WO2010136273A1

WO2010136273A1 - Hydraulic system for a machine for producing a fiber web

Info

Publication number: WO2010136273A1
Application number: PCT/EP2010/055282
Authority: WO
Inventors: Arto Ikonen; Ville Hopponen; Eero Suomi
Original assignee: Metso Paper, Inc.
Priority date: 2009-05-29
Filing date: 2010-04-21
Publication date: 2010-12-02
Also published as: AT511575A5; CN102449319A; DE102009026605A1; AT511575B1

Abstract

The invention relates to a hydraulic system for a paper or cardboard making machine, comprising at least one hydraulic actuator (3) and at least one accumulator (11, 12) for storing a hydraulic working fluid under pressure, at least one digital hydraulic pressure controller (4) being provided which is associated with the hydraulic actuator (3) and which sets the pressure of the working fluid in the hydraulic actuator (3). In order to make a high-pressure working fluid available, a pump (10) is used to feed the high-pressure working fluid to the accumulator (11, 12) and to charge it. A plurality of accumulators (11, 12) can be present in the system having a plurality of hydraulic actuators while the pump (10) is designed as a common pump charging the accumulators (11, 12). According to an embodiment, the pump (10) is a mobile pump which is mobile relative to the respective accumulators (11, 12) and which can be releasably connected thereto.

Description

Hydraulic system for a machine for producing a fibrous web

description

The invention relates to a hydraulic system for a machine for producing a fibrous web, in particular a paper or board machine.

In paper machines, hydraulics is widely used as actuation and control means; In particular, actuators are hydraulically driven, with which large forces can be set and exercised with high accuracy.

Typically, a working fluid, e.g. Hydraulic oil used, which is pressurized by a pump. The introduction of the pressurized hydraulic oil into a hydraulic actuator, e.g. a hydraulic cylinder or hydraulic motor is typically controlled by a proportional control valve or proportional valve, which may be electrically, hydraulically, or pneumatically driven.

Such a control valve has a slidable or displaceable spool or spool which, in response to its location in an associated valve housing, can adjust a desired pressure at the outlet by controlling the pressure of hydraulic oil delivered by the pump. The mobility of the control piston in the valve housing necessarily requires a certain clearance or gap between the control piston and valve housing, so that an internal leakage of the control valve is unavoidable. The gap size must not be too narrow, otherwise the valve would be too susceptible to contamination in the hydraulic oil. Recently, alternative pressure regulators have been developed, which in this application are to be referred to throughout as digital hydraulic pressure regulators. If such digital hydraulic pressure regulator used as a pressure reducer, they are referred to throughout the present application as a digital hydraulic pressure reducer.

The operation of the digital hydraulic pressure regulator, for example, in the journal fluid no. 7-8, 2008 p. 12, 13 described in more detail. The improved readability of this application, the method of operation of digital hydraulic pressure regulator is again summarized very briefly:

In the simple case, a digital hydraulic pressure regulator consists of a series of valves connected in parallel, which have only ON / OFF functions; So simple ON / OFF switching valves are that allow or interrupt a flow and can be consistently referred to in this application as valves. The valves are all connected to a common supply line on the one hand and to a common output line on the other. The valves themselves may be conventional solenoid valves, i. Be valves with electromagnetic drive. Of course, other forms of drive can be chosen.

By connecting or installing throttle elements or by the valves themselves, it is ensured that the valves have different flows when they are open. If, for example, four valves are provided, then the flow rates Q in the individual, in each case by the associated valve selectively releasable passages in the ratio of 1: 2: 4: 8 to each other; at a larger number of valves will continue this series accordingly.

By opening and closing individual valves or valve combinations, which are determined and selected on the basis of mathematical models by a computer, a very rapid and precise pressure adjustment in the output line or in the actuator connected thereto can now be achieved. This is achieved by replacing the analogue control curve of the initially described proportional control valve with a digitally generated (approximate) control curve. Due to the omission of non-linearities and / or hysteresis of the analogue proportional valve, this curve can be a step-like approximated straight line which allows a control point to approach a control point quickly and (virtually) free of overshoot.

Another advantage of the digital hydraulic control is that the valves are either open or closed, i. To maintain a desired pressure in a closed (and unchanged) system, the valves are simply closed and there are no internal leakage flows. This is a clear difference to the conventional proportional valve, which is always flowed through by a hydraulic oil flow. This constantly costs energy for the hydraulic pumps, e.g. in the paper machine.

Thus, it can be seen that the use of digital hydraulic pressure regulators allows the hydraulic pumps to operate less often or shorter, which saves energy.

However, there is still a need to reduce the energy consumption of a machine for producing a fibrous web, especially a paper or board machine to further reduce.

This object is achieved with a hydraulic system for a machine for producing a fibrous web, in particular a paper or board machine, with the features of claim 1.

According to the invention, a hydraulic system for a machine for producing a fibrous web, in particular a paper or board machine, proposed that at least one hydraulic actuator, at least one high pressure accumulator for storing a hydraulic working fluid under pressure, a pump to the working fluid at high pressure in the high pressure accumulator feed and charge, and has at least one digital hydraulic pressure regulator, which is assigned to the hydraulic actuator and adjusts the pressure of the working fluid in the hydraulic actuator.

The following explanations always refer to a paper machine; However, this term is expressly to include all types of machines for the production of fibrous webs, so in particular also board machines, (hard) fibreboard machines and the like.

If a digital hydraulic pressure regulator is used instead of a conventional proportional valve, with the position of the hydraulic actuator unchanged, the hydraulic fluid consumption, ie the internal leakage flow in the regulator, is zero. In a paper machine many adjustable elements are required and available; but the adjustment is not often, but only in relatively rarely occurring operations, such as start-up operations, web breaks and Neueinfädelungen the web, Tambourwechsel or maintenance. The actuating movements, which are usually carried out by means of acting on the adjustable elements hydraulic cylinders, thereby include a movement of a hydraulic cylinder and / or possibly a pressure build-up to produce any mechanical compressive forces, eg pressure between two rollers.

It has been found that, with the elimination of the permanent leakage current in proportional valves, there is actually such a low requirement for working fluid that it is energetically unfavorable to repeatedly switch on and off a pump of sufficiently large size for the leakage flow. The inventors have now found that the consumption of working fluid can also be covered by a high-pressure accumulator, wherein the high-pressure accumulator is charged with a pump from time to time.

As explained above, the hydraulic system for a paper machine usually has a multiplicity of hydraulic actuators, it being possible to associate with each individual actuator its own high-pressure accumulator or several actuators together a common high-pressure accumulator. In both cases, a single pump can be provided which charges several high pressure accumulators or the one high pressure accumulator. In the case of multiple high-pressure accumulator these can be charged one after the other individually, so that a small pump, which is designed for the filling of a high-pressure accumulator, sufficient.

The expense of providing, installing and maintaining piping to supply the hydraulic system with hydraulic oil is considerable in a conventional paper machine. The materials used must be for the to be corrosion-resistant, there are enormous distances to cope with, because a conventional paper machine is simply large (several tens of meters long), so that here the material consumption of high-quality pipe material is a real cost factor. In addition, there are flow losses in the management of the oil flows in the lines, which must be compensated either by larger pipe cross-sections, ie more material consumption, or by higher pump power, ie higher energy consumption.

By assigning individual high-pressure accumulators to individual actuators or groups with multiple actuators, a functional and spatial breakdown of the pressure supply can be achieved, i. individual local pump stations are provided, which are independent of each other, so that long strands can be omitted.

With a fast set of digital valves as a digital hydraulic pressure regulator on a pressure accumulator, the pressure in, for example, a nip or nip can be precisely controlled even though the level of supply pressure varies slightly or decreases. The set of valves is installed in the pressure accumulator to control the pressure or the volume flow delivered by the pressure accumulator. When the accumulator is depleted, ie, the energy stored therein has been released, the set of digital valves switches to the pump pressure. The pressure control is carried out directly with the pumped working fluid and at the same time the accumulator is recharged. Then the pump switches off again and it is again taken working fluid from the accumulator. Considerations have shown that the need for working fluid in an average frequent and average continuous operation of the actuators is so low that appropriately sized high-pressure accumulators are charged only in a several-week rhythm. Therefore, it is provided in an advantageous embodiment of the invention to operate the hydraulic system instead of stationary mounted and connected pumps with a mobile, movable to the respective high-pressure accumulators and releasably connectable pump. Such a mobile pump, for example in the form of a pump carriage, could be equipped with an appropriate power supply, possibly its own tank, suitable quick connections, control devices, etc., so that the high-pressure accumulators can be charged easily and possibly with fresh or purified working fluid.

There are a variety of places in a paper machine, where several actuators act the same, so are used in parallel working. In these cases, e.g. in arrangements for reel change, means for opening nips, frame sections, web feedthroughs or the like, because of the sheer size of the machine parts involved, several hydraulic cylinders are provided which, for example, lift or lower a roller at both ends. Preferably, each such group of similarly acting hydraulic actuators is assigned its own digital hydraulic pressure regulator, which then sets the pressure for the whole group. This requires a pipe connection among the members of a group.

However, if the same-acting group members are located far apart, each actuator can be connected to its own digital hydraulic pressure regulator. If the actuator is a hydraulic cylinder is, are in an advantageous embodiment of the invention, the valves of the digital hydraulic pressure regulator mounted directly on the hydraulic cylinder. This design is not only compact, but there are also few hydraulic connection points available. This improves reliability because there are few places that could leak.

Because of the relatively simple construction of the pressure regulator, it is in terms of the quality of

Regulation result provided in an advantageous embodiment, to make the pressure control function on a hydraulic cylinder so that the regulation of the pressure takes place on both sides of a piston of the hydraulic cylinder.

In this or other embodiments of the invention, the hydraulic cylinder may be connected to its own digital hydraulic pressure regulator, its own high-pressure accumulator and its own tank for storing pressureless working fluid.

In an alternative embodiment of the hydraulic system according to the invention, the actuator is a hydraulic motor which is provided parallel to an electric drive motor with a rotating element of the machine to be driven. The hydraulic motor can be designed as a drive auxiliary unit or as a brake assist unit or for these two functions with the rotatably driven element selectively coupled.

A paper machine is a machine designed for continuous operation, but a standstill of the machine is unavoidable. Railway breaks, the replacement of wearing parts and similar activities make it required to stop or start the machine. For continuous operation, an electric drive for the rotating or circulating elements is usually provided, ie of rollers, cylinders, drums, belts, screens, etc. of which there are a plurality in a paper machine. Starting the paper machine requires that all these rotating elements, which are large and heavy and correspondingly sluggish, standstill on the

Continuous operating speed to be accelerated. To achieve this in a short time, considerable benefits of electric drives are required; Achievements that are well above the drive power required for continuous operation. Electric motors with these powers are large, expensive and oversized for continuous operation.

Hydraulic motors reach from the state high torques and thus can be suitable auxiliary drives for starting the paper machine. If you provide the hydraulic motor with a pressure accumulator for the working fluid, then the memory can provide high power for a short time. For the case of starting the paper machine which is rare in relation to continuous operation, construction expenditure and energy can be saved if part of the starting torque is supplied by a hydraulic motor instead of a large electric motor. With a responsive, digitally-hydraulic pressure regulator, the hydraulic motor can be well controlled, allowing sensitive torque application with this solution. Hydraulic motors have a simple construction compared to electric motors and can be made of simple materials.

In an arrangement as Anfahrunterstützung the hydraulic motor with its own digital hydraulic Pressure regulator, its own pump, its own high-pressure accumulator and a separate tank for storing pressureless working fluid provided and mounted as a compact unit at the desired location.

The starting assistance can also be designed in the form of a hybrid drive from an electric motor with an engageable hydraulic motor.

Further, it is possible to use the hydraulic motor as a pump during operation, which replenishes the accumulator again; In addition, a part of the mechanical power of the electric motor may temporarily drive the hydraulic motor as a pump to gradually fill the pressure accumulator.

The control accuracy of the digital hydraulic pressure regulator improves when the pressure drop across the regulator decreases. When the pressure of the working fluid at the input of the regulator is within the range of the pressure to be set by the regulator, the desired pressure can be set more accurately and more quickly. However, the accumulator (s) used are intended to store at high pressures in order to achieve a large memory content (i.e., long run times of the working fluid supply).

To set the pressure of the working fluid at the inlet of the digital hydraulic pressure regulator in a suitable range, a used as a pressure reducer digital hydraulic pressure regulator can be used. This may possibly be simpler in design than the digital-hydraulic pressure regulator performing the actual control task, ie, for example, having a few valves or having simple upper and lower ones Control values work or similar, the control task simplifying measures can be taken.

A digital hydraulic reducer can be associated with any digital hydraulic pressure regulator, a group of such regulators, or just any pressure accumulator. For example, if a common high-pressure accumulator is provided for a plurality of actuators to which a plurality of individual digital hydraulic pressure regulator is connected, may be provided between the high-pressure accumulator and the pressure regulators a common digital hydraulic pressure reducer or it may be a digital hydraulic pressure reducer for each digital hydraulic pressure regulator, the or supplied to the respective pressure regulator. In the latter case, the individual digital hydraulic pressure reducers can each set a different, the control task of the subsequent digital hydraulic pressure regulator adjusted pressure of the working fluid.

It is also possible to provide between the digital hydraulic pressure reducer and the one or more digital hydraulic pressure regulators one or in each case an intermediate storage which stores working fluid with the reduced pressure and delivers it to the one or more digital hydraulic pressure regulators.

The invention can be practiced with numerous modifications and options, some of which are described below. These modifications contribute to a simplified hydraulic system design and / or energy consumption reduction. There are different types of hydraulic cylinders, the single-acting plunger cylinder or the double-acting differential cylinder. In a differential cylinder, pressure-effective surfaces are formed on both the piston side and the rod side, so that the piston rod of the cylinder ultimately occupies a position which depends on the load acting on the rod and the difference of the pressures on the piston side and the rod side. In a common mode of operation, when the position of the piston is to be adjusted, working fluid is fed under pressure on the cylinder side into the pressure chamber, the volume of which is to increase, while a corresponding amount of working fluid is discharged from the pressure chamber, whose volume is to decrease.

In this case, working fluid is discharged at a pressure level well above that of the reservoir, hereinafter referred to as a tank. This means that the previously invested pump energy, which is contained in this part of the working fluid to be discharged, is discharged into the tank unused. By an overflow valve, which connects the two pressure chambers of the cylinder with each other, the working fluid flows at high pressure level from one pressure chamber to the other and it is only necessary to apply the pumping energy, which is required to increase the pressure in this volume. This saves energy.

With the help of a suitable switching valve and a simplified structure of a digital pressure regulator can be achieved in conjunction with a differential cylinder.

A conventional digital hydraulic pressure regulator usually has a series or bank of valves connected in parallel for the supply of working fluid to a pressure chamber of the Differential cylinder and a bank of parallel-connected valves for discharging working fluid from this pressure chamber. As a rule, a differential cylinder with two pressure chambers are assigned a total of four valve banks. With a switching valve (4/2-way valve) can now be achieved a simplification of the structure by each a valve bank is connected to one cylinder pressure chamber, while the switching valve, the two valve banks alternately with the tank or the pump (or the pressure source) combines.

If digital hydraulic pressure regulators are used together with hydraulic cylinders, a particular advantage is that these regulators have no leakage current. Therefore, oil volumes and piston position are very closely related, i. If one measures the volume of oil supplied to the cylinder, one can infer the actual position of the piston. In the operation of such a cylinder, the piston position may be an important quantity, in particular in the setting of accurate distances at high forces or with respect to a synchronization of movements.

The conventionally used sensors for this task are arranged on the outside of the cylinder and thus exposed to the adverse environmental conditions of, for example, paper machines, where it is often dusty and / or humid. As a result, this sensor is prone to failure.

Due to the close relationship between the volume of oil delivered by the regulator and the piston position, it is proposed in a further development of the invention that conclusions be drawn from a volume flow measurement in the oil flow, for example with gear flow meters, to the piston position. In this case, the flow meter may be mounted at a position which is detected by the piston rod (whose position is to be removed) is removed. In addition, you can encapsulate such flow meters, since they only need to capture something that takes place inside them. In this way, a robust piston position detection is possible. Even if a measurement error occurs in the detection of the flow, the system, especially if the return flow to and from the cylinder are separately detected and evaluated, is sufficiently accurate to detect malfunctions.

It should also be possible to deduce the displaced oil volume from the operation of the digital hydraulic controller by summing up the individual flows through the individual valves of a regulator, taking into account the opening times. In this way, possibly even any flow meter can be saved. In this case, it is possible to use the knowledge that the opening times of the individual valves for the control are calculated anyway and can be closed from the offset with the individual flow rates through the corresponding valves to the present in the respective pressure chamber volume (ie the piston position).

The digital hydraulic control arrangements described above are usually operated with hydraulic oil, that is, the working fluid is an oil. The use of oil is for the usual control valves for lubrication of the control piston basically required or at least beneficial. Since the digital hydraulic controllers only use simple shut-off valves, this lubrication requirement no longer exists or no longer exists to that extent. Therefore, the working fluid may also be an aqueous emulsion (eg, an oil / water emulsion similar to the drilling mud) or even simple water. In addition to a significant reduction in the effort that will be made In order to protect the environment from pollution by leaking oil, there are also technical advantages.

The viscosity of oil is temperature dependent. In digital hydraulic regulators fixed throttles for adjusting the flow rates through the individual valves are usually provided, the throttle effect shows significant dependence on the viscosity of the working fluid. In the case of water or aqueous emulsions, the temperature has only a slight influence on the viscosity, so that the temperature sensitivity of the hydraulic system is low. Thus, it is not necessary to consider the temperature of the working fluid at the site of the digital hydraulic controller.

The invention will be explained below with reference to various aspects with reference to exemplary embodiments with reference to the drawings. It shows:

1 shows a section of a hydraulic system with pressure accumulators and digital hydraulic pressure reducers for supplying a plurality of hydraulic circuits, each with different working pressure in a schematic circuit diagram.

2 shows a section of a hydraulic system with a pressure accumulator, digital hydraulic pressure regulators and a hydraulic differential cylinder in a schematic diagram;

Fig. 3 is a circuit diagram of a pump assembly usable with the hydraulic system of Fig. 2; 4 shows a section of a hydraulic system with a digital hydraulic pressure regulator, an overflow valve and a hydraulic differential cylinder in a schematic diagram;

5 shows a section of a hydraulic system with two pressure accumulators with different working pressure, digital hydraulic pressure reducer, digital hydraulic pressure regulators and hydraulic differential cylinders in a schematic diagram;

6 shows a section of a hydraulic system with a simplified digital hydraulic pressure regulator, a changeover valve and a hydraulic differential cylinder in a schematic diagram;

Fig. 7 shows an arrangement for detecting the piston position of differential cylinders in a hydraulic system with digital pressure regulators.

In the following description of the figures, the same or functionally identical elements are designated by the same reference numerals, so that the general functional description is made only with reference to a figure and then referred to it. Further, if in the following text of pressure reducers, pressure regulators or flow controllers, so these are, unless otherwise stated, digital hydraulic pressure reducer, pressure regulator or flow regulator work using the beginning of the description explained digital hydraulic principle.

Fig. 1 shows a portion of a hydraulic system with pressure accumulators and digital hydraulic pressure reducers for supplying a plurality of hydraulic circuits, respectively various working pressure in a schematic diagram. In a supply section 1, a pump 10 is provided and pushes working fluid from a tank 20 into a high pressure line 100. The high pressure line 100 is connected to a high pressure or pump pressure accumulator 11, which is fed by the pump 10 with working fluid under high pressure and this under high Pressure stores.

From the high-pressure line 100 branch off four hydraulic circuits (short: circle) 101, 102, 103 and 104. Each circuit 101, 102, 103 and 104 has its own pressure reducer 13. On the input side of the lowest in Fig. 1 pressure reducer 13 of the circuit 104, a high pressure sensor 15 is connected in front of the pressure reducer. This high-pressure sensor 15 is used to control the pump 10 and the pump pressure accumulator 11. Further, the individual circuits 101, 102, 103 and 104 have this high-pressure sensor 15 in common, but each have their own low-pressure sensors 12. After in the circuit of FIG. 1, the pressure at the inlet of each pressure reducer 13 corresponds to the pressure detected by the high-pressure sensor 15 can the measured value from the high-pressure sensor 15 of the pressure regulation in the individual pressure reducers 13 is based on the measured value of the respectively associated low-pressure sensor 14 of the individual circuits 101, 102, 103 and 104.

Each of the circuits 101, 102, 103 and 104 has its own low pressure accumulator 12 which stores the working fluid at the pressure set by the pressure reducer 13 and, if necessary, supplies it to the associated hydraulic circuit.

By using a low-pressure accumulator 12 in the respective hydraulic circuit 101, 102, 103 and 104 control deviations of the pressure reducer 13 are attenuated. In addition, no constantly running pump is required, even if Several hydraulic circuits 101, 102, 103 and 104 must be supplied with working fluid and have different levels of consumption of working fluid. Furthermore, the arrangement shown has the advantage that the

Low-pressure accumulator 12 are dimensioned so that, even if in all connected hydraulic circuits 101, 102, 103 and 104, the maximum working fluid requirement occurs, the respective low-pressure accumulator 12 can supply the required amount of working fluid with sufficient pressure without being designed for the maximum working fluid requirements, accordingly large pump must be provided.

In such a case, the pump pressure accumulator 11 can also provide sufficient working fluid in the line 100 in the short term, so that the individual low-pressure accumulators 12 can be refilled quickly. The pump 10 can already run during this time but also beyond to recharge the pump pressure accumulator 11. Because of the storage capacity of the high pressure supply, a lower power pump can be used.

Fig. 2 shows a portion of a hydraulic system with a pressure accumulator 11, a digital hydraulic pressure regulator 4 and a hydraulic differential cylinder 3 in a schematic diagram. One

Supply section 1 with a pump pressure accumulator 11, a pump port 16 and a tank 20 supplies the pressure regulator 4 with two regulator sections 41, 42 for operating a differential cylinder 3. Sensors 19 detect the pressure in the two pressure chambers 31 and 34 of the differential cylinder 3, which by a piston 33 are separated by a piston rod 36. The pressure in the rod-side pressure chamber 31 acts on the rod-side piston surface 32, while the pressure in the piston-side pressure chamber 34 presses on the piston surface 35. With the Regulator sections 41 and 42 can be set to fill and pressure in the two pressure chambers 31 and 34, so that the piston rod 36 in the desired position and with the desired force with a machine element connected thereto (not shown) cooperates.

The pressure in the pressure supply 1, from which the cylinder 3 is to be controlled, is measured by means of pressure sensor 14 and, based thereon, the target pressure in the pressure chambers 31 and 34 is set. With 45, a spill valve is referred to, which allows a connection of the two pressure chambers 31 and 34 optionally. The function of this overflow valve 45, which can be switched to passage, will be explained later with reference to FIG. 4.

Fig. 3 shows a circuit diagram of a pump unit, which is usable with the hydraulic system according to FIG. The pump accumulator 11 in the hydraulic system according to FIG. 2 is dimensioned so that a multiplicity of working cycles of the hydraulic cylinder 3 from FIG. 2 can be carried out with the amount of working fluid stored therein. The consumption of working fluid for the pressure control by the regulator sections 41 and 42 is inherently very low, as already explained in the introduction.

The mobile pump unit 5 has a pump 10, a motor 18, a pressure relief valve 21 and a tank 20. Furthermore, components such as chassis, wheels, power supply for the motor 18 and other elements are provided, which are not shown here. The mobile pumping unit 5 is further provided with a delivery port 16 and a receiving port 17. These connections are preferably designed as quick couplings (not shown), so that the mobile pump unit 5 with the pressure supply 1 of Hydraulic system of Fig. 2 can be connected easily and without tools.

With rough calculations it can be shown that e.g. the cylinders for closing and pressing against each other rollers to form a nip also taking into account the need to open the nip at web break and close, with a charged pressure accumulator several weeks independent of a pump are operable. Since the charging process does not take long, can be ensured with a mobile pump unit, the pressure supply of many such equipped with pressure accumulator actuators in the hydraulic system with very little effort. In addition, because pipelines, the pump (s) itself and of course a large number of pipe connections can be saved, the capital expenditure is lower and the operational reliability increases.

The use of the mobile pumping unit also allows easy replacement or easy cleaning of the working fluid. Thus, the extracted from the tank, to be pumped with the pump in the pressure accumulator working fluid to be filtered. In this way, dirt particles or other solids from the working fluid can be removed, whereby damage to downstream components of the hydraulic circuit is prevented by these solids. Because the filters used only need to be present once, larger and possibly more efficient filters can be used. Optionally, the result, for example, when heavy contaminants occur at a filling point, ie when filling a pressure accumulator, for troubleshooting or fault diagnosis in the hydraulic system can be used. If the tank (not shown) assigned to the respective filling station is designed to be removable, then this tank can be exchanged for an empty tank and the pressure accumulator is filled with fresh (purified or new) working fluid. In this way, the replacement of the working fluid can be achieved regularly and almost completely in a simple manner, without stopping the machine, because the pressure supply is still available, even while the pressure accumulator is charged (filled).

Fig. 4 shows a portion of a hydraulic system with a digital hydraulic pressure regulator, a spill valve and a hydraulic

Differential cylinder in a schematic diagram. In this figure, analogous to FIG. 2, a digital-hydraulic pressure regulator 4 is shown, which has a piston rod-side regulator section 41 and a cylinder-side regulator section 42. This pressure regulator 4 is connected to a differential cylinder 3 and regulates the pressure and possibly the charge in the piston rod-side pressure chamber 31 and the cylinder-side pressure chamber 34 by controlled working fluid supplied to the chambers or discharged from them.

The pressure provided by a pressure source (not shown) is measured with the pressure sensor 14, while the pressures set by the regulator sections 41 and 42 in the two pressure chambers 31 and 34 are detected by pressure sensors 19.

Further, a connecting line with an overflow valve 45 is connected between the two controller sections 41, 42, which in the closed state, the controller sections 41, 42 and the pressure chambers 31, 34th separates each other. When the spill valve 45 opens, the two pressure chambers are connected or shorted together. As a rule, there is a load or force on the piston rod which tends to push the piston rod into the cylinder. If now the piston rod of the load to be drawn into the cylinder following, as occurs for example when opening a roll gap, the overflow valve 45 is opened and the control valves of the piston rod side controller section remain closed. The working fluid thus flows partly into the piston-side pressure chamber 31 and partly into the tank (not shown). The outflow into the tank is controlled by the cylinder-side regulator section 42 and thus controls the lowering speed of the piston rod.

Because the working fluid is short-circuited to fill the piston side pressure chamber 31, this amount of working fluid need not be taken out of the pressure supply. The working fluid must therefore not be first funded by the pump and brought to high pressure, in order then to be fed with regulated down pressure in the pressure chamber 31. Overall, the volume to be moved by the pump is reduced, saving energy.

Further, because the piston rod side controller section 41 remains off, eliminating the billing and control effort here. This halves the computational effort and the computing power in the computer of the controller and also saves the drive energy for the actuation of the valves.

In addition, results in a load of, for example, the piston rod with a mass from above, against which the cylinder from under counter, that the pressure in the piston rod-side chamber of a differential cylinder can be significantly smaller than the pressure in the cylinder-side chamber. If now the overflow valve is opened, the pressure between the two chambers is compensated. Due to the amount of fluid displaced between the chambers, the piston rod is moved a short distance following the mass. This movement is a very desirable opening pressure.

Fig. 5 shows a portion of the hydraulic system with two pressure accumulators 11, 12 with different working pressure, a digital hydraulic pressure reducer 13, digital hydraulic pressure regulators 4 and hydraulic differential cylinders 3 in a schematic diagram. A pump 10 pumps working fluid from a tank 20 into a pressure accumulator 11, which is connected via a supply line 100 on the high pressure side with the pressure reducer 13. In the pressure reducer 13, the working fluid is regulated down to a pressure which is not too high above the pressure to be delivered by the pressure regulators 4 to the cylinders 3. This approach is recommended because the quality of control (accuracy, overshoot, etc.) of digital hydraulic pressure regulators is better if the pressure difference is not very large.

In the arrangement of FIG. 5, working fluid is stored in the pressure accumulator 11 under high pressure. Working fluid having reduced pressure by the pressure reducer 13 is received in a low pressure accumulator 12. From the low-pressure accumulator 12, the two pressure regulators 4 are supplied with working fluid so as to drive the two cylinders 3, which are designed as differential cylinders.

The arrangement shown in Fig. 5 is a form suitable for a nip form of a hydraulic system, the two Cylinder has as actuators, for example, attack the two journals of a roller to adjust the roller and open a nip or to press the roller in a certain way against its counterpart.

For this purpose, the pressure in the pressure chambers 31, 34 of each cylinder 3 is separately controllable; such a regulation has already been described.

The concept shown in FIG. 5, which uses a low-pressure accumulator 12 common to a plurality of subsequent digital hydraulic pressure regulators, has the advantage, for example, that pressure fluctuations behind the pressure reducer 13 are damped. At the same time, a pressure accumulator also provides a working fluid reservoir that is capable of delivering larger volume flows in a short time. In the present case, the pressure reducer 13 can be designed for low volume flows (smaller valves require smaller drives with the same response), since the low-pressure accumulator 12 is able to deliver, if required, large volume flows of working fluid at a pressure level to the pressure regulator 4, the corresponds to the outlet pressure of the pressure reducer.

In FIG. 5, the pressure sensor, which detects the pressure in the high-pressure accumulator, is denoted by 15, while the pressure sensor for the low-pressure accumulator 12 is designated by 14. The pressures at the respective output of the individual controller sections 41, 42 are detected by pressure sensors 19.

The devices called pressure accumulators can pressure accumulator with a gas cushion with or without membrane, but also spring accumulator with a displaceable against a spring piston in a cylinder or other be equivalent memory. These stores can store the stored energy in the form of fluid (s) under pressure for a long time and without loss; Losses due to heating and / or friction occurring during storage or removal are negligible.

Fig. 6 shows a portion of a hydraulic system with a modified digital hydraulic pressure regulator 43, a switching valve 44 and a hydraulic

Differential cylinder 3 in a schematic diagram.

With the pressure regulator 43 of FIG. 6, the pressures and

Filling volumes of the pressure chambers 31, 34 of the as

Differential cylinder 3 configured actuator controlled; this was previously explained in detail with another controller design, so that a repetition is omitted here.

The pressure regulator 43 has two rows of valves 431 and 432 connected in parallel within the rows; these series of parallel valves are also referred to as valve banks. The valve banks may have the same structure as in the previously explained in detail pressure regulators 41, 42.

The pressure regulator 43 has a structure such as a regulator portion 41, 42 of the pressure regulator 4 described above with reference to Figs. 2, 4 and 5, which is a half pressure regulator. In addition, a changeover valve 44 is provided which can interchange the connection of the two valve banks 431 and 432 with the pressure feed line 100 and the discharge line 120 to the tank 20. The switching valve designed as a 4/2-way control valve is preferably a poppet valve which selectively pressurizes the piston rod-side valve bank 431 or the cylinder-side valve bank 432. The respective other valve bank is connected to the tank 20. The respective pressurized valve bank can supply working fluid into the connected pressure chamber 31, 34 of the cylinder 3, while working fluid from the other pressure chamber 31, 34 flows via the other valve bank into the tank.

During the movement of the piston, the volume of one pressure chamber decreases while the volume of the other pressure chamber increases; There are no operating conditions in which both pressure chambers are pressurized simultaneously or both are discharged simultaneously. Consequently, to retract the piston rod of the cylinder, the valve bank 431 may be connected to the pressure line 100, while in the pressure control for adjusting the force of the cylinder 3, only the cylinder-side pressure chamber 34 is pressurized by the valve bank 432, which then - by switching the switching valve 44 - is connected to the pressure line 100.

With this pressure regulator 43, the required number of valves can be halved compared to the pressure regulator 4 (FIGS. 2, 4 and 5). Thus, the investment costs for the hydraulic system of the machine can be reduced.

FIG. 7 shows an arrangement for detecting the piston position of differential cylinders 3 in a hydraulic system with digital pressure regulators 4.

A pump 10 supplies working fluid to two pressure regulators 4, each connected to a differential cylinder 3, via a flow meter 51, which measures the volume flow of working fluid supplied to the system by the pump 10. Flow meter 52 detects the flow of working fluid into the cylinder-side pressure chamber of the By the lossless operation of the digital hydraulic pressure regulator, the amount of working fluid detected by the flow meters 52 corresponds to the actual amount present in the respective cylinder-side pressure chambers, which is a reliable measure of the piston position.

Moving heavy loads, such as Rolling in a paper machine with two hydraulic cylinders 3 is always a synchronization problem of the movement of the two piston rods. The result of the flow measurements is a position sensor for the piston position, with the flow meters 52 should measure accurately. Preferably, gear systems are used that are relatively accurate. In addition, the flow measurement with the flow meter 51 in the supply line provides a further measured value, which can be used for the plausibility check of the results of the flow meter 52 for the pressure chambers.

Due to the indirect measurement, the absolute value for the piston position can also be slightly faulty, but the two measured values (each for one cylinder 3), which are detected simultaneously while being exposed to the same external influences, can be taken as indications of how synchronous they are The two pistons move, or whether the movements deviate from each other in an impermissibly strong manner. These findings can be used to improve synchronization, if necessary, with appropriate measures. Furthermore, it can also be concluded from the measured values of malfunctions in the hydraulic system.

Claims

claims

1. Hydraulic system for a machine for producing a fibrous web, in particular a paper or board machine, with at least one hydraulic actuator (3), at least one pressure accumulator (11, 12) for

Storage of a hydraulic working fluid under pressure, and at least one digital hydraulic pressure regulator (4) associated with the hydraulic actuator (3) and the

Pressure of the working fluid in the hydraulic actuator (3) sets.

2. A hydraulic system according to claim 1, further comprising a pump (10) to feed the working fluid at high pressure in the pressure accumulator (11, 12) and to charge this.

3. Hydraulic system according to claim 1 or 2, characterized in that the machine has a plurality of hydraulic actuators (3) and a plurality of pressure accumulators (11, 12), while the pump (10) is provided as a common pump, the accumulator

(11, 12).

4. Hydraulic system according to claim 1, 2 or 3, characterized in that the pump (10) is a mobile, to the respective pressure accumulators (11, 12) movable and detachably connectable thereto pump.

5. Hydraulic system according to claim 1, 2, 3 or 4, characterized in that each hydraulic actuator (3) or each group of equivalent hydraulic Actuators (3) is assigned its own digital hydraulic pressure regulator (4).

6. Hydraulic system according to one or more of claims 1 to 5, characterized in that the actuator is a hydraulic cylinder (3).

7. Hydraulic system according to claim 6, characterized in that the valves of the digital hydraulic pressure regulator (4) are mounted directly on the hydraulic cylinder (3).

8. A hydraulic system according to claim 6 or 7, characterized in that the pressure control function on the hydraulic cylinder (3) comprises the regulation of the pressure on both sides of a piston (33) of the hydraulic cylinder (3).

9. Hydraulic system according to claim 6, 7 or 8, characterized in that the hydraulic cylinder (3) with its own digital hydraulic pressure regulator (4), a dedicated pressure accumulator (11, 12) and a separate tank (20) connected to store unpressurized working fluid is.

10. Hydraulic system according to one or more of claims 1 to 5, characterized in that the actuator (3) is a hydraulic motor which is operatively connected in parallel with an electric drive motor with a rotating element to be driven of the machine.

11. A hydraulic system according to claim 10, characterized in that the hydraulic motor as a drive auxiliary unit or as a brake assist unit with the rotationally driven element is selectively coupled.

12. A hydraulic system according to claim 10 or 11, characterized in that the hydraulic motor is connected to its own digital hydraulic pressure regulator (4), its own pressure accumulator (11, 12) and a separate tank (20) for storing pressureless working fluid.

13. Hydraulic system according to claim 4 with claim 9 or 12, characterized in that the mobile pump (10) with the pressure accumulator (11, 12) and the tank (20) is connectable and the working fluid from the tank (20) into the pressure accumulator

(11, 12).

14. A hydraulic system according to claim 1, characterized in that the pressure accumulator (11) is provided with a downstream digital hydraulic pressure reducer (13) whose output to the at least one, the actuator (3) or the group of actuators associated digital hydraulic pressure regulator (4). is delivered.

15. Hydraulic system according to claim 1, characterized in that a common pressure accumulator (11, 12) is provided for a plurality of actuators (3) to which a plurality of individual digital hydraulic pressure regulator

(4) is connected, wherein between the accumulator (11) and the pressure regulators (4) is a common digital hydraulic pressure reducer (13) or a digital hydraulic pressure reducer (13) proceed for each digital hydraulic pressure regulator (4), the or the respective pressure regulator ( 4).

16. A hydraulic system according to claim 14 or 15, characterized in that between the digital hydraulic pressure reducer (13) and the digital hydraulic pressure regulator (4) or the digital hydraulic pressure regulators (4) Pressure accumulator (12) is provided which stores working fluid with the reduced pressure and to the or the digital hydraulic pressure regulator (4) outputs.

17. A hydraulic system according to claim 15 or 16, characterized in that the individual digital hydraulic pressure reducer (13) set individual, mutually different pressures for each downstream digital hydraulic pressure regulator (4).