Fuel cell hybrid system for a mobile work machine

Abstract

The invention relates to a fuel cell hybrid system (1) for a mobile work machine, in particular a forklift truck, comprising a hydrogen-powered fuel cell unit (5) and a battery (6), wherein the fuel cell unit (5) is configured to charge the battery (6), and a control unit configured to determine the state of charge (SOC) of the battery (6). The battery (6) exhibits a substantially linear voltage characteristic in a state of charge range (A). The control unit is configured to increase the state of charge (SOC) of the battery (6) to a range (B) in which the substantially linear voltage characteristic of the battery (6) is exceeded, in order to calibrate the state of charge (SOC).The control unit is further configured to perform the calibration of the state of charge (SOC) of the battery (6) at a location of the working machine where, following the calibration of the state of charge of the battery (6), no recuperation of braking energy from the working machine into the battery (6) takes place during a specified operating time of the working machine.

Description

[0001] The invention relates to a fuel cell hybrid system for a mobile work machine, in particular an industrial truck, having a hydrogen-operated fuel cell device and a battery, wherein the fuel cell device is configured to charge the battery, and having a control device configured to determine the charge state of the battery.

[0002] In mobile work machines, in particular industrial trucks, with an electric drive system, it is known to use a fuel cell hybrid system, which comprises a fuel cell device and a battery, to supply energy to the electric drive system.

[0003] Known fuel cell hybrid systems comprise a hydrogen-powered fuel cell device to which oxygen or ambient air is supplied at a cathode region and hydrogen from a hydrogen tank at an anode region. In the fuel cell device, the oxygen from the ambient air is reacted with the hydrogen, generating electrical energy. The electrical power generated by the fuel cell device is used to charge a battery of the fuel cell hybrid system. Such a fuel cell hybrid system may also contain a power-voltage converter, for example a DC / DC converter. Such a power-voltage converter ensures that the electrical power generated during operation of the fuel cell device is independent of the battery's state of charge (SOC).

[0004] Fuel cell hybrid systems for mobile machinery also use batteries that exhibit a substantially linear voltage characteristic over a wide state-of-charge range. During operation of the machine, the battery of the fuel cell hybrid system, in particular, operates within this state-of-charge range, for example, between 30% and 80% state-of-charge (SOC). If the battery exhibits a substantially linear voltage characteristic within this state-of-charge range, a control device cannot accurately determine the battery's state-of-charge (SOC).However, during operation of the working machine, the state of charge of the battery of the fuel cell hybrid system must be determined at regular intervals, since the state of charge (SOC) of the battery must not be too high in order to ensure recuperation of braking energy from the working machine, for example during downhill travel of the working machine, into the battery to maintain the braking capability of the working machine.

[0005] The present invention is based on the object of providing a fuel cell hybrid system for a mobile work machine, in particular an industrial truck, of the type mentioned at the outset, in which a determination of the state of charge (SOC) of the battery of the fuel cell hybrid system is made possible in a simple manner.

[0006] This object is achieved according to the invention in that the battery has a substantially linear region of the voltage characteristic curve in a state of charge range and the control device is designed to increase the state of charge of the battery to a range in which the substantially linear region of the voltage characteristic curve of the battery is exceeded in order to calibrate the state of charge of the battery, and wherein the control device is designed to carry out the calibration of the state of charge of the battery at a location of the work machine at which no recuperation of braking energy from the work machine into the battery takes place following the calibration of the state of charge of the battery in a predetermined operating time of the work machine.

[0007] In the fuel cell hybrid system according to the invention, a lithium iron phosphate battery (LiFePo battery) is provided as the battery according to a preferred embodiment. Such a battery is operated in a state of charge range between 30% and 80% of the state of charge (SOC) during use of the work machine, in which the battery exhibits a substantially linear range of the voltage characteristic and thus a substantially linear voltage characteristic.

[0008] In order to be able to easily determine the state of charge (SOC) of the battery with the control device in such a fuel cell hybrid system with a battery that has a substantially linear range of the voltage characteristic curve in a state of charge range, for example, a lithium iron phosphate battery, the control device is designed to calibrate the state of charge of the battery by increasing the state of charge of the battery to a range in which the substantially linear range of the voltage characteristic curve of the battery is exceeded. In particular, for this purpose, the state of charge (SOC) of the battery is increased to a value greater than, for example, 80%.

[0009] In order to ensure that the braking capability of the work machine is maintained at such a charge level of the battery, the control device is further designed to carry out the calibration of the charge level of the battery at a location of the work machine at which no recuperation of braking energy from the work machine into the battery takes place and is to be expected following the calibration of the charge level of the battery in a predetermined operating time of the work machine.If the calibration of the battery's state of charge is carried out at a location of the work machine in which no recuperation of braking energy is to be expected during downhill travel of the work machine over a specified operating time of the work machine, the work machine can then be operated with the increased state of charge of the battery, whereby overcharging of the battery is prevented by recuperation of braking energy during downhill travel of the work machine.

[0010] According to an advantageous embodiment of the invention, the control device is designed to increase the state of charge of the battery to a range that is larger than the state of charge range in which the battery has the essentially linear region of the voltage characteristic curve. To calibrate the state of charge of the battery, the control device thus charges the battery beyond the state of charge range in which the battery has the essentially linear region of the voltage characteristic curve. Preferably, the control device is designed to increase the state of charge of the battery to a range greater than 80%. In such a charging range, the linear region of the voltage characteristic curve is exceeded for the battery, for example a lithium iron phosphate battery, so that the state of charge of the battery can be easily calibrated based on the battery voltage in this charging range.

[0011] According to an advantageous embodiment of the invention, the control device is designed to increase the battery's state of charge by operating the fuel cell device. Since the fuel cell device charges the battery, the battery's state of charge can be easily increased for calibration purposes by operating the fuel cell device accordingly.

[0012] According to an advantageous embodiment of the invention, the control device determines the location of the work machine based on a height of the work machine measured by an altitude measuring device. Based on the height of the work machine, in particular the height of the work machine above sea level, a location of the work machine suitable for calibrating the battery's state of charge can be easily determined, at which location no recuperation of braking energy from the work machine into the battery during a downhill journey is to be expected following the calibration of the battery's state of charge during a predetermined operating time of the work machine. A GPS altimeter, for example, can be used as the altitude measuring device.

[0013] According to an advantageous embodiment of the invention, the control device determines the location of the work machine based on a movement pattern of the work machine. Based on a movement pattern detected during operation of the work machine, a location of the work machine suitable for calibrating the battery's state of charge can also be easily determined, at which location no recuperation of braking energy from the work machine into the battery is expected during downhill travel following the calibration of the battery's state of charge during a predetermined operating time of the work machine.

[0014] The invention further relates to a method for operating a fuel cell hybrid system of a mobile work machine, in particular an industrial truck, with a hydrogen-operated fuel cell device and with a battery, wherein the battery is charged by the fuel cell device, and with a control device by which the charge state of the battery is determined, in particular a method for operating the above-mentioned fuel cell hybrid system.

[0015] In terms of the method, the stated object is achieved in that a battery is used which has a substantially linear range of the voltage characteristic curve in a state of charge range, and the control device for calibrating the state of charge of the battery increases the state of charge of the battery to a range in which the substantially linear range of the voltage characteristic curve of the battery is exceeded, and wherein the control device carries out the calibration of the state of charge of the battery at a location of the work machine at which, following the calibration of the state of charge of the battery, no recuperation of braking energy from the work machine into the battery is expected within a predetermined operating time of the work machine. The method has the advantages already mentioned above with regard to the fuel cell hybrid system.

[0016] According to an advantageous embodiment of the invention, the state of charge of the battery is increased to a range that is larger than the state of charge range in which the battery exhibits the substantially linear region of the voltage characteristic. Preferably, the state of charge of the battery is increased to a range greater than 80%.

[0017] According to an advantageous embodiment of the invention, the control device increases the charge state of the battery by operating the fuel cell device.

[0018] According to an advantageous embodiment of the invention, the control device determines the location of the work machine based on a height of the work machine measured by means of a height measuring device.

[0019] According to an advantageous embodiment of the invention, the control device determines the location of the work machine based on a movement pattern of the work machine.

[0020] The invention further relates to a mobile work machine, in particular an industrial truck, having an electric drive system and a fuel cell hybrid system according to the invention, wherein the fuel cell hybrid system is designed to supply the electric drive system of the work machine with electrical energy, and wherein the fuel cell hybrid system has a housing which is designed to be inserted into a battery receiving space of the work machine.

[0021] In such work machines, the fuel cell hybrid system can be installed in the battery compartment of the work machine instead of a traction battery, for example, a lead-acid battery. Due to the limited space and dimensions of the battery compartment, the space available for the fuel cell hybrid system intended as a replacement for a traction battery is also limited.

[0022] The invention has a number of advantages.

[0023] In the fuel cell hybrid system according to the invention, a cost-effective lithium iron phosphate (LiFePo) battery, for example a LiFePo4 battery, can be used. The calibration of this battery's state of charge can be carried out in a controlled manner without limiting the battery's recuperation capacity when driving downhill on the mobile machine.

[0024] Further advantages and details of the invention are explained in more detail with reference to the embodiment shown in the schematic figures. Fig. 1 a perspective view of the fuel cell hybrid system according to the invention, Fig. 2 a schematic representation of the fuel cell hybrid system according to the invention and Fig. 3 a voltage characteristic of the battery of the fuel cell hybrid system of the Fig. 1 and Fig. 2.

[0025] In the Fig. 1 shows a fuel cell hybrid system 1 according to the invention for a mobile work machine, in particular an industrial truck, with an electric drive system that can be used as a replacement for a traction battery in a battery receiving space of the work machine.

[0026] The fuel cell hybrid system 1 has a rectangular housing 2 within which the components of the fuel cell hybrid system 1 are installed.

[0027] The fuel cell hybrid system 1 has a Fig. 2 shows a hydrogen-powered fuel cell device 5.

[0028] The fuel cell device 5 is preferably designed as a fuel cell stack, a so-called fuel cell stack. The fuel cell device 5 is preferably designed as an air-cooled fuel cell device 5, which is cooled by a cooling air flow generated by a fan device (not shown in detail). Alternatively, the fuel cell device 5 can be designed as a liquid-cooled fuel cell device 5.

[0029] The fuel cell hybrid system 1 also has a Fig. 2, which is designed, for example, as a lithium iron phosphate battery (LiFePo battery). The battery 6 of the fuel cell hybrid system 1 is charged by the fuel cell device 5.

[0030] The battery 6 supplies an electric drive system 7 of the mobile work machine with electrical energy. The electric drive system 7 can be an electric drive motor of the mobile work machine or an electric pump motor of a hydraulic system of the mobile work machine. As shown in the Fig. 2 by means of the double arrow between the battery 6 and the electric drive system 7, recuperation of braking energy of the mobile work machine, for example by generator operation of the electric drive motor, can take place in the battery 6.

[0031] The fuel cell hybrid system 1 further comprises a control device (not shown in detail) which is designed to determine the state of charge (SOC) of the battery 6, for example based on the voltage of the battery 6.

[0032] In the Fig. 3 shows a voltage characteristic of the battery 6 of the fuel cell hybrid system 1, which is designed, for example, as a lithium iron phosphate battery.

[0033] In the Fig. 3, the state of charge (SOC) of battery 6 is plotted in % on the abscissa. The voltage U0 of battery 6 is plotted in volts V on the ordinate.

[0034] From the Fig.3 shows that the battery 6 of the fuel cell hybrid system 1 has a substantially linear region of the voltage characteristic curve in a state of charge range A, which in the illustrated embodiment extends between 30% to 80% SOC, and thus has a substantially constant voltage characteristic curve. In range B, which adjoins the state of charge range A at the top and extends between 80% to 100% SOC in the illustrated embodiment, the voltage increases according to the curve shown. In range C, which adjoins the state of charge range A at the bottom and extends between 30% to 0% SOC in the illustrated embodiment, the voltage decreases according to the curve shown.

[0035] During operation of the work machine, the battery 6 of the fuel cell system 1, in particular, is operated in the state of charge range A, preferably between 30% and 80% state of charge (SOC). Since the voltage characteristic of the battery 6 is almost constant in this range, the control device cannot precisely determine the state of charge (SOC) of the battery 6 based on the voltage of the battery 6.

[0036] However, during operation of the work machine, the state of charge (SOC) of battery 6 must be determined at regular intervals.

[0037] For this purpose, in order to calibrate the state of charge of the battery 6, the control device increases the state of charge (SOC) of the battery 6 by operating the fuel cell device 5 to a range in which the linear range of the voltage characteristic of the battery 6 is exceeded. For this purpose, the state of charge (SOC) of the battery 6 is preferably increased to range B, which is greater than the state of charge range A, in which the battery 6 has the essentially linear range of the voltage characteristic with the essentially constant voltage characteristic. For this purpose, the state of charge (SOC) of the battery 6 is preferably increased to range B, in particular to the range between 90% and 100% state of charge (SOC), in which a pronounced increase in voltage occurs.

[0038] The voltage of battery 6 measured in this process can be used to calibrate a SOC characteristic curve of battery 6 in the control device.

[0039] The calibration of the charge state of the battery 6 is carried out at a location of the working machine at which, following the calibration of the charge state of the battery 6, no recuperation of braking energy from the working machine into the battery 6 is to be expected during a specified operating time of the working machine.

[0040] The control device can determine a suitable location for the work machine based on the height of the work machine above sea level measured by means of a height measuring device, for example a GPS altimeter.

[0041] Alternatively or additionally, the control device can determine a suitable location of the work machine based on a movement pattern of the work machine.

[0042] A suitable location of the working machine is therefore used to calibrate the SOC battery characteristic curve.

[0043] At a location where no recuperation of braking energy into the battery 6 is expected, the state of charge (SOC) of the battery 6 is increased by operating the fuel cell device 5 until the state of charge (SOC) of the battery 6 exceeds the linear range of the voltage characteristic curve. This calibrates the battery SOC.

[0044] The invention is not limited to the design of the battery 6 as a lithium iron phosphate battery (LiFePo battery). The battery 6 can also have a different cell chemistry. The invention is applicable to all battery types that have a substantially linear range of the voltage characteristic and thus a substantially constant voltage characteristic in a state of charge range A, in which the battery 6 is operated during normal operation of the work machine.

Claims

[1] Fuel cell hybrid system (1) for a mobile work machine, in particular an industrial truck, with a hydrogen-operated fuel cell device (5) and with a battery (6), wherein the fuel cell device (5) is designed to charge the battery (6), and with a control device designed to determine the state of charge (SOC) of the battery (6), characterized byin that the battery (6) has a substantially linear region of the voltage characteristic curve in a state of charge range (A), and the control device is designed to increase the state of charge (SOC) of the battery (6) to a range (B) in which the substantially linear region of the voltage characteristic curve of the battery (6) is exceeded in order to calibrate the state of charge (SOC) of the battery (6), and wherein the control device is designed to carry out the calibration of the state of charge (SOC) of the battery (6) at a location of the work machine at which, following the calibration of the state of charge of the battery (6), no recuperation of braking energy from the work machine into the battery (6) takes place within a predetermined operating time of the work machine. [2] Fuel cell hybrid system according to claim 1, characterized byin that the control device is designed to increase the state of charge (SOC) of the battery (6) to a range (B) which is larger than the state of charge range (A) in which the battery (6) has the substantially linear range of the voltage characteristic. [3] Fuel cell hybrid system according to claim 1 or 2, characterized by that the battery (6) is designed as a lithium iron phosphate battery. [4] Fuel cell hybrid system according to one of claims 1 to 3, characterized by that the control device is designed to increase the state of charge (SOC) of the battery (6) by operating the fuel cell device (5). [5] Fuel cell hybrid system according to one of claims 1 to 4, characterized by that the control device determines the location of the work machine on the basis of a height of the work machine measured by means of a height measuring device. [6] Fuel cell hybrid system according to one of claims 1 to 4, characterized by that the control device determines the location of the work machine based on a movement pattern of the work machine. [7] Method for operating a fuel cell hybrid system (1) of a mobile work machine, in particular an industrial truck, with a hydrogen-operated fuel cell device (5) and with a battery (6), wherein the battery (6) is charged by the fuel cell device (5), and with a control device by which the state of charge (SOC) of the battery (6) is determined, in particular method for operating the fuel cell hybrid system according to one of claims 1 to 6, characterized bythat a battery is used as the battery (6) which has a substantially linear range of the voltage characteristic curve in a state of charge range (A), and the control device for calibrating the state of charge (SOC) of the battery (6) increases the state of charge (SOC) of the battery (6) to a range (B) in which the substantially linear range of the voltage characteristic curve of the battery (6) is exceeded, and wherein the control device carries out the calibration of the state of charge (SOC) of the battery (6) at a location of the work machine at which, following the calibration of the state of charge (SOC) of the battery (6), no recuperation of braking energy from the work machine into the battery (6) is expected within a predetermined operating time of the work machine. [8] Method according to claim 7, characterized bythat the state of charge (SOC) of the battery (6) is increased to a range (B) which is larger than the state of charge range (A) in which the battery (6) has the substantially linear range of the voltage characteristic. [9] Method according to claim 7 or 8, characterized by that the control device increases the state of charge (SOC) of the battery (6) by operating the fuel cell device (5). [10] Method according to one of claims 7 to 9, characterized by that the control device determines the location of the work machine on the basis of a height of the work machine measured by means of a height measuring device. [11] Method according to one of claims 7 to 9, characterized by that the control device determines the location of the working machine based on a movement pattern of the working machine. [12] Mobile work machine, in particular industrial truck, with an electric drive system and a fuel cell hybrid system (1) according to one of claims 1 to 6, wherein the fuel cell hybrid system (1) is designed to supply the electric drive system (7) of the work machine with electrical energy, and wherein the fuel cell hybrid system (1) has a housing (2) which is designed to be inserted into a battery receiving space of the work machine.

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