking device 38 to activate the stroking device 38.

[0083] If the first cam 34 (see Figure 2 ) When the stroke device 38 is activated, causing valve lift, the pressure in the fluid line 72 suddenly increases. The check valve 78 is closed by moving the locking element 80 into the valve seat (see Fig. 9 ). Fluid cannot escape from the self-travelling device 38. The rocker 14 rotates. The backflow preventer 62 thus additionally functions as a hydraulic valve clearance compensation device, in particular in combination with a stroke device 38 which is only hydraulically locked in the activated position, i.e. in particular no mechanical locking element is provided (e.g. no locking piston).

[0084] The present invention is not limited to the preferred exemplary embodiments described above. On the contrary, a large number of variants and modifications are possible, which also utilize the concept of the present invention and therefore fall within the scope of protection. In particular, the present invention also claims protection for the subject matter and features of the dependent claims that are independent of the cited claims. In particular, the individual features of independent claim 1 are disclosed independently of each other. In addition, the features of the dependent claims are also disclosed independently of all the features of independent claim 1 and, for example, independently of the features related to the presence and / or construction of the camshaft, the first rocker, the second rocker, the fluid supply line and / or the valve device of independent claim 1. All range specifications herein are to be understood as being disclosed in the following manner: all values ​​falling within the respective range are disclosed individually, for example also as preferably narrower outer limits of the respective range, respectively.

[0085] Reference numerals list

[0086] 10Variable valve train

[0087] 12 Camshaft

[0088] 14 First Joystick

[0089] 16 Second joystick

[0090] 18 rocker shaft

[0091] 20 valve bridge

[0092] 22 exhaust valves

[0093] 24 Adjusting bolt

[0094] 26 Adjusting bolt

[0095] 28 protrusion

[0096] 30 Cam follower

[0097] 32 Cam Follower

[0098] 34 First Cam

[0099] 36 Second Cam

[0100] 38 First stroke device

[0101] 40 Second stroke device

[0102] 42 Accommodation Room

[0103] 44 piston

[0104] 46 Elastic element

[0105] 48 Fluid Chamber

[0106] 50 fluid pipeline

[0107] 52 Security Agency

[0108] 54 Slender hole

[0109] 56 Pressurized fluid source

[0110] 58 Reservoir

[0111] 60 valve device

[0112] 62 First Backflow Preventer

[0113] 64 Second backflow preventer

[0114] 66 Fluid supply lines

[0115] 68 Fluid discharge line

[0116] 70 Pressurized fluid supply unit

[0117] 72 fluid pipeline

[0118] 74 Fluid discharge part

[0119] 76 Piston

[0120] 78 Check Valve

[0121] 80 locking elements

Claims

1. A variable valve mechanism (10) for switching an exhaust valve (22) of an internal combustion engine to an engine braking mode, wherein: The variable valve mechanism (10) comprises: a camshaft (12) having a first cam (34) designed as a normal operating cam and a second cam (36) designed as an engine braking cam; A first rocker (14) having a first stroke device (38), wherein the first stroke device is designed to selectively establish or disconnect a first effective connection between the first cam (34) and the exhaust valve (22) through the first rocker (14); A second rocker (16) having a second stroke device (40), wherein the second stroke device is designed to selectively establish or disconnect a second effective connection between the second cam (36) and the exhaust valve (22) through the second rocker (16); a fluid supply line (66); as well as A valve device (60) is designed to selectively connect the first travel device (38) or the second travel device (40) to the fluid supply line (66), wherein the valve device (60) is designed as a directional valve.

2. The variable valve mechanism (10) according to claim 1, further comprising: Fluid discharge line (68), in, The valve device (60) is designed to selectively connect the first stroke device (38) or the second stroke device (40) to the fluid discharge line (68).

3. The variable valve mechanism (10) according to claim 2, wherein: The valve device (60) is designed as follows: - in a first position, connecting the first stroke device (38) to the fluid supply line (66) and connecting the second stroke device (40) to the fluid discharge line (68), and - In a second position, the first stroking device (38) is connected to the fluid discharge line (68) and the second stroking device (40) is connected to the fluid supply line (66).

4. The variable valve mechanism (10) according to claim 2, further comprising: a first backflow preventer (62) arranged in the fluid connection between the valve device (60) and the first stroke device (38), and / or A second backflow preventer (64) is arranged in the fluid connection between the valve device (60) and the second stroke device (40).

5. The variable valve mechanism (10) according to claim 4, wherein: The first backflow preventer (62) is designed to act as a hydraulic valve clearance compensation device for the first operative connection, and / or The second backflow preventer (64) is designed to act as a hydraulic valve clearance compensation device for the second operative connection.

6. The variable valve mechanism (10) according to claim 5, wherein: The first backflow preventer (62) is designed to act as a hydraulic valve clearance compensation device for the first operative connection in a position of the first backflow preventer (62) blocking a backflow from the first stroke device (38).

7. The variable valve mechanism (10) according to claim 5, wherein: The second backflow preventer (64) is designed to act as a hydraulic valve clearance compensation device for the second operative connection in a position of the second backflow preventer (64) blocking a backflow from the second stroke device (40).

8. The variable valve mechanism (10) according to claim 4 or 5, wherein: The first backflow preventer (62) is designed as follows: - in a first position, allowing fluid from the first stroke device (38) to flow back to the valve device (60) and / or the fluid discharge line (68), - in a second position, fluid is allowed to flow from said valve means (60) to said first travel means (38), - in a third position, blocking the return flow of fluid from the first stroke device (38) to the valve device (60), and / or The second backflow preventer (64) is designed as follows: - in a first position, allowing fluid from the second stroke device (40) to flow back to the valve device (60) and / or the fluid discharge line (68), - in a second position, fluid is allowed to flow from said valve means (60) to said second travel means (40), and - In a third position, a backflow of fluid from the second stroke device (40) to the valve device (60) is blocked.

9. The variable valve mechanism (10) according to claim 8, 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 adjusted according to the fluid supply pressure and the fluid back pressure on the first backflow preventer (62) and / or the second backflow preventer (64).

10. The variable valve mechanism (10) according to any one of claims 1 to 7, wherein: When the fluid is applied, the first stroke device (38) establishes the first effective connection, and when the fluid is applied, the second stroke device (40) establishes the second effective connection, or When a fluid is applied, the first stroke device (38) disconnects the first operative connection, and when a fluid is applied, the second stroke device (40) disconnects the second operative connection.

11. The variable valve mechanism (10) according to any one of claims 1 to 7, wherein: The first stroke device (38) and the second stroke device (40) have the same structure and / or the same function.

12. The variable valve mechanism (10) according to any one of claims 1 to 7, wherein: The first stroke device (38) and / or the second stroke device (40) can only be locked hydraulically and / or have no mechanical locking elements.

13. The variable valve mechanism (10) according to any one of claims 1 to 7, wherein: The first stroke device (38) and / or the second stroke device (40) comprises: - a receiving chamber (42); - a piston (44) which is movably arranged in the receiving chamber (42); - a cam follower (30, 32) connected to the piston (44) for movement; - a fluid chamber (48) delimited by said piston (44); and - an elastic element (46) arranged for prestressing the piston (44).

14. The variable valve mechanism (10) according to any one of claims 1 to 7, wherein: The valve device (60) is designed as a 4-2-way valve or a 4-3-way valve.

15. The variable valve mechanism (10) according to any one of claims 1 to 7, wherein: The valve device (60) is also designed as follows: - In a third position, the first stroke device (38) and the second stroke device (40) are connected to a fluid discharge line (68).

16. The variable valve mechanism (10) according to claim 15, wherein: The valve device (60) is used to keep the exhaust valve (22) closed.

17. The variable valve mechanism (10) according to any one of claims 1 to 7, wherein: The first operative connection and the second operative connection act on the exhaust valve (22) and a further exhaust valve (22), or The first effective connection acts on the exhaust valve (22) and on a further exhaust valve (22), and the second effective connection acts only on the exhaust valve (22).

18. The variable valve mechanism (10) according to any one of claims 1 to 7, wherein: The second cam (36) is designed to initially keep the exhaust valve (22) closed during the compression stroke and / or the exhaust stroke and to open the exhaust valve before reaching the top dead center of the piston movement, and / or The first cam (34) is designed so that the exhaust valve (22) is opened during an exhaust stroke and is substantially closed during an intake stroke, a compression stroke, and an expansion stroke.

19. The variable valve mechanism (10) according to claim 18, wherein: The second cam (36) is designed to open the exhaust valve between 100 crankshaft angle degrees and 60 crankshaft angle degrees before reaching the top dead center.

20. A motor vehicle having a variable valve mechanism (10) according to any one of the preceding claims.

21. A motor vehicle according to claim 20, wherein: The motor vehicle is a multi-purpose vehicle.

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