EP0461638A1 - Synchronisation device for a lifting platform - Google Patents

Abstract

In order to permit synchronisation of two supporting members (6 and 7) of a lifting platform, in particular for motor vehicles, which supporting members (6 and 7) can each be lifted individually by means of a hydraulic lifting cylinder (2 or 3), each supporting member is connected directly or indirectly in a fixed manner to a synchronisation rod (9 or 10). The two synchronisation rods are connected in an articulated manner (12, 13) to a control rod (11). A control cylinder (19) is connected between the control rod (11) and at least one synchronisation rod (9). If there is only one control cylinder, a shuttle valve (67), among other things, is required in order to obtain the synchronisation of the supporting members (6 and 7) via the hydraulic control system. Instead, a second control cylinder (20) can be connected between the control rod (11) and the other synchronisation rod (10). <IMAGE>

Description

The invention relates to a synchronous device for a lifting platform with two, in particular hydraulic lifting cylinders, on the extendable elements of which a support member is arranged for the load to be lifted. The two extendable elements are generally each the piston of the lifting cylinder, but in special cases it can also be an extendable cylinder in which the piston is mounted so that it can be extended. The two support members are possibly elongated, plate-like elements, wherein in the case of a motor vehicle lifting platform, the left wheels of the vehicle and the right wheels drive onto the other. In the following, for the sake of simplicity, we will only speak of a motor vehicle lift, without this being intended to be restrictive. In the same way, only hydraulic lifting cylinders are used because the pneumatic because of the compressibility of the medium, at least in motor vehicle lifts, is usually of no importance.

The two lifting cylinders are usually fed by a common pressure source. For various reasons, for example due to different loads on the two support members, it can happen that one support member is raised faster than the other. This leads to an inclined position of the motor vehicle, which can be associated with considerable risk of accidents. The above naturally applies not only to the lifting of the motor vehicle, but also to the lowering, it being possible for the two supporting members to have the same stroke position at the beginning.

For safety reasons in particular, an unequal lifting and lowering of the two support members on a lift is generally not acceptable. For this reason, various synchronizing devices have been developed. One is, for example, that a toothed rack is attached directly or indirectly to each support member, which is raised and lowered together with the support member. A toothed pinion meshes in a fixed, rotating manner with each rack. Because these two pinions are rotatably coupled via a shaft, they inevitably have to rotate at the same speed and as a result the two racks can can only be raised and lowered at the same speed, which then causes the synchronism of the two support members.

The racks and of course the pinions must be protected from dirt and damage. With the pinions, this is relatively easy in the case of a pit for the lifting platform, but not with the toothed racks, because they extend beyond the top of the pit. In addition, even if the racks are tightly encircled in the area of the upper pit edge, dirt can get into the pit via the tooth gaps and thus reach the pinions stored there. What applies to dirt is especially true for water.

The object of the invention is therefore to develop a synchronous device of the type described above so that the ingress of dirt, water and the like. is prevented in the area of the extendable parts of the synchronizing device in the passage area of a pit cover or the like.

This object is achieved in that the stroke-determining means are connected to the two supporting members of this lifting platform, which act on a common control mechanism which compensates for a possible stroke difference. If, for example, one support member is raised faster than the other support member, the control means assigned to the other support member causes an increased control via the control member Inflow of the pressure medium used, which as long as a faster lifting of this initially lagging support member results until this second support member is raised to the same height as the first support member and thus the equality of both support members has been achieved again.

A particularly expedient embodiment of this synchronizing device according to the invention is characterized in that a synchronizing rod extending in the direction of displacement of the extendable element is connected to each support member and these two synchronizing rods are each connected via a joint to a control rod serving as the respective stroke determining means, and in that at a distance from one of these joints, a control cylinder is articulated at both ends to one of the synchronizing rods and the control rod, the connections of which serve as inputs for lifting with the pressure source of the medium and the outputs of which are each flow-connected to the input of one of the lifting cylinders, and that for single-acting lifting cylinders a shuttle valve is connected between the latter and the control cylinder or a control cylinder is inserted between each synchronous rod and the control rod, with the returning medium from the lifting cylinders via the switched over stopped change valve and the control cylinder or flows via the second control cylinder to a liquid container.

This particular design of the synchronizing device according to the invention dispenses with toothed racks and instead provides for the use of synchronizing rods which have a smooth outer jacket and, for example, have a round or rectangular cross section. If they penetrate a cover, in particular a pit cover, the passage point can be sealed in any position of the support members without any problems. There is also the fact that synchronous racks with a conventional, in particular circular, cross-sectional profile are comparatively simple components which cause significantly lower costs than racks which one has to manufacture in motor vehicle lifts from particularly high-quality and therefore expensive and expensive to machine material. These savings in material and manufacturing costs are offset by the costs of the control cylinder with shuttle valve or the two control cylinders. However, these costs, including the costs for hydraulic lines and additional hydraulic elements, are lower overall than the costs for the gear drive, so that there is also a cost advantage in addition to the advantage of pollution protection.

If the extendable element connected to the support member of one lifting cylinder extends faster than that of the other support member, this leads to a pivoting of the control rod about its two bearing ends. It takes an inclined position in relation to its starting position. This also causes a change in position of the joint or the joints of the control cylinder or relative to the other joint on the synchronizer rod. In other words, the distance between the two joints of the or each control cylinder changes and this leads to a displacement of the control piston in the cylinder of the or each control cylinder. This displacement movement of the control piston effects a control of the flow in the sense that, for example, when lifting the load, the leading lifting cylinder is fed less and the lagging more medium is supplied. As soon as the two support members have returned to the same height level, the control piston in the cylinder of its control cylinder also returns to its starting position, the control piston being returned just as steadily as the tracking support member being tracked.

This process takes place analogously when the two support members are lowered. However, because the direction of flow through the control cylinder or cylinders is reversed, the inputs becoming outputs and vice versa, an action on the control piston of the or each control cylinder is necessary in the opposite direction. This is achieved when only one control cylinder is used by interposing a shuttle valve, which is switched from lifting to lowering when the lifting cylinders are switched. If two control cylinders are used instead, these can be connected to the lifting cylinders in a suitable manner, thereby making the use of a shuttle valve unnecessary.

The control rod is preferably assigned to the lower ends of the synchronizing rods. This means that the control cylinder (s) are located above the control rod. Overall, the arrangement is such that the control cylinders do not reach a pit cover or the upper pit edge in any position of the lifting cylinders.

A further development of the invention provides that the geometric axis of the control rod extends approximately perpendicular to that of the synchronizing rods and the geometric axis of the control piston of the or each control cylinder encloses an angle of approximately 45 ° with the geometric axis of the control rod. Of course, this also includes an angle of approximately 45 ° with the geometric axis of the assigned synchronizing rod. Both apply to the initial position or the correct stroke position of both support members.

Another embodiment of the invention is that the cylinder of the control cylinder is articulated to the control rod and a piston rod connected to the piston of the control cylinder is articulated to the associated synchronizing rod, but the reverse arrangement is also possible. The two hinge axes of the control cylinder run perpendicular to the plane defined by the synchronous rods and the control rod, the preferred case being that the control rod is at least approximately in the vertical plane defined by the two synchronous rods.

A particularly simple and therefore also inexpensive to produce embodiment of this synchronizing device is characterized in that two cables or chains or the like are used as the means determining the respective stroke of the two support members. are provided, which are fastened on the one hand to the support members and, on the other hand, wound on a horizontal, fixed, rotatably mounted shaft, the two mutually facing ends of which are connected in a rotationally fixed manner to the compensating control element. As a compensating control element, for example, a hydraulic rotary valve having an inlet connection and two outlet connections can be provided, in its sleeve-like housing pivotable about its longitudinal central axis, two interlocking and mutually rotatable slide bodies with at least one radial inlet bore, one central distributor bore and at least two radial outlet bores are stored.

Fig. 1

Schematisch und teilweise in vertikaler Richtung geschnitten eine Vorderansicht der Hebebühne mit einer ersten Ausführungsform der Gleichlaufvorrichtung,

Fig. 2

ebenfalls schematisch einen Hydraulikplan dieser Ausführungsform,

Fig. 3

einen Hydraulikplan einer zweiten Variante der Erfindung.

Fig. 4

eine schematische Darstellung einer weiteren Ausführungsform und

Fig. 5

einen zu dieser letzten Ausführungsform gehörigen Hydraulikplan.

Further advantageous refinements of this synchronizing device result from the claims and the following description of three exemplary embodiments. The drawings show these exemplary embodiments. Here represent:

Fig. 1

Schematically and partially in vertical section, a front view of the lifting platform with a first embodiment of the synchronizing device,

Fig. 2

also schematically a hydraulic diagram of this embodiment,

Fig. 3

a hydraulic diagram of a second variant of the invention.

Fig. 4

a schematic representation of a further embodiment and

Fig. 5

a hydraulic diagram associated with this last embodiment.

In the first two exemplary embodiments, the lifting platform is installed in a pit 1 and has two hydraulic lifting cylinders 2 and 3. The extendable element of each lifting cylinder, in particular a piston 4 or 5, carries a support member 6 or, at its free, upper end in use. 7. The lifting platform is preferably used for lifting motor vehicles, in which case, for example, the left support member 6, the two left wheels and the right support member 7 support the two right wheels of the motor vehicle to be lifted. It is obvious that the two support members 6 and 7 must be at the same height in each stroke position, otherwise the vehicle will assume an inclined position. For various reasons, but especially if the right side of the lift is heavier than the left or vice versa, it can happen without special measures that when lifting or lowering the vehicle one support member leads the other.

The synchronism of the two support members is achieved with the aid of a synchronizing device, which is described in more detail below. In principle, synchronous devices are already known. Instead of the toothed racks protruding there above when the support members are raised above the pit edge 6, the synchronizing device according to the invention of the lifting platform provides for the use of two synchronizing rods 9 and 10. The upper end of each synchronous rod is connected directly or indirectly to the associated support member. The synchronizing rods have a simple, for example a circular cross section, so that they can be sealed and passed through a pit cover in the area of the plane of the pit edge 8 upwards without any problems. In this way, dirt and water are prevented from penetrating the passage of each synchronous rod. The two synchronizing rods are connected to one another, in particular at their lower end, via a control rod 11. The connection takes place in each case via a schematically drawn joint 12 or 13. As a result, the control rod 11 running in the starting position or in a parallel stroke position of the support members 6 and 7 perpendicular to the synchronizing rods 9 and 10 can assume the inclined position shown in FIG. 1 with dashed lines . This oblique position is associated with the lagging position of the support member 7, which is also shown in broken lines in FIG. 1. Only for the sake of order it is added at this point that the two synchronized rods 9 and 10 are of course parallel to the geometric axis of the associated hydraulic lifting cylinder 2 and 3 and thus also extend parallel to the stroke direction 14 of the two support members 6 and 7.

At a distance from the joint 12 or 13, a control cylinder 19 or 20 is mounted on a schematically drawn further joint 15, 16 or 17, 18, respectively. If, as in the exemplary embodiment, the control rod 11 is located at the lower ends of the synchronizing rods 9 and 10, the control cylinders 19 and 20 lie above the control rod 11. The distance between the further joints 15 and 16 from the associated joint 12 or the further joints 17 and 18 of the associated joint 13 is preferably chosen to be the same, so that the geometric axis of each control cylinder with the geometric axes of the control rod on the one hand and the associated synchronizing rod on the other hand is 45 ° in each case. From the latter it follows that the lower end of each control cylinder 19 or 20 is articulated on the control rod 11, while the upper end is articulated in a manner not shown with the associated synchronous rod 9 or 11.

Each control cylinder 19 consists of a cylinder 21 or 22 and a piston 23 or 24. A rod 25 serves for the articulated connection of the cylinder 21 via the joint 16 to the control rod 11, while a rod 26 supports the cylinder 22 via the joint 18 the control rod connects. The piston 23 of the control cylinder 19 is connected to a piston rod 27, while between the piston 24 and the joint 17 a piston rod 28 of the control cylinder 20 is inserted.

Because the joints 15 and 17 are stationary relative to their synchronous rods 9 and 10, pivoting the control rod 11, for example in the direction of arrow 55, leads to a greater distance between the joints 15 and 16 and thus to a relative displacement of the piston 23 in the cylinder 21 of the Control cylinder 19. The same happens on the other side of the control cylinder 20, but in the opposite direction. The pressure medium coming from a pressure source 56 for the hydraulic lifting cylinders 2 and 3 flows via line 29, from the pressure shaft 56, which is preferably designed as a pump, to the hydraulic control cylinder 19. From there, two lines 30 and 31 lead to the inlet 32 of the lifting cylinder 2 and to the inlet 33 of the lifting cylinder 3. Because these hydraulic lifting cylinders are single-acting lifting cylinders, the inlet 32 or 33 also forms the outlet when the support members 6 and 7 are LOWERED.

In the first, in the fig. 2 and 3 shown variant with two control cylinders, each outlet 32, 33 is hydraulically connected to the other control cylinder 20 via further lines 34 and 35. From there, a return line 36 leads to a symbolically drawn collecting container 37 for the hydraulic fluid. From this the pump sucks the medium again, whereby it first flows through a filter 38. Before it reaches the control cylinder 19, it preferably flows through a pressure relief valve 39.

FIG. 2 shows the schematic hydraulic diagram for the first embodiment of the synchronizing device shown in FIG. 1. From the pressure relief valve 39, the medium under pressure exits via the line 40, from which a branch line 41 branches off before reaching the control cylinder 19, but which can also be connected directly to the pressure relief valve. The piston of each control cylinder 19 or 20 is provided with three annular grooves, so that annular spaces 42 and 43 or 52 and 53 are formed. The line 40 opens directly into the annular space 42 on the left in FIG. 2 if no cylindrical annular space is assigned to it, while the branch line 41 is hydraulically connected to the annular space 43. The line 30 exits the annular space 42 and the line 31 exits the annular space 43. A check valve 44 is installed in the former and a check valve 45 is installed in the latter. This is part of a magnetic changeover valve 46. In this way it can be switched from one-sided passage to the lifting cylinder to double-sided passage, whereby a hydraulic connection path from the cylinder space 47 of the lifting cylinder 2 to the further line 34 can be created, this path when switching the lift release on lowering by actuating the solenoid switch valve 46. The inlets and outlets for the lines 40, 41 and 30, 31 of the control cylinder 19 - and of course the same also applies to the control cylinder 20 - are so matched to the width of the ring grooves that the control of the hydraulic flows described below when moving the piston 23 with the help of the control rod 11 can cause.

Analog to the left side of FIG. 2, check valves 48 and 49 are inserted into lines 31 and 35, respectively. The check valve 49 is part of the magnetic changeover valve 50. The cylinder space of the right hydraulic lifting cylinder 3 is designated 51. The two annular spaces of the control cylinder 20 bear the reference numbers 52 and 53. The branch line 54 is connected to the latter. Due to the annular grooves, the piston 23 is divided into the two outer elements 57 and 58 and a middle element 59. Corresponding elements 60 and 61 and 62 have the piston 24. In a manner not shown, in the starting position of the pistons 23 and 24, a cylinder annular space, preferably of smaller width, can be assigned to each piston annular space. The assignment and dimensioning must then be such that a change in the outflow cross-section is achieved with each displacement of the piston, the reduction in one outflow cross-section simultaneously resulting in an increase in the other outflow cross-section for each piston 23 or 24. This is used for control purposes in the manner described below.

Assuming according to FIG. 1 that the left support member 6 leads when LIFTING compared to the right support member 7 shown with dashed lines, so that the control rod 11 assumes the dashed oblique position, this leads to a displacement of the piston 23 and its output or 2 in a sliding position. In FIG. 1, this means a relative shift the piston 23 to the top left or the cylinder 21 to the bottom right. The joints 17 and 18 approach each other, which is why on the right side the piston 24 is displaced relative to the cylinder 20 downward to the left.

A displacement of the piston 23 in the direction of the arrow 63 and the piston 24 in the direction of the arrow 66 corresponds to these displacement movements in FIG. 2 applies to lines 40 and 41- this piston displacement causes a reduction in the outflow cross-section to line 30 and / or the inflow cross-section from line 40 with the help of the outer element 57 and at the same time an increase in the inflow cross-section of line 41 and / or the outflow cross-section to line 31 by means of the right outer element 58 of the piston 23. From this it follows that the right edge of the outer element 57 on the one hand and the left edge of the right outer element 58 are respectively control edges for the corresponding cylinder annular spaces or the inflow and outflow cross sections of the four lines . The same naturally applies to the right control cylinder 20.

Because less medium can now flow via line 30 than via line 31 in the manner described, the left cylinder space 47 of the left hydraulic cylinder 2 becomes less Medium supplied as the right cylinder chamber 51 of the right hydraulic lifting cylinder 3. This causes the piston 64 of the right hydraulic cylinder 3 to move up faster than the piston 65 of the left hydraulic lifting cylinder 2 is possible and thereby the lagging support member 7 is raised more than that Support member 6. As soon as both support members have returned to the same height, the control rod 11 also returns to its starting position and thus the center position or starting position of the control pistons 23 and 24 is reached again. Of course, the trailing position of the support member 7 is shown in FIG. 1 exaggerated for clarity. In reality, there is constant regulation in the sense mentioned.

The same happens analogously when lowering. If it is assumed that the right support member 7 according to FIG. 1 leads ahead when lowering, this results in a displacement of the piston 24 of the control cylinder 20 in the direction of arrow 66 in the manner explained above. As a result, the right outer element 61 throttles the flow of the medium emerging from the cylinder space 51 and flowing via the lines 35 and 54, while the medium emerging from the cylinder space 47 of the left hydraulic lifting cylinder 2 via the lines 34 and 36 due to the enlargement of the orifice cross section Line 34 and line 36 can flow out accelerated with the aid of the left outer element 60, which leads to a faster lowering of the left support member 6 compared to the right support member 7 and thus leads to a level compensation or due to the constant regulation to the desired synchronization. Incidentally, it is pointed out again at this point that the backflow of the medium via lines 34 and 35 is possible in that the two magnetic changeover valves 46 and 50 were previously switched over to passage.

In the second embodiment of the synchronizing device (FIG. 3), a control cylinder 19 is sufficient. Instead of the second control cylinder, a shuttle valve 67 is used here. When the two support members are LIFTED, the line 30 is hydraulically connected to the line 68 to the check valve 45 of the magnetic changeover valve 46, while when LOWERING, a hydraulic connection of the line 30 via the line 69 and the check valve 49 of the magnetic changeover valve 50 to the cylinder chamber 51 is created. This switching from straight passage to crossover passage on shuttle valve 67 achieves, on the one hand, tracking of the remaining support member and, on the other hand, lowering of the lagging support member. Before lowering, the two magnetic changeover valves 46 and 50 must of course also be switched over here. It remains to be added that in the LIFT 31 with 69 and in the LOWER 69 with 30.

So that the pressure medium cannot get into the line 36 during LIFTING, an electromagnetically reversible magnetic changeover valve 70 is also used in the latter. When lifting is the passage blocked on the solenoid changeover valve 70, while it is released during lowering by reversing this solenoid changeover valve.

In the line 40, which connects the pressure source 56 to the left annulus 42 and via the line 41 also to the right annulus 43 of the piston 23 of the control cylinder 19, a check valve 71 is inserted before the branching of the line 41. In addition, a further check valve 72 is inserted in the return line 36 to the liquid container 37, which prevents the pressure medium from flowing directly into the liquid container 37 when the support members 6 and 7 are LIFTED. The check valve 72 is part of the magnetic changeover valve 70. This is switched to free passage when the support members 6 and 7 are LOWERED.

4 shows a third embodiment of the synchronizing device according to the invention, in which the same components are again identified by the same reference numerals. In this case, two horizontal shafts, designated 73 and 74, are rotatably mounted in the lower region of the pit 1. Cable drums 78 are arranged on the two outer ends 76 and 77 of these two shafts 73 and 74, on each of which an associated cable 79, 80 is wound. The free ends 81 and 82 of these two cables 79 and 80 are attached to the supporting members 6 and 7 belonging to the two lifting devices 2 and 3. The two inner ends 83 and 84 of these horizontal shafts 73 and 74 on the other hand, a control slide 85, which compensates for a possible stroke difference, is connected in a rotationally fixed manner to a rotary slide valve (not shown).

The function of this design of the synchronizing device is particularly simple. As soon as a stroke difference occurs during operation of the lifting device, the cable runs 86 and 87 located between the two cable drums 78 and the support members 6 and 7 have different lengths 1 1 and 1 2, which causes a rotation of the two horizontal shafts 73 and 74 and thus also of the two Rotary slide of the control member 85 results. When the two rotary valves are rotated relative to one another, however, the flow cross-sections of the control member 85 change in such a way that a somewhat larger amount of pressure oil is now supplied to the currently trailing lifting cylinder of the relevant lifting device 2 or 3, and the existing stroke difference is thus compensated for.

This previously discussed compensation of a possible stroke difference is not only very simple and can be repeated as often as desired, but is also particularly safe and insensitive to faults. In addition, this design can also be produced very easily, which in turn results in a corresponding reduction in the production costs.

The hydraulic plan shown in FIG. 5, which largely corresponds to the hydraulic plan according to FIG. 3, belongs to this third design. In this case, however, instead of the control cylinder 19 shown in FIG. 3, the control member 85 already treated, which is equipped with two rotary valves, is provided.

Claims (15)

Synchronization device for a lifting platform with two, in particular hydraulic lifting cylinders (2, 3), on the extendable elements (4, 5) of which a support member (6, 7) is arranged for the load to be lifted, characterized in that with the two support members in each case Stroke-determining means are connected, which act on a common control element which compensates for a possible stroke difference. Synchronous device according to claim 1, characterized in that a synchronous rod (9, 10) extending in the direction of displacement of the extendable element (4, 5) is connected to each support member (6, 7) and these two synchronous rods (9, 10) each have one Joint (12, 13) are connected to a control rod (11) serving as their respective stroke-determining means, and that at a distance from one of these joints a control cylinder (19, 20) is articulated at both ends (15, 16; 17, 18) with a the synchronous rods (9, 10) and the control rod (11) connected whose connections serve as inputs to the pressure source (56) of the medium and whose outputs are each flow-connected to the input (32, 33) of one of the lifting cylinders (2, 3), and that in single-acting lifting cylinders between the latter (32, 33) and the control cylinder (19) is connected to a shuttle valve (67) or between the control rod (11) is assigned to the lower ends of the synchronization rods (9, 10). Synchronization device according to claim 2, characterized in that the control rod (11) is assigned to the lower ends of the synchronization rods (9, 10). Synchronous device according to claim 2 or 3, characterized in that the geometric axis of the control rod (11) is approximately perpendicular to that of the synchronous rods (9, 10) and the geometric axis of the control piston (23, 24) of the or each control cylinder (19, 20) encloses an angle of approximately 45 ° with the geometric axis of the control rod (11). Synchronous device according to at least one of the preceding claims 2 to 4, characterized in that the cylinder (21, 22) of the control cylinder (19, 20) is articulated with the control rod (11) and one with the piston (23, 24) of the control cylinder (19 , 20) connected piston rod (27, 28) is connected in an articulated manner to the associated synchronizing rod (9, 10). Synchronization device according to at least one of the preceding claims 2 to 5 with a control cylinder (19), characterized in that the piston (23) of the control cylinder (19) is provided with two piston ring grooves, each of which has an annular groove of the cylinder (21 ) with two lines (40, 30 or 41, 31) or two lines (40, 30 or 41, 31), respectively, with the lines (40, 30) of the one annular piston groove (42) at LIFT the support members (6, 7) the connection of one lifting cylinder (2) to the pressure source (56) and the lines (41, 31) of the other piston ring groove (43) the connection of the other lifting cylinder (3) to the pressure source ( 56), and that between the control cylinder (19) and the lifting cylinder (2, 3) a shuttle valve (67) is used, which in its switch position when lowering the support members (6, 7) via the piston ring grooves (42, 43 ) the lifting cylinders (2, 3) with a return line (36) to the liquid container (37 ) connects. Synchronous device according to claim 6, characterized in that in the connecting line (68) from the shuttle valve (67) to one lifting cylinder (2) a magnetic switch valve (46) and in the connecting line (69) to the other lifting cylinder (3) a magnetic switching valve (50) is used, whereby the magnetic changeover valves can be flowed through in both directions when lifting towards the lifting cylinder and when lowering . Synchronous device according to claim 6 or 7, characterized in that the shuttle valve (67) can be flowed through straight when LIFTING and crosswise when LOWERING . Synchronization device according to at least one of claims 6 to 8, characterized in that a nonreturn valve (71) or (72) is inserted between the pressure source (56) and the control cylinder (19) and in the return line (36) to the liquid container (37) which can be flowed through against the piston annular spaces and block the flow from the piston annular spaces to the pressure source (56) or to the liquid container (37), the check valve (72) in the return line (36) being part of a magnetic changeover valve (70) forms. Synchronous device according to at least one of claims 2 to 5 with two control cylinders (19, 20), characterized in that the piston (23, 24) of each control cylinder (19, 20) with two piston ring grooves (42, 43; 52, 53) is provided, which in the starting position each have an annular groove in the cylinder (21, 22) with two lines (40, 30; 41, 31 or 34, 36; 35, 54) or two lines (40, 30; 41, 31 and 34, 36; 35, 54) are assigned, the one piston annular groove (42) of the one control cylinder (19) via the line (30) with the one lifting cylinder (2) and the other piston annular groove (43 ) via the line (31) with the other lifting cylinder (3) and also the one piston ring groove (52) the other control cylinder (20) via the line (34) with the one lifting cylinder (2) and the other piston ring groove (53) via the line (35) with the other lifting cylinder (3) are hydraulically connected, in addition to each of these Lines (30, 31; 34, 35) a check valve (44, 45, 48, 49) with flow direction to the lifting cylinder (2, 3) is used. Synchronous device according to claim 10, characterized in that the check valve (45 or 49) of the line (34 or 35) are each part of a magnetic changeover valve (46 or 50) which are switched to free passage when LOWERING . Synchronous running device according to claim 1, characterized in that two means (79, 80), chains or the like as the means which determine the respective stroke of the two support members (6, 7). are provided, which are fastened on the one hand to the support members and, on the other hand, wound on a horizontal, fixed, rotatably mounted shaft (73, 74), the two mutually facing ends (83, 84) of which are connected in a rotationally fixed manner to the compensating control element (85). Synchronous device according to claim 12, characterized in that the ends of the two cable pulls (79, 80), chains or the like facing away from the two support members (6, 7). Drums (78) arranged in a rotationally fixed manner on the horizontal shafts (73, 74) are wound. Synchronous device according to claims 12 and / or 13, characterized in that a hydraulic rotary valve (85) having an inlet connection and two outlet connections is provided as the compensating control element, in its sleeve-like housing pivotable about its longitudinal central axis, two interlocking and mutually rotatable slide bodies with at least each a radial inlet bore, a central distributor bore and at least two radial drain bores each. Synchronization device according to claim 14, characterized in that the cross sections of the drain bores interacting in pairs are different.

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