EP3674252B1 - Method for operating a hydraulic system of an industrial truck - Google Patents

Method for operating a hydraulic system of an industrial truck Download PDF

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Publication number
EP3674252B1
EP3674252B1 EP19212033.5A EP19212033A EP3674252B1 EP 3674252 B1 EP3674252 B1 EP 3674252B1 EP 19212033 A EP19212033 A EP 19212033A EP 3674252 B1 EP3674252 B1 EP 3674252B1
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EP
European Patent Office
Prior art keywords
hydraulic
viscosity
temperature
mode
warm
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EP19212033.5A
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German (de)
French (fr)
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EP3674252A1 (en
Inventor
Björn Bullermann
Sebastian Schauer
Niko Siemering
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STILL GmbH
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STILL GmbH
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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B66—HOISTING; LIFTING; HAULING
    • B66F—HOISTING, LIFTING, HAULING OR PUSHING, NOT OTHERWISE PROVIDED FOR, e.g. DEVICES WHICH APPLY A LIFTING OR PUSHING FORCE DIRECTLY TO THE SURFACE OF A LOAD
    • B66F9/00—Devices for lifting or lowering bulky or heavy goods for loading or unloading purposes
    • B66F9/06—Devices for lifting or lowering bulky or heavy goods for loading or unloading purposes movable, with their loads, on wheels or the like, e.g. fork-lift trucks
    • B66F9/075—Constructional features or details
    • B66F9/20—Means for actuating or controlling masts, platforms, or forks
    • B66F9/22—Hydraulic devices or systems
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B21/00—Common features of fluid actuator systems; Fluid-pressure actuator systems or details thereof, not covered by any other group of this subclass
    • F15B21/04—Special measures taken in connection with the properties of the fluid
    • F15B21/042—Controlling the temperature of the fluid
    • F15B21/0427—Heating
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B21/00—Common features of fluid actuator systems; Fluid-pressure actuator systems or details thereof, not covered by any other group of this subclass
    • F15B21/04—Special measures taken in connection with the properties of the fluid
    • F15B21/045—Compensating for variations in viscosity or temperature
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/20—Fluid pressure source, e.g. accumulator or variable axial piston pump
    • F15B2211/205—Systems with pumps
    • F15B2211/20507—Type of prime mover
    • F15B2211/20515—Electric motor
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/20—Fluid pressure source, e.g. accumulator or variable axial piston pump
    • F15B2211/205—Systems with pumps
    • F15B2211/2053—Type of pump
    • F15B2211/20538—Type of pump constant capacity
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/50—Pressure control
    • F15B2211/505—Pressure control characterised by the type of pressure control means
    • F15B2211/50509—Pressure control characterised by the type of pressure control means the pressure control means controlling a pressure upstream of the pressure control means
    • F15B2211/50518—Pressure control characterised by the type of pressure control means the pressure control means controlling a pressure upstream of the pressure control means using pressure relief valves
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/50—Pressure control
    • F15B2211/505—Pressure control characterised by the type of pressure control means
    • F15B2211/50509—Pressure control characterised by the type of pressure control means the pressure control means controlling a pressure upstream of the pressure control means
    • F15B2211/50536—Pressure control characterised by the type of pressure control means the pressure control means controlling a pressure upstream of the pressure control means using unloading valves controlling the supply pressure by diverting fluid to the return line
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/50—Pressure control
    • F15B2211/52—Pressure control characterised by the type of actuation
    • F15B2211/526—Pressure control characterised by the type of actuation electrically or electronically
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/50—Pressure control
    • F15B2211/55—Pressure control for limiting a pressure up to a maximum pressure, e.g. by using a pressure relief valve
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/60—Circuit components or control therefor
    • F15B2211/62—Cooling or heating means
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/60—Circuit components or control therefor
    • F15B2211/63—Electronic controllers
    • F15B2211/6303—Electronic controllers using input signals
    • F15B2211/633—Electronic controllers using input signals representing a state of the prime mover, e.g. torque or rotational speed
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/60—Circuit components or control therefor
    • F15B2211/63—Electronic controllers
    • F15B2211/6303—Electronic controllers using input signals
    • F15B2211/6343—Electronic controllers using input signals representing a temperature
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/60—Circuit components or control therefor
    • F15B2211/665—Methods of control using electronic components
    • F15B2211/6651—Control of the prime mover, e.g. control of the output torque or rotational speed
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/60—Circuit components or control therefor
    • F15B2211/665—Methods of control using electronic components
    • F15B2211/6658—Control using different modes, e.g. four-quadrant-operation, working mode and transportation mode

Definitions

  • the invention relates to a method for operating a hydraulic system of an industrial truck with a hydraulic pump driven by a drive motor which, when operated in a working mode, generates a volume flow of hydraulic fluid which supplies at least one consumer of working hydraulics and/or steering hydraulics.
  • Generic industrial trucks such as forklifts, generally have a hydraulic system with a hydraulic circuit that includes a hydraulic pump driven by a drive motor.
  • a hydraulic oil is usually used as the hydraulic fluid for the hydraulic circuit.
  • the hydraulic pump generally supplies several consumers with the hydraulic fluid, for example consumers of a working hydraulic system, for example a lifting drive for raising and lowering a load-carrying device, a tilting drive for tilting a mast on which the load-carrying device is arranged such that it can be raised and lowered, and optionally one or several additional consumers, for example a sideshift device for the load handling device, and/or a hydraulic steering system.
  • the driver of the industrial truck When activating a consumer, the driver of the industrial truck operates an actuator, for example a joystick or a manual control lever, and according to the deflection of the actuator a specific target speed is specified, at which the drive motor that drives the hydraulic pump is operated. With the setpoint speed and the delivery volume of the hydraulic pump, a certain volumetric flow (delivery quantity) delivered by the hydraulic pump results, with which the consumer is supplied.
  • an actuator for example a joystick or a manual control lever
  • Constant displacement pumps are often used in industrial trucks. These are hydraulic pumps with a constant displacement volume per revolution and thus with a constant flow rate at a constant drive speed.
  • the hydraulic pump designed as a fixed displacement pump is thus activated when a Consumer operated with a controlled speed that is solely dependent on the deflection of the actuator.
  • a setpoint speed is generated, with which the hydraulic pump designed as a constant pump is operated, ie different setpoint speeds are generated for different deflections of the actuator.
  • Variable displacement pumps with an adjustable and thus changeable displacement volume are also known.
  • More advanced industrial trucks have oil temperature sensors to control the hydraulic pump. That's it DE 10 2017 106 390 A1 a method for operating a hydraulic system of an industrial truck is known, in which the volume flow of the hydraulic pump is controlled as a function of the temperature of the pressure medium in such a way that the influences of the pressure medium temperature on the volume flow are compensated. A constant volume flow of the hydraulic pump is thus made available over the entire operating temperature range of the pressure medium for a specific control signal of the actuator.
  • the standard ambient temperature window for operating an industrial truck is defined from -20 °C to +40 °C. Due to the increase in temperature of the hydraulic fluid associated with operation, there is a hydraulic fluid temperature window of -20 °C to +95 °C.
  • the viscosity of the hydraulic fluid is either in the lower or in the upper range of the temperature window, resulting in perceptible changes in comfort. in the In the lower temperature range, the viscosity of the hydraulic fluid is too high and malfunctions or failures can occur. Even after a large number of optimizations, an impairment of the vehicle properties in this area cannot be ruled out.
  • the present invention is based on the object of designing a method of the type mentioned at the outset in such a way that the operation of the hydraulic system in the area with high viscosity of the hydraulic fluid can be minimized in terms of time.
  • At least one operating parameter that characterizes the viscosity of the hydraulic fluid in the hydraulic system is recorded and evaluated in a data processing device, wherein when an operating state is detected in which the viscosity of the hydraulic fluid exceeds a predetermined upper threshold value, the hydraulic pump in is operated in a warm-up mode that is independent of the working mode or superimposed on the working mode, in which the hydraulic pump is controlled in such a way that the viscosity of the hydraulic fluid is reduced.
  • the temperature of the hydraulic fluid is expediently recorded as an operating parameter. If the specification of the hydraulic fluid is known, the temperature of the hydraulic fluid is a measure of its viscosity. Viscosity increases with decreasing temperature.
  • the operating parameters are evaluated in the data processing device, which is expediently integrated into the vehicle control system.
  • the aim is to minimize the persistence of the hydraulic fluid temperature in the lower range of the hydraulic fluid temperature window over time. This minimizes the duration in which the industrial truck is operated with a high viscosity of the hydraulic fluid.
  • the viscosity of the hydraulic fluid in the hydraulic system is too high, it is preferably determined by measuring the temperature of the hydraulic fluid, and the data processing device moves around an operating point when the viscosity is high Expanded hydraulic fluid. At this operating point, the hydraulic pump is additionally activated.
  • the temperature of the hydraulic fluid is measured directly by means of a temperature sensor in a hydraulic circuit of the hydraulic system.
  • the temperature of the hydraulic fluid is detected indirectly by measuring the motor temperature of the drive motor, in particular an electric drive motor, or indirectly by measuring the converter temperature of a converter controlling an electric drive motor.
  • the temperature of the hydraulic fluid can be deduced from the motor temperature or the converter temperature by means of a model calculation.
  • a model calculation is advantageously also provided for operating point detection, ie for detecting that the viscosity of the hydraulic fluid is too high.
  • a model calculation is carried out in the data processing device, which calculates the respective operating state from stored specification data of the hydraulic fluid and the detected operating parameter and recognizes the operating state in which the viscosity of the hydraulic fluid exceeds the predetermined upper threshold value.
  • the model calculation can use the measured values of the hydraulic oil temperature and the data stored in the data processing device for specifying the hydraulic fluid used, in particular with regard to the viscosity behavior. From these values, the model calculates the operating point at which the industrial truck is located and uses this to calculate the operating status "Hydraulic oil viscosity too high".
  • a message is preferably displayed on a display and/or operating unit of the industrial truck. In this way, the driver can be informed about this operating state and the associated warm-up mode.
  • the driver can then manually activate the warm-up mode by activating the hydraulic pump accordingly, for example operating the hydraulic pump at a higher speed and/or letting it run idle for a longer period of time in order to increase the temperature of the hydraulic fluid and thus reduce its viscosity.
  • the warm-up mode is automatically activated by the data processing device when the operating state is detected, in which the viscosity of the hydraulic fluid exceeds the predetermined threshold value.
  • the speed, for example the idling speed, of the hydraulic pump is preferably increased in the warm-up mode.
  • the hydraulic fluid circulating in the hydraulic circuit can be conveyed into the hydraulic oil tank, for example via an input pressure compensator in a control valve block of the working hydraulics, without driving a consumer of the working hydraulics and/or the steering hydraulics, which increases the temperature of the hydraulic fluid.
  • the speed of the hydraulic pump can also be increased when a consumer is actuated, in which case the hydraulic pump is then operated at a speed that is too high for the required consumer flow, so that the hydraulic circuit in turn circulates via the inlet pressure compensator in a control valve block of the working hydraulics, in which the excess volume flow of the hydraulic pump is pumped to the hydraulic oil tank and the temperature of the hydraulic fluid is increased.
  • the maximum speed of the hydraulic pump is preferably reduced in the warm-up mode. As a result, damage to the hydraulic pump can be effectively avoided when the viscosity of the hydraulic fluid and cavitation in the hydraulic pump are high.
  • a further preferred embodiment of the invention provides that in the warm-up mode the hydraulic pump is operated at idle without a request from the consumer. Instead of operating the hydraulic pump at a standstill when consumers are not actuated, the hydraulic pump is therefore operated at idle when consumers are not actuated.
  • the hydraulic fluid is circulated in the hydraulic circuit or conveyed into a hydraulic tank, for example via a Input pressure compensator in a control valve block of the working hydraulics without driving the consumer, which increases the temperature of the hydraulic fluid.
  • a further preferred embodiment of the invention provides that in the warm-up mode when a consumer is actuated, the dynamics of the setpoint specifications for the activation of the consumer and/or for the activation of the hydraulic pump are adapted as a function of the operating parameter, in particular the temperature of the hydraulic fluid.
  • the dynamics of the target value specifications for controlling the consumer for example the dynamics of triggering signals (target value specification) for a directional control valve controlling the consumer, and/or the dynamics of the target value specifications for controlling the hydraulic pump, for example the dynamics of a triggering signal (target value specification) for ramping up the drive motor driving the hydraulic pump to a target speed or the dynamics of a control signal (target value specification) for setting a target displacement volume of a variable displacement pump, to be adapted to the higher viscosity of the hydraulic fluid in the cold state.
  • the dynamics of the setpoint specifications of the corresponding control signals are preferably reduced when the viscosity of the hydraulic fluid is high and thus with increasing viscosity of the hydraulic fluid.
  • the viscosity of the hydraulic fluid is responsible for the system dynamics of the hydraulic system.
  • dynamic setpoint specifications are thus reduced when the viscosity of the hydraulic fluid is high, so that the setpoint values, for example corresponding control signals, adapt to the system dynamics of the hydraulic system without significantly changing the system dynamics of the hydraulic system.
  • electrical setpoint specifications for example electrical control signals
  • the electrical setpoint specifications become more sluggish as the viscosity of the hydraulic fluid increases, without the system dynamics of the hydraulic system and thus the system performance of the hydraulic system changing.
  • the response time of the hydraulic pump becomes slower when the viscosity of the hydraulic fluid is high, which reduces the likelihood of cavitation occurring in the hydraulic pump when the viscosity of the hydraulic fluid is high.
  • a further preferred embodiment of the invention provides that, in the warm-up mode, a pressure-limiting valve of the hydraulic system, the setting pressure of which can be changed electrically, is activated as a function of the operating parameter, in particular the temperature of the hydraulic fluid.
  • the set pressure of the pressure-limiting valve of the hydraulic system is preferably reduced for this purpose.
  • the pressure relief valve of the hydraulic system ensures the maximum permissible working pressure of the hydraulic system. In the warm-up mode, the maximum permissible working pressure is thus adapted to the viscosity of the hydraulic fluid and thus to the warm-up process of the hydraulic fluid. This can prevent impermissible pressure peaks during the warm-up mode.
  • the hydraulic pump is operated in the warm-up mode until the viscosity of the hydraulic fluid falls below a predetermined lower threshold value.
  • the hydraulic pump can be operated for a period of approx. 20 minutes at a constant idle speed of approx. 1,000 revolutions per minute without the consumer requesting it, in order to increase the temperature of the hydraulic fluid from -7 °C to +15 °C .
  • the invention offers a number of advantages
  • the hydraulic pump can be operated at pressure operating points that are not in the limit range when the hydraulic pump is activated in idle mode.
  • the invention also means that the components of the working hydraulics can be operated within their specification. Likewise, cavitation of the hydraulic pump can be prevented.
  • the figure shows a graphic representation of the time profile of the temperature of the hydraulic fluid in the warm-up mode of the hydraulic pump using the method according to the invention.
  • the time in seconds s is plotted on the horizontal x-axis, while the temperature of the hydraulic fluid of the hydraulic system in °C is plotted on the vertical y-axis.
  • the industrial truck is a battery-powered industrial truck with a hydraulic system for operating working hydraulics and/or steering hydraulics.
  • the hydraulic system works with a commercially available hydraulic oil as the hydraulic fluid.
  • the hydraulic system has a hydraulic oil pump designed as a fixed displacement pump, which is driven by a drive motor designed as an electric motor.
  • the hydraulic oil temperature is measured directly in the hydraulic circuit using a temperature sensor.
  • the measured values are transmitted to a data processing device on the industrial truck that is integrated into the vehicle control.
  • Data on the specification of the hydraulic oil, in particular on the viscosity behavior, are stored in the data processing device.
  • the Data processing device Based on the temperature readings and the specification data of the hydraulic oil, the Data processing device calculated using a model calculation of the operating state of the truck.
  • the industrial truck is put into operation at an ambient temperature of -10°C.
  • the hydraulic oil temperature in the hydraulic system is -7°C at the start time.
  • the model calculation in the data processing device results in an operating state in which the viscosity of the hydraulic oil exceeds a predetermined upper threshold value.
  • the data processing device thus recognizes that the hydraulic oil has too high a viscosity for regular operation in the working mode. Malfunctions and/or failures of the working hydraulics and/or the steering hydraulics could occur here.
  • the data processing device therefore automatically activates the warm-up mode and informs the driver of this by means of a message on the display and operating unit of the industrial truck.
  • the hydraulic pump In the warm-up mode, the hydraulic pump is controlled in such a way that it idles at a constant and increased idle speed of 1,000 revolutions per minute. No consumer is actuated.
  • the hydraulic oil is pumped into the hydraulic oil tank as it circulates in the hydraulic circuit, for example via an inlet pressure compensator in a control valve block of the working hydraulics, without driving a consumer of the working hydraulics and/or the steering hydraulics. Over time, the hydraulic oil heats up until it has the required temperature at which the viscosity of the hydraulic oil is low enough for regular operation in the work mode.
  • this oil temperature threshold value of +15° C. means that the viscosity of the hydraulic oil falls below a predetermined lower threshold value.
  • the data processing device therefore automatically stops the warm-up mode and informs the driver of this by means of a message on the display and operating unit of the industrial truck.
  • the regular working mode can then be started, in which the consumers of the working hydraulics and/or the steering hydraulics are driven with the volume flow of the hydraulic oil pump or the hydraulic pump is operated at a reduced idle speed or the hydraulic pump is operated at a standstill when consumers are not actuated.

Description

Die Erfindung betrifft ein Verfahren zum Betreiben einer Hydraulikanlage eines Flurförderzeugs mit einer von einem Antriebsmotor angetriebenen Hydraulikpumpe, die beim Betrieb in einem Arbeitsmodus einen Volumenstrom einer Hydraulikflüssigkeit erzeugt, welcher mindestens einen Verbraucher einer Arbeitshydraulik und/oder eine Lenkungshydraulik versorgt.The invention relates to a method for operating a hydraulic system of an industrial truck with a hydraulic pump driven by a drive motor which, when operated in a working mode, generates a volume flow of hydraulic fluid which supplies at least one consumer of working hydraulics and/or steering hydraulics.

Gattungsgemäße Flurförderzeuge, beispielsweise Gabelstapler, weisen in der Regel eine Hydraulikanlage mit einem Hydraulikkreis auf, der eine von einem Antriebsmotor angetriebene Hydraulikpumpe umfasst. Als Hydraulikflüssigkeit wird für den Hydraulikkreis üblicherweise ein Hydrauliköl verwendet. Von der Hydraulikpumpe werden in der Regel mehrere Verbraucher mit der Hydraulikflüssigkeit versorgt, beispielswiese Verbraucher einer Arbeitshydraulik, beispielsweise einen Hubantrieb zum Heben und Senken eines Lastaufnahmemittels, einen Neigeantrieb zum Neigen eines Hubgerüstes, an dem das Lastaufnahmemittel anhebbar und absenkbar angeordnet ist, und gegebenenfalls ein oder mehrere Zusatzverbraucher, beispielsweise eine Seitenschiebereinrichtung für das Lastaufnahmemittel, und/oder eine Lenkungshydraulik.Generic industrial trucks, such as forklifts, generally have a hydraulic system with a hydraulic circuit that includes a hydraulic pump driven by a drive motor. A hydraulic oil is usually used as the hydraulic fluid for the hydraulic circuit. The hydraulic pump generally supplies several consumers with the hydraulic fluid, for example consumers of a working hydraulic system, for example a lifting drive for raising and lowering a load-carrying device, a tilting drive for tilting a mast on which the load-carrying device is arranged such that it can be raised and lowered, and optionally one or several additional consumers, for example a sideshift device for the load handling device, and/or a hydraulic steering system.

Bei der Ansteuerung eines Verbrauchers wird von dem Fahrer des Flurförderzeugs ein Stellglied, beispielsweise ein Joystick oder ein Handbedienhebel, betätigt und entsprechend der Auslenkung des Stellgliedes eine bestimmte Solldrehzahl vorgegeben, mit der die Hydraulikpumpe antreibende Antriebsmotor betrieben wird. Mit der Solldrehzahl und dem Fördervolumen der Hydraulikpumpe ergibt sich ein bestimmter von der Hydraulikpumpe geförderter Volumenstrom (Fördermenge), mit dem der Verbraucher versorgt wird.When activating a consumer, the driver of the industrial truck operates an actuator, for example a joystick or a manual control lever, and according to the deflection of the actuator a specific target speed is specified, at which the drive motor that drives the hydraulic pump is operated. With the setpoint speed and the delivery volume of the hydraulic pump, a certain volumetric flow (delivery quantity) delivered by the hydraulic pump results, with which the consumer is supplied.

Häufig werden bei Flurförderzeugen Konstantpumpen eingesetzt. Dabei handelt es sich um Hydropumpen mit konstantem Verdrängungsvolumen pro Umdrehung und damit mit konstantem Förderstrom bei konstanter Antriebsdrehzahl. Die als Konstantpumpe ausgeführte Hydraulikpumpe wird somit bei der Ansteuerung eines Verbrauchers mit einer gesteuerten Drehzahl betrieben, die allein abhängig ist von der Auslenkung des Stellglieds. Je nach Auslenkung des Stellglieds wird eine Solldrehzahl generiert, mit der die als Konstantpumpe ausgebildete Hydraulikpumpe betrieben wird, d.h. für unterschiedliche Auslenkungen des Stellglieds werden unterschiedliche Solldrehzahlen generiert.Constant displacement pumps are often used in industrial trucks. These are hydraulic pumps with a constant displacement volume per revolution and thus with a constant flow rate at a constant drive speed. The hydraulic pump designed as a fixed displacement pump is thus activated when a Consumer operated with a controlled speed that is solely dependent on the deflection of the actuator. Depending on the deflection of the actuator, a setpoint speed is generated, with which the hydraulic pump designed as a constant pump is operated, ie different setpoint speeds are generated for different deflections of the actuator.

Bekannt sind auch Verstellpumpen mit einstellbarer und somit veränderbarem Verdrängungsvolumen.Variable displacement pumps with an adjustable and thus changeable displacement volume are also known.

Herkömmliche Standard-Flurförderzeuge besitzen keine Einrichtungen zur Erfassung der Temperatur der Hydraulikflüssigkeit der Hydraulikanlage. Die Hydraulikpumpe wird unabhängig von der Temperatur und der Viskosität der Hydraulikflüssigkeit der Hydraulikanlage betrieben. Diese Standard-Flurförderzeuge bieten den Bedienpersonen keine Möglichkeit, beispielsweise die Arbeits- und/oder Lenkungshydraulik auf bestimmte Einsatzbedingungen und Fluidtemperaturen zu konfigurieren.Conventional standard industrial trucks do not have any devices for detecting the temperature of the hydraulic fluid in the hydraulic system. The hydraulic pump is operated independently of the temperature and the viscosity of the hydraulic fluid in the hydraulic system. These standard industrial trucks do not offer the operators the option of configuring, for example, the working and/or steering hydraulics for specific operating conditions and fluid temperatures.

Weiter entwickelte Flurförderzeuge verfügen über Öltemperatursensoren zur Steuerung der Hydraulikpumpe. So ist aus der DE 10 2017 106 390 A1 ein Verfahren zum Betrieb einer Hydraulikanlage eines Flurförderzeugs bekannt, bei der der Volumenstrom der Hydraulikpumpe in Abhängigkeit von der Temperatur des Druckmittels derart gesteuert wird, dass eine Kompensation der Einflüsse der Druckmitteltemperatur auf den Volumenstrom erfolgt. Somit wird bei einem bestimmten Stellsignal des Stellglieds über den gesamten Temperaturbetriebsbereich des Druckmittels ein konstanter Volumenstrom der Hydraulikpumpe zur Verfügung gestellt.More advanced industrial trucks have oil temperature sensors to control the hydraulic pump. That's it DE 10 2017 106 390 A1 a method for operating a hydraulic system of an industrial truck is known, in which the volume flow of the hydraulic pump is controlled as a function of the temperature of the pressure medium in such a way that the influences of the pressure medium temperature on the volume flow are compensated. A constant volume flow of the hydraulic pump is thus made available over the entire operating temperature range of the pressure medium for a specific control signal of the actuator.

Das Standardfenster der Umgebungstemperatur für den Betrieb eines Flurförderzeugs ist von -20 °C bis +40 °C definiert. Aufgrund der mit dem Betrieb einhergehenden Temperaturerhöhung der Hydraulikflüssigkeit ergibt sich ein Hydraulikflüssigkeitstemperaturfenster von -20 °C bis +95 °C.The standard ambient temperature window for operating an industrial truck is defined from -20 °C to +40 °C. Due to the increase in temperature of the hydraulic fluid associated with operation, there is a hydraulic fluid temperature window of -20 °C to +95 °C.

Aufgrund des doppelt logarithmischen Zusammenhangs zwischen der Temperatur und der Viskosität der Hydraulikflüssigkeit ergibt sich ein Optimierungsproblem. Entweder ist die Viskosität der Hydraulikflüssigkeit im unteren oder im oberen Bereich des Temperaturfensters, so dass es zu wahrnehmbaren Komfortveränderungen kommt. Im unteren Temperaturbereich ist die Viskosität der Hydraulikflüssigkeit zu hoch und es kann zu fehlerhaften Funktionen oder Ausfällen kommen. Auch nach einer Vielzahl an Optimierungen ist eine Beeinträchtigung der Fahrzeugeigenschaften in diesem Bereich nicht ausgeschlossen.Due to the double logarithmic relationship between the temperature and the viscosity of the hydraulic fluid, an optimization problem arises. The viscosity of the hydraulic fluid is either in the lower or in the upper range of the temperature window, resulting in perceptible changes in comfort. in the In the lower temperature range, the viscosity of the hydraulic fluid is too high and malfunctions or failures can occur. Even after a large number of optimizations, an impairment of the vehicle properties in this area cannot be ruled out.

Der vorliegenden Erfindung liegt die Aufgabe zugrunde, ein Verfahren der eingangs genannten Art so auszugestalten, dass der Betrieb der Hydraulikanlage im Bereich mit hoher Viskosität der Hydraulikflüssigkeit zeitlich minimiert werden kann.The present invention is based on the object of designing a method of the type mentioned at the outset in such a way that the operation of the hydraulic system in the area with high viscosity of the hydraulic fluid can be minimized in terms of time.

Diese Aufgabe wird erfindungsgemäß dadurch gelöst, dass mindestens ein, die Viskosität der Hydraulikflüssigkeit der Hydraulikanlage kennzeichnender, Betriebsparameter erfasst und in einer Datenverarbeitungseinrichtung ausgewertet wird, wobei bei Erkennung eines Betriebszustands, in dem die Viskosität der Hydraulikflüssigkeit einen vorbestimmten, oberen Schwellenwert überschreitet, die Hydraulikpumpe in einem vom Arbeitsmodus unabhängigen oder dem Arbeitsmodus überlagerten Warmlaufmodus betrieben wird, in dem die Hydraulikpumpe derart angesteuert wird, dass die Viskosität der Hydraulikflüssigkeit erniedrigt wird.This object is achieved according to the invention in that at least one operating parameter that characterizes the viscosity of the hydraulic fluid in the hydraulic system is recorded and evaluated in a data processing device, wherein when an operating state is detected in which the viscosity of the hydraulic fluid exceeds a predetermined upper threshold value, the hydraulic pump in is operated in a warm-up mode that is independent of the working mode or superimposed on the working mode, in which the hydraulic pump is controlled in such a way that the viscosity of the hydraulic fluid is reduced.

Dabei wird zweckmäßigerweise als Betriebsparameter die Temperatur der Hydraulikflüssigkeit erfasst. Bei bekannter Spezifikation der Hydraulikflüssigkeit ist die Temperatur der Hydraulikflüssigkeit ein Maß für deren Viskosität. Mit sinkender Temperatur steigt die Viskosität.The temperature of the hydraulic fluid is expediently recorded as an operating parameter. If the specification of the hydraulic fluid is known, the temperature of the hydraulic fluid is a measure of its viscosity. Viscosity increases with decreasing temperature.

Die Auswertung der Betriebsparameter erfolgt in der Datenverarbeitungseinrichtung, welche zweckmäßigerweise in die Fahrzeugsteuerung integriert ist.The operating parameters are evaluated in the data processing device, which is expediently integrated into the vehicle control system.

Ziel ist es, die Verharrung der Hydraulikflüssigkeitstemperatur im unteren Bereich des Hydraulikflüssigkeitstemperaturfensters zeitlich zu minimieren. Damit wird die Dauer, in der das Flurförderzeug mit hoher Viskosität der Hydraulikflüssigkeit betrieben wird, minimiert.The aim is to minimize the persistence of the hydraulic fluid temperature in the lower range of the hydraulic fluid temperature window over time. This minimizes the duration in which the industrial truck is operated with a high viscosity of the hydraulic fluid.

Hierzu wird eine zu hohe Viskosität der Hydraulikflüssigkeit der Hydraulikanlage bevorzugt über eine Temperaturmessung der Hydraulikflüssigkeit ermittelt, und die Datenverarbeitungseinrichtung um einen Betriebspunkt bei hoher Viskosität der Hydraulikflüssigkeit erweitert. In diesem Betriebspunkt erfolgt eine zusätzliche Ansteuerung der Hydraulikpumpe.For this purpose, if the viscosity of the hydraulic fluid in the hydraulic system is too high, it is preferably determined by measuring the temperature of the hydraulic fluid, and the data processing device moves around an operating point when the viscosity is high Expanded hydraulic fluid. At this operating point, the hydraulic pump is additionally activated.

Dabei wird die Temperatur der Hydraulikflüssigkeit gemäß einer bevorzugten Ausgestaltung direkt mittels eines Temperatursensors in einem Hydraulikkreis der Hydraulikanlage gemessen.According to a preferred embodiment, the temperature of the hydraulic fluid is measured directly by means of a temperature sensor in a hydraulic circuit of the hydraulic system.

Eine alternative Variante besteht darin, dass die Temperatur der Hydraulikflüssigkeit indirekt über eine Messung der Motortemperatur des Antriebsmotors, insbesondere eines elektrischen Antriebsmotors, oder indirekt über die Messung der Umrichtertemperatur eines einen elektrischen Antriebsmotor ansteuernden Umrichters erfasst wird. Dabei kann mittels einer Modellrechnung aus der Motortemperatur bzw. der Umrichtertemperatur auf die Temperatur der Hydraulikflüssigkeit geschlossen werden.An alternative variant is that the temperature of the hydraulic fluid is detected indirectly by measuring the motor temperature of the drive motor, in particular an electric drive motor, or indirectly by measuring the converter temperature of a converter controlling an electric drive motor. In this case, the temperature of the hydraulic fluid can be deduced from the motor temperature or the converter temperature by means of a model calculation.

Zur Betriebspunkterkennung, also der Erkennung einer zu hohen Viskosität der Hydraulikflüssigkeit, ist vorteilhafterweise ebenfalls eine Modellrechnung vorgesehen. Hierzu wird in der Datenverarbeitungseinrichtung eine Modellrechnung durchgeführt, die aus hinterlegten Spezifikationsdaten der Hydraulikflüssigkeit und dem erfassten Betriebsparameter den jeweiligen Betriebszustand berechnet und den Betriebszustand, in dem die Viskosität der Hydraulikflüssigkeit den vorbestimmten, oberen Schwellenwert überschreitet, erkennt.A model calculation is advantageously also provided for operating point detection, ie for detecting that the viscosity of the hydraulic fluid is too high. For this purpose, a model calculation is carried out in the data processing device, which calculates the respective operating state from stored specification data of the hydraulic fluid and the detected operating parameter and recognizes the operating state in which the viscosity of the hydraulic fluid exceeds the predetermined upper threshold value.

Beispielsweise kann die Modellrechnung die Messwerte der Hydrauliköltemperatur und die in der Datenverarbeitungseinrichtung hinterlegten Daten zur Spezifikation der verwendeten Hydraulikflüssigkeit, insbesondere bezüglich des Viskositätsverhaltens, verwenden. Aus diesen Werten errechnet das Modell, in welchem Betriebspunkt sich das Flurförderzeug befindet, und bildet daraus den Betriebszustand "zu hohe Hydraulikölviskosität".For example, the model calculation can use the measured values of the hydraulic oil temperature and the data stored in the data processing device for specifying the hydraulic fluid used, in particular with regard to the viscosity behavior. From these values, the model calculates the operating point at which the industrial truck is located and uses this to calculate the operating status "Hydraulic oil viscosity too high".

Bei Erkennung des Betriebszustands, in dem die Viskosität der Hydraulikflüssigkeit den vorbestimmten, oberen Schwellenwert überschreitet, wird vorzugsweise eine Meldung auf einer Anzeige- und/oder Bedieneinheit des Flurförderzeugs angezeigt. Auf diese Weise kann der Fahrer über diesen Betriebszustand und den damit verbundenen Warmlaufmodus informiert werden.When the operating state is detected, in which the viscosity of the hydraulic fluid exceeds the predetermined upper threshold value, a message is preferably displayed on a display and/or operating unit of the industrial truck. In this way, the driver can be informed about this operating state and the associated warm-up mode.

Der Fahrer kann dann manuell den Warmlaufmodus aktivieren, in dem er die Hydraulikpumpe entsprechend ansteuert, also beispielsweise die Hydraulikpumpe mit erhöhter Drehzahl betreibt und/oder längere Zeit im Leerlauf laufen lässt, um die Temperatur der Hydraulikflüssigkeit zu erhöhen und somit deren Viskosität zu senken.The driver can then manually activate the warm-up mode by activating the hydraulic pump accordingly, for example operating the hydraulic pump at a higher speed and/or letting it run idle for a longer period of time in order to increase the temperature of the hydraulic fluid and thus reduce its viscosity.

Gemäß einer Weiterbildung des Erfindungsgedankens wird bei Erkennung des Betriebszustands, in dem die Viskosität der Hydraulikflüssigkeit den vorbestimmten Schwellenwert überschreitet, von der Datenverarbeitungseinrichtung automatisch der Warmlaufmodus aktiviert.According to a development of the idea of the invention, the warm-up mode is automatically activated by the data processing device when the operating state is detected, in which the viscosity of the hydraulic fluid exceeds the predetermined threshold value.

Dabei wird im Warmlaufmodus vorzugsweise die Drehzahl, beispielsweise die Leerlaufdrehzahl, der Hydraulikpumpe erhöht. Dabei kann die Hydraulikflüssigkeit im Umlauf des Hydraulikkreises, beispielsweise über eine Eingangsdruckwaage in einem Steuerventilblock der Arbeitshydraulik, in den Hydrauliköltank gefördert werden, ohne einen Verbraucher der Arbeitshydraulik und/oder die Lenkungshydraulik anzutreiben, wodurch die Temperatur der Hydraulikflüssigkeit erhöht wird. Die Erhöhung der Drehzahl der Hydraulikpumpe kann auch bei Betätigung eines Verbrauchers erfolgen, wobei dann die Hydraulikpumpe mit einer für den angeforderten Verbraucherstrom zu hohen Drehzahl betrieben wird, so dass wiederum ein Umlauf des Hydraulikkreises über die Eingangsdruckwaage in einem Steuerventilblock der Arbeitshydraulik erfolgt, in dem der überschüssig geförderte Volumenstrom der Hydraulikpumpe zum Hydrauliköltank gefördert wird und die Temperatur der Hydraulikflüssigkeit erhöht wird.In this case, the speed, for example the idling speed, of the hydraulic pump is preferably increased in the warm-up mode. The hydraulic fluid circulating in the hydraulic circuit can be conveyed into the hydraulic oil tank, for example via an input pressure compensator in a control valve block of the working hydraulics, without driving a consumer of the working hydraulics and/or the steering hydraulics, which increases the temperature of the hydraulic fluid. The speed of the hydraulic pump can also be increased when a consumer is actuated, in which case the hydraulic pump is then operated at a speed that is too high for the required consumer flow, so that the hydraulic circuit in turn circulates via the inlet pressure compensator in a control valve block of the working hydraulics, in which the excess volume flow of the hydraulic pump is pumped to the hydraulic oil tank and the temperature of the hydraulic fluid is increased.

Dabei wird vorzugsweise im Warmlaufmodus die maximale Drehzahl der Hydraulikpumpe reduziert. Dadurch können Schäden an der Hydraulikpumpe bei hoher Viskosität der Hydraulikflüssigkeit und Kavitation in der Hydraulikpumpe wirksam vermieden werden.The maximum speed of the hydraulic pump is preferably reduced in the warm-up mode. As a result, damage to the hydraulic pump can be effectively avoided when the viscosity of the hydraulic fluid and cavitation in the hydraulic pump are high.

Eine weitere bevorzugte Ausgestaltung der Erfindung sieht vor, dass im Warmlaufmodus die Hydraulikpumpe ohne Anforderung des Verbrauchers im Leerlauf betrieben wird. Anstelle bei unbetätigten Verbrauchern die Hydraulikpumpe im Stillstand zu betreiben, wird somit die Hydraulikpumpe bei unbetätigten Verbrauchern im Leerlauf betrieben. Dabei wird die Hydraulikflüssigkeit im Hydraulikkreis umgewälzt beziehungsweise in einen Hydrauliktank gefördert, beispielsweise über eine Eingangsdruckwaage in einem Steuerventilblock der Arbeitshydraulik, ohne den Verbraucher anzutreiben, wodurch die Temperatur der Hydraulikflüssigkeit erhöht wird.A further preferred embodiment of the invention provides that in the warm-up mode the hydraulic pump is operated at idle without a request from the consumer. Instead of operating the hydraulic pump at a standstill when consumers are not actuated, the hydraulic pump is therefore operated at idle when consumers are not actuated. The hydraulic fluid is circulated in the hydraulic circuit or conveyed into a hydraulic tank, for example via a Input pressure compensator in a control valve block of the working hydraulics without driving the consumer, which increases the temperature of the hydraulic fluid.

Eine weitere bevorzugte Ausgestaltung der Erfindung sieht vor, dass im Warmlaufmodus bei Betätigung eines Verbrauchers die Dynamik der Sollwertvorgaben für die Ansteuerung des Verbrauchers und/oder für die Ansteuerung der Hydraulikpumpe in Abhängigkeit von dem Betriebsparameter, insbesondere der Temperatur der Hydraulikflüssigkeit, angepasst wird. Im Warmlaufmodus kann hierzu die Dynamik der Sollwertvorgaben für die Ansteuerung des Verbrauchers, beispielsweise die Dynamik von Ansteuersignalen (Sollwertvorgabe) für ein den Verbraucher steuerndes Wegeventil, und/oder die Dynamik der Sollwertvorgaben für die Ansteuerung der Hydraulikpumpe, beispielsweise die Dynamik eines Ansteuersignals (Sollwertvorgabe) zum Hochlaufen des die Hydraulikpumpe antreibenden Antriebsmotors auf eine Solldrehzahl oder die Dynamik eines Ansteuersignals (Sollwertvorgabe) zum Einstellen eines Soll-Verdrängungsvolumens einer Verstellpumpe, an die höhere Viskosität des Hydraulikflüssigkeit im kalten Zustand angepasst werden. Bevorzugt wird die Dynamik der Sollwertvorgaben der entsprechenden Ansteuersignale bei hoher Viskosität der Hydraulikflüssigkeit und somit mit zunehmender Viskosität der Hydraulikflüssigkeit reduziert. Im kalten Zustand und somit bei hoher Viskosität der Hydraulikflüssigkeit ist die Viskosität der Hydraulikflüssigkeit verantwortlich für die Systemdynamik der Hydraulikanlage. Mit der Anpassung der Dynamik der Sollwertvorgaben werden somit dynamische Sollwertvorgaben bei hoher Viskosität der Hydraulikflüssigkeit reduziert, so dass sich die Sollwerte, beispielsweise entsprechende Ansteuersignale, an die Systemdynamik der Hydraulikanlage anpassen ohne die Systemdynamik der Hydraulikanlage maßgeblich zu verändern. Bei elektrischen Sollwertvorgaben, beispielsweise elektrischen Ansteuersignalen, werden hierdurch mit zunehmender Viskosität der Hydraulikflüssigkeit die elektrischen Sollwertvorgaben träger ohne dass sich die Systemdynamik der Hydraulikanlage und somit die Systemperformance der Hydraulikanlage verändert. Die Reaktionszeit der Hydraulikpumpe wird hierdurch bei hoher Viskosität der Hydraulikflüssigkeit träger, wodurch die Wahrscheinlichkeit des Auftretens von Kavitation in der Hydraulikpumpe bei hoher Viskosität der Hydraulikflüssigkeit verringert wird.A further preferred embodiment of the invention provides that in the warm-up mode when a consumer is actuated, the dynamics of the setpoint specifications for the activation of the consumer and/or for the activation of the hydraulic pump are adapted as a function of the operating parameter, in particular the temperature of the hydraulic fluid. In the warm-up mode, the dynamics of the target value specifications for controlling the consumer, for example the dynamics of triggering signals (target value specification) for a directional control valve controlling the consumer, and/or the dynamics of the target value specifications for controlling the hydraulic pump, for example the dynamics of a triggering signal (target value specification) for ramping up the drive motor driving the hydraulic pump to a target speed or the dynamics of a control signal (target value specification) for setting a target displacement volume of a variable displacement pump, to be adapted to the higher viscosity of the hydraulic fluid in the cold state. The dynamics of the setpoint specifications of the corresponding control signals are preferably reduced when the viscosity of the hydraulic fluid is high and thus with increasing viscosity of the hydraulic fluid. In the cold state and thus when the hydraulic fluid has a high viscosity, the viscosity of the hydraulic fluid is responsible for the system dynamics of the hydraulic system. With the adaptation of the dynamics of the setpoint specifications, dynamic setpoint specifications are thus reduced when the viscosity of the hydraulic fluid is high, so that the setpoint values, for example corresponding control signals, adapt to the system dynamics of the hydraulic system without significantly changing the system dynamics of the hydraulic system. In the case of electrical setpoint specifications, for example electrical control signals, the electrical setpoint specifications become more sluggish as the viscosity of the hydraulic fluid increases, without the system dynamics of the hydraulic system and thus the system performance of the hydraulic system changing. As a result, the response time of the hydraulic pump becomes slower when the viscosity of the hydraulic fluid is high, which reduces the likelihood of cavitation occurring in the hydraulic pump when the viscosity of the hydraulic fluid is high.

Eine weitere bevorzugte Ausgestaltung der Erfindung sieht vor, dass im Warmlaufmodus eine elektrisch im Einstelldruck veränderbares Druckbegrenzungsventil der Hydraulikanlage in Abhängigkeit von dem Betriebsparameter, insbesondere der Temperatur der Hydraulikflüssigkeit, angesteuert wird. Bevorzugt wird hierzu bei hoher Viskosität der Einstelldruck das Druckbegrenzungsventil der Hydraulikanlage reduziert. Das Druckbegrenzungsventil der Hydraulikanlage sichert den maximal zulässigen Arbeitsdruck der Hydraulikanlage ab. Im Warmlaufmodus wird somit der maximal zulässige Arbeitsdruck an die Viskosität der Hydraulikflüssigkeit und somit an den Aufwärmprozess der Hydraulikflüssigkeit angepasst. Dadurch können unzulässige Druckspitzen während des Warmlaufmodus verhindert werden. Zudem können hierdurch bei einem Hubantrieb mit mehreren Hubzylindern, die jeweils eine Hubstufe betätigen, beispielsweise einen Freihub und einen Masthub, Hubfolgefehler durch eine falsche Ausfahrreihenfolge der Hubzylinder verhindert werden.A further preferred embodiment of the invention provides that, in the warm-up mode, a pressure-limiting valve of the hydraulic system, the setting pressure of which can be changed electrically, is activated as a function of the operating parameter, in particular the temperature of the hydraulic fluid. In the case of high viscosity, the set pressure of the pressure-limiting valve of the hydraulic system is preferably reduced for this purpose. The pressure relief valve of the hydraulic system ensures the maximum permissible working pressure of the hydraulic system. In the warm-up mode, the maximum permissible working pressure is thus adapted to the viscosity of the hydraulic fluid and thus to the warm-up process of the hydraulic fluid. This can prevent impermissible pressure peaks during the warm-up mode. In addition, in the case of a lifting drive with a plurality of lifting cylinders, each of which actuates a lifting stage, for example a free lift and a mast lift, this can prevent lifting sequence errors due to the lifting cylinders being extended in the wrong order.

Vorteilhafterweise wird die Hydraulikpumpe so lange im Warmlaufmodus betrieben, bis ein vorbestimmter, unterer Schwellenwert der Viskosität der Hydraulikflüssigkeit unterschritten wird. Hierzu kann beispielsweise die Hydraulikpumpe für eine Dauer von ca. 20 Minuten im Leerlauf mit einer konstanten Leerlaufdrehzahl von ca. 1.000 Umdrehungen pro Minute ohne Anforderung des Verbrauchers betrieben werden, um die Temperatur der Hydraulikflüssigkeit von -7 °C auf +15 °C zu erhöhen.Advantageously, the hydraulic pump is operated in the warm-up mode until the viscosity of the hydraulic fluid falls below a predetermined lower threshold value. For example, the hydraulic pump can be operated for a period of approx. 20 minutes at a constant idle speed of approx. 1,000 revolutions per minute without the consumer requesting it, in order to increase the temperature of the hydraulic fluid from -7 °C to +15 °C .

Die Erfindung bietet eine ganze Reihe von Vorteilen;The invention offers a number of advantages;

Aufgrund der verkürzten Betriebsphase mit kalter und zähfließender Hydraulikflüssigkeit ergibt sich ein geringerer Verschleiß der Hydraulikpumpe, so dass die Standzeit der Hydraulikpumpe erhöht wird. Außerdem werden die optimalen Betriebspunkte bezüglich Schmierung, Filterung und Reibung schneller erreicht. Durch Umgehung des Verbrauchers im Warmlaufmodus kann bei Ansteuerung der Hydraulikpumpe im Leerlaufbetrieb die Hydraulikpumpe bei Druckarbeitspunkten betrieben werden, die nicht im Grenzbereich liegen.Due to the shortened operating phase with cold and viscous hydraulic fluid, there is less wear on the hydraulic pump, so that the service life of the hydraulic pump is increased. In addition, the optimum operating points in terms of lubrication, filtering and friction are reached more quickly. By bypassing the consumer in the warm-up mode, the hydraulic pump can be operated at pressure operating points that are not in the limit range when the hydraulic pump is activated in idle mode.

Darüber hinaus ergibt sich eine Komforterhöhung durch Unterbinden bzw. statistisches Reduzieren von Hubfolgefehlern. Auch eine Schwergängigkeit der Lenkungshydraulik im Arbeitsmodus kann durch einen vorgeschalteten oder überlagerten Warmlaufmodus vermieden werden. Außerdem wird eine gleichbleibende Arbeitsgeschwindigkeit der Verbraucher der Arbeitshydraulik und/oder der Lenkungshydraulik kurz nach dem Betriebsstart des Flurförderzeugs bei niedrigen Hydraulikflüssigkeitstemperaturen ermöglicht.In addition, there is an increase in comfort by preventing or statistically reducing stroke sequence errors. A sluggishness of the steering hydraulics in working mode can also be caused by a preceding or superimposed warm-up mode be avoided. In addition, a constant working speed of the consumers of the working hydraulics and/or the steering hydraulics is made possible shortly after the start of operation of the industrial truck at low hydraulic fluid temperatures.

Schließlich wird mit der Erfindung auch erreicht, dass die Komponenten der Arbeitshydraulik innerhalb ihrer Spezifikation betreiben werden können. Ebenso kann eine Kavitation der Hydraulikpumpe unterbunden werden.Finally, the invention also means that the components of the working hydraulics can be operated within their specification. Likewise, cavitation of the hydraulic pump can be prevented.

Insgesamt wird somit die Lebensdauer der Hydraulikpumpe erhöht und ein konstantes Betriebsverhalten der Hydraulikanlage erzielt.Overall, the service life of the hydraulic pump is thus increased and constant operating behavior of the hydraulic system is achieved.

Weitere Vorteile und Einzelheiten der Erfindung werden anhand des in der schematischen Figur dargestellten Ausführungsbeispiels näher erläutert.Further advantages and details of the invention are explained in more detail with reference to the embodiment shown in the schematic figure.

Die Figur zeigt eine grafische Darstellung des zeitlichen Verlaufs der Temperatur der Hydraulikflüssigkeit im Warmlaufmodus der Hydraulikpumpe durch das erfindungsgemäße Verfahren. Auf der horizontalen x-Achse ist die Zeit in Sekunden s aufgetragen, während auf der vertikalen y-Achse die Temperatur der Hydraulikflüssigkeit der Hydraulikanlage in °C aufgetragen ist.The figure shows a graphic representation of the time profile of the temperature of the hydraulic fluid in the warm-up mode of the hydraulic pump using the method according to the invention. The time in seconds s is plotted on the horizontal x-axis, while the temperature of the hydraulic fluid of the hydraulic system in °C is plotted on the vertical y-axis.

Im vorliegenden Ausführungsbeispiel handelt es sich bei dem Flurförderzeug um ein batterie-elektrisch betriebenes Flurförderzeug mit einer Hydraulikanlage zum Betreiben einer Arbeitshydraulik und/oder einer Lenkungshydraulik. Die Hydraulikanlage arbeitet mit einem handelsüblichen Hydrauliköl als Hydraulikflüssigkeit. Die Hydraulikanlage weist eine als Konstantpumpe ausgebildete Hydraulikölpumpe auf, die von einem als Elektromotor ausgebildeten Antriebsmotor angetrieben wird.In the present exemplary embodiment, the industrial truck is a battery-powered industrial truck with a hydraulic system for operating working hydraulics and/or steering hydraulics. The hydraulic system works with a commercially available hydraulic oil as the hydraulic fluid. The hydraulic system has a hydraulic oil pump designed as a fixed displacement pump, which is driven by a drive motor designed as an electric motor.

Die Hydrauliköltemperatur wird direkt im Hydraulikkreis mittels eines Temperatursensors gemessen. Die Messwerte werden an eine, in die Fahrzeugsteuerung integrierte, Datenverarbeitungseinrichtung des Flurförderzeugs übermittelt. In der Datenverarbeitungseinrichtung sind Daten zur Spezifikation des Hydrauliköls, insbesondere zum Viskositätsverhalten, hinterlegt. Anhand der Temperatur-Messwerte und der Spezifikations-Daten des Hydrauliköls wird in der Datenverarbeitungseinrichtung mittels einer Modellrechnung der Betriebszustand des Flurförderzeugs berechnet.The hydraulic oil temperature is measured directly in the hydraulic circuit using a temperature sensor. The measured values are transmitted to a data processing device on the industrial truck that is integrated into the vehicle control. Data on the specification of the hydraulic oil, in particular on the viscosity behavior, are stored in the data processing device. Based on the temperature readings and the specification data of the hydraulic oil, the Data processing device calculated using a model calculation of the operating state of the truck.

Das Flurförderzeug wird bei einer Umgebungstemperatur von -10°C in Betrieb genommen. Die Hydrauliköltemperatur in der Hydraulikanlage beträgt zur Startzeit -7°C. Die Modellrechnung in der Datenverarbeitungseinrichtung ergibt auf Basis dieser niedrigen Hydrauliköltemperatur und den hinterlegten Spezifikations-Daten des verwendeten Hydrauliköls einen Betriebszustand, in dem die Viskosität des Hydrauliköls einen vorbestimmten, oberen Schwellenwert überschreitet. Die Datenverarbeitungseinrichtung erkennt also, dass das Hydrauliköl für einen regulären Betrieb im Arbeitsmodus eine zu hohe Viskosität aufweist. Es könnte hier zu fehlerhaften Funktionen und/oder Ausfällen der Arbeitshydraulik und/oder der Lenkungshydraulik kommen.The industrial truck is put into operation at an ambient temperature of -10°C. The hydraulic oil temperature in the hydraulic system is -7°C at the start time. Based on this low hydraulic oil temperature and the stored specification data for the hydraulic oil used, the model calculation in the data processing device results in an operating state in which the viscosity of the hydraulic oil exceeds a predetermined upper threshold value. The data processing device thus recognizes that the hydraulic oil has too high a viscosity for regular operation in the working mode. Malfunctions and/or failures of the working hydraulics and/or the steering hydraulics could occur here.

Daher aktiviert die Datenverarbeitungseinrichtung automatisch den Warmlaufmodus und informiert den Fahrer darüber durch eine Meldung auf der Anzeige- und Bedieneinheit des Flurförderzeugs.The data processing device therefore automatically activates the warm-up mode and informs the driver of this by means of a message on the display and operating unit of the industrial truck.

Im Warmlaufmodus wird die Hydraulikpumpe derart angesteuert, dass sie mit einer konstanten und erhöhten Leerlaufdrehzahl von 1.000 Umdrehungen pro Minute im Leerlauf läuft. Es ist kein Verbraucher betätigt. Dabei wird das Hydrauliköl im Umlauf des Hydraulikkreises in den Hydrauliköltank gefördert, beispielsweise über eine Eingangsdruckwaage in einem Steuerventilblock der Arbeitshydraulik, ohne einen Verbraucher der Arbeitshydraulik und/oder die Lenkungshydraulik anzutreiben. Im Lauf der Zeit erwärmt sich dabei das Hydrauliköl, bis es die erforderliche Temperatur aufweist, bei der die Viskosität des Hydrauliköls niedrig genug für einen regulären Betrieb im Arbeitsmodus ist.In the warm-up mode, the hydraulic pump is controlled in such a way that it idles at a constant and increased idle speed of 1,000 revolutions per minute. No consumer is actuated. The hydraulic oil is pumped into the hydraulic oil tank as it circulates in the hydraulic circuit, for example via an inlet pressure compensator in a control valve block of the working hydraulics, without driving a consumer of the working hydraulics and/or the steering hydraulics. Over time, the hydraulic oil heats up until it has the required temperature at which the viscosity of the hydraulic oil is low enough for regular operation in the work mode.

Wie aus der grafischen Darstellung hervorgeht, ergibt sich zunächst nach dem Start der Hydraulikölpumpe im Warmlaufmodus eine Totzeit von 14 Sekunden. Nach 60 Sekunden steigt die Öltemperatur auf -5 °C. Nach 215 Sekunden (also unter 3 Minuten) wird die 0 °C -Grenze erreicht. Eine Öltemperatur von +5 °C ergibt sich nach 510 Sekunden (unter 9 Minuten). Nach 815 Sekunden (unter 14 Minuten) wird eine Öltemperatur von +10 °C erreicht. Schließlich wird der vorbestimmte Öltemperatur-Schwellenwert von +15 °C nach 1.400 Sekunden (also unter 24 Minuten) erreicht.As can be seen from the graphic representation, there is a dead time of 14 seconds after the start of the hydraulic oil pump in the warm-up mode. After 60 seconds, the oil temperature rises to -5 °C. The 0 °C limit is reached after 215 seconds (less than 3 minutes). An oil temperature of +5 °C results after 510 seconds (less than 9 minutes). An oil temperature of +10 °C is reached after 815 seconds (less than 14 minutes). Finally, the predetermined oil temperature threshold of +15 °C is reached after 1,400 seconds (i.e. less than 24 minutes).

Aufgrund der Modellrechnung in der Datenverarbeitungseinrichtung wird bei diesem Öltemperatur-Schwellenwert von +15 °C ein vorbestimmter, unterer Schwellenwert der Viskosität des Hydrauliköls unterschritten. Bei diesem Wert ist bei der vorliegenden Spezifikation des Hydrauliköls davon auszugehen, dass ein regulärer Betrieb im Arbeitsmodus ohne Probleme möglich ist.Based on the model calculation in the data processing device, this oil temperature threshold value of +15° C. means that the viscosity of the hydraulic oil falls below a predetermined lower threshold value. With this value, given the specification of the hydraulic oil, it can be assumed that regular operation in work mode is possible without problems.

Die Datenverarbeitungseinrichtung stoppt daher automatisch den Warmlaufmodus und informiert den Fahrer darüber durch eine Meldung auf der Anzeige- und Bedieneinheit des Flurförderzeugs. Daraufhin kann der reguläre Arbeitsmodus gestartet werden, bei dem die Verbraucher der Arbeitshydraulik und/oder der Lenkungshydraulik mit dem Volumenstrom der Hydraulikölpumpe angetrieben werden bzw. die Hydraulikpumpe mit einer reduzierten Leerlaufdrehzahl betrieben wird bzw. die Hydraulikpumpe bei unbetätigten Verbrauchern im Stillstand betrieben ist.The data processing device therefore automatically stops the warm-up mode and informs the driver of this by means of a message on the display and operating unit of the industrial truck. The regular working mode can then be started, in which the consumers of the working hydraulics and/or the steering hydraulics are driven with the volume flow of the hydraulic oil pump or the hydraulic pump is operated at a reduced idle speed or the hydraulic pump is operated at a standstill when consumers are not actuated.

Claims (12)

  1. Method for operating a hydraulic system of an industrial truck having a hydraulic pump which is driven by a drive motor and, during operation in a working mode, generates a volume flow of a hydraulic liquid which supplies at least one load, characterized in that at least one operating parameter which characterizes the viscosity of the hydraulic liquid of the hydraulic system is recorded and evaluated in a data processing device, wherein, when an operating state in which the viscosity of the hydraulic liquid exceeds a predetermined, upper threshold value is identified, the hydraulic pump is operated in a warm-up mode which is independent of the working mode or is superimposed on the working mode and in which the hydraulic pump is driven in such a way that the viscosity of the hydraulic liquid is lowered.
  2. Method according to Claim 1, characterized in that the operating parameter recorded is the temperature of the hydraulic liquid.
  3. Method according to Claim 2, characterized in that the temperature of the hydraulic liquid is directly measured by means of a temperature sensor in a hydraulic circuit of the hydraulic system.
  4. Method according to Claim 2, characterized in that the temperature of the hydraulic liquid is indirectly recorded via measurement of the motor temperature of the drive motor.
  5. Method according to one of Claims 1 to 4, characterized in that a model calculation is carried out in the data processing device, the model calculation calculating the respective operating state from stored specification data relating to the hydraulic liquid and the recorded operating parameter and identifying the operating state in which the viscosity of the hydraulic liquid exceeds the predetermined, upper threshold value.
  6. Method according to one of Claims 1 to 5, characterized in that, when the operating state in which the viscosity of the hydraulic liquid exceeds the predetermined, upper threshold value is identified, a message is displayed on a display and/or operator control unit of the industrial truck.
  7. Method according to one of Claims 1 to 6, characterized in that, when the operating state in which the viscosity of the hydraulic liquid exceeds the predetermined threshold value is identified by the data processing device, the warm-up mode is automatically activated.
  8. Method according to one of Claims 1 to 7, characterized in that the rotation speed of the hydraulic pump is increased in the warm-up mode.
  9. Method according to one of Claims 1 to 8, characterized in that the hydraulic pump is operated at idling speed without demand by the load in the warm-up mode.
  10. Method according to one of Claims 1 to 9, characterized in that, when the load is operated, the dynamics of the target value specifications for driving the load and/or the hydraulic pump are adapted depending on the operating parameter, in particular the temperature of the hydraulic liquid, in the warm-up mode.
  11. Method according to one of Claims 1 to 10, characterized in that a pressure-limiting valve of the hydraulic system which can be varied electrically in terms of setting pressure is actuated depending on the operating parameter, in particular the temperature of the hydraulic liquid, in the warm-up mode.
  12. Method according to one of Claims 1 to 11, characterized in that the hydraulic pump is operated in the warm-up mode until a predetermined, lower threshold value for the viscosity of the hydraulic liquid is undershot.
EP19212033.5A 2018-12-20 2019-11-28 Method for operating a hydraulic system of an industrial truck Active EP3674252B1 (en)

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JP4725345B2 (en) * 2006-02-08 2011-07-13 日立建機株式会社 Hydraulic drive industrial machine
BR112014016456A8 (en) * 2012-01-13 2017-07-04 Crown Equip Corp method for operating a material handling vehicle and material handling vehicle
DE102017106390A1 (en) 2017-03-24 2018-09-27 Still Gmbh Method for operating a hydraulic system of a truck

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