EP1430201B1 - Method for operating an electrohydraulic valve control system of an internal combustion engine, computer program and control and regulating device for operating an internal combustion engine - Google Patents

Abstract

The invention relates to an electrohydraulic valve control system (10) of an internal combustion engine, comprising at least one actuator (24) which acts on a gas exchange valve (38). Said actuator, in turn, comprises at least one working chamber (30) which is connected to a high-pressure hydraulic accumulator (16) for actuating the actuator (24) in such a way that it moves from a first position to a second position, and which is separated from a low-pressure return line (56). In order to actuate the actuator (24) in such a way that it moves back from the second position into the first position, the working chamber (30) is connected to the low-pressure return line (56) and is separated from the high-pressure hydraulic accumulator (16). In order to easily maintain the pressure constant or to cause a pressure drop in the high-pressure hydraulic accumulator (16), the working chamber (30) is simultaneously connected to the high-pressure hydraulic accumulator (16) and to the low-pressure return line (56).

Description

State of the art

The invention relates firstly to a method for operating an electrohydraulic valve control of an internal combustion engine, having at least one actuator operating on a gas exchange valve having at least one working space, which is connected to actuate the actuator from a first position to a second position with a high-pressure hydraulic accumulator and a low pressure -Rücklauf separated and which is connected to an actuation of the actuator from the second position to the first position back to the low-pressure return and separated from the high-pressure hydraulic accumulator.

Such a method is known from the market (see DE-A-198 26047). Electrohydraulic valve controls of internal combustion engines allow the control of the gas exchange valves regardless of the position of the crankshaft or the camshaft. As a result, including gasoline savings and improvements in the emission characteristics of an internal combustion engine are possible.

In an electrohydraulic valve control known from the market, the shaft of the gas exchange valve is connected to a hydraulic actuator. This has two working spaces on both sides of the piston end faces, which are different in size. The small face is constantly subjected to high pressure from a high-pressure hydraulic accumulator, which in turn is fed by a hydraulic pump. The large end face of the piston is optionally also connected to the high-pressure hydraulic accumulator or to a low-pressure return line. Depending on results in a force resultant, which opens or closes the gas exchange valve.

In the known method, the amount of hydraulic fluid flowing from the high-pressure hydraulic accumulator via the actuator to the low-pressure return and used to actuate the actuator can vary widely. The amount of fluid delivered by the hydraulic pump into the high-pressure hydraulic accumulator can also vary, for example when the hydraulic pump is driven directly by the internal combustion engine and then there is a speed-dependent delivery rate of the hydraulic pump.

In order nevertheless to be able to achieve a relatively constant pressure associated with the operating point in the high-pressure hydraulic accumulator, an overpressure or pressure regulating valve has been provided which, if a certain pressure is exceeded, discharges hydraulic fluid from the high-pressure hydraulic accumulator. Also, a regulation of the flow rate through the hydraulic pump is known. Furthermore, dynamic pressure peaks in the high-pressure hydraulic accumulator can be passively smoothed, for example, by a large volume of the high-pressure hydraulic accumulator.

The said measures, with which the pressure in the high-pressure hydraulic accumulator can be kept constant, however, are relatively complex and react in part only sluggishly to pressure changes in the high-pressure hydraulic accumulator. Also, a large-scale high-pressure hydraulic accumulator for smoothing pressure peaks is disadvantageous, since usually in the engine compartment, for example. Of motor vehicles, only little space is available. The same disadvantage is also due to a pressure control valve.

The present invention therefore has the object, a method of the type mentioned in such a way that the pressure in the high pressure hydraulic accumulator can be kept constant in a simple manner.

This object is achieved in a method of the type mentioned in that a pressure maintenance or a pressure reduction in the high-pressure hydraulic accumulator is effected in that the working space is connected simultaneously with the high-pressure hydraulic accumulator and the low-pressure return.

Advantages of the invention

The measure according to the invention allows a direct connection from the high-pressure hydraulic accumulator to the low-pressure return without additional components such. B. a pressure control valve, are necessary. To make this possible, an operating state is expressly permitted in which the working space is simultaneously connected to the high-pressure hydraulic accumulator and the low-pressure return of the electro-hydraulic valve control. If, for example, determined by a sensor, the need arises to remove hydraulic fluid from the high-pressure hydraulic accumulator to the pressure in this To keep constant, this can be done according to the invention in a simple manner via the working space for low-pressure return.

Since the usually used switching valves have a short reaction time and a highly dynamic switching behavior, even short-term fluctuations in the pressure in the high-pressure hydraulic accumulator can be smoothed. On the one hand, therefore, a pressure regulating valve can be dispensed with by the method according to the invention. Furthermore, the high-pressure hydraulic accumulator can build smaller. As a result, costs are saved in the production of the electro-hydraulic valve control and the electro-hydraulic valve control requires less space.

Advantageous developments of the invention are specified in subclaims.

In a first development, it is said that for maintaining pressure or reducing pressure in the high-pressure hydraulic accumulator, the working chamber of an actuator is connected simultaneously to the high-pressure hydraulic accumulator and the low-pressure return, whose associated gas exchange valve is currently closed. This development of the method according to the invention is particularly useful when the actuation of the actuator and an opening of the gas exchange valve by applying the full pressure. In the closed state of rest of the gas exchange valve is thus in the working space of the actuator usually at a pressure which is less than the full high pressure of the high-pressure hydraulic accumulator.

When connecting the high-pressure hydraulic accumulator via the working space of the actuator with the low-pressure return line However, there is a pressure in the working space of the actuator, which is below the full pressure in the high-pressure hydraulic accumulator. The closed rest position of the gas exchange valve is thus not affected by this connection of the working space simultaneously with the high pressure hydraulic accumulator and the low pressure return.

It is particularly preferred if the working pressure of an actuator is simultaneously connected to the high-pressure hydraulic accumulator and the low-pressure return to maintain pressure or pressure reduction in the high-pressure hydraulic accumulator whose associated gas exchange valve just can not open due to a high internal cylinder pressure. As a result, an unintentional opening of the gas exchange valve is effectively prevented in response to pressure fluctuations in the working space "sensitive" actuator.

It is also possible that the working space of an actuator, which is to be moved from the first position to the second position, is connected to the high-pressure hydraulic accumulator immediately before the separation from the low-pressure return, and / or the working space of an actuator, the of the second position is to be moved to the first position, is connected immediately before the separation of the high pressure hydraulic accumulator with the low pressure return.

In this case, an already intended actuation of the actuator is used to dissipate hydraulic fluid from the high-pressure hydraulic accumulator. This is made possible by a shift of the time at which the connection of the working space with the low-pressure return or the high-pressure hydraulic accumulator takes place. Thus, there is an overlap of the periods in which the Working space is connected to the low-pressure return and the high-pressure hydraulic accumulator. This makes it possible to integrate the pressure maintenance or the pressure reduction in the high pressure hydraulic accumulator in the normal operation of an actuator.

Particularly preferred is that development of the method according to the invention, in which the working space of an actuator is then temporarily connected simultaneously to the high-pressure hydraulic accumulator and the low-pressure return when the internal combustion engine is operated at low speed. This development takes into account the fact that at low speed generally a lower pressure in the high-pressure hydraulic accumulator is advantageous. Since such a targeted pressure reduction in the high-pressure hydraulic accumulator was previously not possible, instead, the drive strategy of the actuator had to be changed at low speeds. This can be omitted in the method further developed according to the invention.

In another development, it is proposed that the pressure maintenance or pressure reduction is combined by a simultaneous connection of the working space of an actuator with the low-pressure return and the high-pressure hydraulic accumulator with a control or regulation of the flow through a hydraulic pump. While very rapid and highly dynamic influence on the pressure in the high-pressure hydraulic accumulator can be taken by the said connection of the working space, the control or regulation of the flow through the hydraulic pump allows a long-term and quantitatively significant adjustment of the pressure in the high-pressure hydraulic accumulator.

The inventive method is particularly preferred when the actuator has two working spaces, which are separated by differently sized and oppositely acting pressure surfaces on a piston, and the one working space is constantly subjected to high pressure and the other working space with the high-pressure hydraulic accumulator and the low-pressure return can be connected. With such actuators very short switching times can be realized, which facilitates the implementation of the method according to the invention.

In order to avoid cavitation during the outflow of hydraulic fluid from the working space to the low-pressure return line, in the method according to the invention, the hydraulic fluid from the working space can also flow into a low-pressure hydraulic accumulator. Thus, the pressure difference is reduced in the outflow of the hydraulic fluid, which counteracts the occurrence of cavitation.

The invention also relates to a computer program programmed for use in a method according to any one of the preceding claims

The invention further relates to a control apparatus for operating an internal combustion engine, which is suitable for use in the above method.

drawing

Figur 1

eine schematische Darstellung einer elektrohydraulischen Ventilsteuerung einer Brennkraftmaschine;

Figur 2

ein Diagramm, in dem der Druckverlauf in einem Hochdruck-Hydraulikspeicher von Fig. 1 über der Zeit dargestellt ist; und

Figur 3

ein Diagramm, in dem der Druck im Hochdruck-Hydraulikspeicher von Fig. 1 über einer Drehzahl der Brennkraftmaschine dargestellt ist.

Hereinafter, a particularly preferred embodiment of the invention with reference to the accompanying drawings will be explained in detail. In the drawing show:

FIG. 1

a schematic representation of an electro-hydraulic valve control of an internal combustion engine;

FIG. 2

a diagram in which the pressure in a High-pressure hydraulic accumulator of Figure 1 is shown over time. and

FIG. 3

a diagram in which the pressure in the high-pressure hydraulic accumulator of Fig. 1 is shown over a rotational speed of the internal combustion engine.

Description of the embodiment

In FIG. 1, an electrohydraulic valve control as a whole carries the reference numeral 10. It initially comprises a reservoir for hydraulic fluid, which in the present case bears the reference numeral 12 and which may be the oil sump of the internal combustion engine. From the hydraulic reservoir 12, the hydraulic fluid is conveyed from a controllable high-pressure hydraulic pump 14 into a high-pressure hydraulic accumulator 16. A hydraulic line 18 leads from the high-pressure hydraulic accumulator 16 via a pressure regulating valve 20 to a solenoid valve 22.

The hydraulic line 18 leads from the solenoid valve 22 on to an actuator 24. This is a hydraulic cylinder with a double-acting piston 26. The piston 26 is guided in a housing 28. In Fig. 1 above the piston 26, a first working space 30 is formed between this and the housing 28. This is connected to the solenoid valve 22. In Fig. 1 below the piston 26, a second working space 32 is formed between this and the housing 28. This is connected via a branch line 33 with that portion of the hydraulic line 18, which is located between the high-pressure hydraulic accumulator 16 and the solenoid valve 22.

The upper end surface 34 of the piston 26 in FIG. 1 is overall larger than the lower end surface 36 of the piston 26 which delimits the second working space 32. The piston 26 is therefore a so-called "differential piston". The piston 26 is connected to a gas exchange valve 38. This comprises a valve rod 40 and a valve element 42. Through the valve element 42, an opening (without reference numeral) of a combustion chamber 44 can be closed or opened. The combustion chamber 44 is present in an engine block 46 of an internal combustion engine (without reference number).

From the first working space 30 of the actuator 24, a hydraulic line 48 via a second solenoid valve 50 leads to a low-pressure hydraulic accumulator 52. This is in turn connected via a pressure control valve 54 with a low-pressure return 56, which eventually returns to the hydraulic reservoir 12. From the first working chamber 30 of the actuator 24, a hydraulic line 58 leads via a pressure regulating valve 60 back to the high-pressure hydraulic accumulator 16.

The two solenoid valves 22 and 50 are actuated by magnetic actuators 62 and 64 and are each pressed by a compression spring 66 and 68 in their rest position. The first solenoid valve 22 is in its rest position 70, in which the magnetic actuator 62 is not energized, closed, whereas it is open in the actuated switching position 72. The second solenoid valve 50, however, is open in its closed position 74 and closed in the actuated switching position in which the magnetic plate 64 is energized. This switch position bears the reference numeral 76.

The electro-hydraulic valve control 10 also includes a control and regulating device 78. This is the output side connected to the magnetic actuators 62 and 64. Furthermore, it can also control the hydraulic pump 14. On the input side, the control and regulating device 78 is connected to a pressure sensor 80, which detects the pressure in the high-pressure hydraulic accumulator 16. Further, the control and regulating device 78 is connected to a speed sensor for the crankshaft of the internal combustion engine. This speed sensor bears the reference number 82.

The electrohydraulic valve control 10 is operated as follows (the method described hereafter is stored as a computer program on a ferrite RAM (not shown) in the control and regulation unit 78). To open the gas exchange valve 38, the piston 26 in Fig. 1 after move down. This is achieved in that from the rest position 74, the second solenoid valve 50 is energized and thus closed. The connection between the first working space 30 and the low-pressure hydraulic accumulator 52 is thus interrupted.

Subsequently, the magnetic controller 62 of the first solenoid valve 22 is energized by the control and regulation unit 78, then that this solenoid valve 22 moves from its closed rest position 70 into the open switching position 72. Thus, the first working space 30 is connected to the high-pressure hydraulic accumulator 16. In the first working space 30 thus essentially the prevailing in the high-pressure hydraulic accumulator 16 hydraulic pressure.

Since the lower end face 36 is smaller than the upper end face 34 of the piston 26, but now in both working spaces 30 and 32 of the actuator 24, the same pressure prevails, namely substantially the pressure prevailing in the high-pressure hydraulic accumulator 16, results in a resultant force in Fig. 1 down, so that the piston 26 moves in this direction. As a result, the valve rod 40 and the valve element 42 in Fig. 1 is moved down, the gas exchange valve 38 is thus opened.

If the gas exchange valve 38 is closed again, first the first solenoid valve 22 is de-energized by the control and regulating device 78 so that it is pressed by the open switch position 72 by the compression spring 66 in the closed switching position 70. The connection between the high pressure hydraulic accumulator 16 and the first working space 30 is thus interrupted again.

Then, the second solenoid valve 50 is de-energized by the control and regulating device 78, so that this moves due to the compression spring 68 from the closed switching position 76 in the open rest position 74. The first working space 30 is again connected to the low-pressure hydraulic accumulator 52. Thus, the pressure in the first working chamber 30 decreases until a force resulting results, which moves the piston 26 upwards again. As a result, the gas exchange valve 38 closes.

If the control and regulating device 78 is informed via the pressure sensor 80 that the pressure in the high-pressure hydraulic accumulator 16 is higher than a setpoint pressure, the first solenoid valve 22 is controlled by the control and regulating device 78 into its open switching position 72, whereas the second solenoid valve 50 remains in its open rest position 74. It is assumed that the internal combustion engine is in an operating state in which the gas exchange valve 38, which is connected to the actuator 24, should remain closed. By said operation of the first solenoid valve 22 is now a direct connection from the high pressure hydraulic accumulator 16 via the first solenoid valve 22, the first working space 30 and the second solenoid valve 50 to the low pressure hydraulic accumulator 52 before.

By an appropriate design of the hydraulic lines 18 and 48 can be achieved that in this state, the pressure in the first working chamber 30 is never so high that an undesirable movement of the piston 26 is induced. Due to the direct connection from the high-pressure hydraulic accumulator 16 to the low-pressure hydraulic accumulator 52, hydraulic fluid can flow from the high-pressure hydraulic accumulator 16 directly to the low-pressure hydraulic accumulator 52, without this leading to an actuation of the actuator 24. Thus, the pressure in the high-pressure hydraulic accumulator 16 can be selectively reduced or kept constant.

If it is to be reliably prevented that the gas exchange valve 38 can open during this state, the direct connection between high-pressure hydraulic accumulator 16 and low-pressure hydraulic accumulator 52 is preferably established when, due to a high pressure prevailing in the combustion chamber 44, the valve element 42 is pressed into its closed position becomes.

The outflow of hydraulic fluid from the high-pressure hydraulic accumulator 16 to the low-pressure hydraulic accumulator 52 is simply terminated by the control and regulating device 78, the first solenoid valve 22 is again de-energized, so that it returns to its closed rest position 70. In the first working space 30, the pressure prevailing in the low-pressure hydraulic accumulator 52 then sets in again.

However, the electrohydraulic valve control 10 can still be operated in another way to keep the pressure in the high-pressure hydraulic accumulator 16 constant or lower:

Thus, the connection of the high-pressure hydraulic accumulator 16 with the low-pressure hydraulic accumulator 52 can be coupled to an actuation of the actuator 24. Upon actuation of the actuator 24 to the effect that the gas exchange valve 38 opens, for example. Immediately before the energization of the magnetic actuator 64 of the second solenoid valve 50, whereby this passes from its open rest position 74 to the closed switching position 76, already the solenoid valve 22 of its closed Resting position 70 are controlled in the actuated and open switching position 72.

Thus, just before the second solenoid valve 50 is closed, a direct connection between the high pressure hydraulic accumulator 16 and the low pressure hydraulic accumulator 52 through which hydraulic fluid can flow out of the high pressure hydraulic accumulator 16 occurs. In the same way, when the gas exchange valve 38 is to be closed again, immediately before the Stromlos circuit of the magnetic actuator 62 of the first solenoid valve 22, whereby this returns from its open switching position 72 back to the closed rest position 70, already the second solenoid valve 50 are brought from its closed switching position 76 in the open rest position 74.

This also results in a short-term direct connection from the high-pressure hydraulic accumulator 16 to the low-pressure hydraulic accumulator 52 and further to the low-pressure return 56, flows through the hydraulic fluid from the high-pressure hydraulic accumulator 16 and thus the pressure can be kept constant or lowered in this.

By such short-term operations of the valves and such a short-term direct connection between the high-pressure hydraulic accumulator 16 to the low-pressure return line 56, the pressure in the high-pressure hydraulic accumulator 16 can be kept constant, as shown in FIG. The amount of fluid to be discharged is controlled by the duration of the direct connection. In this figure, the pressure without a corresponding actuation of the solenoid valves 22 and 50 is shown in dashed lines, the pressure curve, which can be made by a corresponding actuation of the solenoid valves 22 and 50, shown in solid line.

When the engine is operated at low speed, this is detected by the tachometer 82 and delivered a corresponding signal to the control and regulation unit 78. This can then control the solenoid valves 22 and 50 so that the pressure in the high-pressure hydraulic accumulator 16 is lowered. Typically, the operating pressure is lowered from the usual 200 bar to about 50 bar. If the speed increases again, a direct fluid connection between the high-pressure hydraulic accumulator 16 and the low-pressure return is avoided, so that the pressure due to the ongoing promotion by the high-pressure hydraulic pump 14 in the high-pressure hydraulic accumulator 16 again increases. The relationship between speed n of the engine and pressure P in the high-pressure hydraulic accumulator 16 is shown in FIG. The pressure setting in the high-pressure hydraulic accumulator 16 may possibly be assisted by a corresponding control of the high-pressure hydraulic pump 14.

Claims (10)

1. Method for operating an electrohydraulic valve control system (10) of an internal combustion engine, having at least one actuator (24) which acts on a gas exchange valve (38) and has at least one working space (30) which, to actuate the actuator (24) from a first position into a second position, is connected to a high-pressure hydraulic reservoir (16) and disconnected from a low-pressure return (56), and which, to actuate the actuator (24) from the second position into the first position, is connected back to the low-pressure return (56) and is disconnected from the high-pressure hydraulic reservoir (16), characterized in that the pressure is kept constant or lowered in the high-pressure hydraulic reservoir (16) by the working space (30) being simultaneously connected to the high-pressure hydraulic reservoir (16) and the low-pressure return (56).
2. Method according to Claim 1, characterized in that, to keep the pressure constant or to lower the pressure in the high-pressure hydraulic reservoir (16), the working space (30) of an actuator (24) is simultaneously connected to the high-pressure hydraulic reservoir (16) and the low-pressure return (56) whereof the associated gas exchange valve (38) is currently closed.
3. Method according to Claim 2, characterized in that, to keep the pressure constant or to lower the pressure in the high-pressure hydraulic reservoir (16), the working space (30) of an actuator (24) is simultaneously connected to the high-pressure hydraulic reservoir (16) and the low-pressure return (56) whereof the associated gas exchange valve (38) currently cannot open on account of a high pressure in the combustion chamber (44).
4. Method according to one of the preceding claims, characterized in that the working space (30) of an actuator (24) which is to be moved from the first position into the second position is connected to the high-pressure hydraulic reservoir (16) immediately before it is disconnected from the low-pressure return (56), and/or the working space (30) of an actuator (24) which is to be moved from the second position into the first position is connected to the low-pressure return (56) immediately before it is disconnected from the high-pressure hydraulic reservoir (16).
5. Method according to one of the preceding claims, characterized in that the working space (30) of an actuator (24) is then from time to time connected simultaneously to the high-pressure hydraulic reservoir (16) and the low-pressure return (56) when the internal combustion engine is operating at a low speed.
6. Method according to one of the preceding claims, characterized in that the delivery quantity is additionally controlled or regulated by the hydraulic pump (14).
7. Method according to one of the preceding claims, characterized in that the actuator (24) has two working spaces (30, 32), which are separated from one another by pressure surfaces (34, 36) of different sizes and acting in opposite directions at a piston (26), and one working space (32) is constantly exposed to high pressure while the other working space (30) can be connected to the high-pressure hydraulic reservoir (16) and the low-pressure return (56).
8. Method according to one of the preceding claims, characterized in that the hydraulic fluid flows out of the working space (30) into a low-pressure hydraulic reservoir (52).
9. Computer program, characterized in that it is programmed for use in a method according to one of the preceding claims.
10. Control and regulating device (78) for operating an internal combustion engine, characterized in that it is programmed for use in a method according to one of Claims 1 to 8.

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