HYDRAULIC ARRANGEMENT WITH LOAD-HOLDING FUNCTION AND CONTROL METHOD OF THE HYDRAULIC ARRANGEMENT

Description

[0001] The present invention relates to a hydraulic arrangement according to the preamble of patent claim 1 and to a method for controlling a hydraulic arrangement according to patent claim 12.

[0002] A hydraulic arrangement, for example a hydraulic axis, in particular a linear axis and / or a compact axis, comprises a hydraulic cylinder in a closed hydraulic circuit or, if compensation of differential volume is necessary, in a partially closed hydraulic circuit. The hydraulic cylinder can be designed as a constant-pressure or differential cylinder, or as a multi-surface cylinder. With a low oil volume, the axis can be used to move, press, join, or close parts with high dynamics, precision, and force. Typical applications for such axes include presses, injection molding machines, hexapods for simulators, and the like. If the axis is designed as a servo-hydraulic axis with a servo drive, it exhibits extremely high positioning accuracy and also good electrical / electronic networking capabilities.

[0003] A servo-hydraulic axis of this type is shown in the applicant's data sheet RD 08137 / 2018 - 02. The compact axis features a servo motor, a hydraulic control block, a hydraulic cylinder, a hydraulic accumulator, and control elements such as valves, as well as power electronics. The hydraulic servo-hydraulic axis can be position- and / or force-controlled. This allows the axis to be operated with displacement-force and displacement-time profiles adapted to the specific application.

[0004] To maintain the position of the axis against a load, the state of the art knows various modes. In one mode, the axis remains in its position or force control and the pump remains fluidly connected to the axis. The displacement or speed of the servo motor is controlled in such a way that only the internal leakage of the system - the pump - that occurs when holding the load is compensated. Another mode is made possible by the use of a load-holding valve that blocks the pressure medium flow path between the loaded cylinder chamber and the pressure side of the hydraulic pump. In this way, the servo motor can be switched to torque-free operation, which shortens the duration of its power consumption and reduces wear.When the pump resumes the load following the position or force secured by the load holding valve, an unwanted movement of the axle may occur when the load holding valve opens if the pressure between the pump and the load holding valve is not adapted to the load on the axle.

[0005] The publication US 2016 010 26 85 A1 shows a servo-hydraulic axis and a method for controlling it when holding the load using a pump and a load-holding valve, as well as when the pump resumes the load after holding it using a load-holding valve. The starting position is the torque-free servomotor, the stationary pump, and the closed load-holding valve that holds the load. A target-actual deviation of the axis position is continuously determined. If the deviation lies within a 5% tolerance band, the control of the servomotor and the load-holding valve remains unchanged. If the deviation leaves the tolerance band, this is the signal for the pump to resume the load in order to adjust the target position again. For this purpose, a target direction of rotation and target speed and a corresponding control signal for the servomotor are determined from the deviation.To enable resumption and reaching the target position, the load-holding valve must be controlled or opened. To prevent the unwanted movement of the axis described above, the pump pressure on this side of the load-holding valve is first brought to the load pressure on the other side of the load-holding valve. To achieve this, the servo motor is controlled with the previously determined control signal before - after a time constant in the millisecond range has elapsed - the load-holding valve is controlled. This is followed by the simultaneous control of the load-holding valve (opening) and servo motor (ramping up to the target speed). When a 5% band of the target position of the axis is reached, this speed ramp is flattened to prevent overshoot.If the new target position is reached and the deviation remains within the 5% tolerance band for a configurable time constant, a) the load holding valve is closed and b) the servo motor - and thus the pump - is ramped down to 0 speed. The energy-saving load holding state is thus resumed via the load holding valve. According to US 2016 010 26 85 A1, the signal to hold the load via the load holding valve and the signal to resume the load via the pump are issued automatically on the one hand and solely depending on the actual position of the axis. In addition, a time constant can be effective that slightly delays switching to load holding mode via the load holding valve, so that the position of the axis can be maintained in normal operation for a certain time even though the condition is met.

[0006] However, such a solution requires, on the one hand, position detection and, on the other hand, the servo motor must be controlled in a complex manner in order to equalize the pressure levels on both sides of the load-holding valve before the load-holding valve is opened.

[0007] Further comparably relevant prior art can be found in WO 2020 / 239 258 A1, US 2008 / 295 504 A1, US 2020 / 262 677 A1, DE 10 2011 056 894 A1 and in the technical article "A Method for Smoothly Disengaging the Load-Holding Valves of Energy-Efficient Electro-Hydraulic Systems", in "The 2st International Electronic conference on Actuator Technology: Materials, Devices, and Applications, January 1, 2020, page 36, XP093098679, Basel, Switzerland, DOI: 10.3390, / IeCAT2020-08478.

[0008] In contrast, the object of the invention is to provide a hydraulic arrangement which overcomes or at least reduces the disadvantages of the prior art and in particular enables a smooth switching from a load holding mode with simple pressure adjustment.

[0009] Brief description of the invention The object is achieved by a hydraulic arrangement having the features according to claim 1 and by a method having the features according to claim 12.

[0010] The present invention relates to a hydraulic arrangement comprising a hydraulic cylinder and a hydraulic pump for supplying the latter with pressure medium, which hydraulic pump is drivable by an electric motor, in particular a servo or stepper motor, of the arrangement and is fluidly connected to a cylinder chamber via a pressure medium flow path. A check valve is provided in the pressure medium flow path, by means of which the pressure medium flow path can be hydraulically isolated to hold a load of the hydraulic cylinder without a drive. According to the invention, a control unit of the hydraulic arrangement is designed to determine or detect an operating variable of the electric motor upon hydraulic separation of the pressure medium flow path, and to adjust the detected or determined operating variable on the electric motor upon setting a condition upon the occurrence of which the pressure medium flow path is opened.Adjustment means setting a control variable, in particular a control current, and then adjusting the electric motor to the control variable.

[0011] The pressure medium flow path between the cylinder chamber and the hydraulic pump can be hydraulically shut off by the shut-off valve. When the shut-off valve is closed, the hydraulic cylinder can hold a load without requiring power from the hydraulic pump. The shut-off valve therefore fulfils the function of a load-holding valve. Opening the shut-off valve deactivates the load-holding function of the hydraulic arrangement. A control unit of the hydraulic arrangement detects or determines the operating variable of the electric motor while the shut-off valve is closing. If the condition is set or detected that the load-holding function should be terminated and fluid is required by the hydraulic pump, the detected or determined operating variable of the electric motor that drives the hydraulic pump is set by the control unit.Deactivating the load holding function of the hydraulic arrangement thus corresponds to a resumption of the load by the hydraulic pump following holding by means of the load holding valve.

[0012] In other words, the shut-off valve in the pressure medium flow path can be controlled via a control unit of the arrangement depending on at least the detected or determined operating variable of the arrangement. The at least one operating variable is an operating variable of the electric motor.

[0013] The load on the motor-pump unit or the operating variable of the electric motor can therefore be secured and reduced in a controlled manner at the time the shut-off valve is shut off as a reference for resumption, in order to be raised again to the value of the operating variable at the time of shut-off when resuming, without any significant pressure change or movement occurring in the loaded cylinder chamber.

[0014] Preferably, the detected or determined operating variable of the electric motor is set before the shut-off valve is opened and a fluidic connection is established between the hydraulic cylinder and the hydraulic pump.

[0015] The hydraulic arrangement has the following advantages. By adjusting the recorded or determined operating variable before the check valve opens, the electric motor and thus the hydraulic pump are adapted to the load level or pressure level in the cylinder chamber. This avoids any discontinuity in force or position caused by a sudden adjustment of the different pressure levels when the check valve opens. Because the electric motor is controlled or regulated via an operating variable of the electric motor, the control system is simpler to design and less prone to errors. Furthermore, force, position, and / or pressure sensors in the cylinder chamber are not absolutely necessary. This can save costs.

[0016] The object of the present invention is further achieved by a method for controlling a hydraulic arrangement having a hydraulic cylinder and a hydraulic pump. The method according to the invention comprises the following steps: The check valve in the pressure medium flow path between the hydraulic cylinder and the hydraulic pump of the hydraulic arrangement is closed. While the check valve is closing, the operating variable of the electric motor that drives the hydraulic pump is determined or detected. In a next step, it is recognized that a condition for resumption (of the load by the hydraulic pump) exists. The determined or detected operating variable is then adjusted on the electric motor. As a final step, the check valve is opened.

[0017] Closing the check valve switches the hydraulic system to load-holding mode. When the load-holding function is deactivated, the determined or recorded operating variable can first be set on the electric motor, and then the check valve can be opened. The determined or recorded operating variable can, in particular, reflect the load on the hydraulic pump and thus on the electric motor.

[0018] Resumption involves deactivating the load-holding function and thus opening the check valve (with a time delay). This resumption places the hydraulic cylinder back under control (the control unit of the hydraulic system).

[0019] The method according to the invention, in particular, aligns the load or pressure level of the cylinder chamber and the hydraulic pump before the check valve opens. The aligned pressure levels on both sides of the check valve prevent unwanted movement of the cylinder piston when the check valve opens.

[0020] Advantageous further developments of the present invention are the subject of the appended subclaims.

[0021] Preferably, the operating variable of the electric motor is proportional to a pressure in the cylinder chamber. The operating variable can thus indicate the load on the electric motor during the hydraulic separation of the fluid line by the shut-off valve. The load on the electric motor can depend on the pressure in the cylinder chamber. The operating variable, which is proportional to the pressure in the cylinder chamber, can therefore be a measure of the load on the electric motor. Since an operating variable of the electric motor is determined or recorded, a pressure measurement in the cylinder chamber is optional. Since the operating variable of the electric motor can be recorded at the electric motor, the control or activation of the electric motor can be kept simpler.

[0022] According to an optional feature of the present invention, the operating variable of the electric motor can be determined from its load or is determined from its load. Thus, the load of the electric motor can represent a load on the electric motor of the hydraulic pump.

[0023] Preferably, the operating variable of the electric motor can be determined from its current consumption or is determined from its current consumption. The current consumption of the electric motor can be easily measured. If the current consumption of the electric motor is known, the torque of the electric motor can be determined. Thus, by measuring the current consumption, the pressure in the cylinder chamber or the force acting on the cylinder can be determined. This could eliminate the need for sensors in the cylinder chamber, which could save costs. Furthermore, the pressure in the cylinder chamber or the force acting on the cylinder could be influenced by a control current from the electric motor.

[0024] According to a further optional feature of the present invention, the operating variable of the electric motor is its torque. The torque of the electric motor can be proportional to the pressure in the cylinder chamber and can be calculated from the known operating variables of the electric motor. The torque as an operating variable can thus indicate the load on the electric motor.

[0025] The load holding function can be deactivated by a condition. Various processes or events can be considered as conditions for deactivating the load holding function.

[0026] When the check valve is open, a hydraulic / fluidic connection can exist between the hydraulic cylinder and the hydraulic pump. This allows a control unit of the hydraulic system to regulate or control the movement, pressure, and / or position of the hydraulic cylinder using a control current from the electric motor that drives the hydraulic pump. When the check valve is closed, the fluidic connection can be severed, and the hydraulic cylinder can no longer be controlled. Deactivation of the load-holding function can therefore correspond to the opening of the check valve, thus resuming control by the control unit.

[0027] Preferably, the condition is that the load-holding function is deactivated. Deactivation of the load-holding function can be time-controlled or can be initiated by a user. For example, the condition can be a command to deactivate the load-holding function.

[0028] The condition can also be the input of a control word. The control word can be used to manually command the deactivation of the load holding function and thus the resumption of control.

[0029] According to a further optional feature of the present invention, the condition can be the pressure and / or force leaving a predetermined range. If the force on the cylinder and / or the pressure in the cylinder chamber is detected, a deviation from the target value that is greater than a predetermined tolerance deviation can be the condition for deactivating the load holding function. It can be advantageous in this case that the actual pressure in the cylinder chamber or the actual force on the cylinder does not have to be determined from the operating variable of the electric motor, thus preventing deviations from the determination in the control system.

[0030] Pressure loss in the cylinder chamber or force changes on the cylinder could occur, for example, due to a leak in the check valve or load changes on the cylinder. If the pressure in the cylinder chamber or the force on the cylinder drops below a predefined limit, the check valve can be opened to increase or decrease the pressure in the cylinder chamber using the hydraulic pump. This prevents the cylinder chamber pressure from falling below or rising above a permissible level.

[0031] Preferably, the condition can be that a position of the hydraulic cylinder or a piston rod of the hydraulic cylinder lies outside a predetermined range. If the position of a cylinder piston or piston rod is detected, a deviation in the piston position that exceeds a predefined tolerance deviation can trigger deactivation of the load holding function. This allows unwanted piston movements and thus a decrease / increase in cylinder pressure to be detected and prevented.

[0032] According to a further optional feature of the present invention, the condition can be a change in a position setpoint of the hydraulic cylinder or the piston rod of the hydraulic cylinder. If a user enters or requests a new setpoint for the position of the cylinder piston, the load holding function can be deactivated to move the hydraulic cylinder to the new setpoint using the hydraulic pump. This allows the hydraulic arrangement to respond promptly to user inputs.

[0033] When the condition is met, the detected or determined operating variable of the electric motor is first set, and then the shut-off valve is opened. This allows a hydraulic connection to be established between the hydraulic cylinder and the hydraulic pump. The load-holding function is then deactivated, and the axle is in closed-loop control.

[0034] Optionally, before the first step of blocking the pressure medium flow path by the shut-off valve, it can be checked whether a condition for activating the load-holding function exists at all. Only when activation of the load-holding function is requested by reaching a predetermined pressure in the cylinder chamber and / or by a manual control word can the shut-off valve be closed and, in particular, the pressure medium flow path shut off.

[0035] Preferably, a pressure in the pressure medium flow path(s) is detected during the closing of the shut-off valve. The pressure can be detected, for example, by pressure sensors in the pressure medium flow path(s). The pressure detected when the shut-off valve is closed could serve as a reference to which the electric motor and thus the hydraulic pump are adjusted when control is resumed or when the load-holding function is deactivated.

[0036] According to a further optional feature of the present invention, the control of the hydraulic cylinder operates during the closing of at least one check valve. When the check valve is open, a hydraulic / fluidic connection can exist between the hydraulic cylinder and the hydraulic pump. Thus, the control unit can control the hydraulic cylinder via a control current from the electric motor that drives the hydraulic pump. As long as the check valve is not completely closed, the control of the control unit acts on the hydraulic cylinder. Thus, it may be possible to detect or determine the operating variable of the electric motor during the closing of the check valve.

[0037] Preferably, control of the hydraulic cylinder using the hydraulic pump or electric motor is terminated after the shut-off valve closes. When the shut-off valve closes, the hydraulic arrangement is in load-holding mode. The hydraulic / fluidic connection between the hydraulic cylinder and the hydraulic pump may be interrupted. This may make it impossible to control the hydraulic cylinder via (the control of) the hydraulic pump.

[0038] Preferably, the operating variable of the electric motor is reduced after the shut-off valve has been closed. In particular, the torque and thus the load on the electric motor are reduced by torque control that follows a profile for reducing the load on the electric motor. By reducing the operating variable, in particular the torque, of the electric motor, energy is saved during load-holding mode.

[0039] The complete closure of at least one shut-off valve can be ensured either by a timer or by position monitoring. The closure of the shut-off valve can be a condition for reducing the operating size of the electric motor.

[0040] According to a further optional feature of the present invention, the operating variable, in particular the torque, of the electric motor is increased when the condition occurs to the detected or determined value of the operating variable when the shut-off valve is closed.

[0041] Preferably, the operating size of the electric motor, in particular the torque, is increased before the shut-off valve opens.

[0042] Preferably, the operating variable is stored in a memory unit of the control unit of the hydraulic system when the shut-off valve closes. In particular, the torque of the electric motor, and thus the load on the electric motor, is stored when the shut-off valve closes. The stored value can be retrieved when the condition occurs and optionally adjusted, and the operating variable can be increased until the stored value is reached. Short description of the characters

[0043] Fig. 1 shows a hydraulic arrangement according to the present invention; Fig. 2 shows a time course of a force of a hydraulic cylinder and a torque of an electric motor; and Fig. 3 shows a flowchart of a method for controlling the hydraulic arrangement according to the present invention. Detailed description of the characters

[0044] A hydraulic arrangement 1 has according to Fig. 1 a hydraulic pump or machine 4 driven by an electric motor 2, and at least one of three hydraulic cylinders 6, 8, and 10 supplied with pressure medium by the hydraulic pump 4. Basic features of the hydraulic arrangement 1 are known from WO 2020 / 260 124 A1. Accordingly, the differences from WO 2020 / 260 124 A1 will be discussed.

[0045] A first working flow path 12 and a second working flow path 14 extend from the hydraulic pump 4. The first working flow path 12 has a branch 16, at which a third working flow path 18 branches off. A shut-off valve 20, designed as a 2 / 2-way switching valve, is arranged in this branch.

[0046] Starting from the branch 16, the first working flow path 12 extends further, with a further shut-off valve 22 being arranged, via which the first working flow path 12 can be shut off. The shut-off valve 22 is also simply designed as a 2 / 2-way switching valve.

[0047] In continuation of the first working flow path 12, this has branches 24 and 26. A working connection 28 branches off from branch 24, and working connections 30E and 30A branch off from branch 26.

[0048] A shut-off valve 32 is arranged in the second working flow path 14, via which the second working flow path 14 can be shut off. The second working flow path 14 continues via the shut-off valve 32 to a branch 34. A working connection 40 branches off from the branch 34. Starting from the branch 34, the second working flow path 14 extends to a branch 36. Working connections 38, 42 branch off from the branch 36.

[0049] The third working flow path 18 continues beyond the check valve 20 to a branch 44, from which a third working port 46 branches off to the hydraulic cylinder 10. The third working port 46 can be connected by a (switchable) configuration 50B.

[0050] In the hydraulic arrangement 1, the hydraulic cylinders 6, 8 with two piston surfaces or the hydraulic cylinder 10 with three piston surfaces can be supplied with pressure medium, depending on the configuration.

[0051] For this purpose, a connecting flow path 48 is provided, via which the first working flow path 12 can be fluidly connected to the third working flow path 18 downstream of the shut-off valve 20. A receptacle 50E is provided in the connecting flow path 48. A receptacle 50A, of identical design in the exemplary embodiment, is provided in the first working flow path 12 in a section between the branch 16 and an inlet of the connecting flow path 48.

[0052] A locking device 52 designed as a screw, in particular M18 x 1.5 (in this case according to DIN 906), can be inserted or is inserted into the respective receptacle 50E, 50B, 50A. Due to the identical design of the receptacles 50E, 50A with M18 thread in the exemplary embodiment, exactly one locking device 52 can be inserted into the corresponding receptacle 50E, 50A, depending on the desired configuration E, A.

[0053] The circuit structure is configurable by the closure means 52. A detailed explanation of the circuit structure of the hydraulic arrangement is described in WO 2020 / 260 124 A1 and is therefore omitted here. Receptacles 50A, 50B, and 50E, and thus configurations A1 and E1, are optional.

[0054] The second working flow path 14 has a pressure sensor 54 downstream of the check valve 32. The pressure sensor is optional. The pump-side part of the hydraulic arrangement 1 also has an optional pressure sensor 56. The working ports 40 and 46 are fluidly connected via the check valve 58 and can be short-circuited.

[0055] To enable a load-holding function of the hydraulic arrangement 1, one of the check valves 20, 22, 32, and 58 can block the fluid line or the pressure medium flow path between the hydraulic pump 4 and the respective hydraulic cylinder 6, 8, and 10. For example, in configuration A, the working port 28 can be blocked by the check valve 20, and in configuration E, the working port 28 can be blocked by the check valve 22. This allows the respective hydraulic cylinders 6, 8, and 10 to hold a load without requiring a drive from the hydraulic pump 4.

[0056] To accommodate differential volumes resulting from different piston area sizes of the hydraulic cylinders 6, 8, 10, the hydraulic arrangement has an accumulator flow path 62, which can be fluidically connected to the respective working flow path 12, 14 via pressure relief valves 64 preset to a pressure value. A gas-loaded hydraulic accumulator 60 is connected to the accumulator flow path 62.

[0057] The following operation can be performed with each of the check valves 20, 22, 32, and 58. For ease of understanding, check valve 32 is considered as an example.

[0058] For example, the working connection 40 is fluidically separated from the hydraulic pump 4 via the check valve 32. This enables the load-holding function, by which a load on the hydraulic cylinder 10 can be held without drive. When the load-holding function is active, the hydraulic pump 4 and thus also the electric motor 2 can be switched off or the load on the electric motor 2 can be reduced. The timing of the closing of the check valve 32 and the reduction of the torque of the electric motor 2 is determined in the Fig. 2 clarified.

[0059] Fig. 2 shows, by way of example, a temporal progression of a force on the hydraulic cylinder 10 or a pressure in the cylinder chamber 41 of the hydraulic cylinder 10 and a torque of the electric motor 2. The basic temporal progression is identical for all other working connections and cylinder chambers of the hydraulic cylinders 6, 8, and 10. The pressure in the cylinder chamber 41 is detected, for example, by a pressure sensor 54 in the cylinder chamber 41. In a first range B1, the check valve 32 is open. When the check valve 32 is open, there is a fluidic connection between the hydraulic cylinder 6 and the hydraulic pump 4. This allows the hydraulic cylinder 10 to be controlled via a control current from the electric motor 2, which drives the hydraulic pump 4. When the check valve 32 is open, the hydraulic cylinder 10 can therefore be controlled via a control unit of the hydraulic arrangement 1. The load-holding function is therefore not active in this range. The external load increases the torque of the electric motor 2.This increases the load on the hydraulic pump 4 and the pressure in the cylinder chamber 41. The torque of the electric motor 2 is increased until the detected force Factual reaches a force setpoint Fsetpoint or a predetermined tolerance range close to the force setpoint Fsetpoint and, optionally, a detected position reaches a position setpoint xsetpoint or a predetermined tolerance range close to the position setpoint xsetpoint.

[0060] The load-holding function can therefore be activated by a detected signal. The detected signal can, for example, be the detected force on the hydraulic cylinder 10, which lies within a predefined target range, and can be activated simultaneously with the optionally reached position within a predefined target range of the hydraulic cylinder 10, and simultaneously with the achievement of a predetermined torque on the electric motor 2. Furthermore, the load-holding function can be activated by manual commanding via a control word.

[0061] When the detected force Fact and optionally the detected position xact reach the predetermined tolerance range, a time t1 begins to run. The predetermined tolerance range can, for example, be a certain percentage of the force setpoint, optionally of the position setpoint, to be achieved. The time t1 is referred to as the debounce time. The debounce time is intended to prevent the hydraulic arrangement 1 from reacting to short-term force / position fluctuations. When the time t1 has elapsed, the load holding function is activated. The check valve 32 is closed. The closing process of the check valve 32 requires the time period t2. When the check valve 32 is completely closed, i.e. in the second range B2, the cylinder piston is no longer controlled by the control unit of the hydraulic arrangement 1. The fluid passage between the hydraulic pump 4 and the hydraulic cylinder 10 is therefore hydraulically separated by the check valve 32.The torque of electric motor 2 is then reduced to zero. The control of electric motor 2 follows a predetermined profile for load or torque reduction.

[0062] Due to a leakage of the check valve 32 and a simultaneous pressing load on the cylinder 10 or other pressure losses, the force applied to the hydraulic cylinder 10 can slowly decrease in range B2 during the active load-holding mode. If the force changes outside a predetermined (limit) range, the load-holding function is deactivated. A hysteresis adjustment Fhyst can also be incorporated into the predetermined limit range.

[0063] Optionally, the position of cylinder 10 can also be detected by a position sensor (not shown). If the cylinder position leaves a predetermined (limit) range due to (unintentional) movement caused by leakage, a signal can be issued to deactivate the load holding function. A hysteresis adjustment xhyst can also be incorporated into the predetermined limit range.

[0064] If the load holding function is deactivated, the torque of the electric motor 2 is increased to the last (detected) value before the check valve 32 was closed. When the torque reaches the setpoint, a time period t3 is waited. The time period t3 is intended to ensure that the desired torque is set, but can also be 0 seconds. The check valve 32 is then opened. The opening process of the check valve 32 requires a time period t4. When the check valve is open, a fluidic connection is restored between the hydraulic cylinder 10 and the hydraulic pump 4. The commanded force and / or position is restored. The force on the hydraulic cylinder 10 thus increases to the setpoint, or the position is adjusted back to the setpoint. Since the torque of the electric motor 1 was increased before the check valve 32 was opened, the pressure in the corresponding lines is reduced before the check valve 32 is opened oradjusted to the chamber load. From the moment the check valve 32 is fully open, the hydraulic cylinder is again controlled by the control unit. The load-holding function is thus completely deactivated. The third range, B3, is thus reached.

[0065] The last detected value of the electric motor 2 can, for example, be the detected torque of the electric motor 2 when closing the shut-off valve 32. This value can be stored in a memory unit and retrieved when the torque increases.

[0066] However, it is also conceivable that the electric motor 2 is controlled by the detected pressure on the pump side of the hydraulic arrangement 1 when the hydraulic pump 4 is restarted. In this case, a pressure sensor would have to be present on the cylinder side and on the pump side in order to adjust the respective pressures to each other before the shut-off valve opens.

[0067] Fig. 3shows a flowchart of a method according to the invention for controlling the hydraulic arrangement 1 with the hydraulic cylinders 6, 8, 10 and the hydraulic pump 4. In step S1, the check valve 32 in the working flow path or pressure medium flow path 14 between the hydraulic cylinder 10 and the hydraulic pump 4 is closed. Closing the check valve 32 requires the time period t2. In step S2, an operating variable of the electric motor 2, which drives the hydraulic pump 4, is determined or detected while the check valve 32 is closing. This can be either a torque of the electric motor 2 or a pressure in the cylinder chamber 41. The determined or detected operating variable can, for example, be stored in a memory unit of the hydraulic arrangement 1. In step S3, it is determined whether a condition for deactivating the load-holding function or for resuming control exists.In step S4, the determined or detected operating variable is adjusted on the electric motor 2. This means that the electric motor 2 increases its torque, for example, until the torque is reached that was determined or detected when the check valve 32 closed. In step S5, the check valve 32 is opened. This deactivates the load-holding function. When the check valve 32 is open, the hydraulic cylinder 6 is again controlled by the control unit of the hydraulic system 1.

[0068] Before step S1, an optional step S0 can be executed, in which it is checked (by the control unit) whether a condition for activating the load-holding function exists. This condition can be an automatic detection of whether the pressure medium flow path should be shut off when a predetermined force or pressure range is reached. Reaching the predetermined force or pressure range can be detected by the sensors in the pressure medium flow path. The condition for activating the load-holding function can also be a manual command via a control word.

[0069] The condition for deactivating the load-holding function can, for example, be a manual deactivation of the load-holding function. It can also be a control word that commands resumption of control. The condition can also be, for example, that a detected force on the hydraulic cylinder or a pressure in the cylinder chamber leaves a predetermined tolerance range. Furthermore, the condition can be that a detected position of the cylinder piston leaves a predetermined tolerance range. A change in a position setpoint of the cylinder piston can also be a condition for deactivating the load-holding function.

[0070] The sequence of the control method according to the invention is explained in detail below. Initially, the load-holding function is deactivated. Subsequently, the locking of the locking valve 32 is activated either automatically or manually, and then the locking valve 32 is closed. The complete closing of the locking valve 32 can be monitored over time or implemented via position monitoring.

[0071] If the shut-off valve 32 is completely closed, the hydraulic cylinder 10 is taken out of control and the torque of the electric motor 2 is reduced in a controlled manner to 0 Nm.

[0072] If the load holding function is deactivated while the load holding function is active, or if a resumption of control of the hydraulic cylinder 10 is requested, the torque of the electric motor 2 is increased. If the load holding function is not deactivated, a check is first made to determine whether the position setpoint of the cylinder piston has been changed. If this is the case, a check is made to determine whether automatic movement of the cylinder piston is desired. The pressure in line 14 is adjusted to the pressure in line section 41 before the shut-off valve 32 is closed. If automatic movement of the cylinder piston is desired, the change in the position setpoint of the cylinder piston can be ignored for the duration of the resumption. In this case, the change in the position setpoint of the cylinder piston only becomes active when the shut-off valve 32 is fully open. After the resumption command is activated, the torque of the electric motor 2 is increased.A waiting time t3 can be allowed to elapse. This ensures that the torque corresponds to the setpoint.

[0073] Subsequently, the shut-off valve 32 is opened. The opening duration of the shut-off valve 32 may require a time period t4. After the shut-off valve 32 is fully opened, the hydraulic cylinder 10 is again in the control of hydraulic arrangement 1. A setpoint change in the position of the cylinder piston is active and is no longer ignored. The load-holding function is thus completely deactivated.

Claims

1. Hydraulic arrangement (1), comprising a hydraulic cylinder (6, 8, 10), and a hydraulic pump (4) for the pressure medium supply thereof, which hydraulic pump is drivable by an electric motor (2) and is fluidically connectable to a cylinder chamber via a pressure medium flow path (12, 14, 18), in which one or more shut-off valves (20, 22, 32, 58) are provided by which the pressure medium flow path (12, 14, 18) is hydraulically disconnectable for drive-free holding of a load of the hydraulic cylinder (6, 8, 10), wherein the hydraulic arrangement (1) comprises a control unit, characterized in that the control unit is designed to determine or to detect an operating variable of the electric motor (2) when the pressure medium flow path (12, 14, 18) is hydraulically disconnected, and to adjust the detected or determined operating variable at the electric motor (2) when a condition is set, upon the occurrence of which the pressure medium flow path (12, 14, 18) is opened.

2. Arrangement (1) according to Claim 1, wherein the operating variable of the electric motor (2) is proportional to a pressure in the cylinder chamber.

3. Arrangement (1) according to Claim 1 or 2, wherein the operating variable of the electric motor (2) can be determined or is determined from its loading.

4. Arrangement (1) according to any one of Claims 1 to 3, wherein the operating variable of the electric motor (2) can be determined or is determined from its current consumption.

5. Arrangement (1) according to any one of Claims 1 to 4, wherein the operating variable of the electric motor (2) is its torque.

6. Arrangement (1) according to Claim 1, wherein the operating variable of the electric motor (2) is a detected pressure in the pressure medium flow path (12, 14, 18), wherein the electric motor (2) is adjusted in such a way that the detected pressure is applied when the pressure medium flow path (12, 14, 18) is opened.

7. Arrangement (1) according to any one of Claims 1 to 6, wherein the condition is a deactivation of a load-holding function.

8. Arrangement (1) according to any one of Claims 1 to 6, wherein the condition is a manually set control word.

9. Arrangement (1) according to any one of Claims 1 to 6, wherein the condition is that a detected force on the hydraulic cylinder (6, 8, 10) or pressure in the cylinder chamber lies outside a predetermined tolerance range.

10. Arrangement according to any one of Claims 1 to 6, wherein the condition is that a detected position of the hydraulic cylinder (6, 8, 10) lies outside a predetermined tolerance range.

11. Arrangement (1) according to any one of Claims 1 to 6, wherein the condition is a change of a position setpoint of the hydraulic cylinder (6, 8, 10).

12. Method for controlling a hydraulic arrangement (1) having a load-holding function with at least one hydraulic cylinder (6, 8, 10) and a hydraulic pump (4), comprising the following steps: - closing a shut-off valve (20, 22, 32, 58) in a pressure medium flow path (12, 14, 18) between the hydraulic cylinder (6, 8, 10) and the hydraulic pump (4); - determining or detecting an operating variable of an electric motor (2) which drives the hydraulic pump (4) during the closing of the shut-off valve (20, 22, 32, 58); - identifying that there is a condition for deactivating the load-holding function; - adjusting and tracking the determined or detected operating variable at the electric motor (2); and - opening the shut-off valve (20, 22, 32, 58).

13. Method according to Claim 12, wherein the hydraulic cylinder (6, 8, 10) is controlled by a control unit of the hydraulic arrangement (1) while the shut-off valve (20, 22, 32, 58) closes.

14. Method according to Claim 13, wherein a control of the hydraulic cylinder (6, 8, 10) by the control unit is ended after the shut-off valve (20, 22, 32, 58) is completely closed.

15. Method according to any one of Claims 12 to 14, wherein the operating variable of the electric motor (2) is reduced after the shut-off valve (20, 22, 32, 58) is completely closed.