EP3418514A1 - Method for switching off a combustion engine and device for same - Google Patents

Abstract

The invention relates to a method for switching off an internal combustion engine. The method includes initiating a shutdown process. The method includes reducing vibration of the internal combustion engine during the shutdown operation by switching actuation of a first exhaust valve (20) of the internal combustion engine by means of a sliding cam system (11) for opening or keeping open in the compression stroke and the exhaust stroke. Alternatively or additionally, the method comprises switching to an engine braking operation in which a first exhaust valve (20) of the internal combustion engine is initially kept closed in the compression stroke and / or exhaust stroke to compress air and before decompression of the compressed air occurs before a top dead center piston movement is opened.

Description

The invention relates to a method for switching off an internal combustion engine and a variable valve train.

From the WO 2014/100185 A1 For example, an engine valve operating device for decompressing a moto cylinder during engine shutdown is known. The system may include a rocker arm pivotally attached to a rocker arm shaft. The system may also include a structure mounted adjacent the rocker arm in a fixed position relative to the rocker arm. A locking piston may be slidably disposed between the rocker arm and the structure. The lock piston may be selectively extended to engage both the rocker arm and the structure to limit pivotal movement of the rocker arm and maintain the engine valves in an open state during the shutdown operation.

The invention is based on the object to provide an alternative or improved method for switching off an internal combustion engine to reduce vibrations during shutdown and a device for this purpose.

The object is achieved by a method and a device according to the independent claims. Advantageous developments are specified in the dependent claims and the description.

The method for shutting down an internal combustion engine includes initiating a shutdown process. The method further includes reducing vibration of the internal combustion engine during the shutdown process by switching actuation of a first exhaust valve of the internal combustion engine by means of a sliding cam system to open or hold open the compression stroke and the exhaust stroke. Alternatively or additionally, the method includes switching to an engine braking operation in which a first exhaust valve of the internal combustion engine is initially kept closed in the compression stroke and / or exhaust stroke for compressing air and is opened to decompress the compressed air before a top dead center piston movement.

By opening the first exhaust valve, in particular in the compression stroke during the shutdown process, a swinging (rocking) of the internal combustion engine prevented or diminished. This leads to a reduced generation of noise during shutdown. The sliding cam system provides a reliable and fast method of switching. When switching to the engine braking mode, the provision of a new means for actuating the first exhaust valve during the shutdown operation may be omitted and the system used for shifting in the engine braking operation. Thus, one and the same system can be used for both the engine braking operation and the shutdown operation.

It is understood that during the shutdown process no fuel is supplied to the cylinders. The operation of the intake valves can in particular remain unchanged.

In a particularly preferred embodiment, the engine is switched into the engine braking mode by means of a variable valve train, in particular a sliding cam system.

In an advantageous development, the sliding cam system has a cam carrier rotatably and axially displaceably arranged on a camshaft of the internal combustion engine with a first cam for normal operation and a camshaft offset in a longitudinal direction of the second cam for engine braking operation and / or actuation of the first exhaust valve during the Shutdown on. The sliding cam system selectively engages the first cam and the first exhaust valve in operative connection or the second cam and the first exhaust valve.

In normal operation, the first exhaust valve is preferably opened only during the exhaust stroke.

In one embodiment, the method further comprises switching from the first cam to the second cam by the shift cam system at the beginning of the shutdown procedure. During the shutdown process, the first exhaust valve is actuated by means of the second cam.

The second cam preferably opens the first exhaust valve in the compression stroke and in the exhaust stroke or keeps the first exhaust valve open in the compression stroke and in the exhaust stroke. Alternatively or additionally, the second cam initially holds the first exhaust valve closed in the compression stroke and / or in the exhaust stroke and opens the first exhaust valve before reaching the top dead center of the piston movement.

In another embodiment, the first exhaust valve is opened between 100 ° CA and 60 ° CA (crank angle) before reaching top dead center. Alternatively or additionally closes the first exhaust valve after opening in the exhaust stroke in the range between the top dead center and 30 ° CA after top dead center. Alternatively or additionally closes the first exhaust valve after opening in the compression stroke in the range between the bottom dead center and 30 ° CA after the bottom dead center. Thus, on the one hand an effective engine braking operation can be displayed and on the other hand, a motor vibration can be reduced during the shutdown of the engine.

In one embodiment variant, the second cam of the sliding cam system remains in operative connection with the first outlet valve at the end of the switch-off operation. Alternatively, at the end of the turn-off operation, the first cam is switched by the sliding cam system. The state of the sliding cam system at the end of the shutdown process can significantly influence a starting process of the internal combustion engine.

In a further embodiment, the method comprises detecting an engine temperature of the internal combustion engine and / or an engine operating time of the internal combustion engine. The switching of the operation of the first exhaust valve of the internal combustion engine by means of the shift cam system for opening or keeping open in the compression stroke and the exhaust stroke and / or the switching to the engine braking operation is performed when the detected engine temperature is less than or equal to a predetermined engine temperature threshold and / or the detected operating time is smaller or equal to a predetermined operating time threshold. This can be dispensed with the (re) circuit, for example, at a low engine temperature.

In one embodiment, the method further includes maintaining a second exhaust valve of the internal combustion engine closed during the shutdown operation. The second exhaust valve is associated with the same cylinder of the internal combustion engine as the first exhaust valve. Thus, a load of the variable valve train can be reduced because not all the exhaust valves of a cylinder are opened against the pressure in the cylinder.

In an advantageous development, the closed-hold of the second exhaust valve has a switchover to a cam-free section of the sliding cam system.

In one embodiment, in a first group of cylinders, by switching the actuation by means of the shift cam system, the first exhaust valve is in the compression stroke and exhaust stroke open or kept open and / or a first group of cylinders of the internal combustion engine is switched during the shutdown in the engine braking operation. In a second group of cylinders, actuation of the exhaust valve during the shutdown operation remains unchanged. Thus, a wear of the (re) switching system can be reduced.

In particular, the first group and / or the second group may have none, one, several or all cylinders.

In an advantageous embodiment, the number of cylinders in the first group and / or the second group is determined as a function of at least one operating parameter of the internal combustion engine, in particular a temperature of the internal combustion engine and / or an operating time of the internal combustion engine. Thus, for example, at a low engine temperature, fewer cylinders may be assigned to the first group.

In a preferred embodiment, an assignment to the first group and / or to the second group takes place in a rolling manner, in particular rolling between successive shutdown processes. Thus, wear of the switching system for the plurality of cylinders can be made uniform.

The invention also relates to a variable valve train for an internal combustion engine of a motor vehicle, in particular a commercial vehicle. The variable valve train has a first exhaust valve, a camshaft and at least one sliding cam system. The sliding cam system has a cam carrier, which is arranged rotatably on the camshaft and axially displaceable and has a first cam and a second cam. The first cam and the second cam are offset in a longitudinal direction of the camshaft. The variable valve train includes a control unit configured to perform the method as disclosed herein.

The term "control unit" refers to a control electronics, which can take over control tasks and / or regulatory tasks depending on the training.

Preferably, the cam carrier is arranged axially displaceable between a first axial position and a second axial position on the camshaft. The valve drive also has a transmission device. In the first axial position of the cam carrier, the transfer device is operatively connected between the first cam and the first exhaust valve. In the second axial position of the cam carrier, the transfer device is operatively connected between the second cam and the first exhaust valve. The first cam is designed for normal operation of the internal combustion engine, in which the first cam keeps the first exhaust valve open in the exhaust stroke. The second cam is designed for an engine braking operation of the internal combustion engine, in which the second cam initially holds the first exhaust valve closed in the compression stroke and / or in the exhaust stroke and opens the first exhaust valve before reaching a top dead center of a piston movement of a piston of the internal combustion engine.

It is understood that while the second cam is engaged with the first transfer device, the intake valve (s) continue to open only during the intake stroke. However, there is no fuel injection and mixture ignition.

The first cam and the second cam may have a different cam contour and / or be arranged offset in relation to one another in a circumferential direction of the cam carrier.

In one embodiment, the cam carrier has a third cam formed like the first cam and a cam free portion. The first cam, the second cam, the third cam and the cam-free portion are arranged offset in a longitudinal direction of the camshaft. In particular, the first cam is adjacent to the second cam and the third cam is adjacent to the cam-free portion. The integration of a third cam and the cam-free portion allows a second exhaust valve to be operated differently during braking operation and during shutdown than the first exhaust valve. In normal operation, however, the second exhaust valve can be operated as the first exhaust valve, since the third cam and the first cam are formed equal.

The cam-free section is also referred to as zero cam. The cam-free portion has a cylinder jacket surface without elevation for actuating the transmission device.

The valve drive preferably has a second outlet valve, which in particular is assigned to the same cylinder as the first outlet valve, and a second transmission device. The second transmission device is in the first axial position of the cam carrier in operative connection between the third cam and the second outlet valve. In the second Axial position of the cam carrier keeps the second transmission device, the second exhaust valve due to the formation of the cam-free portion closed. Here, the cam-free portion may be engaged or disengaged from the second transmission device.

It is understood that the second transmission device in the second axial position of the cam carrier is not in operative connection with any other cam of the cam carrier.

This embodiment has the advantage that only the first exhaust valve is used for the braking operation and during the shutdown. The second exhaust valve remains closed during the entire cycle when the first exhaust valve is used for the braking operation. Thus, the loads on the variable valve train can be reduced. In particular, when opening an exhaust valve against the pressure in the cylinder large surface pressures between the cam and the contact surface of the transmission device arise. In embodiments where both exhaust valves are actuated during braking operation, the variable valve train must be made correspondingly more robust.

In an alternative embodiment, the valve train further comprises a second exhaust valve, which is associated in particular with the same cylinder as the first exhaust valve. In addition, in the first axial position of the cam carrier, the first transmission device is in operative connection between the first cam and the second outlet valve and, in the second axial position, in operative connection between the second cam and the second outlet valve.

The first cam and the third cam may have a same cam contour and / or be aligned (aligned) in a circumferential direction of the cam carrier.

This embodiment has the advantage that both exhaust valves are used for the braking operation. Both exhaust valves are operated via the same transmission device and the same cam.

In one embodiment variant, the cam carrier has a first engagement track for axial displacement of the cam carrier in a first direction. The first engagement track extends in particular spirally.

The first engagement track is configured to axially displace the cam carrier in engagement with an actuator, for example from the first axial position to the second axial position or from the second axial position to the first axial position.

In a particularly preferred embodiment, the first engagement track is arranged in the cam-free portion. In other words, the first engagement track extends in the zero cam.

Such a configuration has the advantage that the cam-free portion is used for a first for the axial displacement. On the other hand, the cam-free section ensures that the second exhaust valve is not opened during engine braking operation and during shutdown. Due to the functional integration, a space for the cam carrier can be reduced.

In a further embodiment variant, the first engagement track and / or the cam-free section is arranged between the first cam and the third cam or at one end of the cam carrier. The arrangement of the cam, the cam-free portion and the first engagement track can be flexibly adapted to the respective requirements.

In one embodiment, the cam carrier has a second engagement track for axially displacing the cam carrier in a second direction opposite to the first direction. The second engagement track is disposed between the first cam and the third cam or at one end of the cam carrier. The second engagement track may in particular extend helically.

The second engagement track is configured to axially displace the cam carrier in engagement with an actuator, for example from the first axial position to the second axial position or from the second axial position to the first axial position. The first and second engagement tracks provide a reliable way to move the cam carrier.

In a further embodiment, the variable valve train includes a first actuator configured to selectively engage the first engagement track for translating the cam carrier in the first direction. Alternatively or additionally, the variable valve drive has a second actuator, which is designed to selectively engage with the second engagement track for displacing the cam carrier in the second direction.

Advantageously, the camshaft has a locking device with an elastically biased element which engages in the first axial position of the cam carrier in a first recess in the cam carrier and engages in the second axial position of the cam carrier in a second recess in the cam carrier.

The locking device has the advantage that the cam carrier can be fixed in the first and second axial position. The cam carrier can thus not move unintentionally along a longitudinal direction of the camshaft.

In a further embodiment, the first transmission device and / or the second transmission device as a lever, in particular a rocker arm or a drag lever, or a plunger is formed. A drag lever can be used for example in an overhead camshaft. A rocker arm can be used, for example, in an underlying camshaft.

In a further embodiment, the camshaft is arranged as an overhead camshaft or an underlying camshaft. Alternatively or additionally, the camshaft is part of a double camshaft system, which additionally has a further camshaft for actuating at least one inlet valve.

In a further embodiment, the camshaft for the exhaust valve (s) and / or the further camshaft for the intake valve (s) may comprise a phaser. The phase adjuster is designed to adjust a rotational angle of a camshaft relative to a rotational angle of a crankshaft. Thus, the phaser allows an adjustment of the timing for the respective valves. The phase adjuster can be designed, for example, as a hydraulic phase adjuster, in particular as a swivel motor phaser. Such an embodiment has the advantage that the flexibility of the system is further enhanced by the combination with the displaceable cam carrier.

In a further embodiment, the second cam is designed so that the first exhaust valve is opened after opening in the compression stroke with a larger valve lift than after opening in Ausschiebetakt. Alternatively or additionally, the second cam is designed so that the first exhaust valve is opened with a smaller valve lift than in the first cam. The provision of multi-stage valve lifts that are smaller than the Valve strokes during normal operation reduces the load on the valve train. In particular, when opening an exhaust valve against the pressure in the cylinder, the valve train is heavily loaded.

In embodiments where the second cam is also used to actuate the second exhaust valve, the embodiments herein relating to the action of the second cam on the first exhaust valve are equally applicable to the second exhaust valve. In embodiments where the third cam is used to actuate the second exhaust valve, the embodiments herein relating to the action of the first cam on the first exhaust valve apply equally to the third cam and the second exhaust valve.

In addition, the invention relates to a motor vehicle, in particular commercial vehicle, with a variable valve train as disclosed herein. The commercial vehicle may be, for example, a bus or a truck.

Figur 1

eine perspektivische Ansicht eines beispielhaften variablen Ventiltriebs;

Figur 2

eine weitere perspektivische Ansicht des beispielhaften variablen Ventiltriebs;

Figur 3

eine Draufsicht auf eine Nockenwelle des beispielhaften variablen Ventiltriebs;

Figur 4

eine Längsschnittansicht der Nockenwelle von Figur 3 entlang der Linie A-A;

Figur 5

ein beispielhaftes Ventilsteuerungsdiagramm des variablen Ventiltriebs;

Figur 6A

eine erste Querschnittansicht der Nockenwelle von Figur 4 entlang der Linie B-B;

Figur 6B

eine zweite Querschnittansicht der Nockenwelle von Figur 4 entlang der Linie C-C;

Figur 7

ein beispielhaftes Verfahren zum Abschalten eines Verbrennungsmotors gemäß der vorliegenden Offenbarung; und

Figur 8

ein Diagramm, das verschiedene Motordrehzahlverläufe, Turboladerdrehzahlverläufe und Ladedruckverläufe in Abhängigkeit von der Zeit zeigt.

The preferred embodiments and features of the invention described above can be combined with one another as desired. Further details and advantages of the invention will be described below with reference to the accompanying drawings. Show it:

FIG. 1

a perspective view of an exemplary variable valve train;

FIG. 2

another perspective view of the exemplary variable valve train;

FIG. 3

a plan view of a camshaft of the exemplary variable valve train;

FIG. 4

a longitudinal sectional view of the camshaft of FIG. 3 along the line AA;

FIG. 5

an exemplary valve timing diagram of the variable valve train;

FIG. 6A

a first cross-sectional view of the camshaft of FIG. 4 along the line BB;

FIG. 6B

a second cross-sectional view of the camshaft of FIG. 4 along the line CC;

FIG. 7

an exemplary method for shutting down an internal combustion engine according to the present disclosure; and

FIG. 8

a diagram showing various engine speed curves, turbocharger speed curves and charge pressure curves as a function of time.

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

The following is with reference to the FIGS. 1 to 6B First, a particularly preferred embodiment of a variable valve train is described, which is suitable both for carrying out the method for switching off the internal combustion engine disclosed herein and for performing an engine braking operation. The internal combustion engine can be comprised, in particular, in a motor vehicle, preferably a commercial vehicle, for example a bus or a lorry. Subsequently, referring to the FIGS. 7 and 8th in particular, the method for switching off the internal combustion engine described. The method may utilize the variable valve train or other variable valve train disclosed herein, in particular with a modified shift cam system.

In the FIGS. 1 and 2 a variable valve train 10 is shown. The variable valve train 10 has a camshaft 12 and a cam carrier 14. In addition, the variable valve train 10 has first and second transfer devices 16 and 18 and first and second exhaust valves 20 and 22. In addition, the variable valve drive 10 has a first actuator 24 and a second actuator 26. The cam carrier 14, the transmission devices 16 and 18 and the actuators 24 and 26 form a sliding cam system 11.

The camshaft 12 is formed as an output camshaft which actuates output valves 20 and 22. The camshaft 12 is part of a dual camshaft system (not shown in detail) that additionally includes an intake camshaft (not shown) for actuating one or more intake valves. The camshaft 12 is disposed in common with the intake camshaft as the overhead camshaft. The camshaft 12 and the intake camshaft thus form a so-called DOHC system (double overhead camshaft). Alternatively, the camshaft 12 could also form a so-called SOHC system (single overhead camshaft). In other embodiments, the camshaft 12 may also be arranged as an underlying camshaft.

On the camshaft 12 of the cam carrier 14 is arranged rotationally fixed. The cam carrier 14 is additionally arranged axially displaceable along a longitudinal axis of the camshaft 12. The cam carrier 14 may be axially displaceable between a first stop 28 and a second stop 30.

With reference to the FIGS. 1 to 4 the cam carrier 14 is described below. The cam carrier 14 has three cams 32, 34 and 36 which are offset from each other in a longitudinal direction of the cam carrier 14 and the camshaft 12. The first cam 32 is disposed at a first end of the cam carrier 14 and configured for normal operation, as described in detail later by way of example. The second cam 34 is disposed adjacent to the first cam 32 and configured for engine braking operation, as also described in detail later by way of example. The engine braking operation may be used to slow down and / or brake the motor vehicle when going downhill. The engine braking operation may be used in addition to reducing the vibration of the engine when switching off. The third cam 36 is spaced from the second cam 34 and the second end of the cam carrier 14. The third cam 36 is designed for normal operation. The third cam 36 is shaped like the first cam 32.

The cam carrier 14 also has a first cam-free section 38 and a second cam-free section 40. The first cam-free portion 38 is disposed at the second end of the cam carrier 14. The second cam-free portion 40 is disposed between the second cam 34 and the third cam 36. In the first cam-free portion 38, a first engagement track (shift gate) 42 extends spirally about a longitudinal axis of the cam carrier 14. In the second cam-free portion 40, a second engagement track (shift gate) 44 extends spirally around the longitudinal axis of the cam carrier 14th

For displacing the cam carrier 14 between the stops 28 and 30, the actuators 24 and 26 (FIGS. FIGS. 1 and 2 ) with extendable elements (not shown in detail) selectively engage in the engaging tracks 42, 44. Specifically, the first actuator 24 may selectively engage the first engagement track 42 for shifting the cam carrier 14 from one axial position to another axial position. In a first axial position of the cam carrier 14 abuts against the second stop 30. In a second axial position of the cam carrier 14 abuts against the first stop 28. In the FIGS. 1 to 4 the cam carrier is shown in the first axial position. The second actuator 26 in turn can selectively engage in the second engagement track 44. Then, the cam carrier 14 is shifted from the first axial position to the second axial position. The first actuator 24 and the second actuator 26 are controlled by a schematically illustrated control unit 27 (FIG. FIGS. 1 and 2 ).

The displacement is triggered by the fact that the extended element of the respective actuator 24, 26 is stationary with respect to an axial direction of the camshaft 12. Consequently, the slidable cam carrier 14 due to the spiral shape of the engaging tracks 42, 44 in a Longitudinal direction of the camshaft 12 is displaced when the extended element engages in the respective engagement track 42, 44. At the end of the sliding operation, the displaceable element of the respective actuator 24, 26 is guided by the respective engagement track 42, 44 opposite to the extension direction and thus retracted. The displaceable element of the respective actuator 24, 26 comes out of engagement with the respective engagement track 42, 44th

The first transmission device 16 and the second transmission device 18 (FIG. FIGS. 1 and 2 ) establish an operative connection between the cam carrier 14 and the outlet valves 20, 22. The first exhaust valve 20 is operated (opened) when the first cam 32 or the second cam 34 pushes the first transmission device 16 down. The second exhaust valve 22 is operated (opened) when the third cam 36 presses the second transmission device 18 down.

Is the cam carrier 14 in the first axial position (as in the FIGS. 1 to 4 1), the first transfer device 16 is operatively connected between the first cam 32 and the first exhaust valve 20. In other words, the first transfer device 16 in the first axial position of the cam carrier 14 is not operatively connected between the second cam 34 and the first exhaust valve 20. The first exhaust valve 20 is operated in accordance with a contour of the first cam 32. In the second axial position of the cam carrier 14, the first transmission device 16 is operatively connected between the second cam 34 and the first exhaust valve 20. The first exhaust valve 20 is operated in accordance with a contour of the second cam 34.

In the first axial position of the cam carrier 14, the second transfer device 18 is operatively connected between the third cam 36 and the second exhaust valve 22. The second exhaust valve 22 is operated in accordance with a contour of the third cam 36. In the second axial position of the cam carrier 14, the second transfer device 18 does not actuate the second exhaust valve 22. In the second axial position of the cam carrier 14, a contact portion 18A of the second transmission device 18 is at the same axial position with respect to the camshaft 12 as the first cam-free portion 38. The first cam-free portion 38 has no protrusion for actuating the second transmission device 18. When the cam carrier 14 is in the second axial position, the second exhaust valve 22 is not actuated.

The first cam-free portion 38 thus has two functions. On the one hand, the first cam-free section 38 receives the first guide track 42. On the other hand, the first cam-free Section 38 that no actuation of the second exhaust valve 42 in the second axial position of the cam carrier 14 takes place. This functional integration is favorable for space reasons.

In the illustrated embodiment, the first transmission device 16 and the second transmission device 18 are each formed as a drag lever. In other embodiments, the transfer devices 16 and 18 may be formed as rocker arms or plungers. In some embodiments, the transfer devices 16 and 18 may include cam followers, for example in the form of rotatable rollers.

With reference to FIG. 4 a locking device 46 is shown. The locking device 46 has an elastic element 48 and a blocking body 50. The elastic element 48 is arranged in a blind hole of the camshaft 12. The elastic member 48 biases the locking body 50 against the cam carrier 14. In an inner peripheral surface of the cam carrier 14, first and second recesses 52 and 54 are arranged. To lock the cam carrier 14, the locking body 50 is pressed into the first recess 52 when the cam carrier 14 is in the first axial position. In the second axial position of the cam carrier 14, the blocking body 50 is pressed into the second recess 54.

With reference to FIG. 5 are described below, the control of the first exhaust valve 20 and its influence on a cylinder pressure. FIG. 5 shows a complete four-stroke cycle consisting of compression, expansion, ejection and suction.

The curve A describes the profile of the cylinder pressure in engine braking operation when the second cam 34 is in operative connection with the first exhaust valve 20. The curve B shows the course of the valve lift of the first exhaust valve 20 when the first cam 32 is in communication with the first exhaust valve 20 (i.e., during normal operation). The third curve C shows the course of the valve lift of an intake valve both during normal operation and in engine braking operation. The curve D shows the course of the valve lift of the first exhaust valve 20 when the second cam 34 is in operative communication with the first exhaust valve 20 (i.e., during engine braking operation).

Curve B shows that the exhaust valve is open during normal operation during the exhaust stroke. The curve C shows that the intake valve is open in normal operation and in braking operation during the intake stroke (intake stroke).

The curve D shows that the exhaust valve at the end of the compression stroke in the range of top dead center at about 60 ° CA to 100 ° CA before top dead center is slightly opened. At top dead center, the exhaust valve is opened further and closes at the end of the expansion stroke approximately at bottom dead center. The opening of the exhaust valve at the end of the compression stroke causes the compressed air in the cylinder to be pushed through the opened exhaust valve into the exhaust system through the piston moving toward top dead center. The compression work previously done brakes the crankshaft and thus the internal combustion engine. The cylinder pressure initially increases in the compression stroke, but then drops due to the opening of the exhaust valve even before top dead center (see curve A). The open exhaust valve during the expansion stroke causes air from the exhaust pipes to be drawn back into the cylinder. At the end of the expansion stroke, the cylinder is substantially filled with air from the exhaust system.

The curve D also shows that the exhaust valve initially remains closed after reaching bottom dead center at the end of the expansion stroke. At the end of the Ausschiebetaktes the exhaust valve opens in the region of top dead center. The opening is again at about 60 ° CA to 100 ° CA before top dead center. The closed exhaust valve during the exhaust stroke causes the air sucked in the expansion stroke to be compressed by performing work. The cylinder pressure increases (curve A). The Verstellungsarbeit brakes the crankshaft and thus the internal combustion engine. The opening of the exhaust valve at the end of the exhaust stroke causes the air to be pushed into the exhaust system through the opened exhaust valve. In the intake stroke, the cylinder is again filled with air through the or the open intake valves (curve C). The cycle starts again.

As explained above, the use of the second cam to control the exhaust valve results in a double compression with subsequent decompression, thus ensuring engine braking functionality. In addition, when the engine braking operation is set during the engine shutdown, vibration of the internal combustion engine is reduced because engine vibration in the compression stroke due to the opening of the exhaust valve before reaching top dead center is reduced.

As can be seen when comparing curves B and D, the valve lift of the exhaust valve is lower in braking mode (curve D) than in normal mode (curve B). The valve lift is also in two stages when opening the exhaust valve in the compression and expansion stroke. These measures cause the load of the variable valve train is reduced during braking operation, as by the opening of the exhaust valve against the pressure in the cylinder can occur high loads on the valve train.

The FIG. 6A shows a cross section through the second cam 34th Die FIG. 6B shows a cross section through the first cam 32nd

The second cam 34 is to obtain the curve D from FIG. 5 educated. For this purpose, the second cam 34 in particular has a first elevation 34A, a second elevation 34B and a third elevation 34C. The first, second and third elevations 34A-34C are circumferentially offset around the second cam 34. The first bump 34A leads to the opening of an exhaust valve at the end of the compression stroke. The second bump 34B extending from the first bump 34A results in an expanded opening of an exhaust valve during the expansion stroke. The third bump 34C leads to an opening of an exhaust valve at the end of the exhaust stroke.

The first protrusion 34A has the smallest height of the protrusions 34A-34C measured in a radial direction of the camshaft 12. The second protrusion 34B has the largest height of the protrusions 34A-34C measured in a radial direction of the camshaft 12. The third protrusion 34C is smaller than that second bump 34B and larger than the first bump 34A. Different heights of the elevations 34A-34C lead to correspondingly different valve lifts (cf. FIG. 5 ).

The first, second and third elevations 34A-34C are each arranged circumferentially offset from a protrusion 32A of the first cam 32. The first cam 32 is for obtaining the curve B from FIG. 5 educated. The protrusion 32A of the first cam 32 leads to an opening of an exhaust valve during the Ausschiebetaktes. The protrusion 32A is measured higher in a radial direction of the camshaft 12 than the protrusions 34A-34C. The valve lift through the bump 32A is greater than through the bumps 34A-34C.

The FIG. 6B also shows the locking device 46 with the elastic member 48, the locking body 50 and the first recess 52nd

The following is with reference to the FIGS. 7 and 8th an exemplary method for switching off an internal combustion engine described.

In step S100, a shutdown process is initiated. This can be done for example by turning an ignition key or by pressing an off button.

Once the shutdown has been initiated, an engine braking operation may be initiated. This can be done on the second cam 34 (see, for example FIG. 1 ) are switched in step S102. It is possible that in all cylinders of the internal combustion engine or only in a part of the cylinder, a changeover is made.

The switching on the second cam 34 causes the first exhaust valve 20 is now kept closed in the compression stroke and the exhaust stroke and opened before reaching the top dead center of the piston movement for decompression of the compressed air.

In the FIG. 8 For example, the displacement motion (vibration) I of the internal combustion engine over the time t during the shutdown operation for a usual shutdown operation (dotted line E) and a shutdown operation according to the present disclosure (solid line F) are shown. First, the internal combustion engine is in an idling in the range t1. At a time T1, the shutdown process is initiated. In the area t2 the respective shutdown process is shown.

During the normal switch-off process, the combustion engine starts to oscillate after the start of the switch-off process. The unwanted swing results from the circumstances that the cylinders are on the one hand in different cycles and on the other hand, all valves are closed during compression in the compression stroke.

In the turn-off operation according to the present disclosure, the vibration of the engine can be reduced or prevented. By switching to the second cam 34, the first exhaust valve 20 is opened in the compression stroke before reaching top dead center. That is, not all valves are closed in the compression stroke, which at least reduces a swinging. This is qualitatively indicated by the solid line in FIG. 8 shown. The remaining oscillatory motion results from the energy of the flywheel of the engine and the inertia of the system.

The first exhaust valve 20 can be operated with the second cam 34 until the internal combustion engine stops. However, it is also possible that, for example, falls below a predetermined engine speed threshold (step S106) at the end of the shutdown again to the first cam 32 is switched (step S108). The position of the shift cam system 11 at the end of the turn-off operation may have an influence on a start of the internal combustion engine.

The method disclosed here for switching off the internal combustion engine can be modified and / or supplemented in a variety of ways.

For example, it is possible for the shift cam system 11 to shift multiple cylinders into engine braking during the shutdown procedure. The more cylinders are switched to the engine braking operation, the better it can prevent or reduce a swinging of the engine.

The number of shift cam systems 11 which switch to engine braking operation during the shutdown operation may be determined in dependence on at least one operating parameter of the internal combustion engine. The operating parameter may in particular be a temperature of the internal combustion engine and / or an operating time of the internal combustion engine. Thus, for example, at a comparatively low temperature of the internal combustion engine and a short operating time of the internal combustion engine, a (slight) swinging up of the internal combustion engine can rather be accepted. It is also possible that no shift cam system 11 switches to engine braking operation in response to a low temperature of the engine and / or a short operating time of the engine.

In embodiments in which a group of cylinders is switched to engine braking during the shutdown process and a second group of cylinders is not switched to engine braking during the shutdown operation, assignment to the groups may be accomplished by rolling. The rolling assignment can be done during a shutdown or preferably between different shutdowns. Thus, wear under the sliding cam systems 11 of the plurality of cylinders can be made uniform.

As explained above, the method of shutting down the engine may use the shift cam system 11. In particular, the control unit 27, the actuators 24 and 26 (see FIG. 1 ) according to the herein disclosed method for switching off the internal combustion engine. However, the method may also employ another shift cam system having a switchover between a first cam for normal operation and a second cam for a shutdown operation. The second cam may for example also be designed so that it is specially designed for the shutdown and in particular keeps at least one exhaust valve of the cylinder open at least during the compression stroke and the Ausschubtaktes.

The invention is not limited to the preferred embodiments described above. Rather, a variety of variants and modifications is possible, which also make use of the inventive idea and therefore fall within the scope. In particular, the invention also claims protection of the subject matter and the features of the subclaims independently of the claims referred to.

LIST OF REFERENCE NUMBERS

10

Variable valve train

11

Sliding cam system

12

camshaft

14

cam support

16

First transmission device (first drag lever)

18

Second transmission device (second drag lever)

18A

contact area

20

First exhaust valve

22

Second exhaust valve

24

First actor

26

Second actor

27

control unit

28

First stop

30

Second stop

32

First cam

32A

survey

34

Second cam

34A-34C

surveys

36

Third cam

38

First cam-free section

40

Second cam-free section

42

First intervention lane

44

Second intervention lane

46

locking device

48

Elastic element

50

blocking body

52

First recess

54

Second recess

A

cylinder pressure

B

Auslassventilsteuerkurve

C

Inlet valve cam

D

Auslassventilsteuerkurve

t

timeline

T1

switch-off

t1

first range (engine idling)

t2

second area (shutdown)

I

Deflection / Vibration

e

Vibration course with ordinary shutdown

F

Vibration history at shutdown according to method disclosed herein

Claims (15)

A method for switching off an internal combustion engine, comprising: Initiating a shutdown process; and Reducing a vibration of the internal combustion engine during the shutdown by: a) switching an operation of a first exhaust valve (20) of the internal combustion engine by means of a sliding cam system (11) for opening or keeping open in the compression stroke and in the exhaust stroke; and or b) switching to an engine braking operation in which a first exhaust valve (20) of the internal combustion engine is initially kept closed in the compression stroke and / or exhaust stroke for compression of air and is opened before decompression of the compressed air before reaching a top dead center of a piston movement. The method of claim 1, wherein by means of a variable valve train (10), in particular a sliding cam system (11), the internal combustion engine is switched to the engine braking mode. Method according to claim 1 or claim 2, wherein the sliding cam system (11) comprises a cam carrier (14) arranged rotationally fixedly and axially displaceably on a camshaft (12) of the internal combustion engine with a first cam (32) for normal operation and one in a longitudinal direction of the camshaft ( 12) staggered second cams (34) for engine braking operation and / or actuation of the first exhaust valve (20) during the shutdown operation, wherein the shift cam system (11) selectively operatively connects the first cam (32) and the first exhaust valve (20) sets or sets the second cam (34) and the first outlet valve (20) in operative connection. The method of claim 3, further comprising: Switching from the first cam (32) to the second cam (34) through the sliding cam system (11) at the beginning of the shutdown operation; and Actuating the first exhaust valve (20) by means of the second cam (34) during the shutdown operation. The method of claim 4, wherein: the second cam opens or holds open the first outlet valve (20) in the compression stroke and in the exhaust stroke; and or the second cam initially holds the first exhaust valve (20) closed in the compression stroke and / or in the exhaust stroke and opens the piston movement before reaching top dead center. Method according to one of the preceding claims, wherein: the first exhaust valve (20) opens between 100 ° CA and 60 ° CA before reaching top dead center; and or the first exhaust valve (20) closes after opening in the exhaust stroke in the range between the top dead center and 30 ° CA after top dead center; and or the first exhaust valve (20) closes after opening in the compression stroke in the range between the bottom dead center and 30 ° CA after bottom dead center. Method according to one of the preceding claims, wherein: at the end of the turn-off operation, the second cam (34) of the sliding cam system (11) remains in operative communication with the first exhaust valve (20); or is switched on the first cam (32) by the sliding cam system (11) at the end of the shutdown. The method of any one of the preceding claims, further comprising: Detecting an engine temperature of the internal combustion engine and / or an engine operating time of the internal combustion engine; wherein the switching of the operation of the first exhaust valve (20) of the internal combustion engine by means of the sliding cam system (11) for opening or keeping open in the compression stroke and in the exhaust stroke and / or the switching to the engine braking operation is carried out if: the detected engine temperature is less than or equal to a predetermined engine temperature threshold; and or the detected operating time is less than or equal to a predetermined operating time threshold. The method of any one of the preceding claims, further comprising:
Keeping a second exhaust valve (22) of the internal combustion engine closed during the shut-off operation, wherein the second exhaust valve (22) is associated with the same cylinder of the internal combustion engine as the first exhaust valve (20). The method of claim 9, wherein closing the second exhaust valve (22) comprises switching to a cam-free portion (38) of the push cam system (11). Method according to one of the preceding claims, wherein in a first group of cylinders, by switching actuation by means of the shift cam system (11), the first exhaust valve (20) opens or stays open in the compression stroke and exhaust stroke and / or a first group of cylinders of the internal combustion engine is switched to the engine braking mode during the shutdown process; and or in a second group of cylinders, actuation of the exhaust valve (20) during the shutdown process remains unchanged. The method of claim 11, wherein a number of cylinders in the first group and / or the second group in dependence on at least one operating parameter of the internal combustion engine, in particular a temperature of the internal combustion engine and / or an operating time of the internal combustion engine is determined. The method of claim 11 or claim 12, wherein an assignment to the first group and / or the second group rolling, in particular rolling between successive shutdown occurs. Variable valve train (10) for an internal combustion engine of a motor vehicle, in particular a commercial vehicle, comprising: a first exhaust valve (20); a camshaft (12); a sliding cam system (11) having a cam carrier (14) rotatably mounted on the camshaft (12) and axially displaceable and having a first cam (32) and a second cam (34), wherein the first cam (32) and the second cams (34) are offset in a longitudinal direction of the camshaft (12); and a control unit (27) adapted to carry out the method according to one of the preceding claims. Motor vehicle, in particular utility vehicle, with a variable valve train (10) according to claim 14.

Images