DE102018222425A1 - Hydrostatic drive, especially for a press or an injection molding machine - Google Patents

Abstract

The invention relates to a hydrostatic drive. This has a cylinder arrangement on which a hydrostatic piston surface of different size can be pressurized for a rapid traverse to be delivered and for a subsequent press cycle, a first hydraulic machine whose flow rate of pressure fluid can be changed and the one for rapid traverse with a piston located in front of a first piston surface , in a rapid hydraulic pressure pressurized first cylinder chamber and with a second cylinder chamber located in front of a second piston surface can be operated in a closed hydraulic circuit, a second hydraulic machine, the flow rate of pressure fluid can be changed and for the pressing process with a third piston surface located in the press chamber pressurized, third cylinder chamber and with a fourth cylinder chamber located in front of a fourth piston surface can be operated in a closed hydraulic circuit, and valves which, during the transition from the rapid traverse to the press gear, the pressure In order to achieve a smooth transition between the rapid traverse and the press traverse without stopping or an uncontrolled movement of the cylinder arrangement, the valves are passive valves, the condition of which results from the flow rate specifications for the two hydraulic machines.

Description

The invention relates to a hydrostatic drive, which is provided in particular for a press or an injection molding machine or the like. The hydrostatic drive has a cylinder arrangement on which differently sized hydrostatic piston surfaces can be pressurized for a rapid feed to be delivered and for a subsequent press run, a first hydraulic machine, the flow rate of which pressure fluid can be changed, and the one for the rapid feed with a first one Piston surface located in the rapid traverse, pressurized first cylinder chamber and can be operated in a closed hydraulic circuit with a second cylinder chamber located in front of a second piston surface, a second hydraulic machine, the volume of pressure fluid that can be changed and which for the press cycle with a front cylinder located in front of a third piston surface. in the press cycle pressurized third cylinder chamber and with a fourth cylinder chamber located in front of a fourth piston surface can be operated in a closed hydraulic circuit, and a valve arrangement which, during the transition from Rapid traverse to the press gear influences the hydraulic fluid flow.

A hydrostatic drive of this type is from the EP 0 311 779 A2 known. There, a rapid traverse cylinder designed as a synchronous cylinder with a piston with small piston areas and a press cylinder or power stroke cylinder also embodied as a synchronous cylinder are mechanically connected to one another via a common piston rod. There are two hydraulic machines that are adjustable in their stroke volume and that can be driven together by an electric motor. The flow rates through the two hydraulic machines are reversible. The two hydraulic machines are connected in parallel to each other with first connections to a first cylinder chamber of the rapid traverse cylinder and with second connections to a second cylinder chamber of the rapid traverse cylinder and can be operated with the rapid traverse cylinder in a closed hydraulic circuit. A directional control valve with two switching positions and with four connections, of which a first is connected to the first cylinder chamber, a second to the second cylinder chamber of the press cylinder and a third to the first connections of the two hydraulic machines and a fourth can be connected to the second connections of the two hydraulic machines controls the transition from rapid to pressing. In rapid traverse, the directional control valve assumes a switch position in which its third connection and fourth connection are blocked against the first connection and against the second connection and the first connection and the second connection are connected to one another. The press cylinder is thus locked against the two hydraulic machines. Both hydraulic machines work in parallel with each other only with the rapid traverse cylinder in a closed hydraulic circuit. Hydraulic fluid is displaced from one cylinder chamber of the press cylinder into the other cylinder chamber via the directional valve. Switching the directional valve into the other switching position leads to the transition from rapid to press. The direct connection between the two cylinder chambers of the press cylinder via the directional control valve is blocked, one cylinder chamber is connected to the first connections and the other cylinder chamber to the second connections of the two hydraulic machines. Rapid traverse cylinders and press gear cylinders are now connected in parallel to each other and will be operated with the hydraulic machines in a closed hydraulic circuit.

The disadvantage here is that when the directional control valve is switched over, depending on the overlap selected, the cylinder chambers of the press cylinder can be shut off from one another for a short time or opened both to one another and to the hydraulic machines. This leads to the cylinders stopping or to a brief, uncontrolled movement. This behavior disrupts the process flow in many applications.

If the 4/2-way valve were to be broken down into three 2/2 way valves, each with its own actuating element, these individual valves would have to be connected to one another in a precisely controlled time. This is difficult to achieve.

The invention is therefore based on the object of designing the hydrostatic drive with the features mentioned at the beginning in such a way that the transition from rapid traverse to press cycle takes place in a controlled manner and the process flow is thereby improved.

This is achieved in that the valve arrangement comprises a plurality of passive valves, the state of which results from the delivery quantity specifications for the two hydraulic machines. Switching between small piston area and large piston area is thus carried out by the two hydraulic machines, the delivery rates of which can be changed. The passive valves react to the pressures resulting from the delivery rates of the hydraulic machines without external control. One hydraulic machine can convey a different amount of liquid than the other hydraulic machine at the same time.

The passive valves are preferably non-return valves, a first non-return valve being fluidly arranged between the third and fourth cylinder chamber of the cylinder arrangement and opening from the fourth cylinder chamber to the third cylinder chamber, and a second non-return valve between a first line leading from the first hydraulic machine to the first cylinder chamber and one is arranged from the second hydraulic machine to the third cylinder chamber leading second line and opens from the second line to the first line. There are preferably no further valves in the first line and in the second line.

The speed of the cylinder arrangement, that is to say the rapid speed, is preferably predetermined by the delivery rate of the first hydraulic machine during the rapid traverse to be delivered. During the rapid traverse, an amount of liquid corresponding to the rapid traverse speed is displaced from the fourth cylinder chamber into the third cylinder chamber. In principle, this can be done solely via the check valve, which is arranged between the third and the fourth cylinder chamber. However, it seems favorable if the delivery rate of the second hydraulic machine is greater than zero and the second hydraulic machine conveys pressure fluid from the fourth cylinder chamber to the third cylinder chamber during the rapid traverse to be delivered. In particular, the delivery rate of the second hydraulic machine is at a maximum during the rapid feed to be delivered. Because you do not want to use an oversized pump and do not want to work at oversized speeds, the maximum delivery rate of the second hydraulic machine is still smaller than the amount of liquid to be shifted between the fourth cylinder chamber and the third cylinder chamber, so that the amount also flows through the first check valve.

During the transition from the rapid feed to the press gear to be delivered, the delivery rate of the second hydraulic machine is initially set so that it corresponds to the desired press speed. If the delivery rate of the first hydraulic machine is then reduced to such an extent that the inflow of hydraulic fluid from the first hydraulic machine into the first cylinder chamber would result in a speed of the cylinder arrangement that is lower than the pressing speed, the second hydraulic machine then determines the speed of the cylinder arrangement and the pressure decreases in the first cylinder chamber and the pressure in the third cylinder chamber increases. When the pressure in the third cylinder chamber has become equal to the pressure in the first cylinder chamber, the second hydraulic machine also delivers into the first cylinder chamber, increasing its delivery rate when the speed should not or must not drop. The speed of the cylinder arrangement can be determined with the aid of a displacement sensor and the delivery rate of the second hydraulic machine can be regulated according to the desired speed profile. The delivery rate of the first hydraulic machine must be at least in the same ratio smaller than the delivery rate of the second hydraulic machine as the piston area adjacent to the first cylinder chamber is smaller than the piston area adjacent to the third cylinder chamber.

It can be provided that at least one of the two hydraulic machines is adjustable in its stroke volume. The delivery quantities can then be changed relative to one another, even if the two hydraulic machines can be driven together by a single speed-controlled electric motor.

However, there can also be two speed-controlled electric motors, the first hydraulic machine being drivable by a first electric motor of the two speed-controlled electric motors and the second hydraulic machine being driven by a second electric motor of the two speed-controlled electric motors. In addition, both hydraulic machines can be adjustable in their stroke volume, that is, with regard to the amount of liquid flowing through them per revolution, so that a change in the delivery rate of each hydraulic machine is possible by changing the speed and / or by changing the stroke volume.

If the two hydraulic machines are those with a constant displacement, two speed-controlled electric motors are advantageously present and one of the two hydraulic machines can be driven by a first speed-controlled electric motor and the second of the two hydraulic machines by a second speed-controlled electric motor. The delivery rate or swallowing rate, that is to say the amount of liquid flowing through a hydraulic machine per unit of time, can then only be changed by changing the speed of the electric motor and thus of the hydraulic machine.

The two hydraulic machines can be fluidly connected to the second cylinder chamber, a valve being arranged between the hydraulic machines and the fourth cylinder chamber, with which a flow of liquid from the hydraulic machines to the fourth cylinder chamber can be shut off, and between the third cylinder chamber and the fourth cylinder chamber a switching valve is arranged which can be actuated arbitrarily and has a first switching position in which the third cylinder chamber and the fourth cylinder chamber are separated from one another and a second switching position in which the third cylinder chamber and the fourth cylinder chamber are fluidly connected to one another. In the blocking position of the switching valve arranged between the third cylinder chamber and the fourth cylinder chamber, pressure fluid can flow from the fourth cylinder chamber into the third cylinder chamber during the rapid feed to be delivered via the check valve arranged between the two said cylinder chambers. The switching valve is brought into its open switching position for the return stroke in rapid traverse.

The valve arranged between the hydraulic machines and the fourth cylinder chamber can be a Check valve that blocks from the fourth cylinder chamber to the hydraulic machines.

While the first cylinder chamber can be fluidly connected to a low-pressure accumulator via a check valve opening towards it, the second cylinder chamber via a check valve opening towards it and the third cylinder chamber via a check valve opening towards it, the fourth cylinder chamber can be fluidically connected directly to a low-pressure accumulator be connected.

Two exemplary embodiments of a hydrostatic drive according to the invention are shown in the drawings. The invention will now be explained in more detail with reference to these drawings.

• 1 das erste Ausführungsbeispiel, bei dem die beiden Hydromaschinen in ihrem jeweiligen Hubvolumen verstellbar sind und von einem einzigen drehzahlgeregelten Elektromotor angetrieben werden, und
• 2 das zweite Ausführungsbeispiel, bei dem die beiden Hydromaschinen jeweils ein konstantes Hubvolumen haben und getrennt voneinander von jeweils einem drehzahlgeregelten Elektromotor angetrieben werden.

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• 1 the first embodiment, in which the two hydraulic machines are adjustable in their respective stroke volume and are driven by a single speed-controlled electric motor, and
• 2nd the second embodiment, in which the two hydraulic machines each have a constant stroke volume and are driven separately from each other by a speed-controlled electric motor.

The hydrostatic drives shown in the figures each comprise a rapid traverse cylinder designed as a synchronous cylinder 10 and a press gear or power gear cylinder, also designed as a synchronous cylinder 11 . A plurality of rapid traverse cylinders can also be provided which are parallel to one another in a hydraulic circuit. Likewise, several press cylinder can be provided, which are parallel to each other in a hydraulic circuit.

The rapid traverse cylinder contains in a cylinder housing 12th a piston 13 which is a first cylinder chamber 14 from a second cylinder chamber 15 separates and that with a piston rod passing through the cylinder housing 16 is firmly connected to one side of the piston 13 has the same diameter as on the other side.

The piston rods of the two cylinders 10 and 11 are about a traverse 17th which is part of a powder press, for example, mechanically connected to each other so that they always move together. With the help of a displacement sensor 18th the position of the traverse can be recorded. The speed and acceleration of the traverse can also be derived from this.

The press cylinder also contains 11 in a cylinder housing 22 a piston 23 which is a third cylinder chamber 24th from a fourth cylinder chamber 25th separates and that with a piston rod passing through the cylinder housing 26 is firmly connected to one side of the piston 23 has the same diameter as on the other side. The cylinder chambers 24th and 25th facing ring surfaces A1 and A2 of the piston 23 are much larger, for example ten times larger than those of the cylinder chambers 14 and 15 facing ring surfaces A3 and A4 of the piston 13 .

Each of the hydrostatic drives shown has a first hydraulic machine 30th and a second hydraulic machine 32 on. Each of the hydro machines 30th and 32 can be flowed through by a hydraulic fluid in two opposite directions and work in both flow directions both as a pump and as a hydraulic motor.

A first job connection 33 the first hydromachine 30th is over a line 34 continuously and without the interposition of a valve with the cylinder chamber 14 of the rapid traverse cylinder 10 fluidly connected. The second work connection 35 the first hydromachine 30th is over a line 36 continuously and without the interposition of a valve with the cylinder chamber 15 of the rapid traverse cylinder 10 fluidly connected. The hydromachine 30th and the rapid traverse cylinder 10 are operated together in a closed hydraulic circuit.

A first job connection 37 the second hydromachine 32 is over a line 38 continuously and without the interposition of a valve with the cylinder chamber 24th of the press cylinder 11 fluidly connected. The second work connection 39 the second hydromachine 32 is with the second working connection 35 the first hydromachine 30th interconnected and thus to the line 36 connected.

The two lines 34 and 38 are via a check valve 40 by the line 38 to lead 34 opens, fluidly connected.

The fourth cylinder chamber 25th is over a line 45 with the line 36 and thus with the two work connections 35 and 39 of the two hydro machines 30th and 32 fluidly connected. On the line 45 is a check valve 46 arranged by the cylinder chamber 25th to lead 36 opens. Between the check valve 46 and the cylinder chamber 25th is a low pressure accumulator 47 , in which there is a pressure in the range of, for example, 2 to 3 bar, directly to the line 45 connected.

Between the two cylinder chambers 24th and 25th of the press cylinder 11 is a check valve 50 arranged by the cylinder chamber 25th to the cylinder chamber 24th opens and in reverse direction locks. Via the check valve 50 can act as hydraulic fluid from the cylinder chamber 25th into the cylinder chamber 24th to be ousted. Parallel to the check valve 50 is a 2/2-way seat valve 51 arranged, which assumes a locked rest position under the action of a spring and by controlling a switching magnet 52 can be switched arbitrarily to a through position. The two valves 50 and 51 can also be combined to form a single valve, for example an unlockable check valve or a logic valve with a check valve function.

The lines 34 , 36 and 38 are each via a check valve that opens towards them 53 with a low pressure accumulator 54 fluidly connected, in the same way as in the low pressure accumulator 47 a pressure in the range of 2 to 3 bar is present.

The two exemplary embodiments are only with respect to the two hydraulic machines 30th and 32 and their drive differently designed. In the embodiment according to 1 The two hydraulic machines, which can be swashplate type axial piston machines, for example, are adjustable in their stroke volume. The two hydraulic machines are operated together by a speed-controlled electric motor 60 driven. In the embodiment according to 2nd are the two hydraulic machines so-called constant machines, so they have a fixed, unchangeable stroke volume. The hydromachine 30th is controlled by a speed-controlled electric motor 61 and the hydro machine 32 from another speed-controlled electric motor 62 driven. By changing the speed of the associated electric motor, the delivery rate of a hydraulic machine can be changed independently of the delivery rate of the other hydraulic machine.

It is now assumed that in 1 a press ram, not shown, attached to the traverse is in a starting position at the beginning of a press cycle. At the beginning of a press cycle, the press ram should be moved or fed to a die in rapid traverse. The switching valve 51 is in its locked position. The hydro machines 30th and 32 are by the electric motor 60 driven. The direction of rotation of the electric motor 60 and thus the direction of rotation of the hydraulic machine 30th chosen so that the hydromachine 30th the cylinder chamber 15 Hydraulic fluid is removed and into the cylinder chamber 14 promotes. This builds up pressure that is necessary to move the crossbar. The check valve 40 prevents from the hydro machine 30th pumped hydraulic fluid into the line 38 and thus into the cylinder chamber 24th of the press cylinder 11 flows. The speed and the displacement of the hydraulic machine 30th are set so that the of the cylinder chamber 14 inflow of hydraulic fluid the desired rapid traverse speed of the rapid traverse cylinder 10 results. About the traverse 17th is from the rapid traverse cylinder 10 the press cylinder 11 dragged along. To do this, it must come from the cylinder chamber 25th of the press cylinder 11 Hydraulic fluid can be displaced. This happens once via the check valve 50 , about the hydraulic fluid from the cylinder chamber 25th into the cylinder chamber 24th flows. In addition, the displacement of the hydraulic machine 32 set so that part of out of the cylinder chamber 25th Hydraulic fluid to be displaced via the check valve 46 and the hydro machine 32 the cylinder chamber 24th is fed. Because the piston surfaces A3 and A4 of the press cylinder 11 compared to the piston surfaces A1 and A2 of the rapid traverse cylinder are very large, on the other hand the two hydraulic machines 30th and 32 are of the same size or of a similar size, that is via the hydraulic machine 32 amount of fluid flowing compared to that through the check valve 50 flowing amount of liquid relatively small. A reduction in the volume flow through the check valve 50 is however advantageous.

Before the pressing speed is reached at the end of the rapid traverse, the hydraulic machine is regulated to such a delivery rate that it takes into account the size of the areas A3 and A4 of the press cylinder 11 corresponds to the desired pressing speed. Now the delivery rate of the hydraulic machine 30th reduced to the desired pressing speed and possibly below. The ratio between the delivery rate of the hydraulic machine 30th and the delivery rate of the hydraulic machine 32 is at most as large as the ratio between the areas A1 and A3 . This reduces the pressure in the cylinder chamber 14 off while in the cylinder chamber 24th pressure builds up, the passive check valve 50 and the switching valve in its blocking position 51 prevent a pressure drop in the low pressure branch of the drive. The pressure in the line 38 and in the cylinder chamber 24th continues to rise until finally the passive check valve 40 opens and a pressure equalization in the direction of the cylinder chamber 14 he follows. It is then pressed over both surfaces A1 and A3 with both hydraulic machines. The pressing speed is measured with the help of the displacement sensor 18th by adjusting the delivery rate of the hydraulic machine 32 regulated.

For decompression, the direction of conveyance of both hydraulic machines is reversed from the direction during the pressing process. After decompression, the switching valve 51 operated. The withdrawal is now done by the hydraulic machine 30th the cylinder chamber 14 removed hydraulic fluid into the cylinder chamber 15 of the rapid traverse cylinder 10 promotes, the check valve 46 The administration 36 and the cylinder chamber 15 to the low pressure accumulator 47 and to the cylinder chamber 25th of the press cylinder 11 shut off and build up pressure in the cylinder chamber 15 of the rapid traverse cylinder 10 and enables rapid traverse. The switching valve 51 is actuated so that hydraulic fluid from the cylinder chamber 24th into the cylinder chamber 25th of the press cylinder can overflow. The hydromachine 32 is set to zero displacement.

Reference list

10th

Rapid traverse cylinder

11

Press gear or power cylinder

12th

Cylinder housing from 10

13

Piston of 10

14

first cylinder chamber in 10

15

second cylinder chamber in 10

16

Piston rod from 10

17th

traverse

18th

Displacement sensor

22

Cylinder housing from 11

23

Piston of 11

24th

third cylinder chamber in 11

25th

fourth cylinder chamber in 11

26

Piston rod from 11

30th

first hydromachine

32

second hydromachine

33

first work connection from 30th

34

Line between 33 and 14

35

second working connection from 30th

36

Line between 35 and 15

37

first work connection from 32

38

Line between 37 and 24th

39

second working connection from 32

40

check valve

45

management

46

check valve

47

Low pressure accumulator

50

check valve

51

2/2 directional seat valve

52

Switching magnet

53

check valve

54

Low pressure accumulator

60

Electric motor

61

Electric motor

62

Electric motor

A1

Area in 10

A2

Area in 10

A3

Area in 11

A4

Area in 11

QUOTES INCLUDE IN THE DESCRIPTION

This list of documents listed by the applicant has been generated automatically and is only included for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• EP 0311779 A2 [0002]

Claims (14)

Hydrostatic drive for a press or an injection molding machine or the like with a cylinder arrangement (10, 11), on which a hydrostatic piston surface (A1, A3) of different sizes can be pressurized for a rapid traverse and a subsequent press cycle, with a first hydraulic machine (30), the delivery quantity of hydraulic fluid can be changed, and those for rapid traverse with a first cylinder chamber (14) located in front of a first piston surface (A1), pressurized in rapid traverse and with a second cylinder chamber (15 ) can be operated in a closed hydraulic circuit, with a second hydraulic machine (32), the volume of pressure fluid that can be changed, and with a third cylinder chamber (24), which is pressurized in front of a third piston surface (A3) and with for the press cycle one in front of a fourth piston surface (A4) th cylinder chamber (25) can be operated in a closed hydraulic circuit, and with a valve arrangement (40, 50) which influences the flow of hydraulic fluid during the transition from rapid traverse to the press cycle, characterized in that the valve arrangement comprises a plurality of passive valves (40, 50), the state of which results from the delivery quantity specifications for the two hydraulic machines (30, 32). Hydrostatic drive after Claim 1 , wherein the valves are check valves (40, 50) and wherein a first check valve (50) is arranged between the third cylinder chamber (24) and fourth cylinder chamber (25) and opens from the fourth cylinder chamber (25) to the third cylinder chamber (24) and a second check valve (40) between a first line (34) leading from the first hydraulic machine (30) to the first cylinder chamber (14) and a second line (38) leading from the second hydraulic machine (32) to the third cylinder chamber (24) is arranged and opens from the second line (38) to the first line (34). Hydrostatic drive after Claim 2 , the speed of the cylinder arrangement (10, 11) being predetermined by the delivery rate of the first hydraulic machine (30) during the rapid traverse to be delivered. Hydrostatic drive after Claim 3 , wherein the delivery rate of the second hydraulic machine (32) is greater than zero and the second hydraulic machine (32) conveys hydraulic fluid from the fourth cylinder chamber (25) to the third cylinder chamber (24) during the rapid feed to be delivered. Hydrostatic drive after Claim 4 , wherein the delivery rate of the second hydraulic machine (32) is maximum during the rapid feed to be delivered. Hydrostatic drive after Claim 4 or 5 , With the transition from the rapid feed to the press gear to be delivered, the delivery rate of the first hydraulic machine (30) is so small that the inflow of hydraulic fluid from the first hydraulic machine (30) into the first cylinder chamber (14) results in a speed of the cylinder arrangement (10, 11) , which is smaller than the pressing speed, and wherein the delivery rate of the second hydraulic machine (32) is adjusted so that the pressing speed results. Hydrostatic drive according to one of the preceding claims, wherein at least one of the two hydraulic machines (30, 32) is adjustable in its stroke volume. Hydrostatic drive after Claim 7 A speed-controlled electric motor (60) is provided, by which the two hydraulic machines (30, 32) can be driven together. Hydrostatic drive according to one of the Claims 1 to 7 , wherein there are two speed-controlled electric motors (61, 62) and wherein the first hydraulic machine (30) by a first electric motor (61) of the two electric motors (61, 62) and the second hydraulic machine (32) by a second electric motor (62) two electric motors (61, 62) can be driven. Hydrostatic drive according to one of the Claims 1 to 6 There are two speed-controlled electric motors (61, 62), the first hydraulic machine (30) being driven by a first electric motor (61) of the two speed-controlled electric motors (61, 62) and the second hydraulic machine (32) by a second electric motor (62) of the two speed-controlled electric motors (61, 62) can be driven and each of the two hydraulic machines (30, 32) is a hydraulic machine with a constant stroke volume. Hydrostatic drive according to one of the preceding claims, wherein the two hydraulic machines (30, 32) are fluidly connected together with the second cylinder chamber (15), a valve (46) being arranged between the hydraulic machines (30, 32) and the fourth cylinder chamber (25) , with which a liquid flow from the hydraulic machines (30, 32) to the fourth cylinder chamber (25) can be shut off, and wherein between the third cylinder chamber (24) and the fourth cylinder chamber (25) a switching valve (51) is arranged, which is arbitrary can be operated and a first switch position in which the third Cylinder chamber (24) and the fourth cylinder chamber (25) are separated from one another, and has a second switching position in which the third cylinder chamber (24) and the fourth cylinder chamber (25) are fluidly connected to one another. Hydrostatic drive after Claim 11 , wherein the valve arranged between the hydraulic machines (30, 32) and the fourth cylinder chamber (25) is a check valve (46) which blocks from the fourth cylinder chamber (25) to the hydraulic machines (30, 32). Hydrostatic drive according to one of the preceding claims, wherein the first cylinder chamber (14) via a check valve (53) opening towards it, the second cylinder chamber (15) via a check valve opening towards it and the third cylinder chamber (24) via check valve (53) opening towards it can be fluidly connected to a low-pressure accumulator (54). Hydrostatic drive according to one of the preceding claims, wherein the fourth cylinder chamber (25) is fluidly connected directly to a low-pressure accumulator (47).

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