DE102018132587A1 - Method for controlling a variable valve train - Google Patents

Abstract

The invention relates to a method for controlling a variable valve train (2) of an internal combustion engine. To ensure that the drag torque of the internal combustion engine is reduced to a maximum from the start when the engine is started, the method provides that the following procedural steps are carried out after the internal combustion engine has been switched off and before the engine is started: a) Switching over or pretensioning switching elements (44) of the switchable rocker arms ( 22) by means of the switching device into its switching position, in which the stroke curves of the secondary cams (12a, 12b) are transmitted to the associated gas exchange valves (52) with the secondary lift cams (18), b) turning the camshaft (4) from its rest position by means of the camshaft adjuster in at least one direction of rotation up to an angle of rotation position up to which at least one rocker arm (22) not previously switched over is reached or swept by an associated switching window of the valve train, and c) turning the camshaft (4) back into its rest position by means of the camshaft adjuster.

Description

The invention relates to a method for controlling a variable valve train of an internal combustion engine, which has a switching device for the stroke switching of switchable stroke transmission elements of at least one functionally identical gas exchange valve per cylinder from a primary cam of a camshaft to a secondary cam, the secondary cam having an after-lift cam which is in the compression stroke of the respective cylinder is effective, as well as with a camshaft adjuster for phase adjustment of the camshaft in relation to a camshaft gear that is in drive connection with the crankshaft of the internal combustion engine, by means of which the drag torque of the internal combustion engine is reduced when the engine is started.

The internal combustion engine is based on a four-stroke internal combustion engine which has separate camshafts for actuating its gas exchange valves, i.e. is provided with at least one intake camshaft for actuating intake valves and with at least one exhaust camshaft for actuating exhaust valves. At least one of the camshafts has at least one primary cam with a main lifting cam and at least one secondary cam with a main lifting cam and a post-lifting cam for at least one gas exchange valve per cylinder. The secondary lift cam is arranged or formed on the circumferential side of the secondary cam in such a way that the respective gas exchange valve is opened in the compression stroke of the relevant cylinder.

The switching device for changing the stroke of the switchable stroke transmission elements preferably has a single electrical actuator, for example an electric motor or an electromagnet, by means of which the switching elements of the stroke transmission elements can be switched over to a switching position in a single switching operation if the assigned cams of the camshaft are just in their base circle or can be tapped at their main lifting cams, or can be pretensioned in the switching direction by means of assigned spring elements if one of the two cams is tapped just outside its base circle or its main lifting cam. The switching elements that are not initially shifted into their switching position are then switched over when the camshaft is rotated further. Corresponding switching devices of a variable valve train are for example from the US 2017/0198613 A1 and the DE 10 2017 101 792 B4 known.

The camshaft adjuster for phase adjustment of the camshaft is preferably also electrically operable, that is to say adjustable via an electric motor or an electromagnet. A corresponding electromechanical camshaft actuator is, for example, in the DE 11 2004 001 754 B4 described.

Compared to hydraulically active actuators for switching switchable rocker arms and hydraulic camshaft actuators, the energy supply and the control of electric motors and electromagnets can be implemented more easily, in a space-saving and more cost-effective manner, since this avoids the use of costly high-pressure accumulators and frequently fault-prone control valves.

Modern motor vehicles, which have only one internal combustion engine as the drive source, are often equipped with a start / stop device, by means of which the internal combustion engine is switched off when the vehicle is at a standstill, for example at traffic light stops, as well as in overrun mode and when driving without propulsion to save fuel and reduce pollutant emissions becomes. Likewise, the combustion engine in vehicles with a parallel hybrid drive, which can be driven alternately by internal combustion engine or electric motor, is switched off when changing to electric driving mode, when the vehicle is at a standstill and in overrun mode and when there is no drive forward. The internal combustion engine, which is associated with a high load on an electric starter motor or a starter generator and also requires a high charging capacity of the associated electric accumulator, must accordingly be started again frequently. There is therefore great interest among vehicle manufacturers in keeping the drag torque of the internal combustion engine when starting the engine as low as possible.

From the DE 10 2017 104 629 A1 a variable valve train of an internal combustion engine is known, the switching device of which comprises a plurality of switchable rocker arms. The rocker arms each have an inner lever for tapping a primary cam of a camshaft and an outer lever for tapping two secondary cams arranged axially on both sides of the primary cam on the camshaft. In one possible application of the valve train, the secondary cams each have, in addition to a main lift cam, a secondary lift cam which is arranged on the circumferential side in such a way that the assigned gas exchange valves in the switched state of the rocker arm, in which the outer levers are coupled to the inner levers of the rocker arms, in the compression stroke of the cylinders be opened. The rocker arms are switched over before or at the start of an engine start, the post-lifting cams decompressing the work spaces in the compression stroke of the cylinders thus ensure a lower drag torque of the internal combustion engine during engine start.

A disadvantage of this known control method, however, is that the switchable rocker arms cannot be completely switched over before the engine is started because the camshaft in question usually remains in a rotational position when the internal combustion engine is switched off, in which not all primary and secondary cams of the inner levers and External levers of the assigned rocker arms can be tapped in their base circle or on their main lift cams, i.e. not all rocker arms can be switched over immediately. When starting the engine, at least one full revolution of the camshaft or two revolutions of the crankshaft is therefore required before all rocker arms are switched over and decompression in the compression stroke is effective for all cylinders. The drag resistance of the internal combustion engine is therefore relatively high at the start of an engine start and is only lowered after a few engine revolutions.

The present invention was therefore based on the object of presenting a method for controlling a variable valve train of the type mentioned at the outset, with which the drag resistance of an internal combustion engine is reduced to a maximum from the start when the engine is started.

1. a) Umschalten oder Vorspannen von Schaltelementen der schaltbaren Schlepphebel mittels der Schaltvorrichtung in ihre Schaltstellung, in welcher die Hubkurven der Sekundärnocken mit den Nachhubnocken auf die zugeordneten Gaswechselventile übertragen werden,
2. b) Verdrehen der Nockenwelle mittels des Nockenwellenstellers aus ihrer Ruheposition in mindestens einer Drehrichtung bis in eine Drehwinkellage, bis zu der mindestens ein zuvor nicht umgeschalteter Schlepphebel von einem zugeordneten Schaltfenster des Ventiltriebs erreicht oder überstrichen wird, und
3. c) Rückdrehen der Nockenwelle mittels des Nockenwellenstellers in ihre Ruheposition.

This object is achieved in connection with the features of the preamble of claim 1 in that the following method steps are carried out after the internal combustion engine has been switched off and before the engine is started:

1. a) switching or pretensioning of switching elements of the switchable rocker arms by means of the switching device into their switching position, in which the stroke curves of the secondary cams are transmitted to the associated gas exchange valves with the secondary lift cams,
2. b) rotating the camshaft by means of the camshaft adjuster from its rest position in at least one direction of rotation to an angle of rotation position up to which at least one rocker arm not previously switched is reached or swept by an associated switching window of the valve train, and
3. c) turning the camshaft back into its rest position by means of the camshaft adjuster.

The invention accordingly relates to a method for controlling a variable valve train of an internal combustion engine, which has a switching device for switching the stroke of switchable stroke transmission elements of at least one functionally identical gas exchange valve per cylinder from a primary cam of a camshaft to a secondary cam, the secondary cam having a post-cam which is in the compression stroke of the respective one Cylinder is effective, and with a camshaft adjuster for phase adjustment of the camshaft in relation to a camshaft gear that is in drive connection with the crankshaft of the internal combustion engine, by means of which the drag torque of the internal combustion engine is reduced when the engine is started.

When the internal combustion engine is switched off, the valve train and the camshaft with the primary and secondary cams remain in any rest position in which most of the switchable rocker arms can be switched. The exact position of the rest position of the camshaft is however absolutely and relative to the camshaft sprocket unknown, because the usual camshaft and crankshaft sensors require a minimum speed of the respective shaft and are not effective when the engine is stopped. The rocker arms are switchable when the primary and secondary cams of the camshaft are being tapped off by the tapping elements of the primary and secondary levers of the rocker arms on their base circle or on their main lift cam. Thus, these rocker arms are immediately switched with the switching device by shifting one switching element into its switching position, and when the camshaft rotates, the lift curves of the respective secondary cam are then transferred to the associated gas exchange valves with the lift cam.

At least one of the switchable rocker arms may not be switchable in the rest position of the camshaft because the assigned secondary cam of the camshaft is being tapped by its secondary lift cam by the secondary lever of the rocker arm and thus there is a differential stroke between the primary lever and the secondary lever on the rocker arm. This differential stroke is at least temporarily canceled according to the invention in that the camshaft is rotated by means of the camshaft adjuster from its rest position in at least one direction of rotation to an angle of rotation position up to which the rocker arm not previously switched is reached or swept by an associated switching window of the valve train. When the switching window reaches or passes through the rocker arm in question, the rocker arm is switched over by a spring element that is tensioned when the switching device is switched over and is effective on the assigned switching element. Finally, the camshaft is turned back into its rest position by means of the camshaft adjuster so that it has a starting position for the next engine start that is favorable with respect to the standstill position of the crank mechanism of the internal combustion engine.

Since with the implementation of the method according to the invention all switchable rocker arms are switched over before the next engine start, the working spaces of all cylinders are decompressed in the compression stroke from the start when the engine is started, which leads to a lower drag torque of the internal combustion engine and thus to a lower load on the starter or starter Generator and the accumulator leads.

If the camshaft adjuster is adjustable or is to be adjusted in both directions of rotation, it is provided that the camshaft is first rotated by the camshaft adjuster by half the angular width of the secondary lift cam in a first direction of rotation, then rotated in the opposite direction by the entire angular width of the secondary lift cam, and is then turned back to its rest position by half the angular width of the secondary lift cam in the first direction of rotation. Since the most unfavorable standstill position of the valve drive in this case is such that the secondary cam in question is picked up by the tapping element of the secondary lever just in the middle of the secondary lift cam, the rocker arm in question is switched by rotating the camshaft in both directions of rotation by half the angular width of the Nachhubnockens ensured.

On the other hand, if the camshaft adjuster is adjustable or should only be adjusted in one direction of rotation, it is provided that the camshaft adjuster is first rotated by the angular width of the secondary lift cam in its main direction of rotation, that is to say "late", and finally by the angular width of the Nachhubnockens is rotated counter to their main direction of rotation in their rest position. Since the most unfavorable standstill position of the valve drive in this case is such that the secondary cam in question is picked up by the tapping element of the secondary lever just at the beginning of the secondary lift cam, the rocker arm concerned is switched by the rotation of the camshaft by the angular width of the secondary lift cam. The rotation of the camshaft in the "late" and back direction reliably prevents an open gas exchange valve from colliding with the piston of the relevant cylinder.

Since the camshaft adjuster with the camshaft can remain in any desired position within the swiveling range limited by two end stops when the internal combustion engine is switched off, it is possible that the camshaft adjuster cannot rotate the camshaft completely over the intended angle of rotation range, but the camshaft adjuster previously reached an end stop. It is therefore provided that the camshaft is only rotated up to the relevant end stop of the camshaft adjuster if this end stop is reached before the end position of the intended range of rotation angles. This procedure makes sense, since the rotational angle position corresponding to the standstill position of the crank drive when the camshaft is rotated can nevertheless be swept or reached by the shift window of the relevant rocker arm. If this is not the case, the drag resistance of the internal combustion engine is initially increased by the compression resistance of this cylinder at the beginning of the subsequent engine start.

In a possible development of the method according to the invention, it is provided that after the internal combustion engine is switched off and before the engine is started, the rotational angle positions of the camshaft and the camshaft gear or the crankshaft are recorded and stored by means of rotational angle sensors which are effective when the engine is at a standstill. Since the required direction of rotation and the angular distance between the closest shift window of the at least one rocker arm not previously switched over and the angular position corresponding to the standstill position of the crank mechanism can thus be determined and are thus known, the camshaft adjuster is first adjusted by the angular distance between the shift window of the previously not shifted The rocker arm and the angle of rotation position corresponding to the standstill position of the crank mechanism are rotated in the respective direction of rotation and finally rotated back to their rest position by the same angle of rotation in the opposite direction of rotation. Since the rotational angle position corresponding to the standstill position of the crank drive is now approached specifically by the camshaft of the relevant rocker arm by turning the camshaft, there are fewer and / or shorter rotational angles of the camshaft by the camshaft adjuster, which leads to a faster changeover of all rocker arms overall.

If, which is possible with a five-cylinder in-line engine, for example, there are two rocker arms that have not been switched before and whose shift windows are in the same direction of rotation as the angular position corresponding to the standstill position of the crank drive, the camshaft adjuster is initially moved by the angular distance of the most distant shift window of the latter Turn the rocker arm in the relevant direction of rotation and then turn it back to its rest position by the same angle of rotation in the opposite direction of rotation. The rotational angle position corresponding to the standstill position of the crank mechanism is inevitably swept over by the closer shift window of the other rocker arm, whereby this rocker arm is also switched over.

If, which is also possible with a straight five-cylinder engine, for example, there are two rocker arms that have not previously been switched over and whose shift windows are in opposite directions of rotation to the angular position corresponding to the standstill position of the crank drive, the camshaft is first adjusted by the angular distance of the camshaft adjuster in a first direction of rotation lying switching window of one rocker arm rotated in this direction of rotation, then rotated by this angle of rotation and the angular distance of the switching window of the other rocker arm lying in the opposite direction of rotation in the opposite direction of rotation, and finally turned back to its rest position by the last angular distance in the first direction of rotation.

If the angular distance to the shift window of one of the rocker arms in question lies outside one of the end stops of the camshaft actuator, the respective rotation of the camshaft is omitted until the rotational angle position corresponding to the standstill position of the crank drive is omitted. The drag resistance of the internal combustion engine at the beginning of a subsequent engine start is then initially increased by the compression resistance of this cylinder. If the shift windows of two rocker arms not previously switched are in the same direction of rotation to the rotational angle position corresponding to the standstill position of the crank drive, in this case the camshaft is first moved by the camshaft adjuster by the angular distance of the closest shift window of these finger levers to the rotational angle position corresponding to the standstill position of the crank drive in the relevant direction of rotation rotated and finally rotated back to the rest position by the same angle of rotation in the opposite direction. If the shift windows of two rocker arms not previously switched are in opposite directions of rotation to the rotational angle position corresponding to the standstill position of the crank drive, in this case the camshaft is only moved by the camshaft adjuster by the angular distance of the shift window of the other finger lever to the rotational angle position corresponding to the standstill position of the crank drive rotated in the relevant direction of rotation and finally rotated back to the rest position by the same angle of rotation in the opposite direction of rotation.

• 1a Ventilhubkurven eines Verbrennungsmotors mit einer ersten Stillstandposition des Kurbeltriebs in einem Diagramm,
• 1b die Ventilhubkurven des Verbrennungsmotors gemäß 1a mit einer zweiten Stillstandposition des Kurbeltriebs in einem Diagramm,
• 1c die Ventilhubkurven des Verbrennungsmotors gemäß 1a und 1b mit einer Verstellung der Nockenwelle mit einem Schaltfenster eines Schlepphebels in die der zweiten Stillstandposition des Kurbeltriebs entsprechende Drehwinkellage in einem Diagramm,
• 2a eine Nockenwelle und einen schaltbaren Schlepphebel eines variablen Ventiltriebs in einer ersten Drehwinkellage der Nockenwelle in einer axialen Seitenansicht,
• 2b die Nockenwelle und den schaltbaren Schlepphebel gemäß 2a in der ersten Drehwinkellage der Nockenwelle in einer radialen Seitenansicht,
• 3a die Nockenwelle und den schaltbaren Schlepphebel gemäß 2a und
• 2b in einer zweiten Drehwinkellage der Nockenwelle in einer axialen Seitenansicht, und
• 3b die Nockenwelle und den schaltbaren Schlepphebel gemäß den 2a bis 3a in der zweiten Drehwinkellage der Nockenwelle in einer radialen Seitenansicht.

To further clarify the invention, the description is accompanied by a drawing with an embodiment. In this shows

• 1a Valve lift curves of an internal combustion engine with a first standstill position of the crank mechanism in a diagram,
• 1b the valve lift curves of the internal combustion engine according to 1a with a second standstill position of the crank mechanism in a diagram,
• 1c the valve lift curves of the internal combustion engine according to 1a and 1b with an adjustment of the camshaft with a shift window of a rocker arm to the rotational angle position corresponding to the second standstill position of the crank drive in a diagram,
• 2a a camshaft and a switchable rocker arm of a variable valve train in a first rotational angle position of the camshaft in an axial side view,
• 2 B the camshaft and the switchable rocker arm according to 2a in the first angular position of the camshaft in a radial side view,
• 3a the camshaft and the switchable rocker arm according to 2a and
• 2 B in a second angular position of the camshaft in an axial side view, and
• 3b the camshaft and the switchable rocker arm according to 2a to 3a in the second rotational angle position of the camshaft in a radial side view.

The following explanation of the inventive method for controlling a variable valve train 2nd is carried out, for example, using a four-cylinder in-line engine, its intake valves and exhaust valves via separate camshafts, namely an intake camshaft 4th and an exhaust camshaft. In the 2a to 3b is this valve train 2nd with two different angles of rotation of the intake camshaft 4th each shown in sections in an axial and a radial side view.

The intake camshaft 4th points for at least one inlet valve 52 one primary cam per cylinder 6 with a base circle 8th and a main lift cam 10th and two axially on both sides of the primary cam 6 arranged secondary cams 12a , 12b with one base circle each 14 , a main lifting cam 16 and a post lift cam 18th on. The post lift cam 18th is the main lifting cam in the main direction of rotation 20th the intake camshaft 4th arranged on the circumference in such a way that the inlet valve 52 is opened in the compression stroke of the respective cylinder. The primary and secondary cams 6 , 12a , 12b each have a switchable rocker arm 22 with the assigned inlet valve 52 in actuating connection or via this with the assigned inlet valve 52 connectable.

The switchable rocker arms 22 each have an inner lever acting as a primary lever 24th and an outer lever effective as a secondary lever 26 on. The inner lever 24th is largely frame-shaped and on its underside at its end on a support element inserted into a bearing bore of a cylinder head, not shown here 60 with integrated hydraulic valve lash adjuster and opposite on the valve stem 54 of the associated intake valve 52 supported. The inlet valve 52 is via a valve spring designed as a coil spring 58 that on one on the valve stem 54 attached spring plate 56 is supported, loaded in the closing direction, i.e. upwards in the drawing, with a spring force. The inner lever is on its top 24th via a tapping element designed as a rotatably mounted roller 28 with the assigned primary cam 6 the camshaft 4th in tap contact. The outer lever 26 has one the primary lever 24th encompassing frame-like shape and is via a valve pin arranged on the valve side 48 pivotable on the primary lever 24th stored. As tap elements 36a , 36b has the secondary lever 26 a web-shaped projection on each side, each with an upwardly convex outer sliding surface 38a , 38b on.

Due to the spring force of two axially on both sides around the hinge pin 48 arranged, designed as leg springs pressure springs 50a , 50b is the outer lever 26 opposite the inner lever 24th towards the camshaft 4th loaded with a spring force and is with the mentioned sliding surfaces 38a , 38b in tapping contact with the assigned secondary cams 12a , 12b held. The main lifting cams 10th , 16 of the primary cam 6 and the secondary cam 12a , 12b have different curvatures, but cause the same stroke of the inner and outer lever 24th , 26 , since they roll with differently curved outer walls 28 or the sliding surfaces 38a , 38b the ledges 36a , 36b of the secondary lever 26 work together.

As a coupling element 32 for positive connection of the outer lever 26 with the inner lever 24th is an axially movable in a cross hole 30th of the primary lever 24th guided coupling bolt provided, which by means of a in a transverse bore 42 of the secondary lever 26 axially movable switching pin 44 against the restoring force of a spring element designed as a coil spring 34 in an opposite coupling hole 40 of the secondary lever 26 can be moved ( 2 B) . The shift pin 44 protrudes with its axially outer end 46 from the secondary lever 26 out and stands on this via a connection element, not shown here, designed as a leaf spring with a switching rail in an actuating connection. The shift rail, also not shown, is above the rocker arm 22 parallel to the intake camshaft 4th arranged and longitudinally displaceable by means of an actuator. The structure and mode of operation of a similarly constructed variable valve train are shown, for example, in FIG DE 10 2017 101 792 B4 described in detail.

In the 2a and 2 B is the intake camshaft 4th in a first angular position in which the primary cam 6 off the roll 28 of the inner lever 24th on its base circle 8th as well as the secondary cams 12a , 12b from the sliding surfaces 38a , 38b of the outer lever 26 each on their post lift cam 18th be tapped. This places between the inner lever 24th and the outer lever 26 a differential stroke, which leads to a non-aligned position of the coupling and transverse bores 30th , 40 , 42 as well as the coupling and switching bolt 32 , 44 leads. The rocker arm 22 is thus in this angular position of the intake camshaft 4th not switchable. This also applies to a downshift when the rocker arm 22 already switched and the outside lever 26 with the inner lever 24th is coupled because the coupling and switching bolts 32 , 44 then loaded by transverse forces and thus jammed.

In the 3a and 3b is the intake camshaft 4th in their main direction of rotation 20th rotated 90 ° further and is now in a second angular position in which the primary cam 6 off the roll 28 of the inner lever 24th as well as the secondary cams 12a , 12b from the sliding surfaces 38a , 38b of the outer lever 26 each on their base circle 8th , 14 be tapped. This is the difference in stroke between the inner lever 24th and the outer lever 26 canceled, and the coupling and cross holes 30th , 40 , 42 as well as the coupling and switching bolts 32 , 44 align coaxially. The rocker arm 22 is thus in this angular position of the intake camshaft 4th switchable. This also applies to a downshift when the rocker arm 22 already switched and the outside lever 26 with the inner lever 24th is coupled because the coupling and switching bolts 32 , 44 then free of lateral forces and therefore not trapped.

In the diagram of the 1a are the stroke curves of a four-cylinder in-line engine with the firing order 1 - 3rd - 4th - 2nd shown above the crank angle ° KW of the crankshaft. When the internal combustion engine is switched off, the valve train is 2nd with a rest position of the intake camshaft 4th stopped, in which there is one of four switch windows represented by cross-hatched vertical bars. The shift windows are of a theoretical nature and indicate the angular positions of the intake camshaft 4th , in which all switchable rocker arms 22 are switchable at the same time. That the valve train 2nd Stopping exactly in such a switching window when the internal combustion engine is switched off is, however, relatively unlikely. The standstill position of the crank mechanism of the internal combustion engine The corresponding angle of rotation position is marked by a thick vertical and dashed line.

On the other hand, it is more likely that the valve train 2nd when switching off the internal combustion engine with the intake camshaft in a rest position 4th stops, not all rocker arms 22 are switchable at the same time. In the diagram of the 1b the crank mechanism is in a standstill position, in which only the rocker arm 22 of the second, third and fourth cylinders are switchable because the primary and secondary cams 6 , 12a , 12b the intake camshaft 4th with these cylinders just on their base circle 8th , 14 (Cylinder 2nd and cylinder 4th ) or on their main cam 10th , 16 (Cylinder 3rd ) can be tapped. The rocker arm 22 the first cylinder, on the other hand, cannot be switched because the assigned secondary cams 12a , 12b right there on their lift cam 18th and the relevant primary cam 6 on its base circle 8th be tapped, and thus a differential stroke between the inner lever 24th and the outer lever 26 is present.

Around all switchable rocker arms 22 Switch over before starting the engine and thus the post-lift cams that act as decompression cams 18th In order to be able to activate all cylinders, the method according to the invention provides that the shift bolts are used first 44 all switchable rocker arms 22 by means of the switching device in its switching position, in which the stroke curves of the secondary cams 12a , 12b with the lift cam 18th on the assigned intake valves 52 be transferred, switched over or biased inwards in the switching direction. In the present example, the rocker arms are thus 22 the cylinder 2nd to 4th immediately to the transfer of the lift curves of the post lift cams 18th switched. On the rocker arm, which is initially not switchable 22 of the first cylinder, however, becomes the shift pin 44 via the leaf spring that is between the shift rail and the outer end 46 of the shift pin 44 is arranged, biased inwards in the coupling direction. Then the intake camshaft 4th rotated by means of an assigned camshaft adjuster in the direction of the rotational angle position corresponding to the standstill position of the crank drive until it passes through the closest shift window of the rocker arm not previously switched 22 of the first cylinder is swept or reached.

In the diagram of the 1c the moment at which the intake camshaft is shown 4th just occupies an angle of rotation position in which this together with the relevant switching window and the stroke curves of the primary and secondary cams 6 , 12a , 12b so far in the direction of "late" or in the main direction of rotation 20th the intake camshaft 4th is rotated that the angle of rotation position corresponding to the standstill position of the crank mechanism within the switching window of the rocker arm 22 of the first cylinder and is therefore switched due to the bias of the associated leaf spring. Finally, the intake camshaft 4th rotated back into its rest position by means of the camshaft adjuster so that it has a starting position for the next engine start that is favorable with respect to the standstill position of the crank mechanism.

Since with the implementation of the inventive method all switchable rocker arms 22 Even before the next engine start, the working spaces of all cylinders are decompressed in the compression cycle right from the start, which leads to a lower drag torque of the internal combustion engine and thus to a lower load on the starter or starter generator and the accumulator.

Reference symbol list

2nd

Variable valve train

4th

Camshaft, intake camshaft

6

Primary cam

8th

Base circle of the primary cam

10th

Main lift cam

12a, 12b

Secondary cam

14

Base circles of the secondary cams

16

Main lift cam

18th

Post lift cam, decompression cam

20th

Main direction of rotation of the camshaft

22

Switchable stroke transmission element, rocker arm

24th

Inner lever, primary lever

26

Outer lever, secondary lever

28

Tap element, role

30th

Cross hole in the inner lever

32

Coupling element, coupling bolt

34

Spring element, coil spring

36a, 36b

Tapping elements, projections on the outer lever

38a, 38b

Sliding surfaces on the outer lever

40

Coupling hole in the outer lever

42

Cross hole in the outer lever

44

Switching element, switching pin

46

Outer end of the shift pin

48

Hinge pin

50a, 50b

Pressure spring, leg spring

52

Gas exchange valve, inlet valve

54

Valve stem

56

Spring plate

58

Valve spring, coil spring

60

Support element

° KW

Crank angle

° NW

Camshaft angle

ΔKW _NH

Angular width of the post lift cam ( 18th ) in ° KW

ΔNW _NH

Angular width of the post lift cam ( 18th ) in ° NW

QUOTES INCLUDE IN THE DESCRIPTION

This list of documents listed by the applicant has been generated automatically and is only included for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• US 2017/0198613 A1 [0003]
• DE 102017101792 B4 [0003, 0027]
• DE 112004001754 B4 [0004]
• DE 102017104629 A1 [0007]

Claims (8)

Method for controlling a variable valve train (2) of an internal combustion engine, which has a switching device for switching the stroke of switchable stroke transmission elements (22) of at least one gas exchange valve (52) with the same function per cylinder from a primary cam (6) of a camshaft (4) to a secondary cam (12a, 12b ), the secondary cam (12a, 12b) having a post-lift cam (18), which is effective in the compression stroke of the respective cylinder, and with a camshaft adjuster for phase adjustment of the camshaft in question (4) relative to a camshaft wheel that is in drive connection with the crankshaft of the internal combustion engine , by means of which the drag torque of the internal combustion engine is reduced when the engine is started, characterized in that the following procedural steps are carried out after the internal combustion engine is switched off and before the engine is started: a) Switching over or preloading switching elements (44) of the switchable rocker arms (22) in the middle ls the switching device into its switching position, in which the stroke curves of the secondary cams (12a, 12b) are transmitted with the secondary lift cams (18) to the associated gas exchange valves (52), b) turning the camshaft (4) by means of the camshaft adjuster from its rest position into at least a direction of rotation up to an angular position up to which at least one rocker arm (22) not previously switched over is reached or swept by an assigned switching window of the valve drive, and c) turning the camshaft (4) back into its rest position by means of the camshaft adjuster. Procedure according to Claim 1 , characterized in that the camshaft (4) is first rotated by the camshaft adjuster by half the angular width (ΔNW _NH / 2 = ΔKW _NH / 4) of the secondary lift cam (18) in a first direction of rotation, then by the entire angular width (ΔNW _NH = ΔKW _NH / 2) of the Nachhubnockens (18) is rotated in the opposite direction, and finally by half the angular width (ΔNW _NH / 2) of the Nachhubnockens (18) is rotated back to its rest position in the first direction of rotation. Procedure according to Claim 1 , characterized in that the camshaft (4) is first rotated by the camshaft adjuster by the angular width (ΔNW _NH = ΔKW _NH / 2) of the secondary lift cam (18) in its main direction of rotation (20), and finally by the angular width (ΔNW _NH ) of the Nachhubnockens (18) against its main direction of rotation (20) is rotated back to its rest position. Procedure according to one of the Claims 1 to 3rd , characterized in that the camshaft (4) is only rotated up to the relevant end stop of the camshaft adjuster if this end stop is reached before the end position of the intended range of rotation angles. Procedure according to Claim 1 , characterized in that after switching off the internal combustion engine and before starting the engine, the rotational angle positions of the camshaft (4) and the camshaft gear or the crankshaft are recorded and stored by means of rotational angle sensors effective when the engine is at a standstill, and that the camshaft (4) is initially adjusted by the camshaft adjuster Angular distance between the switching window of at least one rocker arm (22) not previously switched and the angular position corresponding to the standstill position of the crank mechanism is rotated in the relevant direction of rotation and finally rotated back to its rest position by the same angle of rotation in the opposite direction of rotation. Procedure according to Claim 5 , characterized in that in the presence of two rocker arms (22) not previously switched over, the shift windows of which are in the same direction of rotation as the angular position corresponding to the standstill position of the crank drive, the camshaft (4) by means of the camshaft adjuster initially by the angular distance of the most distant shift window the relevant rocker arm (22) is rotated in this direction of rotation, and is finally rotated back to its rest position by the same angle of rotation in the opposite direction of rotation. Procedure according to Claim 5 , characterized in that when there are two rocker arms that have not previously been switched over and whose shift windows are located in opposite directions of rotation to the rotational angle position corresponding to the standstill position of the crank drive, the camshaft (4) is initially moved by the camshaft adjuster by the angular distance of the shift window lying in a first direction of rotation a rocker arm (22) is rotated in this direction of rotation, then rotated in the opposite direction of rotation by this angle of rotation and the angular distance of the switching window of the other rocker arm (22) lying in the opposite direction of rotation, and finally turned back to its rest position by the last angular distance in the first direction of rotation becomes. Procedure according to one of the Claims 5 to 7 , characterized in that the respective rotation of the camshaft (4) is omitted until the rotational angle position corresponding to the standstill position of the crank mechanism is reached, if the angular distance to the switching window of the relevant one Rocker arm (22) is outside one of the end stops of the camshaft adjuster.

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