CN112443403A - Valve mechanism and method for actuating a gas exchange valve - Google Patents

Valve mechanism and method for actuating a gas exchange valve Download PDF

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Publication number
CN112443403A
CN112443403A CN202010922886.0A CN202010922886A CN112443403A CN 112443403 A CN112443403 A CN 112443403A CN 202010922886 A CN202010922886 A CN 202010922886A CN 112443403 A CN112443403 A CN 112443403A
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China
Prior art keywords
valve
exhaust
intake
flank
respective cylinder
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CN202010922886.0A
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Chinese (zh)
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CN112443403B (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
    • F01L1/047—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
    • 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
    • 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 valve train for actuating intake and exhaust valves of an internal combustion engine has an intake camshaft, each intake camshaft including an intake valve opening flank and an intake valve closing flank; and exhaust camshafts, each exhaust camshaft including an exhaust valve opening flank and an exhaust valve closing flank. The exhaust valve closing flank and the intake valve opening flank are designed such that at full load and part load the intake valve starts to open before cylinder top dead center and the exhaust valve is fully closed after top dead center. The exhaust valve closing flank is designed such that the exhaust valve closes initially 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 the complete closing of the inlet valve. The intake valve opening flank is designed such that the intake valve opens initially with a relatively small gradient and then with a relatively large gradient, wherein the relatively small gradient starts to open the intake valve in the range of 90 ° to 60 ° KW before top dead center at full load.

Description

Valve mechanism and method for actuating a gas exchange valve
Technical Field
The invention relates to a valve mechanism 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 valvetrain includes an intake camshaft that carries intake cams for actuating intake valves of cylinders of the internal combustion engine. Furthermore, the valve train comprises an exhaust camshaft carrying exhaust cams for actuating the exhaust valves of the cylinders of the internal combustion engine.
Each intake cam includes an intake valve opening flank for opening a respective intake valve and an intake valve closing flank for closing the respective intake valve. Each exhaust cam includes an exhaust valve opening flank following the respective exhaust valve and an exhaust valve closing flank for closing the respective exhaust valve.
DE 102016112447 a1 discloses a valve train in which a cam lever interacts with a cam of a camshaft, wherein a roller of the cam lever sweeps a cam profile of the respective cam and transmits the cam profile via a tappet 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 102016112448B 4, in which case a roller of a cam rod sweeps a cam profile of a cam and transmits the cam profile to a gas exchange valve via a pushrod (however, without a rocker arm).
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 an internal combustion engine. The valve overlap is characterized in that the respective intake valve starts to open even before top dead center of the respective cylinder, and the respective exhaust valve of the respective cylinder is fully closed only after top dead center of the respective cylinder. The pressure difference between the charge air pressure in the respective exhaust port and the exhaust gas back pressure in the respective exhaust port can then be used in order to sweep the remaining exhaust gas from the combustion chamber of the respective cylinder into the exhaust port by means of fresh air.
Furthermore, valve trains with variable valve actuation are known from practice in order to provide different valve actuations for the gas exchange valves of the cylinders in full load and partial load. In this way, the cylinder charge can be improved, in particular at partial load.
There is a need for a valve train which makes it possible for an internal combustion engine to operate optimally not only at full load but also at part load, so that good cooling of the exhaust valves is ensured (in particular in all load ranges) and consumption disadvantages are avoided.
Disclosure of Invention
Starting from this point, the invention is based on the following objectives: a new valve mechanism and a corresponding method for actuating a gas exchange valve are created.
This object is solved by a valve mechanism according to the invention for actuating a gas exchange valve of a cylinder of an internal combustion engine. Each cylinder comprising at least one inlet valve and at least one exhaust valve as gas exchange valves, having an inlet camshaft carrying inlet cams for the inlet valves of the cylinder, wherein each inlet cam comprises an inlet valve opening flank and an inlet valve closing flank having an exhaust camshaft carrying exhaust cams for the exhaust valves of the cylinder, wherein each exhaust cam comprises an exhaust valve opening flank and an exhaust valve closing flank; there is a camshaft adjustment device for the intake camshaft, via which the intake cam is adjustable relative to the exhaust cam in order to provide a different valve actuation for the intake valves of the cylinders at full load of the internal combustion engine than at part load of the internal combustion engine. The exhaust valve closing flank of the exhaust cam and the intake valve opening flank of the intake cam are formed in such a way that, at full and part load on each cylinder, the at least one intake valve starts to open before the top dead center (OT) of the respective cylinder and the at least one exhaust valve is fully closed after the 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 closes initially 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 occurs in the region of 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 a range between 60 ° KW and 30 ° KW before complete closing of the at least one intake valve. The inlet valve opening flank of the inlet cam is formed in such a way that at least one inlet valve of the respective cylinder opens initially 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 at least one inlet 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.
The valvetrain includes an intake camshaft that carries intake cams for intake valves of the cylinders, where each intake cam includes an intake valve open side and an intake valve closed side. The valve train comprises an exhaust camshaft carrying exhaust cams for the exhaust valves of the cylinders, wherein each exhaust cam comprises an exhaust valve opening flank and an exhaust valve closing flank. The valve train further comprises a camshaft adjustment device for an intake camshaft, via which the intake cam is adjustable relative to the exhaust cam in order to provide a different valve actuation for the intake valves of the cylinders at full load of the internal combustion engine than at part load of the internal combustion engine.
The exhaust valve closing flank of the exhaust cam and the intake valve opening flank of the intake cam are designed in such a way that at full and part load on each cylinder at least one intake valve starts to open before the top dead center of the respective cylinder and at least one exhaust valve is fully closed after the top dead center 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 closes initially 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 occurs in the region of 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 completely closing the at least one intake valve. KW represents a crankshaft angle.
The inlet valve opening flank of the inlet cam is designed in such a way that at least one inlet valve of the respective cylinder opens initially with a relatively small gradient and subsequently with a relatively large gradient, wherein the relatively small gradient starts to open the at least one inlet valve of the respective cylinder in a range between 90 ° KW and 60 ° KW before top dead center of the respective valve at full load of the internal combustion engine, and wherein a change from the relatively small gradient to the relatively large gradient occurs in the region of top dead center of the respective cylinder at full load. KW represents a crankshaft angle.
In the valve mechanism, the camshaft adjusting device makes it possible to adjust the intake cam relative to the exhaust cam. The exhaust valve closing flank of the exhaust cam and the intake valve opening flank of the intake cam are formed in a defined manner in order 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 in order to sweep exhaust gases out into the exhaust port and in the process cool the exhaust valve of the cylinder. On the other hand, the consumption disadvantage is avoided by the defined contour of the exhaust valve closing flank of the exhaust cam and of the intake valve opening flank of the intake cam. A sufficient period of valve overlap is available, both at full load and at part load, in order to ensure good cooling of the exhaust valve in all load ranges without consumption disadvantages.
Preferably, during a change from full load to part load, the camshaft adjustment device adjusts the intake cam by an angle β towards hysteresis. At part load, the relatively small gradient of the intake valve opening flank begins opening at least one intake valve in the range between (90 ° - β) KW and (60 ° - β) KW before top dead center of the respective valve. At part load, a relatively small gradient fully closes at least one exhaust valve in a range between (60 ° + β) KW and (30 ° + β) KW before fully closing at least one intake valve. Preferably, β is equal to between 30 ° KW and 50 ° KW. KW represents a crankshaft angle.
This allows the internal combustion engine to be operated particularly advantageously both at partial load and at full load. During both full load and part load, sufficient 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 exhaust valve as gas exchange valves, wherein the or each inlet valve of the respective cylinder is actuated to open and close starting from an inlet cam comprising an inlet valve opening flank and an inlet valve closing flank, wherein the or each exhaust valve of the respective cylinder is actuated to open and close starting from an exhaust cam comprising an exhaust valve opening flank and an exhaust valve closing flank. During a change between full and part load of the internal combustion engine, adjusting the intake cams relative to the exhaust cams to provide different valve actuation for the intake valves at full load than at part load, wherein at full and part load on each cylinder, the intake valve opening flank 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 flank 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 flank 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 top dead center (OT) of the respective cylinder, and wherein the relatively small gradient fully closes the at least one exhaust valve of the respective cylinder in a range between 60 ° KW and 30 ° KW before fully closing the at least one intake valve at full load of the internal combustion engine. The inlet valve opening flank of the inlet cam initially opens at least one inlet valve of the respective cylinder with a relatively small gradient and subsequently opens at least one inlet 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 at least one inlet 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 result from the dependent claims and the following description. Exemplary embodiments of the invention are explained in more detail by means of the figures without being limited thereto. There is shown:
FIG. 1 is a representation of the open and closed sides of an intake cam and an exhaust cam of a valvetrain according to the present invention at full load;
fig. 2 is a representation of the open and closed sides of the intake and exhaust cams of a valvetrain according to the present invention at partial load.
Detailed Description
The basic structure of a valvetrain of an internal combustion engine is known to those skilled in the art to which reference is made herein.
Thus, a valve train for actuating gas exchange valves of cylinders of an internal combustion engine comprises an intake camshaft carrying intake cams. The intake cams are used for actuating gas exchange valves formed as intake valves of a cylinder of an internal combustion engine, wherein each intake cam comprises an intake valve opening flank for opening a respective intake valve and an intake valve closing flank for closing the respective intake valve.
Further, the valve train includes an exhaust camshaft carrying exhaust cams. The exhaust cam is used to actuate a gas exchange valve, formed as an exhaust valve, of a cylinder of the internal combustion engine in order to open and close the exhaust valve. Thus, each exhaust cam includes an exhaust valve opening flank for opening a respective exhaust valve and an exhaust valve closing flank for closing the respective exhaust valve.
Furthermore, the valve train comprises a camshaft adjusting device. With the camshaft adjusting device, the intake camshaft can be adjusted in order to adjust the intake cams relative to the exhaust cams 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 and intake valves of a cylinder is shown for full load operation (see fig. 1) and for part load operation (see fig. 2), wherein the curved profile 10 corresponds to the actuation of the exhaust valve by the opening and closing flanks of the exhaust cam, and the curved profile 11 corresponds to the actuation of the intake valve by the opening and closing flanks of the intake cam.
The opening of the respective exhaust valve is defined by the exhaust valve opening flank 10a of the respective exhaust cam and the closing of the respective exhaust valve is defined by the exhaust valve closing flank 10b of the respective exhaust cam. The exhaust valve opening flank 10a is shown in continuous line drawing and the exhaust valve closing flank 10b is shown in dashed line drawing. The opening of the respective inlet valve according to the curved profile 11 is defined by the inlet valve open flank 11a, while the closing of the respective inlet valve according to the curved profile 11 is defined by the inlet valve closed flank 11 b. The intake valve open side 11a is shown in dashed lines and the intake valve closed side 11b is shown in continuous lines.
Fig. 1 and 2 show that the exhaust valve follows the curve profile 10 from the angle alphaA1Starts to open and at an angle alphaA2Is completely closed. The exhaust valve opening flank 10a is at an angle alphaA1Begins to open the respective exhaust valve. The exhaust valve closing flank 10b is at an angle alphaA2The respective exhaust valve is fully closed. At full and part load, these angles αA1And alphaA2Are the same.
According to the curve profile 11, the inlet valve is at an angle alphaE1Or αE1Begin to open and are each at an angle alphaE2And αE2Is completely closed. The intake valve open sides 11a are each at an angle αE1And αE1Where the respective intake valve begins to open, wherein the intake valve closing flanks 11b are each at an angle alphaE2And αE2The respective 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 defines the curve profile 11) is adjusted relative to the exhaust cam (which defines the curve profile 10), i.e. towards a hysteresis, in relation to the full load operation of fig. 1. The adjustment is performed by an angle β. Thus, the following formula applies:
α*E1=αE1+β
α*E2=αE2+β
the exhaust valve closing flank 10b of the exhaust cam and the intake valve opening flank 11a of the intake cam are formed in such a way that the respective intake valve starts to open before the so-called top dead center (OT) of the respective cylinder both at full load (see fig. 1) and at partial load (see fig. 2), i.e. at angle α at full load in fig. 1E1Begins to open and is at an angle a under partial load according to fig. 2E1Begins to open and in each case at least one exhaust valve of the respective cylinder is after the top dead center (OT) of the respective cylinder, i.e. in each case at an angle alphaA2And completely closed.
Furthermore, the exhaust valve-closing flank 10b of the exhaust cam is embodied in such a way that at least one exhaust valve of the respective cylinder closes initially with a relatively large gradient and subsequently 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 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 flank 10b is at an angle αA2At least one exhaust valve of the respective cylinder is closed, the angle alphaA2At angle alpha under full loadE2Between 60 deg. KW and 30 deg. KW before at least one inlet valve is completely closed. KW represents a crankshaft angle.
At part load, the relatively small gradient of the exhaust valve closing flank 10b is also at the angle αA2At least one exhaust valve of the respective cylinder is closed, however, the angle alphaA2At an angle αE2Between (60 ° + β) KW and (30 ° + β) KW before at least one intake valve of the respective cylinder is completely closed. KW represents a crankshaft angle.
Furthermore, the intake opening flank 11a of the intake cam is designed in such a way that at least one intake valve of the respective cylinder opens initially with a relatively small gradient and subsequently with a relatively large gradient.
At full load of the internal combustion engine (see fig. 1), the relatively small gradient is at the angle αE1At least one inlet valve of the corresponding cylinder is started to open, the angle alphaE1In the range between 90 deg. KW and 60 deg. KW before top dead center of the respective cylinder.
At part load, the relatively small gradient of the open side of the inlet valve is at an angle αE1At least the inlet valve of the corresponding cylinder is opened, the angle alphaE1Then in the range between (90 ° - β) KW and (60 ° - β) KW before top dead center OT of the respective valve. KW represents a crankshaft angle.
At full load, a change from a relatively small gradient of the intake valve open flank 11a to a relatively large gradient of the intake valve open flank 11a occurs in the region of the top dead center OT of the respective cylinder. At part load, the change from a relatively small gradient of the intake valve open flank 11a to a relatively large gradient of the intake valve open flank 11a is adjusted with a beta-hysteresis with respect to full load.
By the above configuration of the intake and exhaust valves and the exhaust valve closing flank 10b of the exhaust cam and the intake valve opening flank 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 beginning 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 αA2 – αE1Define, and operate at part loadIn the formula of alphaA2 – α*E1And (4) limiting. The angular range of the valve overlap 12 is therefore sufficiently large both at full load and at partial load to ensure cooling of the exhaust valve via the charge air in all load ranges without consumption disadvantages.
List of reference numerals
10a exhaust valve open side
10b exhaust valve closing flank
11a intake valve open side
11b intake valve closing flank
12 valve overlap.

Claims (10)

1. A valve mechanism 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 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 flank (11 a) and an intake valve closing flank (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 flank (10 a) and an exhaust valve closing flank (10 b),
having a camshaft adjustment device for the intake camshaft, via which the intake cam is adjustable relative to the exhaust cam in order to provide a valve actuation for the intake valves of the cylinders at full load of the internal combustion engine that differs from the valve actuation at partial load of the internal combustion engine,
wherein the exhaust valve closing flank (10 b) of the exhaust cam and the intake valve opening flank (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 the top dead center (OT) of the respective cylinder and the at least one exhaust valve is fully closed after the 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 closes initially 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 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 a range between 60 ° KW and 30 ° KW before complete closing of the at least one intake valve,
wherein the inlet valve opening flank (11 a) of the inlet cam is formed in such a way that the at least one inlet valve of the respective cylinder opens initially 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 inlet 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.
2. A valve train as claimed in claim 1, characterized in that the camshaft adjusting device adjusts the intake cam with an angle β towards hysteresis during a change from full load to part load.
3. A valve train according to claim 2, characterized in that the 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 centre (OT) of the respective valve at part load.
4. A valve train according to claim 2 or 3, characterized in that at part load a 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 inlet valve.
5. A valve train according to any of claims 2 to 4, characterized in that β equals between 30 ° KW and 50 ° KW.
6. A method for actuating a gas exchange valve of a cylinder of an internal combustion engine,
wherein each cylinder comprises at least one inlet valve and at least one exhaust valve as gas exchange valves,
wherein the or each intake valve of the respective cylinder is actuated to open and close starting from an intake cam comprising an intake valve opening flank (11 a) and an intake valve closing flank (11 b),
wherein the or each exhaust valve of the respective cylinder is actuated to open and close starting from an exhaust cam comprising an exhaust valve opening flank (10 a) and an exhaust valve closing flank (10 b),
wherein during a change between full 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 part load on each cylinder the intake valve opening flank (11 a) of the respective intake cam starts to open at least one intake valve before top dead center (OT) of the respective cylinder and the exhaust valve closing flank (10 b) 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,
wherein the exhaust-valve-closing flank (10 b) of the exhaust cam initially closes at least one exhaust valve of the respective cylinder with a relatively large gradient and subsequently closes at least one exhaust valve of the respective cylinder with a relatively small gradient, wherein a change from a relatively large gradient to a relatively small gradient takes place in the region of 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 a range between 60 DEG KW and 30 DEG KW before complete closing of at least one intake valve,
wherein the inlet valve opening flank (11 a) of the inlet cam initially opens at least one inlet valve of the respective cylinder with a relatively small gradient and subsequently opens at least one inlet 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 at least one inlet 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.
7. The method of claim 6, wherein the intake cam is adjusted via an intake camshaft with an angle β retard during a change from full load to part load of the internal combustion engine.
8. A method according to claim 7, characterised in that at part load a relatively small gradient starts to open at least one inlet valve of the respective cylinder in a range between (90 ° - β) KW and (60 ° - β) KW before top dead centre (OT) of the respective valve.
9. Method according to claim 7 or 8, characterized in that at part load, a 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 inlet valve.
10. Method according to any one of claims 7 to 9, characterized in that β is equal to between 30 ° KW and 50 ° KW.
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