Control procedure for industrial trucks

Abstract

Control method for an industrial truck with a travel drive consisting of an electric motor, in particular an asynchronous three-phase motor, wherein the torque of the electric motor can be regulated by a control unit as a function of the speed, wherein the control unit controls power electronics of the power supply of the electric motor, wherein a normal state and at least one further energy-saving state can be set by a signal to the control unit and the control unit sets a normal characteristic curve of the torque (20) of the electric motor as a function of the speed in the normal state and sets a reduced characteristic curve of the torque (21) of the electric motor as a function of the speed in the energy-saving state.

Description

[0001] The invention relates to a control method for a forklift truck.

[0002] Despite optimized drive systems, industrial trucks such as counterbalance forklifts and reach trucks still have relatively high energy consumption, resulting in significant energy costs, particularly fuel costs for combustion engine-powered trucks. Furthermore, energy costs are expected to rise in the future, both for charging battery-powered trucks and for fuel used in combustion engine trucks.

[0003] The usage profile of industrial trucks varies greatly, and in many cases, usage profiles occur in which the industrial truck does not continuously drive and pick up or put down a load, but rather in which such usage times are interrupted by waiting times.

[0004] When a forklift is driven at maximum possible speed and acceleration, energy consumption is highest when calculated per unit of distance traveled. However, if the driver does not utilize the full possible speed or acceleration, it becomes difficult to assess whether the resulting reduction in working speed is justified by the energy savings, and whether these energy savings are sufficient to achieve, for example, the desired interval between battery changes.

[0005] Furthermore, additional electrical consumers are usually switched on by the driver and remain active until they are switched off again. This can lead, for example, to a seat heater operating even though the driver is not sitting in the seat equipped with the heater. Particularly when briefly leaving the forklift, for example for order picking, consumers are often not switched off by the driver and continue to draw power from a battery or another energy source, such as a generator driven by a diesel or gas engine.

[0006] From DE 42 05 770 A1 a vehicle with an internal combustion engine, electric generator and electric motor is known.

[0007] DE 102 60 355 A1 discloses a forklift truck with an electric drive.

[0008] The present invention is therefore based on the objective of providing a control method for a forklift truck that leads to a reduction in energy consumption without noticeably impairing the handling performance of the forklift truck.

[0009] This problem is solved by a method having the features of claim 1 and a forklift truck having the features of claim 15. Advantageous embodiments of the invention are specified in the dependent claims.

[0010] The problem is solved according to the invention by a control method for a forklift truck with a drive system consisting of an electric motor, in particular an asynchronous three-phase motor, wherein the torque of the electric motor can be controlled by a control unit as a function of the speed. The control unit controls power electronics for the electric motor's power supply. A normal state and at least one further energy-saving state can be set by means of a signal to the control unit, and the control unit sets a normal torque characteristic of the electric motor as a function of the speed in the normal state and a reduced torque characteristic of the electric motor as a function of the speed in the energy-saving state.

[0011] When using an electric motor as a drive system, especially a three-phase motor, the torque can be controlled cost-effectively and efficiently, for example by controlling the inverters.

[0012] This allows the energy consumption of the industrial truck to be favorably influenced by controlling the torque characteristic curve as a function of rotational speed and thus speed. Reducing the torque primarily results in a slight decrease in the truck's dynamics, as the acceleration is reduced. However, energy consumption decreases disproportionately. The method according to the invention allows for adaptation to different operating profiles of industrial trucks. For example, in an operating profile with frequent short idle times, the energy-saving mode leads to longer operating times for the industrial truck and shorter idle times, as the acceleration times are extended. Overall, however, the same throughput is achieved, but with lower energy consumption.

[0013] Advantageously, the reduction of torque occurs primarily in a range of medium speeds within the speed band of the drive system, particularly in a speed band from 0 rpm to 5000 rpm in a range between 500 rpm and 3000 rpm.

[0014] Reducing power output in the mid-range significantly lowers energy consumption. However, the loss of dynamics is relatively minor and not perceived as disruptive. Because the reduction occurs in the middle part of the performance curve, top speed and acceleration remain unchanged. The gradeability and tractive force of the forklift truck are maintained. Reaching top speed takes a slightly longer time.

[0015] Advantageously, several energy-saving states with reduced torque characteristics can be set.

[0016] This allows for more precise adaptation to different usage profiles.

[0017] In a favorable embodiment, a battery powers the drive system, and the control unit measures or calculates the energy consumption of the industrial truck over a measurement period. Based on the battery's state of charge and the desired operating time before a battery change, it determines and sets a required energy-saving mode. The measurement or calculation of power consumption and the setting of the energy-saving mode can be repeated.

[0018] This allows for automatic adjustment and ensures that premature battery replacement is not necessary, which leads to greater disadvantages and costs than the slower operating speed.

[0019] Alternatively, the control unit could measure idle times or speeds traveled during operation and use this data to determine an operating profile. From this profile, a usable energy-saving state, and thus maximum energy savings for the continued operation of the industrial truck, could then be determined.

[0020] It is advantageous to be able to set an initial energy-saving mode when putting the industrial truck into operation.

[0021] This allows an energy-saving state to be set from the moment the vehicle is put into operation, e.g. at the start of a work shift, and prevents the driver from subjectively getting the impression that the industrial truck is losing power.

[0022] In a favorable embodiment, the signal is sent to the control unit from a switch that can be operated by a driver.

[0023] This allows the desired energy saving to be switched on or, in the case of multiple levels, adjusted.

[0024] The signal to the control unit can be sent by a wireless receiving unit, in particular an RFID receiving unit, and the wireless receiving unit can establish a connection with a central computer.

[0025] This allows the energy-saving mode to be set depending on the operating range of the industrial truck, for example, when low energy consumption is required due to terrain conditions or the transport tasks typically performed there, to ensure, for instance, that a battery lasts for an entire shift. If several industrial trucks using the inventive method are connected to a central computer, e.g., in a warehouse, and continuously transmit their data, such as battery charge level and operating profiles, to the central computer, this central computer can assign an optimal energy-saving mode to each industrial truck, depending on its planned use.

[0026] Advantageously, consumers can be switched off if the industrial truck is inactive for a minimum period of time or if a driver's seat is unoccupied, and switched back on when the driver's seat is occupied again or a control command is sent to the industrial truck.

[0027] This can save up to 50% of the energy required by these consumers.

[0028] Potentially beneficial consumers of power could be a driver's compartment heater and / or a driver's seat heater and / or searchlights. Another potential consumer could be the headlights, which might switch to parking lights.

[0029] In a favorable embodiment, consumers used depending on the direction of travel, in particular searchlights and windscreen wipers, can be switched off when driving in the opposite direction.

[0030] The object of the invention is also solved by a forklift truck with a drive system whose torque can be controlled by a control unit depending on the speed, in which the control unit performs a previously described method.

[0031] Further advantages and details of the invention are explained in more detail with reference to the exemplary embodiments shown in the schematic figures. Here, Fig. 1 a counterbalance forklift truck in which the control method according to the invention is used, in side view, Fig. 2. A torque-to-speed diagram of the drive motor of the counterbalance forklift truck. Fig. 1, Fig. 3 an operating phase diagram of the counterbalance forklift truck of the Fig. 1 with the control method according to the invention during normal operation and Fig. 4 an operating phase diagram of the counterbalance forklift truck of the Fig. 1 with the control method according to the invention during operation in energy-saving mode.

[0032] The Fig. Figure 1 shows a forklift truck in which a control method according to the invention is used, in a side view with a lifting mast 1 on which load-handling devices 2 can be lifted with a load. A driving headlight 3 is directed forward and a searchlight 4 is mounted on a driver's cab 5. A driver's seat 6 is located in the driver's cab 5. The drive wheels 7 of the industrial truck, which is designed as an electric counterbalance forklift with a counterweight 8, are driven by a three-phase motor (not shown). A control unit (also not shown) can regulate the torque of the three-phase motor depending on the speed.

[0033] Fig. Figure 2 shows a diagram of the torque versus the speed of the three-phase motor of the counterbalance forklift truck. Fig. 1. The torque is shown on the vertical axis as a percentage of the maximum value. The horizontal axis shows the rotational speeds from 0 to 6000 rpm. The upper line with the circular dots shows the torque curve of normal operating conditions 20. Starting at 0 rpm, the torque remains at 100% up to 1000 rpm and then drops to below 20% at 3000 rpm.

[0034] The line below with the rectangular dots shows the torque curve in energy-saving mode 21. The torque remains at 100% only up to 500 rpm and then drops below the normal-state torque curve 20 until 3000 rpm. Above this value, both curves 20 and 21 are identical again.

[0035] Fig. Figure 3 shows an operating phase diagram of the counterbalance forklift truck. Fig. Figure 1 shows the control method according to the invention during normal operation. Operating phases are shown sequentially in time, as indicated by the arrow. An operating period of 160 minutes (30) with a final battery charge level of 63% is followed by a standby period (31) of 15 minutes. An operating period of 180 minutes (32) with a final battery charge level of 22% is followed by a standby period (33) of 10 minutes. After a further operating period (34) of 90 minutes, the battery is discharged, and the forklift cannot be used during the remaining period (35), e.g., part of a work shift.

[0036] Fig. Figure 4, in contrast, shows an operating phase diagram of the counterbalance forklift truck. Fig.Figure 1 shows the operation of the control method according to the invention during the energy-saving state. The operating phases are again shown sequentially in time, as indicated by the arrow. An operating period of 165 minutes (40) with a final battery charge level of 66% is followed by a standby period of 10 minutes (41). An operating period of 185 minutes (42) with a final battery charge level of 28% is followed by a standby period of 4 minutes (43). After a further operating period of 93 minutes (44), the battery charge level is 9%, and the forklift can continue to be used for a remaining period of 22 minutes (45). However, the same throughput was achieved up to this remaining period (45); only the standby periods (41, 43) were shortened, and the operating periods (40, 42, 44) were correspondingly extended.

[0037] Thus, energy savings and more efficient use of a forklift truck can be achieved through the method according to the invention by adapting it to the operating profile and its downtime. Since the torque is only reduced in the medium speed range, the same maximum speed and starting tractive effort are achieved. Only the acceleration is reduced. However, this already leads to a significant energy saving.

[0038] Additionally, the driving light 3 and the searchlight 4 can be switched off or switched to parking lights when the forklift is reversing or the driver's seat 6 is unoccupied. When the driver's seat is occupied again, they are switched back on.

Claims

[1] Control method for a forklift truck with a drive system consisting of an electric motor, in particular an asynchronous three-phase motor, wherein the torque of the electric motor can be controlled by a control unit depending on the speed, wherein the control unit controls a power electronics supply of the electric motor, wherein a normal state and at least one further energy-saving state can be set by means of a signal to the control unit and the control unit sets a normal characteristic curve of the torque (20) of the electric motor depending on the speed in the normal state and sets a reduced characteristic curve of the torque (21) of the electric motor depending on the speed in the energy-saving state. [2] Control method according to claim 1, characterized by that the reduction in torque essentially takes place in a range of medium speeds within the speed band of the drive system. [3] Control method according to claim 2, characterized by , that the reduction of torque occurs in a speed range of 0 rpm to 5000 rpm within a range between 500 rpm and 3000 rpm. [4] Control method according to any one of the preceding claims, characterized by , that several energy-saving states with reduced torque characteristics are set. [5] Control method according to any one of claims 1 to 4, characterized by , that a battery is used to power the drive system and the control unit measures or calculates the energy consumption of the industrial truck over a measurement period and determines and sets a required energy saving state from the battery's state of charge and a desired operating time until a battery change. [6] Control method according to claim 5, characterized by that the measurement or calculation of electricity consumption and the setting of the energy-saving state are repeated. [7] Control method according to claim 5 or 6, characterized by , that an initial energy-saving state can be set when the industrial truck is put into operation. [8] Control method according to any one of the preceding claims, characterized by , that the signal to the control unit is sent from a switch that can be operated by a driver. [9] Control method according to any one of the preceding claims, characterized by that the signal is sent to the control unit from a wireless receiving unit, in particular an RFID receiving unit. [10] Control method according to claim 9, characterized by that the wireless receiving unit can establish a connection with a central computer. [11] Control method according to any one of the preceding claims, characterized by, that consumers are switched off when the industrial truck is inactive for a minimum period of time or a driver's seat (6) is unoccupied, and are switched on again when the driver's seat (6) is occupied again or a control command is given to the industrial truck. [12] Control method according to claim 11, characterized by , that the consumers are a driver compartment heater and / or a driver seat heater and / or searchlights (4) [13] Control method according to claim 11 or 12, characterized by , that one consumer is the driving light (3) which is switched to parking light. [14] Control method according to any one of the preceding claims, characterized by , that consumers used depending on the direction of travel, in particular searchlights (4) and windscreen wipers, are switched off when driving in the opposite direction. [15] Industrial truck with a drive system whose torque can be controlled by a control unit depending on the speed, wherein the control unit performs a method according to one of claims 1 to 14.

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