DE102004048288A1 - Variable valve train of an internal combustion engine - Google Patents

Abstract

The invention relates to a variable valve train with a device which serves for a mode-dependent secondary lift of a gas exchange valve (5) for an exhaust gas back suction. This is in operative engagement with a cam follower (2) which is acted upon by a cam (6) and supported on a hydraulic valve clearance compensation element (4). The lash adjuster element (4) is connected to a hydraulic fluid feed path (12) and to a hydraulic fluid drainage path (15) which can be closed by shut-off means (14), wherein a high-pressure chamber (16) of the lash adjuster element (4) is connected to the hydraulic fluid flow path (15) via a passage opening (22). communicates. The cam (6) has relative to a base circle (8) a cam lobe (9) for generating a Primärhubs the gas exchange valve (5) and a Nockeneinformung (10), in which the cam follower (2) with hydraulic elongation of the high-pressure chamber (16) is immersed , In an operating mode of the internal combustion engine, the primary stroke and the secondary stroke occur as soon as the cam follower (2) emerges from the cam indentation (10) onto the base circle (8).

Description

Territory of invention

The The invention relates to a variable valve train of an internal combustion engine with a device that is at least a mode-dependent secondary lift a gas exchange valve for an internal exhaust gas recirculation serves. Such a trained valve train preferably forms the mechanical basis for the implementation of homogeneous self-ignition combustion processes.

background the invention

A valve train with a mode-dependent secondary lift of the gas exchange valve has already been proposed for a device which is to serve as an engine brake in air-compressing internal combustion engines. Motor brakes are used as a safety-relevant supplement to the service brake usually as a retarder for commercial vehicles and are based on the principle that the drag torque of the engine located in overrun and not fueled by increasing the charge exchange work can be significantly increased and the vehicle is slowed down. For this purpose, the exhaust valve is opened again during the compression phase, so that the cylinder charge is not compressed gas-spring-like, but is pushed into the outlet channel by applying Ausschiebearbeit. So is in the DE 40 07 287 A1 describes an engine brake, in which a roller tappet picks off a cam having a cam lobe next to a conventional cam lobe and a base circle, which -in the direction of cam follow-connects to the cam lobe. The roller tappet is hydraulically extendable beyond an integral hydraulic lash adjuster by having a chamber that fills with hydraulic fluid as the roller tappet passes through the cam lobe. The inflow and outflow of hydraulic fluid to and from the chamber is controlled by a hydraulic valve, which is closed when the engine brake is activated in the phase in which the cam follower from the cam indentation on the base circle emerges. In this case, the roller tappet generates an additional stroke during the compression phase. In the fired operation of the internal combustion engine, however, the chamber can empty again via the then open hydraulic valve, so that the roller tappet shortens when retracted from the Nockeneinformung back to its original length and generates no additional stroke on the exhaust valve.

adversely on the roller tappet the The above document is its complex structure, since an inner housing, the the piston of the hydraulic valve clearance compensation element in one leads hollow cylindrical recess, also on its outer circumference high-precision has to be machined to make the chamber leak-gap like the environment seal.

Task of invention

Compared to the known prior art, the invention is based on the object To create a valve train, the internal back sucking of Exhaust gas in sufficient quantity and with sufficiently accurate and fully variable adjustable dosage allows in particular an internal combustion engine with so-called homogeneous self-ignition to operate. The valve train is also simple and therefore inexpensive to produce is.

Summary the invention

The subject of the present invention is therefore a valve gear which can be produced cost-effectively and which serves for exhaust gas recirculation. This is in particular the prerequisite for operation of the internal combustion engine with homogeneous and self-igniting charge. Such, also referred to as HCCI (Homogeneous Charge Compression Ignition) combustion method is used both in self-ignited diesel internal combustion engines as well as externally ignited gasoline internal combustion engines, at least in part-load operation of the internal combustion engine mainly for the purpose of emission reduction. The combustion process characterized by start of combustion, center of gravity and duration, maximum cylinder pressure increase and peak pressure is determined in the HCCI process essentially by controlling the charge composition and the charge temperature profile. It turns out that in this combustion method, a high charge temperature for controlling the ignition timing is desired. A very effective means for increasing the charge temperature is to increase the residual gas content, ie to increase the content of untrushed or purged exhaust gas returned to the cylinder of the previous combustion cycle in the cylinder charge for the next combustion cycle. In this case, the residual gas content on the operating point of the internal combustion engine must be fully variable, with residual gas quantities of 60% of the cylinder charge and more may be required. Residual gas components can no longer be provided at this altitude via internal exhaust gas recirculation through conventional valve overlap or via an arrangement for external exhaust gas recirculation. Moreover, the HCCI process reacts with unacceptable combustion processes extremely sensitively to changes conditions of the charge properties, so that in addition to the provision of residual gas in the required amount also a combustion cycle-faithful, high-precision and cylinder-specific dosing of the residual gas content is required.

By the features of the invention lies a variable valve train with at least one inlet and at least an exhaust valve, of which at least one gas exchange valve with a cam follower acted upon by at least one cam is in active connection. This therefore also includes a valve train in, in which the cam follower formed switchable by coupling means is and strokes several cams in dependence selectively transfers from its coupling state to the gas exchange valve. But also valve trains, the hub of the gas exchange valve by means of a Continuously vary cams and other adjusting elements, should be included in the scope of protection.

Of the Cam follower is on a hydraulic valve clearance compensation element supportable stored, this with a Hydraulikmittelzulaufpfad as well with a closable by shut-off hydraulic fluid drainage path connected is. A high-pressure chamber of the lash adjuster, which through an inner lateral surface and an inner end face of a hollow cylindrical housing as well a front side of a housing longitudinally movable out Piston is limited, stands over one in the housing located passage opening in communication with the hydraulic fluid drain path. The cam has a cam lobe and cam indentation relative to a base circle, taking the cam lobe outside the base circle is located and a Primärhub the gas exchange valve generated and the Nockeneinformung lies within the base circle, in which the cam follower dips in hydraulic elongation of the high-pressure chamber.

In an operating mode in which the internal combustion engine with the exhaust gas recirculation according to the invention operated, the primary stroke and the secondary stroke of the at least one gas exchange valve. Prerequisite for this is that the shut-off is closed as soon as the cam follower is out of the Cam indentation on the base circle emerges. In this case remains the hydraulic fluid enclosed in the high-pressure chamber, and the opposite Cam indenting raised base circle provides an additional Cam elevation that generates the secondary stroke.

In another mode of operation of the internal combustion engine takes place only the primary stroke the at least one gas exchange valve. Here is the shut-off open, as soon as the cam follower from the cam indentation on the base circle austaucht. In this mode, the gas exchange valve experiences no secondary stroke, because the high-pressure chamber on the opened Draining the shut-off device until the valve train has a hydraulic shut-off Has length, which corresponds to the base circle of the cam.

Consequently becomes the basic function of the hydraulic valve clearance compensation element, namely Automatically compensate for play in the valve gear, at the same time used to drive the valve train when submerging the cam follower hydraulically extend into the cam indentation. This additional function means on the part of the hydraulic valve clearance compensation element only a minimal overhead, because only an additional Through opening in the high pressure room is required.

Especially for one Operation of the internal combustion engine in the homogeneous auto-ignition combustion process it is according to claim 2 necessary that the duration of the secondary lift and thus the amount of recirculated exhaust gas fully variable with an arbitrary time, to which the Blocking means open is, is adjustable. moreover it is according to the claims 8 and 9 expediently provided that the duration of the secondary lift for each Cylinder of the internal combustion engine individually and for each revolution the cam from a controller recalculated and re-adjustable.

In A variant according to claim 3, it is proposed that the secondary stroke on an outlet valve which partially or completely within the stroke of the intake valve is located. In this preferred embodiment is already exhaust gas ejected into the exhaust passage during the Intake stroke of the internal combustion engine via the then opened again exhaust valve sucked back into the combustion chamber.

It may also be appropriate according to claim 4, that the secondary stroke an inlet valve which partially or completely within the stroke of the exhaust valve is located. In this alternative embodiment Exhaust gas is Ausschiebetakt the internal combustion engine in the inlet channel pushed out and while sucked back into the combustion chamber of the intake stroke.

A Combination of these options is required 5 proposed. Accordingly, it can be used to adjust the amount and temperature of Restgases be advantageous, both exhaust gas from the inlet duct as also sucked back from the outlet channel.

The valve train according to the invention can be particularly easily represent on a finger follower valve drive according to claim 6, the hydraulic valve clearance compensation element is designed as a support element, the cam follower in shape a rocker arm pivots and is stored in a hollow cylindrical recess of the internal combustion engine resting. The support element has between the high-pressure chamber and a spherical end for supporting the finger lever an antechamber which is connected by means of at least one passage of the housing with the opening into the recess Hydraulikmittelzulaufpfad and open check valve with the high-pressure chamber. The high pressure chamber is in turn connected via the passage opening of the housing with the opening into the recess hydraulic fluid drainage path. Between the Hydraulikmittelzulaufpfad and the hydraulic fluid flow path is formed by a housing and recess sealing gap.

A sees further expedient embodiment according to claim 7, the use of an electro-hydraulic 2/2-way valve as a simple and inexpensive Barrier for the hydraulic fluid drainage path. However, it is also at the stake of equally acting shut-off means such as electro-hydraulic Proportional valves or electro-hydraulic 3/2-way valves thought.

In Claim 10 is proposed that the force of a spring means the cam follower applied in the direction of the cam indentation. This supports the hydraulic elongation of the valve clearance compensation element.

In appropriate training The invention is according to claim 11, that the hydraulic fluid supply path is provided with a hydraulic fluid delivery device, whose outlet pressure level is higher than that of a lubricating oil pump for the Lubricating oil circuit the internal combustion engine is in communication. This is a Supply of the hydraulic valve clearance compensation element with sufficient Volume flow of hydraulic fluid ensured, so that in the operating mode with exhaust gas recirculation as well at higher Speeds of the internal combustion engine, a fast and complete filling of the high-pressure chamber guaranteed is.

When Hydraulic means according to claim 12 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.

The Invention will be explained in more detail in the following embodiment.

Short description the drawings

In The accompanying drawings are a cam follower valve train for an exhaust valve as an embodiment for the Valve gear according to the invention in various angular positions of the cam shown. Show it:

1 a valve drive according to the invention with a longitudinal section through a support element at the time of valve closing after passing through the cam lobe,

2 the valve gear after 1 at a time when the finger follower is completely submerged in the cam indentation,

3 the valve gear after 1 at a time during the secondary stroke,

4 a control diagram of the internal combustion engine with secondary lift to an exhaust valve.

Full Description of the drawings

The 1 shows you as a rocker arm 1 trained cam follower 2 on one as a support element 3 trained hydraulic valve clearance compensation element 4 in the stroke direction of a gas exchange valve 5 is pivotally mounted. The rocker arm 1 is in a conventional manner via a cam 6 by means of a towing lever 1 connected and rotatably mounted roller 7 in the direction of actuation of the gas exchange valve 5 driven. Of course, instead of the role 7 also one with the rocker arm 1 rigidly connected sliding surface can be provided as a cam contact.

The cam 6 rotates clockwise in the embodiment and has relative to a base circle 8th a cam lobe 9 and a cam indentation 10 on. The cam lobe 9 is outside the base circle 8th and generates a primary lift of the gas exchange valve 5 , The cam indentation 10 lies within the base circle 8th ,

The support element 3 is in a hollow cylindrical recess 11 the internal combustion engine resting and with a Hydraulikmittelzulaufpfad 12 as well as a hydraulic valve 13 as a shut-off device 14 connected by a hydraulic fluid flow path 15 is closable. A high pressure room 16 of the valve clearance compensation element 3 , which by an inner circumferential surface 17 and an inner face 18 a hollow cylindrical housing 19 as well as a front side 20 one in the housing 19 longitudinally guided piston 21 is limited, is about one in the housing 19 located passage opening 22 with the hydraulic fluid drainage path 15 in connection.

It is of secondary importance, whether the passage opening 22 on the inner coat area 17 , as shown, in the high-pressure chamber 16 opens or whether the passage opening 22 on the inner front side 18 in the high pressure room 16 empties. It only needs to be ensured that the passage opening 22 for a low-resistance discharge of hydraulic fluid from the high-pressure chamber 16 over a sufficiently large cross section with the hydraulic fluid drainage path 15 communicates. Furthermore, it is located between an inner wall 23 the recess 11 and an outer circumferential surface 24 of the housing 19 a sealing gap 25 providing a hydraulic short between the hydraulic fluid supply path 12 and the hydraulic fluid drain path 15 prevented. Such a hydraulic short circuit would result in the high pressure space 16 over the hydraulic fluid supply path 12 could empty.

The supply of the support element 3 with hydraulic fluid is shown purely schematically. These include the hydraulic fluid intake path 12 , the hydraulic fluid drain path 15 , the hydraulic valve 13 and a hydraulic fluid delivery device 26 that may be identical to the lubricating oil pump of the internal combustion engine. The hydraulic fluid conveyor 26 but can also be connected in parallel to the lubricating oil pump or in series with this. In all these cases, the hydraulic means for supplying the support element 3 identical to the lubricating oil of the internal combustion engine. Another alternative embodiment is that the hydraulic fluid is a different fluid from the lubricating oil of the internal combustion engine. In this case, then the supply of the support element 3 in a separated from the lubricating oil circuit of the internal combustion engine hydraulic fluid circuit. If the hydraulic fluid conveyor 26 is not identical to the lubricating oil pump of the internal combustion engine, it is advantageous that the output pressure level of the hydraulic fluid delivery device 26 higher than that of the lubricating oil pump. Thus, in the operating mode with exhaust gas recirculation even at higher speeds of the internal combustion engine, a fast and complete filling of the high-pressure chamber 16 guaranteed.

The supply of the high pressure room 16 with hydraulic fluid in a conventional manner: the piston 21 the support element 3 has an anteroom 27 on, by means of passages 28 of the housing 19 and the piston 21 with the in the recess 11 opening hydraulic fluid intake path 12 and with the check valve open 29 with the high pressure room 16 connected is. The check valve 29 is in the front 20 of the piston 21 integrated. A spring means 30 causes the lash adjuster element 4 always has the desire, the valve train by driving apart of pistons 21 and housing 19 hydraulically extend to compensate for mechanical valve clearance.

Also within the base circle 8th located cam indentation 10 is by the lash adjuster 4 interpreted as a mechanical valve clearance. In 2 is the cam 6 in an angular position, in which the role 7 of the rocker arm 1 completely in the cam indentation 10 located. Here is the valve clearance compensation element 4 under magnification of the high-pressure chamber 16 extended accordingly. After exiting the role 7 from the cam indentation 10 is the role 7 on the base circle 8th , wherein in the illustration according to 3 a secondary stroke of the gas exchange valve 5 he follows.

The formation of the secondary lift of the gas exchange valve 5 depends on angular positions of the cam 6 to which the hydraulic valve 13 opens and closes. This connection is in 4 illustrated by valve lifts "VL" in a schematic timing diagram of the internal combustion engine by way of example for a designated "SL-EX" secondary stroke on an exhaust valve. The primary lift of the exhaust valve designated PL-EX ends at "EXC" after the top dead center "TDC" of the internal combustion engine, while an intake valve is already opened with a primary stroke "PL-IN". A bottom dead center of the internal combustion engine is designated "BDC".

"EXC" is the earliest possible angular position of the cam 6 to which the hydraulic valve 13 opens, otherwise the hydraulic fluid pressure in the high pressure chamber 16 during the primary lift of the exhaust valve collapse and the exhaust valve stops from the cam 6 would close controlled. In the event that no secondary stroke is to take place on the outlet valve, the hydraulic valve closes 13 at the earliest to the angular position "HVC" to shorten the valve clearance compensation element 4 on a the base circle 8th to ensure appropriate hydraulic length.

If a secondary lift of the exhaust valve occurs, this ends at the latest to the angular position of the cam 6 "SLC", wherein a cancellation of the secondary lift at the latest to the angular position "HVO" by opening the hydraulic valve 13 is initiated.

For the renewed primary lift of the exhaust valve is the hydraulic valve 13 at the latest to the designated with "EXO" angular position of the cam 6 closed again.

The 1 - 3 and the timing chart after 4 apply with appropriate modification of the angular position of the cam indentation 10 analogously also for a secondary stroke at the inlet valve or for a combination of secondary strokes at the inlet and outlet valve.

1

cam follower

2

cam follower

3

supporting

4

Lash adjuster

5

Gas exchange valve

6

cam

7

role

8th

base circle

9

cam lobe

10

Nockeneinformung

11

recess

12

Hydraulic fluid supply path

13

hydraulic valve

14

shutoff

15

Hydraulic fluid flow path

16

High-pressure chamber

17

inner lateral surface

18

inner front

19

casing

20

front

21

piston

22

Through opening

23

inner wall

24

outer jacket surface

25

sealing gap

26

Hydraulic fluid delivery device

27

anteroom

28

Through opening

29

check valve

30

spring means

VL

valve

TDC

Oberer dead

BDC

lower dead

PL-EX

Primary stroke of the exhaust valve

PL-IN

Primary stroke of the inlet valve

SL-EX

Secondary stroke of exhaust valve

SLC

Latest end of the secondary hub the exhaust valve

EXC

outlet valve Closing time = Earliest opening angle of

hydraulic valve

HVO

Latest opening angle of the hydraulic valve

HVC

Earliest closing angle of the hydraulic valve

EXO

outlet valve Closing time = Latest dwell of

hydraulic valve

Claims (12)

Variable valve train of an internal combustion engine having a device which is connected to a mode-dependent secondary lift of at least one gas exchange valve ( 5 ) for an exhaust gas back-suction, preferably in a homogeneous auto-ignition combustion method, with the following features: • the valve drive has at least two gas exchange valves ( 5 ), at least one of which is an intake valve and at least one of which is an exhaust valve; At least one of the at least two gas exchange valves ( 5 ) is associated with one of at least one cam ( 6 ) acted upon cam follower ( 2 ) in operative connection, which cam follower ( 2 ) on a hydraulic valve clearance compensation element ( 4 ) is supported supportable; • the valve clearance compensation element ( 4 ) is connected to a hydraulic fluid intake path ( 12 ) as well as with a by blocking means ( 14 ) closable hydraulic fluid drain path ( 15 ), wherein a high pressure room ( 16 ) of the valve clearance compensation element ( 4 ), which by an inner circumferential surface ( 17 ) and an inner end face ( 18 ) of a hollow cylindrical housing ( 19 ) as well as an end face ( 20 ) one in the housing ( 19 ) longitudinally movably guided piston ( 21 ) is limited to one in the housing ( 19 ) passage opening ( 22 ) with the hydraulic fluid drain path ( 15 ); The at least one cam ( 6 ) has relative to a base circle ( 8th ) a cam lobe ( 9 ) and a cam indentation ( 10 ), whereby the cam lobe ( 9 ) outside the basic circle ( 8th ) and a primary lift of the gas exchange valve ( 5 ) and the Nockeneinformung ( 10 ) within the basic circle ( 8th ), in which the cam follower in hydraulic elongation of the high-pressure chamber ( 16 immersed); In an operating mode of the internal combustion engine, the primary stroke and the secondary stroke of the at least one of the at least two gas exchange valves take place ( 5 ), the blocking means ( 14 ) is closed as soon as the cam follower ( 2 ) from the cam indentation ( 10 ) on the base circle ( 8th ) and wherein, in another operating mode of the internal combustion engine, only the primary stroke of the at least one of the at least two gas exchange valves ( 5 ), wherein the blocking means ( 14 ) is opened as soon as the cam follower ( 2 ) from the cam indentation ( 10 ) on the base circle ( 8th ) emerges. Valve gear according to claim 1, wherein a duration of the secondary stroke with arbitrarily selectable time of opening the shut-off ( 14 ) is fully variable adjustable. Valve gear according to claim 1, wherein the at least one of the at least two gas exchange valves ( 5 ) is an exhaust valve whose secondary stroke is partially or fully within the stroke of the intake valve. Valve gear according to claim 1, wherein the at least one of the at least two gas exchange valves ( 5 ) is an intake valve whose secondary stroke is partially or completely within the stroke of the exhaust valve. Valve gear according to claim 1, wherein both the Inlet valve and the exhaust valve to perform the secondary stroke, wherein the secondary lift of the intake valve partially or completely within the primary stroke of the exhaust valve and the secondary stroke of the exhaust valve is partially or completely within the Primärhubs the intake valve. Valve gear according to claim 1, wherein the cam follower ( 2 ) a drag lever ( 1 ) and the valve clearance compensation element ( 4 ) a drag lever ( 1 ) pivotally supporting support element ( 3 ), which is in a hollow cylindrical recess ( 11 ) of the internal combustion engine is resting and one between the high-pressure chamber ( 16 ) and a spherical end for supporting the finger lever ( 1 ) an anteroom ( 27 ), which with the in the recess ( 11 ) hydraulic fluid intake path ( 12 ) and with open check valve ( 30 ) with the high-pressure chamber ( 16 ), which high-pressure space ( 16 ) via the passage opening ( 22 ) of the housing ( 19 ) with the in the recess ( 11 ) opening hydraulic fluid drain path ( 15 ), wherein between the hydraulic fluid supply path ( 12 ) and the hydraulic fluid drain path ( 15 ) through an outer surface ( 24 ) of the housing ( 19 ) and the recess ( 11 ) formed sealing gap ( 25 ) is located. Valve gear according to claim 1, wherein the blocking means ( 14 ) is an electro-hydraulic 2/2-way valve. Valve gear according to claim 2, wherein the duration of the secondary stroke for each revolution of the cam ( 6 ) is recalculated by a control unit and is newly adjustable. Valve gear according to claim 8, wherein in the case of mehrzylindrigen internal combustion engine, the duration of the secondary lift cylinder individually from the control unit calculated and adjustable. Valve gear according to claim 1, wherein the cam follower ( 2 ) by the force of a spring means ( 30 ) in the direction of the cam indentation ( 10 ) is acted upon. Valve gear according to claim 1, wherein the hydraulic fluid supply path ( 12 ) with a hydraulic fluid delivery device ( 26 ), whose output pressure level is higher than that of a lubricating oil pump for the lubricating oil circuit of the internal combustion engine, is in communication. Valve gear according to claim 11, wherein the hydraulic means oil the internal combustion engine is.