Industrial truck and method for operating an industrial truck

Abstract

The invention relates, among other things, to a forklift truck (2) with a lifting mast (4) which is designed with a free lifting stage driven by at least one free lifting cylinder (8) and with at least one or more mast lifting stages driven by at least one mast lifting cylinder (12), wherein a load handling device (6) is movable along the lifting mast (4), preferably in a vertical direction, by means of the free lifting stage and / or by means of the at least one mast lifting stage, wherein a common hydraulic circuit is provided for the at least one free lifting cylinder (8) and for the at least one mast lifting cylinder (12), wherein a lifting sequence detection device is provided to detect a lifting sequence when the at least one free lifting cylinder (8) and / or when the at least one mast lifting cylinder (12) is actuated.

Description

[0001] The invention relates to a forklift truck with a lifting mast, which is designed with a free-lift stage driven by at least one free-lift cylinder and with at least one or more mast lift stages driven by at least one mast lift cylinder, wherein a load-handling device is movable along the lifting mast, preferably in a vertical direction, by means of the free-lift stage and / or by means of the at least one mast lift stage. The invention further relates to a method for operating a forklift truck.

[0002] Industrial trucks, such as forklifts, often have a mast with one or more mast lift stages, which are hydraulically operated by one or more mast lift cylinders. The mast comprises a fixed mast section connected to the vehicle and typically two extension sections: a center mast and an inner mast, which are extended by the mast lift cylinder. A free lift cylinder moves a free lift stage, which allows a load-handling attachment, such as forks, to travel along the inner mast of the main mast. The free lift stage moves the load-handling attachment along this mast stage and allows the operator to adjust the height of the load-handling attachment without extending the mast and thus without changing the overall height of the truck.

[0003] When initiating or during a lifting operation, the load-handling device is first extended according to the free stroke, without extending the lifting mast. After the free stroke is complete and the free stroke cylinder has reached its end position, the mast lift is executed.

[0004] The stroke sequence of free lift and mast lift is usually controlled by the surface area ratios of the hydraulic cylinders driving the load-handling device or the mast sections. The surface area ratios of the hydraulic cylinders for the free lift and the mast lift are designed such that the hydraulic pressure required to lift the free lift cylinder is lower than the hydraulic pressure required to lift the mast lift cylinder.

[0005] The pressure during the free stroke is lower than during the mast stroke due to the surface area and loads. Therefore, the free stroke occurs first, followed by the mast stroke. The hydraulic supply lines to the free stroke stage are, by design, significantly longer than those to the mast stroke stage. For example, EP 3 495 904 A1 discloses a hydraulic system for a forklift truck, in which an additional valve is provided during the free stroke to optimize the area control.

[0006] It is an object of the invention to ensure the flawless operation of a forklift truck, particularly in free lift mode.

[0007] This problem is solved by a forklift truck with a lifting mast, which is designed with a free lift stage driven by at least one free lift cylinder and with at least one or more mast lift stages driven by at least one mast lift cylinder, wherein a load handling device can be moved along the lifting mast, preferably in a vertical direction, by means of the free lift stage and / or by means of the at least one mast lift stage, wherein a common hydraulic circuit is provided for the at least one free lift cylinder and for the at least one mast lift cylinder, wherein a lift sequence detection device is provided to detect a lift sequence when the at least one free lift cylinder and / or when the at least one mast lift cylinder is actuated.

[0008] The invention is based on the idea that stroke sequence errors in the free stroke of a forklift truck can be avoided by using a stroke sequence detection device to detect the stroke sequence when the at least one free stroke cylinder and / or the at least one mast stroke cylinder is actuated. This particularly prevents the mast stroke of a forklift truck from extending before the free stroke has reached its end stop.

[0009] In one embodiment, it is provided that the stroke sequence detection device detects the stroke speed of the at least one free-lift cylinder, and that the stroke speed of the at least one free-lift cylinder is limited to a predetermined maximum stroke speed for the at least one free-lift cylinder by means of the stroke sequence detection device.

[0010] A further development of the industrial truck is characterized by the fact that the lifting sequence detection device records the lifting speed of the free lift stage, whereby the lifting sequence detection device limits the lifting speed of the free lift stage to a predetermined maximum lifting speed. Because the lifting speed, especially the maximum speed, in the free lift of the mast is limited, no lifting sequence errors occur.

[0011] The industrial truck is further developed in that the maximum lifting speed of the at least one free-lift cylinder and / or the maximum lifting speed of the free-lift stage is determined, in particular predetermined, as a function of a characteristic map, in particular a lifting speed characteristic map, of the free-lift stage, wherein in particular the characteristic map comprises at least one or more operating parameters selected from the group of operating parameters: load to be moved or moved by the industrial truck, mast type, hydraulic oil temperature, hydraulic oil viscosity, pressure differential of the hydraulic oil in the free-lift stage and the at least one mast lifting stage. The maximum permissible lifting speed is determined as a function of various parameters.Input variables are determined, and in particular, a characteristic map makes it possible to model, for example, complex relationships between the recorded parameters and the load weight of a load to be lifted. Using the characteristic map, especially the lifting speed characteristic map, parameters such as the weight of a load, the type of lifting mast, the temperature of the hydraulic oil, and / or a pressure difference in the mast sections are taken into account.

[0012] In a preferred embodiment of the industrial truck, it is provided that the lifting height of the load means in the free lift and / or the lifting height of the load means in the mast lift is detected by means of the lifting sequence detection device.

[0013] According to one embodiment of the industrial truck, the lift sequence detection device includes a lift height measuring device for the free lift stage and / or a lift height measuring device for at least one mast lift stage. The lift height measuring device makes it possible to actively monitor the lift sequence and detect any lift sequence error. If a lift sequence error is detected, the lift sequence detection device can reduce the maximum lift speed, particularly of the free lift cylinder, until, for example, the area control of the free lift and mast lift is restored and the lift sequence error ceases. The (correct) lift sequence is generally ensured by the area ratios of the free lift cylinder and the mast lift cylinder. Due to its larger piston area, the free lift cylinder requires less pressure to extend than the mast lift cylinder.

[0014] Preferably, in one embodiment, the stroke sequence detection device comprises at least one proximity switch in the free stroke stage and / or at least one proximity switch in the at least one mast stroke stage. Within the scope of the invention, multiple proximity switches in the free stroke stage and / or in the at least one mast stroke stage may also be provided.

[0015] According to a further advantageous embodiment, the industrial truck is further developed in that a pressure difference between a pressure of a hydraulic fluid in a supply line common to the at least one free lift cylinder and the at least one mast lift cylinder and a pressure of the hydraulic fluid in a supply branch for the at least one free lift cylinder is determined or can be determined by means of the stroke sequence detection device.

[0016] Furthermore, one embodiment of the industrial truck is characterized in that, if the pressure difference between the pressure of the hydraulic fluid in the common supply line and the pressure of the hydraulic fluid in the supply branch for the at least one free-lift cylinder is equal to or exceeds a predetermined pressure of the hydraulic fluid in a supply branch for the at least one mast lift cylinder, the lifting speed of the at least one free-lift cylinder is reduced.

[0017] Furthermore, in another preferred embodiment, it is provided that if the pressure difference between the pressure of the hydraulic fluid in the common supply line and the pressure of the hydraulic fluid in the supply branch for the at least one free-lift cylinder falls below a predetermined pressure of the hydraulic fluid in a supply branch for the at least one mast lift cylinder, and if the pressure difference is tested within a predetermined tolerance range, the lifting speed of the at least one free-lift cylinder is kept constant.

[0018] The industrial truck is further enhanced in that, if the pressure difference between the pressure of the hydraulic fluid in the common supply line and the pressure of the hydraulic fluid in the supply branch for the at least one free-lift cylinder falls below the predetermined pressure of the hydraulic fluid in a supply branch for the at least one mast lift cylinder, and if the pressure difference is tested outside a predetermined tolerance range, the lifting speed of the at least one free-lift cylinder is increased.

[0019] Furthermore, the problem is solved by a method for operating a forklift truck, as described above. To avoid repetition, explicit reference is made to the above explanations.

[0020] Further features of the invention will become apparent from the description of embodiments according to the invention, together with the claims and the accompanying drawings. Embodiments according to the invention may fulfill individual features or a combination of several features.

[0021] Within the scope of the invention, features marked with "in particular" or "preferably" are to be understood as optional features.

[0022] 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 shows a forklift truck in a schematically simplified perspective view, Fig. 2a and 2b show a schematic lifting process of a load handling device on a forklift truck according to the prior art, Fig. 3 shows a schematically simplified circuit diagram of a hydraulic system and Fig. 4a to 4c show schematically different flowcharts for the control or regulation of lifting sequences on a forklift truck.

[0023] In the drawings, identical or similar elements and / or parts are provided with the same reference numbers, so that a re-presentation is omitted.

[0024] Fig. 1 Figure 2 shows a material handling vehicle, for example a forklift truck, with a lifting mast 4, comprising for example a first mast lifting stage 41, the inner mast, and a second mast lifting stage 42, the middle mast. The lifting mast 4 is supported by a Fig. 1 The mast lifting cylinder (not shown) is driven (multiple mast lifting cylinders may also be provided).

[0025] The lifting mast 4 comprises, in addition to the inner mast 41 and the center mast 42, a fixed support mast connected to the vehicle frame. The center mast is driven, for example, by the mast lifting cylinder, and the inner mast is also coupled to the center mast, for example, via a chain, so that these two extension masts extend simultaneously. Furthermore, the industrial truck 2 includes a free-lift stage with a load-handling attachment 6, for example, a fork, which is vertically movable along the inner mast of the lifting mast 4. For this purpose, the free-lift stage includes a free-lift cylinder 8. The free-lift cylinder 8 can move the load-handling attachment 6 along the first mast stage 41 of the lifting mast 4.

[0026] Fig. 2a und 2b The figures schematically show the lifting process of the industrial truck 2, whereby the load handling device 6 is first lifted by means of the free lift stage (see figure). Fig. 2a ) and then, in a predetermined order, the mast lift stage 41 and the mast lift stage 42 (see Fig. 2b ) will be extended.

[0027] A simplified circuit diagram of a hydraulic system 10 of the industrial truck 2 for lifting a load is shown in Fig. 3 Schematic representation. Return lines for the hydraulic fluid, especially hydraulic oil, have not been shown.

[0028] The hydraulic system 10 serves to supply and move a mast lift cylinder 12 and the free lift cylinder 8, which moves the load-handling device 6, with a hydraulic fluid 24, in particular a hydraulic oil. The hydraulic fluid 24 is pumped or conveyed from a reservoir 20 into a supply line 31 by means of a hydraulic pump 28. A check valve 27 is arranged in the supply line 31 to prevent the hydraulic fluid 24 from flowing back into the reservoir 20. A pressure sensor 23 is arranged on the supply line 31 to detect the pressure p1 of the hydraulic fluid 24 in the supply line 31. Furthermore, a temperature sensor 22 is arranged on the supply line 31 to measure the temperature of the hydraulic fluid 24 in the supply line 31.

[0029] At an end distribution point 32 of the supply line 31, the supply line 31 is connected to a supply branch 35 for the free-lift cylinder 8 and to a supply branch 36 for the mast lift cylinder 12 in order to supply hydraulic fluid 24 to the free-lift cylinder 8 via the supply branch 35 and to the mast lift cylinder 12 via the supply branch 36. A pressure sensor 34 is arranged on the supply branch 36 for the free-lift cylinder 8 in order to measure the pressure p 2 of the hydraulic fluid in the supply branch 35.

[0030] The free-lift cylinder 8 and the mast lift cylinder 12 have different piston cross-sections. These are selected such that, at an initial hydraulic fluid pressure p2, the free-lift cylinder 8 extends first. When the free-lift stage reaches the upper limit of the lifting mast 4, specifically the first mast lift stage 41, the hydraulic fluid pressure 24 in the hydraulic system 10 continues to rise until it reaches the value pM, which is higher than p2. Upon exceeding this hydraulic pressure, the mast lift stages 41 and 42 begin to extend.

[0031] The individual lifting cylinders 8 and 12 of the mast lifting stages 41 and 42 can be designed such that their different cross-sections ensure that the first mast lifting stage 41 extends first, followed by the second mast lifting stage 42. The correct lifting sequence of the mast lifting stages 41 and 42 is ensured by the surface area ratios of the free lifting cylinder 8 and the mast lifting cylinder 12. Due to its larger piston area, the free lifting cylinder 8 requires lower pressure to extend than the mast lifting cylinder 12.

[0032] The pressure p1 at distribution point 32 is measured by pressure sensor 23 in the supply line 31. The pressure p2 is measured at the inlet of the free-lift cylinder 8 by pressure sensor 24. The temperature of the hydraulic fluid 24, in particular hydraulic oil, in the supply line 31 is detected by temperature sensor 22.

[0033] If, during the lifting process of the load starting in the free stroke, the differential pressure pd = p1 - p2 in supply branch 35 for the free stroke cylinder 8 reaches or exceeds the pressure pM required for extending the mast lift cylinder 12, the pressure in supply branch 36 to the mast lift cylinder 12 consequently also increases. If the pressure difference pd is greater than or equal to the pressure pM, this leads to the mast lift cylinder 12 extending unintentionally as a stroke sequence error, even though the free stroke cylinder 8 is not yet fully extended. The differential pressure pd increases with increasing flow rate of the hydraulic fluid 24 in supply branch 35. The pressure difference is measured by the two pressure sensors 23 and 34 at the inlet and outlet of supply branch 35 for the free stroke cylinder 8 and increases with increasing flow rate.The pressure difference pM depends on the increasing flow velocity of the hydraulic fluid and the internal resistances of the supply branch 35. With increasing temperature of the hydraulic fluid 24 in the supply line 31 and the supply branches 35, 36, the pressure difference pd (= p1 - p2) is . Due to the different area ratios or cross-sectional areas of the pistons of the free-lift cylinder 8 and the mast lift cylinder 12, the pressure limit pM depends on the load applied.

[0034] In Fig. 4a The diagram schematically depicts a flowchart for a lifting sequence of the free-lift cylinder 8 and the mast lifting cylinder 12. During a lifting operation, after initiating the lifting start (step S10), it is checked whether the differential pressure pd ≥ p M (step S11). If this is the case, the lifting speed of the free-lift cylinder 8 is reduced to prevent a lifting sequence error (step S12). Step S11 is then executed again.

[0035] In the other case, where the differential pressure pd < p M, step S13 checks whether the differential pressure pd is within a predetermined tolerance range. If so, step S14 maintains the stroke speed of the free-lift cylinder 8. Otherwise, step S15 increases the stroke speed of the free-lift cylinder 8. The pressure monitoring according to the invention provides a stroke sequence detection device that prevents stroke sequence errors when actuating the free-lift cylinder 8 and / or the mast stroke cylinder 12.

[0036] In Fig. 4b A schematic flowchart for preventing a lifting sequence error using a characteristic map K is shown. After the lifting process starts in step S10, and the lifting mast type of the forklift truck is entered or recorded in step S20, followed by the hydraulic fluid temperature being recorded in step S21, the maximum lifting speed of the free-lift cylinder 8 is determined using a characteristic map K. For this purpose, the forklift truck has a corresponding control unit, such as an on-board computer or similar device, in which the parameters for the characteristic map are stored. By determining the maximum lifting speed of the free-lift cylinder 8, a lifting sequence error is also prevented.

[0037] If no pressure sensors are used to monitor the lifting sequence, it can be determined, based on series of measurements, at which lifting speeds, viscosities of the hydraulic fluids used, and / or temperatures of the hydraulic fluids the differential pressure reaches a critical value. The critical pressure value can vary depending on the lifting mast type and / or load. The maximum lifting speed of the free-lift cylinder 8 can be determined using a characteristic map that considers the dependencies of the lifting mast type, the temperature (viscosity) of the hydraulic fluid, and, if applicable, other parameters on the differential pressure. In particular, the maximum lifting speeds of the free-lift cylinder 8 are designed for the most unfavorable load case. If a pressure sensor (see below) is used, the differential pressure can be determined using a specific parameter. Fig. 3 , reference 23) is used, the stroke sequence can be controlled depending on a load dependency.

[0038] In the exemplary embodiment in Fig. 4c A flowchart is schematically depicted, where the lifting sequence detection is performed using position / speed monitoring. After the lifting process starts in step S10, a subsequent step S31 checks whether the mast lift cylinder 12 is actuated or extended while the free lift cylinder is extending. If this is the case, the lifting speed of the free lift cylinder is reduced in step S32. Step S31 is then performed again. If, however, step S31 determines that the mast lift cylinder 12 does not extend while the free lift cylinder 8 is actuated, step S33 specifies that the monitoring should not intervene in the lifting process of the free lift cylinder 8.

[0039] Whether the free-lift cylinder 8 and / or the mast lift cylinder 12 are actuated or extended is determined, for example, by means of a stroke height measuring device for the free-lift cylinder 8 and / or the mast lift cylinder 12. In another embodiment, the lifting sequence can also be actively monitored by one or more proximity switches in the free-lift stage and / or in the mast lift stage of the industrial truck 2.

[0040] For example, by monitoring the mast stroke, for example by means of the cylinder rods of the lifting cylinders, a corresponding control or regulation for the stroke sequence can be designed, so that the stroke speed of the free stroke cylinder 8 is reduced as soon as an unwanted stroke movement is measured or detected for the mast stroke cylinder 12.

[0041] The in Fig. 4a and 4b The variants shown can also be used with the one in Fig. 4c The illustrated embodiment can be combined, thereby increasing the safety of the hydraulic system 10.

[0042] Furthermore, a combination of the in Fig. 4b and 4c The illustrated embodiments (combination of a characteristic map control with a position monitoring system) are conceivable, which ensures that the maximum stroke speed of the free-stroke cylinder 8 (as input variable) depends on the in Fig. 4b The factors described are close to the maximum possible stroke speed of the free-stroke cylinder 8. In the event of control variables occurring, the Fig. 4c The depicted path monitoring shows a stroke sequence error.

[0043] 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. Bezugszeichenliste

[0044] 2 Forklift truck 4 Mast 6 Load handling device 8 Free lift cylinder 10 Hydraulic system 12 Mast lift cylinder 20 Reservoir 22 Temperature sensor 23 Pressure sensor 24 Hydraulic fluid 27 Check valve 28 Hydraulic pump 31 Supply line 32 Distribution point 34 Pressure sensor 35 Supply branch 36 Supply branch 41 First mast lift stage 42 Second mast lift stage

Claims

1. Industrial truck (2) with a lifting mast (4) which is designed with a free lifting stage driven by at least one free lifting cylinder (8) and with at least one or more mast lifting stages driven by at least one mast lifting cylinder (12), wherein a load handling device (6) is movable along the lifting mast (4), preferably in a vertical direction, by means of the free lifting stage and / or by means of the at least one mast lifting stage, wherein a common hydraulic circuit is provided for the at least one free lifting cylinder (8) and for the at least one mast lifting cylinder (12), wherein a lifting sequence detection device is provided to detect a lifting sequence when the at least one free lifting cylinder (8) and / or when the at least one mast lifting cylinder (12) is actuated.

2. Industrial truck (2) according to claim 1, characterized by the fact thatby means of the stroke sequence detection device a stroke speed of the at least one free stroke cylinder (8) is detected, wherein by means of the stroke sequence detection device the stroke speed of the at least one free stroke cylinder (8) is limited to a predetermined maximum stroke speed for the at least one free stroke cylinder (8).

3. Industrial truck (2) according to claim 1, characterized by the fact that The stroke sequence detection device detects the stroke speed of the free stroke stage, whereby the stroke speed of the free stroke stage is limited to a predetermined maximum stroke speed of the free stroke stage by means of the stroke sequence detection device.

4. Industrial truck (2) according to one of claims 1 to 3, characterized by the fact thatthe maximum lifting speed of the at least one free-lift cylinder (8) and / or the maximum lifting speed of the free-lift stage is determined, in particular predetermined, as a function of a characteristic map, in particular a lifting speed characteristic map, of the free-lift stage, wherein in particular the characteristic map includes at least one or more operating parameters selected from the group of operating parameters: load to be moved or moved by the industrial truck (2), mast type, oil temperature of the hydraulic oil, viscosity of the hydraulic oil, pressure difference of the hydraulic oil in the free-lift stage and the at least one mast lifting stage.

5. Industrial truck (2) according to one of claims 1 to 4, characterized by the fact that The lifting height of the load device in free lift and / or the lifting height of the load device in mast lift is detected by means of the lifting sequence detection device.

6. Industrial truck (2) according to claim 5, characterized by the fact thatThe lift sequence detection device includes a lift height measuring device for the free lift stage and / or a lift height measuring device for at least one mast lift stage.

7. Industrial truck (2) according to claim 5 or 6, characterized by the fact that The stroke sequence detection device has at least one proximity switch in the free stroke stage and / or at least one proximity switch in the at least one mast stroke stage.

8. Industrial truck (2) according to one of claims 1 to 7, characterized by the fact that by means of the stroke sequence detection device a pressure difference is determined or can be determined between a pressure of a hydraulic fluid (24) in a supply line (31) common to the at least one free lift cylinder (8) and the at least one mast lift cylinder (12) and a pressure of the hydraulic fluid (24) in a supply branch (35) for the at least one free lift cylinder (8).

9. Industrial truck (2) according to claim 8, characterized by the fact thatIf the pressure difference between the pressure of the hydraulic fluid (24) in the common supply line (31) and the pressure of the hydraulic fluid (24) in the supply branch (35) for the at least one free-lift cylinder (8) is equal to or exceeds a predetermined pressure of the hydraulic fluid (24) in a supply branch (36) for the at least one mast lift cylinder (12), the lifting speed of the at least one free-lift cylinder (8) is reduced or is reduced.

10. Industrial truck (2) according to claim 8 or 9, characterized by the fact thatwhen the pressure difference between the pressure of the hydraulic fluid (24) in the common supply line (31) and the pressure of the hydraulic fluid (24) in the supply branch (35) for the at least one free-lift cylinder (8) falls below a predetermined pressure of the hydraulic fluid (24) in a supply branch (36) for the at least one mast lift cylinder (12), and when the pressure difference is tested within a predetermined tolerance range, the lifting speed of the at least one free-lift cylinder (8) is kept constant.

11. Industrial truck (2) according to claim 8 or 9, characterized by the fact thatIf the pressure difference between the pressure of the hydraulic fluid (24) in the common supply line (31) and the pressure of the hydraulic fluid (24) in the supply branch (35) for the at least one free-lift cylinder (8) falls below a predetermined pressure of the hydraulic fluid (24) in a supply branch (36) for the at least one mast lift cylinder (12), and if the pressure difference is tested outside a predetermined tolerance range, the lifting speed of the at least one free-lift cylinder (8) is increased or is 12. Method for operating a forklift truck (2) according to any one of claims 1 to 11.

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