EP2060754A2 - Hydraulic unit for a cylinder head for a combustion engine with a variable valve stroke - Google Patents

Abstract

The hydraulic unit (5) has a slave unit (8) activating a gas-exchange valve. A hydraulic housing is provided with a bottom part (20) and a top part (22). A master unit (6), a slave unit, a high-pressure chamber, a hydraulic valve (10) and a medium-pressure chamber (12) are in connection with the hydraulic housing. A low-pressure chamber (16) used as a hydraulic medium reservoir is formed in the top part and communicates with the medium-pressure chamber through a choke opening that is formed through a separating wall extending between the low-pressure chamber and the medium-pressure chamber.

Description

Name of the invention Hydraulic unit for a cylinder head of an internal combustion engine with hydraulically variable valve train description Field of the invention

• ■ zumindest eine antriebseitige Gebereinheit,
• ■ zumindest eine ein Gaswechselventil betätigende, abtriebseitige Nehmereinheit,
• ■ zumindest ein ansteuerbares Hydraulikventil,
• ■ zumindest einen Mitteldruckraum,
• ■ zumindest einen Hochdruckraum, der im Übertragungssinn zwischen der zugehörigen Gebereinheit und der zugehörigen Nehmereinheit angeordnet und über das zugehörige Hydraulikventil mit dem zugehörigen Mitteldruckraum verbindbar ist, und
• ■ ein Hydraulikgehäuse mit einem Gehäuseunterteil und einem Gehäuseoberteil
  umfasst, wobei wenigstens die Gebereinheit, die Nehmereinheit, der Hochdruckraum, das Hydraulikventil und der Mitteldruckraum im Verbund mit dem Hydraulikgehäuse zu der an den Zylinderkopf montierbaren Hydraulikeinheit gehören.

The invention relates to a hydraulic unit for a cylinder head of an internal combustion engine with a hydraulically variable valve train, the

• At least one drive-side transmitter unit,
• At least one gas exchange valve-actuating, output-side slave unit,
• At least one controllable hydraulic valve,
• ■ at least one medium-pressure space,
• ■ at least one high-pressure chamber, which is arranged in the transmission sense between the associated transmitter unit and the associated slave unit and connectable via the associated hydraulic valve with the associated medium-pressure space, and
• ■ a hydraulic housing with a lower housing part and an upper housing part
  wherein at least the transmitter unit, the slave unit, the high-pressure chamber, the hydraulic valve and the intermediate-pressure space in combination with the hydraulic housing belong to the hydraulic unit which can be mounted on the cylinder head.

Background of the invention

Such a hydraulic unit is considered from the considered generic DE 10 2006 008 676 A1 previously known. In the hydraulic unit proposed there, all essential, required for the hydraulically variable transmission of cam lobes on the gas exchange valves components are combined in a common hydraulic housing. This is composed of a lower housing part, in which the components mentioned are included and in which the pressure chambers extend, and a housing upper part closing the housing upper part together. The lower housing part is formed very compact design, and the upper housing part is also a substantially flat plate, so that in total each of the intermediate pressure chambers is limited to a correspondingly small volume.

However, a small-volume medium-pressure space can be problematic during the starting process of the internal combustion engine, especially if it is a starting operation at low outside temperatures and after a long stoppage of the internal combustion engine. This is due to the fact that the hydraulic fluid supply to the internal combustion engine does not yet deliver sufficient hydraulic fluid flow into the medium-pressure space during the starting process and only the hydraulic fluid volume remaining in the medium-pressure space and shrunk at low temperatures is insufficiently large for a complete refilling of a then-expanding high-pressure space. This problem applies to a greater extent in a short time repetitive starting operations, since in this case the hydraulic fluid consumption from the medium-pressure space can be greater than the nachgeförderte from the hydraulic fluid supply to the internal combustion engine volume. Such multi-start operations are typical, for example, for taxi cabs at taxi stands.

Based on the above-cited document, this problem could be defused only limited by extension of the medium-pressure space in the direction of the then equipped with appropriate cavities housing top, as well as in this case the formation of gas bubbles in the medium pressure space and their suction in the expanding high-pressure chamber can not be safely excluded would.

Object of the invention

The present invention is therefore the object of a hydraulic unit of the type mentioned in such a way that the disadvantages mentioned are eliminated by simple means. Accordingly, even with a compact hydraulic housing with a corresponding volume-limited medium-pressure space always safe and complete refilling of the expanding during the starting process of the engine high-pressure chamber to be ensured with hydraulic fluid.

Summary of the invention

The solution of this problem arises from the characterizing features of claim 1, while advantageous developments and refinements of the invention are the dependent claims can be removed. Accordingly, it is provided that in the housing upper part serving as a hydraulic fluid reservoir low pressure space is formed, the low-pressure chamber communicates only via at least one throttle opening with the medium-pressure space and wherein the throttle opening passes through a running between the low-pressure space and the central pressure space partition.

By running in the upper housing part low pressure space on the one hand during the starting process of the internal combustion engine required hydraulic fluid reservoir for the high-pressure chamber is expanded and on the other hand eliminates the risk of initially described suction of gas bubbles as far as possible. The latter results from the partition, which separates the low-pressure chamber from the medium-pressure chamber, so that during the stoppage phase of the engine and thereby cooling and thus shrinking hydraulic fluid, the formation of gas bubbles in the medium pressure space is prevented by suction of hydraulic fluid from the low pressure chamber.

Furthermore, it is provided in the case of inclined to gravity installation of the hydraulic unit in the internal combustion engine and / or the hydraulic unit with the internal combustion engine that the throttle opening extends at a geodetically deep point of the partition. This ensures even with possibly only slightly filled low pressure space, for example due to very low ambient temperatures and correspondingly strong shrinking hydraulic fluid, a bubble-free suction of hydraulic fluid from the low-pressure chamber in the medium-pressure space.

In a further advantageous embodiment of the invention, the upper housing part to be provided with at least one opening into the cylinder head vent opening for the low pressure chamber. Thus, gas bubbles that are deposited during operation of the internal combustion engine from the medium-pressure chamber via the throttle opening in the low-pressure space, permanently escape from the hydraulic unit into the interior of the cylinder head.

The safety of a complete refilling operation of the high-pressure chamber can be increased in particular with regard to multiple starts within a short time by a volume ratio of the pressure chambers with (V _L + V _M ) / V _H ≥ 2, if V _{L is} the volume of the low-pressure space, V _M the volume of Medium pressure space and V _{H is} the volume of the high-pressure chamber. In other words, the hydraulic fluid reservoir available for refilling the high-pressure chamber should be at least twice as large as the high-pressure chamber, which of course is also important for such valve trains in which two slave units are connected to a single transmitter unit for the simultaneous actuation of two gas exchange valves ,

In a structurally preferred embodiment of the invention, the partition should be formed as a housing intermediate part of the assembled in sandwich construction of the housing parts hydraulic housing. Alternatively, however, it may also be provided an integrally formed on the upper housing part partition, in which case such a housing upper part may be prepared for example by hydroforming.

In the case of the abovementioned sandwich construction of the hydraulic housing, the housing upper part should be coated with a sealing material made of elastomer material, at least in the area of contact with the housing intermediate part. The sealing means which prevent an emptying of the low-pressure space can be either an elastomer seal which is printed or sprayed locally on the sealing surface of the housing upper part or an elastomer coating applied over the entire surface of the housing upper part. Alternatively, of course, a separate seal between the upper housing part and the intermediate housing part, for example in the form of a paper seal possible.

In further embodiments of the invention, the upper housing part can be made either in a thermoforming process of aluminum or steel material or in an injection molding of plastic.

If it is possible and expedient, finally, the aforementioned features and embodiments of the invention should also be combined with each other as desired.

Brief description of the drawings

Figur 1

eine schematische Darstellung eines hydraulisch variablen Ventiltriebs;

Figur 2

eine erfindungsgemäße Hydraulikeinheit in perspektivischer Darstellung und

Figur 3

einen Querschnitt durch die Hydraulikeinheit aus Figur 2.

Further features of the invention will become apparent from the following description and from the drawings, in which an embodiment of the invention is shown. Unless otherwise stated, the same or functionally identical features or components are provided with the same reference numbers. Show it:

FIG. 1

a schematic representation of a hydraulically variable valve train;

FIG. 2

a hydraulic unit according to the invention in a perspective view and

FIG. 3

a cross section through the hydraulic unit FIG. 2 ,

Detailed description of the drawings

• eine antriebseitige Gebereinheit 6, hier in Form eines vom Nocken 3 angetriebenen Pumpenstößels 7;
• eine abtriebseitige Nehmereinheit 8, hier in Form eines das Gaswechselventil 4 unmittelbar betätigenden Nehmerkolbens 9;
• ein ansteuerbares Hydraulikventil 10, hier in Form eines elektromagnetischen 2-2-Wege-Schaltventils;
• einen zwischen der Gebereinheit 6 und der Nehmereinheit 8 verlaufenden Hochdruckraum 11, aus dem bei geöffnetem Hydraulikventil 10 Hydraulikmittel in einen Mitteldruckraum 12 abströmen kann;
• ein an den Mitteldruckraum 12 angeschlossener Druckspeicher 13 mit einem federkraftbeaufschlagten Ausgleichskolben 14;
• ein in Richtung des Mitteldruckraums 12 öffnendes Rückschlagventil 15, über das die Hydraulikeinheit 5 an den Hydraulikmittelkreislauf der Brennkraftmaschine angeschlossen ist und
• erfindungsgemäß einen als Hydraulikmittelreservoir dienenden Niederdruckraum 16, der lediglich über eine Drosselöffnung 17 in einer zwischen dem Niederdruckraum 16 und dem Mitteldruckraum 12 verlaufenden Trennwand 18 an den Mitteldruckraum 12 angeschlossen ist.

In FIG. 1 the basic structure of a hydraulically variable valve train 1 and features belonging to the invention are disclosed schematically. A section of a cylinder head 2 of an internal combustion engine with a cam 3 of a camshaft and a gas exchange valve 4 spring-loaded in the closing direction is shown. The variability of the valve train 1 is generated by means of a hydraulic unit 5 arranged between the cam 3 and the gas exchange valve 4. the following components include:

• a drive-side transmitter unit 6, here in the form of a driven by the cam 3 pump tappet 7;
• a driven-side slave unit 8, here in the form of a gas piston valve 4 directly actuating slave piston 9;
• a controllable hydraulic valve 10, here in the form of an electromagnetic 2-2-way switching valve;
• a high-pressure space 11 running between the transmitter unit 6 and the receiver unit 8, from which hydraulic fluid can flow into an intermediate-pressure space 12 when the hydraulic valve 10 is open;
• a pressure accumulator 13 connected to the medium-pressure chamber 12 with a compensating piston 14, which is acted on by spring force;
• a check valve 15 opening in the direction of the medium-pressure chamber 12, via which the hydraulic unit 5 is connected to the hydraulic fluid circuit of the internal combustion engine and
• According to the invention serving as a hydraulic fluid reservoir low pressure chamber 16 which is connected only via a throttle opening 17 in a running between the low pressure chamber 16 and the medium pressure chamber 12 partition 18 to the central pressure chamber 12.

The known operation of the hydraulic valve train 1 can be summarized in that the high-pressure chamber 11 between the transmitter unit 6 and the slave unit 8 acts as a hydraulic linkage, which - neglecting leaks - proportional to the stroke of the cam 3 displaced by the pump plunger 7 hydraulic volume as a function of the opening time and the opening duration of the hydraulic valve 10 in a first, the slave piston 9 acting sub-volume and in a second, in the medium pressure chamber 12 including pressure accumulator 13 effluent partial volume is split. As a result, not only the timing, but also the lifting height of the gas exchange valve 4 can be set fully variable.

As it is described below Figures 2 and 3 becomes clear, the hydraulic unit 5 as a further essential part of a common hydraulic housing 19, so that the hydraulic unit 5 can be mounted as a preassembled and optionally already filled with hydraulic fluid assembly in the cylinder head 2 of the internal combustion engine. The executed for a 4-cylinder inline hydraulic unit 5 is in general view FIG. 2 out. The composite in sandwich construction hydraulic housing 19 consists of a lower housing part 20, formed as intermediate housing part 21 partition wall 18 and a housing upper part 22. While the housing parts 20, 21, 22 are screwed together at various Verschraubungspunkten 23 hydraulically sealing, the lower housing part 20 separate Verschraubungspunkte 24 to Attaching the entire hydraulic unit 5 in the cylinder head 2 of the internal combustion engine.

The four transmitter units 6 each comprise a support element 25 accommodated in the housing lower part 20, a rocker arm 26 pivotally mounted thereon and having a rotatably mounted roller 27 for a low-friction cam tapping From the intermediate housing part 21 outgoing bracket 28 serve as captive for the drag lever 26 mounted in the cylinder head 2 hydraulic unit 5. This is also designed so that each of the transmitter units 6 with two slave units 8 interacts. In other words, only one cam 3 and one transmitter unit 6 are required for each pair of identical gas exchange valves 4, ie intake valves or exhaust valves of a cylinder of the internal combustion engine, wherein the hydraulic volume displaced by the pump tappet 7 simultaneously acts on both slave units 8. On the transmitter units 6 opposite side of the hydraulic unit 5, the respective one encoder unit 6 and the two slave units 8 associated hydraulic valves 10 can be seen with electrical connectors 29, wherein the normally open hydraulic valves 10 in a known per se and not shown here in valve receptacles are fixed in the housing base 20.

The already in FIG. 2 On the basis of the bulges in the upper housing part 22 recognizable low-pressure spaces 16 go clearly from a in FIG. 3 shown cross section through the hydraulic unit 5 before. In this cross section, the pressure accumulator 13 connected to the medium-pressure chamber 12 is also shown with the compensating piston 14, which is acted on by spring force. The throttle opening 17 connecting the low-pressure chamber 16 with the medium-pressure chamber 12 is arranged such that it extends at a geodetically low point of the housing intermediate part 21 of the hydraulic unit 5 inclined to gravity g in and / or with the internal combustion engine. As explained above, this ensures that only bubble-free hydraulic fluid from the low-pressure chamber 16 is sucked into the medium-pressure space 12. Although in FIG. 3 only one throttle opening 17 is shown, each of the medium-pressure spaces 12 can also communicate with the associated low-pressure space 16 via two or more throttle openings 17. Conversely, it would also be conceivable to associate each of two medium-pressure chambers 12 with two or more low-pressure chambers 16 separated from one another.

Gas bubbles, which pass through the throttle opening 17 from the medium-pressure chamber 12 into the low-pressure chamber 16 during operation of the internal combustion engine, can be deposited into the interior of the cylinder head 2 via a vent opening 30 extending in the upper housing part 22 and opening into the cylinder head 2.

In order to prevent a loss of hydraulic fluid from the low pressure chamber 16, in particular during the stoppage phase of the internal combustion engine, the upper housing part 22 is coated with a sealing material made of elastomer material, not shown here. In the illustrated embodiment, this coating is not limited only to the contact region to the intermediate housing part 21, but is located on the entire surface of the upper housing part 22 produced here in a deep-drawing of sheet steel.

How it finally works with a FIG. 1 is explained, the volume designated by V _{L of} the low-pressure chamber 16 on the one hand, taking into account the space available in the cylinder head 2 and on the other hand, to be sized as large as possible with an always sufficient hydraulic fluid reservoir. This means that the volume ratio (V _L + V _M ) to V _{H has} a value of at least 2, if with V _{M of} the hydraulic valve 10, the pressure accumulator 13, the partition 18 and the check valve 15 limited volume of the medium-pressure space 12 and with V _H the volume of the high-pressure chamber 11 delimited by the transmitter unit 6, by the slave unit or units 8 and by the hydraulic valve 10 is designated.

List of reference numbers

1

valve train

2

cylinder head

3

cam

4

Gas exchange valve

5

hydraulic unit

6

generator unit

7

pump plunger

8th

receiver unit

9

slave piston

10

hydraulic valve

11

High-pressure chamber

12

Medium-pressure chamber

13

accumulator

14

balance piston

15

check valve

16

Low-pressure chamber

17

throttle opening

18

partition wall

19

hydraulic housing

20

Housing bottom

21

Intermediate housing part

22

Housing top

23

screw fixing

24

screw fixing

25

supporting

26

cam follower

27

role

28

hanger

29

Connector of the hydraulic valve

30

vent

Claims (8)

Hydraulic unit (5) for a cylinder head (2) of an internal combustion engine with hydraulically variable valve train (1), the At least one drive-side transmitter unit (6), ■ at least one gas exchange valve (4) actuated, output side slave unit (8), At least one controllable hydraulic valve (10), At least one medium-pressure space (12), ■ at least one high-pressure chamber (11) which is arranged in the transmission sense between the associated transmitter unit (6) and the associated receiver unit (8) and via the associated hydraulic valve (10) with the associated medium-pressure space (12) is connectable, and A hydraulic housing (19) having a housing lower part (20) and an upper housing part (22)
comprising, wherein at least the transmitter unit (6), the receiving unit (8), the high-pressure chamber (11), the hydraulic valve (10) and the medium-pressure space (12) in conjunction with the hydraulic housing (19) to that to the cylinder head (2) mountable Hydraulic unit (5) are, characterized in that in the upper housing part (22) serving as a hydraulic medium reservoir low pressure space (16) is formed, wherein the low-pressure chamber (16) communicates only via at least one throttle opening (17) with the medium-pressure space (12), which throttle opening (17) passes through a between the low pressure chamber (16) and the central pressure chamber (12) extending partition (18). Hydraulic unit according to claim 1, characterized in that in a gravitational inclined installation case of the hydraulic unit (5) in and / or with the internal combustion engine, the throttle opening (17) extends at a geodetically deep point of the partition wall (18). Hydraulic unit according to claim 1, characterized in that the housing upper part (22) with at least one in the cylinder head (2) opening vent opening (30) for the low pressure space (16) is provided. Hydraulic unit according to claim 1, characterized in that the low-pressure space (16) has a volume V _L , the medium-pressure space (12) has a volume V _M and the high-pressure space (11) has a volume V _H with a volume ratio (V _L + V _M ) / V _H ≥ 2. Hydraulic unit according to claim 1, characterized in that the partition wall (18) is formed as a housing intermediate part (21) of the composite in a sandwich construction of the housing parts (20, 21, 22) hydraulic housing (19). Hydraulic unit according to claim 5, characterized in that the housing upper part (22) is coated at least in the contact region to the housing intermediate part (21) with a sealing means made of elastomer material. Hydraulic unit according to claim 1, characterized in that the housing upper part (22) is made in a deep-drawing process of aluminum or steel material. Hydraulic unit according to claim 1, characterized in that the housing upper part (22) is made in an injection molding of plastic.

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