DE102004057574A1 - Variable valve train of an internal combustion engine - Google Patents

Abstract

The invention relates to a variable valve train (1) of an internal combustion engine for actuating a gas exchange valve (3). Its movement follows a stroke of a cam (5) and a stroke of the cam (5) superimposed and the stroke of the cam (5) independent stroke of a plunger (13). In the stroke direction, a volume change of a working space (18) of a hydraulic lifting device (19) acts on the tappet, which is in fluidic operative connection with a hydraulic fluid conveying device (25). This is intended to delimit a pressure chamber (22) with a volume (36) that can be displaced by a wall (27) of the hydraulic fluid delivery device (25) displaceable in the pressure chamber (22) while displacing hydraulic fluid from the pressure chamber (22) into the working chamber (18). is reducible.

Description

Territory of invention

The The invention relates to a variable valve train of an internal combustion engine for operation a gas exchange valve. Its movement follows a stroke of a cam and a hub of the cam superimposed and independent from the hub of the cam Stroke of a pestle. On the ram works in the stroke direction a volume change a working space of a hydraulic lifting device, which in fluidic operative connection with a hydraulic fluid conveyor stands.

background the invention

Generic valve trains, in which the stroke of the gas exchange valve from a superposition of an output from the cam stroke and a variably adjustable stroke of a hydraulic lifting device, which acts independently of the cam on the movement of the gas exchange valve, are known in the art. For example, describes the DE 101 56 309 A1 a bucket tappet drive with hydraulic lifting device.

These serves to lift a stroke generated by the cam one from the cam independent hub to overlap at the gas exchange valve. For this purpose is located between the inside of the cup bottom and the valve stem a pressure piston whose relative movement to the bucket tappet volume change a pressure chamber adjacent to the pressure chamber is generated. Of the Pressure room is in turn about channels inside the bucket tappet as well in the tappet guide the Internal combustion engine to a pressure or volume flow adjustable hydraulic supply connected.

In the DE 102 42 866 A1 is also proposed a variable valve train on the example of a finger lever drive with a hydraulic lifting device, which is integrated in a rocker arm bearing pivot bearing.

Although already a highly variable valve lift with the aforementioned valve trains can be generated, these valve trains have some disadvantages. In Both publications, the hydraulic control of the lifting device is carried out through hydraulic systems consisting of diverse components to meet different Tasks exist. So are for pressure generation and promotion the hydraulic medium usually several hydraulic fluid pumps, for pressure storage one or more pressure accumulators, which in case of different pressure levels are hydraulically interconnected by means of pressure regulator, and to Timed to be controlled supply and discharge of the hydraulic fluid in the or to provide a hydraulic valve from the lifting device.

The complexity so trained hydraulic fluid systems not only causes a high financial expenditure due to the number of components and - variety, but with high space requirements also highest demands on the Resilience of the entire system. This includes complex sealing measures, the leakage in particular in the area of high pressure ensure applied components. Farther is possibly also an additional one Component-claiming control of the volumetric flow of the hydraulic fluid pumps with regard to an acceptable energy balance of the internal combustion engine required. After all is here with large Shen Hydraulic fluid volumes, which are in the immediate sphere of influence of hydraulic lifting device, i. between lifting device and hydraulic valve, to be expected. Large hydraulic fluid volumes known to have a negative effect on the stiffness and thus on the Dynamics of the valve train, which rests on them.

Task of invention

task The invention is therefore a variable valve train of the aforementioned Art to create, in which the cited disadvantages with simple Funds are eliminated. The variable valve train and in particular his hydraulic supply and control should therefore possible economical be produced and a low system complexity one have low space requirement with high reliability. Finally, should the hydraulically generated variability of the valve train only with least possible Energy expenditure for Pressure generation and promotion connected to the hydraulic medium and almost free of losses in the Be valvetrain stiffness and dynamics.

Summary the invention

The solution This object is apparent from the features of claim 1, whose advantageous developments and refinements the dependent claims are. Accordingly, the object is achieved in that the hydraulic fluid delivery a pressure chamber with a volume limited by a in the Pressure chamber displaceable wall of the hydraulic fluid conveyor under displacement of Hydraulic fluid can be reduced from the pressure chamber into the working space is.

The subject of the present invention is Thus, a valve gear to be produced inexpensively, which makes it possible with low system complexity, to superimpose the stroke of a cam and a stroke of the cam independent stroke of a hydraulic lifting device on the gas exchange valve. The low complexity of the system is essentially achieved by integrating the functions hydraulic fluid delivery and pressure generation and the time-adjustable supply and removal of hydraulic fluid into and out of the hydraulic lifting device all in the simply constructed hydraulic fluid delivery device. Moreover, the control of the hydraulic fluid delivery device is purely on demand with correspondingly low energy consumption, resulting in a favorable efficiency of the internal combustion engine. Finally, it is structurally possible to arrange the pressure chamber in the immediate vicinity of the hydraulic lifting device. As a result, the hydraulic fluid volumes, on which the valve gear is supported, are kept small in view of good valve train rigidity and dynamics.

A expedient embodiment the valve train according to claim 2, that the wall as a displacer is trained. This should at least by a slide of the hydraulic fluid conveyor in Vorhubrichtung, d. H. in the sense of a volume decrease of the pressure chamber, be acted upon. A fastening which also acts in the return stroke direction of the displacer on the slide is so far not mandatory, as the displacer in the return stroke direction with hydraulic fluid pressure, in particular by the on the gas exchange valve in its closing direction acting valve spring is applied, is acted upon. An attachment of the displacer on the slide both in Vorhub- and in Rückhubrichtung up to a one-piece Component with a simultaneously acting as a displacer slide can depending on the characteristic of the application of force by the hydraulic fluid delivery device nevertheless be appropriate.

In a particularly preferred embodiment according to claim 3 is the hydraulic fluid conveyor have an electromagnetic loading means through which the slider is displaceable at least in the pre-stroke direction. The slider can be in operative connection with an anchor or yourself Anchor, by the electromagnetic force effect of the loading means moves between a basic position and a stroke position.

Of the Valve gear should according to claim 4 also a secondary stroke the gas exchange valve during a enable stroke-free base circle phase of the cam. This results advantageous ways Recirculate exhaust gas internally in high and precisely adjustable quantities. This form of exhaust gas recirculation is in particular basis for an operation of the internal combustion engine in homogeneous and self rousing Charge. Such, also as HCCI method (Homogeneous Charge Compression Ignition) referred burning process is in both self-ignited diesel internal combustion engines as well as ignited by others Otto internal combustion engines at least in part-load operation of the internal combustion engine mainly can be used for the purpose of emission reduction. The combustion process in the HCCI process, essentially by controlling the charge composition and the charge temperature profile. It shows, that in this combustion process, a high charge temperature for control the ignition timing he wishes is. A very effective way to increase the charge temperature is the increase the residual gas content, i. the increase the salary at not rinsed out or rinsed out and recirculated exhaust gas into the cylinder the previous combustion cycle in the cylinder charge for the next combustion cycle. The residual gas content must be at the operating point of the internal combustion engine can be fully variably adjusted, with residual gas amounts of 60% of the cylinder charge and more required could be. Residual gas shares can at this altitude no more about one internal exhaust gas recirculation through conventional valve overlap or over a device for external exhaust gas recirculation can be provided. moreover The HCCI process reacts extremely sensitively with unacceptable combustion processes on changes the charge characteristics, so in addition to the provision of residual gas in the required amount also a combustion cycle-faithful, high-precision and cylinder-individual Dosing of the residual gas content is required.

Of the secondary stroke takes place according to claim 5, preferably at an outlet valve. In the event of the above explained exhaust gas recirculation is already exhaust gas ejected into the exhaust passage during the intake stroke the internal combustion engine over the then again opened Exhaust valve sucked back into the combustion chamber.

In contrast, however, it is also possible to operate the valve gear according to the invention as an engine brake in particular in air-compressing internal combustion engines for safety-relevant supplementation of the service brake. Such engine brakes are usually used as a continuous brake in commercial vehicles and are based on the principle that the drag torque of the combustion engine located in overrun and not fueled by increasing the charge exchange work can be significantly increased and the vehicle is slowed down. In this case, the exhaust valve is opened again during the compression phase, so that the cylinders Charge is not compressed gas-spring-like, but is pushed with the application of Ausschiebearbeit in the outlet channel.

Regarding exhaust gas recirculation It can according to claim 6 but also be appropriate that the secondary stroke takes place at an inlet valve. In this alternative embodiment Exhaust gas is in Ausschiebetakt the internal combustion engine at wiedermalig open Inlet valve is pushed out into the inlet channel and during the Suction cycles sucked back into the combustion chamber.

A Combination of these aforementioned possibilities of exhaust gas recirculation is also possible. Accordingly, it can be used to adjust the amount and temperature of the residual gas be advantageous, both exhaust gas from the inlet channel and from to suck back the outlet channel.

in the Case of a multi-valve internal combustion engine is according to claim 7 appropriate that a group of similar valve trains, d. H. a group of Intake valves or a group of exhaust valves of a cylinder the engine respectively exactly one hydraulic fluid conveyor assigned. This allows the number of components and thus the cost and space requirements of the hydraulic fluid conveyor further reduce.

Of the Valve gear should according to claim 8 over one hydraulic lash adjuster. there It may be advantageous according to claim 9, that the working space of hydraulic lifting device identical to a compensation chamber the lash adjuster is.

A particularly expedient embodiment the valve train is proposed in claim 10, wherein the valve train as a drag lever drive and the hydraulic lifting device as a drag lever stock swivel bearing are formed.

When Hydraulic means according to claim 11 for the sake of simplicity that oil the internal combustion engine used. Conceivable, however, is possible also the use of any other suitable fluids in one Hydraulic fluid circuit, which then from the lubricating oil circuit of the internal combustion engine to be separated.

Short description the drawings

Further Features of the invention will become apparent from the following description and from the drawings, in which the valve gear according to the invention by way of example with reference to a drag lever drive with hydraulic valve clearance compensation is shown. Show it:

1 the drag lever drive with the gas exchange valve and

2 the drag lever drive at hydraulically generated stroke of the gas exchange valve.

Full Description of the drawings

In 1 is the valve train according to the invention 1 an internal combustion engine on the example of a drag lever drive 2 disclosed. Shown is a gas exchange valve 3 that has a rocker arm 4 from a cam 5 is operated in the opening direction. The rocker arm 4 is on a pivot bearing 6 that of a hollow cylindrical recess 7 the internal combustion engine is received, in the direction of actuation of the gas exchange valve 3 stored and has a rotatably mounted roller 8th as low-friction contact surface 9 to the cam 5 , This has a cam lift phase 10 that have a lift on the gas exchange valve 3 generated, and a lift-free base circle phase 11 ,

The pivot bearing 6 has a hollow cylindrical housing 12 in which one the drag lever 4 stocked pestle 13 and a balance piston 14 a hydraulic valve clearance compensation device 15 are guided longitudinally movable. The pestle 13 can do this together with the balance piston 14 in one piece or as a balance piston 14 be formed separate component. A towing lever 4 opposite end face 16 of the balance piston 14 limits a compensation room 17 the valve clearance compensation device 15 whose principle operation is familiar to the person skilled in the art.

The compensation room 17 is at the same time a working space in the embodiment shown in the figures 18 one in the pivot bearing 6 integrated hydraulic lifting device 19 , The workroom 18 is about a passage 20 in the case 12 of the pivot bearing 6 as well as via a supply line 21 with a pressure room 22 in hydraulic connection. The pressure room 22 is through a hollow cylindrical recess 23 the internal combustion engine and a front side 24 a hydraulic fluid conveyor 25 , which in the illustrated embodiment with a hollow cylindrical guide pin 26 into the recess 23 screwed in, limited.

At the front 24 the hydraulic fluid conveyor 25 is a wall 27 arranged for the displacement of hydraulic fluid from the pressure chamber 22 in the workroom 18 is relocatable. The wall 27 is here as a displacer 28 executed by a slider 29 is charged and in an inner circumferential surface 30 of the guide pin 26 longitudinally movable and sealing gap-like in Vorhub- and Rückhubrichtung "P" and "R" is performed. One of the inner circumferential surface is used 30 outgoing shoulder 31 as acting in the return direction "R" and the basic position forming stop for the displacer 28 , The slider 29 is in turn by an agent 32 displaced, in the embodiment shown electromagnetically in the form of a solenoid 33 is trained.

The slider 29 stands in operative connection with an armature, which by an electromagnetic force effect of the solenoid 33 between the basic position and a stroke position moves. The lifting magnet 33 can be designed as a so-called Einfachhubmagnet, the electromagnetic force acts only in Vorhubrichtung "P" and its provision is effected by external forces acting in Rückhubrichtung "R" forces.

Alternatively, the solenoid 33 Also be designed as a so-called Umkehrhubmagnet whose electromagnetic force acts depending on the excitation current both in the pre-stroke direction "P" and in the return stroke direction "R". Both the single-stroke magnet and the reverse-stroke magnet can be designed as a proportional or quasi-proportional magnet. Proportional magnets are Gleichstromhubmagnete that represent approximately proportional to the input of an excitation current depending on the application, a reproducible output in the form of a certain path of the armature or a certain force of the armature. Quasiproportionalmagneten are also Gleichstromhubmagnete with an input variable dependent output variable, but their ratio is not proportional to each other in the rule, but follows a non-linear characteristic.

Thus, with a known current-path characteristic or current-force characteristic, in particular with proportional solenoids or quasi-proportional magnets designed as reversing-stroke magnets, the movement of the slide both in the pre-stroke direction "P" and in the return-stroke direction "R" and thus that of the hydraulic-medium conveyor 25 influenced opening and closing speed of the gas exchange valve 3 to be regulated by current control. Here by it is above all possible, valve train noise caused by too fast closing of the gas exchange valve 3 caused to be avoided.

Depending on the design of the solenoid 33 and other constructive circumstances, it may be sufficient on the one hand, displacement piston 28 and slider 29 just line up without mechanical fasteners. On the other hand, it may also be expedient in particular when using Umkehrhubmagneten, the displacer 28 on the slide 29 to attach so that the displacer 28 also in Rückhubrichtung "R" from the slide 29 is actively acted upon. The same applies to the connection between slides 29 and armature of the solenoid 33 , if these components are not already formed in one piece.

The design of the hydraulic fluid conveyor 25 and their connection to the pressure room 22 comprehensive hollow cylindrical recess 23 is to be designed by suitable, but not further illustrated measures so that the pressure chamber 22 as well as the hydraulic lifting device 19 ideally always completely filled with hydraulic fluid and free of gas bubbles in view of a rapid and reproducible pressure build-up. Moreover, by suitable sealing measures in particular an escape of hydraulic fluid from the pressure chamber 22 and from the hydraulic fluid delivery device 25 to permanently prevent the environment of the internal combustion engine. Finally, there is a possibly between the displacer 28 and the inner circumferential surface 30 of the guide pin 26 training and the pressure chamber 22 leaving leakage flow in a hydraulic fluid circuit of the internal combustion engine.

The operation of the hydraulic lifting device 19 results from the following described interaction with the hydraulic fluid conveyor 25 , The valve train 1 is located in 1 in a position where the cam lobe phase 10 according to cam direction 34 just finished and the gas exchange valve 3 just closed, so the role 8th of the rocker arm 4 the base circle phase 11 of the cam 5 taps. At the same time is the displacer 28 the hydraulic fluid conveyor 25 in the basic position, in which the displacer 28 with the shoulder 31 of the guide pin 26 in contact. Based on this position of the valve train 1 can mechanical valve clearance, if necessary, during the cam lift phase 10 by sinking the balance piston 14 and the pestle 13 in a the cam 5 opposite direction arises, be compensated. To refill from the equalization room 17 displaced hydraulic fluid is the valve lash adjuster 15 in a conventional manner a hydraulic fluid supply 35 assigned.

How out 2 can be seen, follows a movement of the gas exchange valve 3 one the stroke of the cam 5 superimposed hub, which is hereinafter referred to as hydraulically generated stroke, then, when the displacer 28 the hydraulic fluid conveyor 25 through the slider 29 in the pre-stroke direction "P" with a decrease in volume 36 of the pressure chamber 22 is relocated. This is the result the pressure room 22 displaced hydraulic fluid passes through the supply line 21 and the passage 20 in the case 12 of the pivot bearing 6 in the workroom 18 the hydraulic lifting device 19 , By increasing the volume of the workspace 18 become the balance piston 14 and the pestle 13 in the direction of the cam 5 relocated. At the same time pressed by the plunger 13 acted on rocker arms 4 the gas exchange valve 3 in the opening direction, placing it around the cam 5 supported roll 8th swings. A limitation on the movement of the displacement piston 28 in Vorhubrichtung "P" can be done, for example, characterized in that the displacer 28 on a floor 37 the hollow cylindrical recess 23 strikes.

An abort of the hydraulically generated stroke of the gas exchange valve 3 begins with a return of the displacer 28 in the return stroke direction "R." This increases the volume 36 of the pressure chamber 22 with simultaneous decrease in volume of the work space 18 and backflow of the valve train 1 pressurized hydraulic fluid from the working space 18 in the pressure room 22 , By the volume decrease of the work space 18 become the pestle 13 and the balance piston 14 from the rocker arm 4 moved back in a cam-distant direction.

The retraction of the displacement piston 28 in the return stroke direction "R" can depend on the above-described embodiment of the solenoid 33 be done by the slide 29 in Rückhubrichtung "R" only force-free and thus of the pressurized displacer 28 is reset. Alternatively, the course of movement of the slider 29 also in Rückhubrichtung "R" from the solenoid 33 be weg- or force controlled. The latter possibility is with regard to a Öffnungsverlaufsformung and in particular to the closing operation of the gas exchange valve 3 more advantageous embodiment of the lifting magnet 33 because the gas exchange valve 3 both the movement of the cam 5 as well as the movement of the displacer 28 according to the mechanical and hydraulic gear ratios follows.

The valve gear according to the invention 1 was the example of a drag lever drive 2 with a hydraulic valve lash adjuster 15 having pivot bearing 6 described. However, the idea of the invention can equally be implemented in other types of valve train without hydraulic valve lash adjuster, such as cup drives, tilting or rocker arm drives or pushrod drives.

While the 1 and 2 to a hydraulically generated stroke of the gas exchange valve 3 during the base circle phase 11 of the cam 5 Of course, the hydraulically generated stroke can of course be to any position of the cam within the mechanical limits of the valvetrain 1 respectively.

The scope of the invention should also include valve trains, which are formed switchable by coupling means to strokes more cams depending on the coupling state selectively to the gas exchange valve 3 transferred to. This applies equally to valve trains that control the stroke of the gas exchange valve 3 vary continuously by means of a cam and other adjusting elements.

1

valve train

2

Finger lever drive

3

Gas exchange valve

4

cam follower

5

cam

6

pivot bearing

7

recess

8th

role

9

approach surface

10

Cam lobe phase

11

Base circle phase

12

casing

13

tappet

14

balance piston

15

Ventilspielausgleichsvor

direction

16

front

17

compensation space

18

working space

19

hydraulic Hebeeinrich

tung

20

passage

21

supply

22

pressure chamber

23

recess

24

front

25

Hydraulic fluid conveying Rich

tung

26

spigot

27

wall

28

displacer

29

pusher

30

Inner surface area

31

shoulder

32

biasing

33

solenoid

34

Cam rotation direction

35

Hydraulic fluid supply

36

volume

37

ground

P

Vorhubrichtung

R

Return stroke direction

Claims (11)

Variable valve train ( 1 ) an internal combustion engine for actuating a gas exchange valve ( 3 ) whose movement is a stroke of a cam ( 5 ) and the hub of the cam ( 5 superposed and from the hub of the cam ( 5 ) independent stroke of a plunger ( 13 ) follows, in the stroke direction a volume change of a working space ( 18 ) a hydraulic lifting device ( 19 ) in fluid communication with a hydraulic fluid delivery device ( 25 ), characterized in that the hydraulic fluid delivery device ( 25 ) a pressure chamber ( 22 ) with a volume ( 36 ), which through a in the pressure chamber ( 22 ) movable wall ( 27 ) of the hydraulic fluid delivery device ( 25 ) under displacement of hydraulic fluid from the pressure chamber ( 22 ) in the working space ( 18 ) is reducible. Valve gear according to claim 1, characterized in that the wall ( 27 ) as displacer ( 28 ) is formed, at least indirectly by a slide ( 29 ) of the hydraulic fluid delivery device ( 25 ) can be acted upon at least in Vorhubrichtung (P). Valve gear according to claim 2, characterized in that the slide ( 29 ) from an electromagnetic loading device ( 32 ) of the hydraulic fluid delivery device ( 25 ) is displaceable at least in Vorhubrichtung (P). Valve gear according to claim 1, characterized in that the gas exchange valve ( 3 ) at least one secondary stroke during a basic circle phase ( 11 ) of the cam ( 5 ). Valve gear according to claim 4, characterized in that the gas exchange valve ( 3 ) is an exhaust valve of the internal combustion engine. Valve gear according to claim 4, characterized in that the gas exchange valve ( 3 ) is an intake valve of the internal combustion engine. Valve gear according to claim 5 or 6, characterized in that exactly one hydraulic fluid delivery device ( 25 ) for several identical valve trains ( 1 ) is provided jointly of a cylinder of the internal combustion engine. Valve gear according to claim 1, characterized in that the valve train ( 1 ) via a hydraulic valve clearance compensation device ( 15 ). Valve gear according to claim 8, characterized in that the working space ( 18 ) of the hydraulic lifting device ( 19 ) identical to a compensation chamber ( 17 ) of the valve clearance compensation device ( 15 ). Valve gear according to claim 1, characterized in that the valve train ( 1 ) as a drag lever drive ( 2 ) and the hydraulic lifting device ( 19 ) as a pivot bearing ( 6 ) are formed. Valve gear according to claim 1, characterized that the hydraulic fluid lubricating oil the internal combustion engine is.