EP0749535B1 - Hydraulic drive unit - Google Patents

Abstract

PCT No. PCT/EP95/00884 Sec. 371 Date May 9, 1996 Sec. 102(e) Date May 9, 1996 PCT Filed Mar. 9, 1995 PCT Pub. No. WO95/24565 PCT Pub. Date Sep. 14, 1995A hydraulic drive unit has a tracking regulator valve (19) for controlling a servo drive (18) of a main control valve (16), where the main control valve controls flow to a hydraulic motor (11). The tracking regulator valve is controlled by an actuating element (42), which is controlled by a comparison of a nominal position value, set by an electric motor (36), and an actual position valve, generated by a mechanical feedback (53) connected to the hydraulic motor. The main control valve includes a slide valve piston (87), which forms a housing for the tracking regulator valve, which has two piston slide valve elements (39, 41). The slide valve piston (87) of the main control valve (16) has an axial through-bore (122) through which passes the actuating element. The servo drive (18) is a dual-action hydraulic cylinder, which includes drive pressure chambers (33, 34) formed by axial blind bores (118, 118') in the valve piston (87) of the main control valve (16) and pistons (138, 138') accommodated in the blind bores.

Description

The invention relates to a hydraulic drive unit one for high drive power and accordingly - if necessary - High throughput of hydraulic oil designed Hydromotor as a power drive, a main control valve, by means of which an inflow of high pressure Hydraulic oil to the power drive as well as the drain at least part of the hydraulic oil supplied to the power drive, e.g. to the pressureless reservoir of the pressure supply unit is controllable, one as double Acting linear cylinder trained hydraulic servo drive for the actuation of the main control valve and with one intended for controlling the servo drive, with Electromotively controlled specification of the setpoint of the position as well as the speed of movement of the movable Elements of the power hydromotor and mechanical feedback the corresponding actual control valve, that if the target and actual values are the same controlled position one - the standstill of the power drive Corresponding - blocked position, which by the position setpoint specification for taking the alternative Driving directions of the power hydraulic motor assigned alternative flow positions can be controlled in which the respective effective flow cross-section with the amount of Deflection of the valve varies monotonously, and that by Position actual value feedback in the sense of taking the Lock position can be controlled, the overrun control valve and the main control valve as by axial relative displacements of their valve pistons and housing elements, the take place along mutually parallel axes, operable Piston slide valves are designed and the piston of the Main control valve, the housing of the follow-up control valve forms.

In a known hydraulic drive unit of this type (US-PS 4,161,905) the overflow control valve has one in one central axial through bore of the piston Main control valve can be moved in a pressure-tight, elongated manner rod-shaped piston, which, seen in the axial direction, drive pressure chambers arranged on both sides of the main control valve piston enforced, by means of the overrun control valve controllable alternative pressurization and relief the servo drive of the main control valve piston is achieved, the piston of the follower control valve also in the case of the axial limits fixed to the housing two end pressure walls of the housing forming drive pressure spaces of the main control valve can be moved in a pressure-tight manner have to be. One end of the follower control valve piston protrudes from the housing of the main control valve out and is firmly connected to a rack at this end, with a pinion of the electromechanical position setpoint specification and actual value feedback combs that is drivable by means of a differential gear, which the phase comparison required for the overrun control mediated between setpoint specification and actual value setting.

The known drive unit is due to that described structure with at least the following disadvantages afflicted:

The manufacture of the through the main control valve and the follower control valve formed assembly is in the for one reliable function required precision extremely complex, since the respective end sections of the piston of the follow-up control valve receiving holes in the housing of the Main control valve and the central bore of its valve piston with the required, exactly aligned arrangement are very difficult to manufacture, and also the exact arrangement of control edges of the piston of the follower control valve to control edges of the piston of the main control valve, if so this one in the locked position of the follow-up control valve should have an exact 0-overlap as possible, is very complex, with the result that the known drive unit with high manufacturing costs.

Another disadvantage is that the large areas the drive pressure chambers of the servo drive for the piston of the Main control valve, each through one of the ring faces of the piston itself are necessarily too large Amounts of tax oil flows, which leads to a highly dynamic operation of the servo motor disadvantageous is because then a lot of energy is required for the servo circuit becomes.

The object of the invention is therefore to provide a drive unit improve the type mentioned in that a precise configuration on the valve piston side and on the housing side Control edges of the overrun control valve with significantly reduced Effort is realizable and the need for hydraulic Tax energy is significantly reduced.

This object is achieved by the characterizing Features of claim 1 solved.

According to this, the overrun control valve has two from one to the parallel to the central longitudinal axis of the main control valve piston, through bore of the main control valve piston Piston elements, this bore in radial Distance from the central longitudinal axis of the main control valve is arranged; is the axial distance of these piston elements for setting a defined overlap on the piston side Control edges and housing-side, within the continuous Bores of the piston of the main control valve arranged Control edges of the follow-up control valve, in particular to set the for a sensitive control operation suitable 0-coverage of such control edges, adjustable. In this way it is achieved with simple means that manufacturing tolerances the piston elements by adjusting them can be perfectly balanced and a manufacturing technique possible the costly committee and high Manufacturing expenses largely excluded.

Furthermore, the piston of the main control valve is one central, axial through hole provided through the one with the output shaft of the setpoint input motor coupled, but axially with respect to this and the piston displaceable setpoint specification element passes through. This Setpoint specification element stands with an actual value feedback element, through the moving part of the power hydromotor in a positive correlation with its - rotational or translational - movements with the same sense of rotation how the setpoint specification element can be driven in rotation, however axially immovable on the housing of the main control valve is stored in the manner of a spindle nut drive in backlash-free thread engagement. The setpoint default element thereby experiences axial deflections in relation to one with the Locked position of the overrun control valve linked middle position of the piston elements, these deflections with the difference between the target and actual position of the movable Part of the power hydraulic motor are directly correlated; these displacements mediate through actuators that rotationally decoupled from the setpoint specification element are, however, perform its axial movements with the Opening and closing operations of the overrun control valve.

With this design, centering is relative to one another Slidable components only in one piece manufacturable part required, which otherwise required, considerable, manufacturing effort is eliminated. This also applies to the actuation of the main control valve provided servo drive, its drive pressure spaces by at a radial distance from the central axial Through bore of the piston arranged to this parallel blind bores of the main control valve piston and this received, axially on the housing of the main control valve supported pistons are limited, which are neither exactly with each other aligned aligned still firmly connected to the housing must be, but only axially fixed to this must be supportable. The so within the wall thickness of the main control valve piston realized drive cylinder, which together with their axially supported pistons form a single-acting hydraulic cylinder and as a pair of cylinders result in a double-acting hydraulic cylinder with relatively small control oil volumes for executing the required deflection strokes of the main control valve piston controllable and can take advantage of the operating pressure the supply source easily for a highly dynamic Operation of the main control valve required actuating forces unfold.

The hydraulic drive unit according to the invention is both for volumetrically controlled rotary hydraulic motors such as e.g. Axial piston motors as well as for precise control hydraulic linear motors, regardless of the speed at which they are operated and is therefore very suitable as a positioning drive.

The advantageous properties of the invention in this regard Drive unit can by a according Claim 2 provided and its basic structure significantly improved after the outlined fine control valve be in the design provided according to claim 3 with two in an axially continuous bore of the valve piston of the main control valve arranged so that it can be displaced in a pressure-tight manner Piston elements in an axially continuous bore the valve piston of the main control valve are, can be easily integrated into these, wherein those for setting a specific one, in the basic position 0 desired small positive overlap of the fine control valve the same required adjustability of their axial Distance in a preferred design by the features of claim 4 is guaranteed.

The fine control valve is by means of the two piston elements in a quasi-resolved construction, as provided according to claim 5, as two 2/3-way valves that can be operated together formed, which is preferred in the piston of the main control valve with the arrangement specified in the feature of claim 6 diametrically opposite the overflow control valve are provided.

Due to the features of claim 7, a construction of the Actuation of both the main control valve and the fine control valve provided intended actuator, with the this, as indicated by the features of claim 8, again integrable into the piston of the main control valve is.

When doing this, the piston of the main control valve, as per Claim 9 provided with two of the opposite End faces of the main control valve piston forth in this is provided blind holes in which to limit one of its drive chambers relative to the bottom side of which is arranged so as to be displaceable in a pressure-tight manner a piston the one on the housing of the main control valve fixed, optionally axially adjustable stop pin is axially supported, these pistons as Free piston, i.e. without a return element in these holes be used.

So far with just a single pair of bores and pistons comprehensive actuating cylinder the required actuating forces Actuation of the main control valve cannot be achieved the actuating cylinder also as by the features of the claim 11 specified, realized with two pairs of bores and pistons be, which in turn is appropriate, this according to claim 12 to be arranged so that there is a compensation of the actuating torque results, which, generally, by an axially symmetric Grouping of the bore and piston pairs around the central one Longitudinal axis of the main control valve piston can be achieved.

The design of the actuating cylinder provided according to claim 13 or a possibly several pairs of bores and pistons comprehensive actuating cylinder arrangement as a differential cylinder unit or combination has the advantage that this too its / its control provided overrun control valve designed as a 3/3-way valve that is easy to construct can be, in turn, dissolved construction Can be implemented using two 2/3-way valves that can be operated simultaneously is.

The design of the differential cylinder with an area ratio of 2/1 of its larger and smaller ones effective piston area results in both directions of actuation the same actuation force.

The design of the piston provided according to claim 15 The main control valve is then special in terms of production technology favorable if the overflow control valve in the main control valve piston the fine control valve and also the actuating cylinder are largely integrated and possibly also elements the feedback device and the setpoint specification device received by a central bore of the central piston part are, which also means the hydraulic Rigidity of the oil columns that determine the drive unit and achieve high loop gain values to let.

Provided and designed according to claims 16 to 18 Position sensors can be used for both the adjustment of the main control valve and the fine control valve and the overrun control valve. and in the operation of the drive unit also for continuous Detection of the overtravel of the control elements, i.e. for a continuous determination of the loop gain of the control loop can be used.

Fig. 1

ein hydraulisches Ersatzschaltbild einer erfindungsgemäßen Antriebseinheit mit einem als Differentialzylinder ausgebildeten, doppelt wirkenden linearen Hydrozylinder als Leistungsantrieb, einem Hauptsteuerventil und einem Feinsteuerventil, die mittels eines ebenfalls als doppelt wirkender Differentialzylinder ausgebildeten Stellantriebs betätigbar sind und mit einem mit elektromotorisch gesteuerter Sollwert-Vorgabe und mechanischer Istwert-Rückmeldung der Position des Antriebskolbens des Leistungsantriebes arbeitenden Nachlaufregelventil,

Fig. 2

eine Längsschnittdarstellung des Hauptsteuerventils und des in dieses integrierten Nachlaufregelventils sowie des Stellzylinders in zwei zueinander rechtwinkligen Ebenen längs der Spurenlinie B-B der Fig. 4 sowie des Leistungs-Antriebs in einer dessen zentrale Längsachse sowie die zentrale Längsachse des Hauptsteuerventils enthaltenden Schnittebene,

Fig. 3

eine zur Darstellung der Fig. 2 analoge Längsschnittdarstellung, die die zentrale Längsachse des Fein-steuerventils enthält, längs der Spurenlinie C-C der Fig. 4,

Fig. 4

die Anordnung von zur Aufnahme von Kolben und Betätigungselementen der Ventile der Antriebseinheit gemäß den Fig. 2 und 3 vorgesehenen Bohrungen des Kolbens des Hauptsteuerventils bezüglich der zentralen Längsachse des Hauptsteuerventils in einer zu dieser rechtwinkligen Schnittebene längs der Linie A-A der Fig. 2 und

Fig. 5a und 5b

Details der Anordnung und Ausbildung von Steuerkanten des Hauptsteuerventils der Antriebseinheit gemäß den Fig. 1 bis 4 in einer stark vergrößerten Schnittdarstellung längs einer die zentrale Achse des Hauptsteuerventils und die zentrale Achse des Leistungsantriebes enthaltenden Radialebene des Hauptsteuerventils.

Further details of the drive unit according to the invention result from the following description of an embodiment with reference to the drawing. Show it:

Fig. 1

a hydraulic equivalent circuit diagram of a drive unit according to the invention with a double-acting linear hydraulic cylinder designed as a differential cylinder as a power drive, a main control valve and a fine control valve, which can be actuated by means of an actuator also designed as a double-acting differential cylinder and with an electromotive-controlled setpoint specification and mechanical actual value. Feedback of the position of the drive piston of the power control working overrun control valve,

Fig. 2

4 shows a longitudinal sectional illustration of the main control valve and the integrated follow-up control valve and the actuating cylinder in two mutually perpendicular planes along the trace line BB of FIG. 4 and the power drive in a sectional plane containing its central longitudinal axis and the central longitudinal axis of the main control valve,

Fig. 3

2 shows a longitudinal sectional view analogous to FIG. 2, which contains the central longitudinal axis of the fine control valve, along the trace line CC of FIG. 4,

Fig. 4

the arrangement of holes for receiving pistons and actuators of the valves of the drive unit according to FIGS. 2 and 3 of the piston of the main control valve with respect to the central longitudinal axis of the main control valve in a section plane perpendicular to this along the line AA of FIGS. 2 and

5a and 5b

Details of the arrangement and design of control edges of the main control valve of the drive unit according to FIGS. 1 to 4 in a greatly enlarged sectional view along a radial plane of the main control valve containing the central axis of the main control valve and the central axis of the power drive.

1, 2 and 3 each designated 10 hydraulic Drive unit consists of an on unfoldability high driving forces and high driving power designed hydraulic motor 11 and a drive control thereof provided, designated a total of 12 electrohydraulic control unit, which in a in the Fig. 1 as firmly connected to the housing 13 of the hydraulic motor 11 Frame 14 shown housing is arranged, which is the geometric Basis for the arrangement of a main control valve 16, a fine control valve 17 of a hydraulic actuator 18 and a follow-up control valve 19 forms which the electro-hydraulic control unit 12 constructed is. The drive unit 10 is intended for use cases where there is high driving force and high driving power arrives where there are correspondingly high hydraulic oil flows occur and be controlled as precisely as possible have to. Possible uses of the drive unit 10 are e.g. the drive of punching, pressing and / or Embossing tools as well as positioning and displacement heavy workpieces in relation to a processing station a machining center where a e.g. cutting Machining the workpiece while moving it takes place relative to a machine-fixed tool.

The hydraulic motor 11 provided as a power drive is at illustrated embodiment as a double-acting linear cylinder with piston rod emerging from the housing on one side 21 trained.

The hydraulic cylinder 11 is connected as a differential cylinder, the pressure on both the rod side Drive chamber 22 of the hydraulic cylinder 11 and the opposite this is delimited by the piston 23 in a pressure-tight manner bottom-side drive chamber 24 with the outlet pressure of the pressure supply unit 26 executes the outward stroke and only the rod side when pressurized Drive chamber 22 and pressure relief of the bottom Drive chamber 24 the pull-in stroke of piston rod 21 executes.

Corresponding to that provided for the drive unit 10 Differential operating mode of the hydraulic cylinder 11 is this only by pressurizing and relieving it bottom driven chamber 24 controlled while the rod side Drive chamber 22 permanently with the outlet pressure of the pressure supply unit is acted upon.

The ratio F ₁ / F _{2 of} the piston piston surface F ₁ on the bottom to the annular piston rod surface F _{2 of} the drive piston 23 of the hydraulic cylinder 11 is in the exemplary embodiment shown, in which the same feed forces can be developed in both alternative directions of movement of the piston 23 should 2/1.

The pressurization and relief of the rod side Drive chamber 24 of the hydraulic cylinder 11 takes place by means of the Main control valve 16 and the fine control valve 17, the are hydraulically connected in parallel and together by means of of the hydraulic actuator 18 are actuated, the in turn as a double-acting linear differential cylinder is formed, one-sided from its housing 27 emerging piston rod 28 rigid with the movable valve elements of the main control valve 16 and the fine control valve 17 is connected, thus together along parallel Axes 29 and 31 can be pushed back and forth.

Also in the actuating cylinder 18, the ratio f ₁ / f _{2 of} the surface f _{1 of} its piston 32, which movably delimits the bottom-side drive chamber 33 of the actuating cylinder 18, to the annular surface f _{2 of} its piston 32, which defines the unilaterally movable delimitation of its rod-side drive chamber 34 forms, into which the high output pressure of the pressure supply unit 26 is permanently coupled, 2/1, so that the deployable in the two alternative directions of movement of the actuating cylinder piston 32, which can be exerted on the movable elements of the main control valve 16 and the fine control valve 17, by pressurization and relief of the bottom control chamber 33 of the actuating cylinder 18 are controllable, have the same amount.

That for the related motion control of the actuator 18 provided overrun control valve 19 works with electrical, e.g. pulsed control of a rotationally driven Stepper motor 36, controllable specification of the target position of the piston 23 of the power hydraulic cylinder 11 and mechanical feedback of the actual position of the drive cylinder piston 23, on the one hand, and mechanical feedback from the Position of the piston 32 of the actuating cylinder 18, on the other hand, which is achieved in that in the illustrated embodiment also the housing 37 of the follow-up control valve 19 rigidly coupled in motion to the piston rod 28 of the actuating cylinder 18 and accordingly along another, parallel to the central longitudinal axis 29 of the actuator 18 extending central longitudinal axis 38 of the follower control valve 19 can be pushed back and forth, along which two Valve bodies 39 and 41 are displaceable relative to the valve housing 37 at which the position setpoint specification as well as the total intended for feedback of actual position value with 42 designated actuator of the follow-up control valve 19 attacks.

The actuating device 42 of the overrun control valve 19 comprises in a coaxial arrangement with respect to a common one central longitudinal axis 43, which is also the axis of rotation of the output shaft 44 of the one, as shown in the Fig. 1 right housing wall 46 arranged stepper motor and the axis of rotation of one on the opposite "left" housing wall 47 rotatable but axially immovable Threaded spindle 48 marked, one as a position setpoint specification element Serving hollow shaft 49 on its stepper motor side End with a parallel toothing of the output shaft 44 of the stepping motor 36 is in meshing engagement and can thus be driven in rotation by means of the stepping motor 36 is. At its opposite end is the hollow shaft 49 provided with an internal thread 51, via which they in meshing engagement with the thread 52 of the threaded spindle 48 stands.

The threaded spindle 48 is by means of a total of 53 designated toothed belt drive, which is assumed to be free of play is drivable in alternative directions of rotation. Of the Timing belt 54 is self-contained and runs over a with the threaded spindle 48 non-rotatably connected toothed roller 56 and via a further toothed roller 57, which is parallel to one extending to the axis of rotation 43 of the threaded spindle 48, fixed to the housing Axis 58 is rotatably mounted, the direction of which central longitudinal axis 59 of the power drive Linear cylinder 11 measured distance from the axis of rotation 43 of the threaded spindle 48 is significantly larger than the maximum Stroke that the piston 23 of the drive cylinder 11 between can carry out its possible end positions.

The toothed belt drive 53 has a to the central longitudinal axis 59 of the linear cylinder 11 run exactly parallel 61, by means of a mechanically rigid connecting element 62 with the piston 23 of the drive cylinder 11 coupled in motion and experiences the same deflections as this one. Through this toothed belt drive 53, the axial Movements of the piston 23 in rotary feedback movements the threaded spindle 48 implemented. The direction of rotation of the rotary Position setpoint specified movements of the hollow shaft 49 by which a certain shifting speed of the piston 21, 23 of the drive cylinder 11 in a predetermined Direction should be achieved and the sense of rotation by the Feedback of the actual position value of the drive cylinder piston 21.23 resulting rotations of the feedback spindle 48 are selected so that if the setpoint and actual value are the same no displacement of the hollow shaft 49 with respect to the threaded spindle 48 occurs, whereas both at the beginning of the control of a position setpoint with which an enlargement the difference between the setpoint and actual value goes hand in hand, as well as upon completion of a change in the setpoint specification, thus reducing the difference between target and Actual value goes hand in hand, in each case opposite relative movements the hollow shaft 49 and the threaded spindle 48 are linked, such that the hollow shaft 49 axial displacements in the experiences both alternative directions.

The overrun control valve, for its further explanation 2 is also his Function according to a 3/3-way valve that, as it were, dissolved Design realized by two 2/3 way valves 19 ', 19' ' is formed as a piston valve body 39 and 41, each represented by the valve symbol in FIG. 1 are in a through bore 63 of the valve housing 37 are slidably guided in a pressure-tight manner.

The two valve bodies 39 and 41 of the follow-up control valve 19 are pushed apart by a centrally arranged spring 64 and clamped between set screws 66 and 67, which in threads from radial to the central longitudinal axis 43 of the Actuating device 42 extending operating arms 68 and 69 are screwed, each with a ball bearing 71 or 72 axially displaceable with the hollow shaft 49 connected, but decoupled from their rotational movements are.

The two valve bodies 39, 41 of the two sub-valves 19 ', 19 '' of the follow-up control valve 19 are by means of the adjusting screws 66.67 adjustable so that the axial distance of control edges 73, 74 of the valve body as shown 1 and 2 "right" sub-valve 19 'and "Left" partial valve 19 '' of the follow-up control valve 19 equal to the axial distance from the control edges 76, 77 of the valve housing 37 of the follow-up control valve 19 is by their Relative movements in alternate directions either Flow path 78 (FIG. 1) of the "right" sub-valve 19 ' is released through which the with the bottom drive chamber 33 of the control cylinder 18 connected control output 79 of the follower control valve 19 with the pressure (P) outlet 81 of the pressure supply unit 26 is connected or a flow path 82 of the "left" partial valve 19 '' of the follow-up control valve 19 is released, through which the - unpressurized - Tank connection 83 of the pressure supply unit 26 with the control connection 79 of the follow-up control valve 19 connected which is in permanent communication via the control path 84 Connection with the bottom drive chamber 33 of the hydraulic actuator 18 is held. These flow positions I of the two sub-valves 19 ', 19' 'of the follow-up control valve 19 corresponds to an absolute locked position II of the other sub-valve 19 '' or 19 ', so that these two sub-valves 19 ', 19' 'after their valve body on equality of the distance of their control edges 73.74 with the distance between the control edges 76, 77 of the common valve housing 37 are set, the function of a 3/3-way valve convey that from its basic position 0, the a value 0 of the coverage of the control edges 73 and 74 of the Valve body 39.41 with the control edges 76.77 of the valve housing 37 corresponds, with 0 both in this basic position the high pressure outlet 81 of the pressure supply unit 26 as also its tank connection 83 against the control connection 79 of the Overrun control valve 19 are shut off by a shift both valve body 39.41 relative to the housing 37 of the follow-up control valve 19 to the right in a functional position can be brought in which the bottom drive chamber 33 of the actuating cylinder 18 with the high outlet pressure of the pressure supply unit 26 is acted upon and against the unpressurized tank connection 83 of the pressure supply unit 26 is blocked off and by a shift relative to the valve housing 37 to the left in a functional position can be brought in which the bottom drive chamber 33 of the actuating cylinder 18 with the unpressurized Tank connection 83 of the pressure supply unit 26 connected and against the high pressure outlet 81 of the pressure supply unit 26 is cordoned off.

The main control valve 16 is the one chosen for explanation Embodiment in which the power drive cylinder 11 is operated as a differential cylinder, the rod-side drive chamber 22 permanently with the outlet pressure of the pressure supply unit 26 is acted upon as 3/3-way slide valve formed, the housing 86 fixed is connected to the housing 13 of the drive cylinder 11. The piston 87 of the main control valve 16, which in FIG. 1 is represented by the 3/3-way valve symbol and in the Fig. 2 and in Fig. 3, in addition to the details also be referred to in a technically realistic Configuration of the main control valve 16 and the follow-up control valve 19 (Fig. 2) and the fine control valve 17 (Fig. 3) is shown, is pressure-tight in a housing bore 88 slidably guided in the radial of the P-connection channel 89 for the pressure medium supply from the pressure supply unit 26 and the T-connection channel 91, on which the to the reservoir 92 of the pressure supply unit 26 leading return line 93 is connected. The control output 94 of the main control valve 16 is through a radial housing channel formed, the one immediately aligned with him Connection channel 96 connects via the hydraulic oil in the inflow bottom drive chamber 24 of the drive cylinder and can flow out of it again.

The control channel 96 of the housing 86 of the main control valve 16 starts from an inner annular groove 97 of the valve housing 86, the between an annular groove 98 of the housing 86, which with the P-connection 83 is permanently in communicating connection and an annular groove 99 of the valve housing 86 is arranged, those with the T-connection channel 91 in permanent communication Connection is established, is arranged.

The piston 87 of the main control valve 16 has a first one outer annular groove 101 provided within the possible Sliding range of the valve piston 87 always in communicating Connection to the P-groove 98 of the valve housing 86 remains and for coupling pressure into the bottom Drive chamber 24 of the drive cylinder 11 by displacement of the valve body 87 as shown in FIG. 2 to the left in overlap with the cross-sectional area of the central annular groove 97 of the housing 86 of the main control valve can be brought, whereby the main control valve in the functional position I arrives in which the T-slot 99 against the control connection channel 94 of the main control valve 16 is cordoned off. Furthermore, the piston 87 with a second outer annular groove 102 provided within the possible Sliding range of the valve piston 87 always in communicating Connection with the T-groove 99 of the valve housing 86 of the main control valve remains and by axial displacement of the valve piston 87, as shown in FIG. 2 to the right, also in cross-section overlap with the central annular groove 97 of the valve housing 86 can be brought, whereby hydraulic oil from the bottom drive chamber 24 of the drive cylinder 11 to the reservoir 92 of the pressure supply unit 26 can flow. In this functional position II of the main control valve 16 is the T-groove 94 against blocked the control channel 94 of the main control valve 16.

In the intermediate position of the Valve piston 87 between its functional positions I and II is both the P-connection channel 89 and the T-connection channel 91 of the main control valve 16 against its control output 94 shut off, with 0 in this basic position Annular groove 97 of the valve housing 86 through between the two External grooves 101, 102 of the valve piston 87 remaining Ring rib 103 is completely closed and by their radial cheeks 104 and 106 formed piston-side control edges 107 and 108 to control edges 109 and 111 (Fig. 3, 5a and 5b) by the circular transition edges are formed with which the radial groove cheeks 110 and 115 of the central housing groove 97 to the central bore 88 of the valve housing 86, in positive and the amount is approximately the same coverage e.

"Positive overlap" here means that the valve piston 87, starting from the home position 0 of the main control valve 16 first by the amount e of the surplus in axial direction must be shifted before, depending on the shift direction, in the respective functional position I or II flow path 112 or 113 to be released opening begins and with increasing displacement releases an increasing cross-section.

Before following further structural and functional details the drive unit 10 will be explained first on the function of the previously expanded functional elements the drive unit 10 received:

If the piston 23 of the drive cylinder 11, starting from a starting position that can be assumed to be known, e.g. of the shown in Fig. 3 the fully retracted State of the piston 23 corresponding end position execute an extension stroke h defined amount, so must for this purpose the bottom-side control chamber 24 of the drive cylinder 11 are pressurized, i.e. the main control valve 16 so long in its functional position shown in FIG. 2 I be brought up to the execution of the Hubes h corresponding target position is reached and with the Reaching this position again in its shown in FIG. 3 Home position. To the main control valve 16 in this functional position is required in accordance the representations of FIGS. 1 to 3 of a shift the valve piston 87 to the left, i.e. a pressure relief the bottom drive chamber 33 of the actuating cylinder 18, which in turn is an - initial - displacement of the pistons 39 and 41 of the follower valve 19 to the left requires so that the partial valve 19 '' of the follow-up control valve 19 the the connection of the bottom drive chamber 33 of the actuating cylinder 18 with the unpressurized reservoir 92 of the pressure supply unit mediating flow path 82 releases. The illustrated design of the threaded spindle 48 with a right-hand thread provided the required shift the valve piston 39 and 41 of the follow-up control valve 19 thereby achieved that the stepper motor 36, viewed in the direction arrow 114 of FIG. 2 for clockwise rotation is controlled in which the hollow shaft 49 rotates and therefore because of your thread engagement with the threaded spindle 48 experiences a shift to the left that the valve piston Execute 39 and 41 of the overrun control valve 19. Due to the resulting release of the flow path 82 of the overrun control valve 19, via the now hydraulic oil from the bottom drive chamber 33 of the actuating cylinder 18 can drain, the piston 32 experiences one Left shift by piston 87 of the main control valve 16 is carried out, which is thereby in its functional position I arrives. This shift will also carried out by the housing 37 of the follow-up control valve, whereby this, as it were, back into the basics 0 of its sub-valves 19 'and 19' 'is returned with the consequence that the drain of hydraulic oil from the bottom Drive chamber 33 of the actuating cylinder 18 interrupted again , whereby the piston 32 of the actuating cylinder 18 in one with a certain opening cross-section of the released Flow path 112 of the main control valve linked Position remains and with this the housing 37 of the Overrun control valve 19. With the onset of the outward movement of the piston 23 of the drive cylinder 11 is over the Toothed belt drive 53 also the threaded spindle 48, in the direction the arrow 116 of FIGS. 1 to 3 seen in the counterclockwise direction rotationally driven. This will make the introductory Phase of the setpoint control shifted to the left Hollow shaft 49 now pushed to the right, whereby also the pistons 39 and 41 of the follow-up control valve 19 relative to the housing 37 are pushed to the right with the consequence that the flow path 78 of the partial valve 19 'of Follow-up control valve 19 opened and thereby hydraulic oil again into the bottom drive chamber 33 of the actuating cylinder 18 is displaced. The actuating cylinder 18 is thereby in Meaning a reduction in the previously released cross-section the flow path 112 of the main control valve 16 driven, which on the one hand the inflow of hydraulic oil in the bottom drive chamber 24 of the drive cylinder 11 is reduced so that its extension speed decreases and on the other hand the housing 37 of the follow-up control valve moved again in that direction - to the right in which the flow path 78 of the sub-valve 19 'of the follow-up control valve 19 is blocked again and the Inflow of hydraulic oil into the bottom drive chamber 33 of the actuating cylinder 18 is interrupted. The piston 32 the actuating cylinder 18 then remains in a reduced one Flow cross section of the still released Flow paths 112 of the main control valve 16 corresponding Stand with the lower movement speed v of the drive piston 23 of the hydraulic cylinder 11 linked is.

The consequence of this is that the threaded spindle 48 also the toothed belt drive 53 now with a lower rotational speed is driven, being one, one constant movement speed v of the drive piston 23 of the drive cylinder 11 corresponding setpoint control by the stepper motor 36 with a constant rate of change of the position setpoint, finally after a few rule games of the type described "steady" state of equilibrium results in which the hollow shaft 49 and the meshing with its thread 51 Engaging threaded spindle 48 with the same angular velocity turn, with the result that the pistons 39 and 41 of the two sub-valves 19 'and 19' 'of the follow-up control valve 19 in the basic positions 0 of these sub-valves 19 ' and 19 '' corresponding positions remain or only minor alternating excursions to these positions exporter and in the basic position I of the main control valve released flow path 112 to an opening cross-section is set in which under the ruling Operating pressure the amount of hydraulic oil in the inflow bottom drive chamber 24 of the drive cylinder 11 - And from the rod-side drive chamber 22nd can be displaced - the desired target value of this Speed corresponds.

With the presupposed type of stepper motor controlled Position and speed setpoint specification is the Stroke that the piston 23 of the drive cylinder 11 in total should perform in the number of electrical control pulses encoded with which the stepper motor 36 to complete Execution of the piston stroke must be controlled, the speed, with which the piston executes this stroke, in the frequency of the control pulses and the direction of rotation in which the stepper motor rotates, e.g. by the polarity of its Control pulses or the phase relationship of two or more Control pulse sequences to each other with which excitation windings of the stepper motor can be controlled in a typical designed to make a 360 ° rotation of its drive shaft 44 is driven with 400 step pulses each lead to a rotation of the output shaft 44 by 0.9 °.

The so far summarized according to structure and function Hydraulic drive unit 10 includes hereafter two coupled together via the overrun control valve 19 Control loops, one of which acts as a follow-up control loop for the Actuator 18 and its second as a follow-up control loop are to be understood for the drive cylinder 11.

The control loop acting on the drive cylinder 11 here has a control loop gain K _v , which is determined by the relationship K v = V S is given, in which v denotes the - constant - speed of movement of the drive piston 23 in the steady - steady - state of the control, and s denotes a stopping distance which represents the "distance" - difference - between the setpoint value, for example, controlled by means of the stepping motor 36 the position of the piston 23 and its actual value. A typical value for the loop gain K _{v of} the power control loop is, for example, a value of 10 s ^-1 .

For reasons of good stability of the control, the loop gain corresponding to the relationship (1) should not be greater than the natural frequency f ₀ to be assumed for the fictitious damping-free case, taking into account a damping that is always present, which is caused by the relationship f 0 = 1 2π · c m is given, in which c denotes the hydraulic rigidity, which is essentially determined by the rigidity of the oil columns enclosed, while m denotes the mass driven by the drive circuit, for example the press bar of a press. From the relationship (2), on the other hand, it follows that the circuit gain of the actuator 18, the pressurization and relief of which is controlled by means of the follow-up control valve 19, can be very high, since the hydraulic stiffness of this control circuit is high due to the short length of the oil column enclosed and the mass to be moved, essentially the mass of the piston 87 of the main control valve 16, is small. Compared to the main drive control loop, for which a loop gain K _v1 of 10 s ^{-1 may be} a typical value, the overrun control loop of the actuator can be operated with a loop gain K _v2 , which can be 50 to 100 times higher than that of the drive control loop .

This makes it possible with a low input power on the setpoint side - essentially the electrical drive power of the setpoint specification motor 36 high hydraulic Control useful services.

To explain the schematic in Fig. 1 and in the Fig. 3 in structural details reproduced fine control valve 17 is now also on the cross-sectional representation 4, which shows the arrangement of the continuous Bore 63 of the follow-up control valve 19, a continuous Valve bore 117 of the fine control valve 17 and two chamber bores 118 of the hydraulic actuator 18 within of the piston 87 of the main control valve 16, the in turn from the through bore 88 of the housing 86 of the main control valve 16 is added.

The central longitudinal axis 38 of the bore 63, the central Longitudinal axes 119 of the two bores 118 for the actuator 18 and the central longitudinal axis 121 of the continuous Bore 117 of the housing for the overflow control valve 19 and the piston 87 of the main control valve forming the fine control valve 17 16 lie on one with the central longitudinal axis 43 a the hollow shaft 49 of the actuating device 42 of the follower valve receiving, with this, apart of a small clearance of longitudinal bore with the same diameter 122 concentric circle of holes and are along the same arranged at equal azimuthal intervals of 90 °, with holes 63 and 117 for the overflow control valve 19 or the fine control valve 17 with respect to the central Longitudinal axis 43 of the central receiving the hollow shaft 49 Bore 122 arranged diametrically opposite one another are likewise the bores 118 for the actuator 18.

Purpose of hydraulically parallel to the main control valve 16 switched fine control valve 17 is a high positioning accuracy of the power drive hydraulic motor 11 also then enable if the piston-side control edges 107 and 108 of the piston 87 and the housing-side control edges 109 and 111 of the main control valve 16, as seen in its basic position, a relatively large positive coverage e have, as explained above with reference to FIGS. 2 and 3 and shown on an enlarged scale in FIG. 5a, to which additional reference is made.

Starting from this basic position it becomes 0 of the main control valve 16 whose piston 87 as a result of its activation actuated by the overrun control valve 19 in Direction of arrow 114 'shifted, i.e. 5a after left, there is an increasing release of the flow path 112 of the main control valve 116 only when its piston 87 in FIG. 5b, to which reference is also made in addition has reached the position shown in dashed lines, i.e. its one - right - piston side control edge 108 and the right housing-side control edge 109 with each other Overlap 0 are arranged opposite one another. Only by further displacement of the valve piston 87 of the main control valve 16 increases with increasing opening cross section Main control valve flow path 112, i.e. its functional position I released. An associated outward movement the piston 23 of the power drive hydraulic motor 11 therefore only begins in practice at the moment to which the overlap of these two control edges 108 and 109 begins to become negative.

Will, after being explained in the meantime by the Overrun control a constant feed rate of Piston 23 of the power hydraulic motor 11 has set that the position shown in solid lines in FIG. 5b of the valve piston 87 of the main control valve 16 relative corresponds to its housing 86, the control of the Stepper motor 16 ended with position setpoint input pulses, so this leads to one in the direction of arrow 116 ' directed displacement of the piston 87 of the main control valve 16 relative to its valve housing 86 and thus already then to a blockage in the functional position I of the Main control valve 16 released flow path 112, if the piston side control edge 108 and the housing side Control edge 109 again in the corresponding to the overlap 0, position shown in broken lines in FIG. 5b have reached, with the result that from reaching this position by moving the piston 87 in the direction of the Arrow 116 'of the drive piston 23 of the power hydraulic motor 11 stops, i.e. before the main control valve 16 again reaches its basic position 0 shown in FIG. 5a is.

The hysteresis of the main control valve 16 caused thereby compared to the functional positions 0 and I or 0 and II of the Sub-valves 19 'and 19' 'of the follow-up control valve 19 would with regard to the end positions of the drive piston 23 of the Power hydromotor 11 lead to an inaccuracy the greater the positive coverage of the piston-side control edges 107 and 108 with the housing side Control edges 111 and 109 in the basic position of the Main control valve 16 is.

Such an inaccuracy with the piston 23 of the power hydraulic motor 11 avoidable positions to avoid the fine control valve 17 is designed such that it one functionally the flow path 112 of the main control valve 116 corresponding flow path 112 ', via which the Output pressure of the pressure supply unit 26 in the bottom Drive chamber 24 of the power hydraulic motor 11 can be coupled or functionally flow path 113 flow path 113 'corresponding to the main control valve 16 already releases when the main control valve 16 for acceptance its functional position I or its functional position II is controlled.

This means that control edges 124 and 126 and control edges 127 and 128 on the housing of the fine control valve 17, by the relative movements of either one flow path 112 'or the other flow path 113' of the fine control valve 17 with a variable flow cross section can be released in the basic position of the fine control valve 17 must have coverage 0 or one of 0 at most, slightly different - positive - coverage may have, and that the basic positions 0 of both the fine control valve 17 and the main control valve 16 exactly, i.e. have to agree as much as possible.

For this purpose, the fine control valve 17 is analogous to the overrun control valve 19 as from two sub-valves 17 'and 17 '' formed, each one according to the basic shape have cylindrical pistons 129 and 131, respectively, of the continuous Bore 117 of the piston 87 of the main control valve 16 formed "housing" of the fine control valve 17th are included.

These pistons 129 and 131 each have an annular groove 132 and 133, their spaced radial groove cheeks over the piston side Control edges 124 and 126 to the cylinder jacket surfaces connect the pressure-tight sliding from the Through hole 117 of the housing of the fine control valve forming piston part of the main control valve piston 87 are.

The pistons 129 and 131 of the two fine control valve elements 17 'and 17 "are provided by a pre-stressed, centrally arranged preloaded spring 134 against one stop pin each 136 or 137, coaxial with the central longitudinal axis 121 of the through bore 117 of the piston 87 of the Main control valve are arranged, the housing of the Fine control valve 17 forms. These stop pins 131 and 137 are as in threaded bores of the housing 86 of the main control valve screw-guided set screws designed, by means of which the positions of the piston-side control edges 124 and 126 of pistons 129 and 131 of the fine control valve with respect to the housing 86 of the main control valve 16 are adjustable. This makes it possible to move along the central axis 121 of the through bore 117 of the piston 87 of the main control valve 16 measured distance of the control edges 124 and 126 of the valve bodies 129 and 131 of the sub-valves 17 'and 17' 'of the fine control valve 17 exactly on those Set the distance on the housing side - at the movable Piston 87 of the main control valve 16 arranged control edges 127 and 128 - due to their design.

The fine control valve 17 can therefore, with the piston held 87 of the main control valve 16, always adjusted accordingly be that the coverage of its piston-side control edges 124 and 126 with its housing-side control edges 127 and 128 is 0 or any desired - small - Value corresponds when the fine control valve 17 is in its Home position.

This alone makes it possible, as it were experimental, i.e. through attempts to position the piston elements To determine 129 and 131 of the fine control valve 17, the one Home position 0 of the main control valve 16 corresponds in the the control edges 107 and 108 of its valve piston 87 with the relevant control edges for the main control valve 109 or 111 same - positive - coverage have the same amount and thereby the fine control valve 17th to the stated position of its valve piston elements 129 and 131 to set.

Due to this adjustability of the pistons 129 and 131 the Fine control valve 17 forming part valves 17 'and 17' ' functionally controlled 2/3-way valves with one of coverage 0 or a very small - positive - Coverage of their control edges 124 and 127 or 126 and 128 corresponding basic position 0, a flow position I and a blocking position II, which is a partial valve 17 'or 17' 'reaches its locked position II, when the other partial valve 17 '' or 17 'in its flow position I arrives at every deflection of the valve piston 87 of the main control valve 16 and with this accompanying displacement of that by this piston 87 formed housing of the fine control valve 17 a defined Changes in the effective flow cross-section linked is under the hydraulic oil in the bottom drive chamber 24 of the drive hydro motor 11 displaceable into it is or can flow out of this, and that with the Blocking this flow path, i.e. the standstill position of the piston 23 of the drive hydraulic motor 11 always one precisely defined position of the piston 87 of the main control valve 16 and the housing of the fine control valve 17 linked is due to the housing-fixed arrangement of its valve pistons 129 and 131 can be specified. With the hydraulic Drive unit 10 is therefore a very precise and sensitive Maintaining a predetermined position of the piston 23 of the Hydraulic motor 11 possible with only low control energy by means of the stepping motor 36 and the overrun control valve 19, as already explained in detail, is taxable.

The one that can be slid back and forth in the housing 86 Piston 87 is in two parts for manufacturing reasons trained and includes an outer, thick-walled jacket-shaped Piston part 87 ', that with the piston-side P and T grooves 101 and 102 is provided, and an inner, cylindrical-block-shaped Piston part 87 '' with the central from the hollow shaft 49 of the actuating device 42 of the follow-up control valve 19 penetrated through hole 122, the Through hole 63 of the follow-up control valve 19, the Through bore 117 of the fine control valve 17 and the chamber bores 118 is provided for the actuator 18.

The chamber bores designated 118 in FIGS. 2, 3 and 4 are designed as blind holes, which according to 2 and 3 from the right front side of the inner piston part 87 '' are introduced into this. In each of these bores 118 there is a cylindrical piston 138, relative to the piston element 87 ″ of the main control valve piston 87 used in a pressure-tight, flexible manner, on one along the central longitudinal axis 119 of the respective bore 118 extending slim stop pin 139 fixed to the housing is axially supported.

The through the two blind bores 118 and the two pistons 138 delimited chambers that run over radial channels of the interior Piston element 87 '' and the outer piston element 87 'in communicating connection with its outer P-groove 101 stand, overall form those in operation of the drive unit permanently below the outlet pressure P of the pressure supply unit held drive chamber 34 of the actuator 18, 1 as the rod-side chamber of the double-acting Actuating drive cylinder 18 is shown.

In a coaxial arrangement with the central longitudinal axis 119 of the Blind bores 138 are in the inner piston part 87 'of the piston 87 of the main control valve 16 also from the left end face blind holes 118 ', into which one cylindrical piston 138 'each relative to the piston element 87 '' is used so that it can be moved in a pressure-tight manner on a along the central longitudinal axis 121 of the respective bore 118 'extending housing-fixed stop pin 139 'is axially supported.

These two blind bores 118 'and the two pistons 138', whose cross-sectional area is larger by a factor of 2 than that arranged axially opposite Blind bores 118 and pistons 138, limited chambers, which alternatively with the overflow control valve 19 unpressurized reservoir 92 of the pressure supply unit or its high pressure outlet 81 can be connected, form a total 1 as the bottom-side drive chamber 33 of the actuator 18 shown drive chamber of the same.

A particularly space-saving design of the electrohydraulic control part of the drive unit 10 is achieved as a whole by the described engineering of the follow-up control valve 19, the fine control valve 17 and the actuator 18 formed by two pairs of pistons and bores in the piston 87 of the main control valve Lengths of the hydraulic oil flow paths also result in high hydraulic rigidity and thereby contribute to high values of the achievable loop gain K _v

The drive unit 10 is only schematic with one electronic position sensor 141 shown, whose output signal is an exact measure of deflections the actuating device 42 of the overrun control valve 19 in the direction of the central longitudinal axis 43 of the actuating device 42 are.

In a special design, the position sensor 141 is through a firmly mounted on the housing 86 of the main control valve 16 Magnetic field sensor realizes the field strength of a on one of the actuating arms 68 or 69 of the follower valve 19 permanently attached permanent magnet 142 detects the is arranged so that under the occurring axial displacements the actuator 42 the field strength on Location of the magnetic field sensor linearly in a very good approximation varies so that the output signal of the magnetic field sensor 141 directly the deflection stroke of the actuating device 42, e.g. the hollow shaft 49 is proportional.

The position sensor 141 can be easily recorded its path / output signal level characteristic and approach the basic positions of the follow-up control valve 19 and Fine control valve 17 or the main control valve 16 calibrated and for a continuous determination of the overtravel s be used.

Alternatively or in addition to the position of the hollow shaft 49 of the actuator 42 detecting position sensor 141, a position transmitter, not shown, can also be provided be the deflections of the valve piston 87 of the Main control valve 16 is detected relative to its housing 86.

1 to 5b are structurally identical or analogous Elements with the same reference numerals. So far in Figures 1-5b reference numerals for elements are, which are not in the explanation of the respective Fig mentioned, but has been described with reference to another Fig are, this is the reference to the relevant part of the description include.

Claims (18)

1. Hydraulic drive unit comprising

   a) a hydraulic motor as a power drive designed for a high driving power and if necessary a corresponding high throughput of hydraulic oil;

   b) a main control valve (16) by means of which an afflux of hydraulic oil at high pressure to the power drive and the efflux of at least a part of the hydraulic oil supplied to the power drive, for example to the zero-pressure supply container of the pressure supply assembly, can be controlled;

   c) a hydraulic servo drive (18) designed as a doubleacting linear cylinder for actuating the main control valve; and with

   d) a follow-up control valve (19) provided to control the servo drive, with a setting, controlled by an electric motor, of the desired values of the positions and therefore also of the speed of movement of the movable element of the power hydraulic motor and mechanical feedback of the corresponding actual values, said control valve, when the desired value and the actual value of the controlled position are equal assumes a blocking position corresponding to stoppage of the power drive, said valve being controllable by the position desired value setting to assume the alternative through-flow positions associated with the alternative driving directions of the power hydraulic motor, in which positions the respective effective through flow cross section varies monotonically with the degree of deflection of the valve from the blocking position and being controlled by the position actual value feedback so as to assume the blocking position;

   e) the follow-up control valve (19) and the main control valve being designed as piston slide valves operable by relative axial displacements of their valve pistons and housing elements that occur along mutually parallel axes, and the piston (87) of the main control valve forming the housing of the follow-up control valve (19);

   characterized by the following features:

   f) the follow-up control valve (19) has two piston elements (39, 41) located within a through-bore (63) of the main control valve piston (67), said bore extending parallel to the central longitudinal axis (43) of the main control valve piston (87) but at a radial distance from said axis, with the axial spacing of said elements (39, 41) being adjustable for adjustment of a defined overlap of piston-side control edges (73, 74) and housing-side control edges (76, 77) of the follow-up control valve (19) located inside the through bore (63) of the piston (87) of the main control valve (16);

   g) the piston (87) of the main control valve (16) is provided with a central axial through bore (122) through which passes a desired value setting element (49) nonrotatably coupled with the driven shaft (44) of a desired value setting motor (36) but axially displaceable with respect to the drive shaft and to the piston (87), said element (49) being in zero-play threaded engagement with an actual value feedback element (48) rotationally drivable by the movable part (23) of the power hydraulic motor (11) in a positive correlation with the rotational or translational movements of the movable part (23) and having the same direction of rotation as the desired value setting element (49) but being axially nondisplaceable, thereby the desired value setting element (49) being subjected to axial deflections relative to a central position correlated with the blocking position (O) of the follow-up control valve (19), said deflections being directly correlated with the difference between the desired and actual positions of the movable part (23) of the power hydraulic motor (11) and enabling the opening and closing actuations of the follow-up control valve (19) by actuating elements (68, 69) which are decoupled rotationally with respect to the desired value setting element (49) but following its axial movements;

   h) the driving pressure chambers (33, 34) of the servo drive (18) provided to actuate the main control valve (16) are delimited by blind holes (118, 118') of the piston (87) of the main control valve (16), said holes extending parallel to the central through-bore (122) and being arranged at a radial distance from the central axial through bore (122) of piston (87), and by pistons (138, 138') that are received by the blind holes and are supported in a fixed position on the housing (86) of the main control valve (16).
2. Drive unit according to Claim 1, characterized in that a fine control valve (17) is provided, connected hydraulically in parallel with main control valve (16) and controllably operable together with the latter from its basic position 0 into its alternative functioning positions (I and II), said fine control valve likewise being designed as a piston slide valve, whose housing-side and piston-side control edges (124, 126 and 127, 128), by the relative movements of which the through-flow paths (112', 113') effective in the alternative functional positions, can be opened with a flow cross section that is proportional to the deflection of its piston elements from the basic position, are adjustable to a -preferably positive- overlap which is present in its basic position, and which is much smaller and corresponds to only 1/20 to 1/5 of the also positive overlap of functionally corresponding control edges (107, 108, 109, 111) of the main control valve (16) in its basic position.
3. Drive unit according to Claim 2, characterized in that the piston arrangement (129, 131) of the fine control valve (17) comprises two piston elements (129 and 131) displaceably mounted in an axial through bore (117) of the piston (87) of the main control valve (16) in a pressure-tight manner, the position of said elements being adjustable with respect to the housing (86) of the main control valve (16).
4. Drive unit according to Claim 3, characterized in that, a - slightly - pretensioned spring (134) is located between the two piston elements (129 and 131) of fine control valve (17), said spring urging each of the piston elements (129, 131) against a respective axial stop pin (136, 137) whose position is variably adjustable in the axial direction.
5. Drive unit according to Claim 3 or Claim 4, characterized in that the two piston elements (129 and 131) and the sections of the bore (117) of the piston (87) of the main control valve (16) provided to receive the fine control valve (17), each form a 2/3-way valve (17' and 17"), one of which assumes its blocking position when the other assumes its through flow position and to which correspond, respectively, equal amounts of positive and negative overlaps of their control edges (124, 127 and 126, 128).
6. Drive unit according to one of Claims 3 to 5, characterized in that the bore (117) of the piston (87) of the main control valve (16) that receives piston elements (129, 131) of the fine control valve (17), and a through bore (63) of the main control valve piston (87) receiving the piston-shaped valve bodies (39 and 41) of the follow-up control valve (19), are arranged diametrically opposed relative to the central longitudinal axis (43) of the piston (87).
7. Drive unit according to one of Claims 1 to 6, characterized in that the hydraulic positioning drive (18) has a housing axially displaceable so as to reciprocate by alternative exposure to pressure and release of pressure in at least one drive chamber (33).
8. Drive unit according to Claim 7, characterized in that the housing of the positioning drive (18) is formed by a part of the piston (87) of the main control valve (16).
9. Drive unit according to Claim 8, characterized in that the piston (87) of main control valve (16) is provided with at least two blind holes (118, 118'), provided at two mutually opposed faces of the piston (87), in each of which holes, for delimiting a respective drive chamber (33 and 34), a piston (138 and 138') is located, which piston is axially supportable on a stop pin (139 or 139') rigidly affixed to the housing (86) of the main control valve (16).
10. Drive unit according to Claim 9, characterized in that the two pistons (138 and 138') of positioning drive (18) are designed as free pistons.
11. Drive unit according to Claim 9 or 10, characterized in that two bore and piston pairs (118, 118', 138, 138') are provided, preferably of the same design, each of which is arranged coaxially with respect to a common central axis (119, 119').
12. Drive unit according to Claim 11, characterized in that the two bore axes (119, 119') of the bores (118, 118'), each of which receives a piston pair (138, 138') of the positioning drive (18) of the piston (87) of the main control valve (16), are arranged diametrically opposed to one another with respect to the central longitudinal axis (43) of said valve (16).
13. Drive unit according to one of Claims 7 to 12, characterized in that the hydraulic positioning drive (18) is designed as a differential cylinder with driving pressure chambers (33 and 34) having different effective cross-sectional areas, with the drive chamber(s) (34), having the smaller effective cross sectional area, being permanently exposed to the high output pressure of the pressure supply assembly (26, 92) during the operation of the drive element (10).
14. Drive unit according to Claim 13, characterized in that the ratio f₁/f₂ of the effective cross-sectional areas f₁ of the drive chamber(s) (33), alternatively exposable to high pressure and relievable of pressure, to the area f₂ of the drive chamber(s) (34) of the positioning drive (18) permanently exposed to the high output pressure of the pressure supply assembly, has a value of 2.
15. Drive unit according to one of Claims 1 to 14, characterized in that the piston (87) of the main control valve (16) consists of two parts with an outer sleeve-shaped piston part (87') provided with external annular grooves (102 and 101) forming control edges (107, 108) on the piston side and with a core (87") which is block-shaped, fitted firmly into the sleeve-shaped piston part (87') in a pressure-tight manner, and is circularly cylindrical in basic shape, in which core the axial through bores (63 and/or 117) are provided for the follow-up control valve (19) and/or the fine control valve (17) and, if provided the blind holes for the drive chambers (33 and 34) of the positioning cylinder (18), and a central through bore (122) is provided to receive the actuating device (42) of the follow-up control valve (19).
16. Drive unit according to one of Claims 1 to 15, characterized by an electronic or electromechanical position sensor (141, 142), said sensor generating an electrical output signal that characteristic of at least the central position of main control valve (16).
17. Drive unit according to one of Claims 1 to 16, characterized by a position sensor (141, 142) which generates an output signal that is characteristic of the position of the actuating element (49, 68, 69) of the follow-up control valve (19), said signal varying in a preferably monotonic relationship with the position of the actuating member, and/or a position sensor which generates an electrical output signal that is characteristic of the position of the piston (87) of the main control valve (16) and varies in a unique correlation with said position.
18. Drive unit according to Claim 16 or 17, characterized in that the position sensor is designed as a magnetic field sensor (141) in locally fixed arrangement, which detects the magnetic field change that results from the movement of a permanent magnet (142) permanently connected with the position-monitored element.

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