EP1807609B1 - Valve drive of an internal combustion engine - Google Patents

Abstract

The invention relates to a valve drive (1) of an internal combustion engine which is used to actuate a gas exchange valve (6). Displacement thereof takes place when a cam (9) is lifted and when a hydraulic force applying device (12) is lifted. A piston (13) of the force applying device can be displaced from a first end position (A) to a second end position by leading a hydraulic medium, which can be pressure-adjusted, from a hydraulic medium line (24) into a pressure chamber (21). The pressure chamber (21) can be connected to the hydraulic medium line (24) by means of a shut-off element (20) which is open towards the pressure chamber (21) and which is arranged in the housing (15) and also by means of at least one passage (26) in the housing (15). The passage (26) is at least partially blocked by an external covering surface (16) of the piston (13) in the first end position (A) thereof.

Description

Field of the invention

The invention relates to a valve train of an internal combustion engine for actuating a gas exchange valve. Its movement follows a stroke of a cam and a stroke of the cam superimposed and independent of the stroke of the cam stroke of a hydraulic force application device. For this purpose, a piston of the force application device is movable relative to a housing of the force application device by time-variable supply of a pressure-adjustable hydraulic fluid from a hydraulic medium line in a pressure chamber formed by the piston and the housing from a first end position to a second end position.

Background of 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 force application 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 valve train with hydraulic force application device. This serves to superimpose a stroke generated by the cam to a stroke independent of the cam on 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 is generated to the bucket tappet by volume change of a pressure chamber adjacent to the pressure chamber. The pressure chamber is in turn connected via channels in the interior of the tappet and in the tappet guide of the internal combustion engine to a pressure or volume flow adjustable hydraulic supply.

In the also generic DE 43 18 293 A1 is proposed a drag lever drive with a pivot bearing whose bearing point for the drag lever is lowered by Absteuern of hydraulic fluid from the pressure chamber of the force application device by means of a control valve. By lowering the bearing point of the cam lift is divided kinematically to the bearing point and the gas exchange valve, so that there is a reduction of the transferred to the gas exchange valve stroke.

Although with the aforementioned valve trains already a largely variable influencing of the cam from the valve lift is possible, with some means for braking the piston movement are provided upon reaching the end positions, the prior art systems have some disadvantages. So the piston is the DE 101 56 309 A1 designed as a stepped piston which displaces hydraulic means with a cylindrical ring portion of an annular space located on the cup bottom. The braking of the piston upon reaching the end position is intended to be generated by displacement of the hydraulic fluid from the annular space via guide gaps between the annular portion and annulus. However, such a design requires double fits of the components, so that the hydraulic force application device is associated with considerable production and quality assurance effort and consequently high production costs. Moreover, the piston is prevented from leaving the end position with high acceleration and thus as quickly as possible, since the annulus above the narrow guide gaps must first be filled with hydraulic fluid again.

In the DE 43 18 293 A1 is located between the housing of the pivot bearing and the hydraulic fluid supply a ball check valve. However, this is arranged montageunfreundlich in the cylinder head of the engine and is also limited in principle due to flow. In this respect, a high acceleration of the piston when leaving its end position is only partially implemented here.

A disadvantage of both above-mentioned writings is also the dependent on the viscosity and thus in particular on the temperature of the hydraulic medium Abbremsverlauf the piston to be considered upon reaching the end position. Both the displacement of the hydraulic fluid through annular gaps, as in the DE 101 56 309 A1 are provided, as well as the connection of the pressure chamber with a relatively long throttle line according to the DE 43 18 293 A1 leads to a significant dependence of the Abbremsverlaufs of the viscosity of the hydraulic fluid. However, this dependence is by no means desirable, especially since the very wide operating temperature range of the internal combustion engine would lead to extremely different and only with high electro-hydraulic control effort to be equalized Abbremsverläufen the piston.

Object of the invention

The present invention is therefore the object of a valvetrain of the type mentioned in such a way that the disadvantages are avoided. The pressure chamber should therefore be equipped with a hydraulically acting device which allows both a targeted and on the viscosity of the hydraulic medium possible independent Abbremsverlauf the piston upon reaching the end position. At the same time a rapid acceleration of the piston when leaving the end position should be feasible. The valvetrain should also be inexpensive to produce in a simple manner and under high-volume conditions.

Summary of the invention

The solution to this problem arises from the features of claim 1, while advantageous developments and refinements the dependent claims are removed.

Accordingly, the object is achieved in that the pressure chamber is connected both via a housing arranged in the housing and the pressure chamber opening to shut-off and at least one passage in the housing with the hydraulic medium line. In this case, the passage is at least partially blocked due to overlap by an outer circumferential surface of the piston in its first end position.

The subject of the present invention is therefore a valve gear which can be produced cost-effectively and which makes it possible to superimpose the stroke of a cam and a stroke of a hydraulic force application device independent of the stroke of the cam on the gas exchange valve. Crucial for the quality of the valve train function is the course of movement of the piston upon reaching and leaving the first end position. When reaching the first end position, it is desirable that the movement of the piston is decelerated rapidly from a high to a low speed, in order to simultaneously ensure a gentle placement of the gas exchange valve in its valve seat. The hydraulic force application device should also be able to generate strokes on the gas exchange valve with a large time cross section, for which a high speed of the piston between the first and the second end position is required.

A preferred embodiment of the valve train according to claim 2, that the pressure chamber is connected both via the passage and via a throttle cross section with the hydraulic medium line. In this case, the throttle cross section should be formed substantially iris-shaped. Such a throttle cross-section produces a largely independent of the viscosity of the hydraulic fluid and thus one above the operating temperature of the internal combustion engine sufficiently uniform deceleration of the piston, while the passage can be consistently designed for a rapid emptying and filling of the pressure chamber out.

In a particularly advantageous embodiment according to claim 3, the valve train according to the invention has a hydraulic valve clearance compensation device, which is arranged in a hollow cylindrical recess of the piston. This makes it possible both to minimize the timing variations of the internal combustion engine caused by mechanical valve clearance and to synchronize the movement of the piston with that of the gas exchange valve. This synchronization significantly promotes a smooth deceleration of the piston. Conversely, a large mechanical valve clearance could cause the piston would not be braked in time and therefore would hit the gas exchange valve with respect to valve train noise and wear excessive speed on his valve seat.

According to claim 4, it is advantageous to define the second end position of the piston by stop means. As a result, on the one hand overshoot of the piston beyond the second end position, as may occur in a malfunction of the valve train, for example, due to an excessive pressure in the hydraulic medium line, effectively prevented. On the other hand, the piston is secured against falling out of the housing in the not yet mounted state of the valve train.

Additionally or alternatively to this stop means, the pressure chamber according to claim 5 also practice a discharge line for the hydraulic fluid relieve when the piston reaches the second end position. For this purpose, at least one outlet opening is located in the housing, which is at most partially blocked by the outer circumferential surface of the piston when reaching the second end position and thus connects the pressure chamber with the drain line.

An advantage of this design is on the one hand a reduced mechanical stress on the stop means and on the other hand the possibility to flush stiffness-reducing gas bubbles in the hydraulic fluid from the pressure chamber.

According to claim 6, it is advantageous if the blocking means is a ball check valve. Such ball check valves have proven themselves many times in practice and are inexpensive to produce.

A particularly preferred embodiment of the valve train results according to claim 7, when the piston is arranged in a pivot bearing, which supports a finger lever pivotally. For this purpose, a camshaft bearing compensating piston of the hydraulic valve lash adjuster is guided in the piston longitudinally movable. It is expedient according to claim 8, to integrate in the drag lever a rotatably mounted roller as a low-friction contact surface to the cam.

The valve train should also allow a secondary stroke of the gas exchange valve during a lift-free base circle phase of the cam according to claim 9. This results in advantageous ways to suck back exhaust gas in high and precisely adjustable amounts internally. This form of exhaust gas recirculation is in particular the basis for operation of the internal combustion engine with homogeneous and self-igniting charge. Such, also referred to as HCCl (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 is determined in the HCCl 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 the increase of the residual gas content, ie the increase in the content of not flushed out or purged and recirculated exhaust gas 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 HCCl process reacts with unacceptable combustion processes extremely sensitive to changes in charge characteristics, so that in addition to the provision of residual gas in the required amount also a combustion cycle-faithful, highly precise and cylinder-specific dosing of the residual gas content is required.

The secondary stroke is carried out according to claim 10, preferably at an outlet valve. In the case of the exhaust gas recirculation explained above, exhaust gas which has already been ejected into the exhaust passage during the intake stroke of the internal combustion engine is sucked back into the combustion chamber via the then opened exhaust valve. 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 still open during the compression phase, so that the cylinder charge is not compressed gas-spring-like, but is pushed by applying Ausschiebearbeit in the exhaust passage.

With regard to exhaust gas recirculation it may also be expedient, according to claim 11, for the secondary stroke to take place at an inlet valve. In this alternative embodiment, exhaust gas is expelled in Ausschiebetakt the internal combustion engine with the intake valve again open in the inlet channel and sucked back into the combustion chamber during the intake stroke.

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

As hydraulic means, the lubricating oil of the internal combustion engine is used according to claim 12 for the sake of simplicity. However, it is also conceivable to use any other suitable fluids in a hydraulic fluid circuit, which would then be separated from the lubricating oil circuit of the internal combustion engine.

Short description of the drawing

Figur 1

den Schlepphebeltrieb bei geschlossenem Gaswechsel- ventil mit einem längsgeschnittenen Schwenklager,

Figur 2

eine vergrößerte Darstellung des Schwenklagers gemäß Figur 1,

Figur 3

den Schlepphebeltrieb gemäß Figur 1 bei geöffnetem Gas- wechselventil,

Figur 4

eine vergrößerte Darstellung des Schwenklagers gemäß Figur 3.

Further features of the invention will become apparent from the following description and from the drawings, in which a drag lever drive is shown as an embodiment of the valve gear according to the invention. Show it:

FIG. 1

the drag lever drive with closed gas exchange valve with a longitudinally slotted pivot bearing,

FIG. 2

an enlarged view of the pivot bearing according to FIG. 1 .

FIG. 3

the drag lever drive according to FIG. 1 with open gas exchange valve,

FIG. 4

an enlarged view of the pivot bearing according to FIG. 3 ,

Detailed description of the drawings

In the FIGS. 1 to 4 the valve drive 1 according to the invention is disclosed using the example of a drag lever drive 2 for an internal combustion engine. As in FIG. 1 shown, is located in a hollow cylindrical recess 3 of the internal combustion engine, a pivot bearing 4, which supports a drag lever 5 in the direction of actuation of a gas exchange valve 6 pivotally. A rotatably mounted in the finger lever 5 roller 7 serves as a low-friction stop surface 8 to a cam 9. The cam 9 has a cam elevation phase 10 which generates a stroke on the gas exchange valve 6, and a lift-free base circle phase eleventh

The pivot bearing 4 is part of a hydraulic force application device 12 and is in FIG. 1 as well as enlarged in FIG. 2 for a first end position "A" of a piston 13 is shown. The gas exchange valve 6 is closed, since at the same time the cam 9 rests with its base circle phase 11 on the roller 7.

In an inner circumferential surface 14 of a cup-shaped housing 15, the piston 13 is guided longitudinally movably with an outer circumferential surface 16. In the first end position "A" is an end face 17 of the piston 13 on a bottom 18 of the housing 15 at. The bottom 18 has an indentation 19 for receiving a shut-off means 20 for a located within the housing 15 pressure chamber 21 which is bounded by the end face 17 of the piston 13. The Abspermittel 20 is formed in this embodiment as a ball check valve 22 which opens to the pressure chamber 21 and a hydraulic connection between, at least one arranged in the bottom 18 of the housing 15 channel 23 and the pressure chamber 21 produces.

The channel 23 in turn is in hydraulic communication with an opening into the recess 3 hydraulic line 24. This is also part of the hydraulic force application device 12 and serves to supply the pressure chamber 21 with hydraulic fluid whose pressure is adjustable via a hydraulic drive device "S-P" shown schematically.

Via a further line 25 communicating with the hydraulic medium line 24 there is also connection to the pressure space 21 via one or more passages 26 opening into the inner casing surface 14 of the housing 15. The passages 26 are partially or completely through in the first end position "A" of the piston 13 the outer circumferential surface 16 of the piston 13 is blocked. The supply line 25 is preferably designed so that the hydraulic fluid line 24 is associated with an annular groove 27 in an outer circumferential surface 28 of the housing 15, wherein from the annular groove 27 and the ball check valve 22 leading to channel 23 emanates. Alternatively, it may of course also be provided to arrange an identically acting annular groove in the recess 3.

The pivot bearing 4 has in the illustrated embodiment via a hydraulic valve clearance compensation device 29 which is arranged in a hollow cylindrical recess 30 of the piston 13 and in a known manner a cam follower 5 overlapping balancing piston 31 and a working space 32, via a supply line 33, a hydraulic fluid supply " S-LA "is assigned.

In order to avoid an undesired spacing of a side facing away from the drag lever 5 end 34 of the housing 15 to a bottom 35 of the recess 3 due to interposed dammed hydraulic means, the ground 35 is connected via a discharge line 36 with a non-pressurized or low-pressure reservoir "T". Due to the pressure-relieving effect of the discharge line 36, it is therefore not necessary to secure the housing 15 against undesired longitudinal movement as a result of dammed up hydraulic medium in the recess 3 of the internal combustion engine.

In the Figures 3 and 4 the piston 13 is in a second end position "B" and the gas exchange valve 6 is opened, wherein the cam 9 still contacts the roller 7 with its base circle phase 11. The movement of the piston 13 from the first end position "A" to the second end position "B" will be described below with reference to FIG FIG. 4 described. The piston 13 leaves the first end position "A" with high acceleration by first a major volume flow of pressurized hydraulic fluid from the hydraulic fluid line 24 via the channel 23 with the ball check valve 22 is open in the pressure chamber 21 passes. During the further movement of the piston 13, the passages 26 are successively released from the outer circumferential surface 16 of the piston 13, so that then the hydraulic fluid can reach the pressure chamber 21 with little resistance via the ball check valve 22 and simultaneously via the supply line 25 and via the passages 26. The low-resistance inflow of the hydraulic fluid into the pressure chamber 21 generates a high speed of the piston 13, so that consequently the second end position "B" is reached in a short time. This is particularly advantageous at high rotational speeds of the internal combustion engine in order to realize a large time cross section of the stroke generated by the hydraulic force application device 12 at the gas exchange valve 6.

The piston 13 is braked in the region of the second end position "B" by stop means 37 again to a standstill. As an example of such a stop means 37, a ring body 39 is inserted in a recess 38 of the housing 15, whose inner diameter is smaller than that of the inner circumferential surface 14 of the housing 15. Exceeding the second end position "B" of the piston 13 is prevented by a lower shoulder 40 of an annular groove 41 of the piston 13 abutting against the annular body 39. The annular groove 41 is to be designed so wide that reaching the first end position "A" is not hindered by contact of an upper shoulder 42 of the annular groove 41 with the annular body 39. As a variant of a similar acting stop means, not shown, also a reverse arrangement is conceivable.

In this case, an annular body would move in an outer recess of the piston 13 with the piston 13 and strike in the second end position "B" against a shoulder of an annular groove 15 located in the housing.

Alternatively or additionally, a hydraulic braking of the piston 13 is possible by the outer circumferential surface 16 of the piston 13 in the region of the second end position "B" one or more outlet ports 43 releases that connect a return line "R" serving drain line 44 with the pressure chamber 21 , In this case, therefore, the piston 13 automatically regulates its second end position "B" by opening the outlet openings 43 just enough so that the volume of hydraulic fluid supplied into the pressure chamber 21 corresponds to the volume of hydraulic fluid discharged from the pressure chamber 21 into the outlet line 44.

However, it should be expressly mentioned at this point that the variability of the hydraulic force application device with respect to the stroke of the piston 13 is not limited by the fact that the piston 13 must reach the second end position "B". Rather, it is possible by suitable control of the hydraulic drive device "SP" that the piston 13 comes to a standstill in any position between the first end position "A" and the second end position "B", then to the end position "A", as follows described to return.

A return movement of the piston 13 in the direction of the first end position "A" begins when the hydraulic drive device "SP" allows a flow of hydraulic fluid from the pressure chamber 21. The expiration of the hydraulic fluid takes place - if necessary after closing the outlet openings 43 -by means of the passages 26 and the allocation 25 into the hydraulic medium line 24, since the ball check valve 22 to the channel 23 is now closed. Shortly before reaching the first end position "A", the piston 13 is braked by its outer circumferential surface 16, the passages 26 closes successively. A gentle placement of the end face 17 of the piston 13 on the bottom 18 of the housing 15 can be ensured that at least one of Passages 26 in the first end position "A" is not completely blocked and can escape only a small volume flow of the hydraulic fluid at a correspondingly reduced speed of the piston 13 from the pressure chamber 21.

A preferred alternative is the possibility of connecting the pressure chamber 21 to the supply line 25 via an orifice-shaped throttle cross-section 45. With the help of such a throttle cross-section 45, a largely independent of the viscosity of the hydraulic fluid deceleration of the piston 13 can be ensured upon reaching the first end position "A". So that the braking effect of the throttle cross-section 45 unfolds optimally, it is expedient to completely close the passages 26 already before reaching the first end position "A" by the outer circumferential surface 16 of the piston 13.

The valve drive 1 according to the invention has been explained using the example of a finger follower valve drive 2 with a pivot bearing 4 as a preferred embodiment. However, the idea of the invention can equally be implemented in other types of valve trains, such as cup drives or pushrod drives. The scope of the invention should also include valve trains, which are designed switchable by coupling means to selectively transfer strokes of several cams depending on the coupling state to the gas exchange valve 6. This applies equally to valve trains that continuously vary the stroke of the gas exchange valve 6 by means of a cam and other adjusting elements.

List of reference numbers and symbols

1

valve train

2

Finger lever drive

3

recess

4

pivot bearing

5

cam follower

6

Gas exchange valve

7

role

8th

approach surface

9

cam

10

Cam lobe phase

11

Base circle phase

12

force applicator

13

piston

14

Inner surface area

15

casing

16

Outer casing surface

17

face

18

ground

19

indentation

20

shutoff

21

pressure chamber

22

Ball check valve

23

channel

24

Hydraulic medium line

25

supply

26

passage

27

ring groove

28

Outer casing surface

29

Valve lash adjuster

30

recess

31

balance piston

32

working space

33

supply line

34

front

35

reason

36

relief line

37

slings

38

puncture

39

ring body

40

lower paragraph

41

ring groove

42

upper paragraph

43

outlet

44

drain line

45

Throttle cross section

A

first end position

B

second end position

S-P

driving

S-LA

Hydraulic medium supply

T

reservoir

R

returns

Claims (12)

1. Valve drive (1) of an internal combustion engine for actuating a gas exchange valve (6), the movement of which follows a stroke of a cam (9) and also a stroke, which is superposed on the stroke of the cam (9) and independent of the stroke of the cam (9), of a hydraulic force-exerting device (12) by virtue of a piston (13) of the force-exerting device (12) being movable relative to a housing (15) of the force-exerting device (12) from a first end position (A) into a second end position (B) by a supply, that varies over time, of a hydraulic medium adjustable in pressure from a hydraulic medium line (24) into a pressure chamber (21) formed by the piston (13) and by the housing (15), characterized in that the pressure chamber (21) is connected to the hydraulic medium line (24) both via a shut-off means (20) which is arranged in the housing (15) and which opens toward the pressure chamber (21) and also via at least one passage (26) in the housing (15), the passage (26) being at least partially blocked on account of its being covered by an outer lateral surface (16) of the piston (13) in the first end position (A) thereof.
2. Valve drive according to Claim 1, characterized in that the pressure chamber (21) is additionally connected to the hydraulic medium line (24) via at least one throttle cross section (45), the throttle cross section (45) being designed substantially in the form of an orifice.
3. Valve drive according to Claim 1 or 2, characterized in that the piston (13) has a hollow cylindrical recess (30) in which a hydraulic valve play compensating device (29) is arranged.
4. Valve drive according to Claim 1, characterized in that the second end position (B) of the piston (13) is defined by stop means (37).
5. Valve drive according to Claim 1, characterized in that the housing (15) has at least one outlet opening (43) which connects the pressure chamber (21) to a discharge line (44) for the hydraulic medium when, in the second end position (B) of the piston (13), the outlet opening (43) is at most partially blocked as a result of its being covered by the outer lateral surface (16) of the piston (13).
6. Valve drive according to Claim 1, characterized in that the shut-off means (20) is a non-return ball valve (22).
7. Valve drive according to Claim 3, characterized in that the piston (13) is arranged in a pivot bearing (4) which serves to pivotably mount a rocker arm (5) on a compensating piston (31), which is guided in a longitudinally movable manner in the piston (13), of the hydraulic valve play compensating device (29).
8. Valve drive according to Claim 7, -characterized in that a rotatably mounted roller (7) is integrated, as a run-on surface (8) for the cam (9), in the rocker arm (5).
9. Valve drive according to Claim 1, characterized in that the gas exchange valve (6) performs at least one secondary stroke during a base circle phase (11) of the cam (9).
10. Valve drive according to Claim 9, characterized in that the gas exchange valve (6) is an outlet valve of the internal combustion engine.
11. Valve drive according to Claim 9, characterized in that the gas exchange valve (6) is an inlet valve of the internal combustion engine.
12. Valve drive according to Claim 1, characterized in that the hydraulic medium is lubricating oil of the internal combustion engine.

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