EP2328747B1 - Accumulator-free hydraulic drive system for a consumer and comprising the same, especially for hydraulic presses, and method for hydraulically driving a consumer without an accumulator - Google Patents

Description

FIELD OF THE INVENTION

The invention relates to a pressure accumulator-free hydraulic drive assembly with the features of the preamble of claim 1. Accordingly, the drive assembly comprises a consumer with two oppositely acting pressure chambers, one of which via a first pressure line and a pump assembly and the other via a second pressure line and the pump assembly Pressure medium can be supplied, for example, to actuate a consumer in the form of a piston / cylinder unit in a working stroke and retrieve in a return stroke to the starting position. The invention further relates to a method for accumulatorless hydraulic driving a consumer according to the features of the preamble of claim 14.

TECHNICAL BACKGROUND

Circuits for the motion control of hydraulic consumers, such as differential cylinders, are today realized in the vast majority in such a way that a working pump is constantly driven by an asynchronous motor. The pumped hydraulic oil flows to a directional valve, in its rest position (closed state), the hydraulic oil, which conveys the pump, flows back to the storage tank without pressure. If the piston of the piston / cylinder unit extend, then the controlling directional valve is switched to a first working position, in which the hydraulic oil flows into the first pressure chamber (piston chamber) of the working cylinder, so that the piston rod extends. The oil displaced in the pressure space opposite the piston chamber with respect to the piston (annular space around the piston rod of the piston / cylinder unit) flows back into the tank via the directional control valve. To return the working piston, the directional control valve is transferred to a second working position, in which the pumped by the working hydraulic oil is pumped into the annular space of the piston / cylinder unit instead of the piston chamber, while the piston chamber is now connected via the return line to the hydraulic oil tank. A pressure limiting valve limits the system pressure to the permissible level. If the limit pressure is exceeded, hydraulic oil can flow off into the tank without pressure.

• In Ruhepausen des Systems läuft der elektrisch betriebene Antriebsmotor ständig weiter und verbraucht Energie;
• soll der Arbeitskolben Arbeit verrichten, so steigt der Systemdruck und das Hydrauliköl wird um etwa 1 % komprimiert. Beim Umsteuern zum Rückhub wird die zuvor im Hydrauliköl gespeicherte Energie nutzlos in Wärme umgesetzt, die das Öl aufheizt und nicht zurück gewonnen werden kann;
• soll mit dem System ein Kolben exakt positioniert werden, so setzt man im Regelfall stufenlos ansteuerbare Proportionalventile oder, seltener, aufwändige Pumpen mit verstellbarem Förderstrom ein. Im ersteren Fall wird beim Drosseln des Ölstroms wiederum Energie vernichtet; im zweiten Fall ist ein erheblicher baulicher Aufwand erforderlich.

Drive arrangements according to this concept have been implemented in large numbers and work reliably and safely. However, the controls also have significant disadvantages:

• During rest periods of the system, the electrically driven drive motor continues to run and consumes energy;
• If the working piston is to work, the system pressure increases and the hydraulic oil is compressed by about 1%. When reversing the return stroke, the energy previously stored in the hydraulic oil is uselessly converted into heat, which heats the oil and can not be recovered;
• If a piston is to be precisely positioned with the system, normally infinitely controllable proportional valves or, more rarely, complex pumps with adjustable flow rate are used. In the former case, when throttling the oil flow, energy is again destroyed; in the second case, a considerable construction effort is required.

With the emergence of powerful, speed and direction variable to be controlled by appropriate inverter electric motors, the above-described basic concept was radically changed. The working pump is now connected switching valveless with the piston chamber of a piston / cylinder unit. The electric drive motor of the pump can be freely parameterized via a converter control in relation to speed and direction of rotation up to standstill. The oil flow delivered by the working pump behaves almost proportionally to the engine speed. In this way, the hydraulic oil flow and thus also the piston movement can be influenced freely. The annular space side of the piston is connected to an accumulator whose pressure is set slightly higher than the counterpressure required to overcome the frictional losses and the gravity of the piston and any appended masses. The actual position of the piston rod is transmitted via a travel sensor to the control device. At standstill phases of the consumer, the electric drive motor is stationary and there is no hydraulic oil conveyed and thus triggered no piston movement. If the working piston is to extend, the electric drive motor begins to rotate, the hydraulic oil flows into the piston chamber and the piston rod extends. The annular space side hydraulic oil volume flows into the accumulator and raises its pressure slightly. After reaching the desired piston position, the electric drive motor comes to a standstill via a corresponding control and the piston position is held. The ability of the system for precise angular control of the electric drive motor allows a very accurate positioning of the working piston. The nominal positions are approached and held under full pressure with an accuracy of up to 1 μm without throttle losses.

For the return stroke of the piston, the direction of rotation of the electric drive motor is now changed. The energy stored in the compressed hydraulic oil in the accumulator on the one hand supports the acceleration of the electric drive motor in the opposite direction, on the other hand, excess compression energy can be converted by the regenerative effect of the electric drive motor into electrical energy and electronically stored either in capacitors of the inverter or fed back into the electrical network. This accumulator hydraulic drive arrangement has many advantages over accumulatorless hydraulic drive arrangements of the type described above, such as a high overall efficiency, a very simple system structure, very low thermal load of the hydraulic oil and less noise emission by the variable speed of the drive motor. Such an accumulator hydraulic drive arrangement is known from DE 103 29 067 A1 or the US 6,379,119 A known.

Many applications have already been realized with this known hydraulic drive arrangement. On the one hand, the limits are reached when the loads or retraction forces from the process are so great that the inherently low pressures of the accumulator are insufficient for a return stroke of the piston or the cylinder diameter and / or the piston stroke are so great that the volume of the accumulator rises above an economically justifiable level. This is the case, for example, in hydraulic machines with forces above about 4000 kN and / or strokes over about 700mm. - Especially with large cylinders, however, the energy advantage would be particularly significant.

A hydraulic drive device in which the accumulator or the passive pressure accumulator is replaced by an active pneumatic component, the font JP 2001-2 14 903 A be removed. There is proposed to improve the controllability and the accuracy of the device to connect each pressure chamber of a piston / cylinder unit with its own, independently controlled motor / pump unit for pressurizing. In this way, the installation of valves in the pressure lines can be avoided.

Also with two pumps operates a device for fall protection hydraulically lifted loads according to JP 08-0 14 208 A , The hydraulic controls the stroke and the return stroke of a piston / cylinder unit with a first pump and a conventional multi-way valve. The function of the directional valve is to switch between the lifting and the return stroke. When the load in the neutral position of the directional control valve slowly starts to decrease when the piston is stopped due to leakage or thermally assisted compression effects and concomitant pressure reduction in the pressure lines, the second pump is switched on to stabilize the load.

A hydraulically operated piston / cylinder unit, in which the piston chamber and the annular space are each supplied by a pump and a directional control valve, the DE 40 30 950 A1 be removed. In the control device described there can be changed by operating multi-way valves either between a lifting or Rückhubfunktion. In addition, for example, in addition to the function "return stroke" a lifting function can be superimposed targeted.

According to the WO 02/04 820 A1 is a drive device with two pumps provided, which are operated by one or two variable speed and Drehrichtungsvariable motors. The engine (s) do not operate continuously but only when the piston / cylinder unit is to be moved, whereby directional valves in the pressure lines for reversing the pressure direction are in principle not required. Only for limiting the pressure in the pressure lines may optionally be provided an arrangement of a plurality of conventional valves or alternatively a multi-way valve.

A drive system for multiple consumers can the US 6,205,780 B1 be removed. Accordingly, two pumps are provided, each working speed and direction variable and can pressurize the or the pressure chambers of one or more consumers with pressure. The assignment of the pumps to other consumers is done by a valve assembly with different switching positions.

In the entire state of the prior art, however, further complications arise in pressure accumulator-free hydraulic systems, especially in the case of large consumers, if, for example, long strokes or return strokes, but in particular large delivery volumes, are to be realized by large consumers in the shortest possible time.

PRESENTATION OF THE INVENTION

Based on this, the invention has the object, speed and direction variable hydraulic drive assemblies waiving accumulator for bulk consumers, especially for hydraulic presses with a need for large volumes to make usable.

To solve this problem and to be able to operate particularly powerful and / or large consumers in pressure accumulator hydraulic drive assemblies quickly and accurately and still be able to realize reasonable costs, a pressure accumulator hydraulic drive assembly with the features of claim 1 is proposed. Accordingly, a pump assembly of a variable speed driven main working pump for working strokes and further provided from a variable speed driven auxiliary pump for return strokes, the conveying direction of the auxiliary pump reversible and the auxiliary pump via a directional control valve with either the first and / or the second pressure chamber of the consumer hydraulically connected or is connectable. With regard to a generic method, the object is achieved by the features of claim 14.

According to a further concern of the invention, a pressure accumulator hydraulic drive assembly with the features of claims 4 or 11 is proposed, which is also of independent inventive importance, so that the Applicant reserves the right to make that solution the subject of a divisional application. This solution provides that in a generic accumulatorless hydraulic drive assembly, the pump assembly consists of a variable speed driven main working pump for working strokes and a variable speed driven auxiliary pump for return strokes, and that a control device is provided, which is to be established by the auxiliary pump, against the pressure in the working space the counter-pressure acting on the consumer controls or regulates the pressure chamber associated with the auxiliary pump. It has been shown that the auxiliary pump at the same volume flow as the main working pump, for example, only 1/10 of the power of the main working pump needed and that the costs incurred by the additional and independently driven auxiliary pump effort is significantly lower than the cost of a suitably designed accumulator. In this case, more favorable space and weight ratios are possible than in a suitably large accumulator.

Optionally, or particularly preferably, it can be provided to realize switching valve-free direct connections between the main working pump and the first pressure chamber or the auxiliary pump and the second pressure chamber of the consumer and thus avoid the possibly dangerous shocks in the system when using directional control valves in the pressure lines.

In order to achieve higher piston speeds of the consumer, it is also possible to realize the per se known concept of an additional rapid traverse pump, in which the electric drive motor of the main working pump simultaneously drives two hydraulic oil pumps whose combined flow allows the working piston to extend faster. Upon reaching a certain, transmitted via a pressure transducer to a converter limit pressure, the rapid traverse pump can be connected by switching a directional control valve with the return tank for hydraulic oil. Then only the second pump delivers. Thus, the required torque of the electric drive motor can be limited to an economically reasonable amount.

Another application of the accumulator-free hydraulic drive assembly according to the invention is to combine the piston / cylinder unit of the consumer with a known rapid traverse piston and filling valves, as they are known from conventional hydraulic controls per se. However, the necessary filling valves with the necessarily large pipes so-called rapid traverse piston are relatively expensive.

It may also be provided that a mechanical gear, in particular a transmission gear, is provided between the main working pump and a drive motor associated with the main work pump. As a result, the rotational speed of the main working pump can be changed with respect to the rotational speed of the drive motor assigned to the main working pump. Due to the interposed, mechanical transmission, which may have a constant ratio, it is possible to increase the usable speed range of the drive motor significantly. Thus, for example, a low-cost, lower-torque motor can be used, or alternatively, a higher-flow pump.

In the drive assembly according to the invention, it may also be useful if the pump assembly consists of a variable speed driven main working pump for working strokes and a variable speed driven auxiliary pump for return strokes, wherein the per revolution funded volume of the main working pump and / or the auxiliary pump is variable. The change in the volume delivered per revolution can preferably be regulated as a function of the pressure generated by the main working pump and / or the auxiliary pump. Because of the inherent inventive importance of this solution, the applicant reserves the right to make it the subject of a divisional application. Optionally, the main working pump and / or the auxiliary pump may be formed in this solution as per se known axial piston pump or vane pump with per revolution variable volume flow. The adjustment of the displacement of the pump can be done mechanically-hydraulically depending on the process pressure or a servo motor. The load-dependent change in the delivery volume per revolution or the Pumpenhubraums to control the Flow rate - ie the delivery volume per time - has the advantage that at low load, a high flow rate is achieved. This is expedient in particular for large consumers connected to the drive arrangement, since these then reach long distances or strokes in a short time. Likewise, at high loads, the operation of the pump can be changed so that by reducing the Pumpenhubraums a lower torque of the drive motor is required, whereby the size of the drive motor can be reduced. At the same time, the possibility is given to achieve large volumes as needed.

If according to a further embodiment, an electrical converter, in particular a frequency converter, is used as a substitute for a hydraulic control for the dangerous direction and speed control of the hydraulic pump, especially if in addition to the inverter, a switchable brake between the electric drive motor of the pump assembly and the inverter is installed, easily higher-quality risk categories can be achieved with little effort. Because of the inherent inventive importance of this solution, the Applicant reserves the right to make that combination the subject of a divisional application. In the meantime, the converters have been certified as having the requirements of the second highest CE risk category 3. If such a converter combined with a hydraulic control of the type described above, ie with a hydraulic gear without safety-relevant switching valves, and is designed to the rest of the electrical control accordingly safe, it can - practically without significant in the field of hydraulics to operate a significant additional effort - a hydraulic drive arrangement can be realized with category 3 classification. In this case, the hydraulic systems are only used as "hydraulic gear" and the hazardous direction and speed control is realized only by the inverter. Such a solution is feasible even with pressure accumulator hydraulic drive arrangements with variable-speed driven hydraulic pumps, as they inter alia in the DE 103 59 067 A1 are described or how they are using only a single driven by the electric drive motor hydraulic pump are known.

It is also possible to achieve the highest risk category 4 with only a small additional effort, in which, in addition to the converter with category 3 classification, a brake is installed between the electric drive motor and the work pump. This creates a redundant system. Brakes with a correspondingly safe design are known, for example, from elevator construction. In addition, the inverter can check the effectiveness of the brake at regular intervals by applying torque to the motor against the active brake, and the process controller checks to see if the rotor is moving improperly.

The aforementioned as well as the claimed and described in the embodiments to be used according to the invention. Components are subject in their size, shape design, choice of materials and technical design no special conditions of exception, so that the well-known in the field of application selection criteria can apply without restriction.

Further details, features and advantages of the subject matter of the invention will become apparent from the subclaims, as well as from the following description of the accompanying drawings, in which - by way of example - an embodiment of a pressure accumulator hydraulic drive assembly is shown. Also, individual features of the claims or of the embodiments may be combined with other features of other claims and embodiments.

BRIEF DESCRIPTION OF THE FIGURES

Fig. 1

das Blockschaltbild einer ersten Ausführungsform einer druckspeicherlosen hydraulischen Antriebsanordnung;

Fig. 2

das Blockschaltbild einer zweiten Ausführungsform einer druckspeicherlosen hydraulischen Antriebsanordnung;

Fig. 3 A/B/C

das Blockschaltbild einer dritten Ausführungsform einer druckspeicherlosen hydraulischen Antriebsanordnung in drei unterschiedlichen Ventilstellungen; sowie

Fig. 4

das Blockschaltbild einer vierten Ausführungsform einer druckspeicherlosen hydraulischen Antriebsanordnung, wobei eine erhöhte Sicherheitskategorie erreicht wird.

In the drawing show

Fig. 1

the block diagram of a first embodiment of a pressure accumulatorless hydraulic drive assembly;

Fig. 2

the block diagram of a second embodiment of a pressure accumulatorless hydraulic drive assembly;

Fig. 3 A / B / C

the block diagram of a third embodiment of a pressure accumulatorless hydraulic drive assembly in three different valve positions; such as

Fig. 4

the block diagram of a fourth embodiment of a pressure accumulatorless hydraulic drive assembly, wherein an increased safety category is achieved.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 1 shows a pressure accumulator-free hydraulic drive assembly in which a driven by an electric variable speed drive motor M1 hydraulic main pump P1 with the piston chamber K acting as a consumer 1 piston / cylinder unit via a pressure line D1 switching valveless is directly connected. In addition, an auxiliary pump P2 driven by an electric variable-speed drive motor M2 is connected to the annular space R of the load 1 via a switch valve-free direct connection D2. The motor / pump unit M1 / P1 determines as a guide unit, the piston movement at least during its working stroke, as is customary even with accumulator-prone hydraulic drive assemblies. With the motor / pump unit M2 / P2, a back pressure is generated, which simulates the function of an accumulator, as it is used in the accumulator hydraulic drive assemblies. For this purpose, the torque of the motor M2 is controlled so that a certain, required for the process back pressure against the working pressure is generated and maintained. This back pressure can be arbitrarily controlled or regulated regardless of the position of the piston or the piston rod. Thus, it is possible to generate high stripping forces at the beginning of the return stroke, for example, in a carried out by the consumer forming process of a workpiece, which are required, for example, to retrieve a forming die during the return stroke from the mold. Likewise, can be long Return strokes, in particular with constant back pressure, can be realized. At standstill or during the downward travel - ie in the initial range of the working stroke - the torque of the drive motor M1 can be reduced in order to save energy.

The motor / pump unit M2 / P2 requires only a low drive power compared to the main working pump, which can be between 2% and 50% of the rated power required by the main working pump. In many cases, about 1/10 of the rated power of the main working pump for the auxiliary pump is cheap and sufficient.

In such an arrangement, the same advantages as in a hydraulic accumulator-laden hydraulic drive arrangement with variable-speed driven hydraulic pump are achieved - even for applications where long strokes and / or large forces from the consumer, ie the piston / cylinder unit are required. In addition, comparatively large delivery volumes can be realized, which are advantageously not limited by the volume of the pressure accumulator. Moreover, the invention not only achieves a more cost-effective construction, but above all very considerable advantages in the energy requirement of the arrangement. All the more so, as the drive assembly can be optionally equipped with one or two axial piston pumps or vane pumps. Characterized in that these pumps are characterized by a variable with respect to the delivery volume per revolution pump stroke, the size and thus the energy and cost of the pump P1, P2 can be further reduced. It may be expedient in the case of use of such pumps to regulate the variable displacement volume per revolution or process pressure-dependent. The function of the displacement reduction is approximately comparable to that of a (mechanical) gearbox: It causes a reduction of the required torque of the drive motor M1 and / or M2. Additionally or alternatively, the arrangement of a mechanical transmission or a gear transmission with a constant ratio between the drive motor M1 (M2) and the pump P1 (P2) may be useful. It allows the usable speed range of the engine (s) to increase. This also reduces the cost and energy expenditure for the drive arrangement according to the invention.

In the arrangement of this first (and subsequent) embodiments, control lines 5A, 5B connect the controller 6 to the variable speed electric drive motors M1, M2. The variable-speed motors M1 and M2 are freely programmable via the control device 6, in particular in the form of a known converter, preferably in the form of a frequency converter, with respect to speed and direction of rotation - if desired, to a standstill. By means of appropriate setpoint specifications for the inverter, the entire speed setting range can be traversed from standstill to the maximum permissible speed in both directions of rotation. The drives can work in all four quadrants of a speed-torque diagram. This means that the drives can either drive right- or left-handed (quadrants I and II or quadrants III and IV) (quadrant I or III) or brake (quadrant II or IV). Since the hydraulic oil flow conveyed by the pumps P1 and P2 behaves approximately proportionally to the engine speed, in this way the oil flow and thus also the piston movement can be influenced freely. Pressure relief valves 4A and 4B limit the system pressure to the permissible level, so that when the set pressure is exceeded, hydraulic oil flows back into the hydraulic oil tank T via the returns 2A and 2B, respectively. The actual position of the piston rod is transmitted via the encoder 8 to the inverter control 6.

A preferred mode of operation is the following: When the load is at a standstill, the motors M1 and M2 are generally almost at rest, unless a leakage or the like is to be compensated. When the engine is stopped, no oil is pumped and thus no piston movement is initiated.

If the piston rod S to be extended, so the motor M1 starts to rotate and the hydraulic oil flows into the piston chamber K (filling mode of the pump P1), so that the piston rod S extends. In this case, the torque of the running in the emptying mode of the pump P2 motor M2 limited to a relatively low value become. The running in the emptying mode of the pump P2 motor M2 prevents, for example, that a hanging on the load load is lowered uncontrollably. The direction of rotation of the motor M2 thus corresponds to the emptying mode of the pump P2, ie hydraulic oil is withdrawn from the annulus controlled while maintaining a certain back pressure against the piston of the consumer or drained. The pump P2 will therefore be put into reverse rotation at low pressure by the volume of hydraulic oil flowing out of the annular space side, ie the motor M1 in turn drives the motor M2 and the motor M2 slows down this drive force since it runs slower than would correspond to the drive torque of the motor M1. The oil flows back to the tank T without pressure after flowing through the pump P2. By way of the control device 6 of the motor M2, the engine braking torque of the motor M2 can be varied and a predefinable counterpressure can thus be maintained. Since both electric motors M1 and M2 are precisely controlled, this allows a very exact positioning of the piston rod, whose target positions can be approached and held under full pressure and without throttle losses with an accuracy of up to 1 micron. If necessary, a position of the piston can be approached exactly at a speed close to 0 with high or even full pressure.

For the return trip now the directions of rotation of the motors M1 and M2 are changed, ie M1 / P1 operate in the emptying mode and M2 / P2 operate in the filling mode for the associated pressure chamber of the consumer 1. This makes it possible to the pressurized cylinder by reversing the pump rotation direction decompress. The stored energy in the compressed hydraulic oil on the one hand supports the acceleration of the motor M1 in the opposite direction. On the other hand, excess compression energy can be converted by the regenerative effect of the motor M1 into electrical energy and stored or fed back into the grid. On the return (return stroke of the piston) further determines the speed of the now reversed in the direction of rotation motor M1, the position and speed of the piston rod S. The generated by the limited drive torque of the motor M2 flow rate of the pump P2 is just so large that the reversed pump P1 pumped from the piston chamber K. Oil quantity on the annulus side R is replaced. By stopping the motor M1, the piston comes to a precise stop position.

The embodiment according to FIG. 2 differs from the one after FIG. 1 by the use of a known so-called rapid traverse piston 3 'and a filling valve 9 and a third pressure line D3, which can be connected via an on / off valve 11 in the bypass to the switching valve-less pressure line D1. The rapid traverse piston 3 'is inserted into the piston of the piston-cylinder unit 1. By closing the valve 11, the pump current of the main working pump P1 is not directed to the main piston, but to the much smaller diameter rapid traverse piston. The piston rod S extends so much faster. Hydraulic oil for filling the piston chamber K is sucked out of the tank T via a non-returnable, serving as a filling valve 9 check valve. After reaching an adjustable pressure, the main piston surface is switched with the valve 11, so that the full piston force can be achieved. During the return stroke, the filling valve 9 is also opened in order to drive at high speed here too.

The embodiment according to the FIGS. 3A to 3C differs from the one after FIG. 1 by the use of the switching valve 13 and the additional pressure line D4, with which the annular space R of the piston rod S with the valve 13 or depending on the switching position of the valve 13 with the piston chamber K of the piston / cylinder unit 1 can be connected.

If the piston rod S extend at rapid traverse speed, the valve 13 is in the in FIG. 3B shown position "parallel arrows" switched. Both motors M1 and M2 are controlled via the control unit 6 with the same direction of rotation and speed. The pump P1 delivers via the pressure line D1 directly into the piston chamber K, the pump P2 via the pressure line D4 also. Via the line D2 while the annular space R is connected to the piston chamber K. The piston rod S extends because of the larger in relation to the surface of the annular space R surface of the piston K from. The thereby displaced via the pressure line D2 from the annular space R oil flows through the line and D4 also in the piston chamber K. On this Way can be realized by the combination of the flow rates of the pumps P1 and P2 and in addition by the use of the annular space side effluent oil quantity high exit speeds.

If, in the further course of the drive stroke, the actual work step begins, in which the cylinder operates with a higher force, the valve 13 is brought into the blocking position shown in FIG. 3A. Annulus R and piston chamber K are again separated, the system works according to the in the FIG. 1 illustrated principle. For this purpose, the control device 6, the mode of operation of the motor M2 to; Instead of running with the same speed and direction as the motor M1 in filling mode, M2 now again generates a specifiable, in particular constant braking torque, as above for the FIG. 1 described (emptying mode). The direction of rotation of M2 is therefore reversed.

For the return or idle stroke, the valve 13 in the in the FIG. 3C shown position "crossed arrows" are switched. The piston chamber K is now connected via the line 12 directly to the tank T. Thus, the usually quite high flow rate of the pump P2 can be used for a high return speed, which is no longer due to the relatively high resistance of the concept according to the FIG. 1 the emptying of the piston chamber K gestattenden pump P1 is limited. In this operating state, the motor M2 (filling mode) is again operated in synchronism with the motor M1 (discharge mode) with regard to the direction of rotation and the speed. Before reaching the upper end position both motors M1 and M2 are brought to a standstill, the valve 13 switches to the middle position according to Figure 3A.

FIG. 4 shows a hydraulic control for a machine that meets the highest CE risk category 4. The picture shows a control similar to the one in the FIG. 1 shown; Controls of pictures 2 to 3 can be changed in the same way. The actual hydraulic control remains completely unchanged. The inverter controller 6, however, receives additional equipment to achieve the risk category 3, including, for example, redundant electrical circuits and specially certified software. Between the motor M1 and the pump P1, an electrically switchable brake B is installed. The braking torque is applied via springs, the ventilation is carried out by an electrically operated coil. For intentional movements of the piston S, the brake is released by switching on the coil, for safe standstill it remains closed. LIST OF REFERENCE NUMBERS 1 consumer 13 switching valve 2A returns 20 pump assembly 2 B returns B brake 3 cylinder D1 first pressure line 3 ' Eilgangkolben D2 second pressure line 4A Pressure relief valve D3 third pressure line 4B Pressure relief valve D4 fourth pressure line 5A control line M1 first drive motor 5B control line M2 second drive motor 6 control device P1 Main working pump 7 Rewind / suction line P2 auxiliary pump 8th encoder K first pressure chamber 9 filling valve R second pressure chamber 10 drive arrangement S piston rod 11 Valve T tank 12 management

Claims (19)

1. Accumulator-free hydraulic drive system for and with a consumer (1), more particularly for presses, with two counteracting pressure chambers (K, R) of which one can be supplied with pressure via a first pressure line (D1) and a pump arrangement (20) and the other via a second pressure line (D2) and the pump arrangement (20),
   characterised in that
   the pump arrangement (20) comprises a speed variably-driven main operating pump (P1) for working stroke and a speed variably-driven auxiliary pump (P2) for return strokes, and
   in that the flow direction of the auxiliary pump (P2) is reversible and by way of a directional valve (13) the auxiliary pump (P2) is or can be optionally hydraulically connected with the first (K) and/or with the second (R) pressure chamber of the consumer (1).
2. Arrangement according to claim 1 characterised in that the annular space (R) and the piston chamber (K) can be optionally hydraulically connected or to each other and disconnected again via a controllable pressure line (D2, D4).
3. Arrangement according to claim 1 or 2 characterised in that the piston chamber (K) can be optionally connected with a drainage line (12) via the directional valve (13).
4. Accumulator-free hydraulic drive system according to any one of claims 1 to 3, characterised in that a control device (6) is provided with which a counterpressure to be built up by the auxiliary pump (P2) and acting against the pressure in the operating chamber of the consumer (1) in the pressure chamber assigned to the auxiliary pump can be controlled or regulated.
5. Arrangement according to claim 4 characterised in that the first pressure line (D1) is a control valve-free direct connection between the main operating pump (P1) and the first pressure chamber (K) and the second pressure line (D2) is a control valve-free direction connection between the auxiliary pump (P2) and the second pressure chamber (R).
6. Arrangement according to any one of claims 1 to 5 characterised in that the nominal output of the auxiliary pump (P2) is between 2% and 50% of the nominal output, preferably around 10% of the nominal output of the main operating pump (P1).
7. Arrangement according to any one of claims 1 to 6 characterised in that between the main operating pump (P1) and a drive motor (M1) assigned to the main operating pump (P1) a mechanical gear mechanism is provided through which the speed of the main operating pump (P1) can be altered in relation to the speed of the drive motor (M1) assigned to the main operating pump (P1).
8. Accumulator-free hydraulic drive system according to any one of claims 1 to 7
   characterised in that
   the volume conveyed per revolution of the main operating pump (P1) and/or the auxiliary pump (P2) can be changed, wherein the change in the volume conveyed per revolution can preferably be regulated as a function of the pressure produced by the main operating pump (P1) and/or the auxiliary pump (P2).
9. Accumulator-free hydraulic drive system according to any one of claims 1 to 9 characterised in that the pump arrangement (20) has at least one pump, driven by a speed-variable electric drive motor, for working strokes of the hydraulic pump system designed as a hydraulic gear mechanism in which the pressure lines (D1, D2) are free of safety-relevant control valves, and in that a control device (6) in the form of an inverter exhibits a known high risk category for the electric device motor as a replacement for a hydraulic control.
10. Arrangement according to claim 9 characterised by a brake (8) that acts between the electric drive motor (M1) and the operating pump (P1).
11. Accumulator-free hydraulic drive system according to the introductory section of claim 1 characterised in that
    the pump arrangement (20) comprises a speed variably-driven main working pump (P1) for working strokes and a speed variably-driven auxiliary pump (P2) for return strokes and
    in that a control device (6) is provided with which a counterpressure to be built up by the auxiliary pump (P2) and acting against the pressure in the operating chamber of the consumer (1) in the pressure chamber assigned to the auxiliary pump can be controlled or regulated.
12. Accumulator-free hydraulic drive system according to the introductory section of claim 1 characterised in that
    the pump arrangement (20) comprises a speed variably-driven main working pump (P1) for working strokes and a speed variably-driven auxiliary pump (P2) for return strokes and
    in that the volume conveyed per revolution of the main operating pump (P1) and/or the auxiliary pump (P2) can be changed, wherein the change in the volume conveyed per revolution can preferably be regulation as a function of the pressure produced by the main operating pump (P1) and/or the auxiliary pump (P2).
13. Accumulator-free, hydraulic drive system according to the introductory section of claim 1 characterised in that the pump arrangement (20) has at least one pump, driven by a speed-variable electric drive motor, for working strokes of the hydraulic pump system designed as a hydraulic gear mechanism in which the pressure lines (D1, D2) are free of safety-relevant control valves, and in that a control device (6) in the form of an inverter exhibits a known high CE risk category for the electric device motor as a replacement for a hydraulic control.
14. Method of accumulator-free hydraulic driving of a consumer (1) with two counteracting pressure chambers (K, R), one of which is supplied with pressure via a first pressure line (D1) and a pump arrangement (20) and the other via a second pressure line (D2) and the pump arrangement (20)
    characterised in that as a replacement for an accumulator, a speed variably-driven main operating pump (P1) is used for working strokes and a speed variably-driven auxiliary pump (P2) for return strokes and by means of a control device (6) the auxiliary pump (P2) builds up or holds a counterpressure against a pressure in the operating chamber and
    in that during the working stroke of the consumer (1) the flow direction of the auxiliary pump (P2) is reversed and the flow of the auxiliary pump (P2) is diverted from an initial connection to the piston chamber (K) of the consumer (1) to a connection with the circular chamber (R) of the consumer (1).
15. Method according to claim 14 characterised in that the speed of the main operating pump (P1) is changed with regard to the speed of a drive motor (M1) assigned to the main operating pump (P1), wherein the change in the speed of the main operating pump (P1) with regard to the speed of the drive motor (M1) assigned to the main operating pump (P1) preferably takes place through a mechanical gear mechanism provided between the main operating pump (P1) and the drive motor (M1) assigned to the main operating pump (P1).
16. Method according to claim 14 of 15 characterised in that the volume conveyed per revolution of the main operating pump (P1) and/or the auxiliary pump (P2) is changed, wherein the change in the volume per revolution preferably takes place as a function of the pressure produced by the main operating pump (P1) and/or the auxiliary pump (P2).
17. Method according to any one of claims 14 to 16 in which the pump arrangement (20) comprises at least one speed variably-driven pump, characterised in that hydraulic oil flows through the pressure lines (D1, D2) without safety-relevant control valves and the at least one speed-variable pump drive motor is controlled with an electrical inverter of a high CE risk category.
18. Method according to claim 17 characterised in that a brake (8) acting between the electrical drive motor (M1) and the operating pump (P1) is redundantly used.
19. Method according to the introductory section of claim 14 in which the pump arrangement (20) comprises at least one speed variably-driven pump, characterised in in that hydraulic oil flows through the pressure lines (D1, D2) without safety-relevant control valves and the at least one speed-variable pump drive motor is controlled with an electrical inverter of a high CE risk category.

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