GB2508501A

GB2508501A - Valve train facilitating adjustable valve lift via a hydraulic plunger

Info

Publication number: GB2508501A
Application number: GB1318330.6A
Authority: GB
Inventors: Anand Goudar; Amol Durge
Original assignee: Daimler AG
Current assignee: Mercedes Benz Group AG
Priority date: 2013-10-16
Filing date: 2013-10-16
Publication date: 2014-06-04
Also published as: GB201318330D0

Abstract

A valve train 10 comprising at least one valve 12, at least one plunger 16 slidable in a corresponding cylinder 14, at least one rocker arm 18 coupling the valve and the plunger, a first chamber 48 bounded at least partially by the cylinder and the plunger and being capable of receiving a fluid, for example a hydraulic fluid, a second chamber 50 bounded at least partially by the cylinder and the plunger, the first chamber being arranged on a first side 52 of the plunger and the second chamber being arranged on a second side 54, at least one duct 56 fluidically connecting the two chambers, and at least one valve SV, for example a solenoid valve, for adjusting the flow of the fluid from one of the chambers through the duct to the other chamber thereby adjusting a valve lift of the valve. The assembly allows for precise adjustments of the valve stroke leading to increased efficiency and power of the associated engine.

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.

Such a valve train for an internal combustion engine, in particular for a motor vehicle, is known from the serial production of the AMG 5.5 litre V8 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 combustion chamber of the internal combustion engine. The valve train further comprises at least one plunger slidably 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.

Furthermore, such a valve train can be found in US 7,325,522 B2, the valve train comprising at least one gas exchange valve for a corresponding combustion chamber of the internal combustion engine, at least one plunger slidably arranged in a corresponding cylinder, at least one rocker arm coupled to the gas exchange valve and the plunger, and a chamber bounded at least partially by the cylinder and the plunger respectively. The chamber is capable of receiving a fluid.

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

This object 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 valve train facilitates a particularly efficient and powerful operation of the internal combustion engine, according to the present invention the valve train comprises a second chamber bounded at least partially by the cylinder and the plunger. The first chamber is arranged on a first side of the plunger and the second chamber is arranged on a second side of the plunger, the second side facing away from the first side. In other words, the first chamber is bounded partially by a first surface of the plunger and the second chamber is bounded partially by a second surface of the plunger, the second surface being opposite of and facing away from the first surface.

The valve train according to the present invention also comprises at least one duct element my means of which the chambers are fluidically connected to one another.

Moreover, the valve train according to the present invention comprises at least one valve element for adjusting the flow of the fluid from one of the chambers through the duct element to the other chamber. By adjusting the flow of the fluid a valve lift of the gas exchange valve can be adjusted.

The valve lift which is also referred to as stroke is adjustable by means of the valve element in such a way that by adjusting the flow through the duct element, an actuation or actuating force exerted by a cam and on the gas exchange valve and/or the plunger via the rocker arm can be adjusted, the cam serving for actuating the gas exchange valve.

Thus, the valve train according to the present invention uses a plunger mechanism which allows for a variable adjustment of the valve lift in a very efficient and effective way.

The flow of the fluid through the duct line can be adjusted very precisely by means of the valve element so that even very small changes of the valve lift can be realized. As 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.

Moreover, the valve train itself can be operated very efficiently. In comparison with an internal combustion engine which does not have the plunger mechanism according to the present invention the engines' power and the torque output can be increased.

Furthermore, fuel consumption can be considerably reduced as well as emissions of 002 particles and N0. Moreover, the valve train allows for a very smooth cold weather operation of the internal combustion engine as well as for a particularly smooth torque delivery. In addition, engine shake at shut-ott can be avoided.

For example, the fluid contained in the chambers is a hydraulic fluid so that the plunger mechanism is designed as a hydraulic plunger mechanism.

Further advantages, features and details ot the invention derive from the following description of a preferred embodiment as well as from the drawing. The features and teature combinations previously mentioned in the description as well as the features and teature combinations mentioned in the following description ot the figures and/or shown in the figures alone can be employed not only in the respective indicated combination but also in other combination or taken alone without leaving the scope of the invention.

Figs. la and lb serve for illustrating the background of the invention.

The drawing shows in: Figs. la-b a schematic perspective view of a valve train in two different operation modes; Fig. 2 a schematic view ot a valve train according to the present invention; and Fig. 3 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 tunction are equipped with the same reference sign.

Figs. 2 and 3 serve for illustrating a variable valve lift mechanism for an internal combustion engine for a motor vehicle, the variable valve litt mechanism comprising a hydraulic plunger mechanism within an enclosed tluid chamber. Moreover, Figs. 2 and 3 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 mechanism for a multi-cylinder internal combustion engine with the same capacity thereby reducing emissions and providing the driver with more ease and tun 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 V8 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 EGO 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 800 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 and leaves the partial load range, cylinders 2, 3, 5 and 8 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.

The cylinder shut-off system is enabled by an engine management system with sixteen 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 valves in the form of intake and exhaust valves of cylinders 2, 3, 5 and 8 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 400 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 a cylinder 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. 1 a and 1 b, 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 and a heel 38.

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 14.

Under low load conditions and when a drive mode is in a certain state, cylinders 2, 3, 5 and 8 are shut down or shut off completely (no injection, no emission) and also the corresponding inlet and exhaust valves represented by the gas exchange valve 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 effected by the cam 26 acts on the gas exchange valve 12 and/or 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 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 combustion 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 drivability (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. 1 a 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 10 in 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 facilitate a variable valve lift of the intake and exhaust valves of said internal combustion engine. By means of 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. 2 which shows a cylinder head 44 of the internal combustion engine, the cylinder head 44 housing 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. 2. 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. 2 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. 2 by dotted lines.

The gas exchange valve 12 is held in its closed position by the spring 20 and opened 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 cam shaft which is rotatable about the axis of rotation A. If a heel of the cam 26 touches the rocker arm 18, the plunger 16 is held in its minimum position Mn 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. As can be seen in Fig. 2, the valve train 10 comprises a first chamber 48 bounded at least partially by the cylinder 14 and the plunger 16 respectively, the first chamber 48 being capable of receiving a fluid in the form of a hydraulic fluid. For example, the hydraulic fluid is oil. Furthermore, the valve train 10 comprises a second chamber 50 bounded at least partially by the cylinder 14 and the plunger 16 respectively.

The first chamber 48 is arranged on a first side 52 of the plunger 16 and the second chamber 50 is arranged on a second side 54 of the plunger 16, the second side 54 facing away from the first side 52. The chambers 48, 50 are fluidically connected to one another by a duct element 56 having a duct 58. The second chamber 50 is capable of receiving said hydraulic fluid, wherein the hydraulic fluid can flow from the first chamber 48 through the duct 58 to the second chamber 50 and vice versa.

The chambers 48, 50 and the duct element 56 or its duct 58 form a fluidically enclosed compartment 60. This means that the chamber 48, 50 and the duct element 56 form an enclosed oil chamber within which the oil can flow form the first chamber 48 to the second chamber 50 and vice versa as illustrated by directional arrows in Fig. 2.

The valve train 10 comprises at least one valve element in the form of a solenoid valve SV. The solenoid valve SV can precisely adjust or control the flow of the hydraulic fluid through the duct 58. Thus, the flow of the hydraulic fluid from the first chamber 48 through the duct 58 to the second chamber 50 and vice versa can be adjusted by means of the solenoid valve SV thereby adjusting the valve lift of the gas exchange valve 12. In other words, by adjusting the flow of the hydraulic fluid through the duct 58 the valve lift of the gas exchange 12 can be adjusted. The flow of the hydraulic fluid through the duct 58 can be adjusted by adjusting a cross-section of the duct 58 by means of the solenoid valve SV, wherein the fluid flowing from the first chamber 48 to the second chamber 50 or vice versa has to flow through said cross-section. Advantageously, the valve lift of the gas exchange valve 12 is varied in dependency on the accelerator paddle input and/or the engine operating mode.

For example, if said cross-section of the duct 58 is fully open, the back pressure in the second chamber 50 is very low for the plunger 16 so that the plunger 16 can be pushed to its maximum depth position Mx by the cam lobe 42 via the rocker arm 18. Thus, the gas exchange valve 12 is not actuated so that the valve lift is zero. This means that the gas exchange valve 12 is completely closed and stays closed so that it stays in its minimum position Mnl.

lithe cross-section of the duct 58 is adjusted to a very low value or even closed, the back pressure in the second chamber 50 is very high for the plunger 16 so that the plunger 16 cannot be moved out of its minimum position Mn by the cam lobe 42 via the rocker arm 18. Thus, the plunger 16 stays in its minimum position Mn and the gas exchange valve 12 is pushed into its maximum position Mx2 by the cam lobe 42 via the locker arm 18. The maximum valve lift possible is achieved.

A valve lift between the minimum position Mnl and the maximum position Mx2 is achieved by varying the cross-section between its maximum value and its minimum value by means of the solenoid valve SV. By varying said cross-section of the duct 58, the back pressure in the second chamber 50 can be adjusted, the back pressure being affected by the non-compressible hydraulic fluid contained in the compartment 60 and acting upon the plunger 16.

As can be seen in Fig. 2, the valve train 10 also comprises at least one limiting element 62 for limiting the movement of the plunger 16 in the cylinder 14. In the present embodiment, the limiting element 62 is arranged in the first chamber 48 on the first side 52 of the plunger. Thereby, the movement of the plunger 16 can be limited in such a way that the spring 22 pushes the plunger 16 in the direction of the minimum position Mn until the plunger 16 reaches its minimum position Mn and into contact with the limiting element 62. Hence, the plunger 16 cannot be moved beyond the minimum position Mn by means of the relaxing spring 22.

Fig. 3 shows various diagrams 72a-i which serve for illustrating different operation modes with different valve lifts and/or valve timings. Each of the diagrams 72a-i has an abscissa 74 shows the time. Each of the diagrams 72a-i also has an ordinate 76 which shows the valve lift of the gas exchange valve 12. The diagrams 72a-f relate to the intake valves of the internal combustion engine, i.e. the diagrams 72a-f relate to the intake side of the internal combustion engine. The diagrams 72g-i relate to exhaust valves of the internal combustion engine, i.e. the diagrams 72g-i relate to the exhaust valve side.

The Diagram 72a illustrates a so-called full opening mode in which the gas exchange valve 12 is pushed into 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, wild driving on the autobahn.

The 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 46 is created resulting in a better air-fuel-mixture, 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 five millimetres. The 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 optimizes volume efficiency and reduces pumping losses as well as undesired back flow into the manifold. Hence, the air mass trapped in the combustion cylinder 46 is optimized.

The 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 optimized combustion control.

The diagram 72f illustrates a completely closed mode in which the gas exchange valve 12 is not opened. This means that the valve lift is zero millimetres.

The completely closed mode is required when some of the cylinders have to be completely shut-off. During low range rpm operation 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.

The diagram 72g illustrates a full opening mode of the gas exchange valve 12 in the form of an exhaust valve 12. The full opening mode of the exhaust valve side is used when the engine is operated in a normal mode.

The 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 recirculation which is also referred to EGR. In the early closing mode, exhaust valves are closed early, depending on how much exhaust gas is to be retained in the combustion cylinders. Thus, very effective EGR can be realized.

The diagram 72i illustrates a complete closing mode of the exhaust valves. The complete closing mode of the exhaust valves is used during cylinder shut-off.

The illustrated modes of the valves can be adjusted and achieved by means of varying the cross-section of the duct 58 by means of the solenoid valves SV. In order to realize certain modes, the cross-section of the duct 58 can be varied several times during the time the cam lobe 42 touches the rocker arm 18 and/or during one revolution of the cam 26 about the rotation axis A thereby varying the actuation force acting upon the gas exchange valve 12 via the rocker arm 18.

The valve train 10 also comprises a plug 64 which is used for ceiling a through opening of the duct element 56. Via said through opening the hydraulic fluid contained in the compartment 60 can be drained from the compartment 60. Furthermore, the compartment can be refilled with the hydraulic fluid via said through opening when the plug 64 is removed.

List of reference signs valve train 12 gas exchange valve 14 cylinder 16 plunger 18 rocker arm spring 22 spring 24 bottom 26 cam 28 nose 38 heel 42 cam loab 44 cylinder head 46 cylinder 48 first chamber 49 cylinder casing second chamber 52 first side 54 second side 56 duct element 58 duct compartment 62 limiting element 64 plug 72a-i diagram 74 abscissa 76 ordinate A roation axis Mn minimum position Mnl minimum position Mx maximum position Mx2 maximum postion

Claims

Claims A valve train (10) for an internal combustion engine (68), the valve train (10) comprising: -at least one gas exchange valve (12) for a corresponding combustion chamber (46) of the internal combustion engine (68), -at least one plunger (16) slidably arranged in a corresponding cylinder (14), -at least one rocker arm (18) coupled to the gas exchange valve (12) and the plunger (16), -a chamber (48) bounded at least partially by the cylinder (14) and the plunger (16), the chamber (48) being capable of receiving a fluid, characterized by -a second chamber (50) bounded at least partially by the cylinder (14) and the plunger (16), the first chamber (48) being arranged on a first side (52) of the plunger (16) and the second chamber (50) being arranged on a second side (54) of the plunger (16), the second side (54) facing away from the first side (52, -at least one duct element (56) by means of which the chambers (48, 50) are fluidically connected to one another, and -at least one valve element (SV) for adjusting the flow of the fluid from one of the chambers (48, 50) through the duct element (56) to the other chamber (50) thereby adjusting a valve lift of the gas exchange valve (12).
2. The valve train (10) according to claim 1, characterized in that the fluid is a hydraulic fluid.
3. The valve train (10) according to any one of claims 1 or 2, characterized in that the valve element (SV) is designed as a solenoid valve (SV).
4. The valve train (10) according to any one of the preceding claims, characterized in that the valve train (10) comprises at least one limiting element (62) for limiting the movement of the plunger (16) in the cylinder (14).
5. The valve train (10) according to any one of the preceding claims, characterized in that the chambers (48, 50) and the duct element (56) form a fluidically enclosed compartment (60).