EP0808422B1 - Process and device for feeding concrete or other thick materials - Google Patents

Description

The present invention relates to a method for conveying concrete or other thick matter from a container into a delivery line by means of two delivery cylinders which can be connected alternately to the container or the delivery line by means of a changeover device, the delivery pistons of which alternately carry out a suction and a pressure stroke, the average piston speed during the suction stroke is at least temporarily greater than during the pressure stroke, whereby during the changeover period t _{u of} the changeover device, the two delivery cylinders are at least temporarily essentially separated from the container and short-circuited to one another with a common connection to the delivery line, and in this state the delivery piston has its pressure stroke still ended and at the same time the other delivery piston already begins its pressure stroke, the corresponding delivery piston only executing its suction stroke when the short-circuit is essentially repeated r canceled and the associated delivery cylinder is connected to the container, and a device for performing the method.

Such a method and an apparatus are known from US Pat US-A-4,343,598 is known. In this device, each delivery cylinder assigned a swivel tube within the container. The outlet openings of the swivel pipes are via a pipe connector merged to the delivery management. By doing so The two swivel tubes should be controlled continuously Flow arise.

Furthermore, from DE-PS 3525003 was a method and Device known in which the first feed cylinder The pressure stroke has not yet ended during the second delivery cylinder already with the pressure stroke with a lower conveying speed begins. After the first delivery cylinder The pressure stroke has ended, the changeover process of the changeover device begins, while the second feed cylinder continues at a lower conveying speed. By doing this is achieved that the concrete in the second delivery cylinder is already moved so that after switching the Switching device does not close the concrete column in the delivery pipe can spring back strongly. This method and the one used All in all, devices have proven themselves very well. In technology, however, there have been recent demands after ever more efficient processes for concrete conveyors become loud. So there are serious aspirations that Length of the delivery pipe and thus in particular to increase the delivery head. Since in the known method during the switching period pumped with each other at a lower conveying speed there is a small pulsation in the flow. This could be neglected in the usual funding conditions , but leads to the now required funding levels and thus large projections, for example in the arm of a concrete conveyor, to vibrations at the end of the conveyor pipe.

It is therefore an object of the present invention simplified method and device for Delivering concrete from a container to a delivery line, reduced by the irregularities in the flow will.

This object is achieved by a generic Method solved in which the short circuit from a single changeover device is brought about, the two feed cylinders disconnects from the container in the event of a short circuit.

The method according to the invention avoids that during the changeover period t _u only a conveying takes place at a lower conveying speed. This is achieved by short-circuiting the two delivery cylinders, which can be replaced in the short-circuited state without loss of changeover times in delivery at full delivery speed. Short-circuiting also automatically compresses the concrete column in the delivery cylinder that begins the pressure stroke. This method avoids pulsation shocks due to the continuous flow provided. The method according to the invention is intended for concrete pumps with a single changeover device (for example a single swivel tube) which works simultaneously with both delivery cylinders.

In an advantageous variant of the method, the properties of the material to be pumped are taken into account even more. This is done in that the delivery piston, which has ended the suction stroke, already begins the pressure stroke during a time period Δ t of the changeover time period t _u , while the other delivery piston has not yet ended its pressure stroke. As a result of this measure, the concrete column can already be pre-compacted in one of the delivery cylinders so that, for example, gas influences or delivery cylinders that are not completely filled do not lead to undesired delivery fluctuations. In a further variant, it is quite sufficient for this to be the case if the speed of the delivery cylinder starting the pressure stroke in the time segment AT is lower than the average speed during the remaining pressure stroke. The start of the pressure stroke of one of the delivery cylinders can be selected with regard to its start time and its speed so that all losses to be taken into account and thus fluctuations are compensated for by, for example, the material to be delivered. In a further variant of the method, both delivery pistons can be moved substantially at half the average speed V _{1 of} the remaining pressure stroke during the time period. This has the advantage that the switch from one to the other delivery piston can take place almost in stages since the partial delivery flows add up to the continuous total delivery flow.

The method according to the invention is advantageously carried out by a device carried out by at least two by one Changeover device alternating with a container or a Delivery line has connectable delivery cylinders, the Delivery pistons alternating with one another suction and one Execute pressure stroke, with the changeover device along the open end areas of the feed cylinder with its inlet opening pivotable swivel tube is. The device is characterized in particular by the fact that the inlet opening and the surrounding closure areas of the swivel tube in such a way are executable that the feed cylinder during a changeover essentially shorted together with the delivery pipe but are essentially separate from the container.

This device has the advantage that known devices in principle can be used in which only the switching device designed differently in the form of a swivel tube must become. The swivel tube must have its inlet opening According to the invention ensure that during the pivoting process or changeover process, at least temporarily a short circuit the two delivery cylinders is manufactured.

Advantageously, the inlet opening can be in the form of a substantially bent around the swivel axis of the swivel tube Be elongated and have a length that is approximately corresponds to the outside distance of the two feed cylinder openings. To safely separate the feed cylinder from the container To achieve this, the locking area can be extended of the elongated hole and have a width, which is essentially the diameter of the feed cylinder openings corresponds. This prevents a short circuit between a delivery cylinder carrying out a pressure stroke and the container will be produced.

The device is preferably controlled hydraulically, for which purpose a cylinder-piston unit in each case in a first embodiment can be provided in which an optional switchable line in the piston-side space of each cylinder leads, with an additional pump for further pressure medium supply of the two pressure chambers of the second cylinder-piston units is arranged, located between the piston ends Pressure chambers of the cylinder-piston units themselves connecting strand of Hydraulic system extends in which one over a Changeover valve either with the additional pump or with a Pressure medium return connectable strand opens, the Sections of the strand between each cylinder and the Muzzle of the strand one by the pressure of the Cylinder closable check valve included, and where the cylinders of the cylinder-piston units in the end area a rod connecting their piston rod side have, which is also optionally via the switching valve connectable to the pressure medium return or the additional pump is. The additional pump for the pressure supply of the pressure stroke beginning cylinder-piston unit ensures that the still pushing delivery pistons no drive energy withdrawn must become. The energy supply to the piston, which is in Movement is timely and simple turn on exactly in size. Because of the in the pressure stroke located cylinder-piston unit, and thus on her associated check valve the pressure of the hydraulic pump pending which exceeds the pressure from the auxiliary pump, only the other piston to be set in motion act upon. This also applies to the downtime of the Piston that has completed the pressure stroke. The additional pump ensures also for a higher than the pressure stroke Speed of the piston in the suction stroke.

Independent control of the cylinder-piston units is achieved in a second embodiment in that the cylinder-piston units each have a separate one Pump can be supplied with pressure medium. With one Can design speed and switching cycles depending on the control of the pumps used to be provided.

The process sequence according to the invention can be carried out at a third embodiment of the device achieve that each have a cylinder-piston unit for Driving the delivery piston is provided, in which one optionally switchable line of a first pump with the piston rod-side space of each cylinder connectable or is separable from these that a second pump for Pressure medium supply to the two piston ends Pressure rooms individually or via a switchable line is connectable to the pressure rooms, and that the piston rod-side spaces of each cylinder together with a pressure medium return can be connected. Reaching the different piston speeds is caused by the Pump control and the area ratio of pistons too Piston rod determined. Furthermore sees this Embodiment before that the two pistons with the same Speed move in the pressure stroke, whereby the Control usually takes place so that one piston in this state ends its pressure stroke and the other this begins. If the second pump has a constant flow thus the pressure medium flow is halved and divides on the two cylinders, so that they each move at half speed, but still together generate a constant flow.

In a third embodiment there is a cylinder-piston unit provided for driving the delivery pistons, in which an optionally switchable line of a first pump each with an adjustable current divider together with the piston-side pressure chamber of each cylinder and the piston rod-side space of every other cylinder is connectable or separable from these, a second Pump for supplying pressure medium to the piston face Pressure rooms individually or via a switchable line is connectable to the pressure rooms, each the flow dividers with the piston-side pressure chambers of the Cables connectable strands can be switched through or are blockable, and the current divider, if this from the first pump, together with one Pressure medium return are connectable. By this arrangement is the different control essentially by to regulate the pumps. The fine adjustment of this device takes place via the second pump.

To use a second pump in a fifth embodiment one cylinder-piston unit is to be dispensed with Driving the delivery piston provided at one optionally switchable line of a pump with the piston rod-side space of each cylinder connectable or is separable from this, a second optional switchable line of this pump with the piston end Pressure chambers of the cylinders can be connected together or by this is separable, the piston end Pressure chambers of the cylinders with a rocker line are interconnected, and wherein the piston-side pressure chambers via an optional switchable line together with a pressure medium return can be connected or separated from this. With this Hydraulic circuit ensures that in one volume displaced at the piston end for the fact that the other piston is moved accordingly. Since the Swing line optionally with the pressure medium return is connectable, can be pushed through the rocking line Volume flow can be influenced.

Furthermore, one cylinder can advantageously each its piston end on a control line the control port side of the other cylinder associated check valve connected. The Swivel tube can be moved by means of a slide Controlled two-way valve can be actuated with a Pump and / or a pressure accumulator is connected.

An embodiment of the invention is as follows explained in more detail using a drawing.

Fig. 1

eine schematisierte, teilweise weggeschnittene Ansicht einer Fördervorrichtung für Beton,

Fig. 2

eine erste Ausführungsform eines vereinfachten hydraulischen Schaltschemas für den Antrieb der Vorrichtung,

Fig. 3

ein schematisiertes Schaltschema der den Förderzylinder zugewandten Stirnseite des Schwenkrohres,

Fig. 4

ein Weg-Zeitdiagramm der beiden Förderkolben gemäß der einer ersten Verfahrensvariante der vorliegenden Erfindung

Fig. 5

fünf Arbeitsstellungen der Kolben-Zylinder-Einheiten gemäß des Diagramms aus Fig. 4,

Fig. 6

ein Weg-Zeitdiagramm einer zweiten Verfahrensvariante gemäß der vorliegenden Erfindung,

Fig. 7

fünf Arbeitsstellungen der Kolben-Zylinder-Einheiten gemäß der zweiten Verfahrensvariante aus Fig. 6,

Fig. 8

eine zweite Ausführungsform eines vereinfachten hydraulischen Schaltschemas für den Antrieb der Vorrichtung,

Fig. 9

eine dritte Ausführungsform eines vereinfachten hydraulischen Schaltschemas für den Antrieb der Vorrichtung,

Fig. 10

eine vierte Ausführungsform eines vereinfachten hydraulischen Schaltschemas für den Antrieb der Vorrichtung, und

Fig. 11

eine fünfte Ausführungsform eines vereinfachten hydraulischen Schaltschemas für den Antrieb der Vorrichtung.

It shows:

Fig. 1

2 shows a schematic, partially cut-away view of a conveying device for concrete,

Fig. 2

a first embodiment of a simplified hydraulic circuit diagram for driving the device,

Fig. 3

2 shows a schematic circuit diagram of the end of the swivel tube facing the delivery cylinder,

Fig. 4

a path-time diagram of the two delivery pistons according to a first method variant of the present invention

Fig. 5

five working positions of the piston-cylinder units according to the diagram from FIG. 4,

Fig. 6

2 shows a path-time diagram of a second method variant according to the present invention,

Fig. 7

five working positions of the piston-cylinder units according to the second method variant from FIG. 6,

Fig. 8

a second embodiment of a simplified hydraulic circuit diagram for driving the device,

Fig. 9

a third embodiment of a simplified hydraulic circuit diagram for driving the device,

Fig. 10

a fourth embodiment of a simplified hydraulic circuit diagram for driving the device, and

Fig. 11

a fifth embodiment of a simplified hydraulic circuit diagram for driving the device.

The conveyor device shown in Fig. 1 shows in a Top view of an approximately funnel-shaped container 1 for receiving of concrete, for example from ready-mixed concrete mixers. The concrete is in an only indicated delivery line 2 via Swivel pipe 3 and a pipe bend 4 promoted. this happens by means of two delivery cylinders 5, the delivery pistons 6 alternately one suction and one pressure stroke To run. The swivel tube 3 is hydraulic via a Slider 7 each in its desired position with respect to The mouth of the two feed cylinders 5 can be pivoted. 1 is the mouth of the suction feed cylinder 6 to the container 1st open so that the cylinder fills from there (see the arrow shown in dashed lines).

The delivery pistons 6 are by means of cylinder-piston units 8 moves, of which in Fig. 1 only the cylinder 9 schematically are indicated. At the junction between the Delivery cylinders 5 and the cylinder-piston units 8 are Housing 10 arranged. Like below is described, the pivot tube 3 in this Embodiment funnel-shaped, so that both Delivery cylinder 5 at the same time as the delivery line 2 are temporarily connectable.

2 shows a first embodiment of a simplified schematics of a hydraulic system for actuation the cylinder-piston units 8 and so coupled delivery piston 6. A delivery cylinder 5 and Delivery pistons 6 are fragmentary and schematized in Connection with one of the cylinder-piston units S indicated. It is also schematized by the Hydraulic system actuated slide 7 indicated.

Each cylinder-piston unit 8 has a piston 11, the Sequence of movements on his piston rod 12 on the Transfer piston 6 transmits.

The drive for the cylinder-piston units in the pressure stroke takes place essentially by means of a hydraulic pump 13. A Auxiliary pump 14 supplies the for certain movement sections Piston additional flow. The hydraulic pipeline network has the following sections:

A line 15 leads from the hydraulic pump 13 to a branching point 16 and from there a line 17 to a two-way valve 18 and a line 19 to a changeover valve 20. From the two-way valve 18, a line 21 leads to the area of a cylinder 9 ₁ on the piston side. the index designations 1 and 2 are used below for the two piston-cylinder units when describing their movement sequences).

A line 22 leads from the two-way valve 18 into the piston-side pressure chamber of the cylinder 9 ₂ . The strands 21 and 22 are thus selectively connectable to the hydraulic pump 13 through the two-way valve 18.

A strand 23 leads from the changeover valve 20 to the one Strand 24 to the other side of a piston 7a in slide 7. In addition, a strand 25 leads from the switching valve 20 to the return 26 such that, depending on the valve position, one side of the slide 7 with the hydraulic pump 13 and the other with the Return 26 is connected.

A wiring harness 27 connects the two piston end regions of the cylinders 9 ₁ and 9 _{2 to} one another. Between the two branches 28 to a switch valve 29. Before the end of the branch 28 into the cylinders 9 ₁ and 9 ₂ , the branch 27 each contains a check valve 30 or 31, each with the closing direction towards the branch 28.

From the changeover valve 29, a line 32 leads to the return 26 and a line 33 to the auxiliary pump 14. In addition, a line 34 leads from the changeover valve 29 into the area of the cylinder-piston units, where it flows into the areas of the cylinders 9 ₁ and 9 _{2 on} the rod side connecting strand 35 opens. This line contains no valves.

A control line 36 runs between the piston-side area of the cylinder 9 ₁ and the control connection side of the check valve 31. Likewise, the cylinder 9 _{2 is} connected to the check valve 30 via a control line 37.

The hydraulic pump 13 is a pressure relief valve 38 which Additional pump 14 assigned a pressure relief valve 39.

With the device described and an additional controlled switching system for the changeover valves 20, 29 and that Two-way valve 18 is a sequence of movements of the pistons 11 achievable, based on Figures 3 to 7 below is described. The sequence of movements applies in the same way for the delivery piston 6 and thus determines the delivery of concrete the container 1 into the delivery line 2.

The following is a first with reference to Figures 3 to 5 Process variant according to the present invention under Use of the device described above described in more detail.

In particular in Fig. 3 it can be seen that the Delivery cylinder 5 facing end face 40 of the swivel tube 3 in is essentially kidney-shaped. In the front 40 there is an arcuate inlet opening 41, the width B essentially the diameter D of the mouth opening 42, 43 of the Delivery cylinder 5 corresponds. The length L of the inlet opening 41 corresponds to the external distance A of the two orifices 42, 43. The inlet opening 41 thus has the shape of a curved one Elongated, whose arc center in the pivot axis 44 of the Swivel tube 3 is. Furthermore, the end face 40 closure areas 45, 46 at the end of each inlet opening 41 on, the smallest distance C from the inlet opening 41 to Outer edge to the diameter D of the mouth openings 42, 43 corresponds. Starting from the end face 40 of the swivel tube 3 this runs funnel-shaped on its second with the Supply line 2 connected end to. The inlet opening 41 is also reduced to the funnel shape corresponding opening at the opposite end. Apart from the transition states can be essentially determined by the The swivel tube 3 is designed according to the invention in FIG. 3 shown, five states for the control of the system are critical to achieve.

In the following description, the corresponding positions of the pistons 11 ₁ and 11 _{2 are} assigned to the respective position of the swivel tube 3 with reference to FIGS. 3 to 5.

The starting position for phase I is the position of the pistons and the swivel tube, as shown in FIGS. 3 and 5. The hydraulic pump 13 acts on the cylinder 9 ₁ via the branch 15, the valve 18 and the branch 21 with a pressure P ₁ . At the same time, the hydraulic pump 13 holds the slide 7 in its position on the right in the figure via the strands 15, 19 and 23 and the valve 20. The right side of the slide is connected to the outlet 26 via the changeover valve 20. The rod-side areas of the cylinders 9 ₁ and 9 ₂ are connected to the return 26 via the strands 35, 34 and the changeover valve 29. The auxiliary pump 14 is connected via the strands 33, 34 and 35 and the valve 29 to the end of the pistons 11 ₁ , 11 _{2 on} the piston rod side. By switching the changeover valve 29, the additional pump 14 now applies a pressure P ₂ to the cylinders 91 and 9 ₂ in their region on the piston rod side. The pressure P ₂ is less than the pressure P ₁ . The piston 11 ₁ therefore presses the liquid to be displaced by it into the line 35 against the pressure P _2. The piston 11 ₁ thus receives an additional pressurization on the rod side for the action of the pump 14. Its return stroke takes place at the speed V ₃ . This stroke movement corresponds to the suction stroke of the associated delivery piston 6.

Because the speed V _{3 is} greater than the speed V1, the piston 11 ₁ has not yet completed its pressure stroke when entering phase II, while the piston 11 _{2 is} already finished with its suction stroke. In the corresponding time-distance diagram in FIG. 4 it can be seen that the changeover time range t _u begins with phase II. During a time period Δt of the changeover time range tu, the piston 11 ₂ and thus the corresponding delivery piston 6 are at a standstill. The advantage lies particularly in the fact that the closure area 46 of the end face 40 is not subjected to unnecessary high pressure. The pivot tube 3 pivots in phase II by switching the valve 20 so far that the orifice 42 is separated from the container 1.

When phase III is reached, both mouth openings 42, 43 and thus both delivery cylinders 5 are now short-circuited with the inlet opening 41 and thus the delivery line 2. In this state, the two-way valve 18 switches. As a result, the hydraulic pump 13 is connected to the area of the cylinder 9 ₂ on the piston side. The piston 11 ₂ now carries out a pressure stroke at the speed V ₁ until the end of phase IV is reached. In phase IV, the swivel tube 3 pivots further in such a way that the outflow region 45 gradually sweeps over the mouth opening 43. The piston 11 ₁ is stationary during this time.

When the orifice 43 is completely separated from the inlet opening 41 and a connection to the container 1 is restored, the auxiliary pump 14 is now on the strands 33, 34, 35 and the switching valve 29 with the piston rod-side areas of the cylinders 91 and 9 ₂ in Connection so that the piston 11 ₂ against the pressure P ₂ presses the liquid to be displaced during the pressure stroke into the strand 35, the piston 11 ₁ thus receiving an additional pressurization on the rod side for the action of the pump 14. Its return stroke takes place at the speed V _3, see phase V. This stroke movement corresponds to the suction stroke of the associated delivery piston 6. At the end of phase III, ie at the beginning of phase IV, the pistons 11 ₁ and 11 _{2 have} exchanged their starting position exactly. The rest of the procedure corresponds to the procedure described, only with the pistons swapped accordingly and the pressurization swapped accordingly.

The movement sequence of the swivel tube 3 shown in FIG. 3 thus takes place between the end of phase I and the beginning of phase V, that is to say during the changeover period of the t _u . The switching positions assigned to the travel-time diagram during the pivoting movement of the pivoting tube 3, see FIG. 3, can be configured variably and do not have to be carried out exactly according to this exemplary embodiment. Overlaps of the phases may even be desirable depending on the operating conditions. 4 clearly shows that the pressure strokes of the cylinders 11 ₁ and 11 ₂ detach at the same conveying speed V ₁ without loss of time at the end of the time interval Δt and thus provide a continuous flow. According to the invention, it is important here that the orifices 42, 43 of the delivery cylinder 6 are short-circuited with the inlet opening 41 and thus the delivery line 2 in this state. Another important point is that both mouth openings 42, 43 are separated from the container 1 and accordingly do not begin their suction stroke until the short circuit is removed again.

On the basis of the path-time diagram for the pistons of the hydraulic device, which essentially corresponds to the stroke sequence of the delivery pistons for the concrete delivery, it can be seen that the entire pressure stroke of a delivery piston takes a longer period, namely t ₁ , than the suction stroke with the duration t ₃ . However, the time total from the suction and pressure stroke, t ₁ + t ₃ , always remains the same, so that the opposite direction of the piston movements on both sides is obtained.

In particular with reference to Figures 3, 6 and 7, a second Process variant according to the present invention closer explained. It will only focus on the essentials Differences from the previous embodiment closer received. For the same and similar procedures and Components are therefore given the same reference numbers.

The device shown in Fig. 2 is in particular by the switching valve 29, the check valves 30, 31, and their Control lines 36, 37 capable of one of the cylinders 9 already to let its pressure stroke begin while the other cylinder 9 has not yet completed its pressure stroke. This is particularly so then advantageous if possible losses, for example through insufficient filling or air pockets in the concrete, must be balanced.

Starting from the end of phase I, that is to say at the beginning of phase II, the additional pump 14 is connected to the front end of the piston 9 ₂ via the strands 33, 28, 27 and the valves 29, 31. The auxiliary pump 14 thus acts on the piston 11 ₂ with a pressure P ₂ from the beginning of phase II to the beginning of phase III during the period Δt. The piston 11 ₁ ends the pressure stroke at the speed V ₁ . The piston 11 ₂ already begins its pressure stroke under the action of the pressure P ₂ at a speed V ₂ which is less than the speed V ₁ . When phase III is reached, the changeover valve 18 switches over and the additional pump 14 is separated from the front end of the piston P ₂ . Due to the pressure stroke with reduced speed V ₂ in the time interval Δt, the concrete column in this delivery cylinder is already pre-compacted, so that, for example, material-related pressure losses can be compensated for. Thus, both pistons press during the period Δt. The one delivery piston, which is still connected to the delivery line 2 via the swivel tube 3, ends its pressure stroke in this period and then stops during the changeover time t _u . At the end of its suction stroke, the other delivery piston is slowly set in motion again in the direction of the pressure stroke with the aid of the additional pump 14. The concrete that has just been sucked into the cylinder in the opposite direction thus also already receives an initial movement in the direction of the mouth opening 42. After the end of the time interval Δt, that is to say after the short circuit has been established between the two orifices 42, 43 and the simultaneous switchover to a larger oil flow rate by the hydraulic pump 13, the speed of the delivery piston changes. The concrete is pressed out of the delivery cylinder into the delivery line 2 without the risk of a sudden transition, a stall or even a return caused by poor filling. After the changeover process has ended, that is to say after the time t _{u has} elapsed, the other delivery piston is moved in the direction of its suction stroke, more quickly than in the pressure stroke. The increase in speed is made possible by the additional pump 14. It ensures that the suction stroke is ended at the moment in which a new pressure stroke is initiated by appropriate switching operations before the other piston has completely completed its pressure stroke.

It is essential in the present invention that the described speed differences between suction and Pressure stroke of each piston and the timing to that Stroke sequence of the other delivery piston, as well as that to the position of the end face at the corresponding times of the suction pipe are coordinated.

In the following, 8 to 11 will be used with reference to FIGS Embodiments of simplified schemes one Hydraulic system explained in more detail. In the following it should only on essential differences to that shown in Fig. 2 Scheme to be entered, why for same and similar Components the same reference numerals are used.

It should be emphasized at this point that the schemes are only the most important ones required to fulfill the function Include components.

The scheme shown in FIG. 8 has two essentially equivalent variable displacement pumps 13, 14 for control purposes. The first variable pump 13 is connected via line 15, a 4/2-way valve 45 and a line 21 to the piston-side pressure chamber of cylinder 9 ₁ . In its other switching position, the directional control valve 45 ensures that the variable displacement pump 13 is connected via the line 15 and the line 46 to the space on the piston rod side of the cylinder 9 ₁ . Likewise, the variable displacement pump 14 is connected via the line 33, a 4/2-way valve 47 and the line 22 to the pressure chamber of the cylinder 9 ₂ on the piston side. In the other switching position of the directional valve 47, the variable displacement pump 14 is connected via the cable 48 with the piston rod side chamber of the cylinder 9 ₂ in connection. The variable pumps 13, 14 are matched to one another. From the circuit it can be seen that each cylinder 9 ₁ , 9 ₂ can be controlled and operated separately via the associated variable displacement pump 13, 14. It follows that the actuation of the variable displacement pumps 13, 14 and the directional control valves 45, 47 is solely responsible for the extension and retraction of the cylinders 9 ₁ , 9 ₂ and their actuation must take place accordingly. Furthermore, an additional pump 49 with a subsequent pressure accumulator 50 is provided, which are connected to the slide 7 via the line 19 and the 4/2-way valve 20. The pressure accumulator 50 ensures that the pump 49 does not have to be in continuous operation. In this context, however, an embodiment is also conceivable in which the pressure accumulator 50 is filled by one of the variable displacement pumps 13, 14 during the downtime of one of the pistons 11 ₁ , 11 ₂ .

The diagram shown in Fig. 9 comprises a variable displacement pump 13, which is connected via a line 15, a 4/3-way valve 51 and the branches 46, 48 to the piston rod-side spaces of the cylinders 9 ₁ , 9 ₂ . The directional control valve 51 has a position in which the strands 46, 48 are separated from the pump 13 and are connected to the pressure medium return 26 via the strand 25. Furthermore, a second variable displacement pump 14 is provided, which is optionally connected via the line 33, a 4/3-way valve 52 and the lines 53, 54 to the pressure chambers of the cylinders 9 ₁ and 9 ₂ on the piston side. In the position shown in FIG. 9, the directional control valve 52 connects both pressure chambers of the cylinders 9 ₁ and 9 ₂ to the pump 14. By means of the control via the two variable pumps 13, 14, one of which is the pressure stroke and the other is the respective suction stroke causes, the speed ratio between the pressure and suction stroke can be kept constant by precisely controlling the directional control valves 51, 52 and the pumps 13, 14. This is particularly the case in this embodiment when both cylinders 9 ₁ and 9 ₂ perform a pressure stroke for a short time (see valve position in FIG. 9) and both piston rod sides of cylinders 9 ₁ and 9 ₂ are connected to the tank during this time. At the same time, the slide 7 is then actuated. This means that when the short circuit on the swivel tube 3 is established, both delivery cylinders 5 are in the pressure stroke at essentially half the average speed V1. The gradual switching from one to the other cylinder 9 ₁ and 9 ₂ had no effect on the total flow rate by adjusting the speeds.

The embodiment shown in Fig. 10 differs from the previous one in that an adjustable flow divider 55, 56 is arranged in each line 46, 48 after the 4/3-way valve 51, from which the lines 46, 48 to the piston rod side Broaching of cylinders 9 ₁ and 9 _{2 are} continued and a second line 57, 58 is connected via a 4/2-way valve 59 to the piston-side pressure chambers of cylinders 9 ₁ and 9 ₂ . In this embodiment, the pressure or suction stroke can be generated by the variable pump 13. During the changeover process of the swivel tube 3, however, the 4/3-way valve 51 connects the lines 46, 48 to the pressure medium return 26 and the 4/2-way valve 49 blocks the lines 57, 58, so that no oil volume from the piston-side pressure chambers of the cylinders 9 ₁ and 9 ₂ can escape. In this state, the variable displacement pump 14 is simultaneously connected to both pressure chambers of the cylinder 9 ₁ and 9 _{2 on} the piston side. These then perform a pressure stroke at the same speed depending on the delivery volume of the variable displacement pump 14. During this process, one cylinder is usually shortly before its end position and the other at the beginning of its pressure stroke. The delivery volume of the variable displacement pump 14 is usually selected so that no delivery flow fluctuations occur. In this process, the parts ratio of the flow dividers 55, 56 and the area ratio of the piston end face and the piston rod side of the cylinders 9 ₁ and 9 _{2 must be} designed in order to obtain a reasonable relationship between pressure stroke and suction stroke speed. The device is fine-tuned by the variable displacement pump 14, which can be set accordingly to generate higher or lower speeds.

Finally, a fifth embodiment of a hydraulic scheme for driving the delivery cylinders 5 is shown in FIG. 11. The line 15 from the variable displacement pump 13 is in turn connected via a 4/3-way valve 51 and the branches 46, 48 to the piston rod-side spaces of the cylinders 9 ₁ and 9 ₂ . In addition, a line 59 branches off from line 15 before directional valve 51 is reached. The line 59 connects the line 15 and thus the pump 13 to a rocker line 61 via a 3/2-way valve 60. The rocker line 61 is connected directly to both pressure chambers 9 ₁ and 9 _{2 on the} piston side. A line 62, which is also connected to the 3/2-way valve 60, leads via a further 3/2-way valve to the pressure medium return 26. At the beginning of the suction stroke of the one cylinder, a small amount of oil from the rocker line 61 via the directional valves 60, 63 to the pressure medium return 26 headed. The space on the piston rod side of this cylinder is then connected to the pump 13. The oil volume from the cylinder starting the suction stroke is now pressed via the rocker line 61 minus the small amount of hydraulic fluid into the piston-side pressure chamber of the other cylinder. The small amount of hydraulic fluid discharged through the directional control valves 62, 63 provides a temporary difference in speed between the suction and pressure stroke. Then after closing the directional control valve 63, both cylinders 9 ₁ and 9 ₂ move at the same speed until the cylinder in the suction stroke reaches the end position. The cylinder in the pressure stroke has not yet reached the end position due to the speed differences just mentioned at the start of the movement. At this time, the 4/3-way valve switches to the position shown in FIG. 11 and the 3/2-way valve 60 also switches to the position shown in FIG. 11. The pump 13 is thus connected via the line 15, the line 59 and the rocking line 61 to the piston-side pressure chambers of the cylinders 9 ₁ and 9 ₂ . As a result, both pistons 11 ₁ and 11 ₂ perform a pressure stroke at the same speed until the cylinder in the pressure stroke from the beginning has reached its end position. During this time, the slide 7 is actuated via the directional valve 20. The counter stroke then takes place in reverse order. The embodiment shown in FIG. 11 offers the possibility of controlling the entire process with only a single pump 13.

Claims (14)

1. A method of feeding concrete or other thick materials from a container (1) into a feeding pipe (2) by means of two feeding cylinders (5) which are alternately connectable by a switching device (3) to said container (1) or said feeding pipe (2), with the feeding pistons (6) of said feeding cylinders (5) alternately performing a suction stroke and a pressure stroke, wherein the average piston speed V₃ during the suction stroke is at least temporarily greater than during the pressure stroke and wherein during the switching period t_u of said switching device (3) the two feeding cylinders (5) are substantially separated from said container (1) at least temporarily and are short-circuited together to form a joint connection with said feeding pipe (2) and in said state said one feeding piston (6) is still finishing its pressure stroke and said other feeding piston (6) already begins its pressure stroke at the same time, with the corresponding feeding piston (6) only performing its suction stroke when the short-circuit is substantially cancelled again and the associated feeding cylinder (6) is connected to said container (1),
   characterized in
   that said short-circuit is established by a single switching device (3) which during short-circuiting jointly separates said two feeding cylinders (5) from said container (1).
2. The method according to claim 1, characterized in
   that said feeding piston (6) which has finished the suction stroke already begins with the pressure stroke during a time interval Δt of the switching period tu while the other feeding piston (6) has not yet finished its pressure stroke.
3. The method according to claim 2, characterized in
   that a speed V₂ of said feeding piston (6) which begins the pressure stroke in time interval Δt is smaller than the average speed V₁ during the remaining pressure stroke.
4. The method according to claim 2 or 3, characterized in
   that during time interval Δt both feeding pistons (6) are substantially moved at half the average speed V₁ of the remaining pressure stroke.
5. An apparatus for performing the method according to any one of claims 1 to 4, comprising at least two feeding cylinders (5) which are alternately connectable by a switching device (3) to a container (1) or a feeding pipe (2), the feeding pistons (6) of said feeding cylinders (5) alternately performing a suction stroke and a pressure stroke, said switching device (3) being a pivot pipe (3) which is pivotable with its inlet opening (41) along the open end portions (42, 43) of said feeding cylinders (5), characterized in
   that said inlet opening (41) and the surrounding closing regions (40, 46) of said pivot pipe (3) are designed such that during a switching operation said feeding cylinders (5) are substantially short-circuited together with said feeding pipe (2), but are substantially separated from said container (1).
6. The apparatus according to claim 5, characterized in
   that said inlet opening (41) is shaped as a substantially elongated hole bent around the pivot axis (44) of said pivot pipe (3), and has a length L which corresponds approximately to the outer distance A of the two mouth openings (42, 43).
7. The apparatus according to claim 5 or 6, characterized in
   that said closing regions (45, 46) are arranged in extension of said elongated hole (41) and have a width C which substantially corresponds to the diameter D of said mouth openings (41, 43).
8. The apparatus according to any one of claims 5 to 7,
   characterized in that a cylinder/piston unit (8) is respectively provided from which a selectively switchable line (17) leads into the chamber of each cylinder (9) provided at the piston side, that an additional pump (14) is arranged for the further supply of pressurized fluid to the two pressure chambers of said two cylinder/piston units (8), that said pressure chambers of said cylinder/piston units (8) at the front side of the piston have extended thereinbetween a connecting line (27) of the hydraulic system in which a line (28) terminates that is selectively connectable via a switching valve (29) to said additional pump (14) or to a pressurized-fluid return means (26), that the sections of said line (27) between each of said cylinders (9) and the mouth of said line (28) respectively include a check valve (30, 31) which is closable by the pressure prevailing in said cylinder (9), and that said cylinders (9) of said cylinder/piston units (8) in the end portion of their piston rod side have a line (35) connecting the said cylinders, which line (35) is also selectively connectable via said switching valve (29) to said pressurized-fluid return means (26) or said additional pump (14).
9. The apparatus according to claim 8, characterized in
   that a respective cylinder (9) is connected at an end provided at the front side of the piston via a control line (36, 37) to the control connection side of a check valve (31, 30) which is assigned to said other cylinder (9).
10. The apparatus according to any one of claims 5 to 7,
    characterized in that a cylinder/piston unit (8) is respectively provided for driving said feeding pistons (6) which can each be fed via said separate pump (13, 14) with pressurized fluid.
11. The apparatus according to any of claims 5 to 7,
    characterized in that a cylinder/piston unit (8) is respectively provided for driving said feeding pistons (6), in which unit a selectively switchable line (15) of a first pump (13) is connectable to or separable from the chamber of each cylinder (9) at the piston rod side, that a second pump (14) for supplying pressurized fluid to the pressure chambers of said cylinders (9) at the front side of said piston is connectable via a switchable line (33) either invidivually or jointly to said pressure chambers, and that the chambers of each cylinder (9) at the piston rod side are jointly connectable to a pressurized-fluid return means (26).
12. The apparatus according to any one of claims 5 to 7,
    characterized in that a cylinder/piston unit (8) is respectively provided for driving said feeding pistons (6), in which unit a selectively switchable line (15) of a first pump (13) is connectable via a respective adjustable flow divider (55, 56) jointly to the pressure chamber of each cylinder (9) at the front side of said piston and to the chamber of each other cylinder (9) at the piston rod side, or is separable therefrom, that a second pump (14) for supplying pressurized fluid to the pressure chambers at the front side of said piston is connectable via a switchable line (33) either individually or jointly to said pressure chambers, that the lines (57, 58) of said flow dividers (55, 56) which lead to said pressure chambers of the cylinders (9) at the front side of said piston are respectively connectable jointly with said pressure chambers or can be blocked together jointly, and that said flow dividers (55, 56) are jointly connectable to a pressurized-fluid return means (26) when said flow dividers (55, 56) are separated from said first pump (13).
13. The apparatus according to any one of claims 5 to 7,
    characterized in that a cylinder/piston unit (8) is respectively provided for driving said feeding pistons (6), in which unit a selectively switchable line (15) of a pump (13) is connectable to or separable from the chamber of each cylinder (9) provided at the piston rod side, that a second, selectively switchable line (59) of said pump (13) is jointly connectable to or separable from the pressure chambers of said cylinders at the front side of said piston, that the pressure chambers of said cylinders (9) provided at the front side of said piston are interconnected via a line (61), and that the pressure chambers provided at the front side of said piston are connectable to or separable from a pressurized-fluid return means (26) via a selectively switchable line (63).
14. The apparatus according to any one of claims 5 to 13,
    characterized in that said pivot pipe (3) is operable by means of a slide (7) via a controlled two-way valve (20) which is connected to a pump and/or an accumulator.

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