Method for operating a hydraulic drive system of an industrial truck

Abstract

Method for operating a hydraulic drive system (1) of an industrial truck, wherein the drive system (1) has a working hydraulic system (2) which, as a consumer, comprises a lifting drive for raising and lowering a load carriage and at least one additional drive (3) which is designed as an attachment (3a) that is attached to the load carriage, wherein a control directional control valve (5) is provided for controlling the attachment (3a), which is connected on the inlet side to a delivery line (14) of a hydraulic pump (10) and on the outlet side to a container line (15) leading to a container (13), wherein the hydraulic pump (10) is driven by a drive motor (11), and wherein, in order to generate a movement of the attachment (3a), the control directional control valve (5) is actuated into a control position (5b; 5c) as a function of the actuation of an operating device (21) and is supplied to the attachment (3a) from the hydraulic pump (10) via the control device (21) that is in the control position (5b;5c) actuated control directional valve (5), pressure medium is supplied, characterized in that a pressure relief valve (16) is provided to protect the drive system (1), which is connected on the inlet side to the delivery line (14) and on the outlet side to the container (13) and is set to a maximum system pressure of the working hydraulics (2), wherein a maximum speed (n_max) of the hydraulic pump (10) adapted to the respective attachment (3a) and a maximum pump pressure (Pmax_Anbau) adapted to the respective attachment (3a), which is smaller than the maximum system pressure of the working hydraulics (2) secured on the pressure relief valve (16), are predetermined, wherein upon actuation of the control directional valve (5) of the attachment (3a) into a control position (5b;5c) as a result of an actuation of the operating device (21), a speed setpoint value (n_soll) for the speed of the hydraulic pump (10) is generated and output to the drive motor (11), the pump pressure present in the delivery line (14) is determined and the speed of the hydraulic pump (10) is regulated such that the pump pressure in the delivery line (14) is lower than the maximum pump pressure (Pmax_Anbau) adapted and predetermined for the respective attachment (3a);

Description

The invention relates to a method for operating a hydraulic drive system of an industrial truck, wherein the drive system has a working hydraulic system which comprises, as a consumer, a lifting drive for raising and lowering a load carriage and at least one additional drive which is designed as an attachment which is attached to the load carriage, wherein a control directional valve is provided for controlling the attachment, said control directional valve being connected on the input side to a delivery line of a hydraulic pump and on the output side to a container line which is guided to a container, wherein the hydraulic pump is driven by a drive motor, and wherein, in order to generate a movement of the attachment, the control directional valve is actuated into a control position as a function of the actuation of an operating device, and pressure medium is supplied to the attachment by the hydraulic pump via the control directional valve which is actuated into the control position.DE 10 2004 011 913 A1 discloses a method of the generic type for operating a hydraulic drive system of an industrial truck according to the features of the preamble of patent claim 1.DE 10 2009 029 840 A1 discloses a hydraulic system with a closed circuit, in which a feed pump is driven by a hydraulic drive motor, wherein the hydraulic drive motor can be operated at a higher pressure and a lower delivery rate than the feed pump.Industrial trucks allow the exchangeable accommodation and operation of different auxiliary drives, each designed as an attachment, which form auxiliary consumers of a working hydraulic system. A corresponding attachment is mounted on a load carriage that can be raised and lowered in a lifting mast and enables special functions in the handling of a load. An attachment can be designed, for example, as a lateral slide for laterally displacing a load fork or as a tine adjustment device for adjusting the distance between fork tines of a load fork or as a rotating device for rotating a load-receiving means or as a clamping device for clamping and holding a load to be received or as a blade for receiving bulk material. An industrial truck can be equipped with a specific attachment. It is also already known to change different attachments on the same industrial truck depending on the use of the industrial truck.Due to the different structural design of the various attachments and the different functions of the attachments, the necessary pump volume flows and thus the rotational speeds of the hydraulic pump, which are optimal for the operation of the corresponding attachment, differ depending on the attachment. It is known here to preset a rotational speed adapted to the corresponding attachment for driving the hydraulic pump in an electronic control device which drives the drive motor of the hydraulic pump. However, it has been found that frequently too high rotational speeds are set for the hydraulic pump.Attachments mounted on industrial trucks generally operate at a working pressure of 120 bar, for example. In this case, the hydraulic pump should supply a delivery pressure and thus a pump pressure which covers the working pressure of the attachment and additionally also the line losses in the pressure medium line which is routed from the hydraulic pump to the attachment. The drive system is set for the operation of the further consumers of the working hydraulics, generally a lifting drive for raising and lowering the load-receiving means and a tilting drive for tilting the lifting mast, in which the load-receiving means can be raised and lowered, to a maximum system pressure of generally 230 bar. This maximum system pressure is secured to the working hydraulics by a pressure limiting valve which is assigned to the delivery line of the hydraulic pump. However, if, in the case of an industrial truck, the rotational speed of the hydraulic pump is predefined during operation of the attachment in such a way that a pump volume flow is supplied and conveyed by the hydraulic pump which is greater than is actually required by the attachment as volume flow and is therefore necessary for operation of the attachment, the line losses in the pressure medium line which is conducted from the hydraulic pump to the attachment increase nonlinearly on account of increasing turbulent flows. In this case, operating states can occur in which, during operation of the attachment, such high rotational speeds for the hydraulic pump are set that the hydraulic pump delivers and builds up the maximum system pressure of the working hydraulics of 230 bar as the delivery pressure in the delivery line and thus as the pump pressure, and a so-called oversupply occurs in which a part of the pump volume flow generated by the hydraulic pump flows out into the container, for example via the opening pressure limiting valve assigned to the delivery line, so that the attachment is supplied with the working pressure of 120 bar and the remaining pump volume flow of the hydraulic pump.In such an operating state, the hydraulic pump thus supplies higher pressures and has a higher rotational speed than would actually be necessary for driving the attachment, so that correspondingly high energy losses occur and the hydraulic pump has a higher energy consumption than would be necessary. If the hydraulic pump were to have a lower rotational speed during operation of the attachment, the line losses in the pressure medium line routed from the hydraulic pump to the attachment would be greatly reduced and a lower pump pressure would be established in the delivery line of the hydraulic pump without the operating speed of the attachment being reduced.The object of the present invention is to provide a method for operating a hydraulic drive system of an industrial truck of the type mentioned at the beginning, with which the attachment is operated with low energy losses.This object is achieved according to the invention in that a pressure limiting valve is provided for securing the drive system, which valve is connected on the input side to the delivery line and is connected on the output side to the container and is set to a maximum system pressure of the working hydraulics, wherein a maximum rotational speed of the hydraulic pump adapted to the respective attachment and a maximum pump pressure adapted to the respective attachment, which is lower than the maximum system pressure of the working hydraulics secured to the pressure limiting valve, are predefined, wherein, when the control path valve of the attachment is actuated into a control position as a result of an actuation of the operating device, a rotational speed setpoint value for the rotational speed of the hydraulic pump, which setpoint value is dependent on the actuation of the operating device, is generated and output to the drive motor, the pump pressure present in the delivery line is determined and the rotational speed of the hydraulic pump is regulated in such a way, the pump pressure in the delivery line is smaller than the predetermined maximum pump pressure adapted to the respective attachment. In the method according to the invention, a maximum rotational speed of the hydraulic pump adapted to the mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted on mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted on mounted mounted mounted mounted mounted mounted mounted mounted mounted on mounted mounted mounted mounted mounted on mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted on mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted on mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted on mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted on mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted on mounted mounted mounted mounted mounted mounted mounted mounted on mounted mounted mounted mounted mounted mounted on mounted mounted mounted mounted mounted mounted on mounted mounted mounted mounted mounted mounted mounted mounted mounted on mounted mounted mounted mounted on mounted mounted mounted mounted mounted mounted mounted on the mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted mounted. The maximum pump pressure adapted to the mounted attachment is smaller than the maximum system pressure of the working hydraulics. If the operating device is operated for the purpose of actuating and thus generating a movement of the attachment and the control directional valve is thus deflected into a control position, a setpoint rotational speed value for the rotational speed of the hydraulic pump, which setpoint rotational speed value is dependent on the actuation of the operating device, is generated and output to the drive motor driving the hydraulic pump. When the attachment is actuated, the pump pressure prevailing in the delivery line is determined and the rotational speed of the hydraulic pump is regulated in such a way that the pump pressure in the delivery line is less than the predefined maximum pump pressure adapted to the respective attachment. In the method according to the invention, starting from the setpoint rotational speed value for the rotational speed of the hydraulic pump to which the drive motor is set at the beginning of the actuation of the attachment, an automatic rotational speed reduction of the rotational speed of the hydraulic pump results. After a settling time, in the method according to the invention, a rotational speed of the hydraulic pump for the actuation and movement of the attachment is established, at which it holds true that the pump pressure supplied by the hydraulic pump is less than the predefined maximum pump pressure. With the method according to the invention, an actuation of the attachment can thus be achieved at an actuation speed specified on the operating device, wherein the hydraulic pump does not enter into an operating state with an oversupply, in which pump delivery flow is delivered lossy into the container. The method according to the invention thus enables operation of the attachment with low energy consumption and with low energy losses.According to an advantageous development of the invention, the rotational speed of the hydraulic pump is regulated during an actuation of the attachment in such a way that the rotational speed of the hydraulic pump is always lower than the setpoint rotational speed value. This achieves the result that, at the beginning of the actuation of the attachment and operation of the hydraulic pump with the setpoint rotational speed value, the rotational speed of the hydraulic pump is lowered by the control system until the pump pressure in the delivery line is less than the predefined maximum pump pressure which is matched to the respective attachment.The setpoint rotational speed value dependent on the actuation of the operating device corresponds here at most to the maximum rotational speed of the hydraulic pump adapted to the respective attachment. The hydraulic pump is thus operated at the maximum with the maximum speed adapted to and predetermined for the respective attachment when the operating device is operated to the maximum.Expediently, according to one embodiment of the invention, the setpoint rotational speed value dependent on the actuation of the operating device is proportional to the actuation of the operating device.Expediently, when the control path valve is actuated into a control position as a result of an actuation of the operating device, the drive motor of the hydraulic pump is operated at a minimum rotational speed.According to a further development of the invention, when presetting the maximum pump pressure adapted to the respective attachment, a loss pressure is observed which occurs in the delivery line of the hydraulic pump and / or in the consumer lines conducted from the control directional valve to the attachment. This achieves the effect that, when the attachment is actuated, the hydraulic pump can build up a pump pressure in the delivery line which is the sum of the working pressure of the respective attachment and the loss pressure in the delivery line and / or the consumer lines, so that, when the attachment is actuated, the hydraulic pump can build up a pump pressure such that the line losses are overcome and the attachment can be operated at the respective working pressure. The attachment is then operated at a working speed predetermined by the actuation of the operating device.According to an advantageous embodiment of the invention, a constant pressure value is used as the loss pressure. Since in industrial trucks the control directional valve with which the attachment is controlled is installed in the vehicle body and the attachment is arranged on the load carriage which can be raised and lowered on the lifting mast, correspondingly long consumer lines are produced for the attachment, in which corresponding pressure losses can occur. With the observation of a constant, for example characteristic, loss pressure in the delivery line and the consumer lines, it is achieved in a simple manner that the attachment can be operated at the respective working pressure. Corresponding loss pressures can be stored or input in an electronic control device.According to an alternative and particularly advantageous development of the invention, the loss pressure is calculated as a function of the temperature of the pressure medium of the drive system. As a result, the additional loss pressure is determined as a function of temperature and thus as a function of the viscosity of the pressure medium, so that the predefined maximum pump pressure of the attachment is adapted as a function of the temperature-dependent and thus viscosity-dependent line losses.In order to determine the pump pressure present in the delivery line, according to an advantageous embodiment of the invention, the pump pressure present in the delivery line of the hydraulic pump can be measured by means of a pressure sensor. A pressure sensor enables a direct measurement and determination of the pump pressure present in the delivery line of the hydraulic pump.In order to be able to dispense with such a pressure sensor in the delivery line of the hydraulic pump, according to an alternative and likewise advantageous embodiment of the invention, in which the drive motor is designed as an electric motor, the current is used in a converter of the electric motor for determining the pump pressure present in the delivery line. On the basis of the current and a corresponding current measurement in the converter which controls the electric motor, the pump pressure present in the delivery line of the hydraulic pump can be determined indirectly.According to an advantageous development of the invention, the set rotational speeds of the hydraulic pump are stored for identical actuations of the attachment and the predefined maximum rotational speed of the hydraulic pump is corrected as a function of the stored rotational speeds of the hydraulic pump.In the method according to the invention, the rotational speed of the hydraulic pump is always adjusted to the same rotational speed in the case of the same actuation of the attachment, i.e. the same actuation of the operating device. If, after repeated and identical actuation of the attachment, the set rotational speeds of the hydraulic pump are stored, the predetermined maximum rotational speed of the hydraulic pump can be corrected and adapted, for example, by means of a statistical evaluation, whereby a reduction in the set-up time is achieved. When storing and / or evaluating the stored set speeds, the temperature of the pressure medium can be taken into account for the temperature, so that the predefined maximum speed of the hydraulic pump is adapted as a function of the temperature. If, for example, a value of 1200 U / min is preset as a maximum rotational speed of the hydraulic pump adapted to the respective attachment and, after repeated, for example five times, identical actuation of the attachment, the rotational speed of the hydraulic pump is adjusted in each case to a value of 800 U / min in order to keep the pump pressure in the delivery line lower than the maximum pump pressure adapted to the respective attachment and preset, the maximum rotational speed of the hydraulic pump adapted to the respective attachment can be automatically adjusted to a value of 900 U / min, for example, and corrected in order to achieve a reduction in the adjustment time.If, after such an adaptation of the maximum rotational speed of the hydraulic pump, during a control process in which, starting from a predefined maximum rotational speed of the hydraulic pump, no lowering of the rotational speed of the hydraulic pump takes place by the control during the actuation of the attachment, so that the pump pressure in the delivery line is kept lower than the predefined maximum pump pressure adapted to the respective attachment, according to a further development of the invention the predefined maximum rotational speed of the hydraulic pump is raised until, during a control process in which, starting from the maximum rotational speed of the hydraulic pump, a lowering of the rotational speed of the hydraulic pump takes place again during the actuation of the attachment by the control, so that the pump pressure in the delivery line is kept lower than the predefined maximum pump pressure adapted to the respective attachment. If, when adapting the maximum rotational speed of the hydraulic pump adapted to the respective attachment, the selection of such a maximum rotational speed of the hydraulic pump has taken place that no further lowering of the rotational speed takes place in order to keep the pump pressure in the delivery line lower than the predetermined maximum pump pressure adapted to the respective attachment, the predetermined maximum rotational speed of the hydraulic pump is thus raised again in order to achieve a lowering of the rotational speed of the hydraulic pump during a control process in order to keep the pump pressure in the delivery line lower than the predetermined maximum pump pressure adapted to the respective attachment. The increase of the predetermined maximum rotational speed of the hydraulic pump can take place continuously or preferably in predetermined steps, for example in steps of 50 μ / min.According to an advantageous development, the method is carried out in an electronic control device of the industrial truck which actuates the drive motor and the control path valve, wherein the electronic control device is operatively connected to the attachment and the necessary working pressure of the attachment and the maximum volume flow of the attachment are transmitted to the electronic control device from the attachment, wherein the electronic control device determines the pump pressure which is adapted to the respective attachment from the transmitted working pressure of the attachment and determines the maximum rotational speed of the hydraulic pump which is adapted to the respective attachment from the transmitted maximum volume flow of the attachment in conjunction with the displacement volume of the hydraulic pump. The working implement mounted on the attachment is thus transmitted to the electronic control device the implement-specific working pressure of the attachment, the maximum volume flow of the attachment and, if appropriate, also the cross sections of the working cylinders of the attachment. From the transmitted working pressure of the attachment, the electronic control device can determine the maximum pump pressure adapted to the attached attachment in conjunction with the line losses, which can be observed constantly or depending on temperature. From the transmitted maximum volume flow of the attachment, the electronic control device, in conjunction with the displacement volume of the hydraulic pump, which can be stored or input in the electronic control device, can determine the maximum rotational speed of the hydraulic pump adapted to the attached attachment. This makes it possible in a simple manner for the attachment mounted on the industrial truck to be able to be operated by the hydraulic pump of the working hydraulics without oversupply with an attachment-specific volume flow and working pressure.According to an advantageous embodiment of the invention, the electronic control device can be operatively connected to the attachment via a wireless connection or alternatively via a cable-bound connection. A wireless connection for transmitting the attachment-specific data to the electronic control device of the industrial truck can be effected, for example, via RFID, WLAN, Bluetooth, Zigbee. A cable-bound connection for transmitting the attachment-specific data to the electronic control device of the industrial truck can be effected, for example, via a CAN bus, via a connecting cable using pulse width modulation or via a connecting cable using Ethernet protocols.Further advantages and details of the invention are explained in more detail on the basis of the exemplary embodiment shown in the schematic figure.The figure shows a circuit diagram of a hydraulic drive system 1 according to the invention of an industrial truck, for example a forklift truck.The drive system 1 has a working hydraulic system 2 which comprises a plurality of consumers. The working hydraulic system 2 has as a load a lifting drive, not shown in detail, which comprises at least one hydraulic lifting cylinder, which is connected to a load carriage, not shown in detail, of the industrial truck for lifting and lowering a load. The load carriage is arranged such that it can be lifted and lowered in a lifting mast. A further consumer, not shown in detail, of the working hydraulics 2 is designed, for example, as a tilting drive of the lifting mast. The illustrated consumer 3 of the working hydraulic system 2 is designed as an additional drive. The additional drive is designed as an attachment 3 awhich is attached to the load carriage.The consumer 3 of the working hydraulic system 2 can be controlled by means of a control directional valve 5, for example a directional control valve restricting into intermediate positions. The other consumers of the working hydraulics 2 can be controlled by means of corresponding control directional valves, not shown in detail. The control directional valves of the consumers of the working hydraulics 2 are combined in a control valve block 6. In the exemplary embodiment shown, the consumer 3 is designed as a double-acting consumer which is connected to the control directional valve 5 by means of consumer lines 7 a, 7 b.To supply the consumers 3 of the working hydraulics 2 with pressure medium, a hydraulic pump 10 is provided, which is operatively connected to a drive motor 11, for example an electric motor 11 a, for driving. The hydraulic pump 10 is operated in an open circuit, which draws pressure medium from a container 13 by means of a suction line 12 and delivers it into a delivery line 14. In the exemplary embodiment shown, the hydraulic pump 10 is designed as a constant pump with a constant delivery volume.The control directional valves 5 of the consumers of the working hydraulics 2 are each connected to the delivery line 14 of the hydraulic pump 10 and to a container line 15 leading to the container 13.The control directional valve 5 has a neutral position 5a in which the connection of the consumer lines 7a, 7b to the delivery line 14 and the container line 15 is shut off.The control directional valve 5 has a first control position 5 bin which the consumer line 7 ais connected to the delivery line 14 and the consumer line 7 bis connected to the container line 15. The control directional valve 5 has a second control position 5c, in which the consumer line 7b is connected to the delivery line 14 and the consumer line 7a is connected to the container line 15. In the exemplary embodiment shown, the control directional valve 5 is designed as a proportional valve which throttles into intermediate positions and which, with increasing actuation into the control positions 5b and 5c, enables an increasing valve opening from the delivery line 13 into the consumer line 7a and 7b.To protect the drive system 1, a pressure limiting valve 16 is provided, which is connected on the input side to the delivery line 14 and is connected on the output side to the container 13. The pressure limiting valve 16 is set to a maximum system pressure of the working hydraulic system 2.In the exemplary embodiment shown, the control directional valve 5 can be actuated electrically and is connected to an electronic control device 20 for actuation.The electronic control device 20 is furthermore connected to an operating device 21 that can be actuated by the operator, for example a joystick, by the actuation of which the operator can specify an actuation of the control path valve 5 and thus can execute an actuation of a movement of the attachment 3 a.The electronic control device 20 is also operatively connected to the drive motor 11 designed as an electric motor 11 ato operate the hydraulic pump 10 at a specific rotational speed.In the figure, the electronic control device 20 is also connected to a pressure sensor 25, by means of which the pump pressure of the hydraulic pump 10 in the delivery line 14 is detected.The electronic control device 20 can furthermore be operatively connected to a sensor device 26 which detects the temperature of the pressure medium of the drive system 1.The electronic control device 20 carries out a method according to the invention, with which the attachment 3 acan be operated with low energy consumption and with low energy consumption.For this purpose, a maximum rotational speed n_max of the hydraulic pump 10 adapted to the respective attachment 3 aand a maximum pump pressure Pmax_Anbau adapted to the respective attachment 3 a, which is lower than the maximum system pressure of the working hydraulics 2 secured to the pressure limiting valve 16, are predefined for the corresponding attachment 3 a, with which the attachment 3 acan be operated.The maximum pump pressure Pmax_Anbau of the corresponding attachment 3 ais composed here of the sum of the apparatus-specific working pressure of the attachment 3 aand a loss pressure which corresponds to the line losses in the delivery line 14 and the consumer lines 7 aand 7 b. The device-specific working pressure of the attachment 3 ais generally specified as the maximum working pressure by a manufacturer of the attachment 3 a.If, during the actuation and thus for a desired movement of the attachment 3 a, the hydraulic pump 10 builds up the maximum pump pressure Pmax_Anbau of the attachment 3 ain the delivery line 14, all line losses in the delivery line 14 and the consumer lines 7 aand 7 bare covered and overcome and the working pressure predefined by the manufacturer of the attachment 3 ais reached at the attachment 3 a.If the operating device 21 is operated and thus deflected accordingly by an operator for actuating the attachment 3 aand thus for generating a desired movement of the attachment 3 a, the electronic control device 20 actuates and thus opens the operating device 21 of the control directional valve 5 in the direction of the control position 5 bor 5 c, as a function of the actuation and thus the deflection of the operating device 21, and furthermore generates a setpoint rotational speed value n_setpoint for the rotational speed of the hydraulic pump 10 as a function of the actuation and thus the deflection of the operating device 21 by the electronic control device 20 and outputs it to the drive motor 11. The setpoint rotational speed value n_setpointis preferably proportional to the actuation and thus the deflection of the operating device 21. The electronic control device 20 in this case furthermore detects, for example by means of the pressure sensor 25, the pump pressure present in the delivery line 14 and regulates the rotational speed of the hydraulic pump 10 by the corresponding actuation of the drive motor 11 in such a way that the pump pressure in the delivery line 14 is less than the predefined maximum pump pressure Pmax_Anbau, which is matched to the respective attachment. After a settling time, in the method according to the invention, a rotational speed of the hydraulic pump 10 is set for the movement of the attachment 3 apredicted at the operating device 21, for which it applies that the pump pressure in the delivery line 14 is less than the prespected maximum pump pressure Pmax_Anbau. The speed of the hydraulic pump 10 that is established and thus the set speed is thus only dependent on the predefined maximum pump pressure Pmax_Anbau of the attachment 3 a.The setpoint rotational speed value n_soll, which is dependent on the actuation and thus on the deflection of the operating device 21, corresponds here at most to the maximum rotational speed n_max of the hydraulic pump 10 that is adapted to the respective attachment 3 a.The rotational speed of the hydraulic pump 10 is regulated here during the actuation of the attachment 3 ain such a way that the rotational speed of the hydraulic pump 10 is always less than the rotational speed setpoint value n_des. Thus, in the method according to the invention, an automatic lowering of the rotational speed of the hydraulic pump 10 is achieved during the actuation of the attachment 3 a.In the invention, there is a minimum rotational speed, for example of 500 rpm / min, at which the hydraulic pump 10 is operated when the attachment 3 ais actuated. A movement of the attachment 3 ais thus available at a minimum rotational speed of the hydraulic pump 10, even if the measured pump pressure in the delivery line 14 should be higher than the predefined maximum pump pressure Pmax_Anbau.The loss pressure, which corresponds to the line losses in the delivery line 14 and the consumer lines 7 aand 7 b, is substantially dependent on the length of the consumer supply line 7 a, 7 b. Since the control directional valve 5 controlling the attachment 3a is arranged in the vehicle body of the industrial truck and the attachment 3a is arranged on the load carriage and is thus raised and lowered in the lifting mast, the loss pressure is characteristic of the vehicle.The loss pressure, which corresponds to the line losses in the delivery line 14 and the consumer lines 7 aand 7 b, can be stored or input as a vehicle-characteristic constant pressure value in the electronic control device 20.With the method according to the invention, even if the loss pressure corresponding to the line losses should be so high in a specific industrial truck that the maximum system pressure of the working hydraulics 2 secured at the pressure limiting valve 16 is virtually reached by the maximum pump pressure Pmax_Anbau and therefore virtually the maximum system pressure of the working hydraulics 2 is built up by the hydraulic pump 10 during the actuation of the attachment 3 ain the delivery line 14 in order to achieve the desired working pressure at the attachment 3 a, for example the maximum pump pressure Pmax_Anbau corresponds to a value of 95% of the maximum system pressure of the working hydraulics 2, an oversupply is prevented from occurring and a part of the volume flow delivered by the hydraulic pump 10 flows off into the container 13 with energy losses and thus unused.In the case of very cold pressure medium, line losses can occur which are greater than the loss pressure observed in the determination of the maximum pump pressure Pmax_Anbau of the attachment 3 a. If the real line losses are higher than the loss pressure on which the determination of the maximum pump pressure Pmax_Anbau of the attachment 3 ais based, a greater reduction in the rotational speed of the hydraulic pump 10 is achieved up to the minimum rotational speed in the method according to the invention. This results in a deceleration of the movement of the attachment 3 arelative to the movement speed of the attachment 3 apredicted by the deflection of the operating device 21. With the method according to the invention, an extension of the service life of the hydraulic pump 10 is thus also advantageously achieved in the case of cold and viscous pressure medium by the greater reduction of the rotational speed of the hydraulic pump 10 up to the minimum rotational speed, since operation of the hydraulic pump 10 at viscous pressure medium and high rotational speeds should be avoided against the background of the service life of the hydraulic pump 10. If the pressure medium heats up during operation of the drive system 1, with the method according to the invention, higher and higher controlled rotational speeds of the hydraulic pump 10 are achieved over time when the attachment 3 ais actuated a plurality of times until the real line losses are in the range of the loss pressure on which the determination of the maximum pump pressure Pmax_Anbau of the attachment 3 ais based.If the electronic control device 20 is operatively connected to the sensor device 26 detecting the temperature of the pressure medium of the drive system 1, the additional loss pressure, which corresponds to the line losses in the delivery line 14 and the consumer lines 7 aand 7 b, can be observed and calculated by the electronic control device 25 in a temperature-dependent and thus viscosity-dependent manner. This makes it possible for the maximum pump pressure Pmax_Anbau of the corresponding attachment 3 ato be able to be adjusted as a function of the temperature-dependent line losses in the delivery line 14 and the consumer lines 7 aand 7 b.By means of the speed control, the electronic control device 20 always controls the hydraulic pump 20 to the same speed with the same actuation and thus with the same movement of the attachment 3 a. The electronic control device 20 can be designed in such a way that for identical actuations of the attachment 3 a, the respectively set rotational speeds of the hydraulic pump 20 are logged and stored and, for example, the predefined maximum rotational speed n_max of the hydraulic pump 10 is corrected and adapted via a statistical evaluation, preferably further as a function of the temperature and thus of the viscosity of the pressure medium, in order to reduce the setting time for the rotational speed of the hydraulic pump 10 during operation of the attachment 3 a. If, for example, a predefined maximum rotational speed n_max of the hydraulic pump 10 adapted to the respective attachment 3 ais a value of 1200 U / min and, after repeated, for example five times, identical actuation of the attachment 3 a, the rotational speed of the hydraulic pump 20 is adjusted by the electronic control device 20 in each case to a value of 800 U / min in order to keep the pump pressure in the delivery line 14 lower than the predefined maximum pump pressure Pmax_Anbau adapted to the respective attachment 3 a, the maximum rotational speed n_max of the hydraulic pump 20 adapted to the respective attachment 3 acan be automatically adjusted by the electronic control device 20 from the value 1200 U / min to a value of 900 U / min, for example, and corrected in order to achieve a reduction in the adjustment time. If, after such an adjustment of the maximum rotational speed n_max, the electronic control device 20 selects a maximum rotational speed n_max for the operation of the hydraulic pump 10 during a subsequent operation of the attachment 3 asuch that no further lowering of the rotational speed of the hydraulic pump 20 results from the regulation in order to keep the pump pressure in the delivery line 14 lower than the predetermined maximum pump pressure Pmax_Anbau adjusted to the respective attachment 3 a, the electronic control device 20 can raise the predetermined maximum rotational speed n_max of the hydraulic pump 10 again, for example stepwise in one or more steps by 50 U / min in each case, until the electronic control device 20 has to carry out a lowering of the rotational speed of the hydraulic pump 10 again during the operation of the attachment 3 a, In order to keep the pump pressure in the delivery line 14 lower than the predetermined maximum pump pressure Pmax_Anbau adapted to the respective attachment.The maximum pump pressure Pmax_Anbau for the respective attachment 3 acan be input by an operator in the electronic control device 20, for example on the basis of the working pressure specified by the manufacturer of the attachment 3 a. The additional loss pressure covering the line losses can be stored in the electronic control device 20 or can be input by the operator. The loss pressure can also be calculated by the electronic control device 20 as a function of temperature in order to adapt the maximum pump pressure Pmax_Anbau of the attachment 3 aas a function of the temperature-dependent line losses.Alternatively, the electronic control device 20 can be operatively connected to the attachment 3 avia a wireless or cable connection, so that the necessary working pressure of the attachment 3 aand the maximum volume flow of the attachment 3 aand, if appropriate, the cross section of the working cylinders can be transmitted from the attachment 3 a. The electronic control device 20 can then calculate the maximum rotational speed n_max of the hydraulic pump 20 adapted to the attachment 3 afrom the working pressure of the attachment 3 ausing the displacement volume of the hydraulic pump 20, which can be stored in the electronic control device 20, by observing the additional loss pressure, the pump pressure Pmax_Anbau adapted to the attachment 3 a. This makes it possible for the attachment 3 ato be able to be operated exactly with the maximum volume flow and working pressure mentioned by the manufacturer of the attachment 3 a, without the hydraulic pump 10 resulting in an oversupply which generates losses.The method according to the invention achieves the effect that, when the attachment 3 ais actuated, the attachment 3 ais actuated at the working speed predefined by the actuation and deflection of the operating device 21, without an oversupply occurring by the hydraulic pump 20. By reducing the rotational speed and thus the torque of the hydraulic pump 20, operation of the attachment 3 awith low energy consumption and with low energy losses is thus achieved. The method according to the invention thus leads to energy saving during the actuation of the attachment 3 aby automatically lowering the rotational speed of the hydraulic pump 10.The invention is not limited to the exemplary embodiment shown. Instead of the direct measurement of the pump pressure in the delivery line 14 by means of the pressure sensor 25, the electronic control device 20 can alternatively estimate the pump pressure in the delivery line 14 indirectly via a current measurement in the converter of the electric motor 1 laand thus determine it.

Claims

Method for operating a hydraulic drive system (1) of an industrial truck, wherein the drive system (1) has a working hydraulic system (2) which comprises, as a consumer, a lifting drive for raising and lowering a load carriage and at least one additional drive (3) which is designed as an attachment (3a) which is attached to the load carriage, wherein, for controlling the attachment (3a), a control directional valve (5) is provided which is connected on the input side to a conveying line (14) of a hydraulic pump (10) and on the output side to a container line (15) which is guided to a container (13), wherein the hydraulic pump (10) is driven by a drive motor (11), and wherein, for generating a movement of the attachment (3a), the control directional valve (5) is connected to a control position (5b) as a function of the actuation of an operating device (21); 5c) and the attachment (3a) is actuated by the hydraulic pump (10) via the control position (5b; 5c) actuated control directional valve (5) supplying pressure medium, characterized in that a pressure limiting valve (16) is provided to protect the drive system (1), which valve is connected on the input side to the delivery line (14) and is connected on the output side to the container (13) and is set to a maximum system pressure of the working hydraulics (2), wherein a maximum rotational speed (n_max) of the hydraulic pump (10) adapted to the respective attachment (3a) and a maximum pump pressure (Pmax_Anbau) adapted to the respective attachment (3a), which is lower than the maximum system pressure of the working hydraulics (2) secured to the pressure limiting valve (16), are predefined, wherein upon actuation of the control directional valve (5) of the attachment (3a) into a control position (5b; 5c), as a result of an actuation of the operating device (21), a setpoint rotational speed value (n_soll) for the rotational speed of the hydraulic pump (10), which setpoint rotational speed value is dependent on the actuation of the operating device (21), is generated and output to the drive motor (11), the pump pressure present in the delivery line (14) is determined and the rotational speed of the hydraulic pump (10) is regulated in such a way that the pump pressure in the delivery line (14) is less than the predefined maximum pump pressure (Pmax_Anbau) adapted to the respective attachment (3a).Method according to Claim 1, characterized in that the rotational speed of the hydraulic pump (10) is regulated in such a way that the rotational speed of the hydraulic pump (10) is always less than the setpoint rotational speed value (n_soll).Method according to Claim 1 or 2, characterized in that the setpoint rotational speed value (n_set) which is dependent on the actuation of the operating device (21) corresponds at most to the maximum rotational speed (n_max) of the hydraulic pump (10) which is matched to the respective attachment (3a).Method according to one of Claims 1 to 3, characterized in that the setpoint rotational speed value (n_set) which is dependent on the actuation of the operating device (21) is proportional to the actuation of the operating device (21).Method according to one of Claims 1 to 4, characterized in that, when the control directional valve (5) is actuated into a control position (5b; 5c), as a result of actuation of the operating device (21), the drive motor (11) of the hydraulic pump (10) is operated at a minimum rotational speed.Method according to one of Claims 1 to 5, characterized in that, when the maximum pump pressure (Pmax_Anbau) which is matched to the respective attachment (3a) is preset, a loss pressure is observed which occurs in the delivery line (14) of the hydraulic pump (10) and / or in the consumer lines (7a, 7b) which are conducted from the control directional valve (5) to the attachment (3a).Method according to claim 6, characterised in that a constant pressure value is used as the loss pressure.Method according to Claim 6, characterized in that the loss pressure is calculated as a function of the temperature of the pressure medium of the drive system (1).Method according to one of Claims 1 to 8, characterized in that, in order to determine the pump pressure present in the delivery line (14), the pump pressure present in the delivery line (14) of the hydraulic pump (10) is measured by means of a pressure sensor (25).Method according to one of Claims 1 to 8, characterized in that the drive motor (11) is designed as an electric motor (11a), and the current is used in a converter of the electric motor (11a) in order to determine the pump pressure present in the feed line (14).Method according to one of Claims 1 to 10, characterized in that, for identical actuations of the attachment (3a), the set rotational speeds of the hydraulic pump (10) are stored and the predefined maximum rotational speed (n_max) of the hydraulic pump (10) is corrected as a function of the stored rotational speeds of the hydraulic pump (10).Method according to Claim 11, characterized in that, in a control process in which, starting from a predefined maximum rotational speed (n_max) of the hydraulic pump (10), during the actuation of the attachment (3a), the rotational speed of the hydraulic pump (10) is not lowered by the control, so that the pump pressure in the feed line (14) is kept lower than the predefined maximum pump pressure (Pmax_Anbau) which is matched to the respective attachment (3a), the predefined maximum rotational speed (n_max) of the hydraulic pump (10) is raised until, in a control process in which, starting from the maximum rotational speed (n_max) of the hydraulic pump (10), during the actuation of the attachment (3a), the rotational speed of the hydraulic pump (10) is lowered by the control, in order that the pump pressure in the delivery line (14) is kept lower than the predefined maximum pump pressure (Pmax_Anbau) adapted to the respective attachment (3a).Method according to one of Claims 1 to 12, characterized in that the method is carried out in an electronic control device (20) which actuates the drive motor (11) and the control directional valve (5), the electronic control device (20) being operatively connected to the attachment (3a), and the working pressure of the attachment (3a) and the maximum volume flow of the attachment (3a) being transmitted to the electronic control device (20) by the attachment (3a), wherein the electronic control device (20) determines the maximum pump pressure (Pmax_Anbau) adapted to the respective attachment (3a) from the transmitted working pressure of the attachment (3a) and determines the maximum rotational speed (n_max) of the hydraulic pump (10) adapted to the respective attachment (3a) from the transmitted maximum volume flow of the attachment (3a) in conjunction with the displacement volume of the hydraulic pump (10).Method according to claim 13, characterised in that the electronic control device (20) is operatively connected to the attachment (3a) via a wireless connection or a cable-bound connection.

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