forklift

Abstract

Industrial truck comprising a battery (10) and a battery management system (20) connected to the battery (10), which is supplied with energy by the battery (10), wherein the battery (10) comprises several battery strings (12a - 12d) each having battery cells (14) connected in series, characterized by a control unit (30) which is configured to selectively connect or disconnect one or more of the battery strings (12a - 12d) from the battery management system (20).

Description

[0001] The invention relates to a forklift truck comprising a battery and a battery management system connected to the battery, which is supplied with energy by the battery, wherein the battery comprises several battery strings, each having battery cells connected in series.

[0002] A forklift truck is used to transport loads. These trucks typically consist of a drive unit and a load unit. The battery, along with the electric drive, is usually located in the drive unit, while the load unit comprises the load-bearing device. For example, the forklift truck might be a forklift, in which case the load unit could include a height-adjustable mast with load forks. In electrically powered forklift trucks, the battery primarily serves to power the drive system, thus enabling the truck to move and, if applicable, to lift the mast. The battery management system itself is also powered by the battery. A battery management system is a generally known control unit for monitoring, regulating, and protecting the battery cells.In particular, the battery management system serves to detect and monitor the battery's state of charge. In conventional batteries, the battery cells are usually grouped into so-called battery strings and connected in series, with the individual battery strings themselves being connected in parallel.

[0003] In conventional industrial trucks, the battery management system typically draws its power from the battery string with the highest voltage. Diodes can be used to determine which battery string is supplying the system. However, if some or all of the battery strings have similar voltages, the commonly used wiring configuration usually makes it impossible to reliably identify which string is currently powering the system. This has several disadvantages. Firstly, because the battery management system is powered by only one battery string at a time, that string is subjected to a higher, continuous load, which can lead to faster cell failure in that string.Secondly, a reliable determination of the state of charge cannot be carried out if it cannot be reliably determined from which of the battery strings the battery management system draws its energy.

[0004] Based on the prior art described above, the invention aims to provide a forklift truck whose battery has the longest possible lifespan.

[0005] US patent 2012 / 0043819 A1 discloses an energy storage device and a charger that incorporates a battery management system for controlling the charging and discharging of the battery. The battery management system is designed for both external power supply and power supply from the battery itself. The battery management system is hierarchically structured as a sequence of individual battery management systems.

[0006] From EP 3 103 182 B1 a battery management system has become known in which a battery management system can react to a standby mode of the battery and a sleep mode of the battery.

[0007] The preamble of the subject matter of claim 1 is known from German patent application DE 10 2017 204 065 A1 and relates to a drive system with a battery which includes several battery strings, wherein these can be selectively connected to the drive system.

[0008] The invention solves the problem by means of a forklift truck according to claim 1. Advantageous embodiments are the subject of the dependent claims, the description and the figures.

[0009] The industrial truck according to the invention of the type mentioned at the outset comprises a control unit which is designed to selectively connect or disconnect one or more of the battery strings from the battery management system.

[0010] As mentioned at the outset, the battery of the industrial truck comprises several battery strings, consisting in particular of battery cells connected in series. These battery strings can, in turn, be connected in parallel to achieve the total battery capacity. The battery management system is powered by the battery. As also mentioned previously, the battery can be used to power the drive system. However, in contrast to the prior art described above, the battery strings are not all permanently connected to the battery management system, but can be selectively connected to it using the control unit according to the invention. The control unit can therefore connect or disconnect individual battery strings, and in particular each battery string, from the battery management system.According to the invention, the control unit allows for the selective connection of individual battery strings to the battery management system or the disconnection of individual battery strings from the battery management system. In other words, in the industrial truck according to the invention, the battery strings can be connected to or disconnected from the battery management system independently of one another. The control unit can thus control the load on the individual battery strings—and therefore on the battery cells within each battery string. For example, a battery string that has previously been heavily loaded can be disconnected from the battery management system by the control unit. This prevents it from being further loaded. Consequently, the control unit can achieve a uniform load on all battery strings by selectively connecting and disconnecting them.In this context, "connecting a battery string" always means connecting the battery string to the battery management system, and "disconnecting a battery string" always means disconnecting the battery string from the battery management system.

[0011] Furthermore, the control unit knows which battery string the battery management system draws its energy from. Specifically, it always draws energy only from the battery string(s) connected to the battery management system by the control unit. This allows for a more reliable determination of the state of charge of the individual battery strings and, in particular, the entire battery. Especially when only one battery string is connected to the battery management system, the state of charge of that battery string can be reliably determined from the supply current and, in particular, the supply voltage of the battery management system. The state of charge of the battery or the individual battery strings can be determined via the control unit or the battery management system. Specifically, the control unit can be part of the battery management system.The control unit can, for example, comprise a microcontroller with software. In particular, the control unit can be designed to prevent mutual interference between the battery strings. For example, a diode can be provided in each of the supply lines leading from the battery strings to the battery management system, preventing charging current from flowing from one battery string to another. Specifically, exactly one battery string can be connected to the battery management system via the control unit at any given time. It is also possible to connect multiple, and in particular all, battery strings to the battery management system simultaneously via the control unit.

[0012] In one embodiment, the control unit is configured to selectively connect or disconnect the battery strings from the battery management system, depending on their respective charge levels. According to this embodiment, the control unit thus connects the individual battery strings to the battery management system's power supply based on their respective charge levels. For example, the control unit can be configured to determine the charge levels of the individual battery strings and connect the string with the highest charge level to the battery management system. Alternatively, the control unit can be configured to connect battery strings whose charge levels exceed a defined threshold to the battery management system and to disconnect those whose charge levels fall below this threshold.The limit can be set, for example, at 50% of the nominal or maximum charge. By connecting and disconnecting the battery strings from / to the battery management system based on the state of charge, the control unit can ensure a uniform discharge of the battery.

[0013] In one embodiment, the control unit is configured to take the supply current of the battery management system into account for determining the state of charge. Specifically, the control unit determines the state of charge(s) of the battery string(s) connected to the battery management system. In particular, the control unit can connect the individual battery strings of the battery to the battery management system sequentially and alternately, whereby the control unit or the battery management system can determine the state of charge of the entire battery from the state of charge of the individual battery strings. The supply current can be measured using an ammeter, whereby a common ammeter can be provided for all battery strings or an individual ammeter for each battery string.For example, each supply line extending between one of the battery strings and the battery management system can have a current meter. In one embodiment, a current meter is arranged in a common supply line leading from the battery strings to the battery management system. Thus, in particular, only one current meter can be provided, which can be used to determine the state of charge of the battery string(s) connected to the battery management system. The individual supply lines of the battery strings mentioned above can be combined into the common supply line.

[0014] In a further embodiment, the control unit is designed to consider one or more of the following parameters to determine the state of charge: string voltages of the battery strings, cell voltages of the battery cells. Consequently, in addition to the aforementioned supply current, the control unit can also consider the string voltages of the connected battery strings and / or the cell voltages of the battery cells in the connected battery strings. This allows for a more reliable determination of the state of charge of the respective battery string or the total battery capacity.

[0015] In one embodiment, the control unit is configured to connect or disconnect the battery strings from the battery management system depending on one or more of the following parameters: time, string voltages, and cell voltages. The control unit can therefore connect or disconnect individual battery strings based on a time factor. For example, the age of the battery cells in a battery string can be considered as a time factor, and the control unit can be configured to connect battery strings with newer cells to the battery management system sooner than battery strings with older cells. This allows the age of the battery cells to be taken into account and thus increases the battery's lifespan.Another form of time-based control involves alternately connecting and disconnecting the individual battery strings to the battery management system at specific intervals. For example, the control unit can initially connect a first battery string to the battery management system for a defined period, while the other battery strings remain disconnected. Subsequently, the control unit can connect a second battery string to the battery management system and disconnect the first. After the defined period has elapsed, the second battery string can again be disconnected, and a third battery string can be connected, once more for a defined period. This period could, for example, be 10 minutes.For example, the control unit can also control the battery strings depending on the energy demand of the battery management system. During a start-up phase of the battery management system, a large number of battery strings, or even all of them, can be connected to supply power to the system. The control unit can also consider the string voltage or the cell voltages of the individual battery cells within the strings. This is particularly useful for determining the state of charge, as mentioned above. However, according to the current configuration, these voltages can also serve as control parameters for switching on and off without explicitly determining the state of charge.

[0016] In one embodiment, the supply lines running between the battery strings and the battery management system each have a switch, with the control unit being configured to actuate the switches independently. The control unit can thus use these switches to connect or disconnect the individual battery strings to supply the battery management system. The control unit can therefore use the switches to connect or disconnect the respective battery strings from the battery management system. The switches can be implemented, for example, as transistors, relays, or similar devices. In another embodiment, the control unit is configured to determine, based on the supply voltages present on the supply lines, whether one of the switches is defective.For this purpose, voltage measuring devices connected to the control unit can measure the voltage, particularly on each individual supply line. From the supply voltage of one of the supply lines, the control unit can determine whether the switch belonging to that supply line is defective. For example, if the control unit sends the switch a command to close, but the corresponding supply line shows no voltage, then the switch is likely defective.

[0017] In one design, the control unit is integrated as part of the battery management system. As mentioned above, the battery management system can therefore encompass the functionalities of the control unit.

[0018] Two embodiments of the invention are explained below with reference to the figures. They schematically show: Fig. 1 a supply circuit for a battery of a forklift truck according to a first embodiment, and Fig. 2 a supply circuit for a battery of a forklift truck according to a second embodiment.

[0019] Unless otherwise stated, the same reference symbols refer to the same objects.

[0020] Fig. Figure 1 shows a power supply circuit for a forklift truck according to a first embodiment. The power supply circuit comprises a battery 10 with battery strings 12a to 12d, collectively designated by reference numeral 12, each of which has several battery cells 14. In the present embodiment, the battery 10 comprises four battery strings 12a to 12d, each with four battery cells. This is purely schematic, however. The battery can also have any other number of battery strings, which can have any other number of battery cells. The individual battery strings 12a to 12d can be selectively connected to consumers (not shown), such as a forklift truck drive, via switches 16. The individual battery strings 12 are connected to a battery management system 20 via supply lines 18.Each of the supply lines 18 has a switch 22, see switches 22a to 22d. Between their switch 22 and the battery management system 20, the supply lines 18 also each have a diode 24. Between the diodes 24 and the battery management system 20, the supply lines 18 converge to form a common supply line 26, which leads to the battery management system 20 and includes a current meter 28.

[0021] According to the invention, a control unit 30 is provided which is configured to selectively connect or disconnect the battery strings 12a to 12d from the battery management system 20. For this purpose, the control unit 30 is configured to control switches 22a to 22d. The switches can be, for example, transistors or relays. The control unit 30 can control the switches 22 independently of one another, with the effect of the control unit 30 on the switches 22 being represented by dashed arrow lines. For example, the control unit 30 can connect battery string 12a to the battery management system 20 by moving switch 22a. Likewise, the control unit 30 can connect battery strings 12b to 12d to the battery management system 20 by moving the other switches 22b to 22d.This enables the individual battery strings 12 to be switched on and off separately for the power supply of the battery management system 20. This allows it to be reliably determined at any time which of the battery strings 12 is supplying power to the battery management system. This, in turn, allows the state of charge of the battery string connected to the battery management system to be reliably determined, especially when only one battery string is connected to the battery management system.

[0022] The state of charge of each connected battery string can be determined, among other things, from the supply current flowing through the respective supply line 18 to the battery management system 20, as measured by the measuring device 28. This supply current can be determined by the current measuring device 28 and tapped by the control unit 30, as shown by the dashed arrow. The voltage present at the respective connected supply line 18 and / or the cell voltages of the battery cells 14 can also be taken into account to determine the state of charge.

[0023] Switching, i.e., selectively connecting or disconnecting the battery strings from the battery management system, can occur depending on various system parameters, such as the state of charge of the battery strings. For example, if the state of charge of battery string 12a is higher than the state of charge of the remaining battery strings 12b to 12d, the battery management system 20 can be supplied primarily via battery string 12a. The control unit 30 can close switch 22a for this purpose. The string voltages or cell voltages can also serve as parameters for switching without prior determination of the state of charge of the battery strings.The control unit can also connect the different battery strings 12 to the battery management system 20 by switching the switches 22, depending on, for example, a time parameter or the current energy demand of the battery management system 20. For example, the control unit 30 can be configured to connect all battery strings 12 to supply the battery management system 20 during a startup phase. After the startup phase, the control unit can, for example, disconnect battery strings 12b to 12d from the battery management system 20 by opening switches 22b to 22d, so that the battery management system 20 is then only supplied with energy via battery string 12a.After a defined period of time – for example, 10 minutes – the control unit 30 can then close switch 22b and open switch 22a, so that the battery management system 20 is powered solely by battery string 12b. The other battery strings 12 can also be switched alternately in this manner; in particular, all battery strings can be switched on and off multiple times in an alternating fashion. This ensures that all battery strings 12 contribute equally to the power supply. The battery cells 14 of the individual battery strings 12 are discharged evenly, and no excessive load occurs on any single battery string.

[0024] The diodes 24 prevent unwanted equalizing currents from flowing between the battery strings 12 in the event that several battery strings 12 are simultaneously connected to the battery management system 20.

[0025] The design in Fig. 2 differs in its design from Fig. 1. The only difference is that a voltage measuring device 32 is provided between the switches 22 and the diodes 24 in each of the supply lines 18. By reading the voltage values, the control unit 30 can determine whether one of the switches 22 is defective. For example, if one of the switches 22 is closed due to activation by the control unit 30, but the corresponding voltage measuring device 32 does not detect a voltage value, this indicates that the switch is defective. Reference symbol list 10 batteries 12 battery strings 12a - 12d battery strings 14 battery cells 16 switches 18 supply lines 20 Battery Management System 22 switches 22a - 22d switch 24 diodes 26 joint supply lines 28 Current meter 30 control unit 32 voltage measuring devices

Claims

[1] Industrial truck comprising a battery (10) and a battery management system (20) connected to the battery (10) which is supplied with energy by the battery (10), wherein the battery (10) comprises several battery strings (12a - 12d) each having battery cells (14) connected in series, characterized by a control unit (30) designed to selectively connect or disconnect one or more of the battery strings (12a - 12d) from the battery management system (20). [2] Industrial truck according to claim 1, characterized by , that the control unit (30) is designed to selectively connect the battery strings (12a - 12d) to the battery management system (20) or to disconnect them from the battery management system (20), depending on their charge levels. [3] Industrial truck according to claim 2, characterized by, that the control unit (30) is designed to take into account the supply current of the battery management system (20) for a determination of the state of charge. [4] Industrial truck according to claim 3, characterized by , that a current measuring device (28) is arranged in a common supply line (26) leading from the battery strings (12a - 12d) to the battery management system (20). [5] Industrial truck according to any one of claims 2 to 4, characterized by , that the control unit (30) is designed to take into account one or more of the following set of parameters to determine the state of charge: string voltages of the battery strings (12a - 12d), cell voltages of the battery cells (14). [6] Industrial truck according to any one of the preceding claims, characterized by, that the control unit (30) is configured to connect or disconnect the battery strings (12a - 12d) from the battery management system (20) depending on one or more of the following set of parameters: time, energy demand of the battery management system (20), string voltages of the battery strings (12a - 12d), cell voltages of the battery cells (14). [7] Industrial truck according to any one of the preceding claims, characterized by , that supply lines (18) running between the battery strings (12a - 12d) and the battery management system (20) each have a switch (22a - 22d), wherein the control unit (30) is designed to control the switches (22a - 22d) independently of each other. [8] Industrial truck according to claim 7, characterized by, that the control unit (30) is designed to determine, on the basis of the supply voltages applied to the supply lines (18, 26), whether one of the switches (22a - 22d) is defective. [9] Industrial truck according to any one of the preceding claims, characterized by , that the control unit (30) is designed as part of the battery management system (20).

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