GB2512925A

GB2512925A - Valve train for an internal combustion engine

Info

Publication number: GB2512925A
Application number: GB1306669.1A
Authority: GB
Inventors: Anand B Goudar; Amol Durge
Original assignee: Daimler AG
Current assignee: Mercedes Benz Group AG
Priority date: 2013-04-11
Filing date: 2013-04-11
Publication date: 2014-10-15
Also published as: GB201306669D0

Abstract

A valve train 10 for an internal combustion engine with a pressure controlled plunger balancing mechanism, the valve train 10 comprising at least one inlet or exhaust valve 12 for a corresponding combustion chamber 46 of the engine, at least one plunger 16 slidably arranged in a corresponding cylinder 14, at least one rocker arm 18 coupled to the gas valve 12 and the plunger 16, and a pressure adjusting device 50 by means of which a pressure of a hydraulic fluid contained in a chamber 48 is adjustable,. The valve lift (VL) of the gas exchange valve 12 can be very precisely adjusted by varying the pressure of the fluid. Additionally the valve train may have a spring actuated failsafe element 60 to lock the plunger in a fixed position. The valve train may also form part of a cylinder shut-off system in which the gas exchange valves are completely closed so as to prevent pumping losses.

Description

Valve Train for an Internal Combustion Engine The invention relates to a valve train for an internal combustion engine, in particular for a motor vehicle, according to the preamble of patent claim 1. 5Uh a

known from the serial production of the AMG 5.5 litre VS naturally aspirated engine which is also referred to as M152. That engine, for example, is used in the 2012 SLK 55 AMG.

The valve train comprises at least one gas exchange valve for a corresponding *0* combustion chamber of the internal combustion engine. The valve train further comprises at least one plunger slideably arranged in a corresponding cylinder of the valve train.

Furthermore, the valve train comprises at least one rocker arm coupled to the gas : exchange valve and the plunger. In dependence of the state of the plunger, the gas exchange valve can be actuated via the rocker arm by at least one cam arranged on a camshaft. The camshaft and the cam are rotatable about an axis of rotation. If the lobe of the cam touches the rocker arm and if, for example, the plunger is locked so that it cannot * slide in the corresponding cylinder, the gas exchange valve is open by the lobe of the cam via the rocker arm.

It is an object of the present invention to further develop a valve train of the previously mentioned kind, which facilitates a particularly efficient and powerful operation of the internal combustion engine.

This task is solved by a valve train having the features of patent claim 1. Advantageous embodiments with expedient and non-trivial developments of the invention are indicated in the other patent claims.

In order to provide a valve train for an internal combustion engine, in particular for a motor vehicle, of the kind indicated in the preamble of patent claim 1, which facilitates a particularly efficient and powerful operation of the internal combustion engine, according to the present invention the valve train comprises a pressure adjusting device by means of which a pressure of a fluid contained in a chamber bounded at least partially by the cylinder and the plunger is adjustable, wherein a valve lift of the valve is adjustable by adjusting the pressure of the fluid by means of the pressure adjusting device. By means of the adjusting device, the fluid, in particular in the form of a hydraulic fluid, can be conveyed into the chamber. Furthermore, by means of the pressure adjusting device the flow of the fluid into the chamber and out of the chamber can be controlled thereby adjusting the pressure prevailing in the chamber.

The valve lift which is commonly also referred to as stroke is adjustable by means of the pressure adjusting device in such a way that by adjusting the pressure in the chamber, an actuation or actuating force effected by the cam and acting on the gas exchange valve and/or the plunger via the rocker arm can be adjusted. Thus, the valve train uses a pressure controlled, in particular a hydraulically presure controlled plunger balancing mechanism which allows for a variably adjustment of the valve lift.

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Advantageously, the pressure in the chamber can be adjusted very precisely so that even very small changes of the valve lift can be realised. As a consequence, the valve lift can be adapted to various operating points of the internal combustion engine very precisely, thus facilitating a very efficient and powerful operation. In comparison with an internal S..

combustion engine which does not have the pressure controlled plunger balancing mechanism the engine's power and the torque output can be increased. Furthermore fuel consumption can be considerably reduced as well as emissions of C02, particles and NO. Furthermore, the valve train allows for a very high smooth cold weather operation of the internal combustion engine as well as for a particularly smooth torque delivery. In addition, engine shake at shut-off can be avoided.

Further advantages, features and details of the invention derive from the following description of the preferred embodiment as well as from the drawing. The features and feature combinations previously mentioned in the description as well as the features and feature combinations mentioned in the following description of the figures and/or shown in the figures alone can be employed not only in the respective indicated combination but also in any other combinations or taken alone without leaving the scope of the invention, Fig. 1 a, lb and 2 serve for illustrating the background of the invention.

The drawing shows in: Fig. la-b a schematic and perspective view cia valve train in two different operation modes respectively; Fig. 2 a schematic front view of a cam for actuating a gas exchange valve of the valve train; Fig. 3a a schematic view of a valve train according to the present invention; Fig. 3b a table with various values of pressures prevailing in different parts of the valve train; Fig. 4 another schematic view of the valve train according to the present invention; and S *SSSS * . : *. Fig. 5 diagrams for illustrating various operation modes of the valve train according to the present invention.

In the figures the same elements or elements having the same functions are equipped * with the same reference sign. S.. *

Fig. 3 to 5 serve for illustrating a variable valve lift mechanism for an internal combustion engine for a motor vehicle, the variable valve lift mechanism comprising a hydraulically pressure controlled plunger balancing mechanism with fail-safe capability. Moreover, Fig. 3 to 5 serve for illustrating a method for improving the fuel economy and for generating a higher torque and power output by means of the variable valve lift for a multi-cylinder internal combustion engine with the same capacity thereby reducing emissions and providing the driver with more ease and fun of driving.

Fig. 1 a and lb each show a valve train 10 for a multi-cylinder engine. For example, the multi-cylinder engine is a 5.5 litre VS naturally aspirated internal combustion engine which features direct injection, for example, at a pressure of 2900 psi, spray-guided combustion and piezo-injectors in conjunction with map-controlled cylinder shut-off, an all-aluminium crank case with honing, four-valve technology with continuous camshaft adjustment, a high compression ratio of 12.6:1, an ECO stop/start system and generator management, and revs to a maximum of more than 7000 rpm. The internal combustion engine has eight combustion chambers which are also referred to as combustion cylinders or cylinders.

By means of a cylinder management cylinder shut-off system, the cylinders 2, 3, 5 and 8 are cut off under partial load. The cylinder shut-off function is available over a wide engine speed range from 600 to 3600 rpm if the driver has selected transmission mode C which designates controlled efficiency. An information system arranged in an instrument cluster in the cockpit of the motor vehicle informs the driver if the cylinder shut-off is active and whether the engine is currently running in four-or eight-cylinder mode, 170 lb-ft of torque is still available in four-cylinder mode providing enough power to ensure plenty of acceleration in most driving situations.

As soon as the driver has the need for more power andjeaycSthepa.!tial load range, cylinders 2, 3, 5 and 6 are activated. The switching from four-to eight-cylinder operation is immediate and imperceptible, leading to no loss of occupant comfort. At an engine speed of 3600 rpm the activation process takes no longer than 30 ms.

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: ** The cylinder shut-off system is enabled by an engine management system with sixteen S. S * hydraulic actuators and a complex oil supply system in the cylinder head of the internal combustion engine. The selectable actuators are integrated into the cylinder head and keep gas exchange valveé in the form of intake and exhaust valves of cylinders 2, 3, 5 and B closed. At the same time fuel supply and ignition of cylinders 2, 3, 5 and 8 are deactivated. This reduces the load-change losses of the four deactivated cylinders. It also increases the efficiency of the four remaining and activated cylinders because the operating point is transferred to a higher load range. The actuators are compact and lightweight, allowing tight valve train operation and engine speeds up to 7200 rpm.

Optimal charging of the combustion chambers is ensured by large intake and exhaust valves. The exhaust valves which are subject to high thermal loads are hollow and sodium-cooled. Four overhead camshafts operate the thirty-two valves of the internal combustion engine via low-maintenance and low-friction cam followers which are also referred to as rocker arms. The internal combustion engine has an infinitely variable camshaft adjustment within a range of 40° on the intake and exhaust sides. The infinitely variable camshaft adjustment depends on the engine load and engine speed, leading to outstanding output and torque values, This also results in consistent idling at low speed. Depending on the engine speed, valve overlap can be varied for the best possible fuel and/or air supply to the combustion chambers and efficient removal of the exhaust gases. The variable camshaft adjustment is carried out hydraulically via four pivoting actuators. These actuators are electromagnetically activated and controlled by the engine control unit. The camshafts are driven by three high-performance silent chains.

The working principle of said cylinder shut-off system is now illustrated with reference to Fig. la, lb and 2. The valve train 10 shown in Fig. la and lb comprises at least one gas exchange valve 12 in the form of a poppet valve, The gas exchange valve 12 shown in Fig. la and lb can be an intake valve or an exhaust valve. The gas exchange valve 12 is assigned to a combustion chamber (cylinder) of the internal combustion engine and serves for controlling a flow of gas into and/or out of the corresponding cylinder.

The valve train 10 also comprises acytinder 14 which is shown in Fig. la and lb in a sectional view. A plunger 16 of the valve train 10 is slideably arranged in the corresponding cylinder 14. Furthermore the valve train 10 comprises a rocker arm 18 * which is coupled to the gas exchange valve 12 and the plunger 16. As can be seen in Fig. : ** Ia and lb, the valve train 10 comprises two springs 20, 22. The spring 20 is at least indirectly supported on the gas exchange valve 12 and is used for moving the gas exchange valve 12 into its closed position. * .. * * *

The spring 22 which is also referred to as plunger spring is at least indirectly supported on the plunger 16 and on a bottom 24 of the cylinder 14. The spring 22 is used for moving *.

the plunger 16 back to its initial position after the plunger 16 had been moved out of its initial position as will be described in the following.

For actuating the gas exchange valve 12 or the plunger 16, a cam 26 shown in Fig. 2 is used. The cam 26 is arranged on a camshaft which is rotatable about an axis of rotation A. Hence, the cam 26 is rotatable about the axis of rotation A, too. The cam 26 has a nose 28 which is also referred to as cam lobe 42 or lobe, a lobe centre line 30, a lobe lift 32, a fLank 34, a clearance ramp 36, a heel 38 and a base circle 40.

In addition, the valve train 10 has a hydraulically activated pin which is not shown in Fig. la and lb. The hydraulically activated pin is a locking element used for locking and releasing the plunger 16. The hydraulically activated pin can be moved between at least one locking position and at least one releasing position by means of a hydraulic fluid. In the releasing position of the pin the plunger 16 can slide in the cylinder 14 and in relation to the cylinder 14. In the locking position the plunger 16 is locked by means of the pin so that the plunger 16 cannot slide in the cylinder 14 and in relation to the cylinder 1& Under low load conditions and when a drive mode is in a certain state cylinders 2, 3, 5 and & are shut down or shut off completely (no injection, no emission) arid also the corresponding inlet and exhaust valves represented by the gas exchange vale 12 are closed completely so as to prevent pumping losses due to a vacuum created in the intake manifold-Shutting the valves completely off is done with the help of sixteen hydraulic actuators and a complex oil supply system.

The rocker arm 18 is used to propagate an actuation or actuating force effected by the cam 26 to the gas exchange valve 12 and/or the plunger 16. In other words, an actuation or actuating force ff ytiiwtam26actson4he1a5 gieJ2at-ffi the plunger 16 via the rocker arm 18. The actuation or actuating force of the cam 26 is also referred to as push of the cam 26 because the cam 26 pushes the gas exchange valve 12 * * and/or the plunger 16 via its cam lobe 42. * .

: ** The spring 20 has a greater tension than the spring 22. During normal operation, the hydraulically activated pin locks the movement of the plunger 16 in the cylinder 14 and the push of the cam 26 or its cam lobe 42 is entirely transferred to the gas exchange valve i.: :* 12. In the cylinder shut-off mode, the hydraulically activated pin is unlocked and the plunger 16 is free to move within the action of the spring 22. Since the tension of the *..

spring 22 is greater than the tension of spring 20, the push of the cam lobe 42 is now completely transferred to the plunger 16 so that the gas exchange valve 12 remains shut.

This working principle can be transferred to the intake and exhaust valves of the cylinders being shut down or shut off.

In internal combustion engines, variable valve timing (VVT), also known as variable valve lift (VVL), is any mechanism or method that can alter the shape or timing of a valve lift event. VVT allows the lift, duration, or timing (in various combinations) of the intake and/or exhaust valves to be changed while the internal combustion engine is in operation. There are many ways in which VVL can be achieved, ranging from mechanical devices to electro-hydraulic and cam-less systems.

The valves within an internal mbustion engine are used to control the flow of intake and exhaust gases into and out of the combustion chambers. The timing, duration and lift of the valve events have a significant impact on engine performance. In a standard internal combustion engine the valve events are fixed, so performance at different loads and speed is always a compromise between drivabihty (power and torque), fuel economy and emissions. An engine equipped with a variable valve actuation system is freed from these constrains allowing performance to be improved over the engine operating range.

Fig. la shows the valve train 10 in a so-called cylinder deactivation mode in which the plunger 16 is activated by the cam 26 via the rocker arm 18 and the gas exchange valve 12 stays completely closed. Fig. lb shows the valve train loin a so-called normal operation mode, in which the gas exchange valve 12 is activated by the cam 26 via the rocker arm 18, hence the gas exchange valve 12 is fully opened by the cam 26.

In the following a mechanism and a method are illustrated which facilaate a variable valve lift bf the iritikflffd exhaust valves ofsar&Internal 0mbustioflSnglne_. By rcffins.9! -the mechanism the depth to which the plunger 16 can be pushed down by the cam lobe 42 via the rocker arm 18 can be controlled. As a consequence, the depth of opening of the gas exchange valve 12 can be controlled or adjusted. * *

* ** Said mechanism is shown in Fig. 3a. Fig. Sa shows a cylinder head 44 of the internal combustion engine, the cylinder head 44 houses the gas exchange valve 12 which can be an intake valve or an exhaust valve. Moreover, a combustion chamber in the form of a : ** cylinder 46 of the internal combustion engine is shown in Fig. 3a. The cylinder 46 is partially bounded by the cylinder head 44 and a cylinder casing 49 respectively.

the gas exchange valve 12 can be moved between a minimum position Mnl and a maximum position Mx2. In the minimum position Mnl the gas exchange valve 12 is closed. This means that the gas exchange valve 12 is in its closed position shown in Fig. 3a by solid lines. If the gas exchange valve 12 is in the maximum position Mx2, the gas exchange valve 12 is in its fully opened position shown in Fig. 3 by dotted lines.

The gas exchange valve 12 is held in its closed position by the spring 20, whereas the gas exchange valve 12 is caused to open by the action or actuation of the rocker arm 18 which is pushed by the cam lobe 42 of the cam 26. The cam 26 is arranged on the camshaft which is rotatable about the axis of rotation A. If the heel 38 of the cam 26 touches the rocker arm 18, the plunger 16 is held to its minimum position Mnl by the action of the spring 22.

If the nose 28 of the cam 26 touches the rocker arm 18, the plunger 16 is pushed to its maximum depth position Mx, The plunger 16 also has a minimum position Mn. The above described operation is possible when there is no fluid pressure in a chamber 48 which is bounded at least partially by the cylinder 14 and the plunger 16 respectively. During this operation, the valve lift of the gas exchange valve 12 is zero. This means that the gas exchange valve 12 is completely closed so that it stays in its minimum position Mnl.

A valve lift between the minimum position Mnl and the maximum position Mx2 is achieved by varying the pressure in the chamber 48. For this purpose, a hydraulic fluid contained in the chamber 48 is used. In order to adjust the pressure of the hydraulic fluid contained in the chamber 48, the valve train io comprises a pressure adjusting device 50.

The hydraulic fluid in the form of a none*compressible fluid is pressurized with the help of a pump 52 of the pressure adjusting device 50. Said nonecompressible fluid can be a, for example, hydraulic oil. The pressure adjusting device 50 also comprises a rail 54 for storing or holdiiSthë presurizetflUidHft0th_w09rth essurizd fluid is stored in the rail 54. S. .*

The pressure of the hydraulic fluid inside the rail 54 is regulated by means of valves in the * form of solenoid valves. Furthermore, the pressure adjusting device 50 also comprises a * *5øø* reservoir 56 which is placed in a return path illustrate d by directional arrows 58, For adjusting a flow of the hydraulic fluid into and out of the chamber 48 and thus for flØ.

adjusting the pressure in the chamber 48, the pressure adjusting device 50 has solenoid valves SVI, SV2. The flow of the hydraulic fluid into the chamber 46 is controlled by means of the solenoid valve SVI. The flow of the hydraulic fluid out of the chamber 46 back to the reservoir 56 via the return path is controlled by means.of the solenoid valve SV2.

Furthermore, said hydraulically activated pin for unlocking the plunger 16 can be seen in Fig. 3a, the pin being designated by the reference 60. A directional arrow 62 illustrates that the pressurized fluid stored in the rail 54 can flow to the other chambers 48 corresponding to the other cylinders of the combustion engine.

The valve train 10 also has a fail-safe mechanism. For said fail-safe mechanism, the pin is used as a fail-safe element. In order to realize the fail-safe mechanism, a slight change is made to the before mentioned working principle of the hydraulically activated pin 60. By default, The pin 60 which is also referred to as lock pin is pushed by a spring into the locking position which would lock the movement of the plunger 16 and hence the internal combustion engine works in lull valve lift mode. In other words, said spring is preloaded in the unlocking position of the pin 60.

During all the other modes the pin 60 is unlocked by means of hydraulic actuation. In other words, the pin 60 is held in its unlocking position against the spring force of the preloaded spring by means of a hydraulic fluid.

If the pressure adjusting device 50 and, for example, the pump 52 and/or one of the solenoid valves, fails which would cause a pressure drop, the spring pushes the pin 60 from its unlocking into its locking position thereby locking the movement of the plunger 16. Hence, the internal combustion engine is still able to run in full valve opening mode.

Fig. 3b shows a table for illustrating how the depth to which the plunger 16 can be pushed by the cam 26iithe inside the chamber 48. In the table, i designates the pressure in the chamber 48.

FurthermOre, P2 designates the pressure in the rail 54 and P3 designates the pressure in * the return path, wherein Atm. designates atmospheric pressure. Moreover, VL designates * various values of the valve lift, the various values being adjustable by adjusting the pressure of the hydraulic fluid contained in the chamber 48. The pressure P1 in the chamber 48 is calibrated in such a way that when the fluid in the chamber 48 is pressurized to the maximum value, for example, 100 bar, the push of the cam lobe 42 : ** opens the gas exchange valve to its maximum depth i.e. to the maximum position Mx2, Said maximum depth is, for example, 10mm.

The pressure values have to be such that when the chamber 48 is fully pressurized the tension of the spring 20 is lesser than the tension of spring 22 (basically this is the opposition force applied by the plunger 16). Hence when the cam lobe 42 pushes the rocker arm 18, the entire push is completely taken by the gas exchange valve 12 making it open to the maximum depth. Now, in order to open the gas exchange valve 12 to a lesser depth than that of the maximum position Mx2, the pressure values in the chamber 48 have to be reduced to lesser values, for example, 80 bar. Said lesser depth is, for

example, 8 mm.

Now that the pressure in the chamber 48 is reduced and the tension of the spring 22 is lesser than the tension of the spring 20, the initial push of the nose 28 is partially absorbed by the plunger 16 after which the push is transferred to the gas exchange valve 12.

Fig. 4 illustrateS the supply of four chambers 48 with the pressurized hydraulic fluid stored in the rail 54. Each chamber 48 corresponds to a plunger of a combustion cylinder of the internal combustion engine. As can be seen from Fig. 4, the pressure inside each chamber 48 is varied with the help of respective solenoid valves SVI and SV2. The solenoid valves SVI 5V2 are electrically connected to an electronic control device 64 which can be an engine management system which is also referred to as engine control unit (ECU).

The solenoid valves SV1, 5V2 maintain the pressure inside the chamberS 48 to a desired value. There are as many ducts from the rail 54 as the number of combustion cylinders.

Separate solenoid valves SV1, SV2 are used to control the pressure inside every individual plunger's 16 chamber 46.

The pressure in the rail 54 would be set to a pressure value corresponding to the maximum opening position of the gas exchange valve 12. Depending on the engine's operation mode and on the position of an accelerator paddle 66 the pressure inside the individual plunger's 16 chamber 48 is controlled by means of the individual solenoid valves SV1, SV2. In Fig. 4, the internal combustion engine is shown very schematically and designated by reference 66. A sensor 70 is used for capturing the engin&S rpm.

The hydraulic fluid in the rail 54 is pressurized by the pump 52 which is driven by the internal combustion engine 68. Alternatively, a separate electric pump can also be used for pressurizing the hydraulic fluid. By adjusting the valve lift to desired values, it is now possible to precisely operate the internal combustion engine in any of the modes described in the following which give the best driving performance fuel economy and cut down emissions.

Fig. 5 shows various diagrams 72a-e which serve for illustrating different operation modes with different valve lifts and/or valve timings. Each of the diagrams 72ae has an abscissa 74 which shows the time. Each of the diagrams 72a-e also has an ordinate 76 which shows the valve lift of the gas exchange valve 12. Diagrams 72a-f relate to the intake valves of the internal combustion engine i.e. diagrams 72a-f relate to the intake valve side of the internal combustion engine. Diagrams 72g-i relate to exhaust valves of the internal combustion engine, i.e. diagrams 72g-i relate to the exhaust valve side.

Diagram 72a illustrates a so-called full opening mode in which the gas exchange valve 12 is pushed to its maximum position Mx2 by the cam 26 via the rocker arm 18. The full opening mode is used, for example when the full power of the internal combustion engine is required, for example while driving on the autobahn. In the full opening mode the solenoid valve SV2 is closed and the solenoid valve SV1 is open so that the pressure in the rail 54 and the pressure in the chamber 48 are the same. For example, said pressure can be 100 bar. The pressure in the return path is atmospheric pressure. In the full opening mode the valve lift has a value of 10 mm.

Diagram 72b illustrates a so-called late opening mode. Since the intake valves are open partially in comparison to the full opening mode, high turbulence in the combustion cylinder is created resulting in a better airfuel-rniXture, hence combusting the fuel in the optimal way. For example, the late opening mode is used during engine start-up and idling post start-up.

In the late opening mode, the intake valves are opened late and closed early. For example, the intake valves (gas exchange valve 12) open only to a depth of 5 mm. Initially the pressure P1 in the chamber 48 is zero, whereas the pressure P2 in the rail 54 is 100 bar. The solenoid valves SV1, 6V2 control the flow of the hydraulic fluid into the chamber * : 48 and in the return path. If the solenoid valve SV1 is opened, the hydraulic fluid can flow from the rail 54 inside the chamber 46. The solenoid valve SV1 is closed when the pressure inside the chamber 46 reaches its desired value, for example, 50 bar.

If the gas exchange valve 12 needs to be opened only to a depth of 4 mm in the next " * intake stroke, the solenoid valve SV2 would be opened such that the pressure inside the chamber 48 drops to 40 bar. The solenoid valve SW is closed after the pressure in the chamber 48 has dropped to 40 bar. If the gas exchange valve 12 (intake valve) has to be opened to a depth of 8 mm in the next intake stroke, the solenoid valve SVI would be opend such that the pressure inside the chamber 48 increases to 80 bar.

Diagrams 72c and 72d illustrate an early closing mode of the intake valves. Such an early closing mode would help improve torque output at low and medium revs. When the internal combustion engine is operated at partial loads, the early closing mode optimises volume efficiency and reduces pumping losses as well as undesired backflow into the manifold. Hence, the air mass trapped in the combustion cylinder is optirnised.

In the early closing mode the pressure in the chamber 48 is maintained at 100 bar, so that the intake valve's opening follows the profile of the cam 26 until half way. Once the nose 28 has completed the opening side the solenoid valve SV2 is opened such that the pressure inside the chamber 48 drops immediately to 0 bar. Thus, the intake valve is closed immediately under the action of the spring 20. Before the next intake stroke, the solenoid valve SV1 is opened until the pressure in the chamber 48 is 100 bar.

Diagram 72e illustrates a multi lift mode, The multi lift mode is used for low loads, for example, during city driving and stop and go traffic. The multi lift mode allows for multiple valve lifts which facilitates optimised combustion control.

In the multi lift mode, at the beginning of the intake stroke the pressure in the chamber 48 is 100 bar. After partial completion of the intake stroke, the solenoid valve SV2 is opened such that the pressure in the chamber 48 drops to 0 bar. As a consequence the intake valve only opens for a brief period of time and closes immediately before the completion of the same intake stroke. The solenoid valve SV1 opens and the pressure in the chamber 48 increases to 100 bar thereby causing the intake valve to open and close * again for a brief period of time. * to * . 0

Diagram 72f illustrates a completely closed mode in which the pressure Fl in the 0.0 chamber 48 isO bar, the pressure P2 inside the rail 54 is 100 bar1 and the pressure P3 in the return path is atmospheric pressure. This leads to valve lift of 0mm, i.e. the gas exchange valve 12 remains fully closed.

The completely closed mode is required when some of the cylinders have to be completely shut off. During low range rpm operation1 to improve the fuel economy, four out of eight combustion cylinders are shut off, hence preventing the air being sucked into the shut off cylinders by keeping the intake valves closed completely. Thereby pumping losses in the manifold can be avoided. In the completely closed mode the solenoid valve SV1 is completely closed and the solenoid valve SV2 is open so that the pressure in the chamber 48 is 0 bar, Diagram 72g illustrates a full opening mode of the gas exchange valve 12 in the form of an exhaust valve. The full opening mode on the exhaust valve side is used when the engine is operated in a normal mode. In the full opening mode the solenoid valve SV2 und the solenoid valve SV1 are open so that the pressure in the rail 54 and the pressure in the chamber 48 are the same, i.e. 100 bar.

Diagram 72h illustrates an early closing mode of the exhaust valves, the early closing mode of the exhaust valves being used, for example, for exhaust gas recircLllation which is also referred to EGR. In the early closing mode, the exhaust valves are closed early, depending Ofl how much of exhaust gas is to be retained in the combustion cylinders.

Thus, very effective EGR can be realised.

in the early closing mode of the exhaust valves, the pressure in the chamber 48 is maintained at 100 bar so that the valve opening follows the profile of the cam 26 until half way. Once the nose 28 has completed the opening side, the solenoid valve SV2 is opened such that the pressure inside the chamber 48 drops immediately to 0 bar, hence the respective exhaust valve is closed immediately under the action of the spring 20.

Before the next outlet stroke happens the solenoid valve SV1 is opened until the pressure in the chamber 46 is 100 bar.

Diagram 721 illustrates a complete closing mode of the exhaust valves. The complete closing mode of the exhaust valves is used during cylinder shut-off. In the complete * * closing mode the solenoid valve SV1 is completely closed and the solenoid valve 5V2 is : *". open so that the pressure in the chamber 48 is 0 bar. S...

By the illustrated method and mechanism for variably adjusting the valve lift, a particularly efficient and powerful operation of the internal combustion engine can be realised. In comparison with an internal combustion engine not having such a mechanism for variably adjusting the valve lift, power and torque output can be increased. Furthermore, fuel * consumption and emissions of co2, particles and No can be reduced considerably.

Moreover, the mechanism also provides a very smooth cold weather operation and a very smooth torque delivery. In addition, engine shake at shut-off can be avoided.

List of reference signs valve train 12 gas exchange valve 14 cylinder 16 plunger rocker arm spring 22 spring bottom 26 cam nose * . lobe lift * 32 flank * ** 34 * . clearance ramp heel base circle * " 40 * * * * cam lope * 44 cylinder head 46 cylinder chamber 49 cylinder casing pressure adjusting device 52 pump rail reservoir directional arrow * 58 pin directional arrow electronic control device * 66 accelerator paddle internal combustion engine sensor diagram 72a-i 74 abscissa 76 ordinate A axis of rotation P1 pressure P2 pressure P3 pressure VL valve lift Atm. atmospheric pressure * * * 0

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* 5555. * S * S. * * . *S** * ** * S

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Claims

Claims A valve train (10) for an internal combustion engine (68). the valve train (10) comprising: -at least one gasexchange valve (12) fora corresponding combustion chamber (46) of the internal combustion engine (68), -at least one plunger (16) slidably arranged in a corresponding cyHnder (14), -at least one rocker arm (18) coupled to the gas exchange valve (12) and the plunger (16), characterized in that the valve train (10) comprises a pressure adjusting device (50) by means of which a pressure of a fluid contained in a chamber (48) bounded at least partially by the cylinder (14) and the plunger (16) is adjustable wherein a valve lift (VL) of the gas exchange valve (12) is adjustable by adjusting the pressure of the fluid.
2 The valve train (10) according to claim I characterized in that the fluid is a hydraulic fluid.
3. The valve train (10) according to any one of claims I or 2. -characterized in that the valve train (10) comprises at least one spring and at least one corresponding fail-safe element (60) movable between at least one locking position in which the plunger (16) is locked and at least one unlocking position in which the plunger (16) is unlocked, the fail-safe element (60) being held in the unlocking position by means of a pressurized medium against a spring force acting upon the safe-fail element and effected by the spring the spring being preloaded in the unlocking position.wherein the fail-safe element (60) is capable of being moved from the unlocking position into the locking position by means of the spring force in the event of a pressure drop of the pressurized medium.
4. The valve train (10) according to claim 3, characterized in that the pressurized medium is the fluid contained in the chamber.
5. The valve train (10) according to any one of the preceding claims, characterized in that the valve train (10) compriseS several plungers (16) arranged in corresponding cylinders (14), the pressure adjusting device (40) having a rail (54) via which : . chambers (48) bounded at least partially by the plungers (16) and the cylinders (14) * respectively are capable of being supplied by the fluid. * ** * * * * ** * * *** *