CN111347713A

CN111347713A - Hydrostatic drive, in particular for a press or injection molding machine

Info

Publication number: CN111347713A
Application number: CN201911317811.3A
Authority: CN
Inventors: G.亨德里克斯
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2018-12-20
Filing date: 2019-12-19
Publication date: 2020-06-30
Anticipated expiration: 2039-12-19
Also published as: DE102018222425A1

Abstract

The invention relates to a hydrostatic drive having: a cylinder device on which a piston surface acting hydrostatically is able to be acted upon with a pressure which is not as great for the rapid stroke of the feed and the subsequent pressing stroke; a first hydraulic machine, the pressure fluid delivery of which can be varied, which for a quick stroke can be operated in a closed hydraulic circuit with a first cylinder chamber located upstream of the first piston face and pressure-loaded in the quick stroke and with a second cylinder chamber located upstream of the second piston face; a second hydraulic press, the pressure fluid delivery of which is variable, which is operable in a closed hydraulic circuit for a press stroke with a third cylinder chamber upstream of the third piston surface, which is pressure-loaded during the press stroke, and with a fourth cylinder chamber upstream of the fourth piston surface; and a valve which influences the pressure fluid flow when changing from the rapid stroke to the pressing stroke. The valves are passive valves, the state of which is derived from a delivery rate preset value for both hydraulic machines.

Description

Hydrostatic drive, in particular for a press or injection molding machine

Technical Field

The invention relates to a hydrostatic drive, in particular for a press or injection molding machine. The hydrostatic drive comprises: a cylinder device on which a piston surface acting hydrostatically is able to be acted upon with a pressure which is not as great for the rapid stroke of the feed and the subsequent pressing stroke; a first hydraulic machine, the pressure fluid delivery of which is variable and which, for a quick stroke, can be operated in a closed hydraulic circuit with a first cylinder chamber located upstream of the first piston face and pressure-loaded in the quick stroke and with a second cylinder chamber located upstream of the second piston face; a second hydraulic press, the pressure fluid delivery of which is variable and which, for a pressing stroke, is operable in a closed hydraulic circuit with a third cylinder chamber upstream of the third piston surface and which is pressure-loaded during the pressing stroke and with a fourth cylinder chamber upstream of the fourth piston surface; and a valve device, which influences the pressure liquid flow when the rapid stroke is changed to the pressing stroke.

Background

Such hydrostatic drives are known from EP 0311779 a 2. There, a quick stroke cylinder, which is embodied as a synchronizing cylinder and a pressure stroke cylinder or power stroke cylinder, which is also embodied as a synchronizing cylinder, which has a piston with a small piston surface, are mechanically connected to one another by a common piston rod. There are two hydraulic machines which are adjustable in terms of their swept volume and which can be driven together by one electric motor. The transport flow can be reversed by two hydraulic machines. The two hydraulic machines are connected parallel to each other by a first connection to a first cylinder chamber of the quick-acting cylinder and by a second connection to a second cylinder chamber of the quick-acting cylinder and can be operated in a closed hydraulic circuit with the quick-acting cylinder. A reversing valve with two switching positions and four connections, of which a first connection is connected to the first cylinder chamber, a second connection is connected to the second cylinder chamber of the press stroke cylinder, and a third connection is connected to the first connections of the two hydraulic machines, and a fourth connection can be connected to the second connections of the two hydraulic machines, controls the conversion from the quick stroke to the press stroke. In the quick travel, the switching valve assumes a switching position in which its third connection and its fourth connection are blocked with respect to the first connection and with respect to the second connection, and the first connection and the second connection are connected to one another. The press stroke cylinder is thus blocked with respect to the two hydraulic machines. The two hydraulic machines work parallel to each other only in a closed hydraulic circuit with the quick-stroke cylinders. The pressure fluid is displaced from one cylinder chamber of the press stroke cylinder into the other cylinder chamber via a switching valve. The changeover of the changeover valve to the other switching position results in a changeover from the quick stroke to the pressing stroke. The direct connection between the two cylinder chambers of the press stroke cylinder is blocked by a switching valve, one cylinder chamber being connected to the first connections of the two hydraulic machines and the other cylinder chamber being connected to the second connection. The quick stroke cylinder and the press stroke cylinder are now connected in parallel with each other and run in a closed hydraulic circuit with the hydraulic machine.

The disadvantage here is that, depending on the selected overlap, the cylinder chambers of the pressure stroke cylinders can be blocked from each other or can be opened both to each other and to the hydraulic machine in a short time when the directional control valve is switched. This leads to a stoppage of the cylinder or also to a temporary uncontrolled movement. This property strongly disturbs the process flow in many application scenarios.

If the 4/2 directional control valve were to be broken down into three 2/2 directional control valves with their own actuating elements, the individual valves would have to be switched in a precisely controlled manner in time with respect to one another. This is difficult to achieve.

Disclosure of Invention

The object of the present invention is therefore to design a hydrostatic drive having the features cited at the outset in such a way that the conversion from the quick stroke to the press stroke takes place in a controlled manner and the process sequence is thereby improved.

This is achieved in that the valve arrangement comprises a plurality of passive valves, the state of which is derived from the delivery rate setpoint for the two hydraulic machines. The change between a small piston surface and a large piston surface is thus accomplished by two hydraulic machines, the delivery volumes of which are variable. Passive valves react to the pressure derived from the delivery of the hydraulic machine without external actuation. One hydraulic machine can here completely convey a different amount of liquid than the other hydraulic machine simultaneously.

The passive valve is preferably a non-return valve, wherein a first non-return valve is arranged fluidically between the third and fourth cylinder chambers of the cylinder arrangement and opens from the fourth cylinder chamber towards the third cylinder chamber, and a second non-return valve is arranged between a first line leading from the first hydraulic machine to the first cylinder chamber and a second line leading from the second hydraulic machine to the third cylinder chamber and opens from the second line towards the first line. In this case, preferably no further valves are located in the first and second lines.

Preferably, the speed of the cylinder arrangement, i.e. the fast stroke speed, is predetermined by the delivery capacity of the first hydraulic machine during the fast stroke of the feed. During the quick stroke, a liquid amount corresponding to the speed of the quick stroke is displaced from the fourth cylinder chamber into the third cylinder chamber. This can in principle be done solely by means of a non-return valve arranged between the third and fourth cylinder chamber. It appears advantageous, however, that during the rapid stroke of the feed the delivery of the second hydraulic machine is greater than zero and that the second hydraulic machine delivers pressure fluid from the fourth cylinder chamber to the third cylinder chamber. The delivery of the second hydraulic machine is particularly greatest during the rapid stroke of the feed. Since it is not desirable to use an excessively large pump and to operate at an excessively high rotational speed, the maximum delivery volume of the second hydraulic machine is still smaller than the volume of liquid to be displaced between the fourth and third cylinder chambers, and the volume therefore also flows through the first non-return valve.

In the case of a change from a rapid feed stroke to a press stroke, the delivery rate of the second hydraulic press is first adjusted in such a way that it corresponds to the desired press speed. If the delivery of the first hydraulic machine is so small that the inflow of pressure fluid from the first hydraulic machine into the first cylinder chamber results in a speed of the cylinder arrangement which is lower than the pressing speed, then the second hydraulic machine determines the speed of the cylinder arrangement and the pressure in the first cylinder chamber drops and the pressure in the third cylinder chamber rises. When the pressure in the third cylinder chamber is equal to the pressure in the first cylinder chamber, the second hydraulic machine is also fed into the first cylinder chamber, wherein its feed becomes greater when the speed does not or should not drop. The speed of the cylinder device can be determined by means of a displacement sensor and the delivery of the second hydraulic machine can be adjusted to the desired speed profile. The delivery capacity of the first hydraulic machine must in this case be smaller than the delivery capacity of the second hydraulic machine at least by the same proportion as the piston surface adjoining the first cylinder chamber is smaller than the piston surface adjoining the third cylinder chamber.

It can be provided that at least one of the two hydraulic machines is adjustable with respect to its displacement 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-regulated electric motor.

However, it is also possible to have two speed-regulated electric motors, wherein the first hydraulic machine can be driven by a first of the two speed-regulated electric motors and the second hydraulic machine can be driven by a second of the two speed-regulated electric motors. The two hydraulic machines can additionally be adjustable with respect to their swept volume, i.e. with respect to the amount of liquid flowing through the machine per revolution, so that the delivery capacity of each machine can be varied by varying the rotational speed and/or varying the swept volume.

If the two hydraulic machines are hydraulic machines with a constant displacement volume, it is advantageous if two speed-regulated electric motors are present, and one of the two hydraulic machines can be driven by the speed-regulated first electric motor and the second of the two hydraulic machines can be driven by the speed-regulated second electric motor. The delivery or throughput, i.e. the amount of liquid passing through the hydraulic machine per time unit, can then be changed only by changing the rotational speed of the electric motor and thus of the hydraulic machine.

The two hydraulic machines can be jointly in fluid communication with the second cylinder chamber, wherein a valve is arranged between the hydraulic machine and the fourth cylinder chamber, with which valve the flow of liquid from the hydraulic machine to the fourth cylinder chamber can be shut off, and wherein a switching valve is arranged between the third cylinder chamber and the fourth cylinder chamber, which switching valve can be actuated at will and has a first switching position in which the third cylinder chamber and the fourth cylinder chamber are separated from each other and a second switching position in which the third cylinder chamber and the fourth cylinder chamber are in fluid communication with each other. In the shut-off position of the switching valve arranged between the third and fourth cylinder chambers, it is possible to let pressure liquid flow from the fourth cylinder chamber into the third cylinder chamber during a rapid stroke of feed through a non-return valve arranged between the two said cylinder chambers. For the return stroke in the quick stroke, it is necessary to bring the switching valve into its open switching position.

The valve arranged between the hydraulic machine and the fourth cylinder chamber may be a non-return valve, which is shut off from the fourth cylinder chamber towards the hydraulic machine.

The first cylinder chamber can be in fluid communication with the low-pressure reservoir via a check valve opening towards the first cylinder chamber, the second cylinder chamber via a check valve opening towards the second cylinder chamber and the third cylinder chamber via a check valve opening towards the third cylinder chamber, while the fourth cylinder chamber can be in direct fluid communication with the low-pressure reservoir.

Drawings

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

fig. 1 shows a first exemplary embodiment in which two hydraulic machines are adjustable in terms of their respective displacement volumes and are driven by a single speed-regulated electric motor; and is

Fig. 2 shows a second exemplary embodiment in which the two hydraulic machines each have a constant displacement volume and are driven separately from one another by a speed-regulated electric motor.

Detailed Description

The hydrostatic drives shown in the figures each comprise a quick stroke cylinder 10, which is embodied as a synchronizing cylinder, and a pressure stroke cylinder or power stroke cylinder 11, which is likewise embodied as a synchronizing cylinder. It is also possible to provide a plurality of quick-travel cylinders, which are situated parallel to one another in the hydraulic circuit. It is likewise possible to provide a plurality of pressure cylinders, which are arranged parallel to one another in the hydraulic circuit.

The quick-stroke cylinder contains a piston 13 in a cylinder housing 12, which separates a first cylinder chamber 14 from a second cylinder chamber 15 and which is firmly connected to a piston rod 16 which passes through the cylinder housing and has the same diameter on one side of the piston 13 as on the other side.

The piston rods of the two

cylinders

10 and 11 are mechanically connected to each other by a cross bar 17, which is for example part of a powder press, so that they always move together with each other. The position of the crossbar can be detected by means of the displacement sensor 18. From this, the speed and acceleration of the crossbar can also be derived.

The press-stroke cylinder 11 also contains a piston 23 in the cylinder housing 22, which separates a third cylinder chamber 24 from a fourth cylinder chamber 25 and which is firmly connected to a piston rod 26 which passes through the cylinder housing and has the same diameter on one side of the piston 23 as on the other side. The annular faces a1 and a2 of the piston 23 facing the

cylinder chambers

24 and 25 are much larger than, for example ten times larger than, the annular faces A3 and a4 of the piston 13 facing the

cylinder chambers

14 and 15.

Each of the hydrostatic drives shown has a first hydraulic machine 30 and a second hydraulic machine 32. Each of the

hydraulic machines

30 and 32 can be traversed by pressure fluid in two opposite directions and operate in both flow directions as a pump and as a hydraulic motor.

The first working connection 33 of the first hydraulic machine 30 is permanently and without intermediate connection valves in fluid communication with the cylinder chamber 14 of the quick-stroke cylinder 10 via a line 34. The second working connection 35 of the first hydraulic machine 30 is permanently and without intermediate connection valves in fluid communication with the cylinder chamber 15 of the quick-acting cylinder 10 via a line 36. The hydraulic machine 30 and the quick-travel cylinder 10 thus operate together in a closed hydraulic circuit.

The first working connection 37 of the second hydraulic press 32 is permanently and without intermediate connection valves in fluid communication with the cylinder chamber 24 of the press stroke cylinder 11 via a line 38. The second working connection 39 of the second hydraulic machine 32 is coupled to the second working connection 35 of the first hydraulic machine 30 and is therefore connected to the line 36.

The two

lines

34 and 38 are in fluid communication with each other through a check valve 40 that opens from the line 38 toward the line 34.

The fourth chamber 25 is in fluid communication with the line 36 and therefore with the two working

connections

35 and 39 of the two

hydraulic machines

30 and 32, through the line 45. A check valve 46 is arranged in the line 45, which check valve opens out from the cylinder chamber 25 into the line 36. Between the check valve 46 and the cylinder chamber 25, a low-pressure accumulator 47, in which a pressure in the range of, for example, 2 to 3 bar is present, is connected directly to the line 45.

Between the two

cylinder chambers

24 and 25 of the pressure stroke cylinder 11, a non-return valve 50 is arranged, which opens from the cylinder chamber 25 to the cylinder chamber 24 and closes in the opposite direction. Through the non-return valve 50, pressure fluid can be displaced from the cylinder chamber 25 into the cylinder chamber 24. Parallel to the non-return valve 50, an 2/2 switching seat valve 51 is arranged, which 2/2 assumes a blocked rest position under the action of a spring and can be switched arbitrarily into the through position by actuating the switching magnet 52. The two

valves

50 and 51 can also be combined to form a single valve, for example to form a non-return valve which can be deactivated or a logic valve which has the function of a non-return valve.

The

lines

34, 36 and 38 are each in fluid communication with a low-pressure reservoir 54, in which, as in the low-pressure reservoir 47, there is a pressure in the range of 2 to 3 bar, via a check valve 53 which opens towards them.

The two embodiments are configured differently only with respect to the two

hydraulic machines

30 and 32 and their drives. In the exemplary embodiment according to fig. 1, the two hydraulic machines, which may be, for example, swash plate axial piston machines, are adjustable with respect to their displacement volume. The two hydraulic machines are driven jointly by a speed-regulated electric motor 60. In the exemplary embodiment according to fig. 2, the two hydraulic machines are so-called metering machines and therefore have a fixed, unchangeable displacement volume. The hydraulic machine 30 is driven by one speed regulated motor 61 and the hydraulic machine 32 is driven by another speed regulated motor 62. By varying the speed of rotation of the associated electric motor, it is thus possible to vary the delivery of one hydraulic machine independently of the delivery of the other.

It is assumed that the punch, not shown, which is fixed to the crossbar in fig. 1, is in the initial position at the start of the press cycle. At the start of the press cycle, the punch should be moved or fed in a rapid stroke towards the die. The on-off valve 51 is in its shut-off position. The

hydraulic machines

30 and 32 are driven by a motor 60. The direction of rotation of the electric motor 60 and thus of the hydraulic machine 30 is selected in such a way that the hydraulic machine 30 takes pressure fluid out of the cylinder chamber 15 and feeds it into the cylinder chamber 14. In which the pressure required for the movement of the cross-bar is built up. The check valve 40 prevents the pressure fluid delivered by the hydraulic machine 30 from flowing into the line 38 and thus into the cylinder chamber 24 of the pressing cylinder 11. The rotational speed and the displacement volume of the hydraulic machine 30 are adjusted in such a way that the pressure liquid quantity flowing to the cylinder chamber 14 results in the desired quick stroke speed of the quick stroke cylinder 10. The hold-down cylinder 11 is dragged along by the fast stroke cylinder 10 via a cross bar 17. For this purpose, it must be possible to force pressure liquid out of the cylinder chamber 25 of the pressing cylinder 11. This occurs once through the non-return valve 50, through which the pressure liquid flows from the cylinder chamber 25 into the cylinder chamber 24. Furthermore, the displacement volume of the hydraulic machine 32 is adjusted in such a way that a portion of the pressure fluid to be displaced from the cylinder chamber 25 is supplied to the cylinder chamber 24 via the non-return valve 46 and the hydraulic machine 32. Because the piston faces A3 and a4 of the pressing cylinder 11 are extremely large compared to the piston faces a1 and a2 of the quick-stroke cylinder, on the other hand, because the two

hydraulic machines

30 and 32 are equally large or not large, the amount of liquid flowing through the hydraulic machine 32 is small compared to the amount of liquid flowing through the check valve 50. However, a reduction in the volume flow through the check valve 50 is advantageous.

Before the pressing speed is reached at the end of the rapid stroke of the feed, the hydraulic press is adjusted to a delivery quantity which corresponds to the desired pressing speed, taking into account the dimensions of the faces A3 and a4 of the pressing cylinder 11. The delivery of the hydraulic press 30 is now reduced to and possibly below the desired pressing speed. The ratio between the delivery capacity of the hydraulic press 30 and the delivery capacity of the hydraulic press 32 is at most as great as the ratio between the planes a1 and A3. The pressure in the cylinder chamber 14 therefore drops, while the pressure builds up in the cylinder chamber 24. The passive non-return valve 50 and the switching valve 51 in its blocking position prevent a pressure drop in the low-pressure branch of the drive. The pressure in the line 38 and in the cylinder chamber 24 rises further until finally the passive non-return valve 40 opens and pressure equalization in the direction of the cylinder chamber 14 is achieved. Then pressed by two hydraulic presses through two faces a1 and A3. The pressing speed is set by adjusting the delivery of the hydraulic press 32 by means of the displacement sensor 18.

For the purpose of pressure reduction, the transport direction of the two hydraulic presses is reversed compared to the direction during pressing. The on-off valve 51 is operated after decompression. The return stroke is now effected in that the hydraulic machine 30 delivers the pressure fluid removed from the cylinder chamber 14 into the cylinder chamber 15 of the quick-action cylinder 10, wherein the non-return valve 46 closes the line 36 and the cylinder chamber 15 to the low-pressure accumulator 47 and the cylinder chamber 25 of the pressure cylinder 11 and builds up a pressure in the cylinder chamber 15 of the quick-action cylinder 10 and a quick stroke is achieved. The on-off valve 51 is operated so that pressure liquid can overflow from the cylinder chamber 24 into the cylinder chamber 25 of the pressing cylinder. The hydraulic machine 32 adjusts the swept volume to zero.

List of reference numerals:

10 quick stroke cylinder

11 pressing stroke or power stroke cylinder

1210 cylinder shell

1310 piston

1410 first chamber

1510 second cylinder chamber

1610 piston rod

17 Cross bar

18 displacement sensor

2211 Cylinder housing

2311A piston

2411 third cylinder chamber

2511 fourth Cylinder Chamber

2611 piston rod

30 first hydraulic press

32 second hydraulic press

3330 first working connection

34 between 33 and 14

3530 second service coupling

36 between 35 and 15

3732 first working connection

38 between 37 and 24

3932 second working joint

40 check valve

45 pipeline

46 check valve

47 low-voltage accumulator

50 check valve

512/2 reversing seat valve

52 switching magnet

53 check valve

54 low voltage memory

60 electric motor

61 electric motor

62 electric motor

The side in A110

The noodle in A210

Face in A311

Face in a 411.

Claims

1. Hydrostatic drive for presses or injection molding machines or the like, comprising: a cylinder device (10, 11) on which, for the rapid stroke of the feed and the subsequent press stroke, a hydrostatic piston surface (A1, A3) can be acted upon with a pressure that is not as great; a first hydraulic machine (30) whose pressure fluid delivery is variable and which can be operated for a quick stroke in a closed hydraulic circuit with a first cylinder chamber (14) which is located upstream of a first piston surface (A1) and is pressure-loaded in the quick stroke, and with a second cylinder chamber (15) which is located upstream of a second piston surface (A2); a second hydraulic press (32), the pressure fluid delivery of which is variable and which, for a pressing stroke, can be operated in a closed hydraulic circuit with a third cylinder chamber (24) upstream of a third piston surface (A3) and which is pressure-loaded during the pressing stroke, and with a fourth cylinder chamber (25) upstream of a fourth piston surface (A4); and a valve device (40, 50) which influences the pressure liquid flow when the rapid stroke is changed to the pressing stroke,

characterised in that the valve arrangement comprises a plurality of passive valves (40, 50), the state of which is derived from a delivery quantity preset value for the two hydraulic machines (30, 32).

2. The hydrostatic drive according to 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 the fourth cylinder chamber (25) and opens from the fourth cylinder chamber (25) towards the third cylinder chamber (24), and a second check valve (40) is arranged 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) and opens from the second line (38) towards the first line (34).

3. The hydrostatic drive according to claim 2, wherein the speed of the cylinder arrangement (10, 11) is predetermined by the delivery volume of the first hydraulic machine (30) during the rapid stroke of the feed.

4. The hydrostatic drive according to claim 3, wherein, during the rapid stroke of the feed, the delivery volume of the second hydraulic machine (32) is greater than zero and the second hydraulic machine (32) delivers pressure fluid from the fourth cylinder chamber (25) to the third cylinder chamber (24).

5. The hydrostatic drive of claim 4, wherein the second hydrostatic machine (32) has the greatest delivery volume during the rapid stroke of feed.

6. The hydrostatic drive according to claim 4 or 5, wherein, in the transition from the rapid stroke of the feed to the pressing stroke, the delivery volume of the first hydraulic machine (30) is so small that the inflow of pressure 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 lower than the pressing speed, and wherein the delivery volume of the second hydraulic machine (32) is adjusted such that a pressing speed is obtained.

7. The hydrostatic drive according to the preceding claim, wherein at least one of the two hydraulic machines (30, 32) is adjustable with respect to its displacement volume.

8. The hydrostatic drive of claim 7, wherein a speed-regulated electric motor (60) is provided, by which the two hydraulic machines (30, 32) can be driven jointly.

9. The hydrostatic drive according to any of claims 1-7, wherein there are two speed-regulated motors (61, 62), and wherein the first hydraulic machine (30) is drivable by a first motor (61) of the two motors (61, 62) and the second hydraulic machine (32) is drivable by a second motor (62) of the two motors (61, 62).

10. The hydrostatic drive according to any of claims 1-6, wherein there are two speed-regulated motors (61, 62), wherein the first hydraulic machine (30) is drivable by a first motor (61) of the two speed-regulated motors (61, 62) and the second hydraulic machine (32) is drivable by a second motor (62) of the two speed-regulated motors (61, 62), and wherein each of the two hydraulic machines (30, 32) is a hydraulic machine with a constant working volume.

11. Hydrostatic drive according to the preceding claim, wherein the two hydraulic machines (30, 32) are in common fluid communication with the second cylinder chamber (15), wherein a valve (46) is arranged between the hydraulic machines (30, 32) and the fourth cylinder chamber (25), with which a flow of liquid from the hydraulic machines (30, 32) to the fourth cylinder chamber (25) can be blocked, and wherein a switching valve (51) is arranged between the third cylinder chamber (24) and the fourth cylinder chamber (25), which switching valve can be actuated at will and has a first switching position, in which the third cylinder chamber (24) and the fourth cylinder chamber (25) are separated from one another, and a second switching position, in which the third cylinder chamber (24) and the fourth cylinder chamber (25) are in fluid communication with one another.

12. The hydrostatic drive according to claim 11, wherein the valve arranged between the hydraulic machine (30, 32) and the fourth cylinder chamber (25) is a check valve (46) which is shut off from the fourth cylinder chamber (25) towards the hydraulic machine (30, 32).

13. Hydrostatic drive according to the preceding claim, wherein the first cylinder chamber (14) can be brought into fluid communication with a low-pressure reservoir (54) via a non-return valve (53) which opens toward the first cylinder chamber, the second cylinder chamber (15) via a non-return valve (53) which opens toward the second cylinder chamber, and the third cylinder chamber (24) via a non-return valve (53) which opens toward the third cylinder chamber.

14. Hydrostatic drive according to the preceding claim, wherein the fourth cylinder chamber (25) is in direct fluid communication with a low-pressure accumulator (47).