Industrial truck and method for operating an industrial truck

Abstract

The invention relates to a forklift truck 1 and a method for operating a forklift truck 1. The forklift truck 1 comprises a pump motor 21, a hydraulic pump 22, a lifting cylinder 25, a load-handling device 6, and a control device 30. The pump motor 21 drives the hydraulic pump 22, which supplies hydraulic fluid to the hydraulic cylinder 25. The lifting cylinder 25 raises and lowers the load-handling device 6. A measuring device measures at least one lifting stability parameter that influences the tilting stability of the forklift truck 1 during a lifting and lowering operation. The control device 30 regulates the torque of the pump motor 21. The control device 30 controls the pump motor 21 such that a maximum torque change per unit time 56 is varied depending on the lifting stability parameter.

Description

[0001] The invention relates to a forklift truck comprising a pump motor, a hydraulic pump, a lifting cylinder, a load-handling device, and a control device. The invention also relates to a method for operating a forklift truck.

[0002] Industrial trucks are continuously being developed to improve their efficiency and speed of operation. For example, the lifting and lowering speed of the load-handling attachment during loading operations is being increased. Furthermore, the maximum lifting height is being continuously raised. This not only accelerates loading speeds but also improves access to high storage locations.

[0003] Increased lifting and lowering speeds, combined with greater lifting height, place increased stress on the forklift. This results in both greater strain on the mast structure and reduced stability. Increased stress on the mast can damage the forklift, while reduced stability can cause it to tip over. In both cases, the operator is at serious risk, in addition to the potential damage to the forklift.

[0004] The object of the invention is to provide a forklift truck and a method for operating a forklift truck which exhibit increased safety during lifting and lowering operations of the load-handling device.

[0005] The problem is solved by a forklift truck comprising a pump motor, a hydraulic pump, a lifting cylinder, a load-handling device, and a control device, wherein the pump motor is configured to drive the hydraulic pump, wherein the hydraulic pump is configured to supply the lifting cylinder with hydraulic fluid, wherein the lifting cylinder is configured to raise and lower the load-handling device, wherein the forklift truck further comprises at least one measuring device, wherein the at least one measuring device is configured to measure at least one lifting stability parameter and transmit it to the control device, wherein the lifting stability parameter influences the tilting stability of the forklift truck during a lifting or lowering operation, wherein the control device is configured to regulate a torque of the pump motor, characterized in that the control device is configured toto control the pump motor in such a way that the maximum torque change per unit of time is varied depending on the stroke stability parameter.

[0006] By varying the maximum torque change per unit of time of the pump motor depending on the lifting stability core size, the tilting stability of the industrial truck during a lifting or lowering operation is improved and the structure of the lifting frame is subjected to less stress.

[0007] The value of such a lifting stability parameter measures its influence on the tipping stability of the industrial truck during the lifting or lowering process. For example, a high value of the lifting stability parameter can mean that the tipping stability of the industrial truck is significantly reduced. Depending on the definition, an increased value of the lifting stability parameter can also conversely mean increased tipping stability of the industrial truck. In any case, the maximum torque change per unit of time is regulated by the control device so that it varies depending on the lifting stability parameter. For example, if tipping stability is reduced due to a change in the lifting stability parameter, the maximum torque change per unit of time is reduced to compensate for the negative impact on tipping stability.

[0008] The torque of the pump motor is transmitted to the hydraulic pump and thus determines the speed at which the load-handling device is raised or lowered. The change in torque of the pump motor per unit of time therefore corresponds to the acceleration or deceleration of the load-handling device.

[0009] It has been found that the tipping stability depends significantly on the acceleration or deceleration of the load-handling device during the lifting or lowering process. The higher the acceleration or deceleration, the more the tipping stability is reduced and the greater the stress placed on the lifting frame structure.

[0010] In addition to the acceleration or deceleration of the load-handling device, there are several other parameters that affect the tilting stability and the load on the lifting frame. These parameters are the lifting stability characteristics. The lifting stability characteristics include, in particular, the load weight, the lifting height, and / or the horizontal travel. Advantageously, according to the invention, the current values ​​of one or more of these lifting stability characteristics are tested. This is done using at least one measuring device. If the evaluation of at least one lifting stability characteristic shows that the industrial truck exhibits high tilting stability, the maximum acceleration or deceleration of the load-handling device, and thus the maximum torque change per unit time of the pump motor, can be set to a high value.However, if it turns out that the tilting stability is low based on the evaluation of the stroke stability parameter, the maximum torque change per unit of time is reduced to compensate.

[0011] The load-handling device is, in particular, a fork or a similar device for receiving loads. The load-handling device is raised and lowered hydraulically by the lifting cylinder. The lifting cylinder is operated by the hydraulic pump, which in turn is driven by the pump motor. Thus, the speed at which the load-handling device is raised and lowered can be regulated by the torque of the pump motor. This regulation is carried out by means of the control device, which is, for example, a computer or a similar data processing device. The control device is, in particular, connected to the pump motor and the at least one measuring device and is configured to read the measuring device and to regulate the torque of the pump motor.

[0012] Preferably, the control device is configured to vary the maximum torque change per unit time by controlling the pump motor in such a way as to compensate for a change in tipping stability caused by a change in the lifting stability parameter. As explained, if the tipping stability decreases due to a change in the lifting stability parameter, the maximum torque change per unit time is reduced to compensate for the decrease in tipping stability. Conversely, if the tipping stability increases due to a change in the lifting stability parameter, the maximum torque change per unit time is increased, as this reduces the loading time without compromising the safety of the forklift truck during operation.

[0013] A preferred characteristic curve is that of the maximum torque change per unit time as a function of at least one stroke stability parameter, in particular strictly monotonically decreasing or increasing, wherein the maximum torque change per unit time is inversely proportional or proportional to the stroke stability parameter. In other words, an increase in the stroke stability parameter always changes the maximum torque change per unit time in only one direction. With a strictly monotonical change in the stroke stability parameter, the maximum torque change will always change monotonically, i.e., either monotonically increasing or monotonically decreasing. In this way, a reduction in rollover stability caused by a change in the stroke stability parameter is never further escalated by a simultaneous increase in the maximum torque change per unit time.

[0014] Preferably, the characteristic curve of the maximum torque change per unit time as a function of the at least one stroke stability parameter differs when the torque increases from the characteristic curve of the maximum torque change per unit time as a function of the at least one stroke stability parameter when the torque decreases. In other words, the acceleration process differs from the braking process of the load-handling device with respect to the influence of the stroke stability parameter on the maximum torque change per unit time. Specifically, a maximum acceleration, rather than a maximum deceleration, is defined for the lifting process. Similarly, a maximum deceleration, rather than a maximum acceleration, is defined for the lowering process.

[0015] According to one embodiment, the at least one measuring device comprises a load measuring device, wherein the load measuring device is configured to measure a load weight of a load resting on the load-handling device as a stroke stability parameter, wherein the control device is configured to control the pump motor in such a way that a maximum torque change per time is varied as a function of the load weight, wherein a characteristic curve of the maximum torque change per time as a function of the load weight is monotonically decreasing.

[0016] A key parameter for lifting stability is therefore the load weight. The higher the load weight, the greater the stress on the lifting frame structure and the lower the tipping stability of the forklift. By measuring the load weight using the load measuring device, the load weight can be determined and the maximum torque change per unit time adjusted accordingly. In particular, the maximum torque change per unit time is reduced with a higher load weight. At the maximum permissible load weight, the maximum torque change per unit time is, for example, lower than when the load weight is zero. The load measuring device is typically located on the load-handling attachment. Specifically, the load measuring device is a pressure sensor for measuring hydraulic pressure or a load cell. The pressure sensor is specifically designed to measure hydraulic pressure in order to indirectly determine the load weight.The load cell, for example, is a strain gauge and is typically mounted on a fork carriage. Both types of load measuring devices enable a precise determination of the current load weight.

[0017] According to a further embodiment, the at least one measuring device comprises a height measuring device, wherein the height measuring device is configured to measure the current lifting height of the load-handling device as a lifting stability parameter, and wherein the control device is configured to control the pump motor such that the maximum torque change per unit time is varied depending on the current lifting height, with a characteristic curve of the maximum torque change per unit time being monotonically decreasing as a function of the current lifting height. The higher the load-handling device is lifted, the more the tipping stability of the industrial truck is reduced. For this reason, the lifting height of the load-handling device is also a lifting stability parameter. In order to compensate for the reduced tipping stability when the load-handling device is lifted to a high height, the maximum torque change per unit time is reduced in particular.In particular, the height measuring device is a laser measuring system on the lifting cylinder, a cable-operated encoder, or a laser distance meter. The laser measuring system on the lifting cylinder measures the lifting height directly at the lifting cylinder using a marked piston rod. The cable-operated encoder measures the lifting height directly by deflecting a cable. The laser distance meter also measures the lifting height directly using known laser distance measurement methods.

[0018] According to a further embodiment, the at least one measuring device comprises a feed measuring device, wherein the feed measuring device is configured to measure a horizontal feed of the load-handling device as a lifting stability parameter, and wherein the control device is configured to control the pump motor such that the maximum torque change per unit time is varied as a function of the feed, wherein a characteristic curve of the maximum torque change per unit time as a function of the feed is monotonically decreasing. Certain industrial trucks, such as reach trucks, have load-handling devices that can be moved horizontally together with the mast. However, the further the mast is moved towards the front load wheels, the lower the tipping stability of the industrial truck. For this reason, the feed of the load-handling device or the mast is also a lifting stability parameter.The term "current mast position" can also be used instead of "feed rate". To compensate for the reduced tilting stability at high feed rates, the maximum torque change per unit time is specifically reduced. The feed rate measuring device is a sensor mounted on the frame, mast, or mast holder of the industrial truck. For example, it is a distance sensor that measures the distance between the truck frame and the extended mast. Specifically, the distance of the mast is measured relative to the position on the frame where the mast rests when not horizontally deflected. The mast holder forms the base for the mast. Since the mast is typically extended together with the mast holder, the sensor specifically measures the distance between the mast and the frame and / or the distance between the mast holder and the frame.

[0019] Preferably, the control device is configured to calculate a characteristic factor for at least two of the lifting stability parameters, wherein the characteristic factors are less than or equal to one. The maximum torque change per unit time is obtained by multiplying the characteristic factors by the maximum possible torque change per unit time. The maximum possible torque change per unit time is the maximum acceleration or deceleration with which the industrial truck can accelerate or decelerate the load-handling device. Multiplying the maximum possible torque change per unit time by the characteristic factors, each of which is less than or equal to one, yields the maximum torque change per unit time, which is therefore also less than or equal to the maximum possible torque change per unit time. The characteristic factors are dimensionless, unlike the quantities from which they are calculated.The calculation of the characteristic factor(s) is primarily carried out using a table in which corresponding values ​​of the characteristic factor are stored for various values ​​of the stroke stability characteristic. From the tables, the corresponding value of the characteristic factor can then be calculated stepwise or by linear interpolation for each measured value of the stroke stability characteristic.

[0020] For example, the following tables result for the load weight, lifting height and feed rate: Lifting height Lifting height factor HH1 F HH,1 HH2 F HH,2 HH3 F HH,3 HH i F HH,i with HH1 < HH2 < HH3 < HH4 < HH i and F HH,1 ≥ F HH,2 ≥ F HH,3 ≥ F HH,4 ≥ F HH,i load weight Load weight factor LG1 F LG,1 LG2 F LG,2 LG3 F LG,3 LG i F LG,i with LG1 < LG2 < LG3 < LG4 < LG i ; and F LG,1 ≥ F LG,2 ≥ F LG,3 ≥ F LG,4 ≥ F LG,i feed feed factor MP1 F MP,1 MP2 F MP,2 MP3 F MP,3 MP i F MP,i with MP1 < MP2 < MP3 < MP4 < MP i ; and F MP,1 ≥ F MP,2 ≥ F MP,3 ≥ F MP,4 ≥ F MP,i

[0021] The table(s) contain, in particular, a value for the associated parameter factor for each value of the lifting stability parameter. Based on this table, a corresponding parameter factor value can be determined for each measured value of the lifting stability parameter. Specifically, the parameter factors are inversely proportional to the lifting stability parameters from which they are calculated.

[0022] Preferably, the control device is configured to calculate a load factor from the load weight, a height factor from the lifting height, and a feed factor from the feed rate, whereby the load factor decreases or remains constant with an increase in load weight, the height factor decreases or remains constant with an increase in lifting height, and the feed factor decreases or remains constant with an increase in feed rate. Thus, the maximum torque change per unit time is obtained by multiplying the load factor by the height factor, the feed factor, and the maximum possible torque change per unit time. This corresponds to the following formula: amax,zul=FH∗FL∗FV∗amax

[0023] This is a max,zul the maximum change in torque per time, F H the altitude factor, F L the load factor, Fv the feed factor and a max the maximum possible change in torque per unit of time.

[0024] The problem is further solved by a method for operating a forklift truck, wherein the forklift truck comprises a pump motor, a hydraulic pump, a lifting cylinder, a load-handling device, and a control device, wherein the pump motor drives the hydraulic pump, wherein the hydraulic pump supplies the lifting cylinder with hydraulic fluid, wherein the lifting cylinder raises and lowers the load-handling device, wherein the forklift truck further comprises at least one measuring device, wherein the at least one measuring device measures at least one lifting stability parameter and transmits it to the control device, wherein the lifting stability parameter influences the tilting stability of the forklift truck during a lifting or lowering operation, wherein the control device regulates a torque of the pump motor, characterized in that the control device controls the pump motor in such a way thatthat the maximum torque change per unit of time varies depending on the stroke stability parameter.

[0025] The process embodies the same advantages, features and characteristics as the previously described industrial truck.

[0026] Preferably, the control device varies the maximum torque change per unit of time by controlling the pump motor in such a way that a change in tilting stability caused by a change in the stroke stability parameter is compensated.

[0027] Preferably, a characteristic curve of the maximum torque change per time is a function of the at least one stroke stability parameter, in particular strictly monotonically decreasing or increasing, wherein in particular the maximum torque change per time is inversely proportional or proportional to the stroke stability parameter.

[0028] Preferably, the characteristic curve of the maximum torque change per time as a function of the at least one stroke stability parameter differs when the torque is increased from the characteristic curve of the maximum torque change per time as a function of the at least one stroke stability parameter when the torque is decreased.

[0029] According to one embodiment, the at least one measuring device comprises a load measuring device, wherein the load measuring device measures a load weight of a load resting on the load-handling device as a stroke stability parameter, wherein the control device controls the pump motor in such a way that a maximum torque change per time is varied depending on the load weight, wherein a characteristic curve of the maximum torque change per time as a function of the load weight is monotonically decreasing.

[0030] According to a further embodiment, the at least one measuring device comprises a height measuring device, wherein the height measuring device measures a current lifting height of the load-handling device as a lifting stability parameter, wherein the control device controls the pump motor in such a way that the maximum torque change per time is varied as a function of the current lifting height, wherein a characteristic curve of the maximum torque change per time as a function of the current lifting height is monotonically decreasing.

[0031] According to a further embodiment, the at least one measuring device comprises a feed measuring device, wherein the feed measuring device measures a horizontal feed of the load-handling device as a stroke stability parameter, wherein the control device controls the pump motor in such a way that the maximum torque change per time is varied as a function of the feed, wherein a characteristic curve of the maximum torque change per time as a function of the feed is monotonically decreasing.

[0032] Preferably, the control device calculates a characteristic factor for at least two of the stroke stability parameters, wherein the characteristic factors are less than or equal to one, wherein the maximum torque change per time results from the product of the characteristic factors with a maximum possible torque change per time.

[0033] Preferably, the control device calculates a load factor from the load weight, a height factor from the lifting height, and a feed factor from the feed rate as characteristic parameters, wherein the load factor decreases or remains the same if the load weight increases, the height factor decreases or remains the same if the lifting height increases, and the feed factor decreases or remains the same if the feed rate increases.

[0034] Within the scope of the invention, features marked with "in particular" or "preferably" are to be understood as optional features.

[0035] The invention is described below, without limiting the general concept, with reference to exemplary embodiments and the drawings, whereby for all details of the invention not explained in detail in the text, explicit reference is made to the drawings. The drawings show: Fig.1 A schematically simplified representation of a forklift truck that lifts a load using a load-handling device, Fig. 2 a schematically simplified representation of a hydraulic system of the industrial truck and an associated control device, Fig. 3 A schematically simplified flowchart of a process for varying the maximum torque change per unit time of a pump motor as a function of a stroke stability parameter, Fig. 4 a characteristic curve of a maximum torque of the pump motor as a function of a load weight, and Fig. 5 a characteristic curve of a maximum torque change per time as a function of the load weight.

[0036] In the drawings, identical or similar elements and / or parts are provided with the same reference numbers, so that a re-presentation is omitted.

[0037] Fig.Figure 1 shows a simplified schematic representation of a forklift truck 1, which in the illustrated embodiment is a reach truck. The forklift truck 1 comprises a driver's cab 2 and several wheels 3. The front wheels 3, which are load wheels, are arranged on a front left and a front right wheel arm 4, between which the mast 5 is located. A load-handling device 6 in the form of a load fork is fixed to the mast 5 and can be raised and lowered. In addition, the mast 5 of a reach truck can be moved forward in a horizontal direction.

[0038] The center of gravity 7 of the industrial truck 1 has a significant influence on the tipping stability of the industrial truck 1. The position of the center of gravity 7 is influenced, among other things, by a lifting height 12 of the load handling device 6 and a forward movement 13 of the mast 5. In addition, in the example shown, a load 8 is arranged on the load handling device 6, which has its own center of gravity 9 and a load weight 11 that is in Fig. The load weight 11 also influences the position of the center of gravity 7 and thus the tipping stability of the industrial truck 1.

[0039] To prevent the industrial truck 1 from tipping over and to reduce the load on its lifting mast, it is advantageous to measure the load weight 11, the lifting height 12, and the feed rate 13 in order to assess the tipping stability of the industrial truck 1 using these lifting stability parameters. If it is determined that the industrial truck 1 has low tipping stability, the acceleration or deceleration of the load handling device 6 can be reduced to compensate. Conversely, if the evaluation of the lifting stability parameters shows high tipping stability, the maximum acceleration or deceleration can be increased instead, as this allows the loading process to be accelerated without the risk of the industrial truck 1 tipping over.

[0040] Fig.Figure 2 shows a simplified schematic diagram of a hydraulic system 20 of a forklift truck 1, as well as a control device 30 connected to the hydraulic system 20. The hydraulic system 20 comprises a pump motor 21, which drives a hydraulic pump 22. The hydraulic pump 22 pumps hydraulic fluid from a tank 23 and directs it via a check valve 24 to a lifting cylinder 25, which raises and lowers the load-handling attachment 6. The hydraulic fluid is returned to the tank 23 via a return line and a 2 / 2-way valve 26.

[0041] A pressure sensor 34 is also connected to the hydraulic lines. This sensor acts as a load measuring device 31 by measuring the pressure of the hydraulic fluid and thus indirectly the load weight 11 acting on the load-handling device. A height measuring device 32, which may be, for example, a laser measuring device or a cable-operated encoder, is connected to the lifting cylinder 25 to determine the lifting height 12 of the load-handling device 6. A feed measuring device 33 is also provided. The feed measuring device 33 may be, for example, a distance meter that measures the distance between the mast 5 and a frame of the industrial truck 1.

[0042] A control device 30 is connected to the pump motor 21, the load measuring device 31, the height measuring device 32, and the feed measuring device 33. This connection, like the connections of the height measuring device 32 to the lifting cylinder 25, is shown as a dashed line to indicate that these are data lines and not hydraulic lines. The control device 30 is configured to read and process the load weight 11, the lifting height 12, and the feed 13 from the corresponding measuring devices 31, 32, and 33. Furthermore, the control device 30 controls the pump motor 21 to regulate the torque of the pump motor 21 in such a way as to compensate for the influence of the lifting stability parameters on the tipping stability of the industrial truck 1.

[0043] Fig.Figure 3 shows a simplified flowchart illustrating a process for controlling a change in the pump motor's torque as a function of the lifting stability parameters. In step 40, a request is transmitted to the control device 30 to raise or lower the load-handling attachment 6. This is triggered, for example, by a corresponding command transmitted to the control device 30 by the operator of the industrial truck 1 via a control element. In step 41, it is checked whether the speed at which the load-handling attachment 6 is moved should be changed. This change in speed corresponds to a change in the torque with which the pump motor 21 drives the hydraulic pump 22.If the speed does not change, the torque values ​​corresponding to the speed values ​​are transmitted to the pump motor 21 in step 42, so that the load-handling device 6 can be raised or lowered in step 48. If, however, the speed is to be changed, step 23 checks whether the speed of the load-handling device 6 should be increased during a lifting operation. If this is not the case, step 45 checks whether a decrease in speed or torque should occur during a lowering operation instead. If this is also not the case, the values ​​from step 42 are transmitted. If, however, it is determined in either step 43 or step 45 that a corresponding change should take place, step 44 checks whether the changes are within the permissible range.Specifically, step 44 checks whether the change in speed and the associated change in torque per unit time are within the permissible range for the maximum torque change per unit time, which was determined using the lifting stability parameters. If the change is within the permissible range, the values ​​are passed on in step 42. If, however, the change is not within the permissible range, the torque change per unit time is adjusted to the maximum permissible torque change per unit time in step 46. Finally, in step 47, the adjusted values ​​are passed on, and in step 48, the lifting or lowering of the load-handling device 6 is executed.

[0044] Overall, the in Fig.The process shown in Figure 3 checks whether changes in torque during a lifting or lowering operation of the load-handling device 6 exceed a maximum torque change per unit of time. If this maximum torque change per unit of time is exceeded, the torque change per unit of time is reduced. In this way, the tilting stability of the industrial truck 1 is ensured during the lifting or lowering operation.

[0045] Fig. Figure 4 shows a characteristic curve 50 of the maximum torque 55 of the pump motor 21 as a function of the load weight 11. As shown, the maximum torque 55 increases sharply with a higher load weight 11. In other words, a comparatively higher maximum torque is available for a heavier load 8.

[0046] Fig.Figure 5 shows a characteristic curve 51 of the maximum torque change per unit time 56 of the pump motor 21 as a function of the load weight 11. This characteristic curve 51 is used to specify the maximum acceleration or deceleration with which the load-handling device 6 may be moved in order to maintain the necessary tipping stability for a given load weight 11. Since the tipping stability is reduced with a higher load weight 11, the maximum torque change per unit time 56 must be reduced to compensate. For this reason, the characteristic curve 51 is shown in Figure 51. Fig. The characteristic curve shown in section 51 is a strictly monotonically decreasing linear characteristic curve.

[0047] The characteristic curves for the stroke height 12 and the feed rate 13 are in Fig.Figure 5 is not shown. They can either be strictly monotonically decreasing, just like characteristic curve 51, or exhibit a different behavior. In any case, the maximum torque change per unit time 56 is calculated from the stroke stability parameters 11, 12, and 13. This is done, for example, by providing a table for each of the stroke stability parameters 11, 12, and 13, which specifies a value for a parameter factor for different values ​​of the stroke stability parameters 11, 12, and 13. By stepwise calculation or linear interpolation, a corresponding load factor, height factor, and feed factor can be assigned to each measured value of the load weight 11, the stroke height 12, and the feed rate 13. Multiplying these parameter factors together and by a maximum possible torque change per unit time yields the maximum torque change per unit time.

[0048] All features mentioned, including those discernible from the drawings alone as well as individual features disclosed in combination with other features, are considered essential to the invention, both individually and in combination. Inventive embodiments may be fulfilled by individual features or by a combination of several features. Reference symbol list 1 forklift truck 2 Driver's cab 3-wheeler 4 radars 5 masts 6 Lifting devices 7 Focus 8 Last 9 Focus 11 Load weight 12 Lifting height 13 Feed 20 Hydraulic system 21 Pump motor 22 Hydraulic pump 23 Tank 24 Check valve 25 lifting cylinders 26 2 / 2 way valve 30 Control device 31 Load measuring device 32 Height measuring device 33 Feed measuring device 34 Pressure sensor Steps 40 to 48 50 characteristic curve 51 Characteristic curve 55 maximum torque 56 maximum torque changes per unit of time

Claims

[1] Industrial truck (1) comprising a pump motor (21), a hydraulic pump (22), a lifting cylinder (25), a load handling device (6) and a control device (30), wherein the pump motor (21) is configured to drive the hydraulic pump (22), wherein the hydraulic pump (22) is configured to supply the lifting cylinder (25) with hydraulic fluid, wherein the lifting cylinder (25) is configured to raise and lower the load handling device (6), wherein the industrial truck (1) further comprises at least one measuring device, wherein the at least one measuring device is configured to measure at least one lifting stability parameter and transmit it to the control device (30), wherein the lifting stability parameter influences the tilting stability of the industrial truck (1) during a lifting or lowering operation, wherein the control device (30) is configured to regulate a torque of the pump motor (21), characterized by, that the control device (30) is configured to control the pump motor (21) in such a way that a maximum torque change per time (56) is varied depending on the stroke stability parameter. [2] Industrial truck (1) according to claim 1, characterized by , that the control device (30) is configured to vary the maximum torque change per time (56) by controlling the pump motor (21) in such a way as to compensate for a change in tilting stability caused by a change in the stroke stability parameter. [3] Industrial truck (1) according to claim 1 or 2, characterized by , that a characteristic curve (51) of the maximum torque change per time (56) as a function of the at least one stroke stability parameter is, in particular, strictly, monotonically decreasing or increasing, wherein in particular the maximum torque change per time (56) is inversely proportional or proportional to the stroke stability parameter. [4] Industrial truck (1) according to claim 3, characterized by , that the characteristic curve (51) of the maximum torque change per time (56) as a function of the at least one stroke stability parameter differs when the torque is increased from the characteristic curve (51) of the maximum torque change per time (56) as a function of the at least one stroke stability parameter when the torque is decreased. [5] Industrial truck (1) according to any one of claims 1 to 4, characterized by, that the at least one measuring device comprises a load measuring device (31), wherein the load measuring device (31) is configured to measure a load weight (11) of a load (8) resting on the load handling device (6) as a stroke stability parameter, wherein the control device (30) is configured to control the pump motor (21) such that a maximum torque change per time (56) is varied as a function of the load weight (11), wherein a characteristic curve (51) of the maximum torque change per time (56) as a function of the load weight (11) is monotonically decreasing. [6] Industrial truck (1) according to any one of claims 1 to 5, characterized by, that the at least one measuring device comprises a height measuring device (32), wherein the height measuring device (32) is configured to measure a current lifting height (12) of the load handling device (6) as a lifting stability parameter, wherein the control device (30) is configured to control the pump motor (21) such that the maximum torque change per time (56) is varied as a function of the current lifting height (12), wherein a characteristic curve (51) of the maximum torque change per time (56) as a function of the current lifting height (12) is monotonically decreasing. [7] Industrial truck (1) according to any one of claims 1 to 6, characterized by, that the at least one measuring device comprises a feed measuring device (33), wherein the feed measuring device (33) is configured to measure a horizontal feed (13) of the load handling device (6) as a stroke stability parameter, wherein the control device (30) is configured to control the pump motor (21) such that the maximum torque change per time (56) is varied as a function of the feed (13), wherein a characteristic curve (51) of the maximum torque change per time (56) as a function of the feed (13) is monotonically decreasing. [8] Industrial truck (1) according to any one of claims 1 to 7, characterized by, that the control device (30) is configured to calculate a characteristic factor for at least two of the stroke stability characteristics, wherein the characteristic factors are less than or equal to one, wherein the maximum torque change per time (56) results from the product of the characteristic factors with a maximum possible torque change per time. [9] Industrial truck (1) according to claims 5, 6, 7 and 8, characterized by , that the control device (30) is configured to calculate a load factor from the load weight (11), a height factor from the lifting height (12) and a feed factor from the feed (13) as characteristic factors, wherein the load factor decreases or remains the same if the load weight (11) increases, the height factor decreases or remains the same if the lifting height (12) increases, and the feed factor decreases or remains the same if the feed (13) increases. [10] Method for operating a forklift truck (1), wherein the forklift truck (1) comprises a pump motor (21), a hydraulic pump (22), a lifting cylinder (25), a load handling device (6) and a control device (30), wherein the pump motor (21) drives the hydraulic pump (22), wherein the hydraulic pump (22) supplies the lifting cylinder (25) with hydraulic fluid, wherein the lifting cylinder (25) raises and lowers the load handling device (6), wherein the forklift truck (1) further comprises at least one measuring device, wherein the at least one measuring device measures at least one lifting stability parameter and transmits it to the control device (30), wherein the lifting stability parameter influences a tilting stability of the forklift truck (1) during a lifting or lowering operation, wherein the control device (30) regulates a torque of the pump motor (21), characterized by, that the control device (30) controls the pump motor (21) in such a way that a maximum torque change per time (56) is varied depending on the stroke stability parameter. [11] Method according to claim 10, characterized by , that the control device (30) varies the maximum torque change per time (56) by controlling the pump motor (21) in such a way as to compensate for a change in tilting stability caused by a change in the stroke stability parameter. [12] Method according to claim 10 or 11, characterized by , that a characteristic curve (51) of the maximum torque change per time (56) as a function of the at least one stroke stability parameter is, in particular, strictly, monotonically decreasing or increasing, wherein in particular the maximum torque change per time (56) is inversely proportional or proportional to the stroke stability parameter. [13] Method according to claim 12, characterized by, that the characteristic curve (51) of the maximum torque change per time (56) as a function of the at least one stroke stability parameter differs when the torque is increased from the characteristic curve (51) of the maximum torque change per time (56) as a function of the at least one stroke stability parameter when the torque is decreased. [14] Method according to any one of claims 10 to 13, characterized by , that the at least one measuring device comprises a load measuring device (31), wherein the load measuring device (31) measures a load weight (11) of a load (8) resting on the load handling device (6) as a stroke stability parameter, wherein the control device (30) controls the pump motor (21) such that a maximum torque change per time (56) is varied as a function of the load weight (11), wherein a characteristic curve (51) of the maximum torque change per time (56) as a function of the load weight (11) is monotonically decreasing. [15] Method according to any one of claims 10 to 14, characterized by , that the at least one measuring device comprises a height measuring device (32), wherein the height measuring device (32) measures a current lifting height (12) of the load handling device (6) as a lifting stability parameter, wherein the control device (30) controls the pump motor (21) such that the maximum torque change per time (56) is varied as a function of the current lifting height (12), wherein a characteristic curve (51) of the maximum torque change per time (56) as a function of the current lifting height (12) is monotonically decreasing. [16] Method according to any one of claims 10 to 15, characterized by, that the at least one measuring device comprises a feed measuring device (33), wherein the feed measuring device (33) measures a horizontal feed (13) of the load handling device (6) as a stroke stability parameter, wherein the control device (30) controls the pump motor (21) such that the maximum torque change per time (56) is varied as a function of the feed (13), wherein a characteristic curve (51) of the maximum torque change per time (56) as a function of the feed (13) is monotonically decreasing. [17] Method according to any one of claims 10 to 16, characterized by , that the control device (30) calculates a characteristic factor for at least two of the stroke stability characteristics, wherein the characteristic factors are less than or equal to one, wherein the maximum torque change per time (56) results from the product of the characteristic factors with a maximum possible torque change per time. [18] Method according to claims 14, 15, 16 and 17, characterized by , that the control device (30) calculates a load factor from the load weight (11), a height factor from the lifting height (12) and a feed factor from the feed (13) as characteristic parameters, wherein the load factor decreases or remains the same if the load weight (11) increases, the height factor decreases or remains the same if the lifting height (12) increases, and the feed factor decreases or remains the same if the feed (13) increases.

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