Method for operating an electrically powered industrial truck

Abstract

Method for operating an electrically driven industrial truck (10) with the following steps: • Charging a battery (34) with a charging current generated by a drive motor (16) when the industrial truck (10) is decelerated, characterized by the following steps: • Determining an angle of inclination of the industrial truck (10), • Determining the charge level of the battery (34), • Limiting the travel speed of the industrial truck (10) to a maximum travel speed (v max ) which is less than a maximum speed of the industrial truck (10) if the loading condition exceeds a specified maximum loading condition and the angle of inclination exceeds a specified maximum angle of inclination.

Description

The invention relates to a method for operating an electrically driven industrial truck, in which a battery is charged with a charging current, which is generated by a travel drive motor during the braking of the industrial truck, and to such an industrial truck.It is known to recover energy in electric motor-driven industrial trucks during braking. For this purpose, the travel drive motor of the industrial truck is operated as a generator during braking, and the charging current generated is fed into the battery. As a result, a longer operating time is possible for a given storage capacity of the battery, or a battery with a lower capacity can be used. If braking is carried out with an approximately full battery and a high charging current is fed into the battery, high battery voltages and thus high voltages can occur at a controller and all further electrical and electronic components of the industrial truck. To protect the electrical assemblies from excessively high voltages, an emergency shutdown is triggered when an upper limit for the voltage is exceeded. This standstill of the industrial truck on the one hand impairs the availability of the industrial truck. On the other hand, critical driving situations can occur because, for example, a spring brake can be triggered when the vehicle is stopped, which abruptly stops the vehicle.The document DE 10 2007 037 693 A1 discloses an industrial truck with a hybrid drive which has a recuperation brake and provides a speed limitation in a ramp or creep travel mode.From the publication DE 601 33 446 T2 a control device for electric hybrid vehicles has become known. The state of charge of a rechargeable battery is controlled depending on route information of a vehicle navigation system.On the basis thereof, the object of the invention is to provide a method for operating an electrically driven industrial truck and such an industrial truck, in which charging of the battery during braking is possible reliably and reliably without the problems explained in the introduction occurring.This object is achieved by the method having the features of claim 1.The method for operating an electrically driven industrial truck has the following steps:charging a battery with a charging current, which is generated by a travel drive motor during the braking of the industrial truck,determining an angle of inclination of the industrial truck,determining a charge state of the battery,limiting the travel speed of the industrial truck to a maximum travel speed that is less than a maximum speed of the industrial truck if the loading state exceeds a predefined maximum loading state and the angle of inclination exceeds a predefined maximum angle of inclination.The industrial truck has at least one driven wheel which is driven by the travel drive motor. The drive wheel may be steerable. This can be a drawbar-guided industrial truck. It can be a low-lift or a high-lift industrial truck. The industrial truck can be a passenger vehicle, or a passenger vehicle with a standing platform or a driver's seat. The industrial truck can have a parking brake that initiates in the event of an emergency shutdown, in particular a spring-loaded brake. In addition to the braking of the industrial truck by the braking action of the travel drive motor when generating the charging current, the industrial truck can have a hydraulic or mechanical service brake.However, it can also be a simple industrial truck that does not have such a further brake.The determination of an angle of inclination of the industrial truck can be effected with the aid of an acceleration or angle sensor. The sensor can detect the spatial orientation of the industrial truck in all three spatial directions. In any case, an inclination of the industrial truck with respect to the horizontal can be detected. The detection of the inclination angle can, as a result, provide a numerical or measured value for the inclination angle, or it can be restricted to information about whether a predetermined maximum inclination angle is exceeded. When the industrial truck is put into operation, in particular when first put into operation after installation of the respective sensor, it may be necessary to learn the sensor when the industrial truck is aligned horizontally in order to calibrate a zero position. The sensor can be integrated into a controller of the industrial truck, in particular into the controller provided for controlling the travel drive motor.The determination of a state of charge of the battery can be carried out on the basis of a measured battery voltage. It is also possible to continuously detect the state of charge of the battery. The determination of the state of charge can be limited to exceeding or falling below a single threshold value for the maximum state of charge. Alternatively, the state of charge may be determined in more detail, for example by determining a percentage value related to the maximum capacity of the battery.The maximum speed of the industrial truck is a maximum permissible travel speed, in particular during operation of the industrial truck on level ground. The current travel speed can be determined by a speed measurement, in particular from a rotational speed of the travel drive motor. In the invention, the travel speed of the industrial truck is limited to a maximum travel speed if the state of charge and the angle of inclination exceed predetermined maximum values. In many driving situations, this makes it possible to prevent the high voltages identified as problematic from arising at all as a result of the charging of the battery during the braking of the industrial truck. The problems recognized are thus counteracted at their root.The invention is based on the finding that the high battery voltages can arise in particular whenever the industrial truck is operated on a slope when the state of charge is already high, because in this situation, when the industrial truck is braked, high charging currents and high voltages caused thereby must be expected. By limiting the travel speed to a value below the maximum speed, it is possible to prevent a strong braking from being required. By limiting the travel speed, the kinetic energy of the industrial truck to be converted into a charging current during generator braking is greatly reduced. By simultaneously taking into account the state of charge, the industrial truck can continue to be operated at maximum speed if the battery is discharged at least to such an extent that an overvoltage is not to be expected during braking. Overall, a largely unaffected operation of the industrial truck is possible and the occurrence of excessively high battery voltages is reliably prevented.The limiting of the driving speed can be effected in particular by automatically adapting a predefined speed setpoint value. The specification of the speed setpoint value can be effected, for example, by an operator via a travel switch.In one embodiment, the limiting of the travel speed takes place only under the additional condition that a current travel direction of the industrial truck is directed downward with respect to the angle of inclination. As a result, the travel speed is limited only in the downward direction if braking from high speed could actually lead to high charging currents. However, in the case of upward travel, the travel speed is not unnecessarily limited. The current direction of travel of the industrial truck can be determined in particular from a drawbar position of the industrial truck, a steering angle of a steered wheel, in particular of a steered drive wheel, and / or from a current drive direction (forward / backward). The determination of the current direction of travel can be effected in a controller of the industrial truck, in particular in the controller responsible for controlling the travel drive motor.In one embodiment, the angle of inclination is always related to a current direction of travel. The check as to whether the predefined maximum angle of inclination is exceeded is therefore not based on the absolute angle of inclination with respect to a horizontal plane, but rather on the angle of inclination with respect to the current direction of travel. Therefore, only an inclination of the industrial truck decisive for the active slope take into account. This makes it possible to avoid an unnecessary restriction of the travel speed on inclined subgrades which are not traveled on or are only partially traveled on in the downward direction.In one embodiment, the limiting of the travel speed is effected by actuating the travel drive motor. In principle, the limiting of the travel speed can be achieved by arbitrary measures, for example by actuating a service brake. However, controlling the travel drive motor to limit the travel speed is particularly simple and can be effected, for example, by adapting a speed setpoint value. At the same time, unnecessary power consumption is prevented by simultaneous driving and braking. In addition, by controlling the travel drive motor, it is possible in a particularly simple manner to achieve a smooth and back-free limiting of the travel speed.In one embodiment, the maximum travel speed assumes different values depending on the state of charge and the angle of inclination. If necessary, a loading state of the industrial truck can additionally be provided, for example in conjunction with industrial trucks with a load sensing system. By limiting the maximum travel speed to different values, an optimum compromise can be found between the reliable avoidance of over-voltages and an impairment of the travel performance of the industrial truck.In one embodiment, in addition to limiting the travel speed, an acceleration of the industrial truck is limited to a maximum acceleration which is smaller in terms of amount than a maximum acceleration of the industrial truck. The maximum acceleration of the industrial truck is a predefined value, which can be input into a travel controller as a parameter, for example. Setting a maximum acceleration of 2 m / s 2 for example, can avoid a load slipping during starting or braking. Limiting the acceleration to a smaller maximum acceleration may have an advantageous effect in two ways. Limiting the positive acceleration, i.e. the acceleration during starting, prevents excessively high travel speeds from being reached in the downward direction. Limiting the negative acceleration, i.e. the deceleration during the braking of the industrial truck, has a direct effect on the charging current generated during the braking and can thus counteract over-voltages at the battery by limiting the charging current, which over-voltages can otherwise also result from a relatively low travel speed in the case of sharp braking. As explained above in connection with the maximum travel speed, the maximum acceleration can also assume different values depending on the state of charge and / or the angle of inclination and / or a state of charge.In one embodiment, a current height of the industrial truck is determined relative to a starting position and the travel speed and / or the acceleration are limited independently of the angle of inclination if the current height exceeds a predefined maximum height. The starting position can be, for example, the height at which the industrial truck is located when it is put into operation. If the current height exceeds this starting position by a predefined maximum height, for example by 2 m, the travel speed and / or the acceleration are limited independently of the angle of inclination, i.e. for example also when the industrial truck is used in a plane. As a result, a rapid driving into a gradient, which could make a strong braking necessary, can be avoided. The restriction for the operation of the industrial truck which means this restriction as a function of reaching a specific height depends on the further operating conditions. For example, if a load is regularly received near the top of a ramp, the high level constraint does not significantly degrade, while effectively preventing the slope from being overcome without the occurrence of battery over-voltages.In one embodiment, the current height is ascertained continuously on the basis of route sections covered and associated inclination angles. The route sections can be detected, for example, by the rotations of a drive wheel. If the angle of inclination is also detected continuously and with respect to the current direction of travel, it is easily possible to determine which height difference was overcome during the route section and the current height can be determined by "integrating" the height differences.The above-mentioned object is also achieved by the electrically driven industrial truck having the features of claim 9.The industrial truck hasa travel drive motor,a battery,a controller for controlling the travel drive motor,a device for charging the battery with a charging current generated by the travel drive motor during the braking of the industrial truck, anda device for determining a state of charge of the battery, whereina device for determining an angle of inclination of the industrial truck, anda device for limiting the travel speed of the industrial truck to a maximum travel speed which is lower than a maximum speed of the industrial truck is provided, wherein the device for limiting is designed such that the limitation takes place if the state of charge exceeds a predefined maximum state of charge and the angle of inclination exceeds a predefined maximum angle of inclination.With regard to the features of the industrial truck, reference is made to the above explanations of the corresponding method features. The means for charging the battery may be integrated into the controller. The device for determining the state of charge of the battery can likewise be integrated into the controller, as can the device for determining the angle of inclination and / or the device for limiting the travel speed. It is understood that the aforementioned devices can be implemented completely or partially in the form of software.The invention is explained in more detail below with reference to an exemplary embodiment shown in two figures. The following are shown: FIG. 1 : shows an electrically driven industrial truck according to the invention, and FIG. 2 : shows a schematic illustration for explaining the process according to the invention.FIG. 1 shows an industrial truck 10 with a drive part 12 and a load part 14. the drive part 12 has an electric travel drive motor 16 and a drive wheel 18 driven by the latter.The industrial truck 10 shown in the figure is a low-lift industrial truck designed as a self-propelled vehicle, which has a fold-out standing platform 24 on the drive part 12 and two arms 26 spaced apart laterally in parallel, between which an operator riding on the standing platform 24 is stopped.The travel drive motor 16 is connected to a controller 30 via a 3-phase power line 28. Via the power line 28, the travel drive motor 16 is supplied with a 3-phase alternating current. Furthermore, the controller 30 is connected via a 2-pole power line 32 to a battery 34 arranged in the load part 14.The load element 14 has two parallel wheel arms 36, which at the same time form a load-bearing means and are each provided with two pivotable load rollers 38.The controller 30 comprises a device for charging the battery 40, a device for determining a state of charge 42, a device for determining an angle of inclination 44, a device for limiting a travel speed 46 and a device for limiting an acceleration 48. all of said devices can be present wholly or partly in the form of software which runs on a computer of the controller 30. This applies in particular to the device for charging the battery 40, the device for limiting a travel speed 46 and the device for limiting an acceleration 48.The device for determining an inclination angle 44 has an acceleration sensor which contains a seismic mass and the sensor data of which enable the determination of an inclination angle of the industrial truck in all three spatial directions.The device for determining a state of charge 42 has a voltage sensor with which the current battery voltage of the battery 34 is measured.The steps of the method according to the invention are explained with reference to FIG. 2. An acceleration sensor 56 provides sensor data that is provided to a device for determining an inclination angle 44. The means for determining an inclination angle 44 calculates, on the basis of the data of the acceleration sensor 56, an inclination angle which is supplied as an input variable to a means for determining a maximum travel speed 50 and a means for determining a maximum acceleration 52.A voltage sensor 58 measures a current battery voltage and provides this measured value to a device for ascertaining a state of charge 42 of the battery 34. This device forwards information about the state of charge to the device for ascertaining a maximum travel speed 50 and to the device for ascertaining a maximum acceleration 52 as further input variables.The maximum travel speed determination means 50 provides a maximum travel speed value v max. The maximum acceleration detector 52 provides a maximum acceleration value a max. The two values a max, v max are provided as input variables to a device for driving the travel drive motor 54. The device for controlling the travel drive motor 54 controls the travel drive motor 16, wherein the travel speed and the acceleration of the industrial truck are limited according to the limit values v max and a max.The travel drive motor 16 is connected to a speed transmitter 60 which provides a value for the current speed of the travel drive motor 16 to a device for determining a current speed 62. This calculates a current travel speed v ist and makes it available to the device for driving the travel drive motor 54. As a further input value, the device for controlling the travel drive motor 54 receives a speed setpoint value v soll, which is determined by a device for determining a speed setpoint value 66 on the basis of a user specification carried out via the travel switch 64. As an alternative to the acceleration sensor 56, an angle sensor 68 may be used which directly outputs an inclination angle which is provided-as indicated by the dashed lines-to the means for determining a maximum travel speed 50 and the means for determining a maximum acceleration 52.The maximum travel speed detection means 50, the maximum acceleration detection means 52 and the drive motor drive means 54 together constitute a travel speed and acceleration limiting means.

Claims

Method for operating an electrically driven industrial truck (10), having the following steps: • charging a battery (34) with a charging current which is generated by a travel drive motor (16) during the braking of the industrial truck (10), characterized bythe following steps: • determining an angle of inclination of the industrial truck (10), • determining a state of charge of the battery (34), • limiting the travel speed of the industrial truck (10) to a maximum travel speed (v max), which is less than a maximum speed of the industrial truck (10) if the state of charge exceeds a predefined maximum state of charge and the angle of inclination exceeds a predefined maximum angle of inclination.Method according to Claim 1, characterized in that the limiting of the travel speed takes place only under the additional condition that a current travel direction of the industrial truck (10) is directed downwards with respect to the angle of inclination.Method according to Claim 1 or 2, characterized in that the angle of inclination is always related to a current direction of travel.Method according to one of Claims 1 to 3, characterized in that the limiting of the travel speed is effected by actuating the travel drive motor (16).Method according to one of Claims 1 to 4, characterized in that the maximum travel speed (v max) assumes different values as a function of the state of charge and the angle of inclination.Method according to one of Claims 1 to 5, characterized in that, in addition to limiting the travel speed, an acceleration of the industrial truck (10) is limited to a maximum acceleration (a max) which is smaller in terms of absolute value than a maximum acceleration of the industrial truck (10).Method according to one of Claims 1 to 6, characterized in that a current height of the industrial truck (10) relative to a starting position is determined and the travel speed and / or the acceleration are limited independently of the angle of inclination if the current height exceeds a predefined maximum height.Method according to Claim 7, characterized in that the current height is ascertained continuously on the basis of route sections covered and associated inclination angles.Electrically driven industrial truck (10) having • a travel drive motor (16), • a battery (34), • a controller (30) for controlling the travel drive motor (16), • a device for charging the battery (40) with a charging current generated by the travel drive motor (16) during braking of the industrial truck (10), and • a device for determining a state of charge of the battery (42), characterized by • a device for determining an angle of inclination (44) of the industrial truck and • a device for limiting the travel speed (46) of the industrial truck to a maximum travel speed (v max), which is less than a maximum speed of the industrial truck (10), wherein the device for limiting the travel speed (46) is designed such that the limiting takes place, if the state of charge exceeds a predefined maximum state of charge and the angle of inclination exceeds a predefined maximum angle of inclination.Industrial truck (10) according to Claim 9, characterized in that the device for limiting the travel speed (46) is designed such that the limitation takes place only under the additional condition that a current direction of travel of the industrial truck (10) is directed downwards with respect to the angle of inclination.Industrial truck according to Claim 9 or 10, characterized bya device for determining an angle of inclination relating to a current direction of travel.Industrial truck according to one of Claims 9 to 11, characterized bya device which specifies different values for the maximum travel speed (v max) as a function of the state of charge and the angle of inclination.Industrial truck according to one of Claims 9 to 12, characterized bya device for limiting an acceleration of the industrial truck (10) to a maximum acceleration (a max), which is smaller in terms of absolute value than a maximum acceleration of the industrial truck (10).Industrial truck according to one of Claims 9 to 13, characterized bya device for determining a current height of the industrial truck (10) relative to a starting position, wherein the device for limiting the travel speed (46) and / or the acceleration (48) is designed such that the limiting of the travel speed and / or the acceleration takes place independently of the angle of inclination if the current height exceeds a predefined maximum height.Industrial truck according to Claim 14, characterized in that the device for ascertaining a current height is designed such that it ascertains the current height continuously on the basis of route sections covered and associated inclination angles.

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