Lift Regulator for a Variable Lift Valve Gear With Two Working Positions

Abstract

A lift regulator for a variable lift valve gear has a cam contour arranged around an axis of rotation of the lift regulator for deflecting a lift adjustment of the valve gear on rotation of the lift regulator about the axis of rotation. The cam contour has a region deflecting from a resting position, a changeover region, and a region deflecting back to the resting position. A variable lift valve gear and a method for operating the variable lift valve gear are disclosed.

Claims

1.-15. (canceled)

16. A lift regulator for a variable lift valve gear, comprising: a cam contour disposed about a rotation axis of the lift regulator so as to deflect a lift adjustment of the valve gear in a rotation of the lift regulator about the rotation axis, wherein the cam contour has a deflection region, a diversion region, and an inflection region, wherein the cam contour further has a deflection switchover compensation region between the deflection region and the diversion region, and/or an inflection switchover compensation region between the deflection region and the inflection region, and wherein, during a rotation about the rotation axis, an absolute value of a gradient (aS) of a variation of a valve lift guide variable (xS, r) of the lift regulator in a switchover compensation region is smaller than in the deflection region and in the diversion region.

17. The lift regulator according to claim 16, wherein the lift regulator is configured as a cam of a camshaft, the valve lift guide variable is a radius of the cam contour of the cam along a circumferential surface of the cam, and the gradient is an acceleration of an envisaged contact point between the cam contour of the cam and the lift adjustment during a rotation of the cam conjointly with the camshaft about the rotation axis of the camshaft.

18. The lift regulator according to claim 16, wherein a value of an average gradient in the deflection switchover compensation region or in the inflection switchover compensation region, respectively, is at most two thirds or half of the gradient of the valve lift guide variable of the adjacent deflection or inflection region, respectively, of the cam contour.

19. The lift regulator according to claim 16, wherein a value of an average gradient in the deflection switchover compensation region or in the inflection switchover compensation region, respectively, is at most one fifth, one eighth or one tenth of the gradient of the valve lift guide variable of the adjacent deflection or inflection region, respectively, of the cam contour.

20. The lift regulator according to claim 16, wherein the gradient in the switchover compensation region varies.

21. The lift regulator according to claim 16, wherein the gradient in the switchover compensation region is substantially constant.

22. The lift regulator according to claim 16, wherein an average gradient in the switchover compensation region is substantially zero.

23. The lift regulator according to claim 16, wherein an average gradient in the deflection switchover compensation region is negative or positive, and/or the average gradient in the inflection switchover compensation region is positive or negative.

24. The lift regulator according to claim 23, wherein a circumferential surface is the cam contour and is specified for deflecting an intermediate lever of the valve gear.

25. A variable lift valve gear for a charge-cycle valve of an internal combustion engine, comprising: a lift adjustment having an operating curve which is disposable at least in a first operating position (A1) for adjusting a partial lift and in a second operating position (A2) for adjusting a maximum lift, wherein the operating curve has a lift region (Bh) and a basic circle region (Bg); a lift regulator according to claim 16; a lifting lever which is deflectable via the operating curve and as a result thereof adjusts a lift of the charge-cycle valve, wherein the valve gear is configured for adjusting the charge-cycle valve at a mutual ratio of the maximum valve accelerations (a.sub.max,A, a.sub.max,E) in the first operating position (A1) and the maximum valve accelerations (a.sub.max,mill,A, a.sub.max,mill,E) in the second operating position (A2), wherein the ratio is a function of the gradient (aS) of the variation (vS) of the valve lift guide variable (xS, r) of the lift regulator in the switchover compensation region.

26. The lift regulator according to claim 25, wherein the lift adjustment is an intermediate lever and the lift regulator is a cam of a camshaft.

27. The valve gear according to claim 25, wherein the valve gear is configured for adjusting the charge-cycle valve so as to have an at least substantially identical maximum valve acceleration (a.sub.max,mill,A, a.sub.max,mill,E) in the first operating position and in the second operating position.

28. The valve gear according to claim 25, wherein the cam contour of the lift regulator is configured for displacing the lift adjustment by way of a ratio of a speed (vS) of the lift adjustment in the first operating position (A1) and a speed (vS) of the lift adjustment in the second operating position (A2), and the ratio is a function of the gradient of the variation of the valve lift guide variable of the lift regulator in the switchover compensation region.

29. The valve gear according to claim 25, wherein the valve gear has a sensor-based and/or model-based temperature detection installation for detecting an exhaust gas temperature and/or at least one other temperature parameter of the internal combustion engine.

30. The valve gear according to claim 29, wherein the temperature detection installation is configured for detecting the exhaust gas temperature and/or the at least one other temperature parameter at an engine-distal end of an exhaust manifold and/or on a turbine inlet of a turbine.

31. The valve gear according to claim 30, wherein the turbine has a variable turbine geometry.

32. A method for operating a variable lift valve gear for a charge-cycle valve of an internal combustion engine, the variable lift valve gear being configured according to claim 25, the method comprising the steps of: determining an exhaust gas temperature in an operating situation of the internal combustion engine; determining whether the valve gear in the operating situation is to be switched to a conventional operating mode or to a Miller operating mode, wherein the operating mode to be switched is determined as a function of the determined exhaust gas temperature; wherein the exhaust gas temperature is determined at an engine-distal end of an exhaust manifold and/or at a turbine inlet of a turbine of an exhaust gas turbocharger of the internal combustion engine, and/or wherein the valve gear when reaching or exceeding a limit value of the exhaust gas temperature is switched to the Miller operating mode.

33. The method according to claim 32, wherein the limit value of the exhaust gas temperature is determined as a function of a material characteristic.

34. The method according to claim 33, wherein the material characteristic is heat resistance of a turbine material and/or of an exhaust gas path material of the exhaust gas turbocharger.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0067] FIG. 1 shows a section through a variable lift valve gear according to an exemplary embodiment of the invention;

[0068] FIG. 2 shows diagrams in which for a rotation of the camshaft of the variable lift valve gear according to FIG. 1 the lift of the charge-cycle valve, or the speed of the valve deflection or the acceleration in the valve deflection, respectively, is in each case plotted in relation to a crank angle of the crankshaft when the valve gear according to FIG. 1 is operated by a method according to an exemplary embodiment of the invention;

[0069] FIG. 3 shows the operating curve of the valve gear according to FIG. 1;

[0070] FIG. 4 shows a cross section through a lift regulator of a variable lift valve gear according to a further exemplary embodiment of the invention;

[0071] FIG. 5 schematically shows a profile of a gradient of a variation of a valve lift guide variable across the circumference of a cam contour of the lift regulator according to FIG. 4 when rotating about the rotation axis of the lift regulator;

[0072] FIG. 6 for a known valve gear having a cam on a camshaft and an intermediate lever as the lift adjustment shows a profile of the intermediate lever movement and of the valve lifts in the conventional operation and in the Miller operation;

[0073] FIG. 7 for the valve gear from FIG. 4 shows a profile of the intermediate lever movement and of the valve lifts in the conventional operation and in the Miller operation; and

[0074] FIG. 8 schematically shows a topology of an internal combustion engine having a variable lift valve gear according to FIG. 4.

DETAILED DESCRIPTION OF THE DRAWINGS

[0075] FIG. 1 shows a section through a variable lift valve gear 1 in the installed position in a cylinder head 15 for an internal combustion engine (not illustrated), when viewed toward a first charge-cycle valve activation unit 3. The charge-cycle valve activation unit 3 is provided for activating charge-cycle valves 2 of identical action. In the present exemplary embodiment the internal combustion engine has four cylinders in line, having in each case two charge-cycle valves 2 of identical action.

[0076] The variable lift valve gear 1 disposed in the cylinder head 15 has a lift adjustment 4, an intermediate lever which on one side by way of a roller (not provided with a reference sign) is mounted so as to be movable by rolling on a guide gate track 6 of a guide gate 7, and on the other side has an operating curve 8.

[0077] As can be derived from FIG. 3, the operating curve is divided into a basic circle region Bg and a lifting region Bh, wherein the operating curve 8, at least in part of the lifting region Bh, has a region BKmax having a consistent maximum curvature Kmax. In a further region Bn adjacent thereto, the lifting region Bh has no curvature or at least a reduced curvature.

[0078] The operating curve 8 by way of a lifting lever 9, a roller cam follower, is operatively connected to a charge-cycle valve 2 in such a manner that the charge-cycle valve 2 along the plotted axis can be deflected by a specific lift h at a speed v and an acceleration a.

[0079] The roller cam follower 9 on the one side is supported on a shank of the charge-cycle valve 2 and on the other side on a clearance compensation element 5, a hydraulic clearance compensation element.

[0080] Furthermore provided is a lift regulator 10 (also referred to as the first adjustment device 10), a cam of a camshaft, having a cam contour NK (=cam contour) for pivoting the intermediate lever 4, counter to a spring force of a spring element 12, about a guide gate proximal point 11, a center of rotation of the roller supported on the guide gate track 6. The cam contour NK is defined by a profile of a radius about the point of rotation of the cam 10 along the plotted circumferential direction U10.

[0081] The intermediate lever 4 by a second adjustment device 13, an eccentric disk on an eccentric shaft, is displaceable along the guide gate track 6 by way of the roller that supports the intermediate lever 4 on the guide gate track 6. In a manner corresponding to an eccentric contour of the second adjustment device 13, the intermediate lever 4 can be displaced between a zero operating position (not plotted here), a first operating position A1 for a Miller operation, as well as a second operating position A2 for a normal operation. The eccentric contour is defined by a radius profile about the point of rotation of the eccentric along the plotted circumferential direction U13.

[0082] In terms of the functional mode of the variable lift valve gear 1 per se, reference is also made to the international patent application WO 2002/092972 A1.

[0083] The second adjustment device 13 thus has a zero setting point for a zero lift, a second setting point for partial lift, and a third setting point for a full lift of the charge-cycle valve 2. Each setting point is represented by a point on the curve of a circular segment of the eccentric disk, i.e. the intermediate lever 4 in terms of the position thereof along the guide gate track 6 is displaced in the rotation of the second adjustment device 13, as a result of which a charge-cycle valve lift that takes place by a rotation of the lift regulator 10 is variable.

[0084] Zero lift means that the charge-cycle valve 2 is stationary, this corresponding to a cylinder shut-off. Partial lift means that the charge-cycle valve 2 has a charge-cycle valve lift that is smaller than a full lift, such as for example in the case of a Miller operation. Full lift means the maximum possible valve lift.

[0085] In further exemplary embodiments, the second adjustment device 13, instead of a cam disk, can also be replaced by linear actuating installations which have different detents or latching installations, respectively, that correspond to the zero lift, the partial lift and the full lift of the charge-cycle valve 2. The activation here can take place electrically and/or mechanically or hydraulically. The activation in the present exemplary embodiment takes place by an electric motor.

[0086] In order to enable at least substantially identical maximum valve acceleration in the first operating position A1 and the second operating position A2, the contours of the lift regulator (cam contour NK), of the lift adjustment 4 (including the operating curve 8), and of the lifting lever 9 have been adapted to one another when designing the valve gear 1.

[0087] In the exemplary embodiment, a customary software tool for optimizing the topology of drive components has been used for adapting the valve gear in a corresponding manner. In order to achieve a mutually corresponding maximum acceleration a.sub.max,A/a.sub.max,E or a.sub.max,mill,A/a.sub.max,mill,E in the first operating position A1 and in the second operating position A2, the cam contour NK, the contour of the intermediate lever in the contact region with the cam 10 and on the operating curve 8, as well as the contact region of the roller cam follower 9 with the operating curve 8 have been adapted to one another.

[0088] In the exemplary embodiment here, only the cam contour NK has been suitably adapted so that the existing valve gear module, the charge-cycle valve activation unit 3, can continue to be used without modification.

[0089] How the cam contour NK, thus the radius profile of the cam 10 along the circumferential direction U10, has to be adapted in the individual specific application so as to achieve the mutually corresponding maximum accelerations a.sub.max,A in the individual case, is a matter for the person skilled in the art while using in a manner known per se a software tool known per se for optimizing the topology and taking into account the requirements resulting from the operating strategy of the motor known in the individual case.

[0090] An embodiment of a method according to an exemplary embodiment of the invention is explained hereunder by means of FIG. 2.

[0091] FIG. 2 shows three diagrams: in the upper diagram the lift h is plotted over the crank angle KW; in the central diagram the lift speed v is plotted over the crank angle KW; and in the lower diagram the lift acceleration a is plotted over the crank angle KW.

[0092] The corresponding development of the variable h, v, a over the crank angle in each of the three diagrams is plotted for a maximum lift hmax (solid line), on the one hand, and for a Miller lift (partial lift; dashed line), on the other hand.

[0093] In the case of a requirement of full load, a conventional (non-Miller) operation having an at least almost maximum opening duration is first set, in particular in that the second operating position of the lift adjustment of the valve gear is set. This operating case is illustrated by solid lines in the diagrams.

[0094] The internal combustion engine is switched over to the Miller operation only once a maximum exhaust gas temperature T has been reached (see the exemplary entry in FIG. 1 in the combustion chamber; this being determined based on a model in the exemplary embodiment), in particular in that the first operating position of the lift adjustment of the valve gear is set. This operating case is illustrated by dashed lines in the diagrams.

[0095] The reduced lift height hmill in the Miller operation—in comparison to the maximum lift hmax—can be derived on the one hand from the upper diagram (lift diagram). On the other hand, a variable camshaft control not illustrated in FIG. 1 ensures that, in terms of the crank angle in the Miller operation, the greatest lift hmill takes place earlier than the greatest lift hmax in the normal operation.

[0096] It can be derived from the central diagram (speed diagram) that a lower maximum speed vmill of the valve 2 during adjustment is sufficient for the Miller operation—in comparison to the maximum speed vmax in the normal operation.

[0097] The adjustment of the cam contour NK according to this exemplary embodiment of the invention can be derived from the lower diagram (acceleration diagram): the highest accelerations a.sub.max,A and a.sub.max,mill,A or a.sub.max,E and a.sub.max,mill,E, respectively, are identical in the normal operation and in the Miller operation. In those crank angle ranges in which the highest accelerations a during deflection or during inflection, respectively, are displayed in the acceleration diagram, the operating curve 8 in the region of the maximum curvature BKmax thereof rolls on the roller cam follower 9.

[0098] As can be derived from FIG. 3, a roller of the roller cam follower 9, depending on the operating mode, contacts the operating curve at the point hmill or at the point hmax, thus in each case in the region Bn.

[0099] FIG. 4 shows a cross section through a lift regulator 10 of a variable lift valve gear 1 according to a further exemplary embodiment of the invention. The valve gear, and thus also the lift regulator 10, can be configured as in the exemplary embodiment according to FIG. 1, or else in another manner.

[0100] It can be derived from the illustration of FIG. 4 that the lift regulator 10 is configured as a cam of a camshaft 20 and is connected in a rotationally fixed manner to the camshaft 20. The cam 10 on the circumferential side thereof has a cam contour NK which at an angular position W, which (with the optional exception of the deflection movement) is fixed, a contact point S for deflecting the lift adjustment 4 bears on the latter.

[0101] The cam contour NK along the circumferential direction U10 of the cam 10 has different circumferential regions: a deflection region 22 for deflecting the lift adjustment 4 from the resting position thereof, a deflection switchover compensation region 24 for adapting the maximum deflection valve accelerations a.sub.max,A in the conventional operation and a.sub.max,mill,A in the Miller operation of the valve gear, a diversion region 26 for adjusting the maximum valve lift, an inflection switchover compensation region 28 for adapting the maximum inflection valve accelerations a.sub.max,E in the conventional operation and a.sub.max,mill,E in the Miller operation of the valve gear, as well as an inflection region 30 for inflecting the lift adjustment 4 to the resting position thereof. The different regions 22, 24, 26, 28 and 30 are only schematically plotted in the illustration, just as the plotted cam contour NK is to be understood to be merely schematic. A person skilled in the art will optimize a real cam contour NK by suitable software, while taking into account the specific parameters of the invention as well as other parameters, for example resulting from the kinematics of the valve gear.

[0102] When the camshaft 20 rotates about the rotation axis 21 thereof at an angular speed co, the distance (thus the radius) between the rotation axis 21 and the contact point S varies at the angular position W so as to correspond to the respective radius of the cam 10 at a specific circumferential position. The dissimilar radii r1 and r2 are plotted in an exemplary manner to aid understanding in FIG. 4.

[0103] In the plotted direction of rotation U10, the deflection region 22 by way of an increasing radius first passes the contact point S and herein deflects the lift adjustment 4 at an increasing speed vS and at a maximum of the acceleration of the contact point aS.

[0104] The deflection switchover compensation region 24 is subsequently passed, in which the radius further increases but, in the context of the invention, the contact point S along an axis of movement L of the contact point S is deflected at a constant speed (cf. solid line in the diagram of FIG. 5) or at a slightly decreasing speed (cf. dashed line in the diagram of FIG. 5).

[0105] When passing the deflection region 26, the radius first increases at an ever slower rate and subsequently decreases ever faster once the maximum of the deflection of the contact point S (and thus of the charge-cycle valve 2) has been passed.

[0106] Subsequently, the inflection switchover compensation region 28 is passed, in which the radius further decreases but, in the context of the invention, the contact point S along the axis of movement L of the contact point S is inflected at a constant or slightly increasing speed.

[0107] The minimum radius r1 by way of which the charge-cycle valve 2 is disposed in the resting position thereof is subsequently reached again in the inflection region 30.

[0108] FIG. 5 schematically shows a profile of a gradient of a variation of a valve lift guide variable over the crank angle KW of the camshaft 20 (thus also across the circumference U) of a cam contour NK of the lift regulator 10 according to FIG. 4 in a rotation about the rotation axis 21 of the lift regulator. The gradient in the exemplary embodiment corresponds to the acceleration aS of the contact point S in a manner corresponding to the deflection by the cam contour NK.

[0109] The contact point S is not displaced in a resting region 32 of the cam contour NK; accordingly, the acceleration aS is equal to zero. The acceleration reaches a positive maximum in the deflection region 22 before it in the deflection switchover compensation region 24 is either equal to zero (solid line) or slightly negative (dashed line with short dashes) or slightly positive (chain-dotted line). The acceleration reaches a negative maximum in the diversion region 26. An absolute value of the acceleration aS in the deflection switchover compensation region 24 is thus smaller than in the two adjacent regions 22 and 26. The same applies in an analogous manner to the inflection switchover compensation region 28 and the two adjacent regions 26 and 30, wherein here, as an alternative to a value of zero for the acceleration aS (solid line) in the inflection switchover compensation region 28, a slightly positive acceleration value (dashed line with long dashes) or a slightly negative acceleration value (double chain dotted line) may be provided.

[0110] FIG. 6 for a known valve gear having a cam on a camshaft and an intermediate lever as a lift adjustment shows a profile of the movement of the intermediate lever and of the valve lifts in the conventional operation and in the Miller operation.

[0111] An optimal valve elevation, thus one having a maximum control cross section, can in particular be implemented for fully variable valve lifts, e.g. those in which an intermediate lever by way of a specific movement with an operating curve fastened thereon push onto a roller cam follower, always only for a specific valve lift (usually the maximum lift). Each other lift (usually the partial lifts) is a consequence of this being conceived with a view to the maximum lift and is not optimal in this instance.

[0112] However, modern valve lift curves significantly differ from the theoretical curves which in turn have very homogenous profiles, in particular because the profiles are adapted to the oscillating behavior of the overall system. This oscillating behavior differs in the various partial lifts. For example, an optimization of the order which is incorporated for the maximum lift acts with less intensity in the partial lift or even acts with the opposite effect and can be compensated for only by a disproportionate reduction in terms of the maximum acceleration.

[0113] A real valve lift curve having a normal operation and a Miller operation—for a known valve gear—is illustrated in FIG. 6 and explained in the following.

[0114] The opening region of the operating curve has to be passed at maximum speed in order to attain the maximum acceleration required for achieving the optimal valve lift curve. The movement of the intermediate lever—this being at least substantially proportional to the displacement path of the contact point xS* of which the profile is plotted here—therefore has to be at its maximum speed vS* at this point/region (cf. reference sign 100 in FIG. 6).

[0115] The length of the opening region is established by the geometry of the operating curve and may fundamentally not differ in terms of partial lifts of the maximum lift.

[0116] The maximum return acceleration of the intermediate lever as well as the maximum inflection valve acceleration a.sub.max,E* of the charge-cycle valve 2 is limited by restoring spring forces. In order to decelerate the ideally high speed of the intermediate lever when passing the opening region, the region of the speed deceleration must start immediately upon passing the opening region. Once the opening region of the operating curve in the rated lift has been passed, the intermediate lever speed vS* accordingly drops (cf. reference sign 200 in FIG. 6).

[0117] As a consequence of the fundamental construction of the fully variable lift regulator, the opening region of the operating curve in the partial lift, thus in the Miller operation, is passed by a region of the intermediate lever movement xS* which presents itself later in comparison to the region at maximum lift (cf. reference sign 300 in FIG. 6). The speed vS* here, as described above, is lower than at the maximum lift, and the maximum valve acceleration a.sub.max,mill,A* is therefore lower and the control cross section is no longer at its maximum/optimum. The same applies in an analogous manner to the closing of the valve.

[0118] In the known valve gears it thus has to be decided already in the stage of the basic design for which valve lift the latter is optimally conceived. This optimum in the known valve gears has been designed by the person skilled in the art so as to be at the maximum lift because the latter influences the system output.

[0119] FIG. 7 for the valve gear from FIG. 4 shows a profile of the intermediate lever movement xS and of the valve lifts hmax and hmill in the conventional operation and in the Miller operation, from which it becomes apparent that the invention here makes a decisive difference which is explained hereunder.

[0120] A maximum valve acceleration a.sub.max,A in the conventional operation of the valve gear 1, or an ideally high speed vS of the intermediate lever movement caused by a long braking phase of the intermediate lever at the maximum lift is very intentionally dispensed with, in favor of only a maximum valve acceleration a.sub.max,mill,A being adjusted also in the conventional operation.

[0121] The remaining maximum acceleration a.sub.max,mill,A is also generated in the partial lift, the Miller lift. Because the opening duration here is shorter, the intermediate lever speed vS must be lower. The maximum intermediate lever acceleration aS at a lower speed vS is generated by a greater curvature BKmax on the operating curve 8. The intermediate lever speed vS in the exemplary embodiment must never be significantly higher than in the Miller partial lift, not even at the maximum lift. In this way, there is an entirely intentional loss in terms of control cross section.

[0122] The intermediate lever movement S has a region of constant speed vS in the deflection switchover compensation region 24 and in the inflection switchover compensation region 28 (cf. reference sign 400 in FIG. 6). This results in that the valve gear 1 in the first operating position A1 and in the second operating position A2 the charge-cycle valve 2 adjusts at an at least substantially identical maximum valve acceleration a.sub.max,mill,A when deflecting or a.sub.max,mill,E when inflecting, respectively.

[0123] The difference between known valve gears and the valve gear 1 according to the invention is visually derived in particular from FIGS. 6 and 7. The known valve gears, as shown in FIG. 6, specifically do not have a mutually corresponding or very similar maximum valve acceleration a.sub.max,A or a.sub.max,mill,A in the normal operation and in the Miller operation. Rather, a maximum valve acceleration a.sub.max,A* is adjusted in the conventional operation, and a lower maximum valve acceleration a.sub.max,mill,A* is adjusted in the Miller operation. The same applies in an analogous manner to the inflection of the valve.

[0124] A minor drop in terms of the intermediate lever speed vS in the deflection switchover compensation region 24 may optionally be expedient in the context of an overall optimization of the system in individual specific applications, but this is not mandatory.

[0125] In terms of optimizing to the oscillation properties of the system, a compromise between a maximum valve lift at conventional full load and a Miller partial lift at Miller full load may be found. To this end, the respective operating lift can be assigned more or less priority in terms of opening duration and/or control cross section, for example, by way of a predetermined deviation from a constant intermediate lever speed vS right through to a slight increase of the speed vS at a conventional lift, or by way of a slight reduction of the speed vS at a Miller partial lift. This, by way of a variation of the illustrated exemplary embodiment, results in slight acceleration values aS in the deflection switchover compensation region 24, or the inflection switchover compensation region 28 that deviate from zero (cf. dashed lines in the diagram in FIG. 5).

[0126] The exact compromise between the Miller partial lift and the maximum lift is to be balanced in particular while taking into account parameters in the context of an optimum in terms of load change, or combustion, respectively.

[0127] FIG. 8 schematically shows a topology of a vehicle drive 50 having an internal combustion engine 52 having a variable lift valve gear 1 which can be configured in particular according to FIG. 1 and/or according to FIG. 4. A method according to an exemplary embodiment of the invention for operating a variable lift valve gear will be explained hereunder by means of the illustration, the variable lift valve gear being potentially configured according to the exemplary embodiment as per FIG. 1 and/or according to the exemplary embodiment as per FIG. 4, for example.

[0128] The vehicle drive 50 additionally has a turbocharger 54, an exhaust gas path 56 and an exhaust gas post-treatment device 58. The illustration of the various fluid paths is highly simplified and is not intended to explain all of the details of the vehicle drive 1 but only the concept of the invention and of specific exemplary embodiments. For example, neither an exhaust gas recirculation nor a divert-air valve or a wastegate is illustrated despite these components as well as other components being installed in many turbocharged engines.

[0129] The internal combustion engine 52 in the exemplary embodiment has four cylinders 60 (but may have more or fewer cylinders) which by means of the charge air supply 6 and an injection unit 14 are supplied with a mixture of air and fuel, wherein the valve gear 1 by way of the charge-cycle valves 2 determines the supply of the charge air into the cylinders 60 and the discharge of the exhaust gases from the cylinders.

[0130] In the illustration of FIG. 8, a temperature sensor 62 is directly ahead of a turbine 64 of the turbocharger 54 in the exhaust gas flow (for example at the downstream end of the exhaust manifold). The temperature sensor 62 is specified for detecting an indicator of an exhaust gas temperature, in particular in real-time, at a predetermined location T3, the temperature sensor 62 being disposed at the latter.

[0131] In terms of the illustrated embodiment of the invention it is however likewise possible that the detection of the temperature does not take place by means of the temperature sensor 62, or not exclusively by the latter, but in particular exclusively by means of a corresponding temperature model 64 for the location T3, or at least by means of a comparison between the indicators detected by the sensor 62 and the temperature model 64.

[0132] Such a temperature model 64, preferably as a function of operational characteristics of the drive 50, has available with sufficient accuracy and reliability a respective temperature to be expected at the observed location T3 of the exhaust gas path 56 for a multiplicity of combinations of the operational characteristics.

[0133] The exhaust gas path moreover has a control means 66 which for transmitting control commands and/or status data and/or sensor data is connected to the temperature sensor 62, to the injection unit 14, to the valve gear 1 as well as to the temperature model 55. The control means 66 can also be configured so as to be integrated with a control means of the internal combustion engine 52, of the drive 50 or of the entire motor vehicle.

[0134] In order for the method to be carried out, the two steps are performed: (i) determining an exhaust gas temperature T in an operating situation of the internal combustion engine 52; (ii) determining whether the valve gear 1 in the operating situation is to be switched to a conventional operating mode or to a Miller operating mode, wherein the operating mode to be switched is determined as a function of the determined exhaust gas temperature T.

[0135] The exhaust gas temperature T here is determined at the location T3, in particular at an engine-distal end of an exhaust manifold of the exhaust gas path 56 and/or at a turbine inlet of a turbine 55, having a variable turbine geometry, of the exhaust gas turbocharger 54 of the internal combustion engine 52. When a limit value Tg of the exhaust gas temperature T is reached or exceeded, the valve gear 1 is switched to the Miller operating mode.

[0136] The limit value Tg of the exhaust gas temperature T is determined as a function of a heat resistance of a turbine material of the exhaust gas turbocharger 54.

LIST OF REFERENCE SIGNS

[0137] 1 Valve gear [0138] 2 Charge-cycle valve [0139] 3 Charge-cycle valve activation unit [0140] 4 Lift adjustment (in particular intermediate lever) [0141] 5 Clearance compensation element [0142] 6 Guide gate track [0143] 7 Guide gate [0144] 8 Operating curve [0145] 9 Lifting lever (in particular roller cam follower) [0146] 10 Lift regulator/first adjustment device (in particular cam of a camshaft) [0147] 11 Guide gate proximal point [0148] 12 Spring element [0149] 13 Second adjustment device (in particular eccentric disk) [0150] 15 Cylinder head [0151] 20 Camshaft [0152] 21 Rotation axis [0153] 22 Deflection region [0154] 24 Deflection switchover compensation region [0155] 26 Diversion region [0156] 28 Inflection switchover compensation region [0157] 30 Inflection region [0158] 32 Resting region [0159] 50 Vehicle drive [0160] 52 Internal combustion engine [0161] 54 Turbocharger [0162] 55 Turbine [0163] 56 Exhaust gas path [0164] 58 Exhaust gas post-treatment device [0165] 60 Cylinder [0166] 62 Temperature sensor [0167] 64 Temperature model [0168] 66 Control means [0169] 100 Reference sign in FIG. 6 [0170] 200 Reference sign in FIG. 6 [0171] 300 Reference sign in FIG. 6 [0172] 400 Reference sign in FIG. 7 [0173] A1 First operating position of the lift adjustment [0174] A2 Second operating position of the lift adjustment [0175] a Acceleration of the charge-cycle valve [0176] a.sub.max,A Maximum acceleration of the charge-cycle valve when deflecting in the conventional operation [0177] a.sub.max,mill,A Maximum acceleration of the charge-cycle valve when deflecting in the Miller operation [0178] a.sub.max,E Maximum acceleration of the charge-cycle valve when inflecting in the conventional operation [0179] a.sub.max,mill,E Maximum acceleration of the charge-cycle valve when inflecting in the Miller operation [0180] aS Acceleration of the contact point [0181] Bg Basic circle region of the operating curve [0182] Bh Lifting region of the operating curve [0183] BKmax Region of a maximum curvature of the utilized operating curve [0184] h Lift of the charge-cycle valve [0185] hmax Maximum lift [0186] hmill Miller lift [0187] Kmax Maximum curvature of the operating curve [0188] KW Crank angle of the internal combustion engine [0189] L Movement axis of the contact point [0190] NK Cam contour (in particular cam contour) of the first adjustment device [0191] OT Top dead center [0192] Phmax Contacting position at hmax [0193] Phmill Contacting position at hmill [0194] r Radius [0195] S Contact point between cam contour and lift adjustment [0196] T3 Position of the temperature sensor in the exhaust gas path [0197] Tg Limit value of the exhaust gas temperature [0198] UT Bottom dead center [0199] U10 Circumferential direction of the first adjustment device [0200] U13 Circumferential direction of the second adjustment device [0201] v Speed of the charge-cycle valve [0202] vS Speed of the contact point [0203] W Fixed angular position in the circumference of the rotation axis of the camshaft [0204] xS Displacement path of the contact point between the cam contour and the lift adjustment [0205] ω Angular velocity of the camshaft