Forklift truck with working hydraulics

Abstract

Industrial truck (1) with a working hydraulic system (2) comprising at least two hydraulic axes (H1, H2) for which a hydraulic pump (10) is provided for supplying hydraulic fluid, wherein each hydraulic axis (H1; H2) has a hydraulic consumer (6; 8) which can be actuated by means of an electrically actuated control valve (15; 16), and wherein an operating element (11; 12) is provided for each hydraulic axis (H1; H2) which, when actuated, generates a control voltage (U1; U2) for the hydraulic axis (H1; H2) as an output signal, wherein an electronic control device (20) is provided which generates a control current (I1; I2) from the control voltage (U1; U2) for actuating the control valve (15; 16) of the hydraulic axis (H1; H2), characterized in that the electronic control device (20) is designed such that the generation of the control current (I2; I1) of the control valve (16; 15) of a hydraulic axis (H2; H1) as a function of the control voltage (U2;U1) of the hydraulic axis (H2; H1) and the control voltage (U1; U2) of at least one further hydraulic axis (H1; H2).;

Description

[0001] The invention relates to an industrial truck with working hydraulics comprising at least two hydraulic axles, for supplying them with pressure medium a hydraulic pump is provided, wherein each hydraulic axle has a hydraulic consumer which can be actuated by means of an electrically actuated control valve, and an operating element is provided for each hydraulic axle which, when actuated, generates a control voltage for the hydraulic axle as an output signal, wherein an electronic control device is provided which generates a control current for actuating the control valve of the hydraulic axle from the control voltage.

[0002] The working hydraulics of an industrial truck comprise several hydraulic axes, for example, a lifting drive as the first hydraulic axis and a tilt drive as the second hydraulic axis. Each hydraulic axis consists of a hydraulic consumer that can be actuated by an electrically actuated control valve. For operation by the driver, a control element is provided for each hydraulic axis. When actuated, this element generates a corresponding control voltage for the hydraulic axis as an output signal. By actuating the control element of a hydraulic axis, the industrial truck driver can specify the appropriate control and actuation of the hydraulic axis.The control voltage generated by the corresponding actuation of the control element and thus by the actuated control element as an output signal represents a volume flow requirement (volume flow setpoint) specified by the driver for the hydraulic axle and a specification of a movement speed of the consumer of the hydraulic axle. From the control voltage of the actuated control element of a hydraulic axle, the electronic control device generates a control current for actuating the electrically actuated control valve of this hydraulic axis in order to generate a corresponding valve deflection of the control valve of this hydraulic axis, which enables the supply of a volume flow to the consumer of this hydraulic axis that corresponds to the volume flow requirement specified by the actuation of the control element.

[0003] In conventional industrial trucks, the control valve of a hydraulic axle is activated only in response to the actuation of the control element assigned to that hydraulic axle, and thus only in response to the control voltage generated by the control element of that hydraulic axle as an output signal. By actuating the control element of a hydraulic axle accordingly, the driver specifies a desired flow rate requirement for the hydraulic axle and thus ultimately a specific valve deflection of the control valve of that hydraulic axle.

[0004] However, if several hydraulic axles are supplied with pressure medium by a single hydraulic pump, the following problems can occur in industrial trucks of this type in which the control valve of a hydraulic axle is only activated in dependence on the control voltage generated as an output signal by the control element of this hydraulic axle.

[0005] If two or more hydraulic axes are operated simultaneously and thus in parallel by appropriate actuation of the control elements, certain operating states can lead to a sudden change in the volume flow supplied to a hydraulic axis via the actuated control valve and thus to a sudden change in the movement speed of the consumer of this hydraulic axis. Such an operating state can occur, for example, if, during the simultaneous actuation of two hydraulic axes, the consumer of the first hydraulic axis moves against a mechanical end stop, so that a higher volume flow is suddenly supplied to the consumer of the second hydraulic axis.Such a sudden change in the flow rate of a second, parallel-actuated hydraulic axis during the simultaneous actuation of two or more hydraulic axes can also occur if a hydraulic axis is equipped with a flow rate limiter and there is an undersupply of this hydraulic axis. In the case of an undersupply, the flow rates of the hydraulic axes requested by operating the control elements are higher than the flow rate supplied by the hydraulic pump, so that the flow rate supplied by the hydraulic pump to the control valves of the consumers is smaller than the sum of the flow rates requested by operating the control elements.If the undersupply of the hydraulic axis is stopped and the hydraulic pump again provides sufficient volume flow for the consumer movements, a sudden and rapid increase in the volume flow and thus in the movement speed of this consumer occurs at the previously undersupplied consumer.

[0006] Due to the sudden and rapid change in the volume flow and thus the movement speed of the consumer of a specific hydraulic axis when several hydraulic axes are operated in parallel and at the same time, if the movement of the consumer of this hydraulic axis is relevant for the stability and stability of the industrial truck, such as a tilt drive with a tilting movement of a load handling device, this can lead to undesirable behavior of the industrial truck, which cannot be compensated for quickly enough by the driver of the industrial truck by changing the operation of the control element assigned to this hydraulic axis due to the sudden change in the movement speed of the consumer of this hydraulic axis.

[0007] From US 5 088 879 A, ​​an industrial truck with a working hydraulic system is known, which comprises at least two hydraulic axles, for the supply of which with pressure medium a hydraulic pump is provided, wherein each hydraulic axle has a hydraulic consumer which can be actuated by means of a corresponding control valve.

[0008] DE 10 2008 048 056 A1 discloses a hydrostatic drive system of an industrial truck.

[0009] The present invention is based on the object of providing an industrial truck of the type mentioned at the outset, in which the occurrence of undesirable sudden and rapid changes in the movement of a hydraulic axis is reduced when several hydraulic axes are actuated simultaneously.

[0010] This object is achieved according to the invention in that the electronic control device is designed such that the generation of the control current of the control valve of a hydraulic axis takes place as a function of the control voltage of the hydraulic axis and the control voltage of at least one further hydraulic axis. When several hydraulic axes are actuated simultaneously and in parallel, the control valve of a hydraulic axis is thus controlled not only as a function of the output signal and thus the control voltage of the control element assigned to this hydraulic axis, but also as a function of at least one output signal and thus the control voltage of an control element that is assigned to a further hydraulic axis. The generation of the control current of the control valve of a specific hydraulic axis thus takes place as a function of the output signals and the control voltages of several control elements.By appropriately changing the control current of the control valve of a specific hydraulic axis depending on the output signal and thus the control voltage of at least one further actuated hydraulic axis, it is thus possible in a simple manner to reduce rapid and sudden changes in the volume flow and thus in the movement speed on a specific hydraulic axis when several hydraulic axes are actuated simultaneously and in parallel.

[0011] According to an advantageous embodiment of the invention, the electronic control device is designed such that the control current of the control valve of a hydraulic axle is limited as a function of the control voltage of at least one further hydraulic axis. When several hydraulic axes are actuated simultaneously and thus in parallel, the control current of the control valve of a specific hydraulic axis is thus limited as a function of the control voltage of at least one further hydraulic axis. By limiting the control current of the control valve of a specific hydraulic axis, the volume flow requirement specified by the driver by actuating the control element of this hydraulic axis is reduced and thus reduced when another hydraulic axis is actuated in parallel and at the same time.This makes it possible to effectively reduce sudden changes in the volume flow to a specific hydraulic axis that are not specified by the driver and thus sudden changes in the speed of movement on this hydraulic axis.

[0012] Advantageously, the electronic control device is designed such that, when several hydraulic axes are actuated simultaneously, the control current of the control valve of a hydraulic axle is reduced depending on the control voltage of at least one other hydraulic axis compared to the control current of the control valve of the hydraulic axis when the hydraulic axis is actuated alone. The control current of the control valve of a specific hydraulic axis is thus reduced when several hydraulic axes are actuated simultaneously compared to the control current of this control valve when this hydraulic axis is actuated alone. This ensures that, when several hydraulic axes are actuated in parallel on one hydraulic axis, the volume flow requirement specified by the driver by actuating the control element is reduced, i.e.The control valve of this hydraulic axle has a small valve deflection, as specified by the driver by operating the control element of this hydraulic axle. This measure can effectively reduce sudden changes in the volume flow to a specific hydraulic axle that are not specified by the driver, and thus sudden changes in the movement speed of this hydraulic axle.

[0013] Particular advantages arise when the control current limit is freely programmable. This allows for easy adaptation to the specific conditions of the industrial truck. Free programmability is defined as a freely definable mathematical function that determines how the control current of the control valve of a specific hydraulic axis is influenced by the control signals and thus the control voltages of other control elements of other hydraulic axes. For example, when several hydraulic axes are operated simultaneously, the control current limit of the control valve of a specific hydraulic axis can be reduced linearly.

[0014] According to an advantageous embodiment of the invention, the working hydraulics has a lifting drive for raising and lowering a load-handling device as a hydraulic axis and a tilting drive for tilting the load-handling device forwards and backwards as a further hydraulic axis, wherein the electronic control device is designed such that when the lifting drive is actuated simultaneously in a lifting operation and the tilting drive, the control current of the control valve of the tilting drive is limited depending on the control voltage of the lifting drive.If the control current of the control valve of the tilt drive is limited depending on the control voltage of the lifting drive and thus depending on the valve deflection of the control valve of the lifting drive specified by the driver, the sudden and rapid increase in the volume flow and thus the movement speed of the tilt drive can be effectively reduced when the lifting drive reaches a mechanical end stop when the lifting drive reaches a mechanical end stop.

[0015] Advantageously, according to a further development of the invention, the electronic control device is designed such that, upon simultaneous actuation of the lifting drive in a lifting mode and the tilt drive, the control current of the control valve of the lifting drive is limited as a function of the control voltage of the tilt drive. If the control current of the control valve of the lifting drive is limited as a function of the control voltage of the tilt drive and thus as a function of the valve deflection of the control valve of the tilt drive specified by the driver, the sudden and rapid increase in the volume flow and thus the movement speed of the tilt drive can be effectively reduced when the lifting drive reaches a mechanical end stop when the lifting drive reaches a mechanical end stop.

[0016] According to an advantageous development of the invention, the electronic control device determines the volume flow provided by the hydraulic pump and, when several hydraulic axes are actuated simultaneously, influences the control current of the control valve of at least one hydraulic axis depending on the volume flow provided by the hydraulic pump. The volume flow provided by the hydraulic pump can be detected by the control device using a flow sensor or, alternatively, calculated from the speed and displacement volume of the hydraulic pump.The control of a hydraulic axle specified by the driver, and thus the flow rate requirement of this hydraulic axle, is thus reduced not only as a function of the control and flow rate requirement of another, parallel-actuated hydraulic axle, but also as a function of the flow rate provided by the hydraulic pump. This ensures that an undersupply of pressure medium at the control valve of the hydraulic axle is avoided or limited to non-critical values. This effectively prevents unwanted sudden and rapid changes in the movement of the consumer after an undersupply to a consumer is eliminated.

[0017] According to a preferred embodiment of the invention, the operating elements are formed by at least one 2-axis joystick. Such 2-axis joysticks provide a control voltage for a first hydraulic axis in a first main actuation direction and a control voltage for a second hydraulic axis in a second main actuation direction. They can be actuated in intermediate positions to actuate two hydraulic axes simultaneously and in parallel.

[0018] Further advantages and details of the invention are explained in more detail with reference to the embodiment shown in the schematic figures. Fig. 1 an industrial truck according to the invention in a side view, Fig. 2 a schematic representation of a working hydraulic system of a state-of-the-art industrial truck and Fig. 3 a schematic representation of a working hydraulic system of an industrial truck according to the invention.

[0019] In the Fig. 1 shows an industrial truck 1 according to the invention. In the illustrated embodiment, the industrial truck is designed as a counterbalance forklift.

[0020] The industrial truck has a working hydraulic system 2 comprising several hydraulic axes H1, H2. In the illustrated embodiment, a first hydraulic axis H1 is formed by a lifting drive 3 for raising and lowering a load-handling device L, and a further second hydraulic axis H2 is formed by a tilt drive 4 for tilting the load-handling device L forwards V and backwards N.

[0021] The industrial truck 1 has a lifting mast 5, in which the load handling device L can be raised and lowered by means of the lifting drive 3. For this purpose, the lifting drive 3 comprises at least one lifting cylinder as a hydraulic consumer 6. The lifting mast 5 can be tilted on a vehicle body 7 about a tilt axis (not shown in detail). In the present exemplary embodiment, the tilt drive 4 serves to tilt the lifting mast 5 forwards V and backwards R and comprises at least one tilt cylinder as a hydraulic consumer 8. A forward tilt V corresponds to a tilt of the lifting mast 5 and thus the load handling device L away from the vehicle body 7, and a backward tilt N corresponds to a tilt of the lifting mast 5 and thus the load handling device L towards the vehicle body 7.

[0022] A hydraulic pump 10 is provided to supply the hydraulic axes H1, H2 of the working hydraulics with pressure medium.

[0023] A driver's workstation is formed in the vehicle body 7 of the industrial truck 1. At least one control element 11, 12 operable by the driver is arranged in the driver's workstation for operating the hydraulic axes H1, H2. Preferably, the control elements 11, 12 for the two hydraulic axes H1, H2 are designed as a 2-axis joystick 13, which, in a first main operating direction, functions as the control element 11 for controlling the first hydraulic axis H1, and, in a second main operating direction, which is preferably perpendicular to the first main operating direction, functions as the control element 12 for controlling the second hydraulic axis H2. By operating such a 2-axis joystick 13 in an operating direction lying between the two main operating directions, the two hydraulic axes H1, H2 can be operated and thus actuated simultaneously by the driver.

[0024] In the Fig. 2 shows a schematic circuit diagram of a working hydraulic system 2 of an industrial truck 1 of the prior art, in which the first hydraulic axis H1 is formed by the lifting drive 3 with the lifting cylinder as the hydraulic consumer 6 and the second hydraulic axis H2 is formed by the tilting drive 4 with the tilting cylinder as the hydraulic consumer 8.

[0025] The hydraulic consumer 6 of the first hydraulic axis H1 can be actuated by means of an electrically actuated control valve 15, which is connected on the input side to the hydraulic pump 10. When the first hydraulic axis H1 is designed as a lifting drive 3, the control valve 15 has a blocking position, a lifting position for raising the load-carrying device L, and a lowering position for lowering the load-carrying device L. For the hydraulic axis H1, the operating element 11 is provided, which, when actuated, generates a control voltage U1 for the hydraulic axis H1 as an output signal. When the operating element 11 is designed as a 2-axis joystick 13, the control voltage U1 for the first hydraulic axis H1 is generated when the joystick 13 is actuated in a first main actuation direction. The control voltage U1 generated by the operating element 11 upon corresponding actuation is fed on the input side to an electronic control device 20.The control device 20 is provided with a calculation device 21, which generates a control current I1 from the control voltage U1 for actuating the control valve 15 of the hydraulic axis H1. The control valve 15 of the hydraulic axis H1 is controlled exclusively as a function of the control voltage U1 of the control element 11. The generation of the control current I1 from the control voltage U1 takes place in the calculation module 21 using the function I1 = f(U1).

[0026] The hydraulic consumer 8 of the second hydraulic axle H2 can be actuated by means of an electrically actuated control valve 16, which is connected on the input side to the hydraulic pump 10. When the second hydraulic axle H2 is designed as a tilt drive 4, the control valve 16 has a blocking position, a first control position for tilting the load-handling device L or the lifting mast 5 forward, and a second control position for tilting the load-handling device L or the lifting mast 5 backward. An operating element 12 is provided for the hydraulic axis H2, which, when actuated, generates a control voltage U2 for the hydraulic axis H2 as an output signal. When the operating element 12 is designed as a 2-axis joystick 13, the control voltage U2 for the second hydraulic axis H1 is generated when the joystick 13 is actuated in a second main actuation direction.The control voltage U2 generated by the control element 12 upon corresponding actuation is supplied to the input side of the electronic control device 20. The control device 20 is provided with a calculation device 22, which generates a control current I2 from the control voltage U2 for actuating the control valve 16 of the hydraulic axis H2. The control valve 16 of the hydraulic axis H2 is controlled exclusively as a function of the control voltage U2 of the control element 11. The control current I2 is generated from the control voltage U2 in the calculation module 22 using the function I2 = f(U2).

[0027] In the working hydraulics of the Fig. 2 of the prior art, the driver thus requests and specifies a volume flow for actuating the consumers 6, 8 and thus a corresponding valve deflection of the control valves 15, 16 of the corresponding hydraulic axis H1, H2 by actuating the operating elements 11, 12, wherein the control valves 15, 16 are adjusted to the requested valve deflection by the electronic control device 20 by controlling the control valves 15, 16 in accordance with the requested volume flow.

[0028] If the driver operates both hydraulic axes H1, H2 simultaneously by actuating the operating elements 11, 12 accordingly, operating conditions can occur in which the volume flow and thus the movement speed of the tilt cylinder 8 on the tilt drive 4 (hydraulic axis 2) increases abruptly and quickly when the lifting cylinder 6 of the lifting drive 3 (hydraulic axis 1) reaches a mechanical end stop during lifting, since an abrupt volume flow excess occurs in the tilt drive 4 and thus the second hydraulic axis H2 and the volume flow delivered by the hydraulic pump 10 only flows to the tilt drive 4.

[0029] In the Fig.3 shows a schematic circuit diagram of a working hydraulic system 2 of an industrial truck 1 according to the invention, in which the first hydraulic axis H1 is formed by the lifting drive 3 with the lifting cylinder as the hydraulic consumer 6 and the second hydraulic axis H2 is formed by the tilting drive 4 with the tilting cylinder as the hydraulic consumer 8.

[0030] The hydraulic consumer 6 of the first hydraulic axis H1 can be actuated by means of the electrically actuated control valve 15, which is connected on the input side to the hydraulic pump 10. When the first hydraulic axis H1 is designed as a lifting drive 3, the control valve 15 has a blocking position, a lifting position for raising the load-handling device L, and a lowering position for lowering the load-handling device L. The control valve 15, designed as a control directional valve, is designed as a proportional valve that throttles in intermediate positions. An operating element 11 is provided for the hydraulic axis H1, which, when actuated, generates a control voltage U1 as an output signal. When the operating element 11 is designed as a 2-axis joystick 13, the control voltage U1 is generated when the joystick 13 is actuated in a first main actuating direction.The control voltage U1 generated by the control element 11 upon corresponding actuation is fed to the input side of the electronic control device 20.

[0031] The hydraulic consumer 8 of the second hydraulic axle H2 can be actuated by means of the electrically actuated control valve 16, which is connected on the input side to the hydraulic pump 10. When the second hydraulic axle H2 is designed as a tilt drive 4, the control valve 16 has a blocking position, a first control position for tilting the load-handling device L or the lifting mast 5 forward, and a second control position for tilting the load-handling device L or the lifting mast 5 backward. The control valve 16, designed as a control directional valve, is designed as a proportional valve that throttles in intermediate positions. An operating element 12 is provided for the hydraulic axis H2, which, when actuated, generates a control voltage U2 as an output signal. When the operating element 11 is designed as a 2-axis joystick, the control voltage U2 is generated when the joystick 13 is actuated in a second main actuation direction.The control voltage U2 generated by the control element 12 upon corresponding actuation is fed to the input side of the electronic control device 20.

[0032] The control device 20 is provided for controlling the control valve 16 of the second hydraulic axis H2 with a calculation device 22, to which, according to the invention, the control voltage U2 of the second hydraulic axis H2 and the control voltage U1 of the first hydraulic axis H1 are supplied on the input side and which, depending on the two control voltages U2, U1, generates a control current I2 for actuating the control valve 16 of the hydraulic axis H2. The control of the control valve 16 of the hydraulic axis H2 is thus carried out according to the invention as a function of the output signals from a plurality of control elements 11, 12 of a plurality of hydraulic axes H1, H2 and thus the control voltages U1, U2 of a plurality of hydraulic axes H1, H2. The generation of the control current I2 from the control voltages U1, U2 thus takes place in the calculation module 22 using the function I2 = f(U2, U1), for example using multi-dimensional characteristic curve fields.

[0033] The control device 20 is provided for controlling the control valve 15 of the first hydraulic axis H1 with a calculation device 21, to which, according to the invention, the control voltage U1 of the first hydraulic axis H1 and the control voltage U2 of the second hydraulic axis H1 are supplied on the input side and which, depending on the two control voltages U1, U2, generates a control current I1 for actuating the control valve 15 of the hydraulic axis H1. The control of the control valve 15 of the hydraulic axis H1 is thus carried out according to the invention as a function of the output signals from several control elements 11, 12 of several hydraulic axes H1, H2 and thus the control voltages U1, U2 of several hydraulic axes H1, H2. The generation of the control current I1 from the control voltages U1, U2 thus takes place in the calculation module 21 using the function I2 = f(U1, U2), for example using multi-dimensional characteristic curve fields.

[0034] In the illustrated embodiment, in which the first hydraulic axis H1 forms the lifting drive 3 and the second hydraulic axis H2 forms the tilt drive 4 of the industrial truck 1, when the lifting drive 3 (lifting operation) and the tilt drive 4 are actuated simultaneously, whereby both control voltages U1 and U2 are generated, the control current I2 of the control valve 16 controlling the tilt drive 4 is limited in the calculation module 22 as a function of the control voltage U1 of the first hydraulic axis H1 and thus as a function of the valve deflection of the control valve 15 controlling the lifting drive 3 in lifting operation, as specified by the driver. The control current I2 is preferably limited by reducing the control current I2 when a control voltage U1 of the first hydraulic axis H1 is present. The reduction of the control current I2 of the second hydraulic axis H2 can take place linearly with increasing control voltage U1.With the same deflection of the control element 12 for controlling the second hydraulic axis H2, the simultaneous actuation of both hydraulic axes H1, H2 and thus an additional parallel operation of the first hydraulic axis H1 results in a lower control current I2 and thus a lower valve deflection of the control valve 16 than with sole actuation of the second hydraulic axis H2. With the simultaneous actuation of both hydraulic axes H2, H1, the valve deflection of the control valve 16 specified by the driver and thus the volume flow (volume flow setpoint) of the second hydraulic axis H2 requested by the driver by actuating the control element 12 is reduced.

[0035] This ensures that, in an operating state in which both hydraulic axes H2, H1 are actuated, the abruptly occurring excess volume flow in the second hydraulic axis H2 is reduced when the volume flow of the first hydraulic axis H1 changes quickly, for example when the consumer 6 of the first hydraulic axis H1 moves against a mechanical end stop. By reducing the control current I2 of the second hydraulic axis H2 and thus reducing the volume flow requirement of the second hydraulic axis H2 specified by the driver as a function of the control voltage U1 during parallel actuation of the first hydraulic axis H1, sudden acceleration and sudden changes in the movement speed of the second hydraulic axis H2 that are not specified by the driver can be reduced.

[0036] In the illustrated embodiment, in which the first hydraulic axis H1 forms the lifting drive 3 and the second hydraulic axis H2 forms the tilt drive 4 of the industrial truck 1, when the lifting drive 3 (lifting operation) and the tilt drive 4 are actuated simultaneously, whereby both control voltages U1 and U2 are generated, the control current I1 of the control valve 15 controlling the lifting drive 3 in lifting operation is limited in the calculation module 21 as a function of the control voltage U2 of the second hydraulic axis H2 and thus as a function of the valve deflection of the control valve 16 controlling the tilt drive 4, as specified by the driver. The control current I1 is preferably limited by reducing the control current I1 when a control voltage U2 of the second hydraulic axis H2 is present. The reduction of the control current I1 of the first hydraulic axis H1 can take place linearly with increasing control voltage U2.With the same deflection of the control element 11 for controlling the first hydraulic axis H1, the simultaneous actuation of both hydraulic axes H1, H2 and thus an additional parallel operation of the second hydraulic axis H2 results in a lower control current I1 and thus a lower valve deflection of the control valve 15 than with sole actuation of the first hydraulic axis H1. With the simultaneous actuation of both hydraulic axes H1, H2, the valve deflection of the control valve 15 specified by the driver and thus the volume flow (volume flow setpoint) of the first hydraulic axis H1 requested by the driver by actuating the control element 11 is reduced.

[0037] In the industrial truck 1 according to the invention, a reduction of rapid speed changes of the consumer movements of the hydraulic axes H2, H1, which result from spontaneous and rapid pressure changes or volume flow changes, is thus achieved in the case of simultaneous and thus parallel actuation of several hydraulic axes H1, H2 by the mutual influence of the hydraulic axes H1, H2, wherein the control current I2 or I1 of a hydraulic axis H2 or H1 is generated during the parallel actuation of another hydraulic axis H1 or H2 as a function of the control voltage U1 or U2 of the parallel actuated hydraulic axis H1 or H2.

[0038] Because the invention allows sudden volume flow changes of a hydraulic axis H2 or H1 to be reduced during the parallel operation of another hydraulic axis H1 or H2, particular advantages arise when the second hydraulic axis H2 is designed as a tilt drive 4, since unwanted and rapid tilting movements of the lifting mast 5 or the load-carrying device L can be avoided when the tilt drive 4 and the lifting drive 3 are operated simultaneously during lifting operation.

[0039] In the invention, a volume flow limitation thus takes place at the control valves 15, 16 of the hydraulic axes H1, H2, which are designed as proportional valves, depending on multi-dimensional characteristic fields of the control voltages U1, U2. Since sudden changes in the volume flow of a hydraulic axis H2 or H1 when another hydraulic axis H1 or H2 is operated in parallel in the industrial truck according to the invention are achieved by influencing (reducing) the control currents I2, I1 of a hydraulic axis H2, H1 and thus by reducing the volume flow requirement of a hydraulic axis H2, H1 specified by the driver, sudden changes in the volume flow of a hydraulic axis H2 or H1 and thus sudden and rapid changes in speed at the consumer 8 or 6 when another hydraulic axis H1 or H2 is operated in parallel can be prevented or compensated for with simple and cost-effective control valves 15, 16.can be reduced and no additional valves are required to reduce sudden volume flow changes of a hydraulic axis H2 or H1.

[0040] The invention is not limited to the illustrated embodiment with two hydraulic axes H1, H2. It is understood that more than two hydraulic axes can be provided, and the influencing (reduction) of the control current of a hydraulic axis during simultaneous actuation of multiple hydraulic axes can be achieved by the control voltages of all hydraulic axes actuated in parallel.

[0041] Instead of a linear reduction of the control current I2 or I1 of a hydraulic axis H2 or H1 as a function of the control voltage U1 or U2 of a simultaneously actuated hydraulic axis H1 or H2, another type of influencing the control current I2 or I1 by the control voltage U1 or U2 can be provided, wherein the influencing, for example a limitation, of the control current I2 or I1 can be carried out by a freely definable mathematical function.

[0042] In addition, the control (requested volume flow) of a hydraulic axle H1 or H2 specified by the driver by actuating the control element 11 or 12 can be reduced not only by the control voltage U2 or U1 and thus by the specified value of one or more hydraulic axes H2 or H1 operated in parallel, but also as a function of the volume flow supplied by the hydraulic pump 10 and thus the available volume flow. When several hydraulic axes H1, H2 are actuated simultaneously, the volume flow supplied by the hydraulic pump 10 can be calculated by the electronic control device 20 or measured using a sensor device and fed to the calculation modules 21, 22. As a result, when several hydraulic axes H1, H2 are actuated simultaneously, an undersupply of the control valve 15, 16 can be avoided or prevented by appropriately reducing the control current I1, I2.be reduced so that when the undersupply is ended, a sudden and rapid increase in the volume flow and thus the movement speed at the consumers 6, 8 is prevented. When several hydraulic axes H1, H2 are actuated simultaneously and thus in parallel, there is a mutual influence of the specifications for the volume flow supply of the control valves 15, 16 and the specifications of the total requested volume flows of the hydraulic axes H1, H2.

Claims

[1] Industrial truck (1) with a working hydraulic system (2) comprising at least two hydraulic axles (H1, H2), for the supply of which with pressure medium a hydraulic pump (10) is provided, wherein each hydraulic axle (H1; H2) has a hydraulic consumer (6; 8) which can be actuated by means of an electrically actuated control valve (15; 16), and for each hydraulic axle (H1; H2) an operating element (11; 12) is provided which, when actuated, generates a control voltage (U1; U2) for the hydraulic axle (H1; H2) as an output signal, wherein an electronic control device (20) is provided which generates a control current (I1; I2) from the control voltage (U1; U2) for actuating the control valve (15; 16) of the hydraulic axle (H1; H2), characterized bythat the electronic control device (20) is designed such that the generation of the control current (I2; I1) of the control valve (16; 15) of a hydraulic axis (H2; H1) takes place as a function of the control voltage (U2; U1) of the hydraulic axis (H2; H1) and the control voltage (U1; U2) of at least one further hydraulic axis (H1; H2). [2] Industrial truck according to claim 1, characterized by that the electronic control device (20) is designed such that the control current (I2; 11) of the control valve (16; 15) of a hydraulic axis (H2; H1) is limited as a function of the control voltage (U1; U2) of at least one further hydraulic axis (H1; H2). [3] Industrial truck according to claim 1 or 2, characterized bythat the electronic control device (20) is designed such that when several hydraulic axes (H2, H1; H1, H2) are actuated simultaneously, the actuation current (I2; 11) of the control valve (16; 15) of a hydraulic axis (H2; H1) is reduced as a function of the control voltage (U1; U2) of at least one further hydraulic axis (H1; H2) compared to the actuation current (I2; 11) of the control valve (16; 15) of the hydraulic axis (H2; H1) when the hydraulic axis (H2; H1) is actuated alone. [4] Industrial truck according to claim 2 or 3, characterized by that the limitation of the control current (I2; 11) is freely programmable. [5] Industrial truck according to one of claims 1 to 4, characterized bythat the working hydraulics (2) has, as a hydraulic axis (H1), a lifting drive (3) for raising and lowering a load-handling device (L) and, as a further hydraulic axis (H2), a tilting drive (4) for tilting the load-handling device (L) forwards (V) and backwards (R), wherein the electronic control device (20) is designed such that when the lifting drive (3) is actuated simultaneously in a lifting operation and the tilting drive (4), the control current (I2) of the control valve (16) of the tilting drive (4) is limited as a function of the control voltage (U1) of the lifting drive (3). [6] Industrial truck according to claim 5, characterized by that the electronic control device (20) is designed such that when the lifting drive (3) in a lifting operation and the tilting drive (4) are actuated simultaneously, the control current (I1) of the control valve (15) of the lifting drive (3) is limited as a function of the control voltage (U2) of the tilting drive (4). [7] Industrial truck according to one of claims 1 to 6, characterized by that the electronic control device (20) determines the volume flow provided by the hydraulic pump (10) and, when several hydraulic axes (H1, H2) are actuated simultaneously, influences the control current (I1; I2) of the control valve (15; 16) of at least one hydraulic axis (H1; H2) as a function of the volume flow provided by the hydraulic pump (10). [8] Industrial truck according to one of claims 1 to 7, characterized by that the operating elements (11, 12) are formed by at least one 2-axis joystick (13).

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