EP1618291B1 - Method for operating a hydraulic actuator, especially a gas exchange valve of an internal combustion engine - Google Patents

Description

State of the art

The invention relates to a method for operating a hydraulic actuator, in particular for a gas exchange valve of an internal combustion engine, in which a movement of an actuating element of the actuator is effected in that a working space of the actuator by means of a valve device with a fluid reservoir, is stored in the hydraulic fluid under pressure, can be connected and disconnected from this, and in which the stroke of the actuating element of the actuator depends on a fluid volume present in the working space.

Such a method is for example from the DE 198 26 047 A1 known. This describes a device for controlling a gas exchange valve of an internal combustion engine and the corresponding operating method. In this case, hydraulic fluid is pumped by a high-pressure pump into a line system in which the hydraulic fluid is stored under very high pressure. A workroom of a Hydraulic cylinder whose piston is connected to a valve element of a gas exchange valve of an internal combustion engine is connected via a 2/2-way valve to the fluid reservoir. An outlet of the working space is also connected via a 2/2-way valve to a low pressure area. Depending on the valve position prevails in the working space of the hydraulic actuator, a high or low pressure, and a corresponding fluid volume is present in the working space, which influences the position of the piston.

The advantage of such a gas exchange valve is that it can be controlled independently of a position of a camshaft of the internal combustion engine. For cost reasons, a detection of the current piston position is dispensed with. This has the consequence that the positioning of the piston of the hydraulic actuator is not regulated, but can only be controlled.

The DE 42 18 320 A1 describes a method for testing a valve driven by a medium, in which variables are measured at different points in time during a switching process and from this function-specific quantities are derived and compared with one another. The DE 101 38 777 A1 describes a method for monitoring the operation of supply lines for operated with a pressurized medium units in which an actual pressure profile is compared with a desired pressure profile.

The present invention has the object, a method of the type mentioned in such a way that the actuator of the actuator can be positioned as precisely as possible.

This object is achieved in a method of the type mentioned in that for determining a current operating behavior of the actuator of the working space briefly connected to the fluid reservoir, detects the corresponding pressure drop in the fluid reservoir, and from the pressure drop using known geometric variables of the actuator, the corresponding stroke is determined, and at least one of opening period and stroke existing value pair is formed.

Advantages of the invention

The determined value pair can be compared, for example, with a value pair determined on a test bench or in a preceding process run. In this way, aging phenomena, changed environmental conditions, and so on, can be detected and taken into account in the control of the valve devices. The output of information is also possible if the current operating behavior of the actuator has changed in an improper manner. This increases the safety in the operation of the actuator, since countermeasures are made possible before the operation of the actuator can lead to damage.

Particularly advantageous embodiments of the method according to the invention are specified in subclaims.

In a first advantageous development, it is proposed that the pressure drop in the fluid reservoir be detected for different periods of time during which the working space of the actuator is connected to the fluid reservoir, and a current characteristic curve is formed from the determined value pairs. The actuator of the hydraulic actuator can be positioned very precisely in this case in normal operation, without complex control and costly installation of a sensor which detects the stroke of the actuator of the hydraulic actuator is required. The precise positioning of the control element is therefore basically possible without additional hardware and therefore inexpensive.

Particularly preferred is also that development of the method according to the invention, in which the actuating element from a known initial position in a known end position brought, detects the corresponding pressure drop in the fluid reservoir, and with the help of the detected pressure drop and the stroke between the initial position and end position, the determined at least one pair of values is normalized. This method eliminates measurement inaccuracies and further improves the precision of the characteristic of the hydraulic actuator. By additionally provided in this development process step, the actual process by which at least one pair of values is determined, so to speak calibrated.

The actuator can be brought into the initial or in the end position simply by the fact that the valve device is correspondingly long in one or the other position. Alternatively or additionally, the achievement of the initial and / or end position of the actuating element can also be detected by means of a knock sensor. This improves the precision of the standardization or calibration mentioned above.

It is also proposed that the at least one value pair be formed taking into account the modulus of elasticity of the hydraulic fluid and / or the elasticity of the fluid reservoir. This also leads to an even higher accuracy of the current characteristic of the hydraulic actuator. In addition, it may also be considered that the modulus of elasticity of the hydraulic fluid is temperature and pressure dependent. The elasticity of the fluid reservoir, ie of its walls, can also change depending on the temperature.

In a further embodiment of the method according to the invention is also stated that the temperature and / or the viscosity of the hydraulic fluid detected during the determination of the current operating behavior of the actuator and the at least one pair of values for a specific viscosity and / or a specific temperature of the hydraulic fluid is formed. In this way, therefore, a whole set of pairs of values or characteristics can be formed, wherein in each case a pair of values or a characteristic applies only for very specific operating or environmental conditions. This also ultimately leads to even better precision in the positioning of the actuating element of the hydraulic actuator.

It is also advantageous if the response time of the valve device is determined from the beginning of the pressure drop in the fluid reservoir. For the accuracy of the positioning of the actuator of the hydraulic actuator, in particular for the temporal accuracy, the response time, ie the time between the generation of the drive signal and the beginning of the pressure drop caused by the movement of the actuating element, is particularly important. In the method according to the invention, this response time can be ascertained, so to speak, "incidentally" and taken into account in the control of the valve device during normal operation of the hydraulic actuator.

It is particularly advantageous if, for determining the current operating behavior of the hydraulic actuator, the fluid reservoir is fluidically separated from a pressure accumulator and / or a high-pressure pump for supplying the fluid accumulator is switched off. Although the inventive method is basically also feasible when a pressure accumulator is connected to the fluid reservoir or promotes a high-pressure pump in the fluid reservoir; In these cases, however, a rather complex consideration of the change in shape of the pressure accumulator (for example by means of a displacement detection at the pressure accumulator) or the delivery rate of High pressure pump required. This can be dispensed with if, as proposed, the fluid reservoir is simply separated from the pressure accumulator or from the high-pressure pump. In addition, this improves the accuracy of the method according to the invention, since the volume of the fluid reservoir is reduced by this measure, which results in a corresponding control of the valve device at the same stroke of the actuating element of the hydraulic actuator to a larger pressure drop, which can be measured with higher accuracy ,

When the hydraulic actuator is used to actuate a gas exchange valve of an internal combustion engine, it is advantageous if the current operating behavior is determined after switching off the internal combustion engine or during a coasting operation of the internal combustion engine. In this case, the inventive method can be carried out without the normal operation of the internal combustion engine is impaired.

In principle, however, it always has to be taken into account that the actuation of the hydraulic actuator for determining the current characteristic curve occurs in such a way that the corresponding gas exchange valve does not collide with either a piston of the internal combustion engine or with another gas exchange valve. For example, during the overrun operation, therefore, a control of the hydraulic actuator is conceivable only in a Teilhubbereich. In a multi-cylinder internal combustion engine, it may therefore be possible that several shutdown phases are required in order to determine the current operating behavior of the actuators of all gas exchange valves.

Furthermore, it can be provided that, when the hydraulic actuator is at rest, the pressure in the fluid reservoir is detected and a message is output when there is an unacceptable pressure drop. This makes it possible to check the tightness or leakage of the hydraulic system or of the fluid reservoir which supplies the actuator. The user can thus recognize the availability of the proper operation of the hydraulic actuator and thus ultimately the gas exchange valve, and optionally automatically stops the operation of the internal combustion engine or limited to a safety area to prevent damage to the internal combustion engine due to an incorrectly working gas exchange valve. It is understood that monitoring of the pressure drop is facilitated when a high pressure pump, which supplies the fluid reservoir with hydraulic fluid, is turned off or completely disconnected from the fluid reservoir. The same applies to a pressure accumulator.

The invention also relates to a computer program which is programmed to carry out the above method and stored on a storage medium.

The subject matter of the present invention is also a control and / or regulating device for an internal combustion engine, which is programmed for use in a method of the above type.

The subject matter of the present invention is also an internal combustion engine, in particular for a motor vehicle, having a control and / or regulating device which is programmed for use in a method of the above type.

drawing

Hereinafter, particularly preferred embodiments of the present invention will be explained in more detail with reference to the accompanying drawings.

Figur 1

eine schematische Darstellung einer Brennkraftmaschine eines Kraftfahrzeugs mit Gaswechselventilen, welche jeweils von einem hydraulischen Aktor betätigt werden, der an ein Hydrauliksystem angeschlossen ist;

Figur 2

eine genauere Darstellung des Hydrauliksystems von Figur 1;

Figur 3

ein Flussdiagramm, welches ein Verfahren zum Betreiben des hydraulischen Aktors von Figur 1 zeigt;

Figur 4

eine Darstellung ähnlich Figur 2 eines alternativen Ausführungsbeispiels eines hydraulischen Systems; und

Figur 5

ein Flussdiagramm ähnlich Figur 3 eines Verfahrens zum Betreiben des hydraulischen Aktors von Figur 1 mit dem hydraulischen System von Figur 4.

In the drawing show:

FIG. 1

a schematic representation of an internal combustion engine of a motor vehicle with gas exchange valves, which are each actuated by a hydraulic actuator which is connected to a hydraulic system;

FIG. 2

a more detailed representation of the hydraulic system of FIG. 1 ;

FIG. 3

a flowchart illustrating a method for operating the hydraulic actuator of FIG. 1 shows;

FIG. 4

a representation similar FIG. 2 an alternative embodiment of a hydraulic system; and

FIG. 5

a flow chart similar FIG. 3 a method for operating the hydraulic actuator of FIG. 1 with the hydraulic system of FIG. 4 ,

Description of the embodiments

In FIG. 1 an internal combustion engine carries the overall reference numeral 10. It is used to drive a Motor vehicle 12, which in FIG. 1 only symbolically represented by a dashed line. The internal combustion engine 10 is a multi-cylinder reciprocating internal combustion engine. For clarity, in FIG. 1 however, only the essential elements of a single cylinder are shown.

The in FIG. 1 The cylinder shown comprises a combustion chamber 14 which is delimited inter alia by a piston 16. Air is supplied to the combustion chamber 14 via an inflow pipe 18 and a first gas exchange valve 20. The first gas exchange valve 20 is thus the intake valve of the combustion chamber 14. The combustion exhaust gases are conducted from the combustion chamber 14 via a second gas exchange valve 22 into an exhaust gas pipe 24. The second gas exchange valve is thus an exhaust valve of the combustion chamber 14.

The intake valve 20 and the exhaust valve 22 are at the in FIG. 1 shown internal combustion engine 10 is not actuated by a camshaft, but in each case by a hydraulic actuator 26 and 28 respectively. The hydraulic actuator 26 is controlled by a hydraulic system 30, the actuator 28 by a hydraulic system 31, the exact configuration is explained in detail below. The hydraulic systems 30 and 31 are in turn controlled by a controller 32.

Fuel enters the combustion chamber 14 of the internal combustion engine 10 via an injector 34, which injects the fuel directly into the combustion chamber 14. The injector 34 is connected to a fuel system 36. The fuel-air mixture located in the combustion chamber 14 is ignited by a spark plug 38, which an ignition system 40 is driven. In a diesel engine, elements 38 and 40 may be omitted.

The hydraulic systems 30 and 31 are constructed identically. They will now be described with reference to hydraulic system 30 FIG. 2 explains:

In a reservoir 42 hydraulic fluid (not shown) is stored. A controllable high-pressure pump 44, which is driven by an electric motor 46, conveys the hydraulic fluid from the reservoir 42 via a check valve 48 into a high pressure line 50. To the high pressure line 50, a pressure accumulator 52 is connected. This may be, for example, a pressure accumulator with a spring-loaded piston. A pressure sensor 54 detects the pressure in the high-pressure line 50 and transmits corresponding signals to the control unit 32.

The hydraulic actuator 26 is a two-way hydraulic cylinder. In a housing 56, a piston 58 is movably arranged. A between the top of the piston 58 ("top" and "below" here and below only the representation in the figures) and the housing 56 existing fluid space forms a first working space 60. A between the bottom of the piston 58, one with This connected piston rod 62 and the housing 56 existing fluid space forms a second working space 64. Between the bottom of the piston 58 and the housing 56, a compression spring 66 is braced. The piston rod 62 is connected to the intake valve 20.

Between the hydraulic actuator 26 and the pressure sensor 54, a storage chamber 68 is present in the high pressure line 50, which is a manifold in the sense of "High pressure rail" forms. The second working space 64 is constantly connected via a branch line 70 to the high-pressure line 50 or the storage chamber 68. Between the storage chamber 68 and the first working chamber 60, a 2/2-way valve 72 is arranged, which is closed in its spring-loaded rest position 74 and opened in its actuated position 76 (the 2/2-way valve 72 is actuated by an electromagnet 78). The high-pressure line 50, the pressure accumulator 52, the storage chamber 68, the branch line 70 and the second working space 64 form a total of a fluid reservoir 80, which is completed in the direction of the high-pressure pump 44 through the check valve 48 and closed to the first working space 60 out through the valve 72 can be.

The first working chamber 60 is connected via a return line 82 to the reservoir 42. In the return line 82, a 2/2-way valve 84 and a check valve 86 are arranged. The 2/2-way valve 84 is opened in its spring-loaded rest position 88 and closed in the actuated position 90. In the closed position 90, it is brought by an electromagnet 92.

During normal operation of the internal combustion engine, a reciprocating movement of the intake valve 20 is effected by an alternating actuation of the two solenoid valves 72 and 84. When the solenoid valve 84 is closed, it is determined by the opening duration of the solenoid valve 72 how much hydraulic fluid enters the working space 60 of the hydraulic actuator 26. The amount of hydraulic fluid present in the first working space 60, in turn, determines the position or the stroke of the piston 58 and ultimately also the stroke of the inlet valve 20 Inlet valve 20 is effected when the solenoid valve 72 is closed by opening the solenoid valve 84.

In order to determine the current operating behavior of the hydraulic actuator 26, the procedure according to a method which is stored as a computer program on a memory 94 of the control unit 32. The method will now be described with reference to FIG. 3 explains:

After a start block 96, the high-pressure pump 44 is turned off in a block 98. In the same block 98, the magnets 78 and 92 of the two solenoid valves 72 and 84 are de-energized. The solenoid valve 72 is thus closed, whereas the solenoid valve 84 is open. The piston 58 is thereby in his in FIG. 2 pressed upper end position. Then, in the block 100, the solenoid valve 84 is brought into its closed position 90. In a block 102, the solenoid valve 72 is opened during a defined period of time dt and then closed again. The pressure drop dp in the fluid reservoir 80 is thereby detected by the pressure sensor 54 (block 104). This is stored with the corresponding period dt as a value pair dp, dt.

In a block 106 it is queried whether the piston 58 into its in FIG. 2 has moved lower end position. This is done by one in the FIGS. 1 and 2 Knock sensor not shown detected. If the answer in block 106 is "no", the solenoid valve 84 is opened in block 108 and then closed again. As a result, the first working chamber 60 is relieved and the piston 58 returns to its in FIG. 2 upper initial position. In a time block 110, the period dt is increased by a fixed difference value dt1. It then returns to block 102.

With the in FIG. 3 Thus, the solenoid valve 72 is thus successively opened during an ever longer period of time, so that a correspondingly larger amount of hydraulic fluid from the fluid reservoir 80 flows into the first working chamber 60 and a correspondingly different pressure drop is detected by the pressure sensor 54. It is understood that a pressure drop at the pressure sensor 54 is detected only when the pressure accumulator 52 is blocked, for example. If this is not possible, the state change of the pressure accumulator 52 would have to be recorded alternatively.

The process loop is run through until the piston 58 at its in FIG. 2 reached the lower stop. In this case, a jump from block 106 to block 112, in which the quotient of pressure drop dpa and the corresponding maximum stroke dha between the upper stop and lower stop of the piston 58 is formed.

In block 114, the corresponding strokes of the piston 58 are calculated from the stored pressure differences dp. This is done according to the formula $$\mathrm{ie}=\frac{\frac{\mathrm{V}\mathrm{0}\mathrm{*}\mathrm{dp}}{{\mathrm{e}}_{\mathrm{OIL}}}}{\mathrm{there}}$$

In the above formula, that is, the stroke of the piston 58, V0 is the original volume in the fluid reservoir 80 before opening the solenoid valve 72, dp the pressure drop detected by the pressure sensor 54, E _OIL the elastic modulus of the hydraulic fluid, and dA the difference between the upper and lower Limiting surface of the piston 58. In this way, pairs of values dp, ie formed, from which further in block 114, a characteristic dh = f (dt) is formed. This characteristic connects the stroke dh of the piston 58 with the corresponding opening duration dt of the solenoid valve 72. This characteristic is then used in normal operation to drive the solenoid valve 72 to achieve a particular desired stroke. The value pairs dp, ie are normalized or calibrated on the basis of the quotient dpa / dha formed in block 112.

Now, referring to the FIGS. 4 and 5 A second embodiment of a hydraulic system 30 is explained. In this case, carry such elements and areas, which equivalent functions to elements and areas of related to the Figures 2 and 3 described embodiment, the same reference numerals. They are not explained again in detail.

At first this is different in FIG. 4 shown hydraulic system 30 of that of the FIG. 2 by an additional solenoid valve 118, which is arranged between on the one hand the check valve 48 and the pressure accumulator 52 and on the other hand the pressure sensor 54. With the additional solenoid valve 118 so the fluid reservoir 80 can be separated from the pressure accumulator 52, which facilitates the detection of the pressure drop dp. Furthermore, in the in FIG. 4 1, a temperature sensor 120 and a viscosity sensor 122 are provided, which detect the temperature or the viscosity of the hydraulic fluid present in the fluid reservoir 80 and pass corresponding signals to the control unit 32.

The current operating behavior of the hydraulic actuator 26 of FIG. 4 is determined by a method which will now be described with reference to FIG. 5 explains:

Unlike the procedure of FIG. 3 will be at the in FIG. 5 shown method in block 100 and the valve 118 is de-energized. As a result, as already explained above, the pressure accumulator 52 is separated from the fluid accumulator 80, and the high-pressure pump 44 is also disconnected from the fluid accumulator 80. This may therefore continue to run, while the in FIG. 5 shown method is performed.

In block 102, during several process loops, the valve 72 is opened during a same time interval dt1. So it is gradually opened up. In block 110, a counter n is incremented by one, and in block 124, a query is made as to whether counter n is greater than a threshold G. The number of measuring operations is thus limited by the limit value G to a fixed value. In block 106, the valve 72 is opened during a period dt2 which is so long that the piston 58 in any case in its in FIG. 4 reaches the lower end position. A detection of this process by means of a knock sensor is therefore not required here. In block 114, the characteristic curve dh = f (dt) is determined and stored for the temperature temples detected by the temperature sensor 120 and the viscosity visc1 of the hydraulic fluid detected by the viscosity sensor 122. If the procedure of FIG. 5 is traversed under different environmental conditions, so a set of characteristics is created, which are each suitable for specific environmental conditions.

The in the Figures 3 and 5 specified methods are preferably initiated immediately after switching off the internal combustion engine 10 from the controller 32. In this case, the control unit 32, the position of the piston 16 of the individual cylinder of the internal combustion engine 10 is known, and it will be in the Figures 3 5 or 5 is performed only for those cylinders which ensure that there is no collision between the inlet valve 22 and the corresponding piston 16 or with other valves. If the method is carried out with a certain degree of regularity after switching off the internal combustion engine, it is nevertheless ensured that the current operating behavior of the hydraulic actuators 26 of the intake valves 20 of all cylinders is known. However, it is also possible to carry out the method during an overrun operation of the motor vehicle, as long as it is ensured that there are no collisions between the piston and the corresponding gas exchange valve.

Incidentally, the current operating behavior of the hydraulic actuators 28 of the exhaust valves 22 is determined in an analogous manner. If necessary, it must also be considered that collisions between the inlet valve 20 and the outlet valve 22 of a cylinder can occur. In a repeated implementation of the in the Figures 3 and 5 In the case of recorded methods, mean values can also be formed, for example, over the last three procedural sequences in order to improve the accuracy of the method result. Furthermore, the response time of the solenoid valve 72 may be determined from the beginning of the pressure drop dp in the fluid reservoir 80.

In embodiments not shown here, the method described above is used in internal combustion engines with intake manifold injection and in diesel internal combustion engines.

Also in an embodiment, not shown, in an operating phase in which the exhaust valve 20 rests, the valve 118 is closed and the evolution of the pressure in the fluid reservoir 80 is monitored. If the pressure drops too much over a certain period of time, a message is displayed. This may consist in an entry in a fault memory, or it may light a warning display for the user of the internal combustion engine 10. It is also conceivable, in such a case, to lay the internal combustion engine 10 completely still or to allow only a limited safety operation in order to avoid further damage to the internal combustion engine 10.

Claims (13)

1. Method for operating a hydraulic actuator (26), in particular for a gas exchange valve (20) of an internal combustion engine (10), in which a movement of an actuating element (58) of the actuator (26) is brought about in that a working space (60) of the actuator (26) can be connected by means of a valve device (72) to a fluid accumulator (80), in which hydraulic fluid under pressure is stored, and can be separated from the said fluid accumulator, and in which the stroke (dh) of the actuating element (58) of the actuator (26) is dependent on a fluid volume present in the working space (60), and in which, to determine a current operating behaviour of the actuator (26), the working space (60) is briefly connected for a defined period of time (dt) to the fluid accumulator (80), the corresponding pressure drop (dp) in the fluid accumulator (80) is detected, the corresponding stroke (dh) is determined from the pressure drop (dp), using known geometric quantities (dA, V0) of the actuator (26), and at least one pair of values is formed which consists of the period of time (dt), during which the valve device (72) is opened and the fluid accumulator (80) is connected to the working space (60) of the actuator (26), and of the determined stroke (dh), characterized in that the stroke is determined from the pressure drop (dp), using known geometric quantities (dA, Vo) of the actuator.
2. Method according to Claim 1, characterized in that the pressure drop (dp) in the fluid accumulator (80) is detected for various periods of time (dt1, dt2), during which the working space (60) of the actuator (26) is connected to the fluid accumulator (80), and a current characteristic curve is formed from the determined pairs of values (dp, dt1, dt2).
3. Method according to one of the preceding claims, characterized in that the actuating element (58) is brought from a known initial position into a known end position, the corresponding pressure drop (dpa) in the fluid accumulator (80) is detected, and at least one determined pair of values is standardised with the aid of the detected pressure drop (dpa) and of the stroke (dha) between the initial position and end position.
4. Method according to Claim 3, characterized in that the attainment of the initial position and/or end position of the actuating element (58) is detected by means of a knock sensor.
5. Method according to one of the preceding claims, characterized in that the at least one pair of values is formed, taking into account the modulus of elasticity (E_OIL) of the hydraulic fluid and/or the elasticity of the fluid accumulator (80).
6. Method according to one of the preceding claims, characterized in that the temperature (temp1) and/or the viscosity (visc1) of the hydraulic fluid are/is detected during the determination of the current operating behaviour of the actuator (26), and the at least one pair of values is formed for a specific viscosity (visc1) and/or a specific temperature (temp1) of the hydraulic fluid.
7. Method according to one of the preceding claims, characterized in that the response time of the valve device (72) from the commencement of the pressure drop (dp) in the fluid accumulator (80) is determined.
8. Method according to one of the preceding claims, characterized in that, to determine the current operating behaviour of the hydraulic actuator (26), the fluid accumulator (80) is separated fluidically from a pressure accumulator (62) and/or a high-pressure pump (44) for supplying the fluid accumulator (80) is switched off.
9. Method according to one of the preceding claims, characterized in that the current operating behaviour of the actuator (26) of a gas exchange valve (20) of an internal combustion engine (10) is determined after the switch-off of the internal combustion engine (10) and/or during an overrun of the internal combustion engine (10).
10. Method according to one of the preceding claims, characterized in that, with the hydraulic actuator (26) stationary, the pressure in the fluid accumulator (80) is detected, and, in the event of an inadmissible pressure drop, a message is output.
11. Computer program, characterized in that it is programmed for carrying out the method according to one of the preceding claims.
12. Control and/or regulation apparatus (32) for an internal combustion engine (10), characterized in that it is programmed for use in a method according to one of Claims 1 to 10.
13. Internal combustion engine (10), in particular for a motor vehicle (12), with a control and/or regulation apparatus (32) which is programmed for use in a method according to one of Claims 1 to 10.

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