EP2510201B1 - Internal combustion engine having electrohydraulic valve control and method for operating said internal combustion engine - Google Patents

Description

Field of the invention

• einen von einem Nocken der Nockenwelle angetriebenen ersten Hydraulikkolben und einen das Gaswechselventil in Öffnungsrichtung antreibenden zweiten Hydraulikkolben,
• einen von dem ersten Hydraulikkolben und dem zweiten Hydraulikkolben begrenzten Druckraum mit veränderlichem Volumen und einen den Druckraum mit einem Druckentlastungsraum verbindenden Steuerkanal,
• ein im Steuerkanal angeordnetes, elektrisch angesteuertes Hydraulikventil, das einen Hydraulikmittelfluss durch den Steuerkanal in geöffneter Stellung des Hydraulikventils zulässt und in geschlossener Stellung des Hydraulikventils sperrt.

The invention relates to an internal combustion engine with electrohydraulic valve control for variable-stroke drive of a spring-loaded in the closing direction gas exchange valve and a method for operating the internal combustion engine. It comprises a camshaft and a hydraulic system arranged in the drive sense between the camshaft and the gas exchange valve, which is connected to a hydraulic fluid supply of the internal combustion engine and has the following:

• a first hydraulic piston driven by a cam of the camshaft and a second hydraulic piston driving the gas exchange valve in the opening direction,
• a pressure chamber of variable volume bounded by the first hydraulic piston and the second hydraulic piston and a control channel connecting the pressure chamber to a pressure relief chamber,
• an arranged in the control channel, electrically controlled hydraulic valve, which allows a flow of hydraulic fluid through the control channel in the open position of the hydraulic valve and locks in the closed position of the hydraulic valve.

The internal combustion engine further comprises an electronic drive means for controlling the hydraulic valve as a function of operating parameters of the internal combustion engine.

Background of the invention

Internal combustion engines with electrohydraulic valve trains, in which a partial volume of the acting as a so-called hydraulic linkage pressure chamber with open hydraulic valve continuously in the pressure relief chamber can be controlled and accordingly the cam predetermined survey is completely, partially or not transferred to the gas exchange valve, are known in the patent literature from a variety of documents. The structural design of the valve control of a generic internal combustion engine goes from the article 'Electrohydraulic valve control with the' MultiAir 'method', the most recently in the Motortechnische Zeitschrift (MTZ), issue 12/2009 has been published. This article also shows an engine map with different lift curves, which - based on the cam lobe - are transmitted to the gas exchange valve in modified form depending on the operating point by means of the downstream hydraulic system. Also shown is the electronic control means for controlling the hydraulic valve, there in the form of an integrated engine control unit. The publication EP1344900 A2 also discloses an internal combustion engine having an electrohydraulic valve train.

Naturally, the operating behavior of electrohydraulic valve trains in a significant amount depends on the properties of the hydraulic fluid and, in particular, on its instantaneous and mainly temperature-induced viscosity state. A major cause of this dependency is the so-called hydraulic valve brake, which is part of the hydraulic system and replaces the valve closing ramp provided on conventional cams with conventional mechanical valve trains. The hydraulic valve brake is known to have the task of forming a decoupled from the cam lift stroke of the gas exchange valve so that the closing gas exchange valve always reaches the valve seat with mechanically and acoustically acceptable Aufsetzgeschwindigkeit. At the same time the hydraulic valve brake is to be designed so that the change in charge of the internal combustion engine affecting target-actual deviations of the gas exchange valve closing timing are minimal.

Hydraulic valve brakes are usually designed so that the displaced by the gas exchange valve side second hydraulic piston hydraulic fluid just before closing the gas exchange valve must pass a throttle point whose hydraulic resistance slows down the Gaswechselventilhubs generated to the predetermined Aufsetzgeschwindigkeit. However, the viscosity-temperature response of the hydraulic fluid, the viscosity of which increases sharply with decreasing temperature, limits the functionality of the hydraulic valve brake to a temperature window in such a way that the closing time of the gas exchange valve below an upper limit temperature fluctuates and / or delayed excessively. In extreme cases, the gas exchange valve does not reach the valve seat and remains - in terms of the charge cycle and combustion process of the engine - in an inadmissible standing between two revolutions of the camshaft.

Object of the invention

The present invention is therefore based on the object, so to train an internal combustion engine with electro-hydraulic valve control of the type mentioned above or to provide a method for operating the internal combustion engine, that the functionality of the electro-hydraulic valve control even at very high viscosity of the hydraulic fluid, i. is given in an extended to lower temperatures towards temperature window.

Summary of the invention

This object is achieved on the device side by virtue of the fact that the electronic drive means is configured to control the hydraulic valve as a function of the operating hydraulic fluid temperature or viscosity and / or the operating pressure in the hydraulic fluid supply such that during an engine operating phase the one or immediately successive revolutions of the camshaft comprises, only a predetermined partial volume of the pressure chamber is filled with hydraulic fluid and the hydraulic valve is at least during each entire elevation phase of the cam in the closed position.

In other words, it is inventively provided that for a certain number of working cycles of the internal combustion engine, only a partial volume the pressure space is filled with hydraulic fluid and this partial volume remains unchanged at least during the cam lobe phase (apart from unavoidable leaks). A controlled by targeted control of the hydraulic valve Absteuerung of hydraulic fluid from the pressure chamber thus takes place in any phase of the cam lobe.

The defined presetting of the partial volume of hydraulic medium located in the pressure chamber is effected by a targeted loss of stroke of the hydraulic linkage during one or more revolutions of the camshaft before the engine operating phase and causes during the engine operating phase that the gas exchange valve opens later with respect to the cam lobe and closes earlier with correspondingly reduced lift height. In the case of highly viscous hydraulic fluid of the hydraulic valve brake between two camshaft revolutions remains a longer time interval in which the gas exchange valve can safely reach the valve seat. The amount of sub-volume is to be adjusted so that the gas exchange valve does not fall below a minimum lifting height and does not exceed a maximum closing time in view of a successful change of charge. This also applies to the case that the hydraulic valve is opened in the phases between the cam lobes and thus allows a refilling of the pressure chamber with hydraulic fluid from the pressure relief chamber.

The applicant's experiments preceding the invention have shown the following: a cycle-faithful, ie at each camshaft rotation Absteuern and refilling the pressure chamber with the aim to significantly reduce the stroke and thus the opening time of the gas exchange valve, on the one hand fail because the high viscosity the hydraulic means prevents a sufficiently fast and complete refilling of the pressure chamber with hydraulic fluid from the pressure relief chamber. This is especially true when the pressure in the hydraulic fluid supply of the internal combustion engine is (still) insufficient. On the other hand, the hydraulic valve has the property of being unable to close at low temperatures against the then high-viscosity hydraulic fluid flow through the control channel. The latter thus prevents the hydraulic valve from closing only during the engaged cam elevation in order to generate a later opening relative to the cam elevation and accordingly earlier closing of the gas exchange valve.

From the above explanations it is clear that the invention in particular favors a successful start and initial warm-up phase of the cold engine at very low ambient temperatures (typically at -30 ° C ambient and engine temperature to ensure a successful startup), especially under such conditions the pressure build-up in the hydraulic fluid supply of the internal combustion engine is particularly delayed. As mentioned above, insufficient pressure in the hydraulic fluid supply of the internal combustion engine can prevent a complete refilling of the pressure chamber to the extent that a controlled modification or reduction of Gaswechselventilhubs by cyclically true Absteuern hydraulic fluid from the pressure chamber is not possible during the cam lobe. In particular, the invention also allows for cold, i. hochviskosem hydraulic means with respect to the cam lift later inlet opening. As explained above, this is not possible in the case of conventional actuation of the hydraulic valve, since the hydraulic valve does not close or does not close sufficiently fast against high-viscosity hydraulic fluid flow in the control passage.

However, the invention is not limited only to its application with cold hydraulic fluid, but can also be used at other operating temperatures of the internal combustion engine.

For the purposes of the invention can be dispensed with a cycle-faithful refilling of the pressure chamber between the cam lobe phases, if the refilling only serves to compensate for unavoidable gap leakage from the pressure chamber and the leaks in the case of very high hydraulic fluid viscosity are negligible. In that regard, during the aforementioned machine operating phase and a control of the hydraulic valve be provided in such a way that the hydraulic valve remains closed not only during the engaged cam lift phase, but during the entire engine operating phase.

In addition, it may be provided that the number of revolutions of the camshaft during the engine operating phase in dependence on the determined at the time of starting the engine hydraulic fluid temperature is predetermined by the electronic drive means. Parameter for this predetermined number of revolutions is substantially the temperature of the hydraulic fluid during the starting process, wherein the parameter-dependent number of revolutions can be determined by test bench tests and stored in a map of the electronic control means as a control variable. As an alternative to the predetermined duration of the engine operating phase, it may also be provided to set this duration as a function of current operating parameters, in particular the hydraulic fluid temperature.

Further, said engine operating phase may be passed once or, if necessary, several times consecutively. For the subsequent "normal operation" of the electro-hydraulic valve control with cycle-faithful control and refilling of the pressure chamber, the electronic control means should be configured to control the hydraulic valve such that during one of the engine operating phase following another engine operating phase, which includes immediately successive revolutions of the camshaft, the pressure space before each elevation phase of the cam is at least almost completely refilled with hydraulic fluid.

• Öffnen des Hydraulikventils zu einem Zeitpunkt innerhalb der Erhebungsphase des Nockens und Schließen des Hydraulikventils zu einem Zeitpunkt derart, dass lediglich ein vorbestimmtes Teilvolumen des Druckraums mit Hydraulikmittel befüllt ist, und
• Halten des Hydraulikventils in der geschlossenen Stellung während einer Maschinenbetriebsphase, die eine oder unmittelbar aufeinanderfolgende Umdrehungen der Nockenwelle umfasst, wobei sich das Hydraulikventil zumindest während jeder gesamten Erhebungsphase des Nockens in der geschlossenen Stellung befindet.

The object on which the invention is based is achieved on the procedural side by the fact that the electronic control device is configured to control the hydraulic valve as a function of the operating hydraulic fluid temperature or viscosity and / or the operating pressure in the hydraulic fluid supply, wherein the following method steps are provided, which follow one another in time:

• Opening the hydraulic valve at a time within the elevation phase of the cam and closing the hydraulic valve at a time such that only a predetermined partial volume of the pressure space is filled with hydraulic fluid, and
• Maintaining the hydraulic valve in the closed position during an engine operating phase including one or immediately consecutive revolutions of the camshaft, wherein the hydraulic valve is in the closed position at least during each entire lobe lift phase.

Brief description of the drawings

Figur 1

eine zeitliche Sequenz von Erhebungen des Nockens und des Gaswechselventils mit zugehörigen Stromverläufen am Hydraulikventil;

Figur 2

eine zeitliche Sequenz entsprechend Figur 1, wobei sich das Hydraulikventil während der gesamten Maschinenbetriebsphase in der geschlossenen Stellung befindet;

Figur 3

die Erhebung des Nockens und des Gaswechselventils während der Maschinenbetriebsphase in vergrößerter Darstellung und

Figur 4

eine Prinzipdarstellung der elektrohydraulischen Ventilsteuerung.

Further features of the invention will become apparent from the following description and from the drawings. Show it:

FIG. 1

a temporal sequence of elevations of the cam and the gas exchange valve with associated flow paths on the hydraulic valve;

FIG. 2

a temporal sequence accordingly FIG. 1 wherein the hydraulic valve is in the closed position throughout the engine operating phase;

FIG. 3

the survey of the cam and the gas exchange valve during the engine operating phase in an enlarged view and

FIG. 4

a schematic diagram of the electro-hydraulic valve control.

Detailed description of the drawings

The starting point of the description is the in FIG. 4 illustrated principle representation of a known electro-hydraulic valve control 1. The valve control 1 is used for variable-stroke drive in the closing direction by a valve spring 2 kraftbeaufschlagten gas exchange valve 3 of an internal combustion engine 4 and comprises as essential components a cam 5 of a camshaft 6, a cam 5 here by means of a tappet 7 driven first hydraulic piston 8, a gas exchange valve 3 in the opening direction driving second hydraulic piston 9, one between the first hydraulic piston 8 and the second hydraulic piston. 9 extending pressure chamber 10 with variable volume and a pressure relief chamber 11 which is connected to the pressure chamber 10 via a control channel 12 and includes a spring-loaded pressure accumulator 13. The arranged in the drive sense between the camshaft 6 and the gas exchange valve 3 hydraulic system is connected to a hydraulic fluid supply 14 of the internal combustion engine, here the lubricant circuit.

In the control channel 12, an electrically controlled hydraulic valve 15 is arranged in the design of a 2/2-way switching valve, which allows in its normally open position a hydraulic fluid flow through the control channel 12 and locks in its energized closed position. The electrical control of the hydraulic valve 15 as a function of operating parameters of the internal combustion engine 4 via an electronic control means 16 as an integral part of the engine control unit.

The known operation of the valve control 1 can be summarized to the effect that the hydraulic medium in the pressure chamber 10 acts as a hydraulic linkage, wherein the predetermined by the cam 5 survey is transmitted with closed hydraulic valve 15 to the gas exchange valve 3 and with open hydraulic valve 15 partially or completely is diverted into the pressure relief chamber 11. The hydraulic decoupling of the cam lobe and the Gaswechselventilhubs requires a hydraulic valve brake 17, which throttles back from the second hydraulic piston 9 hydraulic fluid and so the closing gas exchange valve 3 decelerates to a mechanically and acoustically acceptable Aufsetzgeschwindigkeit the valve seat 18.

In the Figures 1 and 2 is shown in a temporal sequence, such as the normally open hydraulic valve 15 is controlled during the starting process of the internal combustion engine 4 at an ambient and engine temperature well below 0 ° C at correspondingly highly viscous hydraulic fluid and which strokes 19 set at the gas exchange valve 3 relative to the cam lobe 20. In the diagrams of the current profile 21 at the hydraulic valve 15 are shown below and the hub 19 of the gas exchange valve 3 and the cam lobe 20 above.

FIG. 1 In the course of the first cam elevation 20, the energized hydraulic valve 15 is de-energized, so that when the control channel 12 is open, a part of the hydraulic medium in the pressure chamber 10 is displaced into the pressure relief chamber 11 and accordingly the cam elevation 20 is only partially transmitted to the gas exchange valve 3. The times at which the energization 21 of the hydraulic valve 15 is turned off and then turned back on, and the corresponding time interval in which the hydraulic valve 15 is opened and allows refilling of the pressure chamber 10, are such that at the beginning of the second cam lobe only one predetermined partial volume of the pressure chamber 10 is filled with hydraulic fluid. This leads, in conjunction with a suitable control of the hydraulic valve 15, that in the subsequent engine operating phase of the cam elevation 20 is only partially transferred to the gas exchange valve 3, and is clearly visible at the late opening and early closing time and the smaller maximum stroke 19 of the gas exchange valve The duration of the engine operating phase comprises the revolutions 2 to n of the camshaft 6. The actuation of the hydraulic valve 15 takes place in such a way that on the one hand, the hydraulic valve 15 is energized during each entire cam lobe phase 20 and consequently continuously remains closed. On the other hand, the time intervals between the cam elevations 20, in which the hydraulic valve 15 is not energized and consequently open, are dimensioned such that, despite possible refilling of the pressure chamber 10, only a partial volume with a predetermined maximum amount of hydraulic fluid is contained therein. As explained above, the respective subsequent Gaswechselventilhub 19 moves in the predetermined Limits of the minimum required lifting height h-min and the maximum allowable closing time α-max, as in FIG. 3 is shown enlarged.

The predetermined by the electronic drive means 16 number of revolutions of the camshaft 6 during the engine operating phase is dependent on the temperature of the hydraulic fluid during the starting process of the internal combustion engine 4. In the case of the examined by the applicant test rig hardware were at a hydraulic fluid temperature of -20 ° C 40 revolutions and from -30 ° C determined 120 rotations as optimal.

Upon completion of the initial warm-up phase of the engine 4, i. After the engine operating phase with the cam lobes 2 to n, the hydraulic valve 15 is energized between the n-th and n + 1-th cam lobe 20 so that the pressure chamber 10 can be completely refilled with hydraulic fluid. The electronic drive means 16 is configured so that this also applies to all further revolutions of the camshaft 6 during the subsequent further engine operating phase, which begins with the n + 1 th cam lobe 20 and in which the hydraulic valve 15 is closed and opened during the cam lift phase 20 is to produce the stroke variability on the gas exchange valve 3 in a known manner.

FIG. 2 : the essential difference from the sequence according to FIG. 1 is in the control of the hydraulic valve 15 during the engine operating phase with the revolutions 2 to n of the camshaft 6. In this case, the possibility of a cycle-faithful partial refilling of the pressure chamber 10 between the cam lift phases 20 is omitted by the hydraulic valve 15 is energized during the entire engine operating phase ( Current curve 21 at revolutions 2 to n of the camshaft 6) and thus permanently closed. This is useful when refilling the pressure chamber 10 merely serves to compensate for unavoidable gap leakage from the pressure chamber 10 and the leaks in the case of very high hydraulic fluid viscosity are negligibly small.

List of reference numbers

1

valve control

2

valve spring

3

Gas exchange valve

4

Internal combustion engine

5

cam

6

camshaft

7

tappets

8th

first hydraulic piston

9

second hydraulic piston

10

pressure chamber

11

Pressure relief chamber

12

control channel

13

accumulator

14

Hydraulic medium supply

15

hydraulic valve

16

electronic drive means

17

hydraulic valve brake

18

valve seat

19

Gaswechselventilhub

20

cam lobe

21

Current flow at the hydraulic valve

Claims (8)

1. Internal combustion engine having electrohydraulic valve control (1) for the variable-stroke drive of a gas exchange valve (3) loaded with spring force in the closing direction, comprising a camshaft (6) and a hydraulic system which is arranged in the driving direction between the camshaft (6) and the gas exchange valve (3) and which is connected to a hydraulic medium supply (14) of the internal combustion engine (4) and has the following:

   - a first hydraulic piston (8), driven by a cam (5) of the camshaft (6), and a second hydraulic piston (9), driving the gas exchange valve (3) in the opening direction,

   - a pressure space (10), delimited by the first hydraulic piston (8) and the second hydraulic piston (9) and having a variable volume, and a control duct (12) connecting the pressure space (10) to a pressure relief space (11),

   - an electrically activated hydraulic valve (15) which is arranged in the control duct (12) and which permits a hydraulic medium flow through the control duct (12) in the open position of the hydraulic valve (15) and shuts off the said hydraulic medium flow in the closed position of the hydraulic valve (15),

   and comprising an electronic activation means (16) for activating the hydraulic valve (15) as a function of operating parameters of the internal combustion engine (4), characterize in that the electronic activation means (16) is configured to activate the hydraulic valve (15) as a function of the operational hydraulic medium temperature or viscosity and/or of the operational pressure in the hydraulic medium supply (14), in such a way that, during an engine operating phase which comprises one revolution or immediately succeeding revolutions of the camshaft (6), only a predetermined part-volume of the pressure space (10) is filled with hydraulic medium and, at least during each entire elevation phase (20) of the cam (5), the hydraulic valve (15) is in the closed position.
2. Internal combustion engine according to Claim 1, characterised in that the hydraulic valve (15) is in the closed position during the entire engine operating phase.
3. Internal combustion engine according to Claim 1, characterized in that the machine operating phase comprises a starting operation of the internal combustion engine (4).
4. Internal combustion engine according to Claim 3, characterized in that the internal combustion engine (4) has ambient temperature at the time of the starting operation.
5. Internal combustion engine according to Claim 3, characterize in that the number of revolutions of the camshaft (6) during the engine operating phase is predetermined by the electronic activation means (16) as a function of the hydraulic medium temperature ascertained at the time of the starting operation of the internal combustion engine (4).
6. Internal combustion engine according to Claim 1, characterized in that the electronic activation means (16) is configured to activate the hydraulic valve (15) in such a way that, during a further engine operating phase which follows the engine operating phase and which comprises immediately succeeding revolutions of the camshaft (6), the pressure space (10) is refilled at least almost completely with hydraulic medium before each elevation phase (20) of the cam (5).
7. Method for operating an internal combustion engine having electrohydraulic valve control (1) for the variable-stroke drive of a gas exchange valve (3) loaded with spring force in the closing direction, comprising a camshaft (6) and a hydraulic system which is arranged in the driving direction between the camshaft (6) and the gas exchange valve (3) and which is connected to a hydraulic medium supply (14) of the internal combustion engine (4) and has the following:

   - a first hydraulic piston (8), driven by a cam (5) of the camshaft (6), and a second hydraulic piston (9), driving the gas exchange valve (3) in the opening direction,

   - a pressure space (10), delimited by the first hydraulic piston (8) and the second hydraulic piston (9) and having a variable volume, and a control duct (12) connecting the pressure space (10) to a pressure relief space (11),

   - an electrically activated hydraulic valve (15) which is arranged in the control duct (12) and which permits a hydraulic medium flow through the control duct (12) in the open position of the hydraulic valve (15) and shuts off the said hydraulic medium flow in the closed position of the hydraulic valve (15),
   and comprising an electronic activation means (16) for activating the hydraulic valve (15) as a function of operating parameters of the internal combustion engine (4), characterized in that the electronic activation means (16) is configured to activate the hydraulic valve (15) as a function of the operational hydraulic medium temperature or viscosity and/or of the operational pressure in the hydraulic medium supply (14), the following method steps being provided, which succeed one another in time:

   - opening of the hydraulic valve (15) at a time point within the elevation phase (20) of the cam (5) and closing of the hydraulic valve (15) at a time point such that only a predetermined part-volume of the pressure space (10) is filled with hydraulic medium, and

   - holding of the hydraulic valve (15) in the closed position during an engine operating phase which comprises one revolution or immediately succeeding revolutions of the camshaft (6), the hydraulic valve (15) being in the closed position at least during each entire elevation phase (20) of the cam (5).
8. Method according to Claim 7, characterized in that, during a further engine operating phase which follows the engine operating phase and which comprises immediately succeeding revolutions of the camshaft (6), the hydraulic valve (15) is activated such that the pressure space (10) is refilled at least almost completely with hydraulic medium before each elevation phase (20) of the cam (5).

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