EP2644903B1 - Method and hydraulic control device for controlling a consumer - Google Patents

Description

The invention relates to a method for controlling a consumer with two pressure chambers and a hydraulic control arrangement for controlling such a consumer.

Usually, continuously adjustable hydraulic valve devices are used to control pressure fluid flow rates. In this case, proportionally adjustable valves are used whose valve member is designed to be hydraulically or electrically continuously adjustable in order to set an opening cross section for the pressure medium volume flow. For electrically adjustable proportional control valves, Pulse Width Modulation (PWM) can be used to adjust the current on the actuating magnet. The frequency of the pulse width modulation is set higher than a maximum switching frequency of the valve. The PWM pulses are smoothed in a coil of the actuating magnet to an average value. The valve spool is acted upon by a spring counter to the effective direction of the actuating magnet. The adjusting spring force during adjustment corresponds to a force at which the spring and thus the valve slide travel along a path corresponding to the current. The spring is designed so that it can be adjusted at a maximum current to a position corresponding to the maximum opening position of the valve spool.

In recent years, the so-called digital hydraulic has been established, in which instead of proportional control valves switching valves are used, which are driven by pulses, for example in the manner of a PWM.

The term switching valve should be understood in particular a valve having a movable valve member which is biased by a spring in the direction of a basic position (for example, closed) and in a switching position (open) is adjustable. This switching position is occupied by energizing an actuating magnet. It is assumed that the spring biasing the valve member in the direction of the basic position in comparison to the force of the actuating magnet at Nennbestromung is very low, so that only a comparatively short time (with fast switching valves 2ms) is required to apply the current to the actuating magnet to connect the switching valve in the switching position. By choosing the pulse frequency and the pulse duration, a pressure medium volume flow can be adjusted via such a switching valve, similar to a proportionally adjustable valve.

Basically, binary coded parallel architectures pulse code modulation (PCM) and pulse width modulation (PWM) with individual switching valves to distinguish, but can also be combined. By interconnecting a plurality of such switching valves, a volumetric flow can be influenced in order to regulate or control a hydraulic actuator, for example a hydraulic cylinder.

With digital hydraulic motion controllers, multiple DFCUs can be implemented with these switching valves in parallel, ideally doubling from one valve to the next, the maximum achievable flow through such a DFCU The resolution of the volume flow through such a DFCU is predetermined by the number of switching valves An increase in resolution can be achieved by using additional switching valves in a DFCU or by pulse-width-modulated control, whereby a ballistic PWM control is also possible the switching valves is possible.

In the US 5,355,772 A a generic hydraulic control arrangement for controlling a hydraulic cylinder is shown in which a piston rod side annular space of the hydraulic cylinder is acted upon by a predetermined pressure, such as a pump pressure, while the other, bottom pressure chamber via a switching valve arrangement with the pump or a pressure medium sink (tank) is connectable. The desired cylinder position is set, in which the bottom pressure chamber on the Switching valve arrangement supplied a pressure medium volume flow or from this bottom-side pressure chamber, a pressure medium volume flow is discharged, the adjustment then takes place in each case against the pressure in the annular space.

Also the pamphlets US 2002 002 68 69 A1 and WO 2007 028 863 A1 each show a generic method and a generic control arrangement for controlling a consumer.

The disadvantage of this solution is that the volume flow resolution of the control arrangement is very limited, with a speed resolution and positioning accuracy and a pressure control accuracy of a downstream hydraulic actuator is dependent on this volume flow resolution and thus also subject to restrictions.

In contrast, the invention has for its object to provide a method for driving a consumer with two pressure chambers and a hydraulic control arrangement, by which a positioning accuracy of a consumer, in particular the fine control is improved.

This object is achieved with regard to the method by the features of patent claim 1 and with regard to the hydraulic control arrangement by the features of the independent claim 9.

Advantageous developments of the invention are the subject of the dependent claims.

The inventive method is used to control a consumer with two pressure chambers, of which one can be shut off at least via a switching valve arrangement or with a pressure medium source or with a pressure medium sink connectable. According to the method, first of all a pressure medium volume is determined which is to be supplied to or removed from the one pressure chamber in order to set a predetermined nominal chamber pressure in one of the pressure chambers, preferably in the other, preferably blocked pressure chamber, or by a predetermined desired consumer position, For example, set a piston position of a cylinder. In response to this determined pressure medium volume, the switching valve arrangement is then controlled such that the predetermined pressure medium volume is supplied to a pressure chamber or discharged from this pressure space.

The thereby adjusting actual chamber pressure or the actual consumer position is then compared with the corresponding predetermined desired value and, if necessary, the two aforementioned steps are repeated until the desired state is present.

In contrast to the prior art, no pressure medium volume flow to the respective pressure chambers is thus set via the switching valve arrangement, but a predetermined volume of pressure medium is metered into or drained from one of the pressure chambers. The movement of the consumer then takes place in accordance with a compression or decompression of the pressure medium in the other, preferably shut-off pressure chamber.

The compressibility of the pressure medium is thus utilized to perform a fine control. It is in contrast to the prior art, no volume flow but a volume regulated, the duty cycle of the switching valves is determined in advance.

In a particularly preferred embodiment, each pressure chamber is assigned a switching valve arrangement.

In a variant of the invention, the opening duration of the switching valves can be changed in order to supply or remove the pressure medium volume.

During the pressure medium supply or removal to or from a pressure chamber, the respective other pressure chamber is preferably shut off, so that the compressibility of the pressure medium in each shut off pressure chamber is utilized to realize the smallest positioning steps of a consumer.

According to the invention, it is preferred if each pressure chamber is assigned at least one inlet and one outlet switching valve. If the pressure chamber is blocked with the smaller pressure medium volume and the other pressure chamber is connected to the larger volume via the valve arrangement with the pressure medium source or the pressure medium sink, a smaller change in the nominal chamber pressure or the setpoint pressure results for a specific, increased or decreased pressure medium volume. Consumer position, as in the opposite case, when the pressure chamber locked with the larger volume and the pressure fluid volume is supplied to the pressure chamber of smaller volume or discharged from this. In the former way, the higher compressibility in the pressure chamber with the larger Volume used for fine adjustment. If, on the other hand, the pressure chamber with the smaller volume is connected via the valve arrangement to the pressure medium source or the pressure medium sink and the other pressure chamber is blocked by the larger volume, the lower compressibility in the pressure chamber with the smaller volume can be used to change the setpoint chamber pressure or Target consumer position to achieve with little pressure medium volume.

In the event that the two pressure chambers are separated by a piston, the size of the change in the desired chamber pressure or the desired piston position as a function of the pressure medium volume, and thus the sensitivity, in addition via an external force acting on the piston, in particular a spring force influenced.
In an alternative solution, alternately an inlet valve of one chamber and an outlet valve of the other chamber can be controlled offset in time to regulate the consumer position.

In this case, the control of the switching valves can be carried out according to a pulse combination which is selected from a table provided or stored in a data memory of pulse combinations with different pulse duration.

According to the invention, it is preferred if the opening duration of the switching valves is below the switching time for the respective switching valve - d. h., there is a ballistic control.

In the hydraulic control arrangement according to the invention for controlling a consumer with two pressure chambers, it is provided that at least one of these pressure chambers is associated with an inlet and outlet valve designed as a switching valve, via which the pressure chamber can be connected to a pressure medium source or a pressure medium sink. The control arrangement further has a control unit for controlling the inlet and outlet valves such that a chamber pressure of one or the other pressure chamber or a consumer position by compression or decompression of the pressure medium in the other pressure chamber by supplying or removing a pressure medium volume via the one pressure chamber associated Inlet or outlet valve is adjustable. The control unit according to the invention is designed so that the Switching valve arrangements in the sense of the pre-discussed method claims can be controlled.

As already mentioned, it is preferred if each of the pressure chambers is associated with an inlet and an outlet valve. In this case, for example, to set the chamber pressure and / or the consumer position, the inlet valve of the one pressure chamber and the outlet valve of the other pressure chamber are controlled alternately or overlapping each other.

Alternatively, the inlet and outlet valves assigned to one pressure chamber can also be controlled alternately or overlapping, while the other pressure chamber is shut off by the associated inlet and outlet valves, so that the compressibility of the pressure medium in this pressure chamber is utilized for the adjustment.

• Figur 1 ein Schaltschema einer erfindungsgemäßen hydraulischen Steueranordnung zur Ansteuerung eines Verbrauchers mit zwei Druckkammern;
• Figur 2 ein Diagramm zur Verdeutlichung des Schaltstatus eines Schaltventils der Steueranordnung gemäß Figur 1 und
• Figur 3 eine Variante der Steueranordnung gemäß Figur 1.

Preferred embodiments of the invention are explained in more detail below with reference to schematic drawings. Show it:

• FIG. 1 a circuit diagram of a hydraulic control arrangement according to the invention for controlling a consumer with two pressure chambers;
• FIG. 2 a diagram illustrating the switching status of a switching valve of the control arrangement according to FIG. 1 and
• FIG. 3 a variant of the control arrangement according to FIG. 1 ,

An in FIG. 1 its piston 4 divides the hydraulic cylinder 2 in a bottom-side pressure chamber 6 and a piston rod side annular space 8, which are connectable via the control arrangement 1 with a pump P or a tank T. to set the piston position or a piston speed or a chamber pressure.

As explained above, a digital hydraulic control arrangement 1 according to the invention consists of a multiplicity of so-called digital volume flow units (DFCU) which are used in the illustrated embodiment by a respective switching valve 10, 12, 14 and 16 are formed. The switching valves 10, 12 the pressure chamber 6 and the switching valves 14, 16 associated with the annular space 8. The pressure connection of the pump P is connected via a respective working line 18, 20 to the respective pressure chamber 6 or the annular space 8. The two switching valves 12, 14 are arranged in the pressure medium flow path between the pump P and the respective pressure chamber 6, 8. The respective working line 18, 20 can be connected to the tank T via the two other switching valves 10, 16 so that pressure medium can flow out of the associated pressure chamber 6 or the annular space 8. The two switching valves 12, 14 are thus inlet valves, while the two other switching valves 10, 16 represent exhaust valves.

In FIG. 1 are the two pressure ports of the hydraulic cylinder 2 denoted by the reference numeral A, B, accordingly, the two inlet valves 12, 14 control the pressure medium connection from the pump P to port A and from the pump P to port B, while the two exhaust valves 10, 16 control the pressure medium connection from port A to tank T or from working port B to tank T. The switching valves are biased in each case via the aforementioned weak spring 22, 24, 26, 28 in the direction of a closed position and can be adjusted via a respective actuating magnet 30, 32, 34, 36 in the direction of a flow position. By means of these switching valves 10, 12, 14, 16, the respective volumetric flow paths from the pump P to the pressure chambers 6, 8 or from these to the tank T can thus be controlled independently of one another. Due to these resolved control edges an exact fine control is possible.

According to the invention, the control of the valve members of the switching valves 10, 12, 14, 16 takes place after a pulse width modulation (PWM), wherein preferably a ballistic PWM is used. In this mode, the respective switching valve is not completely switched through, but the respective actuating magnet 30, 32, 34, 36 is momentarily energized so that with the introduced energy, the valve member performs only a partial stroke and returns according to its ballistic trajectory back to the closed position. Accordingly, the ballistic drive pulse has a PWM fundamental frequency which is below the maximum switching frequency of the respective switching valve. In other words, a period of the ballistic drive pulse is shorter than a minimum switching time of the respective switching valve 10, 12, 14, 16.

The pressure medium supply of the hydraulic cylinder 2 via the control arrangement shown is carried out according to the so-called Meterlnn MeterOut- (MIMO) method, where there are in principle two options. Common to both options is that the hydraulic cylinder 2 supplied or discharged pressure medium volume, which is necessary to achieve a desired chamber pressure or a cylinder position, is known or can be approximately determined depending on the current pressures and positions. The duty cycle of the switching valves 10, 12, 14, 16 then depends on the pressure medium volume required for setting the cylinder position. In this case, the switching valves 10, 12, 14, 16 are operated for the smallest required pressure fluid volumes in said ballistic mode. For larger volumes of pressure medium, activation can also take place after the "normal" PWM or in another way. Thus, for example, have the DFCUs, as in the embodiment according to FIG. 3 are shown, more than a prescribed switching valve on. The switching valves of each DFCU can be operated alternatively or in addition to the "normal" PWM in pulse code mode.

The energization of the actuating magnet 30, 32, 34, 36 via a control unit 40, which is connected via signal lines 42, 44, 46, 48 with the actuating magnet 30, 32, 34, 36 in order to switch these to energize or de-energized.

In the exemplary embodiment according to the invention, this metered addition or release of pressure medium takes place over the opening duration of the switching valves 10, 12, 14, 16, via which a pressure space is shut off, while pressure medium volume is supplied to the other pressure space or is discharged from this pressure medium volume. D. h., The piston 4 is then supported, so to speak, on the shut-off oil volume, wherein the pressure in this pressure chamber changes depending on the supplied or discharged volume. The movement of the piston 4 is carried out according to the compression or decompression of the pressure medium in the shut-off pressure chamber. This results in a very finely controllable movement of the piston. 4

On the one hand, it is possible to use an inlet valve on one side of the hydraulic consumer and an outlet valve on the other side of the hydraulic consumer. For example, in the circuit according to FIG. 1 the switching valves 14 and 10 are controlled while the other two switching valves 12, 16 remain in their locked position. The two switching valves 10, 14 controlling the pressure medium connection of P → B and of A → T can be actuated offset in time from one another. In principle, it is also possible that the pressure medium connection to the tank controlling switching valve does not trigger.

The second option, which is preferred here, is to control the intake and exhaust valves associated with a pressure chamber. In the specific case, the annular space 8 is to be supplied with a volume of pressure medium or be discharged therefrom, so that correspondingly, as in FIG FIG. 1 indicated the switching valves 14, 16 are actuated, while the two the pressure chamber 6 associated switching valves 10, 12 are de-energized and thus remain in its closed position. The drive pulses are in FIG. 1 symbolically drawn with u _P and u _T. It is assumed that this control takes place after the ballistic mode. In this case, it is preferred if the supply or removal of pressure medium to or from the pressure chamber takes place with the currently larger volume of pressure medium, since this can be compressed more strongly, and thus more sensitive fluid metering is possible. At the in FIG. 1 illustrated embodiment, the pressure medium volume supply or discharge to or from the annular space 8, which currently has a larger pressure medium volume than the pressure chamber 6 accordingly.

For this selected valve switching combination generates, for example, an algorithm based on predetermined parameters opening pulses of different duration and from it pulse combinations for controlling the two switching valves 14, 16. Alternatively, the pulse combinations can also be specified manually.

In addition to the combinations, a temporal offset of the opening pulses is conceivable for the selected switching valves, i. h., the valves are not synchronized.

The generation of the pulse combination will be described in more detail below by way of example.

The pulse length t _pulse can be specified as a multiple of a time unit t ₁ . This unit time t ₁ generally corresponds to the sampling time of control unit 40. It should the time t ₁ is smaller than the switching time t _switching (= time for complete opening) of the valves to be. It is assumed that the time unit t ₁ = t _switch / 5. Are you now as a multiple z. B. [0 4 6] before, the possible pulse combinations result according to Table 1 below. pulse length pulse length pulse combination Valve PB Valve BT 1 4 * t ₁ 0 2 6 * t ₁ 0 3 0 4 * t ₁ 4 4 * t ₁ 4 * t ₁ 5 6 * t ₁ 4 * t ₁ 6 0 6 * t ₁ 7 4 * t ₁ 6 * t ₁ 8th 6 * t ₁ 6 * t ₁

For these different pulse combinations, the volume which this particular combination is expected to produce is calculated. Subsequently, that pulse combination is selected whose calculated volume corresponds to the required fluid volume Vol _ref , which is supplied to the hydraulic cylinder 2 or is discharged therefrom in order to set the desired cylinder position. This pulse combination determined in this way is then output to the actuating magnets 14, 16 via the control unit 40.

In the picture according to FIG. 2 is an example of the switching status of a valve at a pulse length t _pulse = 6t ₁ shown.

As already explained, both the inlet valve and the outlet valve can be actuated offset from one another. In principle, it is also possible to control only one of the two valves 14, 16. In principle, it is also possible to adjust the predetermined cylinder position or travel speed of the cylinder in the manner described above to both pressure chambers 6, 8 to supply pressure medium or release it.

In the embodiment described above, each DFCU is implemented only with a switching valve 10,12, 14, 16, which are controlled according to the strategy explained above. FIG. 3 shows a variant in which each DFCU of a plurality of parallel connected Switching valves exists, with the single flow rate of each switching valve to the next switching valve of a DFCU ideally doubles. The maximum achievable flow, which can be controlled via such a DFCU, then results from the sum of the individual flows of the individual switching valves. The resolution of the volume flow through a DFCU is then restricted to 2 ⁿ -1 stages. At z. B. five valves is thus the resolution of the flow rate limited to 2 ⁵ -1 = 31. An increase in the resolution is possible by using additional switching valves or by the pulse width modulated control (up to the ballistic control) of individual switching valves.

In the method according to the invention, which in principle involves the fine positioning of the cylinder 2, the "smallest" switching valves 10, 12, 14, 16 of each DFCU are correspondingly used for activation. In principle, it is possible to move the cylinder in the range of a predetermined position at a comparatively high speed in the manner of a conventional control, and then perform the fine positioning according to the above-described method utilizing the compressibility of a shut-off fluid volume.

Disclosed are a method for controlling a consumer with two pressure chambers and a digital hydraulic control arrangement for controlling a consumer, wherein for controlling the consumer to a pressure chamber, a predetermined pressure medium volume can be supplied or discharged from this.

LIST OF REFERENCE NUMBERS

1

control arrangement

2

hydraulic cylinders

4

piston

6

pressure chamber

8th

annulus

10

switching valve

12

switching valve

14

switching valve

16

switching valve

18

working line

20

working line

22

feather

24

feather

26

feather

28

feather

30

actuating magnet

32

actuating magnet

34

actuating magnet

36

actuating magnet

40

control unit

42

signal line

44

signal line

48

signal line

Claims (10)

1. Method for the digital hydraulic control of a consumer with two pressure chambers (6, 8), of which at least one can be shut off via a switching valve arrangement, connected to a pressure medium source or connected to a pressure medium sink, characterized by the following steps:

   a) determining a pressure medium volume to be supplied to a pressure chamber (6, 8) or removed from the latter, in order to set a predetermined target chamber pressure or a predetermined target consumer position, for example a piston position of a hydraulic cylinder (2);

   b) controlling the switching valve arrangement in such a way that the predetermined pressure medium volume is supplied to the first-named pressure chamber (6, 8) or removed from the latter;

   c) checking the actual pressure or the actual consumer position and, if appropriate, repeating steps a) and b) until the target state is present.
2. Method according to Patent Claim 1, wherein each pressure chamber (6, 8) is assigned a switching valve arrangement.
3. Method according to Patent Claim 1 or 2, wherein the opening period of the respective switching valve arrangement is changed in order to supply or remove a desired pressure medium volume.
4. Method according to Patent Claim 3, wherein a respective pressure chamber (6, 8) is shut off while the pressure medium volume is supplied to the other pressure chamber (6, 8) or removed from the latter.
5. Method according to one of the preceding patent claims, wherein the pressure chamber (6) having the smaller pressure medium volume is shut off and the other pressure chamber, having the greater pressure medium volume (8), is connected to the pressure medium source or the pressure medium sink via the valve arrangement.
6. Method according to one of the preceding patent claims, wherein each pressure chamber (6, 8) is assigned an inlet valve (12, 14) and an outlet valve (10, 16), and wherein an inlet valve (12, 14) of a pressure chamber (6, 8) and an outlet valve (10, 16) of the other pressure chamber (6, 8) are controlled alternately or in an overlapping manner in order to set the target state.
7. Method according to one of the preceding patent claims, wherein the control of the switching valves (10, 12, 14, 16) is carried out in accordance with a pulse combination, which is selected from a table of pulse combinations having different pulse periods.
8. Method according to one of the preceding patent claims, wherein the opening period of the switching valves lies below the switching time for the respective switching valve (10, 12, 14, 16).
9. Digital hydraulic control arrangement for controlling a consumer having a consumer with two pressure chambers (6, 8), at least one pressure chamber being assigned an inlet (12, 14) and outlet valve (10, 16) of the control arrangement (1), each formed as a switching valve, via which one pressure chamber of the pressure chambers can be shut off, connected to a pressure medium source or connected to a pressure medium sink, and having a control unit (40), characterized in that the control unit (40) is designed to control the inlet valve (12, 14) and the outlet valve (10, 16) according to a method according to one of Claims 1 to 8 in such a way that a chamber pressure in this one or in the other pressure chamber or a target consumer position can be set by compression or decompression of the pressure medium in this other pressure chamber as a result of supplying pressure or removing a pressure medium volume by means of the inlet valve (12, 14) and outlet valve (10, 16) assigned to the first pressure chamber.
10. Control arrangement according to Patent Claim 9, wherein each pressure chamber (6, 8) is assigned an inlet valve and an outlet valve.

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