CN108952876B

CN108952876B - Method for shutting down an internal combustion engine and associated device

Info

Publication number: CN108952876B
Application number: CN201810480049.XA
Authority: CN
Inventors: 斯蒂芬·希尔施曼; 托马斯·玛丽斯澈威思科; 多米尼克·赫那
Original assignee: MAN Truck and Bus SE
Current assignee: MAN Truck and Bus SE
Priority date: 2017-05-18
Filing date: 2018-05-18
Publication date: 2022-05-24
Anticipated expiration: 2038-05-18
Also published as: BR102018009328A2; EP3418514A1; RU2018118229A; DE102017004781A1; BR102018009328A8; RU2018118229A3; RU2757699C2; CN108952876A; EP3418514B1

Abstract

The invention relates to a method for switching off an internal combustion engine. The method includes initiating a shut-down procedure. The method comprises reducing the vibration of the internal combustion engine during the shut-down procedure by: the actuation of a first exhaust valve (20) of the internal combustion engine is switched by means of a sliding cam system (11) in order to open or remain open during the compression stroke and the exhaust stroke. Alternatively or additionally, the method comprises: switching to an engine braking mode, wherein a first exhaust valve (20) of the internal combustion engine is initially closed in the compression stroke and/or in the exhaust stroke in order to compress air and is opened before the top dead center of the piston movement is reached in order to decompress the compressed air.

Description

Method for shutting down an internal combustion engine and associated device

Technical Field

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

Background

An engine valve actuating device for depressurizing an engine cylinder during engine shut-off is known from WO 2014/100185 a 1. The system may include a rocker swingably disposed on a rocker shaft. The system may also have a structure that is disposed in a fixed position relative to the rocker adjacent to the rocker. A locking piston may be slidably disposed between the rocker and the structure. The lockout piston is selectively extendable to engage the rocker arm with the structure to limit the rocking motion of the rocker arm and to maintain the engine valve in an open condition during a shut-off procedure.

Disclosure of Invention

The object of the present invention is to propose an alternative or improved method for switching off an internal combustion engine and a corresponding device in order to reduce vibrations during switching off.

This object is achieved by a method and an apparatus according to the independent claims. Advantageous developments are given in the dependent claims and in the description.

A method for shutting down an internal combustion engine includes initiating a shut down procedure. The method further comprises the following steps: by switching the actuation of the first exhaust valve of the internal combustion engine by means of the sliding cam system in such a way that it opens or remains open during the compression stroke and the exhaust stroke, the vibrations of the internal combustion engine during the switching-off process are reduced. Alternatively or additionally, the method comprises: a switching operation is carried out to an engine braking mode, in which the first exhaust valve of the internal combustion engine is initially closed in the compression stroke and/or in the exhaust stroke in order to compress the air and is opened before the top dead center of the piston movement is reached in order to decompress the compressed air.

By opening the first exhaust valve during the shut-off process, in particular during the compression stroke, the starting oscillation (rocking back and forth) of the internal combustion engine can be prevented or reduced. This results in reduced noise generation during the shut-down. The sliding cam system provides a reliable and fast method for switching. If switching to engine braking operation is made, a new device for actuating the first exhaust valve during the switching-off process can be dispensed with, and the system is used for switching to engine braking operation. The same system can thus be used both for engine braking operation and for the shut-down procedure.

It goes without saying that during the shut-off process, no fuel is supplied to the individual cylinders. The operation of the inlet valves can in particular remain unchanged.

In a particularly preferred embodiment, the switching to the engine braking mode takes place by means of a variable valve drive of the internal combustion engine, in particular a sliding cam system.

In an advantageous development, the sliding cam system has a cam carrier arranged on a camshaft of the internal combustion engine in a rotationally fixed and axially displaceable manner, with a first cam for normal operation and a second cam arranged offset in the longitudinal direction of the camshaft for engine braking operation and/or for actuating the first exhaust valve during a switching-off operation. The sliding cam system selectively places the first cam in operative connection with the first exhaust valve or the second cam in operative connection with the first exhaust valve.

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

In one embodiment, the method further comprises: at the beginning of the switching-off process, the first cam is switched to the second cam by means of a sliding cam system. During the switching off process, the first exhaust valve is actuated by means of the second cam.

Preferably, the second cam opens the first exhaust valve during the compression stroke and the exhaust stroke or maintains the first exhaust valve open during the compression stroke and the exhaust stroke. Alternatively or additionally, the second cam initially keeps the first exhaust valve closed during the compression stroke and/or the exhaust stroke and opens the first exhaust valve before top dead center of piston movement is reached.

In another embodiment, the first exhaust valve is opened between 100 ° KW and 60 ° KW (crank angle) before top dead center is reached. Alternatively or additionally, in the exhaust stroke, the first exhaust valve closes after opening in a region between top dead center and 30 ° KW after top dead center. Alternatively or additionally, in the compression stroke, the first exhaust valve closes after opening in a region between bottom dead center and 30 ° KW after bottom dead center. This makes it possible to produce an efficient engine braking operation on the one hand and to reduce engine vibrations during the switching off of the internal combustion engine on the other hand.

In one embodiment, the second cam of the sliding cam system is held in operative connection with the first exhaust valve at the end of the shut-off operation. Alternatively, at the end of the cutting process, the sliding cam system is switched to the first cam. The state of the sliding cam system at the end of the shut-off process can decisively influence the starting process of the internal combustion engine.

In another design variation, the method includes: the engine temperature of the internal combustion engine and/or the engine operating time of the internal combustion engine are detected. 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 actuation of the first exhaust valve of the internal combustion engine is switched by means of the sliding cam system to open or remain open during the compression stroke and the exhaust stroke and/or to an engine braking operation. This makes it possible, for example, to dispense with (repeat) switching when the engine temperature is low.

In one embodiment, the method further comprises: the second exhaust valve of the internal combustion engine is kept closed during the shut-off. The second exhaust valve is assigned to the same cylinder of the internal combustion engine as the first exhaust valve. The load on the variable valve gear can thereby be reduced, since not all of the outlet valves of the cylinder are opened against the pressure in the cylinder.

In an advantageous refinement, the keeping closed of the second outlet valve comprises: switching to a camless section of the sliding cam system.

In one embodiment, the first exhaust valve is opened or held open during the compression stroke and the exhaust stroke by switching actuation by means of a sliding cam system for the first group of cylinders, and/or the first group of cylinders of the internal combustion engine is switched into engine braking operation during the switching-off process. For the second group of cylinders, the actuation of the exhaust valves remains unchanged during the switching-off process. Wear of the (repeated) switching system can thereby be reduced.

In particular, the first and/or second group may have no cylinders, one, more 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 the temperature of the internal combustion engine and/or the operating time of the internal combustion engine. Thus, for example, when the engine temperature is low, fewer cylinders may be assigned to the first group.

In a preferred embodiment, the assignment of the first group and/or the second group takes place in a rolling manner, in particular between successive shut-off processes. This makes it possible to equalize the wear of the switching system for a plurality of cylinders.

The invention also relates to a variable valve gear for an internal combustion engine of a motor vehicle, in particular a commercial vehicle. The variable valve gear 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 on a camshaft in a rotationally fixed and axially displaceable manner and which has a first cam and a second cam. The first cam and the second cam are arranged offset in the longitudinal direction of the camshaft. The variable valve gear has a control unit which is designed to carry out the method as disclosed herein.

The term "control unit" is intended to mean an electronic control unit which, depending on the design, can assume control and/or regulating tasks.

Preferably, the cam carrier is arranged on the camshaft so as to be axially displaceable between a first axial position and a second axial position. The valve gear also has a transmission. In a first axial position of the cam carrier, the transmission device is in operative connection between the first cam and the first exhaust valve. In the second axial position of the cam carrier, the transmission device is in operative connection between the second cam and the first exhaust valve. The first cam is configured 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 keeps the first exhaust valve closed in the compression stroke and/or in the exhaust stroke and opens the first exhaust valve before the top dead center of the piston movement of the piston of the internal combustion engine is reached.

It goes without saying that during the engagement of the second cam with the first transmission, the one or more inlet valves are still open only during the inlet stroke. But no fuel induction and mixture ignition occurs.

The first cam and the second cam may have different cam profiles and/or be arranged offset from one another in the circumferential direction of the cam carrier.

In one embodiment, the cam carrier has a third cam configured as the first cam, and has a camless section. The first cam, the second cam, the third cam and the camless section are arranged offset in the longitudinal direction of the camshaft. In particular, the first cam abuts the second cam and the third cam abuts the camless segment. The integration of the third cam and the camless section makes it possible for the second exhaust valve to be actuated in braking mode and during the switch-off mode differently from the first exhaust valve. In normal operation, however, the second exhaust valve can be actuated like the first exhaust valve, since the third cam and the first cam are identical in shape.

The camless segment is also referred to as a zero cam. The camless section has a cylinder housing face without a protuberance for actuating the transmission.

The valve drive preferably has a second exhaust valve, which is assigned in particular to the same cylinder as the first exhaust valve, and a second transmission device. The second transmission device is located in the operative connection between the third cam and the second exhaust valve in the first axial position of the cam carrier. In the second axial position of the cam carrier, the second transmission device keeps the second exhaust valve closed because of the cam-free section. In this case, the camless section may be engaged or disengaged with the second transmission.

It goes without saying that the second transmission device is not in operative connection with the other cams of the cam carrier in the second axial position of the cam carrier.

This design has the following advantages: only the first exhaust valve is used for braking operation and during shut-down. When the first exhaust valve is used for braking operation, the second exhaust valve remains closed throughout the cycle. This makes it possible to reduce the load on the variable valve gear. In particular, when the exhaust valve opens counter to the pressure in the cylinder, a large surface pressure is generated between the contact surfaces of the cam and the gear. In the case of a design in which both exhaust valves are actuated during a braking operation, the variable valve drive must be designed accordingly to be more robust.

In an alternative embodiment, the valve drive also has a second exhaust valve, which is assigned in particular to the same cylinder as the first exhaust valve. The first transmission device is additionally in the operative connection between the first cam and the second exhaust valve in a first axial position of the cam carrier and additionally in the operative connection between the second cam and the second exhaust valve in a second axial position.

The first cam and the third cam may have the same cam profile and/or be arranged in circumferential alignment with each other.

This design has the following advantages: two exhaust valves are used for braking operation. Both exhaust valves are actuated by the same transmission and the same cam.

In one design variant, the cam carrier has a first engagement track for axially moving the cam carrier in a first direction. The first engagement track extends in particular helically.

The first engagement track is configured to move the cam carrier axially, e.g., from a first axial position to a second axial position, or from the second axial position to the first axial position, in engagement with the actuator.

In a particularly preferred embodiment, the first engagement track is provided in a camless section. In other words, the first engagement track extends in the zero cam.

This design provides the following advantages: the camless section is used for axial displacement on the one hand. On the other hand, the cam-free section ensures that the second exhaust valve is not opened during engine braking operation and during the shut-off period. By this integration of functions, the installation space of the cam carrier can be reduced.

In a further design variant, the first engagement track and/or the camless 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 camless segment 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 moving the cam carrier in a second direction opposite 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 move the cam carrier axially, e.g., from a first axial position to a second axial position, or from the second axial position to the first axial position, in engagement with the actuator. The first and second engagement tracks provide a reliable possibility for moving the cam carrier.

In another embodiment, the variable valve gear has a first actuator configured to selectively move the cam carrier in a first direction in engagement with the first engagement track. Alternatively or additionally, the variable valve gear has a second actuator configured to selectively move the cam carrier in the second direction in engagement with the second engagement track.

Advantageously, the camshaft has a locking device with an elastic prestressing element which projects into a first recess in the cam carrier in a first axial position of the cam carrier and into a second recess in the cam carrier in a second axial position of the cam carrier.

The locking device has the following advantages: the cam carrier may be fixed in first and second axial positions. The cam carrier thus cannot be inadvertently displaced in the longitudinal direction of the camshaft.

In a further embodiment, the first transmission device and/or the second transmission device is designed as a lever, in particular as a rocker or cam follower (Schlepphebel) or as a tappet. The cam follower may be applied, for example, to an overhead camshaft. The rocker arm can be applied, for example, to a bottom mounted camshaft.

In a further design variant, the camshaft is provided as an overhead camshaft or as a bottom camshaft. Alternatively or additionally, the camshaft is part of a dual camshaft system, which additionally has a further camshaft for actuating at least one intake valve.

In a further embodiment, the camshaft for one or more exhaust valves and/or the further camshaft for one or more intake valves may have a phase adjuster. The phase adjuster is configured to adjust a rotational angle of the camshaft with respect to a rotational angle of the crankshaft. Therefore, the phase adjuster can adjust the control time of the corresponding valve. The phase setter can be designed, for example, as a hydraulic phase setter, in particular as a wobble motor phase setter. This embodiment has the following advantages: the flexibility of the system is further enhanced by the combination with a movable cam support.

In another design variation, the second cam is configured to open with a greater valve stroke after the first exhaust valve opens in the compression stroke than after opening in the exhaust stroke. Alternatively or additionally, the second cam is configured such that the first exhaust valve opens with a smaller valve stroke than the first cam. Providing a multi-step valve stroke that is smaller than the valve stroke during normal operation reduces the load on the valve gear. In particular, the valve drive is heavily loaded when the exhaust valve opens against the pressure in the cylinder.

In embodiments where the second cam is also used to operate the second exhaust valve, those designs herein relating to the effect 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 operate the second exhaust valve, those designs herein relating to the effect of the first cam on the first exhaust valve are equally applicable to the third cam and the second exhaust valve.

The invention also relates to a motor vehicle, in particular a commercial vehicle, having a variable valve drive as disclosed herein. The commercial vehicle may be a bus or a truck, for example.

Drawings

The aforementioned preferred embodiments and features of the invention can be combined with one another as desired. Further details and advantages of the invention are described below with reference to the drawings. Wherein:

FIG. 1 is a perspective view of an exemplary variable valve actuation device;

FIG. 2 is another perspective view of an exemplary variable valve actuation device;

FIG. 3 is a top view of a camshaft of an exemplary variable valve actuation device;

FIG. 4 is a longitudinal cross-sectional view of the camshaft of FIG. 3 taken along line A-A;

FIG. 5 is a graphical illustration of an exemplary valve control profile for a variable valve actuation device;

FIG. 6A is a first cross-sectional view of the camshaft of FIG. 4 taken along line B-B;

FIG. 6B is a second cross-sectional view of the camshaft of FIG. 4 taken along line C-C;

FIG. 7 illustrates an exemplary method for shutting down an internal combustion engine according to the present disclosure; and

FIG. 8 is a graph illustrating different engine speed, turbocharger speed, and boost pressure curves over time.

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

Detailed Description

A particularly preferred embodiment of the variable valve gear, which is suitable both for carrying out the method disclosed herein for switching off the internal combustion engine and for carrying out an engine braking operation, is described first with reference to fig. 1 to 6B. The internal combustion engine may be contained in a motor vehicle, preferably a commercial vehicle, such as a bus or a truck. The method for switching off the internal combustion engine is described in particular with reference to fig. 7 and 8. The method may employ the variable valve gear disclosed herein or another variable valve gear, particularly with an improved sliding cam system.

A variable valve gear 10 is shown in fig. 1 and 2. The variable valve gear 10 has a camshaft 12 and a cam carrier 14. The variable valve gear 10 also has a first transmission 16 and a second transmission 18 and a first exhaust valve 20 and a second exhaust valve 22. Furthermore, the variable valve gear 10 has a first actuator 24 and a second actuator 26. The cam carrier 14, the gear arrangement 16 and the gear arrangement 18 and the actuator 24 and the actuator 26 form a sliding cam system 11.

The camshaft 12 is configured to operate output camshafts of the output valves 20 and 22. The camshaft 12 is part of a dual camshaft system (not shown in detail) which additionally has an intake camshaft (not shown) for operating one or more intake valves. The camshaft 12 is provided as an overhead camshaft together with the intake camshaft. The camshaft 12 and the intake camshaft thus form a so-called DOHC (double over head camshaft) system. Alternatively, the camshaft 12 may also form a so-called SOHC (single overhead camshaft) system. In other embodiments, the camshaft 12 may also be configured as a bottom mounted camshaft.

A cam carrier 14 is arranged on the camshaft 12 in a rotationally fixed manner. The cam carrier 14 is additionally axially displaceably arranged along the longitudinal axis of the camshaft 12. The cam carrier 14 is axially movable between a first stop 28 and a second stop 30.

The cam carrier 14 will now be described with reference to figures 1 to 4. The cam carrier 14 has three

cams

32, 34 and 36, which are offset from one another in the longitudinal direction of the cam carrier 14 and of the camshaft 12. A first cam 32 is provided at a first end of the cam carrier 14 and is designed for normal operation, as will be described in more detail later on by way of example. The second cam 34 is arranged adjacent to the first cam 32 and is designed for engine braking operation, as will also be described in detail by way of example later. Engine braking operation may be used to slow and/or brake the vehicle while traveling downhill. The engine braking operation may also be used to reduce vibration of the internal combustion engine when shut off. The third cam 36 is disposed in spaced relation to 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 camless first section 38 and a camless second section 40. A camless first section 38 is provided at the second end of the cam carrier 14. The camless second section 40 is disposed between the second cam 34 and the third cam 36. In the camless first section 38, a first engagement track (shift gate) 42 extends helically around the longitudinal axis of the cam carrier 14. In the camless second section 40, a second engagement track (switching gate) 44 extends helically around the longitudinal axis of the cam carrier 14.

To move the cam carrier 14 between the stop 28 and the stop 30, the actuator 24 and the actuator 26 (fig. 1 and 2) may be selectively extended into the engagement tracks 42, 44 by extendable components (not shown in detail). Specifically, the first actuator 24 may be selectively extendable into the first engagement track 42 for moving the cam carrier 14 from one axial position to another axial position. In the first axial position, the cam carrier 14 rests against the second stop 30. In the second axial position, the cam carrier 14 rests against the first stop 28. The cam carrier is shown in a first axial position in fig. 1 to 4. The second actuator 26 may also selectively extend into the second engagement track 44. The cam carrier 14 is then moved from the first axial position to the second axial position. The first actuator 24 and the second actuator 26 are controlled by a schematically shown control unit 27 (fig. 1 and 2).

The movement is triggered by: with reference to the axial direction of the camshaft 12, the projecting parts of the

respective actuators

24, 26 are fixed in position. Therefore, when the protruding parts protrude into the respective engagement tracks 42, 44, the movable cam carrier 14 moves in the longitudinal direction of the camshaft 12 due to the helical shape of the engagement tracks 42, 44. At the end of the displacement process, the movable parts of the

respective actuator

24, 26 are guided by the

respective engagement track

42, 44 counter to the extension direction and are retracted thereby. The movable components of the

respective actuators

24, 26 are disengaged from the respective engagement tracks 42, 44.

The first transmission 16 and the second transmission 18 (fig. 1 and 2) produce a functional connection between the cam carrier 14 and the exhaust valves 20, 22. When the first cam 32 or the second cam 34 presses the first transmission 16 downward, the first exhaust valve 20 is operated (opened). When the third cam 36 presses the second transmission 18 downward, the second exhaust valve 22 is actuated (opened).

If the cam carrier 14 is in a first axial position (as shown in fig. 1 to 4), the first transmission 16 is in operative connection between the first cam 32 and the first exhaust valve 20. In other words, in the first axial position of the cam carrier 14, the first gear 16 is not in operative connection between the second cam 34 and the first exhaust valve 20. The first exhaust valve 20 is operated in accordance with the profile of the first cam 32. In the second axial position of the cam carrier 14, the first transmission 16 is in operative connection between the second cam 34 and the first exhaust valve 20. The first exhaust valve 20 is operated in accordance with the profile of the second cam 34.

In the first axial position of the cam carrier 14, the second transmission device 18 is in operative connection between the third cam 36 and the second exhaust valve 22. The second exhaust valve 22 is operated in accordance with the profile of the third cam 36. In the second axial position of the cam carrier 14, the second transmission device 18 does not actuate the second exhaust valve 22. In the second axial position of the cam carrier 14, the contact region 18A of the second transmission device 18 is at the same axial position with reference to the camshaft 12 as the camless first section 38. The camless first section 38 has no protuberance for operating the second transmission device 18. If the cam carrier 14 is in the second axial position, the second exhaust valve 22 is not actuated.

The camless first section 38 thus has two functions. In one aspect, the camless first section 38 houses the first track 42. On the other hand, the camless first section 38 is used to not actuate the second exhaust valve 42 in the second axial position of the cam carrier 14. For reasons of installation space, such functional integration is advantageous.

In the embodiment shown, the first transmission device 16 and the second transmission device 18 are each configured as a cam follower. In other embodiments, the transmission device 16 and the transmission device 18 may be configured as rockers or tappets. In some embodiments, the

transmission devices

16 and 18 may have cam followers in the form of, for example, rotatable rollers.

Referring to fig. 4, a locking device 46 is shown. The locking device 46 has a resilient part 48 and a locking body 50. The elastic element 48 is arranged in a blind hole of the camshaft 12. The elastic element 48 presses the locking element 50 against the cam carrier 14. A first recess 52 and a second recess 54 are provided in the inner circumferential surface of the cam carrier 14. 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 locking body 50 is pressed into the second recess 54.

Referring to fig. 5, the control of the first exhaust valve 20 and its effect on cylinder pressure will now be described. Fig. 5 shows a complete four-stroke cycle consisting of compression, expansion, exhaust and suction.

Curve a depicts the cylinder pressure trend when the second cam 34 is in operative connection with the first exhaust valve 20 in engine braking operation. Curve B depicts the valve travel trend of the first exhaust valve 20 when the first cam 32 is in connection with the first exhaust valve 20 (i.e., during normal operation). The third curve C shows the valve travel profile of the inlet valve during normal operation and in engine braking operation. Curve D shows the valve travel trend of the first exhaust valve 20 when the second cam 34 is in operative connection with the first exhaust valve 20 (i.e. during engine braking operation).

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

Curve D shows that the exhaust valve is slightly open in the region of approximately 60 deg. KW-100 deg. KW before top dead center at the end of the compression stroke. At top dead center, the exhaust valve opens further and closes at approximately bottom dead center at the end of the expansion stroke. The exhaust valve opens at the end of the compression stroke, which causes the compressed air in the cylinder to be pushed through the open exhaust valve into the exhaust system by the piston moving to top dead center. The compression work previously performed causes the crankshaft, and thus the engine, to brake. The cylinder pressure initially rises during the compression stroke but then falls already before the top dead center due to the exhaust valve opening (see curve a). The exhaust valve, which is open during the expansion stroke, causes air from the exhaust line 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.

Curve D also shows that the exhaust valve initially remains closed at the end of the expansion stroke after bottom dead center is reached. At the end of the exhaust stroke, the exhaust valve is opened in the region of the top dead center. The opening is again carried out approximately 60 ° KW to 100 ° KW before top dead center. An exhaust valve that closes during the exhaust stroke causes the air drawn in the expansion stroke to compress with work. The cylinder pressure rises (curve a). Work is applied to brake the crankshaft, and the internal combustion engine is further braked. The opening of the exhaust valve at the end of the exhaust stroke causes air to be pushed into the exhaust system through the open exhaust valve. During the intake stroke, the cylinder is again filled with air through one or more open intake valves (curve C). The cycle starts over.

By using the second cam to control the exhaust valve, as described above, a double compression occurs followed by a decompression, thereby ensuring the engine braking function. Additionally, during the engine-off period when the engine braking operation is set, since the vibration of the internal combustion engine in the compression stroke is reduced by opening the exhaust valve before reaching the top dead center, the vibration of the internal combustion engine is reduced.

As can be seen from reference curves B and D, the valve travel of the exhaust valve is smaller in the braking operation (curve D) than in the normal operation (curve B). Further, the valve stroke has two stages in the compression and expansion strokes when the exhaust valve is opened. These measures lead to a reduction in the load on the variable valve drive during braking operation, since high loads occur on the valve drive as a result of the exhaust valve opening against the pressure in the cylinder.

Fig. 6A shows a cross section of the second cam 34. Fig. 6B shows a cross section of the first cam 32.

The second cam 34 is configured to implement curve D of fig. 5. For this purpose, the second cam 34 has in particular a first elevation 34A, a second elevation 34B and a third elevation 34C. The first bump 34A, the second bump 34B, and the third bump 34C are arranged with a displacement in the circumferential direction around the second cam 34. The first bump 34A causes the exhaust valve to open at the end of the compression stroke. The second bump 34B extending from the first bump 34A causes the exhaust valve to open further during the expansion stroke. The third bump 34C causes the exhaust valve to open at the end of the exhaust stroke.

The first bump 34A has the smallest height among the bumps 34A-34C, as measured in the radial direction of the camshaft 12. The second bump 34B has the largest height among the bumps 34A-34C, as measured in the radial direction of the camshaft 12. The height of the third bump 34C is smaller than the height of the second bump 34B and larger than the height of the first bump 34A. The different heights of the protuberances 34A-34C result in correspondingly different valve strokes (see fig. 5).

The first bulge 34A, the second bulge 34B and the third bulge 34C are each arranged offset in circumferential direction with respect to the bulge 32A of the first cam 32. The first cam 32 is configured to implement curve B of fig. 5. The bulge 32A of the first cam 32 causes the exhaust valve to open during the exhaust stroke. The protuberance 32A is higher than the protuberances 34A-34C, as measured in the radial direction of the camshaft 12. The valve travel through the ridges 32A is greater than the valve travel through the ridges 34A-34C.

Fig. 6B also shows the locking device 46 with the resilient part 48, the locking body 50 and the first recess 52.

An exemplary method for shutting down an internal combustion engine is described below with reference to fig. 7 and 8.

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

Once the shut-down procedure is initiated, engine braking operation may be initiated. For this purpose, in step S102, the switching is made to the second cam 34 (see, for example, fig. 1). It is possible to switch over for all cylinders or only for a part of the cylinders of the internal combustion engine.

Switching to the second cam 34 causes the first exhaust valve 20 to first remain closed during the compression and exhaust strokes and open prior to top dead center of piston motion for decompression of the compressed air.

In fig. 8, the deflection movement (oscillation) I of the internal combustion engine over time t is shown during the shut-off process for the usual shut-off process (dashed line E) and during the shut-off process for the shut-off process according to the invention (solid line F). Initially, the internal combustion engine is in idle operation in the range t 1. The disconnection process is initiated at a time point T1. The corresponding shut-down procedure is shown in the range t 2.

With a normal shut-off process, vibrations of the internal combustion engine occur after the start of the shut-off process. The undesirable vibrations are due to the following: on the one hand, the cylinders are in various strokes and, on the other hand, all valves are closed during the compression stroke during the compression.

With the shut-off process according to the present disclosure, vibration of the internal combustion engine can be reduced or prevented. By switching over to the second cam 34, the first exhaust valve 20 is opened before reaching the top dead center in the compression stroke. That is, not all valves are closed during the compression stroke, thereby at least reducing vibration. This is qualitatively illustrated by the solid line in fig. 8. The remaining vibration motion is due to the energy of the rotating mass of the internal combustion engine and the system inertia.

The first exhaust valve 20 may be operated until a standstill of the internal combustion engine by means of the second cam 34. However, it is also possible, for example, to switch back to the first cam 32 (step S108) at the end of the shut-off process if a predetermined engine speed threshold value is undershot (step S106). The position of the sliding cam system 11 at the end of the shut-off process has an effect on the starting of the internal combustion engine.

The method for shutting down an internal combustion engine disclosed herein may be modified and/or supplemented in a variety of ways.

For example, it is possible for the sliding cam system 11 to switch cylinders into engine braking operation during the switching-off process. The more cylinders that are switched to engine braking operation, the better the vibration of the internal combustion engine can be prevented or reduced.

The number of sliding cam systems 11 which are switched into engine braking operation during the switching-off process can be determined as a function of at least one operating parameter of the internal combustion engine. The operating parameter may be, in particular, the temperature of the internal combustion engine and/or the operating time of the internal combustion engine. Thus, for example, in the case of comparatively low engine temperatures and brief engine operating times (slight) vibrations of the internal combustion engine can be tolerated. It is also possible that no sliding cam system 11 is switched into engine braking operation as a function of the lower temperature of the internal combustion engine and/or the brief operating time of the internal combustion engine.

In some embodiments, where one group of cylinders is switched to engine braking operation during the key-off process and a second group of cylinders is not switched to engine braking operation during the key-off process, the groups may be assigned rollingly. The rolling assignment can be done during the shut-down procedure or, preferably, between different shut-down procedures. Wear can thereby be made even between the sliding cam systems 11 of the multiple cylinders.

As described above, the method for shutting down the internal combustion engine may employ the sliding cam system 11. In particular, the control unit 27 may control the actuator 24 and the actuator 26 (see fig. 1) according to the method for switching off an internal combustion engine disclosed herein. However, the method may also employ another sliding cam system that involves switching between a first cam for normal operation and a second cam for shut-off operation. The second cam can also be designed, for example, such that: it is designed specifically for shut-off operation and in particular such that at least one exhaust valve of the cylinder remains open at least during the compression stroke and the exhaust stroke.

The invention is not limited to the preferred embodiments described above. Rather, there are numerous modifications and variations which may be employed with the concepts of the present invention and which fall within the scope of the protection sought. The invention in particular also claims the subject matter and features of the dependent claims independent of the claims cited.

List of reference numerals

10 variable valve gear

11 sliding cam system

12 camshaft

14 cam support

16 first transmission (first cam follower)

18 second transmission (second cam follower)

18A contact area

20 first exhaust valve

22 second exhaust valve

24 first actuator

26 second actuator

27 control unit

28 first stop

30 second stop

32 first cam

32A bump

34 second cam

34A-34C bumps

36 third cam

38 camless first section

40 second section without cam

42 first engagement track

44 second engagement track

46 locking device

48 resilient member

50 locking body

52 first recess

54 second recess

Pressure of cylinder A

B exhaust valve control curve

C intake valve control curve

D exhaust valve control curve

t time axis

Point in time of T1 switch-off

t1 first Range (Engine No load)

t2 second Range (cutting off Process)

I deflection/vibration

E vibration curve in normal cut-off

F vibration curve at cut-off according to the method disclosed herein

Claims

1. A method for shutting down an internal combustion engine, comprising:

initiating a cut-off process; and

reducing the vibration of the internal combustion engine during the shut-off process, which is performed as follows:

a) switching the operation of a first exhaust valve (20) of the internal combustion engine by means of a sliding cam system (11) in order to open or remain open during a compression stroke and an exhaust stroke; or the like, or, alternatively,

b) switching to an engine braking mode, wherein a first exhaust valve (20) of the internal combustion engine is initially closed in the compression stroke and/or the exhaust stroke in order to compress air and is opened before the top dead center of the piston movement is reached in order to decompress the compressed gas,

wherein the sliding cam system (11) comprises a first cam (32) for normal operation and a second cam (34) for engine braking operation and/or for actuating the first exhaust valve (20) during the switching-off process, and

wherein the sliding cam system (11) selectively places the first cam (32) and the first exhaust valve (20) in operative connection, or places the second cam (34) and the first exhaust valve (20) in operative connection.

2. The method as claimed in claim 1, wherein the switching into the engine braking mode takes place by means of a variable valve drive (10) of the internal combustion engine.

3. The method as claimed in claim 1 or claim 2, wherein the sliding cam system (11) has a cam carrier (14) which is arranged on a camshaft (12) of the internal combustion engine in a rotationally fixed and axially displaceable manner and which carries the first cam (32) and the second cam (34) which is arranged offset in the longitudinal direction of the camshaft (12).

4. The method of claim 3, further comprising:

at the beginning of the switching-off process, switching from the first cam (32) to the second cam (34) by means of the sliding cam system (11);

during the switching off process, the first exhaust valve (20) is actuated by means of the second cam (34).

5. The method of claim 4, wherein:

the second cam causes the first exhaust valve (20) to open or remain open during the compression stroke and the exhaust stroke; and/or the presence of a gas in the gas,

the second cam causes the first exhaust valve (20) to initially remain closed during the compression stroke and/or during the exhaust stroke and open before top dead center of piston movement is reached.

6. The method of claim 1 or 2, wherein:

said first exhaust valve (20) opens between 100 ° KW and 60 ° KW before reaching said top dead centre; and/or the presence of a gas in the gas,

-in the exhaust stroke the first exhaust valve (20) closes after opening in a region between the top dead centre and 30 ° KW after top dead centre; and/or the presence of a gas in the gas,

in the compression stroke, the first exhaust valve (20) closes in a region between bottom dead center and 30 ° KW after opening.

7. The method of claim 3, wherein:

at the end of the switching-off process, a second cam (34) of the sliding cam system (11) remains in operative connection with the first exhaust valve (20); alternatively, the first and second electrodes may be,

at the end of the cutting process, switching to the first cam (32) by means of the sliding cam system (11).

8. The method of claim 1 or 2, further comprising:

detecting an engine temperature of the internal combustion engine and/or an engine operating time of the internal combustion engine;

wherein the actuation of a first exhaust valve (20) of the internal combustion engine is switched by means of the sliding cam system (11) in order to open or remain open during a compression stroke and an exhaust stroke and/or to switch into the engine braking mode if:

the detected engine temperature is less than or equal to a predetermined engine temperature threshold; and/or the presence of a gas in the gas,

the detected run time is less than or equal to a predetermined run time threshold.

9. The method of claim 1 or 2, further comprising:

-keeping a second exhaust valve (22) of the internal combustion engine closed during the shut-off process, wherein the second exhaust valve (22) is assigned to the same cylinder of the internal combustion engine as the first exhaust valve (20).

10. The method of claim 9, wherein the maintaining of the second exhaust valve (22) closed comprises: switching to a camless section (38) of the sliding cam system (11).

11. The method of claim 1 or 2,

in a first group of cylinders, the first exhaust valve (20) is opened or held open in a compression stroke and an exhaust stroke by switching actuation by means of the sliding cam system (11), and/or the first group of cylinders of the internal combustion engine is switched into the engine braking mode during the switching-off process; and/or the presence of a gas in the gas,

in the second group of cylinders, the actuation of the exhaust valve (20) remains unchanged during the switching-off process.

12. The method of claim 2, wherein the variable valve actuation device (10) is a sliding cam system (11).

13. A method according to claim 11, wherein the number of cylinders in the first and/or second group is determined in dependence on at least one operating parameter of the internal combustion engine.

14. The method according to claim 13, wherein the at least one operating parameter is the temperature of the internal combustion engine and/or the operating time of the internal combustion engine.

15. The method of claim 11, wherein the assignment to the first group and/or the second group is done on a rolling basis.

16. The method of claim 13, wherein the assignment to the first group and/or the second group is done on a rolling basis.

17. A method according to claim 11, wherein the assignment to the first and/or second group is made rolling between successive shut-off procedures.

18. A method according to claim 13, wherein the assignment to the first and/or second group is made rolling between successive shut-off procedures.

19. A variable valve gear (10) for an internal combustion engine of a motor vehicle, having:

a first exhaust valve (20);

a camshaft (12);

a sliding cam system (11) having a cam carrier (14) which is arranged on the camshaft (12) in a rotationally fixed and axially displaceable manner and which has a first cam (32) and a second cam (34), wherein the first cam (32) and the second cam (34) are arranged offset in the longitudinal direction of the camshaft (12); and

a control unit (27) designed for implementing the method according to any one of the preceding claims.

20. The variable valve actuation device (10) of claim 19 wherein the motor vehicle is a commercial vehicle.

21. A motor vehicle having a variable valve gear (10) according to claim 19.

22. The motor vehicle of claim 21, wherein the motor vehicle is a commercial vehicle.