VALVE TRAIN FOR AN INTERNAL COMBUSTION ENGINE, INTERNAL COMBUSTION ENGINE WITH SUCH A VALVE TRAIN, AND METHOD FOR OPERATING AN INTERNAL COMBUSTION ENGINE WITH SUCH A VALVE TRAIN

Description

[0001] The invention relates to a valve train for an internal combustion engine, an internal combustion engine with such a valve train, and a method for operating an internal combustion engine with such a valve train.

[0002] A valve train of the type discussed here has at least one gas exchange valve and a first, mechanically driven drive mechanism, hereinafter referred to as the first drive mechanism. Furthermore, the valve train has a second drive mechanism, hereinafter referred to as the second drive mechanism, which is connected to the at least one gas exchange valve for displacing it. The first drive mechanism is operatively connected to the second drive mechanism via a hydraulic coupling device, wherein the hydraulic coupling device has a pressure chamber which can be depressurized via a valve device, wherein the coupling device is configured to couple the first drive mechanism and the second drive mechanism to one another under hydraulic pressure in the pressure chamber and to decouple them from one another when the pressure chamber is depressurized.To relieve pressure in the pressure chamber, a switching valve is fluidically connected to it, which allows the pressure chamber to be relieved when the switching valve is open. This makes it possible to create a fully variable valve train.In this case, the mechanically driven drive mechanism typically specifies a valve lift curve which is only fully converted into a corresponding valve lift of the gas exchange valve if the pressure chamber is kept under hydraulic pressure throughout the entire course of the valve lift curve, wherein the coupling of the first drive mechanism with the second drive mechanism can be at least partially canceled by relieving pressure in the pressure chamber via the switching valve during the course of the valve lift curve, so that so-called sub-curves can be represented for the gas exchange valve, wherein, for example, in comparison to the predetermined valve lift curve, a later opening, a reduced stroke and / or an earlier closing of the gas exchange valve can be brought about.

[0003] A disadvantage of this design is that the switching valve is difficult to adapt to the operation of an internal combustion engine. This particularly affects the selection of a suitable switching valve size for a specific internal combustion engine. It turns out that, in this respect, the product of a flow cross-section and a flow coefficient is particularly crucial for the behavior of the switching valve: If this product is too small, the hydraulic fluid is released slowly from the pressure chamber, resulting in flat flanks for the valve lift of the gas exchange valve, which, in turn, makes the valve react too sluggishly.If the product of the flow cross-section and the flow coefficient is too large, the gas exchange valve may respond quickly to the activation of the switching valve, but this results in high pressure pulsations in the pressure chamber and ultimately in vibrations that make the behavior of the valve train uncontrollable and unpredictable. Further complicating matters is that a separate switching valve must be developed for each series, size, and / or power class of an internal combustion engine, meaning that identical parts cannot be used in production for different internal combustion engines.

[0004] JP S59 37222 A discloses a valve train comprising at least two switching valves fluidically connected in parallel to each other by a pressure chamber. When at least one of the switching valves is open, the pressure chamber can be depressurized via the open switching valve. Hydraulically coupled valve trains are also known from DE 41 32 500 A1, CN 103 925 037 B, US 2016 / 0215661 A1, and WO 85 / 01984 A1.

[0005] The invention is based on the object of creating a valve train for an internal combustion engine, an internal combustion engine with such a valve train and a method for operating an internal combustion engine with such a valve train, wherein the aforementioned disadvantages do not occur.

[0006] The problem is solved by creating the subject matter of the independent claims. Advantageous embodiments emerge from the subclaims.

[0007] The object is achieved in particular by further developing a valve train of the type mentioned above in that the valve device has at least two switching valves which are fluidically connected to the pressure chamber in parallel, via which the pressure chamber can be depressurized when at least one of the switching valves is in the open state, wherein the valve train has a control unit which is configured to control the switching valves with a time offset from one another to represent a variable valve lift of the at least one gas exchange valve during a stroke movement of the gas exchange valve. As a result, the product of flow cross-section and flow coefficient can be increased compared to just one switching valve, wherein at the same time a temporally stepped cross-section release can take place, so that pressure peaks and thus ultimately also pressure pulsations and pressure oscillations in the pressure chamber can be minimized or eliminated.It is therefore possible to simultaneously provide a large overall opening cross-section—particularly preferably larger than when using only one switching valve—while still avoiding pressure pulsations in the pressure chamber and the associated disadvantages. This allows for steeper flanks of a real lift curve for the gas exchange valve, especially steeper valve closing flanks, which leads to fuller lift curves overall.

[0008] In addition, a common parts strategy for different series, sizes, and power classes of internal combustion engines becomes possible. For example, for smaller internal combustion engines, only one switching valve is used – as has been the case up to now. Two or more switching valves can be used for larger internal combustion engines. In particular, the same switching valves can be used for all internal combustion engines. This leads to a simplified design of the various internal combustion engines and a reduction in procurement and logistics costs associated with the switching valves.

[0009] An additional advantage is that the switching valves are redundant, so the valve train remains functional even if one of the switching valves fails. While the valve train's full variability is no longer available, the remaining functionality is sufficient to operate the engine—in the sense of a limp-home or emergency running function—until the next possible maintenance.

[0010] The gas exchange valve can, in particular, be an intake valve or an exhaust valve associated with a combustion chamber of the internal combustion engine. The gas exchange valve is particularly preferably an intake valve.

[0011] The fact that the first drive mechanism is mechanically driven means, in particular, that it is not hydraulically driven. Preferably, the first mechanically driven drive mechanism has a direct mechanical drive connection to a valve drive, in particular to a camshaft. The first drive mechanism is therefore particularly preferably cam-driven. The shape of an outer circumferential surface of a cam interacting with the first drive mechanism defines the valve lift curve, below which sub-curves can be displayed in the lift-time diagram of the gas exchange valve using the hydraulic coupling device.

[0012] The first drive mechanism can also be referred to as the drive-side or cam-side drive mechanism because it is operatively connected to the valve drive.

[0013] The second drive mechanism is preferably mechanically connected to the gas exchange valve for its displacement, particularly preferably purely mechanically, without any additional hydraulic or other non-mechanical couplings. The second drive mechanism can also be referred to as the gas exchange valve-side drive mechanism, since it is directly connected to the gas exchange valve and is therefore directly associated with it.

[0014] The first drive mechanism preferably has a first piston that delimits the pressure chamber of the hydraulic coupling device on one side, as well as a first piston rod connected to the piston. A cam of the valve drive preferably interacts with the first piston rod of the first drive mechanism. However, it is also possible for a deflection mechanism to be connected between the cam and the first piston rod. The deflection mechanism is preferably designed mechanically.

[0015] The second drive mechanism also preferably has a second piston closing off the pressure chamber of the hydraulic coupling device on another side facing away from the first piston of the first drive mechanism, as well as a second piston rod connected to the second piston rod, wherein the second piston rod of the second drive mechanism is connected to the gas exchange valve - preferably via a particularly mechanical deflection mechanism.

[0016] The control unit is configured, in particular, to actuate the switching valves with a time delay but overlapping during the stroke movement of the gas exchange valve. In particular, the control unit is configured to actuate the switching valves. The phrase "during a stroke movement of the gas exchange valve" means, in particular, that the switching valves are actuated, preferably opened, with a time delay but overlapping during the same stroke movement of the gas exchange valve.

[0017] According to a further development of the invention, the switching valves of the valve device are of identical design. In this case, particularly low logistical costs and development effort result because a common parts strategy can be applied not only to one internal combustion engine, but also to different series, sizes, and power classes of internal combustion engines, as already explained.

[0018] According to a further development of the invention, the switching valves are designed as high-speed valves, in particular as so-called high-speed solenoid valves (HSSV). Such valves can be switched very quickly, having discrete switching positions, namely in particular a closed position and an open position. When controlling such a high-speed switching valve, it is typically not possible to influence its switching speed. Rather, it can only be switched digitally. With the valve train proposed here, the temporal switching behavior of the valve device can nevertheless be influenced by controlling the various switching valves with a time offset but overlapping.

[0019] According to a further development of the invention, the control unit is configured to vary the time offset between the actuation of the switching valves. In particular, this makes it possible to influence the temporal behavior of the valve device and thus ultimately also the lifting movement of the gas exchange valve, even if the individual switching valves can only be controlled digitally. In this case, the control unit is particularly configured to vary the time offset between the actuation of the switching valves assigned to the same valve device. The variation of the time offset is preferably dependent on the characteristic map. In this way, an optimal actuation of the valve device and thus also an optimal lifting movement of the gas exchange valve can be selected for each operating point of the internal combustion engine.

[0020] According to the invention, each of the switching valves is assigned an output stage for control. The output stage provides the necessary power to activate and, in particular, open the switching valve(s) assigned to it. An output stage is understood, in particular, to be an electronic device for controlling a switching valve, which is particularly configured to convert a switching signal with the required control power to switch the switching valve and thus drive the switching valve.

[0021] According to a further development of the invention, the valve train comprises a plurality of gas exchange valves assigned to different combustion chambers of an internal combustion engine. Preferably, at least one hydraulic coupling device with a corresponding valve device is assigned to each combustion chamber. It is provided that a common output stage is assigned to at least two, preferably exactly two, switching valves assigned to different combustion chambers, i.e., in particular, different hydraulic coupling devices, with the gas exchange cycles of the different combustion chambers being separated from one another in time.In this way, there is no need to multiply the number of output stages used for the valve train due to the multiplication of the number of switching valves, as the fact that the gas exchange cycles of different combustion chambers of an internal combustion engine having a plurality of combustion chambers differ in time is cleverly exploited. This means, in particular, that the gas exchange cycles of such combustion chambers do not overlap with one another. Particularly preferably, two switching valves assigned to different combustion chambers are each controlled by a common output stage, wherein the gas exchange cycles of the combustion chambers are phase-shifted relative to one another by half a working cycle of the internal combustion engine, i.e. by 360° crankshaft angle in a four-stroke engine. If the output stage sends a control signal, both switching valves assigned to the output stage are controlled.However, this only actually leads to a change in the valve lift for one of the gas exchange valves assigned to the switching valves, since only one of the gas exchange valves is actually triggered to lift via its assigned first actuator, while the other gas exchange valve is currently inactive. Therefore, with the valve train proposed here, twice the number of switching valves can be controlled with the same number of output stages as with a conventional valve train. Therefore, no additional costs arise in connection with the valve train proposed here.

[0022] The object is also achieved by providing an internal combustion engine having a valve train according to one of the previously described embodiments. In connection with the internal combustion engine, the advantages already explained in connection with the valve train are particularly evident.

[0023] In particular, if the time offset between the activation of the switching valves assigned to the same valve device can be varied depending on the characteristic map, the pressure amplitudes and thus ultimately the valve lift of the gas exchange valves can be actively influenced over an entire characteristic map range of the internal combustion engine.

[0024] According to a further development of the invention, the internal combustion engine has a plurality of combustion chambers, with each combustion chamber being assigned at least one gas exchange valve and at least one hydraulic coupling device of the valve train. Preferably, each combustion chamber is assigned at least one intake valve and at least one exhaust valve, with each intake valve particularly preferably being assigned a hydraulic coupling device of the valve train. Alternatively or additionally, however, it is also possible for each exhaust valve to be assigned a hydraulic coupling device. It is likewise possible for the combustion chambers each to have a plurality of intake valves and / or exhaust valves, in particular two intake valves and two exhaust valves.

[0025] The internal combustion engine is preferably designed as a reciprocating piston engine. It is possible for the internal combustion engine to be configured to drive a passenger car, a truck, or a commercial vehicle. In a preferred embodiment, the internal combustion engine is used, in particular, to drive heavy land or water vehicles, for example, mining vehicles, trains (where the internal combustion engine is used in a locomotive or railcar), or ships. It is also possible to use the internal combustion engine to drive a defense vehicle, for example, a tank. One embodiment of the internal combustion engine is preferably also used stationary, for example, for stationary energy supply in emergency power operation, continuous load operation, or peak load operation, wherein the internal combustion engine in this case preferably drives a generator.Stationary application of the internal combustion engine to drive auxiliary units, for example fire pumps on drilling platforms, is also possible. Furthermore, application of the internal combustion engine in the extraction of fossil raw materials and in particular fuels, for example oil and / or gas, is possible. Use of the internal combustion engine in the industrial sector or in the construction sector, for example in a construction or building machine, for example in a crane or an excavator, is also possible. The internal combustion engine is preferably designed as a diesel engine, a gasoline engine, a gas engine for operation with natural gas, biogas, special gas or another suitable gas. In particular, if the internal combustion engine is designed as a gas engine, it is suitable for use in a combined heat and power plant for stationary energy generation.

[0026] The object is finally also achieved by providing a method for operating an internal combustion engine with a valve train which has at least one gas exchange valve and a first, mechanically driven drive mechanism and a second drive mechanism connected to the at least one gas exchange valve, wherein the first drive mechanism is operatively connected to the second drive mechanism via a hydraulic coupling device, wherein the hydraulic coupling device has a pressure chamber which can be depressurized via a valve device and which is designed to couple the first drive mechanism and the second drive mechanism to one another under hydraulic pressure and to decouple them from one another in the depressurized state. The valve device has at least two switching valves which are fluidically connected to the pressure chamber in parallel to one another and via which the pressure chamber can be depressurized when at least one of the switching valves is in the open state.Within the scope of the method, it is provided that the switching valves for achieving a variable valve lift of at least one gas exchange valve are controlled, in particular opened, with a time offset from one another—but in particular with a temporal overlap—during a stroke movement of the gas exchange valve. Within the scope of the method, a valve train according to one of the previously described embodiments is preferably used. In connection with the method, the advantages that have already been explained in connection with the valve train and the internal combustion engine arise, in particular.

[0027] According to a further development of the invention, it is provided that the time offset between the activation of the switching valves is varied - in particular depending on the operating point and particularly preferably depending on the characteristic map.

[0028] It is possible that the valve train control unit is an engine control unit of the internal combustion engine, or that the functionality of the valve train control unit is integrated into a control unit, in particular the engine control unit of the internal combustion engine. However, it is also possible that a separate control unit is assigned to the valve train.

[0029] The method proposed here can be permanently implemented in an electronic arrangement, in particular hardware, of the control unit. However, it is also possible for a computer program product to run on the control unit, which includes instructions on the basis of which the method described here can be carried out. In this respect, a computer program product is also preferred that has machine-readable instructions on the basis of which a method according to one of the previously described embodiments is carried out when the computer program product runs on a computing device, in particular on a control unit.

[0030] A data carrier containing such a computer program product is also preferred.

[0031] Furthermore, a control device is preferred which has such a computer program product or on which such a computer program product runs.

[0032] The description of the valve train and the internal combustion engine on the one hand, and of the method on the other hand, are to be understood as complementary to one another. Method steps that have been described explicitly or implicitly in connection with the valve train and / or the internal combustion engine are preferably, individually or in combination with one another, steps of a preferred embodiment of the method. Features of the valve train and / or the internal combustion engine that have been explained in connection with the method are preferably, individually or in combination with one another, features of a preferred embodiment of the valve train and / or the internal combustion engine. The method is preferably characterized by at least one method step that is determined by at least one feature of an inventive or preferred embodiment of the valve train or the internal combustion engine.The internal combustion engine and / or the valve train is / are preferably characterized by at least one feature which is determined by at least one step of an embodiment of the method according to the invention or a preferred embodiment of the method.

[0033] The invention is explained in more detail below with reference to the drawings, which show: Figure 1 is a schematic representation of an embodiment of an internal combustion engine with a valve train, and Figure 2 is a schematic representation of the functioning of the valve train according to Figure 1 .

[0034] Fig. 1shows a schematic representation of an embodiment of an internal combustion engine 1 with a valve train 3. In this case, the valve train 3 is assigned a plurality of gas exchange valves, in the schematic representation two gas exchange valves 5, 5', which in turn are assigned to different combustion chambers 7, 7' of the internal combustion engine 1, which are also only shown schematically here.

[0035] The operation of the valve train 3 will first be explained in connection with the first gas exchange valve 5. Identical and functionally equivalent elements assigned to the second gas exchange valve 5' are provided with corresponding, primed reference numerals, so that a separate explanation of these elements and their operation is not required. Instead, reference is made to the explanation of the elements provided with unprimed reference numerals. The interaction of the control of the various gas exchange valves 5, 5' in the valve train 3 will then be explained in more detail.

[0036] The gas exchange valves 5, 5' are preferably designed as intake valves. However, it is also possible for them to be designed as exhaust valves, or for corresponding exhaust valves to be assigned to the valve train 1 in addition to the intake valves 5, 5'. The internal combustion engine 1 preferably has more than two combustion chambers 7, 7'. In principle, the number of combustion chambers 7, 7' is not limited. The internal combustion engine 1 can, in particular, have four, six, eight, ten, twelve, sixteen, eighteen, twenty, or twenty-four combustion chambers 7, 7'.

[0037] The first gas exchange valve 5 is assigned a first, mechanically driven drive mechanism 9, which here has in particular a first piston 11 and a first piston rod 13, wherein the first piston rod 13 is operatively connected here to a cam 15 of a camshaft, by means of which the first piston rod 13 and thus at the same time the first piston 11 can be actuated in a stroke-movable manner.

[0038] Furthermore, a second drive mechanism 17 is provided which is mechanically connected to the gas exchange valve 5 for the displacement thereof and which in particular has a second piston 19 and a second piston rod 21, wherein it further has a deflection mechanism 23 via which the second piston rod 21 is mechanically coupled to the gas exchange valve 5.

[0039] The first drive mechanism 9 and the second drive mechanism 17 are operatively connected to one another via a hydraulic coupling device 25, wherein the hydraulic coupling device 25 has in particular a pressure chamber 27 which can be relieved of pressure via a valve device 29, wherein the pressure chamber 27 is designed to couple the first drive mechanism 9 and the second drive mechanism 17 to one another under hydraulic pressure and to decouple them from one another in the pressure-relieved state. For this purpose, the two pistons 11, 19 are arranged together in the pressure chamber 27, so that the second piston 19, when the pressure chamber 27 is under hydraulic pressure, follows a lifting movement of the first piston 11 - mediated via the hydraulic medium -, wherein the second piston 19 can be decoupled from the first piston 11 by relieving the pressure in the pressure chamber 27, so that the coupling via the hydraulic medium is canceled, wherein the second piston 19 can then no longer follow a lifting movement of the first piston 11.

[0040] Accordingly, a variable lift for the gas exchange valve 5 can be achieved via the hydraulic coupling device 25, whereby, in particular, sub-curves can be obtained with reference to a valve lift curve defined by the shape of the cam 15. The valve train 3 is therefore designed as a variable valve train 3 and, in particular, as a fully variable valve train 3.

[0041] The valve device 29 has at least two, here exactly two, switching valves 31, 33 fluidically connected to the pressure chamber 27 in parallel to one another, namely a first switching valve 31 and a second switching valve 33, wherein the pressure chamber 27 can be depressurized by at least one of the switching valves 31, 33 in the open state.

[0042] The valve train 3 also has a control unit 35, of which only two output stages are schematically illustrated here, namely a first output stage 37 and a second output stage 39. The control unit 35 is configured to control, in particular to open, the switching valves 31, 33 with a time delay, but preferably with a temporal overlap, to achieve a variable valve lift during a single stroke movement of the gas exchange valve 5.

[0043] Instead of a single switching valve, as is known from conventional valve trains, via which the pressure chamber 27 can be depressurized, at least the two switching valves 31, 33 are assigned to the pressure chamber 27 in the valve train 3 proposed here, which makes it possible to simultaneously release a comparatively large flow cross-section and minimize pressure pulsations in the pressure chamber 27, namely by implementing a temporally stepped cross-section release in the form of the time-staggered actuation of the switching valves 31, 33. Thus, steeper valve lift flanks, in particular steeper valve closing flanks, can be achieved for the gas exchange valve 5, resulting in overall fuller lift curves.Furthermore, the use of identical parts is possible not only on the internal combustion engine 1, but also in an entire series or in different series, in particular different sizes or power classes of internal combustion engines 1, because the same switching valve can be provided in duplicate to provide larger flow cross-sections.

[0044] In this respect, it is particularly provided that the switching valves 31, 33 as well as the switching valves 31', 33' of the second gas exchange valve 5' are of identical construction.

[0045] The switching valves 31, 33, 31', 33' are preferably designed as high-speed valves, in particular as high-speed solenoid valves (HSSV).

[0046] The control unit 35 is preferably configured to vary the time offset between the actuation of the switching valves 31, 33, 31', 33' assigned to the same valve device 29, 29'. The variation of the time offset can be carried out, in particular, depending on a current operating point of the internal combustion engine 1, and most preferably, depending on a characteristic map. Thus, a suitable valve lift curve and a separate, suitable switching behavior of the switching valves 31, 33, 31', 33' can be represented for each operating point of the internal combustion engine 1.

[0047] Each of the switching valves 31, 33, 31', 33' is assigned an output stage 37, 39. For example, the first switching valves 31, 31' are assigned the first output stage 37, and the second switching valves 33, 33' are assigned the second output stage 39.

[0048] It can be seen that a common output stage 37, 39 is assigned to each of two switching valves 31, 31', 33, 33', which are assigned to different combustion chambers 7, 7', wherein the gas exchange cycles of the combustion chambers 7, 7' are separated in time. In the combustion chambers 7, 7' shown here, it is particularly provided that their working cycles are phase-shifted relative to one another by half a working cycle period, i.e., in a four-stroke engine, by exactly 360° crankshaft angle. Therefore, the two first switching valves 31, 31', which are assigned to the different gas exchange valves 5, 5', can be controlled by a common output stage, here namely the first output stage 37, wherein the two second switching valves 33, 33' can also be controlled by another common output stage, here namely the second output stage 39, which is different from the first output stage 37.The switching valves 31, 33, 31', 33' of the same gas exchange valve 5, 5' are each controlled by different output stages 37, 39, allowing for a temporal offset in the control. However, two switching valves 31, 31', 33, 33' assigned to the different gas exchange valves 5, 5' share a common output stage 37, 39.

[0049] If, for example, the first output stage 37 sends out a control signal, this is received by the first two switching valves 31, 31', whereupon they are controlled. However, this leads to the Figure 1The time or crankshaft angle shown only has an effect on the first gas exchange valve 5, since only its first drive mechanism 9 is currently mechanically actuated by the first cam 15, so that the first gas exchange valve 5 is controlled to a valve lift movement that can be changed via the control of the first switching valve 31. In contrast, the second cam 15' is in a position in which it does not cause any valve lift movement of the second gas exchange valve 5' via its first drive mechanism 9', so that the second gas exchange valve 5' - regardless of the switching behavior of the first switching valve 31' assigned to it - does not perform any lift movement.The control of the first switching valve 31' assigned to the second gas exchange valve 5' in addition to the control of the first switching valve 31 assigned to the first gas exchange valve 5 by the first output stage 37 therefore does not produce any additional effect, which is why it is possible to control the two first switching valves 31, 31' via the common first output stage 37.

[0050] The same applies analogously to the second output stage 39 and the second switching valves 33, 33'.

[0051] The output stages 37, 39 are activated with a time delay, so that the first switching valves 31, 31' and the second switching valves 33, 33' are activated with a time delay - but preferably with an overlap in time.

[0052] Fig. 2 shows a diagrammatic representation of the operation of the valve train 3 according to Figure 1. In a), a diagrammatic plot - in schematic form - of a control current I against the crankshaft angle of the internal combustion engine 1 is shown. The control current I output by the first output stage 37 for the first switching valves 31, 31' is shown as a solid, first curve K1, and the control current I of the second output stage 39 for the second switching valves 33, 33' is shown as a dashed, second curve K2. It can be seen that the first curve K1 and the second curve K2 overlap with one another in time, but have a time offset Δt from one another. This time offset Δt is preferably variable, and can be selected by the control unit 35, preferably depending on the operating point, in particular depending on the characteristic map.

[0053] In b), the product of a flow cross-section A of the switching valves 31, 33 with a flow coefficient Cd is plotted against the crankshaft angle of the internal combustion engine 1. This shows that the release of the flow cross-sections of the individual switching valves 31, 33 behaves additively due to their time-delayed activation. The curve of the total flow cross-section release for the two switching valves 31, 33, which are activated with a time delay but overlapping with each other, thus behaves exactly like the sum of the respective flow cross-section releases for the individual switching valves 31, 33.

[0054] Thus, it is possible to release the total flow cross-section in stages over time and at the same time to minimize, preferably prevent, pressure pulsations in the pressure chamber 27.

[0055] The time offset Δt for the control of the switching valves 31, 33' can preferably be selected such that pressure pulsations arising due to the opening of the various switching valves 31, 33 interfere with each other.

[0056] Overall, it can be seen that the valve train 3, the internal combustion engine 1 and the method proposed here create a very efficient and cost-effective way of realizing a fully variable valve train 3 with steep flanks while avoiding pressure pulsations.

Claims

1. Valve drive (3) for an internal combustion engine (1), having - at least one gas exchange valve (5, 5'); - a first, mechanically driven drive mechanism (9,9'); - a second drive mechanism (17, 17') that for repositioning the at least one gas exchange valve (5, 5') is connected to the latter, wherein - the first drive mechanism (9, 9') is operatively connected to the second drive mechanism (17, 17') by way of a hydraulic coupling installation (25, 25'), wherein - the hydraulic coupling installation (25, 25') has a pressure chamber (27, 27') which is capable of being relieved of pressure by way of a valve installation (29, 29') and which under hydraulic pressure is specified for coupling the first drive mechanism (9, 9') to the second drive mechanism (17, 17'), and in the pressure-relieved state is specified for decoupling the first drive mechanism from the second drive mechanism, wherein - the valve installation (29, 29') has at least two switch valves (31, 33; 31', 33') which are fluidically connected in parallel to the pressure chamber (27, 27') and by way of which the pressure chamber (27, 27') in the opened state is capable of being relieved of pressure by at least one of the switch valves (31, 33; 31', 33'), characterized in that - the valve drive (3) has a control apparatus (35) which, for representing a variable valve stroke of the at least one gas exchange valve (5, 5') during a same stroke movement of the gas exchange valve (5, 5'), is specified for actuating the switch valves (31, 33; 31', 33') in a temporally offset manner, and in that - each of the switch valves (31, 33; 31', 33') is assigned, for actuation, an end stage (37, 39) configured as an electronic installation for actuating the respective switch valve (31, 33; 31', 33'), wherein the end stage (37, 39) is specified for implementing a switching signal by way of the required actuating output for switching the respective switch valve (31, 33; 31', 33'), and for thus driving the switch valve (31, 33; 31', 33').

2. Valve drive (3) according to Claim 1, characterized in that the switch valves (31, 33; 31', 33') of the valve installation (29, 29') are configured so as to be of identical construction.

3. Valve drive (3) according to either of the preceding claims, characterized in that the switch valves (31, 33; 31', 33') are configured as high-speed valves.

4. Valve drive (3) according to one of the preceding claims, characterized in that the control apparatus (35) is specified for varying the temporal offset between the actuation of the switch valves (31, 33; 31', 33').

5. Valve drive (3) according to one of the preceding claims, characterized in that the valve drive (3) has a plurality of gas exchange valves (5, 5') that are assigned to different combustion chambers (7, 7') of an internal combustion engine (1), wherein a common end stage (37, 39) is in each case assigned to at least two switch valves (31, 31'; 33, 33') which are assigned to different combustion chambers (7, 7'), the gas exchange cycles of said different combustion chambers being temporally mutually separated.

6. Internal combustion engine (1) having a valve drive (3) according to one of Claims 1 to 5.

7. Internal combustion engine (1) according to Claim 6, characterized in that the internal combustion engine (1) has a plurality of combustion chambers (7, 7'), wherein each combustion chamber (7, 7') is assigned at least one gas exchange valve (5, 5') as well as at least one hydraulic coupling installation (25, 25') of the valve drive (3).

8. Method for operating an internal combustion engine (1) having a valve drive (3), in particular according to one of Claims 1 to 5, characterized in that switch valves (31, 33; 31', 33') that are fluidically connected in parallel to a same pressure chamber (27, 27') of a hydraulic coupling installation (25, 25') of the valve drive (3) are actuated in a temporally mutually offset manner during a same stroke movement of a gas exchange valve (5, 5') that is assigned to the hydraulic coupling installation (25, 25'), and in that each of the switch valves (31, 33; 31', 33') is assigned, for actuation, an end stage (37, 39) configured as an electronic installation for actuating the respective switch valve (31, 33; 31', 33'), wherein the end stage (37, 39) is specified for implementing a switching signal by way of the required actuating output for switching the respective switch valve (31, 33; 31', 33'), and for thus driving the switch valve (31, 33; 31', 33').

9. Method according to Claim 8, characterized in that the temporal offset in the actuation of the switch valves (31, 33; 31', 33') is varied.