Method for controlling hydraulic drive system

Abstract

To achieve consistent, predictable control behavior for a machine operator when a plurality of hydraulic loads are used simultaneously.SOLUTION: Scaling functions (31, 32, 33, 34, 35) for each load map an input side volumetric flow rate demand to an output side volumetric flow rate demand, and determine scaling coefficients (41, 42, 43, 44, 45) for each load as a ratio between the output side volumetric flow rate demand and the input side volumetric flow rate demand, where the output side volumetric flow rate demand of one stage is used as the input side volumetric flow rate demand of the next stage, and the volumetric flow rate demand is used as the input volumetric flow rate demand of a first stage.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a method for controlling a hydraulic drive system. [Background technology]

[0002] 2. Background of the Invention The working machine may have a hydraulic drive with several functional elements that are individually driven by hydraulic loads (e.g. hydraulic cylinders or hydraulic motors). In the case of conventional hydraulic drives with mechanically and hydraulically controlled participants or hydraulic loads, individual and therefore distributed control devices are used that allow the power consumption of the respective participants or loads to be individually controlled. These control devices or control elements are, for example, valves assigned to the participants or loads, which are directly driven and operated on the basis of presettings of the operator of the working machine, captured, for example, by a joystick. Summary of the Invention [Problem to be solved by the invention]

[0003] Disclosure of the Invention According to the invention, a method for controlling a hydraulic drive system and a computing unit and a computer program for its implementation are proposed having the features of the independent claims. Preferred configurations are the subject of the dependent claims and the following description. [Means for solving the problem]

[0004] According to the invention, for controlling a hydraulic drive system comprising a pressure medium source and a number of hydraulic loads to which pressure medium is supplied via a valve assembly, one or more successive stages of scaling functions are used for the volumetric flow demands of the loads, where each stage of the scaling functions maps the input volumetric flow demand of the load to the output volumetric flow demand of the load, and for each load each scaling function determines a scaling factor between the output volumetric flow demand of the load and the input volumetric flow demand. From the output volumetric flow demands of the last stage of the scaling functions a total volumetric flow demand is determined and the pressure medium source is driven accordingly. For each load, from its scaling factor a total scaling factor is determined, from which a scaled volumetric flow demand is determined. The valve assembly is driven according to the scaled volumetric flow demands of the loads. The use of the scaling functions makes it possible to take into account existing correlations or desired conditions between various hydraulic loads and / or hydraulic machines or their volume flows, coded into the scaling functions, as well as further existing conditions, such as the available power or available torque of the drive motor of the pressure medium source. This makes it possible to avoid undesirable behavior during the joint movement of several parts moved by the load of a machine in which a hydraulic drive system is used, such as jerky movements of individual parts, in which the required volume flow of the pressure medium fluctuates significantly in a short time when the load is switched on or off, i.e. when several hydraulic loads are used simultaneously, a constant control behavior that is predictable for the machine operator can be achieved.

[0005] According to one embodiment, determining the total volume flow request from the output volume flow demands of the last stage scaling functions comprises or is the sum of the output volume flow demands of the last stage scaling functions. In this way, in a simple manner, the volume flow to be provided by the pressure source or at least the minimum volume flow to be provided can be determined.

[0006] The pressure medium source comprises in particular a hydraulic machine and a drive motor driving said hydraulic machine. According to an embodiment, the displacement of the hydraulic machine is adjustable, whereby controlling the pressure medium source as a function of the total volumetric flow demand comprises controlling the displacement of the hydraulic machine. Alternatively or additionally, controlling the pressure medium source as a function of the total volumetric flow demand may comprise controlling or setting the rotation speed of the drive motor. The drive motor may be, for example, an internal combustion engine or an electric machine. Furthermore, the driving of the pressure medium source may be based on a pump pressure demand determined from the pressure demand of the load, whereby the pump pressure demand is determined in particular as being equal to or greater than the maximum of the pressure demand of the load. All in all, these (possible combinations of) embodiments make it possible to appropriately control the pressure medium source as a function of the volumetric flow demand scaled thereon in order to meet the desired demand of the operator.

[0007] According to one embodiment, the scaling function comprises a demand reduction function, which implements for each or at least one load the following steps: determining a multiplier indicating how much one or more second loads different from the first load reduce the volumetric flow request or the input volumetric flow demand of the demand reduction function of the first load, determining a reduced volumetric flow for each second load depending on the volumetric flow request of the respective second load and / or the input volumetric flow demand of the demand reduction function of the respective second load, determining a volumetric flow reduction for the first load based on the reduced volumetric flow of the one or more second loads, determining an output volumetric flow demand of the demand reduction function for the first load based on the input volumetric flow demand of the demand reduction function for the first load and the product of the multiplier and the volumetric flow reduction, where the loads for which these steps are respectively implemented are respectively denoted as first loads. The demand reduction function makes it possible to take into account the known mutual influence of the volumetric flow of the various hydraulic loads in the control. The demand reduction function allows the first load demand to be correspondingly reduced with the second load demand, which is advantageous, for example, when individual movements with full joystick deflection require high speeds, but combined movements with first and second loads, each with full joystick deflection, require relatively low speeds.

[0008] In particular, the output volumetric flow demand of the demand reduction function for each first load may be determined as the input volumetric flow demand of the demand reduction function for the first load minus the product of the multiplier and the volumetric flow reduction.

[0009] According to one embodiment, when determining the volumetric flow reduction of the respective first load, the volumetric flow reduction of the first load is determined as the maximum (or maximum value) of the reduced volumetric flow rates of one or more second loads. Alternatively or additionally (e.g. when different percentages of the volumetric flow reduction are determined by different manners), when determining the volumetric flow reduction of the respective first load, the volumetric flow reduction of the first load is determined as a (particularly weighted) average value of the reduced volumetric flow rates of one or more second loads.

[0010] According to one embodiment, the demand reduction function is the first stage of one or more scaling functions, whereby the input volumetric flow demand to the demand reduction function is the same as the volumetric flow request.

[0011] A computing unit according to the invention, for example a control device for a hydraulic drive system of a mobile work machine, is in particular program-technically designed to carry out the method according to the invention.

[0012] It is also advantageous to implement the method according to the invention in the form of a computer program or computer program product with a program code for implementing all the method steps, since this entails very little cost, especially if the control device to be executed is already existing in any case, since it is also used for further tasks. Suitable data carriers for providing the computer program are, in particular, magnetic, optical and electrical memories, such as hard disks, flash memories, EEPROMs, DVDs, etc. Downloading the program via a computer network (Internet, intranet, etc.) is also possible.

[0013] Further advantages and embodiments of the invention become apparent from the description and the accompanying drawings.

[0014] It is to be understood that the features mentioned above, and those to be further described below, can be used not only in the respective combinations presented, but also in other combinations or alone, without departing from the scope of the invention.

[0015] The invention is illustrated diagrammatically by way of an embodiment in the drawing and will be explained in more detail below with reference to the drawing. [Brief description of the drawings]

[0016] [Figure 1] FIG. 2 is a simplified diagram showing the structure of a hydraulic drive system. [Diagram 2] FIG. 4 illustrates a control method according to one embodiment of the present invention. [Diagram 3] FIG. 2 is a diagram showing the flow in determining the output volume flow demand and the associated scaling factor for a scaling function called the demand reduction function. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Detailed Description of the Drawings FIG. 1 shows, in a simplified manner, the structure of a hydraulic drive system in which the method according to the invention can be used.

[0018] A hydraulic machine 2, in particular a hydraulic pump (also called pump), is provided, by which a pressure medium (hydraulic medium, typically hydraulic oil) is pumped from a tank (hydraulically connected to the suction port of the hydraulic pump) to the hydraulic drive system. The illustrated hydraulic machine 2 is, for example, adjustable, i.e. has an adjustable displacement. The term displacement means the volume of pressure medium delivered per each revolution of the hydraulic machine 2. For example, the hydraulic machine 2 is an axial piston machine, for example of swash plate or tilted shaft design type, where the displacement corresponds to an adjustable swivel angle. The hydraulic machine 2 is driven by a motor or drive motor 4, for example an internal combustion engine, in particular a diesel engine, or an electric motor. The hydraulic machine 2 together with the drive motor 4 forms a pressure medium source 5 of the hydraulic drive system. In general, the pressure medium source may include one or more hydraulic machines and / or one or more drive motors.

[0019] The volume flow rate of pressure medium delivered by the hydraulic machine 2 can be varied by adjusting the displacement. In particular, if the drive motor 4 is an electric motor or machine, the displacement can additionally or alternatively be varied by varying the rotational speed of the electric motor. Correspondingly, in particular, if an electric motor is used as the drive motor 4, hydraulic machines with a constant displacement (constant speed machines or constant speed pumps) can also be used. In the case of an internal combustion engine, rotational speed changes occur relatively slowly, so that in hydraulic drives this is often operated at a constant rotational speed.

[0020] The pressure medium delivered by the hydraulic machine 2 is guided via a hydraulic line (hydraulically connected with the hydraulic port of the hydraulic pump) to a valve assembly 6, formed for example of a valve module or a valve disk, by means of which the inflow and outflow of the pressure medium to a number of hydraulic loads 8 can be controlled, here exemplarily one hydraulic motor and two hydraulic cylinders, which are coupled for example to mechanical parts of the machine in which the hydraulic drive system is used, in order to drive them or to cause their movements. For example, in the case of an excavator, the hydraulic motor can drive the rotational movement of the upper structure relative to the lower structure, and the hydraulic cylinder can cause the swivel movement of an arm or boom element. In general, there may be one or more hydraulic loads, i.e. in particular one or more hydraulic motors and / or hydraulic cylinders. The valve assembly 6 is in particular configured such that the inflow and outflow of the pressure medium to each of the hydraulic loads 8, i.e. to each hydraulic load 8, can be controlled individually or separately, for example by controlling the inflow and outflow throttles in the valve assembly or the cross-section of the valve openings. The hydraulic load is also referred to as the load for short.

[0021] In the hydraulic drive system, an electronic control 10 (computing unit) or control device is provided, which is configured to determine and / or generate control signals for controlling the pressurized fluid source 5 and / or for controlling the valve assembly 6. The control of the pressurized fluid source 5 may involve the control or regulation of the hydraulic machine 2 and / or (for example in the case of an electric motor) the control of the speed of the drive motor 4. These control signals are for example coded in the form of electrical signals and transmitted via control lines (represented by dashed lines) to the respective components or their control units.

[0022] The control signals are determined by the electronic control 10 by implementation of a control algorithm (e.g. in the form of a computer program or computer program module) based on the operating presets of the operator, which are captured by a suitable operating device (e.g. a joystick). The electronic control 10 can, for example, capture the operating presets 12 itself or receive them from the operating device and determine or calculate the corresponding volumetric flow requirements for the individual (hydraulic) loads therefrom. Alternatively, it may be envisaged that a higher-level control captures or receives the operating presets from the operating device, determines or calculates the corresponding volumetric flow requirements for the individual loads therefrom and transmits said volumetric flow requirements 14 to the electronic control.

[0023] The electronic control unit 10 is in particular configured to implement the method according to the invention, for example by executing a computer program stored in the electronic control unit or by executing a computer program module stored in the electronic control unit.

[0024] The hydraulic drive system may be provided with one or more sensors (not shown), which transmit their measurement results, for example via sensor lines, to the electronic control 10. The electronic control 10 may be correspondingly configured to receive or capture the measurement results from the sensors and use them when controlling the hydraulic drive. For example, one or more displacement or swivel angle sensors may be provided for capturing the displacement of the hydraulic pump 2, a rotation speed sensor for capturing the rotation speed of the drive motor 4, one or more pressure sensors for capturing the pressure of the pressure medium at appropriate points of the hydraulic drive, a position sensor (for example an end position sensor) for capturing the position of a piston in a hydraulic cylinder, etc.

[0025] Fig. 2 shows a control method according to an embodiment of the present invention. The control method relates to a hydraulic drive system with a number of hydraulic loads (also called loads for short) and at least one hydraulic machine, as shown, for example, in Fig. 1. The control method is implemented in particular by an electronic control unit of the hydraulic drive system.

[0026] First, by means of the operating device 16, e.g. one or more joysticks, levers, pedals, etc., the operating presets (i.e. load presets or operator presets for a load) 12 of the machine in which the hydraulic drive is used can be captured for each (hydraulic) load. From these operating presets 12, the volumetric flow demand 14 and pressure demand 22 for the load can be determined by means of appropriately defined functions or mappings, e.g. a volumetric flow mapping 18 and a pressure mapping 20. The volumetric flow demand 14 depends for example on the operating preset 12 in a progressive manner, i.e. with an increase in the deflection of the operating device 16, the corresponding volumetric flow demand increases significantly more than linearly.

[0027] From the hydraulic load volumetric flow demand 14, a hydraulic load volumetric flow demand 40 is determined, scaled by means of a scaling function 31, 32, 33, 34, 35 in one or more successive stages, and for each hydraulic load one or more scaling coefficients 41, 42, 43, 44, 45 are determined. These scaling coefficients are determined as the ratio between the output volumetric flow demand and the input volumetric flow demand of a stage (for the same load), for example, here five stages are shown, but generally other numbers greater than one are also possible. These stages form a sequence from the first stage to the last stage, which is identical in the case of only one stage, in particular they are equal to one stage.

[0028] From the scaled volumetric flow demands 40, a (scaled) total volumetric flow demand 50 is determined or calculated. For example, a summation map 52 may be envisaged, which sums up the scaled volumetric flow demands 40 to obtain the total volumetric flow demand 50. Furthermore, it may be envisaged that a pump pressure demand 54 is determined or calculated from the pressure demands 22. For example, it may be envisaged that it is determined or calculated using a maximum value map 56, which selects the maximum value of the pressure demands 22 as the pump pressure demand 54. Alternatively (or additionally), the pump pressure demand 54 can be fixedly pre-set or determined, for example, using a load pressure control. By means of a pump control algorithm 58, from the total volumetric flow demand 50 (taking into account the pump pressure demand 54), a control signal or control command for the pressure medium source 5, i.e. the hydraulic machine 2 and / or the drive motor 4 (in this case, for example an electric motor), can be determined in order to satisfy the total volumetric flow demand 50. That is, the pressure medium source 5 is driven and controlled according to the total volume flow demand 50, i.e. in particular to provide a volume flow rate of pressure medium according to the total volume flow demand (wherein the pump pressure demand should also be met).

[0029] From the one or more scaling factors 41, 42, 43, 44, 45, for each (hydraulic) load a total scaling factor 60 is determined, where optionally additional parameters or variables can be taken into account, such as the number of active loads 62 and / or the motor scaling factor 64 for each of the loads (see below). The determination of the total scaling factor 60 can be done, for example, using a total scaling function 66.

[0030] From the total scaling function 60 and the corresponding operation preset 12 of the load (as shown) or from the total scaling factor 60 and the corresponding volumetric flow demand 14 of the load (not shown), for example by a preset scaling function 70 or demand scaling function, a scaled control preset 72 for the load or a control preset for the valve assembly supplying pressure medium to the load is determined, for example as the product of the total scaling factor 60 and the corresponding (i.e. assigned to the same load) operation preset 12 or volumetric flow demand 14. These control presets 72 can be converted by a valve assembly control algorithm 74 into corresponding control signals for the valve assemblies 6, whereby the drive control of the valve assemblies 6 as a whole is performed in response to the scaled control presets 72.

[0031] The scaling functions 31, 32, 33, 34, 35 of each stage respectively map the input volume flow demand for each of the loads to the output volume flow demand for each of the loads. The output volume flow demand of one stage is then the input volume flow demand of the next stage. The input volume flow demand of the first stage is the volume flow demand 14 of the load. The output volume flow demand of the last stage is the scaled volume flow demand 40 of the load. In the case of only one stage or only one scaling function, the volume flow demand 14 is the input volume flow demand of this scaling function and the scaled volume flow demand 14 is the output volume flow demand of this scaling function. Besides the dependence of the respective input volume flow demands, the scaling functions may also depend on further parameters. Such further parameters may for example be determined or determinable parameters or may be parameters captured within the operating range of the hydraulic drive (for example sensor measurements).

[0032] By means of the scaling functions 31, 32, 33, 34, 35 certain boundary conditions and / or dependencies between the variables of the hydraulic drive can be taken into account in controlling the drive of the hydraulic machine and the valve assembly, so that in particular a desired control behavior can be achieved or an undesired control behavior can be avoided. In general, different scaling functions can be provided to take different aspects into account.

[0033] In particular, a scaling function may be provided, for example a first scaling function 31 in the figure, which determines for each load how much its volumetric flow requirement is reduced based on the volumetric flow requirements of the respective other loads. This scaling function is also called a requirement reduction function and is further explained in relation to FIG. 3. In the example of an excavator, for example, the volumetric flow requirement of the hydraulic cylinder which causes the lifting movement of the boom can be reduced based on the volumetric flow requirement of the hydraulic motor which causes the rotational movement of the superstructure, whereby a predefined percentage of the volumetric flow requirement of the hydraulic motor is taken into account. Conversely, the volumetric flow requirement of the hydraulic motor can be simultaneously reduced by a predefined percentage of the volumetric flow requirement of the hydraulic cylinder. By suitable selection of the percentages to be taken into account, an evenly combined lifting-rotating movement can be achieved, so that for example a sudden and drastic slowdown or stop of the lifting movement is avoided when an additional rotational movement is started. In this example, only two loads are observed, but generally more than two, in particular all loads, are taken into account, whereby the percentages of the volumetric flow requirements of the respective other loads are combined, for example by maximum value selection.

[0034] Further examples of possible scaling functions are briefly discussed below.

[0035] A scaling function, for example the second scaling function 32 in the figure, scales the volumetric flow request or demand of the load based on an input or parameter. Here, for example, the operator can adapt the volumetric flow to an attachment (for example a demolition hammer or a sweeper) by means of a parameter. The target quantities for pumps and valves can then be influenced using individual scaling factors. The output volumetric flow demand of a load arises, for example, by monotonic mapping from the input volumetric flow demand of the same load, where this mapping can depend on the sign of the input volumetric flow demand. This mapping is in particular independent of the input volumetric flow demand of other loads. The scaling or mapping can be different for different loads. This allows implementing desired characteristics of the volumetric flow demand. For example, the mapping of a load can be defined in such a way that the output volumetric flow demand initially increases linearly with its input volumetric flow demand (starting from zero) so that a limit on the load's volumetric flow demand is implemented, and when the input volumetric flow demand exceeds the limit, it is set to a constant maximum output volumetric flow demand.

[0036] A scaling function, for example the third scaling function 33 in the figure, scales the volumetric flow request or demand of the load based on the reference motor speed and the actual or set motor speed. Here, the desired volumetric flow is scaled with the drive speed of the pump or the drive motor (for example a diesel engine). If the operator selects, for example, a relatively low drive motor speed, this corresponds to the operator's request for the machine, in particular its hydraulic load, to run slower. In particular, a ratio between the controlled motor speed and the reference motor speed can be calculated and a scaling factor can be determined depending on this ratio, in which case the direction or sign of the volumetric flow demand can additionally be taken into account.

[0037] A scaling function, for example the fourth scaling function 34 in the figure, scales the volumetric flow request or demand of the load so that it does not exceed the available volumetric flow of the hydraulic machine. For good controllability of the machine, the volumetric flow of the load or the volumetric flow of the pump and the valve opening (particularly of the valve assembly) are adjusted to each other when designing the machine. This adjustment is usually made for individual movements, where the load can at most receive the maximum pump volumetric flow, i.e. the maximum valve opening corresponding to it is selected. Now, if the sum of the load demands in the combined movements exceeds the pump capacity, the individual load cannot deliver the desired volumetric flow. For controllability comparable to that in the individual movements, the valve opening must also be adapted. For this purpose, a reduction or scaling factor is calculated.

[0038] A scaling function, for example the fifth scaling function 35 in the figure, scales the volume flow request or demand of the load so that it does not exceed the available torque and / or available power of the drive motor. If the available power is not sufficient to meet the volume flow request, the requested volume flow must be reduced. As in the previous scaling functions, it is advantageous if the volume flow of the load and the valve opening are matched to each other, i.e. if the volume flow is reduced due to a high load and / or a lack of available power, the valve opening should also be adapted. For the adaptation of the valve opening, a reduction or scaling factor is calculated in this function.

[0039] In particular, cases may arise in which the scaling function implements a trivial mapping for at least one load, i.e. in the scaling function for at least one load, the output volumetric flow demand is equal to the input volumetric flow demand (and correspondingly the scaling factor is equal to 1).

[0040] The number of active loads 62 can be determined, for example, by a number determination function 76 (if this is taken into account when determining the total scaling factor 60). In this case, in order to obtain a continuous progression of the number of active loads 62, a percentage value can be determined for each load from its volumetric flow request, and a percentage function can be used which, starting from zero, corresponds to a volumetric flow request of zero and increases monotonically to one with increasing volumetric flow requests (for example, the percentage function can map all volumetric flow requests below a first threshold to zero, increase with a constant gradient from the first threshold to a second threshold to one, and map all volumetric flow requests above the second threshold in terms of absolute value to one). The percentage values ​​are then added up. Correspondingly, the number of active loads 62 can have a non-integer real value. There are also exceptional conditions in which it is not advantageous to follow the valve slide opening of the loads with a reduction in the volumetric flow. For example, in the individual operations, a volumetric flow restriction based on a lack of available power occurs at the same time, so that it is also disadvantageous to reduce the valve opening. This exception condition (or a similar exception condition) can be recognized by using this function to determine the number of actuators, i.e. hydraulic loads, operated by the operator.

[0041] The motor scaling factors 64 (if they are taken into account when determining the total scaling factor 60) can be determined, for example, by a corresponding decision function (motor scaling decision function 78). In this case, the motor scaling factors 64 are determined on the basis of the volume flow requirement of the respective load and the actual or set motor speed. Here, depending on the speed, in particular a deceleration factor or a motor scaling factor can be predefined in order to bring about an influence on the valve opening independently of one another for each load. In contrast to the preceding function, this function is not based on the desired volume flow but solely on the drive motor speed, in particular on the internal combustion engine speed, so that a different behavior can be achieved on the vehicle. The valve reduction then depends mainly on the set speed and less on the volume flow.

[0042] To determine the total scaling factor 60, the total scaling function 66 evaluates the scaling factors 41, 42, 43, 44, 45 and possibly the motor scaling factor 64, for example depending on the number of active loads 62 and on determined or determinable parameters, and combines the scaling factors 41, 42, 43, 44, 45 and possibly the motor scaling factor 64 (in particular according to determined or determinable parameters). In the simplest case, the scaling factors 41, 42, 43, 44, 45 of the loads can for example be multiplied with each other to determine or calculate the total scaling factor 60 for the respective load. More generally, the individual scaling factors are combined depending on the parameters. This can be done independently of each other (i.e. with different parameters) for the various loads. Depending on the application in the machine, it is advantageous to take into account only selected scaling factors. So, for example, it is advantageous to scale the drive of the slewing mechanism with the speed of the diesel engine, whereas the lowering of the boom is not scaled, since here only gravity acts as the drive. The number of activation functions is also taken into account here in order to avoid unnecessary throttling in individual movements.

[0043] One or more of the scaling functions 31 , 32 , 33 , 34 , 35 and, possibly, the total scaling function 66 and / or the preset scaling function 70 and / or the number decision function 76 and / or the motor scaling decision function 78 can be collectively considered as a volumetric flow division function 80 .

[0044] 3 shows a diagram illustrating the flow of determining the output volume flow demand and the corresponding associated scaling factor for a scaling function called demand reduction function 37. The demand reduction function makes it possible, for example, to determine to what extent the volume flow allocated to an individual load is modified by the desired volume flow of other loads. In particular, this procedure also makes it possible to implement priorities of different loads.

[0045] These steps refer to a load called a first load in order to distinguish it from the other loads called second loads. These steps or the illustrated flows can be applied to several or all loads in order to determine the output volumetric flow demand (and the scaling factor) of each load, the term "first load" being used for the load for which the implementation of the steps is used to determine the output volumetric flow demand and the scaling factor of the demand reduction function, respectively. The starting point (i.e. the variables used in the respective calculations) for the implementation for the various loads (respectively first loads) is in any case the input volumetric flow demand and / or the volumetric flow demand of the demand reduction function (in particular, there is no recursive implementation). If the steps or the illustrated flows for a load are not applied, its output volumetric flow demand is equal to the input volumetric flow demand or the volumetric flow demand of the load (case of trivial mapping as described above). This non-application can also be achieved by a suitable selection of the parameters in the steps in an equivalent manner, for example by setting the multiplier in step 110 for such load to zero.

[0046] In step 110, a multiplier is determined that indicates the percentage by which the volumetric flow demand of the other, second load, different from the first load, reduces the volumetric flow demand of the first load. This percentage can be adjusted by a parameter and in particular can be determined differently for each of the various first loads. This percentage can be specified, for example, as a real number in the interval [0,1] or as a percentage between 0% and 100%. If a hydraulic drive system is integrated in an excavator, for example, the hydraulic cylinder (first load) that causes the movement of the boom could be reduced by 30% (percentage) by the other (second) load.

[0047] In step 120, a reduced volumetric flow rate is determined for each second load, which depends on the desired direction of movement of the first load (i.e. on the sign of the volumetric flow rate demand of the first load) and / or on the volumetric flow rate demand of the respective second load. In the above excavator example, the hydraulic cylinder moving the arm element may be the second load. Here, if the movement of the boom and arm element is in the same direction, the reduced volumetric flow rate for this second load is equal to its volumetric flow demand, or equal to the volumetric flow demand multiplied by a predetermined factor (e.g. if the hydraulic cylinder diameters are different).

[0048] In step 130, a volumetric flow reduction for the first load is determined based on the reduced volumetric flow of the second load. In particular, the maximum value of the reduced volumetric flow of the second load can be selected as the volumetric flow reduction for the first load. Similarly, the determination of the volumetric flow reduction from the reduced volumetric flow can include other calculation methods, for example summing and / or averaging.

[0049] In step 140, the output volumetric flow demand 38 of the demand reduction function 37 is determined based on the volumetric flow demand of the first load and the product of the multiplier (of the first load) and the volumetric flow reduction (of the first load). In particular, the output volumetric flow demand 38 of the demand reduction function 37 may be equal to the volumetric flow demand of the first load minus the product of the multiplier and the volumetric flow reduction.

[0050] In step 150, a scaling factor 39 for the demand reduction function 37 (for the first load) is determined or calculated as the ratio of the output volumetric flow demand determined in step 140 to the volumetric flow request.

Claims

1. A method for controlling a hydraulic drive system, the hydraulic drive system comprising a pressure medium source (5) providing a volumetric flow rate of pressure medium in the hydraulic drive system, and a plurality of hydraulic loads (8), the hydraulic loads (8) being supplied with pressure medium in an individually controllable manner via valve assemblies (6), the method comprising: Receiving or identifying a volumetric flow request (14) for each of a plurality of loads; - using one or more successive stages of scaling functions (31, 32, 33, 34, 35), where for each stage, said scaling function for each load maps the input volumetric flow demand of the respective load to the output volumetric flow demand of the respective load, and a scaling coefficient (41, 42, 43, 44, 45) for each load is determined as the ratio between the output volumetric flow demand and the input volumetric flow demand of the respective load, the output volumetric flow demand of the scaling function of one stage being respectively used as the input volumetric flow demand of the scaling function of the next stage, said volumetric flow request (14) being used as the input volumetric flow demand of the scaling function (31) of the first stage, determining (66) a total scaling factor (60) for each load based on the scaling factors (41, 42, 43, 44, 45) of the respective loads; determining (70) a scaled volumetric flow demand (72) for each load based on the total scaling factor for the respective load; determining (52) a total volume flow demand (50) from the output volume flow demands of the scaling function (35) of the last stage; controlling (74) the valve assembly (6) in response to the scaled volumetric flow demand (72); and controlling (58) the pressure medium source (5) in response to the total volumetric flow demand (50); The method includes:

2. 2. The method of claim 1, wherein determining (52) the total volume flow demand from the output volume flow demands of the scaling function (35) of the last stage comprises or is the sum of the output volume flow demands of the scaling function (35) of the last stage.

3. 3. The method according to claim 1 or 2, wherein the pressure medium source (5) comprises a hydraulic machine (2) with an adjustable displacement, and driving (58) the pressure medium source (5) comprises controlling the displacement of the hydraulic machine (2) depending on the total volumetric flow demand (50).

4. 4. The method according to claim 1, wherein the pressure medium source (5) comprises a hydraulic machine (2) and a drive motor (4) driving the hydraulic machine (2), and the driving control (58) of the pressure medium source (5) comprises controlling the rotation speed of the drive motor (4) depending on the total volumetric flow demand (50), the drive motor (4) being in particular an electric machine.

5. 5. The method according to any one of claims 1 to 4, wherein the volumetric flow demand (14) is determined from operational presets (12) for the load, which are captured using at least one operating device (16).

6. Determining (66) the total scaling factor (60) for the loads is further based on a number of active loads (62); and / or 6. The method according to claim 1, wherein the pressure medium source (5) comprises a hydraulic machine (2) and a drive motor (4) driving the hydraulic machine (2), and wherein determining (66) the overall scaling factor (60) for the loads is further based on a motor scaling factor (64) determined from the volumetric flow requirement (14) of the respective load and an actual motor speed of the drive motor (4) or a set motor speed of the drive motor (4).

7. 7. The method according to claim 1, wherein the driving (58) of the pressure medium source (5) is further based on a pump pressure demand (54) determined from the pressure demands (22) of the loads, the pump pressure demand (54) being determined in particular as being equal to or greater than the maximum pressure demand (22) of the pressure demands (22) of the loads.

8. The scaling function includes a demand reduction function (37), The demand reduction function (37) performs the following steps for each load: Determining (110) a multiplier indicative of the percentage by which one or more second loads different from the first load reduce the volumetric flow request or input volumetric flow demand of the demand reduction function of the first load; determining (120) a reduced volume flow rate for each said second load depending on the volume flow rate demand of each said second load and / or the input volume flow rate demand of a demand reduction function of each said second load; determining (130) a volumetric flow reduction for the first load based on the reduced volumetric flow of one or more of the second loads; determining (140) the output volume flow demand (38) of the demand reduction function (37) for the first load based on the input volume flow demand of the demand reduction function for the first load and the product of the multiplier and the volume flow reduction; The method according to claim 1 , further comprising: implementing the steps: a) determining whether the load is a first load; b) determining whether the load is a first load; and c) determining whether the load is a first load.

9. 9. The method of claim 8, wherein the output volumetric flow demand (38) of the demand reduction function (37) for each of the first loads is determined as an input volumetric flow demand of the demand reduction function for the first load minus the product of the multiplier and the volumetric flow reduction.

10. the reduced volume flow rate for each second load is determined depending on a desired direction of movement of the first load or a sign of the input volume flow rate of the first load; and / or 10. The method according to claim 8 or 9, wherein the reduced volumetric flow rate for each second load is determined depending on a desired direction of movement of the respective second load or a sign of an input volumetric flow rate of the respective second load.

11. 11. The method according to claim 8, wherein in the step (130) of determining the volumetric flow reduction of the first load, the volumetric flow reduction of the first load is determined as the maximum of the reduced volumetric flow rates of one or more of the second loads and / or as a specifically weighted average value of the reduced volumetric flow rates of one or more of the second loads.

12. 12. The method according to any one of claims 8 to 11, wherein the demand reduction function (37) is a first stage of one or more of the scaling functions, whereby the input volumetric flow demand of the demand reduction function is the same as the volumetric flow request (14).

13. A computing unit (10), comprising a processor configured to execute the method according to any one of claims 1 to 12.

14. A computer program comprising instructions for causing a computer to carry out a method according to any one of claims 1 to 12, when the program is executed by the computer.

15. 15. A computer readable data carrier having stored thereon a computer program according to claim 14.

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