EP2846994A1

EP2846994A1 - Method for operating a hydraulic press, and hydraulic press

Info

Publication number: EP2846994A1
Application number: EP13722386.3A
Authority: EP
Inventors: Matthias Graf; Bernd Bodenstein; Manfred Maier
Original assignee: Dieffenbacher GmbH Maschinen und Anlagenbau
Current assignee: Dieffenbacher GmbH Maschinen und Anlagenbau
Priority date: 2012-05-10
Filing date: 2013-05-07
Publication date: 2015-03-18
Anticipated expiration: 2033-05-07
Also published as: US20150083002A1; KR20150006476A; WO2013167630A1; JP2015522419A; RU2014149771A; DE102012104125A1; CN104284772B; EP2846994B1; CN104284772A

Abstract

The invention relates to a hydraulic press (10) and a method for operating a hydraulic press (10) in cycles. The aim of the invention is to lower energy consumption in a method for shaping workpieces by means of a hydraulic press and in a hydraulic press for shaping workpieces. With respect to the method, said aim is achieved in that each cycle has at least one phase in which the storage pressure p_sin the accumulator (15) causes hydraulic fluid to be pressed from a hydraulic accumulator (15) into a chamber (11.1, 11.2) of a hydraulic cylinder (11) of the press (10) in order to move a ram (12) of the press (10) relative to the cylinder (11), said ram, to which a tool (21) for shaping a workpiece can be coupled, being coupled to the cylinder (11); and in that in at least one portion of each cycle, a hydraulic pump (13) driven by a motor (14) delivers hydraulic fluid to the accumulator (15) at a charging volume flow rate, and the storage pressure p_sis adjusted to a reference value P_SOLLby setting the speed of the motor (14) to a nominal motor speed n_N and to at least one intermediate value n_z, where 0 < n_z < n_N. .

Description

Method for operating a hydraulic press and a hydraulic press

The invention relates to a method for operating a hydraulic press according to the preamble of claim 1 and a hydraulic press according to the preamble of claim 22. DE 25 44 794 A1 describes a hydraulic press consisting of a

Press frame, a hydraulic drive, an oil pump and two storage tanks. The hydraulic drive consists of a working cylinder with a working piston of larger diameter and a moving cylinder with a moving piston of smaller diameter. The pistons are firmly connected with each other at a distance. The working cylinder is from the first memory via a directional control valve and the

Movement cylinder fed from the second memory via a servo valve within a closed loop. The control loop consists of one

Setpoint generator, a control amplifier, the servo valve, a position transducer and a measuring amplifier. The directional control valve is designed as a valve with fixed switching positions. To protect the hydraulic system against excessively high pressures, a pressure limiting valve is arranged in the pressure line of the pump leading to the reservoirs. The amount of oil needed to drive the press is supplied by the pump from a tank via the reservoirs. The reservoirs are supplied with a compressible medium from a gas bottle. This document also describes the operation and operation of this press, in which the uppermost position of the hydraulic piston is the starting point. After the system is switched on and the reservoirs are filled, the setpoint generator sends a signal to the control amplifier. This actuates the servo valve in the

Position in which oil is released for the supply of the movement cylinder. The movement piston and thus the working piston firmly connected to it move downwards. This downward movement is transmitted to the transducer. The output signal of the position transducer is converted in the measuring amplifier into a signal proportional to the path, which is compared in the control amplifier with the setpoint signal. Deviations of the two signals are processed in the control amplifier and give correction signals to the servo valve. The control amplifier, the servo valve, the motion cylinder, the displacement transducer and the measuring amplifier So form a closed loop, which allows the movement of the movement piston proportional to an electrical signal coming from the setpoint generator. In this way, the working piston is moved to a precise position until shortly before or on the workpiece. During the second part of the working stroke, the pressing stroke, which is initiated by switching the directional control valve, the working piston is acted upon via the directional control valve from the first reservoir, which was previously filled with an amount of oil metered in accordance with the pressing stroke. This amount of oil causes a predetermined

Continuation of the movement of the working piston, which corresponds to the amount of oil metered in the first reservoir.

After the working piston has carried out the pressing stroke, the directional valve is switched back and the movement piston in the motion cylinder in the

Starting position moved back. The existing oil in the cylinder is thereby conveyed back via the directional control valve in the tank. During the work break, the pump fills the first memory again with the predetermined amount of pressure oil that can be specified by a limit switch on the first memory, which switches an oil valve in the leading to the first memory pressure line of the pump.

In this known method and this known press so the filling of the first memory is controlled to the predetermined amount of pressure oil during the work break by the charging volume flow is adjusted by switching the oil valve and / or changed. Since the first storage is acted upon by the compressible medium from the gas cylinder, this filling control corresponds to a regulation of the pressure prevailing in the first memory pressure to a pressure command variable, which depends on the limit switch and the compressible medium from the gas bottle. In this known control, the charge flow is set to zero by the oil valve is switched to a blocking position in which it separates the first memory from the pressure port of the pump. In a near-term way, the pump driven by the on-going motor increases the pressure in the pressure line until the pressure relief valve responds and connects the pressure port to the tank, causing the pump to idle at full speed. this leads to unnecessarily high energy consumption. In addition, the pump must be designed so large that it can promote the predetermined amount of pressure oil in the memory during the break.

It is an object of the invention to reduce energy consumption in a method for forming workpieces by means of a hydraulic press and a hydraulic press for forming workpieces.

This object is achieved by a method according to claim 1 and a press according to claim 22. Further possible embodiments and variants are described in the subclaims. According to a first aspect, the invention proposes a method for operating a hydraulic press in cycles, in particular for forming workpieces, wherein:

each cycle has at least one phase in which hydraulic fluid from a hydraulic accumulator (15) into a chamber (1 1 .1, 1 1 .2) of a hydraulic cylinder (1 1) of the accumulator pressure p _s prevailing in the accumulator (15) Press (10) is pressed to a to the cylinder (1 1) coupled to the plunger (12) of the press (10), to which a forming tool (21) for forming a workpiece, relative to the cylinder (1 1) move;

In at least part of each cycle, a hydraulic pump (13) driven by a motor (14) delivers hydraulic fluid into the reservoir (15) with a charge flow and the reservoir pressure p _s to a reservoir

Pressure control variable P _S OLL is controlled by a speed of the motor (14) to a rated speed n _{N of} the motor (14) and at least one

Intermediate value n _{z is} set, for which 0 <n _z <n _N holds.

Since thus in this proposed method, the setting of the

Charge volume flow by adjusting the speed of the motor to the rated speed n _N and at least one intermediate value n _z takes place and the energy requirement of the engine, for example, the fuel consumption of an internal combustion engine or the current consumption of an electric motor, at speeds below rated speed n _{N is} less than at rated speed n _N. , the energy consumption compared to that from the DE 25 44 794 A1 known methods can be lowered. As a result, the efficiency of the method can be increased. In addition, a reduction in the speed leads to a noise reduction.

Rated speed is understood here to be the maximum speed which the engine can provide permanently without damage or to which the engine is designed as intended.

The proposed method can be configured as desired in any manner and, for example, have the control of the accumulator pressure p _s in at least one additional phase.

For example, the press may be one of the presses proposed according to the second aspect described below.

The pump may be configured as desired in any manner, such as a gear pump, axial piston pump or radial piston pump.

The motor may be formed as desired in any manner and be, for example, an asynchronous motor, and the adjustment of its speed can be done as needed in any way, for example by means of a frequency converter.

In the closing phase, the driving or setting or lowering or lifting of the plunger takes place on the first lifting height, preferably starting from the third lifting height.

In the working phase, as required by the lowering of the plunger, the plunger can be kept at the second lifting height, for example by the pressure chamber is closed and / or separated from the reservoir and tank or is.

In the reset phase, the driving or setting or lowering or lifting of the plunger takes place on the third lifting height preferably without stopping at the first lifting height.

For example, the maximum pressure that the memory can endure without damage or to which the memory is designed as intended can simply be selected for the pressure guidance variable P _S OLL. The speed is preferably continuously at speeds from zero to

Nominal speed n _N set.

It can be provided that in at least one of the phases

Pressure command P _S OLL is selected as a function of at least one prevailing in one of the chambers chamber pressure p _K.

Then it can be provided that for the function P _S OLL = Ρκ ⁺ K _P , where K _{P is} a pressure correction value with 0 <K _P.

This ensures that the memory always provides sufficient overpressure compared to the often increasing during the phase chamber pressure p _K , on the other hand, however, is not too high, so that the engine does not run unnecessarily fast or the pump does not need to promote unnecessarily strong ,

The pressure correction value K _P can be arbitrarily selected as needed and

For example, be constant at least during part of the phase and / or at least during a part of the other phases. Alternatively or additionally, for example, it can be time-variable at least during part of the phase and / or at least during part of the other phases. Alternatively or additionally, it can be selected, for example, such that the pressure control variable PSOLL is greater than the chamber pressure p _K by a certain percentage. This percentage is for example at least 2% or at least 3% or at least 4% or at least 5% or at least 6% or at least 7% or at least 8% or at least 9% or at least 10% or at least 12% or at least 14% or at least 16 % or at least 18% or at least 20%. Alternatively, or in addition, this percentage is for example at most 2% or at least 3% or at most 4% or at most 5% or at most 6% or at most 7% or at most 8% or at most 9% or at most 10% or at most 12% or at most 14%. or at most 16% or at most 18% or at most 20%.

It can be provided that the regulation of the accumulator pressure p _s takes place in at least one of the phases. It can be provided that

each cycle has a closing phase for closing the press, a working phase for forming the workpiece, a reset phase for opening the press, and a loading phase for removing a deformed workpiece from the press and inserting a workpiece to be formed in the press in this order;

is moved in the closing phase of the plunger to a first lifting height, so that the forming tool touches the workpiece to be formed or is located at a small distance from the workpiece to be formed;

· In the working phase of the ram is further moved to a second lifting height, so that the forming tool presses against the workpiece;

is moved back in the reset phase of the plunger back to the first lifting height and further to a third lifting height, so that the forming tool is released from the formed workpiece and removed;

is held in the loading phase of the plunger at the third lifting height.

Then it can be provided that in the closing phase, the chamber is separated from the memory and connected to a tank or is or the chamber is separated from a tank and connected to the memory or is.

In the first alternative, the plunger can be lowered or moved passively by its own weight and / or actively by a closing drive in the closing direction or actively lifted or moved by a closing drive in the closing direction. This closing drive, for example, in comparison to a hydraulic drive for the working phase, which is preferably formed by a compression chamber in the cylinder and the memory, be smaller and / or weaker and / or faster and / or for example, have an additional hydraulic drive.

In the second alternative, the plunger is actively lowered or raised or moved by the accumulator in the closing direction.

It can be provided that in the working phase, the driving of the plunger takes place by a chamber forming the pressing chamber is separated from a tank and connected to the memory. Then it can be provided that in the return phase, the pressing chamber is separated from the memory and connected to the tank or is.

Thus, the plunger can be actively raised or moved in the return direction by a rear part drive or passively lowered or moved by its own weight and / or actively by a rear part drive in the return direction or moved. This

Rear part drive, for example, in comparison to a hydraulic drive for the working phase, which is preferably formed by a compression chamber in the cylinder and the memory, be smaller and / or weaker and / or faster and / or for example, have an additional hydraulic drive. This additional hydraulic drive preferably has a return chamber in the cylinder, which is separated, for example, by a guided in the cylinder, coupled to the plunger piston from the pressing chamber and separated in the reset phase of the tank and is connected to the memory or is.

It can be provided that in the loading phase, the chamber is closed and / or separated from the memory and a tank or is.

As a result, the plunger can be held at the third lifting height.

It can be provided that in the reset phase, the driving of the plunger takes place by a chamber forming the return chamber is separated from a tank and connected to the memory. Then it can be provided that in the working phase, the return chamber is separated from the memory and connected to the tank or is.

Then, the plunger can be actively raised or moved by a press drive in the closing direction. This press drive may for example be larger and / or stronger and / or slower compared to the hydraulic drive formed by the return chamber and memory and / or for example have an additional hydraulic drive. This additional hydraulic drive preferably has a pressing chamber in the cylinder, which is separated from the return chamber, for example by a guided in the cylinder, coupled to the plunger piston and is separated in the working phase of the tank and connected to the memory or is. In any proposed method, the charge volume flow, in particular for or when regulating the accumulator pressure p _s , can be set to zero in any desired manner as required. For example, it can be provided that the tank is connected to the pressure port, and that the charge flow, in particular for or when regulating the accumulator pressure p _s , is set to zero by connecting a pressure port of the pump to a tank. Alternatively or additionally, it may be provided that the charge volume flow, in particular for or during the regulation of the accumulator pressure p _s , is set to zero by setting the rotational speed of the engine to zero. By setting to zero, too rapid a rise in the accumulator pressure p _{s can be} slowed down or even stopped.

In the first variant, setting to zero can be done quickly.

In the second variant, the setting can be made to zero energy-saving.

It can be provided that:

· In each cycle, a charging duration T _{L is} determined, while the

Charge volume flow is greater than zero;

the charging duration T _{L is} controlled to a charging duration setpoint T _S OLL by the speed is set and / or changed accordingly.

In this way, the most uniform possible running of the motor and the pump, in which speed peaks are avoided, can be achieved if the charging duration setpoint T _S OLL is set as close to or just below the cycle time T _z .

The charging duration setpoint T _S OLL can be selected as required,

for example, such that it is smaller by a certain percentage than the cycle time T _z . This percentage is for example at least 2% or at least 3% or at least 4% or at least 5% or at least 6% or at least 7% or at least 8% or at least 9% or at least 10% or at least 12% or at least 14% or at least 16 % or at least 18% or at least 20%. Alternatively or additionally, this percentage is for example at most 2% or at least 3% or at most 4% or at most 5% or at most 6% or at most 7% or at most 8% or not more than 9% or not more than 10% or not more than 12% or not more than 14% or not more than 16% or not more than 18% or not more than 20%.

It can be provided that:

in a certain cycle, a cycle duration T _z and a charging time T _L , during which the charging volume flow is greater than zero, as well as one over the

Charge duration T _L averaged charge speed n _{L is} determined;

for at least one subsequent cycle, the speed to a

Intermediate value n _{z is} set for which n _z = n _L ^■ T _L : T _z + K _N , where K _{N is} a speed correction value with 0 <K _N <n _L ^■ (1-T _L : T _z ). As a result, as uniform as possible a run of the motor and the pump can be achieved, are avoided in the speed peaks. If 0 <K _N , the speed correction value K _N serves as a safety cushion, so that a pressure and volume reserve can be built up in the memory in the subsequent cycle. If, for example, in the one cycle T _L : T _z = 75% and n _L = 1600 min ^{"1 has been} determined, then 0 <K _N <1600 min ^{" 1} (1-75%) = 400 min ^{"1 should} apply accordingly. Thus, for the subsequent cycle, the third correction value K _{N may be,} for example, 0 min ^"1 or 50 min ^{" 1} or 100 min ^"1 or 150 min ^{" 1} or 200 min ^"1 or 250 min ^{" 1} or 300 min ^"1 or 350 min ^{" 1} and the intermediate value n _z accordingly 1200 min ^"1 or 1250 min ^{" 1} or 1300 min ^"1 or 1350 min ^{" 1} or 1400 min ^"1 or 1450 min ^{" 1} or 1500 min ^"1 or 1550 min ^{" 1} .

Then it can be provided that in the particular cycle:

first the speed is set to the rated speed n _N and

Thereafter, the accumulator pressure p _s , in particular exclusively, is controlled by the fact that the charge volume flow to zero and the speed to the

Nominal speed n _{N is} set.

This is preferably done after starting the press, wherein the particular cycle is in particular the first cycle after starting the press.

In this particular, especially the first cycle, that is, the charging time T _L over the average load speed n _L of the nominal speed _N n correspond. It can be provided that the charge volume flow through the regulation of Storage pressure p _{s is} set and / or changed such that, in particular in each phase or during the entire cycle, the accumulator pressure p _s does not fall below a lower operating pressure pu and / or does not exceed an upper operating pressure p ₀ . Adhering to the lower operating pressure pu, for example, in a memory having a gas as the compression medium, prevent this gas from entering the hydraulic circuit. The upper operating pressure p ₀ may, for example, be the maximum pressure that the accumulator can endure permanently without damage or to which the accumulator is designed as intended. Then it can be provided that pu ^ PSOLL ² Po applies.

It can be provided that:

at least one of the pressure command values P _S OLL and / or at least one of the intermediate values n _z and / or at least one of the charge duration setpoint values T _S OLL and / or at least one of the correction values K _P , K _{N is} stored;

In a later forming order for identical or similar workpieces, the stored values are used as initial values.

Thus, in a later forming order, the method can already be carried out with at least partially optimized values.

It can be provided that the accumulator pressure p _{s is} adjusted by means of an adaptive control.

It may then be provided that in the adaptive control at least one of the pressure-carrying variables P _S OLL and / or at least one of the intermediate values n _z and / or at least one of the charge duration setpoints T _S OLL and / or at least one of the

Correction values K _P , K _{N are} changed. In any proposed method, any separation, such as the

Separating the pressing chamber or the return chamber from the tank or the reservoir, and / or each connecting, for example connecting the pressing chamber or the return chamber with the memory or with the tank or connecting the pressure port with the memory or with the tank, and / or each closing, For example, the closing of the pressing chamber or the return chamber, for example by means of valves. Preferably, at least one valve between the reservoir and the compression chamber and / or at least one valve between the reservoir and the return chamber and / or at least one valve between the reservoir and the pressure port and / or at least one valve between the tank and the compression chamber and / or at least one valve between the tank and the return chamber and / or at least one valve between the tank and the pressure port be provided or seated.

Each valve may be configured as desired in any manner, such as a proportional valve or control valve or riser valve or directional control valve or check valve or pressure relief valve.

Any proposed method may be configured as desired in any manner and may, for example, have at least one additional phase.

Each of the presses used in one of the proposed methods may be configured as desired in any manner, such as at least one additional hydraulic cylinder and / or at least one additional ram and / or at least one additional hydraulic pump and / or at least one additional motor and / or have at least one additional hydraulic accumulator and / or at least one additional tank for hydraulic fluid. Each provided in this press cylinder can be formed as needed in any way and, for example, have at least one additional pressing chamber and / or at least one additional return chamber. Any pump provided in this press may be used as desired in any manner

be formed and, for example, have at least one additional pressure port.

The proposed methods may be combined as desired in any manner, in particular wholly or in part.

According to a second aspect, the invention proposes a hydraulic press, in particular for forming workpieces, comprising:

a hydraulic cylinder having at least one chamber, a plunger coupled to the cylinder and to which a forming tool for forming a workpiece can be coupled; a hydraulic pump having a pressure port,

a motor coupled to the pump and having a rated speed n _N , a hydraulic accumulator connected to at least one of the chambers and the pressure port,

a hydraulic fluid tank connected to at least one of the chambers,

a storage pressure sensor for detecting the storage pressure p _s prevailing in the storage;

a control unit which allows operation of the press in cycles and is connected to the accumulator pressure sensor and the motor;

in which:

the engine is designed such that its speed can be set to the rated speed n _N and to at least one intermediate value n _z for which 0 <n _z <n _N ;

the control unit is designed such that:

hydraulic fluid is forced from the reservoir into at least one of the chambers in at least one phase of each cycle by the accumulator pressure p _s to move the plunger relative to the cylinder;

in at least a part of each cycle, the pump delivers hydraulic fluid into the reservoir with a charge flow and the control unit regulates the reservoir pressure p _s to a pressure command P _S OLL by setting the rotational speed of the engine to the nominal rotational speed n _N and to at least one of the intermediate values n _z .

The proposed press can be designed as desired in any manner and, for example, have the control of the accumulator pressure p _s in at least one additional phase.

The proposed press makes it possible to carry out the method proposed according to the first aspect.

It can be provided that the press additionally has:

at least one chamber pressure sensor for detecting the in one of Chambers of prevailing chamber pressure p _K ;

in which:

the control unit is connected to each chamber pressure sensor;

the control unit is designed such that in at least one of the phases:

- The pressure command P _S OLL as a function of

chooses at least one of the chamber pressures p _K.

Then it can be provided that for the function P _S OLL = Ρκ ⁺ K _P , where K _{P is} a pressure correction value with 0 <K _P. It may be provided that the control unit is designed such that the regulation of the accumulator pressure p _s takes place in at least one of the phases.

It can be provided that:

the control unit is designed such that it:

- In the closing phase moves the plunger to a first lifting height, so that the forming tool touches the workpiece to be formed or is located at a small distance to the workpiece to be formed;

- In the working phase, the ram continues to a second lifting height, so that the forming tool presses against the workpiece;

- In the reset phase moves the plunger back to the first lifting height and further to a third lifting height, so that the forming tool is released from the formed workpiece and removed;

- Holds the plunger at the third lifting height during the loading phase.

Then it can be provided that the control unit is designed such that it separates at least one of the chambers in the closing phase of the memory and connects to the tank or at least one of the chambers separated from the tank and connects to the memory. It can be provided that the control unit is designed such that it causes the driving of the plunger in the working phase by separating a chamber forming the chamber from the tank and connects to the memory.

Then it can be provided that the control unit is designed such that it separates the pressing chamber from the memory in the return phase and connects to the tank.

It can be provided that the control unit is designed such that it closes at least one of the chambers in the loading phase and / or separates from the storage tank and tank. It can be provided that the control unit is designed such that, in the reset phase, it causes the ram to travel by separating a return chamber forming the chamber from the tank and connecting it to the accumulator.

Then it can be provided that the control unit is designed such that it separates the return chamber from the memory in the working phase and connects to the tank.

In any proposed press, the charge volume flow, in particular for or when regulating the accumulator pressure p _s , can be set to zero in any desired manner as required. For example, it can be provided that the tank is connected to the pressure port, and that the control unit is designed such that it sets the charge flow stream to zero by connecting the pressure port to the tank. Alternatively or additionally, it may be provided that the motor is designed such that its rotational speed can be set to zero, and that the control unit is designed such that it sets the charge flow stream to zero by setting the rotational speed to zero. It can be provided that the control unit is designed such that it:

- determined in each cycle, a charging time T _L , while the

Charge volume flow is greater than zero;

the charging duration T _L to a charging duration setpoint T _S OLL regulates by adjusting the speed accordingly and / or changes. It can be provided that the control unit is designed such that it:

in a certain cycle, a cycle duration T _z and a charging duration T _L , during which the charge volume flow is greater than zero, as well as an averaged over the charging time T _L charge speed n _L determined; - For at least one subsequent cycle, the speed to a

Intermediate value n _z for which n _z = n _L ^■ T _L : T _z + K _N , where K _{N is} a speed correction value with 0 <K _N <n _L ^■ (1-T _L : T _z ).

Then it can be provided that the control unit is designed such that in the particular cycle:

- first set the speed to the rated speed n _N and

thereafter regulating the accumulator pressure p _s , in particular exclusively, by setting the charge volume flow to zero and the rotational speed to the nominal rotational speed n _N. It may be provided that the control unit is designed such that it adjusts the charge volume flow by regulating the accumulator pressure p _s and / or changes that the accumulator pressure p _s does not fall below a lower operating pressure pu and / or an upper operating pressure p ₀ not exceeds.

Then it can be provided that pu ^ PSOLL ^ Po holds. It can be provided that the control unit is designed such that it:

- at least one of the pressure command variables PSOLL and / or at least one of the intermediate values _for n and / or at least one of the charging time setpoints T _S OLL and / or stores at least one of the correction values K _P, K _N;

- in a later Umformauftrag for the same or similar

Workpieces use the stored values as initial values.

It may be provided that the control unit is designed such that it can set or set the accumulator pressure p _s by means of an adaptive control. Then it can be provided that the control unit is designed such that it at least one of the pressure command variables PSOLL and / or in the adaptive control at least one of the intermediate values n _z and / or at least one of the charging duration setpoint values T _S OLL and / or at least one of the correction values K _P , K _{N can} change or change.

It can be provided that it additionally has:

at least one valve between the reservoir and the pressure chamber and / or at least one valve between the reservoir and the return chamber and / or

at least one valve between the reservoir and the pressure port and / or

at least one valve between the tank and the pressure chamber and / or at least one valve between the tank and the return chamber and / or at least one valve between the tank and the pressure port;

in which:

the control unit is connected to the valves.

With the help of these valves, the control unit may, for example, separating the pressing chamber or the return chamber from the tank or the memory and / or connecting the pressing chamber or the return chamber with the memory or with the tank or connecting the pressure port with the memory or with the tank and or cause the closure of the compression chamber or the return chamber or perform.

Each valve may be configured as desired in any manner, such as a proportional valve or control valve or riser valve or directional control valve or check valve or pressure relief valve. Each proposed press may be formed as desired in any manner and for example at least one additional hydraulic cylinder and / or at least one additional plunger and / or at least one additional hydraulic pump and / or at least one additional motor and / or at least one additional hydraulic accumulator and / or at least one additional tank for hydraulic fluid and / or at least one additional control unit and / or at least one additional pressure sensor. Everyone Cylinder may be formed as desired in any manner and, for example, have at least one additional pressing chamber and / or at least one additional return chamber. Each pump may be configured as desired in any manner and, for example, have at least one additional pressure port.

The statements relating to one of the aspects of the invention, in particular to individual features of this aspect, also apply analogously to the other aspects of the invention, in particular to corresponding individual features of this aspect. Hereinafter, embodiments and embodiments of the invention will be described by way of example with reference to the accompanying drawings. However, the resulting individual features are not on the individual

Embodiments and embodiments are limited, but may be combined with individual features described above and / or with individual features of other embodiments and embodiments. The details in the drawings are to be interpreted as illustrative, but not restrictive. The reference signs contained in the claims are not intended to limit the scope of the invention in any way, but merely refer to the embodiments shown in the drawings. The drawings show in: FIG. 1 is an overview diagram of a preferred embodiment of a

hydraulic press, wherein the press is in a state according to a closing phase of a cycle of a preferred embodiment of a method for operating the press;

FIG. 2 is a graph of the time history of the accumulator pressure in the memory of the press of FIG. 1, the way of the plunger of the press and the

Speed of the motor of the press over three cycles of the process.

In FIG. 1 schematically shows a preferred embodiment of a hydraulic press 10 which can be operated in cycles, each of which has a closing phase, a working phase, a return phase and a loading phase in this order. The press 10 has a hydraulic cylinder 1 1, a plunger 12, a boost pressure pump or hydraulic pump 13, a motor 14, a hydraulic accumulator 15, a Vorfüllbehälter or tank 16 for

Hydraulic fluid, a control unit 17, three pressure sensors 18.1 to 18.3, three valves 19.1 to 19.3 and a frequency converter 20 on. The cylinder 1 1 has two chambers, namely a pressing chamber 1 1.1 and a

Return chamber 1 1 .2, and a piston 1 1 .3, which is guided in the cylinder 1 1 and the adjacent to its upper side pressing chamber 1 1 .1 of the adjacent to its underside return chamber 1 1 .2 separates. The plunger 12 is attached at its upper end to the underside of the piston 1 1.3 and thus coupled to the cylinder 1 1 and holds at its lower end a coupled thereto forming tool 21 for

Forming a workpiece. The pump 13 has a suction port 13.1 and a pressure port 13.2. The motor 14 is coupled as a drive to the pump 15. The memory 15 is connected to the pressing chamber 1 1.1, the return chamber 1 1 .2 and the pressure port 13.2 and formed by way of example as a hydraulic accumulator with a nitrogen-filled pressure vessel. The tank 16 is connected to the pressing chamber 1 1.1, the return chamber 1 1 .2 and the suction port 13.1.

The motor 14 is an example of a induction motor and has a nominal rotational speed n _N, which is exemplified 2000 min ^'1. The drive 20 is on one hand connected to the motor 14 and on the other hand to the control unit seventeenth The control unit 17 is configured such that the rotational speed of the motor 14 continuously or almost continuously from zero to the nominal speed n _N and thus to zero at the rated speed n _N and at least one intermediate value can be set n _z by appropriately controlling the frequency converter 20, for 0 <n _z <n _N applies ,

The control unit 17 is also connected to the pressure sensors 18, of which a storage pressure sensor 18.1 for detecting the pressure prevailing in the memory 15

Storage pressure p _s is used, a first chamber pressure sensor 18.2 for detecting the prevailing in the pressing chamber 1 1 .1 working pressure p _A and a second

Chamber pressure sensor 18.3 for detecting the in the return chamber 1 1 .2

prevailing reset pressure p _R. The control unit 17 is also connected to the valves 19, which are exemplary directional valves and of which a first valve 19.1 between the pressing chamber 1 1.1 and the memory 15 and between the pressing chamber 1 1.1 and the tank 16 is seated, a second valve 19.2 between the return chamber 1 1 .2 and the memory 15 and between the return chamber 1 1 .2 and the tank 16 is seated and a third valve 19.3 between the pressure port 13.2 and the memory 15 and the

Pressure port 13.2 and the tank 16 is seated. The first valve 19.1 is a 3/3-way valve, so has three connections for hydraulic fluid lines and three

Switch positions, and can optionally separate the pressing chamber 1 1 .1 of the tank 16 and connect to the memory 15 or separate from the memory 15 and connect to the tank 16 or separate from the memory 15 and tank 16. The second valve 19.2 is a 3/3-way valve and can optionally separate the return chamber 1 1.2 from the tank 16 and connect to the memory 15 or separate from the memory 15 and connect to the tank 16 or separate from the memory 15 and tank 16. The third valve 19.3 is a 3/2 way valve, thus has three connections for hydraulic fluid lines and two switching positions, and can selectively disconnect the pressure port 13.2 from the tank 16 and connect to the memory 15 or separate from the memory 15 and connect to the tank 16.

In FIG. 2 are three cycles of a preferred embodiment of a method of operating the press 10 of FIG. 1 and for forming workpieces by means of the press 10 of FIG. 1 schematically illustrated over time the storage pressure p _s in the memory 15, the path H of the plunger 12 and the speed n of the motor 14 over time.

The control unit 17 allows cyclic operation of the press 10 according to this preferred embodiment of the method. It is designed such that in each cycle it lowers the plunger 12 and thus the forming tool 21 coupled to it in the closing phase to a first lifting height H1, in the working phase further lowers to a second lifting height H2 and stops there, in the reset phase back over the first lifting height H 1 and continues to a third lifting height H3 and stops in the loading phase on the third lifting height H3. In FIG. 2 is to recognize the closing phase on the steeply sloping segment of the H-line to recognize the working phase on the adjoining flat sloping and then horizontal segment, the reset phase to recognize the subsequent flat and then steeply rising segment, and the Beschickphase the it subsequent horizontal segment to recognize.

The sinking of the plunger 12 and the forming tool 21 in the closing phase reaches or effects the control unit 17 by separating the pressing chamber 11.1 and the return chamber 11.2 from the memory 15 by correspondingly activating the first valve 19.1 and the second valve 19.2 connects to the tank 16. Thus, the piston 1 1 .3, the plunger 12 and the forming tool 21 are pulled down by their own weight. In this case, hydraulic oil is sucked from the tank 16 into the pressing chamber 1 1.1 and pressed from the return chamber 1 1 .2 in the tank 16. The lowering of the plunger 12 and the forming tool 21 in the working phase reaches or causes the control unit 17 by separating the pressing chamber 1 1.1 from the tank 16 by appropriate activation of the first valve 19.1 and connecting it to the storage 15. The memory 15 is almost fully charged after starting the press 10 and thus at the beginning of the first cycle, so that the accumulator pressure p _{s is} just below an upper operating pressure p ₀ , which corresponds to the maximum pressure that the memory 15 can withstand without damage in the long run can or on which he is designed as intended. Thus, the piston 1 1 .3, the plunger 12 and the forming tool 21 by the in the memory 15 under the accumulator pressure p _s standing hydraulic oil against the forming force

or the forming pressure, pressed down. In this case, hydraulic oil from the memory 15 in the pressing chamber 1 1.1 and from the return chamber 1 1 .2 pressed into the tank 16.

The holding of the plunger 12 and the forming tool 21 in the working phase reaches or causes the control unit 17 by the pressing chamber 1 1 .1 separated from the memory 15 and tank 16 by corresponding driving the first valve 19.1 and so closes. Since thus neither the enclosed in the pressing chamber 1 1.1

Hydraulic oil still flow hydraulic oil in the pressing chamber 1 1.1 can flow, the piston 1 1.3, the plunger 12 and the forming tool 21 are held motionless. The lifting of the plunger 12 and the forming tool 21 in the reset phase reaches or causes the control unit 17 by driving by appropriate of the first valve 19.1, the pressing chamber 1 1 .1 separated from the memory 15 and connects to the tank 16 and by corresponding driving the second valve 19.2, the return chamber 1 1.2 separates from the tank 16 and connects to the memory 15. Thus, the piston 1 1 .3, the plunger 12 and the forming tool 21 are pushed up by the in the memory 15 under the accumulator pressure p _s standing hydraulic oil. In this case, hydraulic oil from the memory 15 in the return chamber 1 1.2 and from the pressing chamber 1 1 .1 pressed into the tank 16.

The control unit 17 is also designed such that it loads the memory 15 as needed in all phases, that is, depending on the currently required working pressure p _A and return pressure p _R , with a charge volume flow.

The loading of the memory 15 reaches or causes the control unit 17 by adjusting the speed of the motor 14 by correspondingly activating the frequency converter 20 so that it drives the pump 13, and disconnects the pressure connection 13.2 from the tank 16 by appropriately activating the third valve 19.3 connects to the memory 15. Thus, the pump 13 sucks hydraulic oil from the tank 16 and pushes it with a charge volume flow that of the means of

Frequency converter 20 set speed of the motor 14 depends, in the memory 15th

In this preferred embodiment, the control unit 17 is also designed such that in all phases, the memory pressure p _s on a

Pressure control PSOLL regulates by the speed and thus the

Charge volume adjusted accordingly, as described in more detail below.

The setting of the speed for demand-pressure control reaches or causes the control unit 17 by the speed by suitable driving of the

Frequency converter 20 continuously from zero to the rated speed n _N and thus to zero, to the rated speed n _N and to intermediate values n _z sets, for the 0 <n _z <n _N n.

The control of the accumulator pressure p _s attains or causes the control unit 17, in that in the FIG. 2 first cycle after starting the press 10 first sets the speed to the rated speed n _N and then the accumulator pressure p _s only by adjusting either the charge flow to zero by setting the speed to zero, or the speed to the

Nominal speed n _N sets as well as a cycle time T _z and a charging time T _L , during which the charge volume flow is greater than zero, and a calculated over the charging time T _L charge speed n _L determined.

In FIG. 2, the control unit 17 for this first cycle has the example

Speed n in the closing phase to 0% of the rated speed n _N , in an initial stage of the working phase to 100% of the rated speed n _N , in a subsequent end portion of the working phase to 0% of the rated speed n _N , in the reset phase and in an initial portion of the feed phase to 100% of

Rated speed n _N and then in a subsequent end portion of the feed phase to 0% of the rated speed n _N. In this example, it has determined the value 75% of the cycle duration T _z for the charging duration T _L and the value 100% of the rated rotational speed n _N for the charging rotational speed n _L. In this preferred embodiment, the control unit 17 is also designed such that it is suitable for the in FIG. 2, when controlling, sets the speed from zero to a maximum intermediate value n _z , for which n _z = n _L ^■ T _L : T _z + K _N , where K _{N is} a speed correction value with 0 <K _N <n _L ^■ (1 - T _L : T _z ). By way of example, the speed ^{correction value} K _N = 5% ^■ n _N applies. Since the control unit 17 has determined T _L : T _z = 75% and n _L = 100% ^■ n _N = n _N in the first cycle, it calculates n _L ^■ T _L : T _z = n _N ^■ 75% for the second cycle and n _z = n _N ^■ 75% + 5% ^■ n _N

= 80% ^■ n _N.

In this preferred embodiment, the control unit 17 is also designed such that it again in the second cycle analogous to the first cycle determines the cycle time T _z , the charging time T _L and the charging speed n _L.

In FIG. 2, the control unit 17 for this second cycle has set, for example, the rotational speed n in an initial portion of the closing phase to 0% of the nominal rotational speed n _N , in a subsequent end phase of the closing phase and

Working phase to 60% of the rated speed n _N , in the reset phase and in an initial section of the loading phase to the maximum intermediate value n _z , ie 80% of the rated speed n _N and then in a subsequent end of the Charging phase to 0% of rated speed n _N It has in this example for the cycle duration T _z the same value as in the first cycle determined, for the charging time T _L a greater value than in the first cycle and for the charging speed n _L a smaller value than in the first cycle.

In this preferred embodiment, the control unit 17 is also designed such that it is suitable for the in FIG. 2 and each subsequent cycle analogously to the first and second Teilzugmittel sets the speed from zero to a maximum intermediate value n _z in the rules for which n _z = n _L ^■ T _L : T _z + K _N , where the cycle duration T _z , the charging time T _L and the charging speed n _L come from the respective previous cycle. (1435)

List of Reference Numerals: P1435

10 press

1 1 cylinder

1 1.1 Press chamber of 1 1

1 1.2 return chamber of 1 1

1 1.3 piston of 1 1

12 pestles

13 pump

13.1 suction connection of 13

13.2 Pressure connection of 13

14 engine

15 memory

16 tank

17 control unit

18 pressure sensors

19 valves

0 Frequency converter 1 Forming tool

Claims

claims

1. A method of operating a hydraulic press (10) in cycles, wherein: each cycle comprises at least one phase, in the ruling by the memory (15) accumulator pressure p _s hydraulic fluid from a hydraulic accumulator (15) in a chamber (1 1 .1, 1 1 .2) of a hydraulic cylinder (1 1) of the press (10) is pressed to a to the cylinder (1 1) coupled plunger (12) of the press (10) to which a forming tool (21) for forming a workpiece can be coupled to move relative to the cylinder (1 1);

in at least a part of each cycle, a hydraulic pump (13) driven by a motor (14) delivers hydraulic fluid into the reservoir (15) with a charge flow and the reservoir pressure p _s to a reservoir

Pressure command PSOLL is controlled by a speed of the motor (14) to a rated speed n _{N of} the motor (14) and at least one

Intermediate value n _{z is} set, for which 0 <n _z <n _N holds.

2. The method of claim 1, wherein in at least one of the phases:

the pressure command PSOLL is selected as a function of at least one in one of the chambers (1 1 .1, 1 1.2) prevailing chamber pressure p _K.

3. The method of claim 2, wherein:

for the function PSOLL = Ρκ + K _P , where K _{P is} a pressure correction value with 0 <K _P.

4. The method according to any one of the preceding claims, wherein:

the control of the accumulator pressure p _s takes place in at least one of the phases.

5. The method according to any one of the preceding claims, wherein:

each cycle a closing phase to close the press (10), one

Working phase for forming the workpiece, a reset phase for opening the press (10) and a loading phase for removing a formed workpiece from the press (10) and for inserting a workpiece to be formed in the press (10) in this order; is moved in the closing phase of the plunger (12) to a first lifting height, so that the forming tool (21) touches the workpiece to be formed or is located at a small distance from the workpiece to be formed;

in the working phase of the plunger (12) is further moved to a second lifting height, so that the forming tool (21) presses against the workpiece;

is moved back in the reset phase of the plunger (12) back to the first lifting height and further to a third lifting height, so that the forming tool (21) dissolves and removes from the formed workpiece;

is held in the loading phase of the plunger (12) at the third lifting height.

Method according to claim 5, wherein in the closing phase:

the chamber (1 1.1, 1 1.2) separated from the memory (15) and connected to a tank (16); or

the chamber (1 1.1, 1 1.2) separated from a tank (16) and connected to the memory (15).

Method according to claim 5 or 6, wherein in the working phase:

the driving of the plunger (12) takes place by forming a chamber

Pressing chamber (1 1.1) separated from a tank (16) and connected to the memory (15).

Method according to claim 7, wherein in the reset phase:

the pressing chamber (1 1.1) separated from the memory (15) and connected to the tank (16).

Method according to one of claims 5 to 8, wherein in the feed phase: the chamber (1 1.1, 1 1.2) is closed and / or separated from the memory (15) and a tank (16).

Method according to one of claims 5 to 9, wherein in the return phase: the driving of the plunger (12) takes place by a chamber forming the

Return chamber (1 1.2) separated from a tank (16) and connected to the memory (15).

1 1. Method according to claim 10, wherein in the working phase:

The return chamber (1 1.2) is separated from the reservoir (15) and connected to the tank (16) is connected.

12. The method according to any one of the preceding claims, wherein:

the tank (16) is connected to the pressure port (13.2);

the charge flow is set to zero by a pressure port

(13.2) of the pump (13) is connected to a tank (16).

13. The method according to any one of the preceding claims, wherein:

the charge flow is set to zero by setting the speed to zero.

14. The method according to any one of the preceding claims, wherein:

in each cycle, a charging duration T _{L is} determined while the

Charge volume flow is greater than zero;

the charging duration T _{L is} controlled to a charging duration setpoint T _S OLL by the speed is set.

15. The method according to any one of the preceding claims, wherein:

in a certain cycle, a cycle duration T _z and a charging duration T _L , during which the charge volume flow is greater than zero, as well as an averaged over the charging time T _L charge speed n _{L is} determined;

for at least one subsequent cycle, the speed to a

Intermediate value n _{z is} set for which n _z = n _L ^■ T _L : T _z + K _N , where K _{N is} a speed correction value with 0 <K _N <n _L ^■ (1-T _L : T _z ).

16. The method of claim 15, wherein in the particular cycle:

first the speed is set to the rated speed n _N and

Thereafter, the accumulator pressure p _s is controlled by the fact that the

Charge volume flow to zero and the speed is set to the rated speed n _N.

17. The method according to any one of the preceding claims, wherein:

the charge volume flow is adjusted by regulating the accumulator pressure p _s such that the accumulator pressure p _s does not fall below a lower operating pressure pu and / or does not exceed an upper operating pressure p _Q.

18. The method of claim 17, wherein:

Pu ^ PSOLL ^ Po applies.

19. The method according to any one of the preceding claims, wherein:

20. The method according to any one of the preceding claims, wherein:

the accumulator pressure p _{s is set} by means of an adaptive control.

21. The method of claim 20, wherein:

at least one of the pressure command values P _S OLL and / or at least one of the intermediate values n _z and / or at least one of the charge duration setpoint values T _S OLL and / or at least one of the correction values K _P , K _{N is} changed during the adaptive control.

22. Hydraulic press (10), comprising:

a hydraulic cylinder (1 1) having at least one chamber (1 1 .1, 1 1 .2);

a plunger (12) which is coupled to the cylinder (1 1) and to which a forming tool (21) for forming a workpiece can be coupled;

a hydraulic pump (13) having a pressure port (13.2);

a motor (14) coupled to the pump (13) and having a rated speed n _N ;

a hydraulic accumulator (15) which is connected to at least one of the chambers (1 1 .1, 1 1 .2) and the pressure port (13.2);

a tank (16) for hydraulic fluid, which is connected to at least one of the chambers (1 1.1, 1 1 .2);

a storage pressure sensor (18.1) for detecting the accumulator pressure p _s prevailing in the accumulator (15);

a control unit (17) allowing operation of the press (10) in cycles and connected to accumulator pressure sensor (18.1) and motor (14);

in which:

the motor (14) is designed such that its speed can be set to the rated speed n _N and to at least one intermediate value n _z for which 0 <n _z <n _N ;

the control unit (17) is designed such that:

- Is pressed in at least one phase of each cycle by the accumulator pressure p _s hydraulic fluid from the memory (15) in at least one of the chambers (1 1 .1, 1 1 .2) to the plunger (12) relative to the cylinder (1 1 ) to move;

in at least part of each cycle the pump (13)

Hydraulic fluid in the memory (15) with a charge volume flow promotes and the control unit (17) the accumulator pressure p _s to a

Pressure command PSOLL regulates by adjusting the speed of the motor (14) to the rated speed n _N and at least one of the intermediate values n _z .

The press (10) of claim 22, further comprising:

at least one chamber pressure sensor (18.2, 18.3) for detecting the chamber pressure p _K prevailing in one of the chambers (1 1 .1, 1 1.2); the control unit (17) is connected to each chamber pressure sensor (18.2, 18.3);

the control unit (17) is designed such that in at least one of the phases:

- The pressure command P _S OLL as a function of

chooses at least one of the chamber pressures p _K.

The press (10) of claim 23, wherein:

A press (10) according to any one of claims 22 to 24, wherein:

the control unit (17) is designed such that:

- The regulation of the accumulator pressure p _s in at least one of the phases he follows.

A press (10) according to any one of claims 22 to 25, wherein:

each cycle a closing phase to close the press (10), one

Working phase for forming the workpiece, a reset phase for opening the press (10) and a loading phase for removing a formed workpiece from the press (10) and for inserting a workpiece to be formed in the press (10) in this order; the control unit (17) is designed such that it:

- moves the plunger (12) to a first lifting height in the closing phase,

so that the forming tool (21) touches the workpiece to be formed or at a small distance from the reshaping

Workpiece is located;

- In the working phase, the plunger (12) continues to a second lifting height, so that the forming tool (21) presses against the workpiece;

- moves in the reset phase, the plunger (12) back to the first lifting height and further to a third lifting height, so that the forming tool (21) dissolves and removes from the formed workpiece;

- Holds the plunger (12) at the third lifting height in the loading phase.

27. The press (10) of claim 26, wherein:

· The control unit (17) is designed such that in the closing phase:

- At least one of the chambers (1 1.1, 1 1 .2) separates from the memory (15) and connects to the tank (16); or

- At least one of the chambers (1 1.1, 1 1 .2) separates from the tank (16) and connects to the memory (15).

A press (10) according to claim 26 or 27, wherein:

the control unit (17) is designed such that it is in the working phase:

- Driving the plunger (12) causes, by a chamber

forming pressing chamber (1 1 .1) from the tank (16) separates and with the

Memory (15) connects. 29. The press (10) of claim 28, wherein:

the control unit (17) is designed such that in the reset phase: - The pressing chamber (1 1.1) from the memory (15) separates and connects to the tank (16).

A press (10) according to any one of claims 26 to 29, wherein:

the control unit (17) is designed such that in the loading phase:

- At least one of the chambers (1 1.1, 1 1 .2) closes and / or from memory (15) and tank (16) separates.

A press (10) according to any one of claims 26 to 30, wherein:

the control unit (17) is designed such that in the reset phase:

- Driving the plunger (12) causes, by a chamber

forming return chamber (1 1 .2) from the tank (16) separates and connects to the memory (15).

The press (10) of claim 31, wherein:

the control unit (17) is designed such that it is in the working phase:

- The return chamber (1 1.2) from the memory (15) separates and connects to the tank (16).

A press (10) according to any one of claims 22 to 32, wherein:

the tank (16) is connected to the pressure port (13.2);

the control unit (17) is designed such that it:

- Sets the charge flow to zero by connecting the pressure port (13.2) to the tank (16).

A press (10) according to any one of claims 22 to 33, wherein:

the motor (14) is designed so that its speed can be set to zero;

the control unit (17) is designed such that it:

- Sets the charge volume flow to zero by setting the speed to zero.

A press (10) according to any one of claims 22 to 34, wherein:

the control unit (17) is designed such that it:

a charge duration T _{L is} determined in each cycle, while that of the

Charge volume flow is greater than zero; the charging duration T _L to a charging duration setpoint T _S OLL regulates by adjusting the speed.

A press (10) according to any one of claims 22 to 35, wherein:

the control unit (17) is designed such that it:

in a certain cycle, a cycle duration T _z and a charging duration T _L , during which the charge volume flow is greater than zero, as well as an averaged over the charging time T _L charge speed n _L determined;

for at least one subsequent cycle, set the speed to an intermediate value n _z for which n _z = n _L ^■ T _L : T _z + K _N , where K _{N is} a speed correction value with 0 <K _N <n _L ^■ (1 - T _L : T _z ) is.

The press (10) of claim 36, wherein:

the control unit (17) is designed such that in the particular cycle:

- first set the speed to the rated speed n _N and

then regulates the accumulator pressure p _s by the fact that they

Charge volume flow to zero and the speed to the rated speed n _N.

A press (10) according to any one of claims 22 to 37, wherein:

the control unit (17) is designed such that it:

- Sets the load flow through the control of the accumulator pressure p _s such that the accumulator pressure p _s does not fall below a lower operating pressure Pu and / or does not exceed an upper operating pressure p ₀ .

The press (10) of claim 38, wherein:

Pu ^ PSOLL ^ Po applies.

A press (10) according to any of claims 22 to 39, wherein:

the control unit (17) is designed such that it:

at least one of the pressure-carrying variables P _S OLL and / or at least one of the intermediate values n _z and / or at least one of the

Charge duration setpoint values T _S OLL and / or at least one of the correction values Κ _Ρ , K _N stores;

41. A press (10) according to any one of claims 22 to 40, wherein:

The control unit (17) is designed such that it:

- Sets the accumulator pressure p _s by means of an adaptive control.

42. The press (10) of claim 41, wherein:

the control unit (17) is designed such that it:

- n _z, and / or at least one of the charging time setpoints T _S OLL and / or at least one of the correction values K _P, K _N are changes in the adaptive control at least one of the pressure command variables PSOLL and / or at least one of the intermediate values.

43. The press (10) of any one of claims 22 to 42, further comprising:

at least one valve (19.1) between the reservoir (15) and the pressing chamber (1 1 .1) and / or

at least one valve (19.2) between the reservoir (15) and the

Return chamber (1 1.2) and / or

at least one valve (19.3) between the reservoir (15) and the

Pressure connection (13.2) and / or

· At least one valve (19.1) between the tank (16) and the baling chamber

(1 1 .1) and / or

at least one valve (19.2) between the tank (16) and the return chamber

(1 1 .2) and / or

at least one valve (19.3) between the tank (16) and the pressure port (13.2);

in which:

the control unit (17) is connected to the valves (19).