CN112443403B - Valvetrain and method for actuating a gas exchange valve - Google Patents

Valvetrain and method for actuating a gas exchange valve Download PDF

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Publication number
CN112443403B
CN112443403B CN202010922886.0A CN202010922886A CN112443403B CN 112443403 B CN112443403 B CN 112443403B CN 202010922886 A CN202010922886 A CN 202010922886A CN 112443403 B CN112443403 B CN 112443403B
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valve
intake
exhaust
cam
relatively small
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CN112443403A (en
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M·埃普
G·利策尔
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MAN Energy Solutions SE
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MAN Energy Solutions SE
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D13/00—Controlling the engine output power by varying inlet or exhaust valve operating characteristics, e.g. timing
    • F02D13/02—Controlling the engine output power by varying inlet or exhaust valve operating characteristics, e.g. timing during engine operation
    • F02D13/0203—Variable control of intake and exhaust valves
    • F02D13/0207—Variable control of intake and exhaust valves changing valve lift or valve lift and timing
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D13/00—Controlling the engine output power by varying inlet or exhaust valve operating characteristics, e.g. timing
    • F02D13/02—Controlling the engine output power by varying inlet or exhaust valve operating characteristics, e.g. timing during engine operation
    • F02D13/0203—Variable control of intake and exhaust valves
    • F02D13/0215—Variable control of intake and exhaust valves changing the valve timing only
    • F02D13/0219—Variable control of intake and exhaust valves changing the valve timing only by shifting the phase, i.e. the opening periods of the valves are constant
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D13/00—Controlling the engine output power by varying inlet or exhaust valve operating characteristics, e.g. timing
    • F02D13/02—Controlling the engine output power by varying inlet or exhaust valve operating characteristics, e.g. timing during engine operation
    • F02D13/0261—Controlling the valve overlap
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01L—CYCLICALLY OPERATING VALVES FOR MACHINES OR ENGINES
    • F01L1/00—Valve-gear or valve arrangements, e.g. lift-valve gear
    • F01L1/02—Valve drive
    • F01L1/04—Valve drive by means of cams, camshafts, cam discs, eccentrics or the like
    • F01L1/08—Shape of cams
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01L—CYCLICALLY OPERATING VALVES FOR MACHINES OR ENGINES
    • F01L1/00—Valve-gear or valve arrangements, e.g. lift-valve gear
    • F01L1/02—Valve drive
    • F01L1/04—Valve drive by means of cams, camshafts, cam discs, eccentrics or the like
    • F01L1/047—Camshafts
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01L—CYCLICALLY OPERATING VALVES FOR MACHINES OR ENGINES
    • F01L13/00—Modifications of valve-gear to facilitate reversing, braking, starting, changing compression ratio, or other specific operations
    • F01L13/0015—Modifications of valve-gear to facilitate reversing, braking, starting, changing compression ratio, or other specific operations for optimising engine performances by modifying valve lift according to various working parameters, e.g. rotational speed, load, torque
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D13/00—Controlling the engine output power by varying inlet or exhaust valve operating characteristics, e.g. timing
    • F02D13/02—Controlling the engine output power by varying inlet or exhaust valve operating characteristics, e.g. timing during engine operation
    • F02D13/0223—Variable control of the intake valves only
    • F02D13/0234—Variable control of the intake valves only changing the valve timing only
    • F02D13/0238—Variable control of the intake valves only changing the valve timing only by shifting the phase, i.e. the opening periods of the valves are constant
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/0002—Controlling intake air
    • F02D2041/001—Controlling intake air for engines with variable valve actuation
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/10—Internal combustion engine [ICE] based vehicles
    • Y02T10/12—Improving ICE efficiencies

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Valve-Gear Or Valve Arrangements (AREA)
  • Output Control And Ontrol Of Special Type Engine (AREA)
  • Valve Device For Special Equipments (AREA)

Abstract

A valvetrain for actuating intake and exhaust valves of an internal combustion engine has intake camshafts, each intake cam including an intake valve opening side and an intake valve closing side; and exhaust camshafts, each of which includes an exhaust valve opening side and an exhaust valve closing side. The exhaust valve closing side and the intake valve opening side are designed such that at full load and partial load, the intake valve starts to open before the cylinder top dead center and the exhaust valve is fully closed after the top dead center. The exhaust valve closing side is designed such that the exhaust valve initially closes with a relatively large gradient and then with a relatively small gradient and, at full load, the relatively small gradient completely closes the exhaust valve in the range of 60 deg. to 30 deg. KW before completely closing the intake valve. The intake valve opening side is designed such that the intake valve initially opens with a relatively small gradient and then with a relatively large gradient, wherein at full load the relatively small gradient starts opening the intake valve in the range of 90 ° to 60 ° KW before top dead center.

Description

Valvetrain and method for actuating a gas exchange valve
Technical Field
The present invention relates to a valve train for actuating a gas exchange valve of a cylinder of an internal combustion engine. Furthermore, the invention relates to a method for actuating a gas exchange valve of a cylinder of an internal combustion engine.
Background
A basic structure of a valve mechanism for actuating a gas exchange valve of a cylinder of an internal combustion engine is known from practice. Thus, the valve train includes an intake camshaft carrying an intake cam for actuating intake valves of cylinders of the internal combustion engine. Further, the valve train includes an exhaust camshaft carrying exhaust cams for actuating exhaust valves of cylinders of the internal combustion engine.
Each intake cam includes an intake valve opening side for opening a corresponding intake valve and an intake valve closing side for closing the corresponding intake valve. Each exhaust cam includes an exhaust valve opening side following the corresponding exhaust valve and an exhaust valve closing side for closing the corresponding exhaust valve.
A valve train is known from DE 10 2016 112 447 A1, in which a cam rod interacts with a cam of a camshaft, wherein a roller of the cam rod sweeps a cam profile of a respective cam and transmits the cam profile via a pushrod and a rocker arm to the respective gas exchange valve, so that the respective gas exchange valve is actuated.
Another valve train for an internal combustion engine is known from DE 10 2016 112 448 B4, in which the rollers of the cam lever sweep the cam profile of the cam and transmit the cam profile via the push rod (however, without rocker arms) to the gas exchange valve.
It is known from practice that there may be a valve overlap between at least one inlet valve and at least one exhaust valve of a respective cylinder of the internal combustion engine. The valve overlap is characterized in that the respective intake valve starts to open even before the top dead center of the respective cylinder, and the respective exhaust valve of the respective cylinder is completely closed only after the top dead center of the respective cylinder. The pressure difference between the charge air pressure in the respective exhaust port and the exhaust back pressure in the respective exhaust port can then be utilized in order to sweep the residual exhaust gas from the combustion chamber of the respective cylinder into the exhaust port by means of fresh air.
Furthermore, valve mechanisms with variable valve actuation are known from practice in order to provide different valve actuation for the gas exchange valves of the cylinders in full load and part load. In this way, cylinder charging can be improved, especially in part load.
There is a need for a valve train that makes it possible to achieve an optimal operation of the internal combustion engine not only at full load but also at partial load, thereby ensuring good cooling of the exhaust valve, in particular over all load ranges, and avoiding consumption disadvantages.
Disclosure of Invention
From this point on, the invention is based on the following objects: a novel valve train and corresponding method for actuating a gas exchange valve is created.
This object is solved by a valve train according to the invention for actuating a gas exchange valve of a cylinder of an internal combustion engine. Each cylinder comprises at least one intake valve and at least one exhaust valve as gas exchange valves, having an intake camshaft carrying intake cams for the intake valves of the cylinders, wherein each intake cam comprises an intake valve opening side and an intake valve closing side having an exhaust camshaft carrying exhaust cams for the exhaust valves of the cylinders, wherein each exhaust cam comprises an exhaust valve opening side and an exhaust valve closing side; a camshaft adjusting device for the intake camshaft is provided, via which the intake cam is adjustable relative to the exhaust cam in order to provide, at full load of the internal combustion engine, intake valves of the cylinders with valve actuation that differs from valve actuation at part load of the internal combustion engine. The exhaust valve closing side of the exhaust cam and the intake valve opening side of the intake cam are formed in such a way that, under full and partial load on each cylinder, the at least one intake valve starts to open before top dead center (OT) of the respective cylinder and the at least one exhaust valve is fully closed after top dead center (OT) of the respective cylinder. The exhaust valve closing flank of the exhaust cam is formed in such a way that at least one exhaust valve of the respective cylinder is initially closed with a relatively large gradient and subsequently with a relatively small gradient, wherein a change from a relatively large gradient to a relatively small gradient occurs in the region of the top dead center (OT) of the respective cylinder, and wherein, at full load of the internal combustion engine, the relatively small gradient completely closes at least one exhaust valve of the respective cylinder in the range between 60 ° KW and 30 ° KW before the complete closing of the at least one intake valve. The intake valve opening sides of the intake cams are formed in such a way that at least one intake valve of the respective cylinder is initially opened with a relatively small gradient and subsequently with a relatively large gradient, wherein at full load of the internal combustion engine the relatively small gradient starts to open the at least one intake valve of the respective cylinder in a range between 90 ° KW and 60 ° KW before the top dead center (OT) of the respective valve, and wherein at full load a change from the relatively small gradient to the relatively large gradient occurs in the region of the top dead center (OT) of the respective cylinder.
The valvetrain includes an intake camshaft that carries intake cams for intake valves of the cylinders, wherein each intake cam includes an intake valve opening side and an intake valve closing side. The valvetrain includes an exhaust camshaft carrying exhaust cams for exhaust valves of the cylinders, wherein each exhaust cam includes an exhaust valve opening side and an exhaust valve closing side. The valve train further comprises a camshaft adjusting device for an intake camshaft, via which the intake cam is adjustable relative to the exhaust cam in order to provide the intake valve of the cylinder with a valve actuation at full load of the internal combustion engine that is different from the valve actuation at partial load of the internal combustion engine.
The exhaust valve closing side of the exhaust cam and the intake valve opening side of the intake cam are designed in such a way that at full and partial load on each cylinder at least one intake valve starts to open before top dead center of the respective cylinder and at least one exhaust valve closes completely after top dead center of the respective cylinder.
The exhaust valve closing flank of the exhaust cam is formed in such a way that the at least one exhaust valve of the respective cylinder is initially closed with a relatively large gradient and subsequently with a relatively small gradient, wherein a change from the relatively large gradient to the relatively small gradient takes place in the region of the top dead center of the respective cylinder, and wherein, at full load of the internal combustion engine, the relatively small gradient completely closes the at least one exhaust valve of the respective cylinder in a range between 60 ° KW and 30 ° KW before the complete closing of the at least one exhaust valve. KW represents the crank angle.
The intake valve opening side of the intake cam is designed in such a way that at least one intake valve of the respective cylinder is initially opened with a relatively small gradient and subsequently with a relatively large gradient, wherein at full load of the internal combustion engine the relatively small gradient starts to open the at least one intake valve of the respective cylinder in a range between 90 ° KW and 60 ° KW before the top dead center of the respective valve, and wherein at full load a change from the relatively small gradient to the relatively large gradient occurs in the region of the top dead center of the respective cylinder. KW represents the crank angle.
In the valve mechanism, the camshaft adjusting device makes it possible to adjust the intake cam with respect to the exhaust cam. The exhaust valve closing side of the exhaust cam and the intake valve opening side of the intake cam are formed in a defined manner so as to provide a defined valve overlap not only at full load but also at partial load, so that charge air is utilized both at full load and at partial load to sweep exhaust gas into the exhaust port and cool the exhaust valve of the cylinder during the process. On the other hand, by the defined profile of the exhaust valve closing side of the exhaust cam and the intake valve opening side of the intake cam, the consumption disadvantages are avoided. In both full and part load, sufficient time periods of valve overlap are available to ensure good cooling of the exhaust valve over all load ranges without consumption drawbacks.
Preferably, the camshaft adjustment device adjusts the intake cam toward hysteresis by an angle β during the change from full load to partial load. At part load, the relatively small gradient of the opening side of the intake valve starts to open at least one intake valve in the range between (90 ° - β) KW and (60 ° - β) KW before the top dead center of the corresponding valve. Under part load, the relatively small gradient completely closes the at least one exhaust valve in a range between (60 ° +β) KW and (30 ° +β) KW before completely closing the at least one intake valve. Preferably, β is equal to between 30 ° KW and 50 ° KW. KW represents the crank angle.
This allows the internal combustion engine to be operated particularly advantageously at both partial load and full load. During both full and partial load, adequate cooling of the exhaust valve is ensured without consumption disadvantages.
The invention also provides a method for actuating a gas exchange valve of a cylinder of an internal combustion engine. Each cylinder comprises at least one inlet valve and at least one outlet valve as gas exchange valves, wherein the or each inlet valve of the respective cylinder starting from an inlet cam comprising an inlet valve opening side and an inlet valve closing side is actuated to open and close, wherein the or each outlet valve of the respective cylinder starting from an outlet cam comprising an outlet valve opening side and an outlet valve closing side is actuated to open and close. During a change between full load and part load of the internal combustion engine, the intake cams are adjusted relative to the exhaust cams to provide different valve actuation for the intake valves at full load than at part load, wherein at full load and part load on each cylinder the intake valve opening side of the respective intake cam begins to open at least one intake valve before top dead center (OT) of the respective cylinder and the exhaust valve closing side of the respective exhaust cam fully closes at least one exhaust valve of the respective cylinder after top dead center (OT) of the respective cylinder. The exhaust valve closing side of the exhaust cam initially closes the at least one exhaust valve of the respective cylinder with a relatively large gradient and subsequently closes the at least one exhaust valve of the respective cylinder with a relatively small gradient, wherein a change from the relatively large gradient to the relatively small gradient occurs in the region of the top dead center (OT) of the respective cylinder, and wherein the relatively small gradient completely closes the at least one exhaust valve of the respective cylinder in the range between 60 ° KW and 30 ° KW before the complete closing of the at least one intake valve at full load of the internal combustion engine. The intake valve opening side of the intake cam initially opens at least one intake valve of the respective cylinder with a relatively small gradient and subsequently opens at least one intake valve of the respective cylinder with a relatively large gradient, wherein at full load of the internal combustion engine the relatively small gradient starts to open the at least one intake valve of the respective cylinder in a range between 90 ° KW and 60 ° KW before top dead center (OT) of the respective valve, and wherein at full load a change from the relatively small gradient to the relatively large gradient occurs in the region of top dead center (OT) of the respective cylinder.
Drawings
Preferred further developments of the invention are obtained from the dependent claims and the following description. Exemplary embodiments of the present invention are explained in more detail by the accompanying drawings without being limited thereto. There is shown:
FIG. 1 is a representation of the open and closed sides of the intake and exhaust cams of a valvetrain under full load according to the present disclosure;
fig. 2 is a representation of the open and closed sides of the intake and exhaust cams of the valvetrain under partial load according to the present invention.
Detailed Description
The basic structure of the valve train of an internal combustion engine is known to those skilled in the art, referred to herein.
Accordingly, a valve train for actuating a gas exchange valve of a cylinder of an internal combustion engine includes an intake camshaft carrying an intake cam. The intake cams are for actuating gas exchange valves of cylinders of an internal combustion engine, which are formed as intake valves, wherein each intake cam comprises an intake valve opening side for opening a respective intake valve and an intake valve closing side for closing the respective intake valve.
Further, the valve train includes an exhaust camshaft carrying an exhaust cam. An exhaust cam is used to actuate a gas exchange valve of a cylinder of the internal combustion engine, which is formed as an exhaust valve, to open and close the exhaust valve. Thus, each exhaust cam includes an exhaust valve opening side for opening the corresponding exhaust valve and an exhaust valve closing side for closing the corresponding exhaust valve.
Furthermore, the valve train comprises a camshaft adjusting device. With the camshaft adjusting device, the intake camshaft may be adjusted so as to adjust the intake cam with respect to the exhaust cam of the exhaust camshaft. Thus, independent valve actuation of the intake valves of the cylinders may be provided for full load of the internal combustion engine and also for part load of the internal combustion engine.
In fig. 1 and 2, the actuation of the exhaust valve and the intake valve of the cylinder is shown for full load operation (see fig. 1) and for part load operation (see fig. 2), wherein the curve profile 10 corresponds to the actuation of the exhaust valve by the opening side and the closing side of the exhaust cam and the curve profile 11 corresponds to the actuation of the intake valve by the opening side and the closing side of the intake cam.
The opening of the respective exhaust valve is defined by the exhaust valve opening side 10a of the respective exhaust cam, and the closing of the respective exhaust valve is defined by the exhaust valve closing side 10b of the respective exhaust cam. The exhaust valve opening side 10a is shown in continuous lines and the exhaust valve closing side 10b is shown in broken lines. The opening of the respective inlet valve according to the curve profile 11 is defined by an inlet valve opening side 11a, while the closing of the respective inlet valve according to the curve profile 11 is defined by an inlet valve closing side 11 b. The intake valve opening side 11a is shown in phantom, and the intake valve closing side 11b is shown in continuous.
Fig. 1 and 2 show that the exhaust valve is from an angle alpha according to a curved profile 10 A1 Starts to open at an angle alpha A2 Is completely closed. The exhaust valve opening side 10a is at an angle alpha A1 Where the opening of the respective exhaust valve is started. The exhaust valve closing side 10b is at an angle alpha A2 Where the respective exhaust valve is fully closed. Under full and partial load, these angles α A1 And alpha A2 Are identical.
According to the curve profile 11, the inlet valve is at an angle alpha E1 Or alpha E1 Opening is started and respectively at angle alpha E2 And alpha is E2 Is completely closed. The intake valve opening side surfaces 11a are respectively at an angle α E1 And alpha is E1 Where the opening of the respective inlet valve is started, wherein the inlet valve closing side 11b is at an angle α, respectively E2 And alpha is E2 The corresponding intake valve is fully closed. As can be seen from a comparison of fig. 1 and 2, in the partial-load operation of fig. 2, the intake cam (which determines the curve profile 11) is adjusted relative to the exhaust cam (which determines the curve profile 10), i.e. is retarded, relative to the full-load operation of fig. 1. The adjustment is performed by means of an angle beta. Thus, the following formula applies:
α* E1 =α E1 +β
α* E2 =α E2 +β
the exhaust valve closing side 10b of the exhaust cam and the intake valve opening side 11a of the intake cam are formed in such a way that they are in phase at both full load (see fig. 1) and partial load (see fig. 2)The intake valve should start to open before the so-called top dead center (OT) of the respective cylinder, i.e. at an angle α at full load in fig. 1 E1 Opening starts at this point and is at an angle α under part load according to fig. 2 E1 Where opening begins and in each case at least one exhaust valve of the respective cylinder is after top dead center (OT) of the respective cylinder, i.e. in each case at an angle alpha A2 At this point, it is completely closed.
Furthermore, the exhaust valve closing side 10b of the exhaust cam is embodied in such a way that at least one exhaust valve of the respective cylinder is initially closed with a relatively large gradient and subsequently closed with a relatively small gradient. A change from a relatively large gradient to a relatively small gradient of the exhaust valve closing side occurs in the region of the top dead center OT of the respective cylinder.
At full load of the internal combustion engine, the relatively small gradient of the exhaust valve closing side 10b is at an angle α A2 At least one exhaust valve of the corresponding cylinder is closed, the angle alpha A2 At an angle alpha under full load E2 Between 60 KW and 30 KW before the at least one inlet valve is completely closed. KW represents the crank angle.
Under partial load, the relatively small gradient of the exhaust valve closing flank 10b is likewise at an angle α A2 At least one exhaust valve of the corresponding cylinder is closed, however, the angle alpha A2 At an angle alpha E2 Between (60 ° +β) KW and (30 ° +β) KW before at least one intake valve of the corresponding cylinder is completely closed. KW represents the crank angle.
Furthermore, the intake opening side 11a of the intake cam is designed in such a way that at least one intake valve of the corresponding cylinder is initially opened with a relatively small gradient and then opened with a relatively large gradient.
At full load of the internal combustion engine (see fig. 1), the relatively small gradient is at angle α E1 At which to start opening at least one inlet valve of the corresponding cylinder, the angle alpha E1 In the range between 90 KW and 60 KW before top dead center of the corresponding cylinder.
Phase of the opening side of the intake valve under partial loadFor small gradients at angle α E1 Where to start opening at least the intake valve of the respective cylinder, the angle α E1 And thus in the range between (90-beta) KW and (60-beta) KW before the top dead center OT of the corresponding valve. KW represents the crank angle.
At full load, a change from a relatively small gradient of the intake valve opening side face 11a to a relatively large gradient of the intake valve opening side face 11a occurs in the region of the top dead center OT of the corresponding cylinder. At partial load, the change from a relatively small gradient of the intake valve opening side face 11a to a relatively large gradient of the intake valve opening side face 11a is regulated with a beta-lag with respect to full load.
By the above configuration of the intake and exhaust valves and the exhaust valve closing side 10b of the exhaust cam and the intake valve opening side 11a of the intake cam, a sufficiently large valve overlap 12 is provided both at full load according to fig. 1 and at partial load according to fig. 2, wherein the valve overlap 12 is characterized by an angular range between the start of opening of the respective intake valve and the complete closing of the respective exhaust valve. At full load according to fig. 1, the valve overlap 12 is therefore defined by α A2 – α E1 Is limited and is operated by alpha in partial load A2 – α* E1 And (3) limiting. The angular range of the valve overlap 12 is thus sufficiently large not only at full load but also at partial load in order to ensure cooling of the exhaust valve via the charge air over all load ranges without consumption disadvantages.
List of reference numerals
10a exhaust valve opening side
10b exhaust valve closing side
11a intake valve opening side
11b intake valve closing side
12. The valves overlap.

Claims (12)

1. A valve train for actuating gas exchange valves of cylinders of an internal combustion engine, wherein each cylinder comprises at least one inlet valve and at least one outlet valve as gas exchange valves,
having an intake camshaft carrying intake cams for the intake valves of the cylinders, wherein each intake cam comprises an intake valve opening side (11 a) and an intake valve closing side (11 b),
having an exhaust camshaft carrying exhaust cams for the exhaust valves of the cylinders, wherein each exhaust cam comprises an exhaust valve opening side (10 a) and an exhaust valve closing side (10 b),
with a camshaft adjusting device for the intake camshaft, via which the intake cam is adjustable relative to the exhaust cam in order to provide, at full load of the internal combustion engine, intake valves of the cylinders with valve actuation that differs from valve actuation at part load of the internal combustion engine,
wherein the exhaust valve closing side (10 b) of the exhaust cam and the intake valve opening side (11 a) of the intake cam are formed in such a way that, at full load and partial load on each cylinder, the at least one intake valve starts to open before top dead center (OT) of the respective cylinder and the at least one exhaust valve closes completely after top dead center (OT) of the respective cylinder,
wherein the exhaust valve closing flank (10 b) of the exhaust cam is formed in such a way that at least one exhaust valve of the respective cylinder is initially closed with a relatively large gradient and subsequently with a relatively small gradient, wherein a change from a relatively large gradient to a relatively small gradient occurs in the region of the top dead center (OT) of the respective cylinder, and wherein, at full load of the internal combustion engine, the relatively small gradient completely closes at least one exhaust valve of the respective cylinder in the range between 60 DEG KW and 30 DEG KW before the complete closing of the at least one intake valve,
wherein the intake valve opening side (11 a) of the intake cam is formed in such a way that at least one intake valve of the respective cylinder is initially opened with a relatively small gradient and subsequently with a relatively large gradient, wherein at full load of the internal combustion engine the relatively small gradient starts to open the at least one intake valve of the respective cylinder in a range between 90 DEG KW and 60 DEG KW before the top dead center (OT) of the respective valve, and wherein at full load a change from a relatively small gradient to a relatively large gradient occurs in the region of the top dead center (OT) of the respective cylinder.
2. A valve train according to claim 1, wherein the camshaft adjustment device retards the intake cam by an angle β during a change from full load to partial load.
3. A valve train according to claim 2, characterized in that said relatively small gradient starts to open at least one inlet valve of the respective cylinder in the range between (90 ° - β) KW and (60 ° - β) KW before top dead center (OT) of the respective valve under part load.
4. A valve train according to claim 2 or 3, characterized in that, under part load, the relatively small gradient completely closes at least one exhaust valve of the respective cylinder in a range between (60 ° +β) KW and (30 ° +β) KW before completely closing at least one intake valve.
5. A valve train according to claim 2 or 3, wherein β is equal to between 30 ° KW and 50 ° KW.
6. A valve train according to claim 4, wherein β is equal to between 30 ° KW and 50 ° KW.
7. A method for actuating a gas exchange valve of a cylinder of an internal combustion engine,
wherein each cylinder comprises at least one intake valve and at least one exhaust valve as gas exchange valves,
wherein the intake valves of the respective cylinders starting from an intake cam including an intake valve opening side (11 a) and an intake valve closing side (11 b) are actuated to open and close,
wherein the exhaust valves of the respective cylinders starting from an exhaust cam comprising an exhaust valve opening side (10 a) and an exhaust valve closing side (10 b) are actuated to open and close,
wherein during a change between full load and part load of the internal combustion engine, the intake cam is adjusted relative to the exhaust cam to provide different valve actuation for the intake valve at full load than at part load,
wherein, at full load and partial load on each cylinder, the intake valve opening side (11 a) of the respective intake cam starts to open at least one intake valve before the top dead center (OT) of the respective cylinder, and the exhaust valve closing side (10 b) of the respective exhaust cam completely closes at least one exhaust valve of the respective cylinder after the top dead center (OT) of the respective cylinder,
wherein the exhaust valve closing side (10 b) of the exhaust cam initially closes the at least one exhaust valve of the respective cylinder with a relatively large gradient and subsequently closes the at least one exhaust valve of the respective cylinder with a relatively small gradient, wherein a change from the relatively large gradient to the relatively small gradient occurs in the region of the top dead center (OT) of the respective cylinder, and wherein, at full load of the internal combustion engine, the relatively small gradient completely closes the at least one exhaust valve of the respective cylinder in a range between 60 DEG KW and 30 DEG KW before the complete closing of the at least one intake valve,
wherein the intake valve opening side (11 a) of the intake cam initially opens at least one intake valve of the respective cylinder with a relatively small gradient and subsequently opens at least one intake valve of the respective cylinder with a relatively large gradient, wherein at full load of the internal combustion engine the relatively small gradient starts to open the at least one intake valve of the respective cylinder in a range between 90 DEG KW and 60 DEG KW before top dead center (OT) of the respective valve, and wherein at full load a change from the relatively small gradient to the relatively large gradient occurs in the region of top dead center (OT) of the respective cylinder.
8. The method of claim 7, wherein the intake cam is adjusted with an angular beta retard via an intake camshaft during a change from full load to partial load of the internal combustion engine.
9. The method of claim 8, wherein at part load, the relatively small gradient begins to open at least one intake valve of the respective cylinder in a range between (90 ° - β) KW and (60 ° - β) KW before top dead center (OT) of the respective valve.
10. A method according to claim 8 or 9, characterized in that at part load the relatively small gradient completely closes at least one exhaust valve of the respective cylinder in a range between (60 ° +β) KW and (30 ° +β) KW before completely closing at least one intake valve.
11. The method according to claim 8 or 9, wherein β is equal to between 30 ° KW and 50 ° KW.
12. The method of claim 10, wherein β is equal to between 30 ° KW and 50 ° KW.
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