EP3608286B1 - Industrial truck with hydraulic lifting system and electronic protection of the lifting system against malfunction - Google Patents

Description

The invention relates to an industrial truck with a lifting system which comprises a fixed part and a vertically movable part with a load-handling device arranged thereon, as well as at least one hydraulic actuator, the hydraulic actuator being connected to a hydraulic system with a hydraulic control device which is configured to control the hydraulic To supply the actuator with a controlled volume flow of a pressure fluid and to bring about a controlled movement of the load-bearing means relative to the stationary part of the lifting system, and an electronically operated valve device that is operatively connected to an electronic control device is switched on in the hydraulic system.

Industrial trucks with hydraulically operated lifting systems are generally known. As a rule, these lifting systems comprise a lifting mast on which a lifting slide with a load-bearing device designed as a load fork is arranged so that it can be moved vertically. To move the lifting carriage, at least one hydraulic lifting cylinder is usually provided as a hydraulic actuator. There are technical standards for such lifting systems which, in the event of a fault, require the lowering speed of the load handling device and / or the load to be limited to 0.6 m / s by means of a device close to the lifting cylinder. As a rule, this is represented by a mechanical valve, a so-called line break safety device, which severely throttles or stops when a limit volume flow is exceeded. Such valves are usually arranged in the area of the cylinder base of the lifting cylinder and, in the case of lifting cylinders with a hollow piston rod, also at the rod end of the piston rod.

Is known by the EP 1 828 045 B1 also the use of an electrically operated valve which is closed in its basic position and thus blocks the lifting cylinder in the basic position designed as a shut-off position and in its operating position allows the drainage of hydraulic fluid from the lifting cylinder.

EP 1 828 045 B1 discloses an industrial truck according to the preamble of claim 1.

The known mechanical line break protection devices are each set to a fixed limit volume flow and are activated suddenly when this limit is exceeded. At high, desired lowering speeds, the sudden collapse leads to high dynamic forces on the load and the lifting system and can also cause the truck to tip over.

The limiting volume flow must be selected with sufficient distance to the nominal volume flow in order to prevent vibrations, e.g. B. at the stroke level transition, lead to collapse of the line break protection. The associated high limiting volume flow then leads to the high loads mentioned above when the line break protection device falls due to the dynamics.

In the case of the electrically operated valve from the EP 1 828 045 B1 is determined by the design of the basic position as a shut-off position that it is closed in the basic position. If it is brought into the basic position after a fault has been detected, hydraulic fluid can no longer flow out of the lifting cylinder. This can have the consequence that the load can no longer be lowered, which requires further measures, e.g. B. for towing the truck, can be dangerous.

Furthermore, in the event of a loss of energy in the industrial truck, the electrically operated valve being actuated into the basic position designed as a blocking position, the lowering movement may stop abruptly, which leads to high dynamic loads on the load and lifting system.

The present invention is based on the object of providing an industrial truck of the type mentioned at the outset which, in the event of a malfunction of the lifting system, can be brought into a safe state without the load being abruptly stopped.

According to the invention, this object is achieved in that the electronically actuated valve device can be actuated automatically into a basic position causing a throttled volume flow of the pressure fluid in the event of a malfunction of the lifting system.

With the invention, with the basic position designed as a throttle position, it is achieved that the standard requirements can also be complied with at lowering speeds> 0.6 m / s. In the event of a fault, the load is not stopped abruptly, but lowered in a controlled manner, and the truck is put in a safe state.

The core of the invention is the use of an electronically actuated valve device as a line break safety device, in which the basic position is designed as a throttle position and which in its basic position allows a throttled volume flow of the pressure fluid to pass. In the operating position, the electronically operated valve device allows the volume flow to flow unhindered, preferably in both directions.

The electrically operated valve device is expediently arranged close to the hydraulic actuator, e.g. the hydraulic cylinder.

The electronically actuated valve device can preferably be actuated between an operating position that brings about an unimpeded volume flow of the pressure fluid and the basic position that brings about a throttled volume flow of the pressure fluid.

According to a preferred embodiment of the invention, the electronically actuated valve device is actuated into the basic position by a spring and into the operating position by means of an electrical actuating device. This enables the electronically operated valve device to be operated in a simple and safe manner in the event of a malfunction of the lifting system by means of the spring in the basic position designed as a throttle position, in which only a throttled volume flow can flow out of the actuator.

According to one embodiment of the invention, the electronically operated valve device can be designed as a switching valve. A switching valve has a simple and inexpensive structure.

According to an alternative embodiment of the invention, the electronically actuated valve device also has intermediate positions between the operating position causing an unimpeded volume flow of the pressure fluid and the basic position causing a throttled volume flow of the pressure fluid.

According to a further development of the inventive concept, the electronically actuated valve device is designed as a proportional valve, which enables a continuous transition between the operating position causing an unimpeded volume flow of the pressure fluid and the normal position causing a throttled volume flow of the pressure fluid. The regulated or controlled transition to the basic position can further reduce the dynamic forces. As a result, even higher lowering speeds of the load handling device are possible.

In a particularly preferred embodiment of the invention, at least one sensor device that is operatively connected to the electronic control device is provided. This sensor device is set up to record operating states of the lifting system as sensor data and to pass the sensor data on to the electronic control device. In addition, the control device is set up to compare the recorded sensor data with data, in particular stored data that are assigned to regular operating states, and to detect a malfunction of the lifting system in the event of a defined deviation. If a malfunction of the lifting system is detected, the electronic control device automatically actuates the electronically actuated valve device into the basic position which causes a throttled volume flow of the pressure fluid. In regular operation, with the electronically actuated valve device being actuated into the operating position designed as a flow position, lowering speeds of the load suspension device and the load of> 0.6 m / s can thus be permitted and achieved. In the event of a fault, the automatic actuation of the electrically actuated valve device into the basic position designed as a throttle position ensures that the lowering speed is limited to, for example, 0.6 m / s.

The sensor device is preferably designed as a speed sensor for detecting the speed of the load-bearing means.

Another embodiment of the invention provides that the sensor device is designed as a lifting height sensor for detecting the actual position of the load handling device and the electronic control device is set up to calculate the speed of the load handling device from the sensor data of the lifting height sensor. With a sensor device designed as a lifting height sensor, the actual position of the load handling device and thus the lifting height of the load handling device can be measured. From the length signal supplied by the lifting height sensor, the lowering speed of the load-bearing means can be calculated in a simple manner in the electronic control device by deriving it over time.

Another embodiment of the invention provides that the sensor device is designed as a pressure sensor for detecting the pressure in the hydraulic system.

The sensor device can also be designed as a volume flow sensor for detecting the volume flow in the hydraulic system.

In a particularly advantageous application of the invention, the electronic control device is set up to reduce the lowering speed to an emergency lowering speed in the event of a defined discrepancy between the detected sensor data of the lowering speed of the load handling device and the data of the regular lowering speed.

A further development of the invention provides that the electronic control device is set up to control the defined deviation of the recorded sensor data from the data in which a malfunction of the lifting system is detected and the electronically operated valve device is automatically moved into the basic position causing the throttled volume flow of the pressure fluid is to continuously adapt to the current speed of the load handling device.

For this purpose, for example, the limit volume flow, at which the electronically operated valve device is brought into the basic position, can be continuously adapted to the currently selected lowering speed, so that in the event of a fault the load is not accelerated to the maximum volume flow before the line break safety device engages. This would be with a conventional mechanical Line break protection is the case. This results in significantly lower loads on the load, the lifting system and the entire industrial truck. With the invention, the lower loads that occur allow higher sink speeds in regular operation than is possible with mechanical line break protection devices.

For this purpose, according to a particularly advantageous embodiment of the invention, it is provided that the electronic control device is set up to detect the defined deviation of the recorded sensor data from the data in which a malfunction of the lifting system is detected and the electronically operated valve device automatically changes the throttled volume flow of the pressure fluid causing, basic position is actuated to continuously adapt to the current speed of the load suspension device.

Influences of temperature and viscosity of the hydraulic fluid can also be taken into account when detecting a fault, and thus when the line break safety device is activated. To this end, a further embodiment of the invention provides that the electronic control device is set up to detect the defined deviation of the recorded sensor data from the data in which a malfunction of the lifting system is detected and the electronically actuated valve device automatically causes the throttled volume flow of the pressure fluid , Basic position is operated to continuously adapt to the temperature and / or viscosity of the pressure fluid in the hydraulic system.

According to an advantageous development of the inventive concept, a check valve is arranged in a bypass line to the electronically actuated valve device, which enables the hydraulic actuator to be filled with pressure fluid without actuating the electronically actuated valve device, and pressure fluid to flow back from the hydraulic actuator via the bypass line prevented by the electronically operated valve device.

Thus, for example, the electronically actuated valve device does not need to be actuated to fill the lifting cylinder in the lifting operation of the load suspension device, since the pressure fluid can flow past the valve via the check valve. The check valve itself prevents the pressure fluid from flowing out of the Lift cylinder can flow past the valve. The advantage of this arrangement is that energy can be saved for the lifting function by eliminating the need to actuate the electronically actuated valve device.

The invention offers a number of advantages:
The invention results in significantly lower loads on the load, the lifting system and the entire industrial truck. The lower loads that occur allow higher lowering speeds of the load handling device in regular operation of, for example, 1.1 m / s or more than is possible with mechanical line break protection devices.

Since the error detection does not take place mechanically, but in the electronic control device, short volume flow peaks that result from the mast dynamics (e.g. overshoots) can be excluded. This prevents the line break protection from collapsing unnecessarily.

In addition, due to the throttled volume flow, which can flow from the hydraulic actuator through the electronically operated valve device in the basic position, when the valve device falls into the basic position, the load is not braked as much as with a completely closed valve (as, for example, in the prior art according to the EP 1 828 045 B1 ). As a result, there are also lower dynamic forces. In addition, when the valve device is in the basic position, the load can be automatically lowered in a controlled manner until the load reaches a safe state.

In contrast to conventional, mechanical line break protection devices, the influences of temperature and viscosity of the hydraulic fluid can also be taken into account when detecting a fault, and thus when the line break protection device is activated.

Figur 1

ein Hubsystem eines Flurförderzeugs mit elektronisch betätigter Ventileinrichtung zur Leitungsbruchsicherung,

Figur 2

eine Variante des Hubsystems mit Ausbildung der elektronisch betätigten Ventileinrichtung als Proportionalventil, und

Figur 3

eine Detaildarstellung einer Anordnung mit Proportionalventil und zusätzlicher Bypass-Leitung mit Rückschlagventil.

Further advantages and details of the invention are explained in more detail with reference to the exemplary embodiments shown in the schematic figures. Show here

Figure 1

a lifting system of an industrial truck with an electronically operated valve device to protect against line breakage,

Figure 2

a variant of the lifting system with the design of the electronically operated valve device as a proportional valve, and

Figure 3

a detailed representation of an arrangement with proportional valve and additional bypass line with check valve.

In the Figure 1 a lifting system 1 of an industrial truck (not shown in detail), for example a forklift or reach truck, is shown.

In the exemplary embodiment shown, the lifting system 1 comprises a lifting frame 2, on which a load-carrying means 4 can be raised and lowered for handling a load Q. In the exemplary embodiment shown, the load-bearing means 4 consists of a lifting carriage which is vertically movable in the lifting frame 2 and to which, for example, a load fork formed by fork prongs is attached as an attachment.

In the illustrated embodiment, the lifting frame 2 has a fixed part 2a, for example a standing mast, and a vertically movable part 2b, for example an extending mast, which can be raised and lowered on the fixed part 2a. The load suspension means 4 can be raised and lowered on the vertically movable part 2b.

The lifting system 1 is actuated by a hydraulic actuator 3 which, in the exemplary embodiment shown, is designed as a hydraulic cylinder which is provided for raising and lowering the load-bearing means 4.

The hydraulic actuator 3, designed as a lifting cylinder, has a cylinder housing 3a, which is arranged on the stationary part 2a, and an extendable piston rod 3b, which is connected to the vertically movable part 2b. A flexible traction means 6, for example a lifting chain, is provided for raising and lowering the load suspension means 4. The flexible traction means 6 is fastened to the load suspension means 4 with a first end. The traction means 6 is guided over a pulley 7 and attached with a second end to the fixed part 2a of the mast 2. In the illustrated embodiment, the deflection roller 7 is arranged on the vertically movable part 2b.

The hydraulic actuator 3 can be actuated by means of a hydraulic control device 30 for raising and lowering the load-bearing means 4. In the exemplary embodiment shown, the hydraulic control device 30 is designed as a control valve 30 which throttles in intermediate positions and has a blocking position 30a designed as a neutral position, a raised position 30b and a lowering position 30c. For this purpose, the control valve 30 is connected to a delivery line 34 of a pump 31, a container line 35 routed to a container 32 and a pressure medium line 36 routed to the actuator 3. The pump 31 sucks pressure medium from the container 32 by means of a suction line 33. In the blocking position 30a of the control valve 30, the connection of the pressure line 36 to the delivery line 34 and the container line 35 is blocked. In the raised position 30b of the control valve 30, the delivery line 34 is connected to the pressure line 36. In the lowering position 30c of the control valve 30, the pressure line 36 is connected to the container line 35.

The control valve 30 can be actuated electrically by means of an electronic control device 20. For this purpose, an electrical actuating device 37 is provided, when activated, the control valve 30 is actuated in the direction of the lowering position 30c. The control valve 30 can be actuated in the direction of the lifting position 30b by means of a further electrical actuating device 38. The actuating devices 37, 38 are designed, for example, as magnets, in particular proportional magnets.

By means of a spring device formed by two springs 39, the control valve 30 is actuated in the non-activated and de-energized state into the blocking position 30a designed as a neutral position.

On the input side, the electronic control device 20 is connected to an actuator 11 that can be operated by an operator, for example a joystick, by actuating a lifting process or a lowering process of the load-bearing means 4 can be initiated and, by actuating it, a lifting speed in the lifting mode and a lifting speed in the lowering mode Lowering speed can be specified.

To determine the lowering speed of the load-bearing means 4, a sensor device 10 is provided, which is connected to the electronic control device 20.

In the exemplary embodiment shown, the sensor device 10 is designed as a lift height sensor 10, with which the lift height of the load-bearing means 4 can be measured. The lifting height sensor 10 can be designed as a cable length sensor 10, which comprises a housing fastened to the stationary part 2a of the lifting system 1 and a cable means 10a connected to the load handling means 4 of the lifting system 1.

From the length signal supplied by the lifting height sensor 10, the lowering speed of the load-bearing means 4 is calculated in the electronic control device 20 by deriving it over time.

The lifting system 1 is also provided with an electronically operated valve device 5 which is connected to the pressure medium line 36 and is arranged on the hydraulic actuator 3 close to the cylinder. In the illustrated embodiment, the valve device 5 is arranged on the cylinder base of the actuator 3 designed as a hydraulic cylinder.

The valve device 5 has an operating position 5b, which is designed as a flow position and enables an unhindered flow of pressure medium from the pressure medium line 36 into the actuator 3 or an unhindered flow of pressure medium from the actuator 3 into the pressure medium line 36, and a basic position 5a , which is designed as a throttle position and causes a throttled volume flow of the pressure fluid that can flow out of the actuator 3 into the pressure medium line 36.

The valve device 5 is actuated by a spring 7 into the basic position 5a. In the direction of the operating position 5b, the valve device 5 can be actuated by the electronic control device 20. For this purpose, there is provided an electrical actuating device 8 which actuates the valve device 5 against the force of the spring 7 into the operating position 5b and which is connected to the electronic control device 20 for control.

In the embodiment of Figure 1 the valve device 5 is designed as a switching valve 15. The electrical actuating device 8 can be designed as a switching magnet.

The Figure 2 shows a variant of the lifting system 1 from Figure 1 , the same components being denoted by the same reference numerals. At the in Figure 2 The variant shown, the electronically actuated valve device 5 is designed as a proportional valve 16 that throttles in intermediate positions. The electrical actuating device 8 can be designed as a proportional magnet which acts on the proportional valve 16 from the basic position 5a against the force of the spring 7 in the direction of the operating position 5b.

The lifting system of the Figures 1 and 2 works as follows:
If a request to lift the load Q is transmitted to the electronic control device 20 via the actuator 11, for example a joystick, the electronic control device 20 controls the hydraulic control device 30 in the direction of the lifting position 30b, so that the pressure fluid, in the present case hydraulic fluid, is conveyed from the container 32 via the suction line 33, the pump 31 and the delivery line 34 of the pump 31 into the pressure line 36. The electrically operated valve device 5 is also controlled by the electronic control device 20 in such a way that the electrical operating device 8 acts on the valve device 5 from the basic position 5a against the force of the spring 7 into the operating position 5b. The pressure fluid can now flow unhindered into the actuator 3, which in the illustrated embodiment is designed as a hydraulic lifting cylinder 3, in particular a plunger cylinder, with a piston rod 3b and a cylinder tube 3a.

If the actuator 11 signals a wish to lower the load Q to the electronic control unit 20, the latter controls the hydraulic control device 30 in the direction of the lowering position 30c, so that the pressure line 36 is connected to the container line 35. The actuating device 8 of the valve device 5 is also activated, so that the valve device 5 is acted upon in the operating position 5b and the hydraulic fluid is unhindered from the Actuator 3 can flow off into the container 32 via the pressure line 36, the hydraulic control device 30 and the container line 35.

If the electronic control device 20 detects an error in one of these operating states (lifting / lowering), in particular an uncontrolled lowering of the load Q, for example caused by a leak in the pressure medium line 36, the activation of the actuating device 8 is terminated so that the spring 7 the valve device 5 is actuated into the basic position 5a designed as a throttle position, in which only a throttled volume flow can emerge from the actuator 3 and flow away. The throttling of the volume flow flowing out of the actuator 3 in the basic position 5a is selected here in such a way that all known legal and normative requirements are met. In the basic position 5a, the throttled volume flow that can flow out of the actuator 3 is preferably dimensioned in such a way that a lowering speed of the load handling device 4 and thus the load Q is limited to a value ≤ 0.6 m / s.

A malfunction of the lifting system 1 can be detected with the sensor device 10, which detects the speed of the load handling device 4 and transmits it to the electronic control 20.

In the non-actuated state of the lifting system 1, the valve device 5 is also in the basic position 5a, so that the speed of the load-bearing means 4 does not need to be monitored.

A malfunction of the lifting system 1 is preferably detected in the electronic control device 20, which is in operative connection with the sensor device 10. The sensor device 10 is set up to detect operating states of the lifting system 1, for example the actual lowering speed of the load-bearing means 4, as sensor data and to forward the sensor data to the electronic control device 20. The electronic control device 20 is set up to compare the recorded sensor data, for example the actual lowering speed of the load-bearing means 4, with data, in particular stored data, which are assigned to regular operating states. These data, which are assigned to regular operating states, can, for example, be the specified target lowering speed assigned to the actuation of the actuator 11 of the load suspension device 4. If a defined deviation occurs between the target lowering speed and the actual lowering speed, in particular if the actual lowering speed is greater than the target lowering speed, which suggests a leak in the pressure medium line 36, the electronic control device 20 detects a malfunction of the lifting system 1 and automatically actuates the electronically actuated valve device 5 by ending the actuation of the actuating device 8 in the basic position 5a, which causes a throttled volume flow of the pressure fluid and is designed as a throttle position.

If the electronic control device 20 detects a malfunction in one of the lifting / lowering operating states, in particular an uncontrolled lowering of the load Q, for example caused by a leak in the pressure medium line 36, the valve device 5 can be automatically actuated into the basic position 5a, which is designed as a throttle position the lowering speed of the load suspension device 4 can be limited to a permissible value of ≤ 0.6 m / s.

If the sensor device 10 has failed as a malfunction, the valve device 5 remains in its basic position 5a or is brought into this position. Emergency operation of the lifting system 1 at very slow lifting and lowering speeds, for example to set down a load Q before repair work, is possible in this way.

The design of the valve device 5 as a proportional valve 16 according to FIG Figure 2 enables a regulated or controlled transition to the basic position 5a, whereby the dynamic forces can be further reduced. As a result, even higher speeds of the load handling device 4 are possible in regular operation (no malfunction).

In the Figure 3 is a detailed representation of an arrangement is shown in which the electrically operated valve device 5 also as a proportional valve 16 according to FIG Figure 2 is formed with the spring 7 and the electrical actuating device 8. The pressure line 36 is connected to the proportional valve 16. In an additional bypass line 45, which bypasses the proportional valve 16, a check valve 40 is arranged, which opens in the direction of the actuator 3. The proportional valve 16 is designed in such a way that it only emits a throttled volume flow in the basic position 5a the actuator 3 can flow. In the operating position 5b, the hydraulic fluid can flow out of the actuator 3 unhindered. Any intermediate positions can be taken.

In order to fill the actuator 3 in the lifting mode, the proportional valve 16 does not need to be actuated, since the hydraulic fluid can flow past the proportional valve 16 via the opening check valve 40. The check valve 40 itself prevents hydraulic fluid from flowing past the proportional valve 16 when it flows out of the lifting cylinder 3. The advantage of this arrangement is that energy can be saved for the lifting function by eliminating the actuation of the proportional valve 16.

It goes without saying that the bypass line 45 with the check valve 40 also in an arrangement of the Figure 1 can be used with an electronically operated valve device 5 designed as a switching valve.

Claims (15)

1. Industrial truck with a lifting system (1) which comprises a fixed part (2a) and a vertically movable part (2b) with a load receiving means (4) arranged thereon and at least one hydraulic actuator (3), wherein the hydraulic actuator (3) is connected to a hydraulic system with a hydraulic control device (30) which is configured to supply the hydraulic actuator (3) with a controlled volume flow of a hydraulic fluid and to bring about a controlled movement of the load-receiving means (4) of the lifting system (1) relative to the fixed part (2a) of the lifting system (1), and an electronically activated valve device (5), which is operatively connected to an electronic control device (20), is connected into the hydraulic system, characterized in that, when there is a malfunction of the lifting system (1), the electronically activated valve device (5) can be activated automatically into a home position (5a) which brings about a throttled volume flow of the hydraulic fluid.
2. Industrial truck according to Claim 1, characterized in that the electronically activated valve device (5) can be activated between an operating position (5b), which brings about an unimpeded volume flow of the hydraulic fluid, and the home position (5a) which brings about a throttled volume flow of the hydraulic fluid.
3. Industrial truck according to Claim 2, characterized in that the valve device (5) is activated into the home position (5a) by a spring (7) and is activated into the operating position (5b) by means of an electrical activation device (8).
4. Industrial truck according to Claim 2 or 3, characterized in that the electronically activated valve device (5) is configured as a switching valve (15) .
5. Industrial truck according to Claim 2 or 3, characterized in that the electronically activated valve device (5) has intermediate positions between the operating position (5b) which brings about an unimpeded volume flow of the hydraulic fluid and the home position (5a) which brings about a throttled volume flow of the hydraulic fluid.
6. Industrial truck according to Claim 5, characterized in that the electronically activated valve device (5) is configured as a proportional valve (16) which permits a continuous transition between the operating position (5b) which brings about an unimpeded volume flow of the hydraulic fluid and the home position (5a) which brings about a throttled volume flow of the hydraulic fluid.
7. Industrial truck according to one of Claims 1 to 6, characterized in that at least one sensor device (10) which is operatively connected to the electronic control device (20) is provided, said sensor device (10) being configured to sense operating states of the lifting system (1) as sensor data and to pass on the sensor data to the electronic control device (20), and the electronic control device (20) is configured to compare the acquired sensor data with data, in particular stored data, which is assigned to regular operating states, and, when there is a defined deviation, to detect a malfunction of the lifting system (1), and, when a malfunction of the lifting system (1) is detected, to activate the electronically activated valve device (5) into the home position (5a) which brings about a throttled volume flow of the hydraulic fluid.
8. Industrial truck according to Claim 7, characterized in that the sensor device (10) is configured as a speed sensor for sensing the speed of the load-receiving means (4).
9. Industrial truck according to Claim 7, characterized in that the sensor device (10) is configured as a lifting height sensor for sensing the actual position of the load-receiving means (4), and the electronic control device (20) is configured to calculate the speed of the load-receiving means (4) from the sensor data of the lifting height sensor.
10. Industrial truck according to Claim 7, characterized in that the sensor device (10) is configured as a pressure sensor for sensing the pressure in the hydraulic system.
11. Industrial truck according to Claim 7, characterized in that the sensor device (10) is configured as a volume flow sensor for sensing the volume flow in the hydraulic system.
12. Industrial truck according to one of Claims 7 to 11, characterized in that the electronic control device (20) is configured, when there is a defined deviation of the acquired sensor data of the lowering speed of the load-receiving means (4) in comparison with the data of the regular lowering speed, to reduce the lowering speed to an emergency lowering speed.
13. Industrial truck according to one of Claims 7 to 12, characterized in that the electronic control device (20) is configured to adapt the defined deviation of the acquired sensor data from the data, at which a malfunction of the lifting system (1) is detected and the electronically activated valve device (5) is activated automatically into the home position (5a) which brings about the throttled volume flow of the hydraulic fluid, continuously to the current speed of the load-receiving means (4).
14. Industrial truck according to one of Claims 7 to 13, characterized in that the electronic control device (20) is configured to adapt the defined deviation of the acquired sensor data from the data, at which a malfunction of the lifting system (1) is detected and the electronically activated valve device (5) is activated automatically into the home position (5a) which brings about the throttled volume flow of the pressure fluid, continuously to the temperature and/or viscosity of the hydraulic fluid in the hydraulic system.
15. Industrial truck according to one of Claims 1 to 14, characterized in that a non-return valve (40), which permits the hydraulic actuator (3) to be filled with hydraulic fluid without activating the electronically activated valve device (5) and which prevents hydraulic fluid from flowing back from the hydraulic actuator (3) via a bypass line (45) which bypasses the electronically activated valve device (5), is arranged in the bypass line (45) which bypasses the electronically activated valve device (5).

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