Hydraulic lifting system

Abstract

Hydraulic lifting system (100, 150, 200, 250, 300), in particular for an industrial truck such as a forklift truck, with at least one lifting cylinder (104, 154, 204, 304) which can be actuated by a hydraulic fluid (102), characterized in that a first lowering branch (S 1 ) and a second sinking branch (S 2 ) in parallel connection to the first sink branch (S 1 ) and each sink branch (S 1,2 ) at least one limiting device (B 1, ..., 6 ), whereby in the event of a fault in one of the sink branches (S 1 , 2 ), such as a line break or the like, a lowering movement of the at least one lifting cylinder (104, 154, 204, 304) is limited to a lowering speed (v).

Description

[0001] The invention relates to a hydraulic lifting system, in particular for an industrial truck such as a forklift truck, with at least one lifting cylinder actuated by a hydraulic fluid.

[0002] According to DIN EN ISO 3691, a hydraulic industrial truck, such as a forklift truck or the like, must be provided with a safety device which, in the event of a fault, in particular a pipe or hose break, in the hydraulic circuit of the industrial truck, limits the lowering speed of a lifting mechanism loaded with its rated load to a value of 0.6 m / s.

[0003] To comply with this regulation, forklifts currently use a fixed-adjustment pipe rupture valve integrated directly into a lifting cylinder or a fixed-adjustment flow control valve. To achieve this purpose, the pipe rupture valve or flow control valve is designed to be permanently set to a flow rate that prevents the lifting mechanism from exceeding the maximum permissible lowering speed of 0.6 m / s under all circumstances.

[0004] One disadvantage is that, even with only a slight load or a completely unloaded hydraulic lifting mechanism, in non-fault situations or during normal operation, the fixed flow control valve prevents a lowering speed higher than the standardized 0.6 m / s. This can lead to a delay in operational processes and, consequently, a reduction in productivity.

[0005] Printed prior art is shown in DE 103 30 344 A1, DE 10 2005 043 447 A1 and DE 10 2018 108 946 A1.

[0006] An object of the invention is to provide an improved hydraulic lifting system for an industrial truck which, in the absence of a fault, allows accelerated lowering when the load is small or completely absent.

[0007] The object mentioned at the outset is achieved in that a first lowering branch and a second lowering branch are assigned to the at least one lifting cylinder and each lowering branch has at least one limiting element, wherein in the event of a fault in one of the lowering branches, such as a line break or the like, a lowering movement of the at least one lifting cylinder is limited to a maximum lowering speed.

[0008] Due to the dual lowering branches, during normal operation or in the absence of a fault in the hydraulic lifting system, the lowering of at least one lifting cylinder is essentially twice as fast. In the context of this description, the term "fault" refers, for example, to a sudden line break, a suddenly slipping line connection, a suddenly bursting or bursting hose, etc. If such a fault occurs in a lowering branch, the associated limiting device automatically reduces the volume flow of the hydraulic fluid in the affected lowering branch to almost zero - apart from any minimal leakage flow, so that the faulty lowering branch no longer has any increasing influence on the lowering speed of the lifting cylinder.In this situation, the limiting device of the intact lowering branch allows just enough volume flow of hydraulic fluid to ensure that the lowering of the lifting cylinder in the event of a fault occurs at a maximum of half the lowering speed compared to normal operation.

[0009] Preferably, the limiting devices are designed to limit the lowering speed of the at least one lifting cylinder to a maximum of 0.6 m / s in the event of a fault in one of the lowering branches. This ensures a standard-compliant lowering speed of the at least one lifting cylinder in the event of a fault in the hydraulic lifting system.

[0010] In a technically advantageous embodiment, the limiting devices each include a pipe rupture safety device. In the event of a pipe rupture in one of the two lowering branches, the pipe rupture safety device automatically and reliably limits the maximum possible lowering speed of the at least one lifting cylinder to 0.6 m / s without external control signals. For this purpose, each pipe rupture safety device only allows a volume flow of hydraulic fluid between approximately zero and a fixed, preset maximum value, which corresponds to the maximum permissible lowering speed of the at least one lifting cylinder of 0.6 m / s in the event of a fault.

[0011] Preferably, each of the two lowering branches has a flow control valve, a variable-speed hydraulic motor, or a switching valve. If each lowering branch is equipped with a flow control valve, a particularly differentiated, precise regulation of the lowering speed of the at least one lifting cylinder is possible. The term electrically actuated "flow control valve" in the context of this description defines a continuous hydraulic actuator that allows a virtually stepless or continuous adjustment of a volume flow of the hydraulic fluid between zero and a design-specific maximum value. Each of the flow control valves has a tank line on the output side, the open end of which opens into a pressureless tank for receiving the hydraulic fluid. The two lowering branches can also be returned downstream of the flow control valves via a common tank line, which is sensible for cost reasons, among other things.Alternatively, for example, only one lowering branch can have a flow control valve, while the other lowering branch is equipped with a variable-speed hydraulic motor. In such a configuration, potential energy can be recovered by the lowering lifting cylinder, for example by the variable-speed hydraulic motor driving a generator-driven electric motor. Using the electrical energy generated in this way, a vehicle battery can be partially recharged during lowering operation, for example, in order to increase the possible operating time with one battery charge. The hydraulic motor can be implemented with a hydraulic pump driven by a hydromotor. If, instead of the hydraulic motor, only a switching valve is used alongside the flow control valve, the control and regulation effort can be considerably reduced.In the context of this description, the term "electrically actuated switching valve" refers to a binary valve that allows a volume flow to be set from zero to a design-dependent maximum value. If a hydraulic motor is integrated into each lowering branch, an increase in the electrical energy recovered when lowering the lifting system is possible. For this purpose, each hydraulic motor is preferably coupled to a generator-operated electric motor, which can also serve as the drive motor. Alternatively, both hydraulic motors can also drive a generator-operated electric motor.

[0012] Preferably, a control and / or regulating unit is provided for monitoring the lowering speed, and at least one sensor, in particular for detecting the lowering speed of the at least one master cylinder, is assigned to the control and / or regulating unit. As a result, the lowering process can be detected with very high accuracy. Using the at least one sensor, in addition to the lowering speed of the at least one master cylinder, its current extension position, acceleration, or the like can also be determined with high measurement accuracy.

[0013] In a further technically advantageous development, it is provided that the at least one flow control valve and / or the hydraulic motor and / or the switching valve form a lowering unit that can be controlled by the control and / or regulating unit depending on the at least one sensor. This makes it possible to monitor and adjust the lowering speed of the at least one master cylinder during normal operation or in the event of a fault. Furthermore, the control and / or regulating unit allows particularly precise and sensitive control of a lowering process depending on measured values ​​from the at least one sensor assigned to the at least one master cylinder.

[0014] In the following, preferred embodiments of the invention are explained in more detail with reference to schematic figures. Fig. 1 a first embodiment of a hydraulic lifting system for an industrial truck with a lifting cylinder, Fig. 2 a second embodiment of a hydraulic lifting system for an industrial truck with two lifting cylinders, Fig. 3 a third embodiment of a hydraulic lifting system for an industrial truck with three lifting cylinders, Fig. 4 a fourth embodiment of a hydraulic lifting system for an industrial truck with two mechanically parallel connected lifting cylinders and Fig. 5 a fifth embodiment of a hydraulic lifting system for an industrial truck with two parallel-connected lifting cylinders and one free lifting cylinder.

[0015] The Fig. Figure 1 illustrates a first embodiment of a hydraulic lifting system for an industrial truck with a lifting cylinder. A hydraulic lifting system 100 includes, among other things, a lifting cylinder 104 actuated with a hydraulic fluid 102, to which a first and a second lowering branch S 1,2 The first sink branch S 1has a first limiting member B 1 and the second sinking branch S 2 accordingly has a second limiting device B 2 . The limiting organs B 1,2 are preferably integrated directly into a cylinder base 106 of the lifting cylinder 102. The limiting members B 1,2 are preferably designed as a pipe rupture protection device. Downstream, the first lowering branch S 1 Here, only as an example, a first flow control valve 110 is integrated. Accordingly, in the second lowering branch S 2a second flow control valve 112 is provided. A first tank line 118 is connected to the first flow control valve 110, and a second tank line 120 is connected to the second flow control valve 112. Open ends 122, 124 of the tank lines 118, 120 connected to the flow control valves 110, 112 on the output side open into a pressureless, open tank 130 or a reservoir for receiving excess hydraulic fluid 102. The two flow control valves 110, 112 form an integrated lowering unit 136.

[0016] Furthermore, the lifting system 100 can have an electronic control and / or regulating unit 140, to which at least one sensor 142 is assigned. With the aid of the at least one sensor 142, at least one lowering speed v of the lifting cylinder 104 can be detected. By means of the control and / or regulating unit 140, the two flow control valves 110, 112 of the lowering branches S 1,2Preferably, the lowering process can be controlled as a function of measurement signals from at least one sensor 142. This allows lowering processes to be implemented with greater accuracy during normal operation of the lifting system 100. Additional sensors can be assigned to the control and / or regulating unit 140, with which, for example, an acceleration or an absolute extension position of the lifting cylinder 104 can be detected. As a result, the lowering process of the lifting cylinder 104 can be controlled and / or regulated even more precisely.

[0017] During normal operation of the hydraulic lifting system 100, the limiting devices B, each designed as a pipe rupture protection device, limit 1,2 the volume flows Q 1,2 of the hydraulic fluid 102 within the respective lowering branch S 1,2automatically to a maximum value that results in a lowering speed v of approximately 0.6 m / s as accurately as possible. This value corresponds to the permissible maximum value of the lowering speed v of the lifting mechanism 100 prescribed by DIN EN ISO 3691 in the event of a fault. Due to the inventive parallel connection of the two lowering branches S 1,2However, during normal operation of the hydraulic lifting system 100, a lowering speed v of the lifting cylinder 104 can be achieved at twice the value, in the range of 1.2 m / s. The structural design of a pipe rupture safety device is sufficiently familiar to a person skilled in the field of hydraulics, so that, for the sake of brevity and conciseness, a more detailed explanation of its operation can be omitted. During normal operation of the hydraulic lifting system 100, the lowering process can optionally also be influenced by means of the two flow control valves 110, 112, which are preferably controlled by the control and / or regulating unit 140.

[0018] In case of a fault, for example within the sinking branch S 1 , the corresponding volume flow Q 1 by the limiting device B 1 reduced to almost zero, so that the faulty sink branch S 1can no longer exert a speed-increasing effect or is blocked. The further lowering of the lifting cylinder 104 while maintaining the standard-compliant lowering speed v of 0.6 m / s is achieved solely by the intact lowering branch S 2 A further adjustment of the lowering speed v of the lifting cylinder 104, especially its further reduction, can be achieved by a controlled actuation of the second flow control valve 112 of the second, still intact lowering branch S 2 by means of the control and / or regulation unit 140. However, if the error occurs in the other sink branch S 2 the volume flow Q 2 by the limiting device B 2 practically reduced to zero and the lowering of the lifting cylinder 104 takes place again at about 0.6 m / s automatically controlled by the first limiting device B 1 in optional cooperation with the first flow control valve 110.

[0019] Instead of the two flow control valves 110, 112, at least one of the two lowering branches S 1,2 Alternatively, a variable-speed hydraulic motor (not shown in the drawing) or a switching valve (also not shown in the drawing) with the switching states "fully closed" or "fully open" can be used. By using a binary switching valve, the volume flows Q 1,2 the sinking branches S 1,2 influencing flow control valves 110, 112, the control and / or regulation effort can be reduced considerably.

[0020] By using at least one speed-adjustable hydraulic motor, a generator-driven electric motor or an electric generator can be driven in rotation if necessary, whereby the potential energy released when the lifting cylinder 104 is lowered can be converted into electrical energy.

[0021] The Fig. 2 illustrates a second embodiment of a hydraulic lifting system for an industrial truck with two lifting cylinders.

[0022] The hydraulic lifting system 150 again comprises the lifting cylinder 104 with the sensor 142 assigned to the control and / or regulating unit 140. The lowering branches S 1,2 with the limiting organs B 1,2 and associated with the flow control valves 110, 112 forming the lowering unit 136. Open ends 122, 124 of the tank lines 118, 120 connected to the outlet side of the flow control valves 110, 112 lead into the tank 130 containing the hydraulic fluid 102. In the area of ​​the cylinder base 106 of the first cylinder 104, the limiting elements B 1,2 the sinking branches S 1,2 installed.

[0023] In contrast to the first embodiment of Fig. 1, a second lifting cylinder 154 with an optional sensor 156 is provided here, which can be operated independently of the first lifting cylinder 104. The additional lifting cylinder 154 is also connected to the two lowering branches S 1,2 connected, whereby corresponding to the first lifting cylinder 104 two limiting devices B 3,4 are integrated in the area of ​​a cylinder base 160 of the second lifting cylinder 154. The limiting member B 3 is the first sink branch S 1 assigned and the limiting organ B 4 is the second sink branch S 2 assigned. Through the two parallel sink branches S 1,2 is in normal operation - analogous to the operation of the hydraulic lifting system of Fig. 1 - again a lowering speed v which is twice as high as the standard lowering speed v of 0.6 m / s in the event of a fault 1,2 of about 1.2 m / s each.

[0024] In case of a fault in one of the two sink branches S 1,2 The respective limiting devices of both lifting cylinders 104, 154 essentially completely shut off. If the fault occurs, for example, in the lowering branch S 1 the limiting devices B 1,3 the volume flow Q 1 practically completely. Accordingly, the limiting organs B 2,4 in case of a fault within the second sink branch S 2 the volume flow Q 2 practically completely. By means of the limiting devices B 1, ..., 4 of the still intact lowering branch S 1,2 The orderly lowering of the lifting cylinders 104, 154 with the permissible lowering speed v of up to 0.6 m / s then takes place by a corresponding limitation of the volume flows Q 1,2. With the help of the two flow control valves 110, 112 of the lowering unit 136, it is possible to further influence the lowering process of the lifting cylinders 104, 154 both in normal operation and in fault operation of the lifting system 150.

[0025] Instead of the two flow control valves 110, 112, at least one of the two lowering branches S 1,2 in turn have a speed-adjustable hydraulic motor for driving a generator-operated electric motor or a binary switching valve.

[0026] The Fig. 3 shows a third embodiment of a hydraulic lifting system for an industrial truck with three lifting cylinders.

[0027] The hydraulic lifting system 200 comprises, in addition to the two independently operable lifting cylinders 104, 154 of Fig. 2 a further, independently operable, centrally positioned lifting cylinder 204 with an associated sensor 206.

[0028] The hydraulic connection of the lifting cylinders 104, 154 to the two lowering branches S 1,2 is analogous to that in Fig. 2. The open ends 122, 124 of the outlet-side tank lines 118, 120 of the flow control valves 110, 112 lead again into the tank 130 for the hydraulic fluid 102. The two flow control valves 110, 112 also form the lowering unit 136. In the two lowering branches S 1,2 the volume flows Q 1,2 of the hydraulic fluid 102. The optional control and / or regulating unit 140 can be coupled with the likewise optional sensors 142, 156, 206. In such a constellation, the respective current lowering speed v 1,2,3 the three lifting cylinders 104, 156 and 204 can be individually recorded and the flow control valves 110, 112 of the lowering unit 136 can be controlled depending on the speed measured values ​​of the three sensors 142, 156, 206.

[0029] A limiting member B, which is arranged in the area of ​​a cylinder base 210 of the middle lifting cylinder 204 5 is connected to the first sink branch S 1 connected, while another limiting device B 6 in the cylinder base 210 of the middle lifting cylinder 204 with the second lowering branch S 2 is hydraulically coupled. The functionality of the lifting system 200 in normal operation or in the event of a fault corresponds to that of the lifting systems in accordance with Fig. 1, Fig. 2, so that in order to avoid duplication of content, reference is made here to the relevant parts of the description.

[0030] Instead of the two flow control valves 110, 112, at least one of the two lowering branches S 1,2 a speed-adjustable hydraulic motor for driving a generator-operated electric motor or a switching valve.

[0031] The first three embodiments of lifting systems have in common that each lifting cylinder is connected to the first and second lowering branch S 1,2 is connected, whereby each lowering branch has a limiting device in the area of ​​a cylinder base of each lifting cylinder.

[0032] The Fig. 4 illustrates a fourth embodiment of a hydraulic lifting system for an industrial truck with two mechanically parallel connected lifting cylinders.

[0033] A fourth embodiment of a hydraulic lifting system 250 with the two lifting cylinders 104, 154, the optional sensors 142 and / or 156 associated therewith (since mechanically coupled), the optional control and / or regulating unit 140, the two lowering branches S 1,2with the flow control valves 110, 112 forming the lowering unit 136 and their outlet-side tank lines 118, 120, whose open ends 122, 124 lead into the tank 130 with the hydraulic fluid 102, is largely identical to the second embodiment of the hydraulic lifting system according to Fig. 2.

[0034] In contrast to the lifting system of Fig. 2, the two lifting cylinders 104, 154 are mechanically connected in parallel by means of a massive coupling link 252 or a bridge, and therefore can no longer be hydraulically actuated independently of each other. As a result, the lowering speed of both lifting cylinders 104, 154 is always essentially the same, both during normal operation and in the event of a fault. The lifting system 250 can thus be used, for example, in a mast lift stage of an industrial truck with increased load capacity, which requires two mechanically parallel lifting cylinders.

[0035] The sinking branches S1,2 are in turn connected to both cylinders 104, 154. As a further difference to the embodiment of Fig. 2, the lower branches S 1,2 in the area of ​​the respective cylinder bases 106, 160 of the lifting cylinders 104, 154 only the limiting element B 1,4 The limiting element B is located 1 of the sinking branch S 1 in the area of ​​the cylinder base 106 of the first lifting cylinder 104 and the limiting member B 4 of the sinking branch S 2 is positioned accordingly in the area of ​​the cylinder base 106 of the second lifting cylinder 154. The lowering branch S 2 has no limiting element in the area of ​​the cylinder base 106 of the first cylinder 104 and the same applies to the lowering branch S 1 in the area of ​​the cylinder base 160 of the second lifting cylinder 154.

[0036] In normal operation or in the absence of a fault in the lifting system 250, the parallel connected lowering branches S 1,2again an accelerated lowering of the coupling member 252, whereby the lowering speed reaches approximately twice the standard lowering speed of 0.6 m / s and thus about 1.2 m / s.

[0037] However, if, for example, within the sinking branch S 1 If an error occurs, the limiting device B assigned to the first lifting cylinder 104 1 practically completely. Since the first sinking branch S 1 in the area of ​​the cylinder base 160 of the second lifting cylinder 154 is not secured by means of a further limiting device, the second lifting cylinder 154 could move without prejudice to the limiting device B provided in the area of ​​the cylinder base 160 4 via the flow control valve 110 of the first lowering branch S 1lower in a practically uncontrolled manner, which is prevented by the mechanical coupling element 252. In such a fault situation, the first lifting cylinder 104 practically "holds" the second lifting cylinder 154 at its current height and at least prevents it from lowering more quickly than the first lifting cylinder 104. This allows both lifting cylinders 104, 154 to lower synchronously at a maximum of the standard lowering speed v of 0.6 m / s, even in the event of a fault. The same applies analogously to a fault within the other, second lowering branch S 2 .

[0038] By using only one limiting device B 1,4 in each of the two sink branches S 1,2 A cost reduction without loss of safety can be achieved compared to the first three embodiments under the condition that the two lifting cylinders 104, 154 are mechanically connected in parallel - for example by means of the massive coupling link 252.

[0039] The Fig. 5 shows a fifth embodiment of a hydraulic lifting system for an industrial truck with two parallel-connected lifting cylinders and one free lifting cylinder.

[0040] The fifth embodiment of a hydraulic lifting system 300 has, analogously to the Fig. 4 again via the two lifting cylinders 104, 154, the sensors 142 and / or 156 assigned to them (since they are mechanically coupled), the control and / or regulating unit 140, the two lowering branches S 1,2with the flow control valves 110, 112 constituting the lowering unit 136 and their outlet-side tank lines 118, 120, whose open ends 122, 124 lead into the tank 130 containing the hydraulic fluid 102. The first and second cylinders 104, 154 are again mechanically connected in parallel or synchronized with each other by means of the coupling member 252, so that the lowering speeds v of the lifting cylinders 104, 154 are always approximately the same. As a difference to the fourth embodiment of Fig. 4, a third hydraulic lifting cylinder 304 is provided here, which, however, is designed to be free-running, i.e., it has no mechanical coupling with the other two lifting cylinders 104, 154. An optional sensor 306 is also assigned to the lifting cylinder 304, with which, for example, a lowering speed v 2of the lifting cylinder 304 can be detected with the aid of the optional control and / or regulating unit 140 in order to be able to regulate the lowering process more precisely in accordance with the other two lifting cylinders 104, 154. The lifting cylinder 304 is connected to the two lowering branches S 1,2 hydraulically connected, wherein as a further difference to the fourth embodiment according to Fig. 4 in the area of ​​a cylinder base 310 of the third lifting cylinder 304 each lowering branch S 1,2 - according to the embodiments of Fig. 1 to 3 - a limiting device designed in the manner of a pipe burst safety device B 5,6 The limiting element B 5 is in the first sink branch S 1 and the limiting organ B 6 is accordingly in the second sink branch S 2 each integrated in the area of ​​the cylinder base 310 of the third lifting cylinder 304.

[0041] During normal operation of the lifting system 300, due to the dual lowering branches S 1,2 a lowering of the three lifting cylinders 104, 154, 304 with a speed v, v 2 which corresponds to twice the maximum lowering speed specified in the standard in the event of a fault and is therefore approximately 1.2 m / s.

[0042] For example, if the sinking branch S 1 If a fault occurs, the two lifting cylinders 104, 154, which are mechanically connected in parallel by means of the massive coupling element 252, behave in the same way as the two lifting cylinders of the fourth embodiment of the lifting system of Fig. 4, so that reference is made to the descriptions therein.

[0043] Due to the fault in the sinking branch S 1 locks the limiting device B 5 practically completely the flow of the hydraulic fluid 102, while the second limiting member B 6of the remaining, intact lowering branch S 2 It is ensured that the free, third lifting cylinder 304 also lowers synchronously with the other two lifting cylinders 104, 154 at the standard lowering speed v of essentially no more than 0.6 m / s.

[0044] Under all circumstances it is ensured that the volume flow Q 1 through the first sink branch S 1 and the volume flow Q 2 through the second sinking branch S 2 neither in normal operation nor in the event of a fault can it become so great that one of the lifting cylinders 104, 154, 304 lowers faster than the maximum lowering speed v of 0.6 m / s prescribed by the standard.

[0045] The fourth and fifth embodiments of the lifting system have in common that at least two lifting cylinders are each connected to both lowering branches S 1,2are connected, wherein only one lowering branch has a limiting element in the region of a cylinder base of each lifting cylinder, and the at least two lifting cylinders are mechanically connected in parallel. Furthermore, at least one further lifting cylinder can be provided, which can be actuated independently of the at least two mechanically coupled lifting cylinders and is thus free and is also connected to both lowering branches. In the region of a cylinder base of the at least one free lifting cylinder, each lowering branch has a limiting element.

[0046] The invention relates to a hydraulic lifting system 100, 150, 200, 250, 300, in particular for an industrial truck such as a forklift truck, with at least one lifting cylinder 104, 154, 204, 304 actuated by a hydraulic fluid 102. According to the invention, a first lowering branch S 1 and a second sinking branch S 2and each sink branch S 1,2 at least one limiting device B 1, ..., 6 where in case of a fault in one of the sink branches S 1,2 , such as a line break or the like, a lowering movement of the at least one lifting cylinder 104, 154, 204, 304 is limited to a lowering speed v. Consequently, during normal operation of the hydraulic lifting system 100, 150, 200, 250, 300, a lowering of the at least one lifting cylinder 104, 154, 204, 304 at twice the lowering speed v prescribed according to DIN EN ISO 3691, i.e. with a lowering speed v of approximately a maximum of 1.2 m / s, which results in a higher productivity of the lifting system 100, 150, 200, 250, 300. In the event of a fault in one of the lowering branches S 1,2 However, for the hydraulic lifting system 100, 150, 200, 250, 300, compliance with DIN EN ISO 3691 is still reliably guaranteed. List of reference symbols 100 hydraulic lifting system (1st var.) 102 Hydraulic fluid 104 lifting cylinders 106 Cylinder base 110 first flow control valve 112 second flow control valve 118 first tank line 120 second tank line 122 open ending 124 open ending 130 tanks 136 lowering unit 140 Control and / or regulation unit 142 Sensor 150 hydraulic lifting system (2nd variant) 154 lifting cylinders 156 Sensor 160 cylinder base 200 hydraulic lifting system (3rd variant) 204 lifting cylinders 206 Sensor 210 cylinder base 250 hydraulic lifting system (4 var.) 252 coupling link 300 hydraulic lifting system (5th variant) 304 lifting cylinders 306 Sensor 310 cylinder base S 1,2 sinking branch B 1, ..., 6Limiting organ v Lowering speed v 1, 2, 3 Lowering speed Q 1,2 Volume flow

Claims

[1] Hydraulic lifting system (100, 150, 200, 250, 300), in particular for an industrial truck such as a forklift truck, with at least one lifting cylinder (104, 154, 204, 304) actuated by a hydraulic fluid (102), characterized by that the at least one lifting cylinder (104, 154, 204, 304) is provided with a first lowering branch (S 1 ) and a second sinking branch (S 2 ) in parallel connection to the first sink branch (S 1 ) and each sink branch (S 1,2 ) at least one limiting device (B 1, ..., 6 ), whereby in the event of a fault in one of the sink branches (S 1 , 2 ), such as a line break or the like, a lowering movement of the at least one lifting cylinder (104, 154, 204, 304) is limited to a lowering speed (v). [2] Hydraulic lifting system (100, 150, 200, 250, 300) according to claim 1, characterized by that the limiting organs (B 1, ..., 6) are designed to limit the lowering speed (v) of the at least one lifting cylinder (104, 154, 204, 304) in the event of a fault in one of the lowering branches (S 1,2 ) to a maximum of 0.6 m / s. [3] Hydraulic lifting system (100, 150, 200, 250, 300) according to claim 2, characterized by that the limiting organs (B 1, ..., 6 ) are each formed with a pipe rupture protection device. [4] Hydraulic lifting system (100, 150, 200, 250, 300) according to claim 1, 2 or 3, characterized by that each of the two sink branches (S 1,2 ) has a flow control valve (110, 112), a speed-adjustable hydraulic motor or a switching valve. [5] Hydraulic lifting system (100, 150, 200, 250, 300) according to one of claims 1 to 4, characterized bythat a control and / or regulating unit (140) is provided for monitoring the lowering speed (v) and at least one sensor (142, 156, 206, 306), in particular for detecting the lowering speed (v) of the at least one lifting cylinder (104, 154, 204, 304), is assigned to the control and / or regulating unit (140). [6] Hydraulic lifting system (100, 150, 200, 250, 300) according to claim 5, characterized by that the at least one flow control valve (110, 112) and / or the hydraulic motor and / or the switching valve form a lowering unit (136) which can be controlled by means of the control and / or regulating unit (140) as a function of the at least one sensor (142, 156, 206, 306).

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