Method for controlling a hydraulic drive system, and hydraulic drive system

Abstract

This invention provides a method for controlling a hydraulic drive system. [Solution] 1) For each consumer device 20, the operating value of the control valve 22 is determined, 2a) the maximum operating value and / or the maximum load pressure are determined. 2b) For the first control valve, if the quotient of the operating value and the maximum operating value is smaller than the first value, and / or the quotient of the load pressure of the consumer device is smaller than the second value, the operating value is increased, 3a) for each consumer device, assuming that pump pressure is applied and the control valve is displaced to its maximum cross-section, the consumer device pump pressure to the consumer device is determined, and the maximum consumer device pump pressure is determined as the minimum pump pressure. 3b) For the second control valve, if the difference between the minimum pump pressure and the load pressure of the consumer device is smaller than the nominal pressure difference of the second control valve, the operating value is increased, 4) the first control valve and / or the second control valve are driven, and / or the pump 2 is driven at the determined minimum pump pressure setting.

Description

Technical Field

[0001] The present invention relates to a method for controlling a hydraulic drive system, a hydraulic drive system, a computing unit for implementing the method, and a computer program.

Background Art

[0002] Background of the Invention A working machine may have a hydraulic drive system with a plurality of functional elements or components individually driven by hydraulic consumers (e.g., hydraulic cylinders or hydraulic motors). In this case, the supply of the pressure medium is effected by a hydraulic pump connected to the individual consumers via a control valve or a directional control valve. Using the control valve, the volume flow rate of the pressure medium to a plurality of different consumers with respective volume flow rate requirements can be controlled.

Summary of the Invention

Problems to be Solved by the Invention

[0003] Disclosure of the Invention According to the present invention, there are proposed a method for controlling a hydraulic drive system having the features described in the independent claims, a hydraulic drive system, a computing unit for implementing the method, and a computer program. Advantageous embodiments are the subject of the dependent claims and the following description.

Means for Solving the Problems

[0004] The present invention utilizes the means of performing the following steps in a method for controlling a hydraulic drive system having a hydraulic pump with a pressure outlet, a plurality of hydraulic consumers, and for each consumer, a control valve and a pressure compensation device associated with the consumer.

[0005] 1) For each consumption device, determine the operating value for the corresponding control valve such that the volumetric flow rate requirement of the consumption device is met, assuming that a nominal pressure difference, determined by the corresponding pressure compensation device, exists across both ends of the control valve.

[0006] 2a) Determine the maximum operating value as the largest of the determined operating values, and / or determine the maximum load pressure as the maximum load pressure of the consumption device, and, 2b) For a first control valve associated with a consuming device having a non-zero volumetric flow rate requirement, if the quotient of the operating value and the maximum operating value is less than a predetermined first value, and / or if the quotient of the load pressure and the maximum load pressure of the consuming device to which the first control valve is associated is less than a predetermined second value, the operating value of the first control valve is changed (especially increased) and the changed operating value is obtained.

[0007] In lieu of or in addition to 2a, 2b), this method is: 3a) Assuming that the pump pressure of each consumption device is applied to the pressure outlet of the pump, and that the passage cross-section of the control valve associated with the consumption device is displaced to its maximum cross-section, determine the pump pressure of each consumption device required to achieve the volumetric flow rate requirement, and determine the maximum pump pressure of each consumption device as the minimum pump pressure, and 3b) For a second control valve associated with a consumption device having a non-zero volumetric flow rate requirement, if the difference between the minimum pump pressure and the load pressure of the consumption device to which the second control valve is associated is smaller than the nominal pressure difference of the second control valve, increase the operating value of the second control valve to obtain the changed operating value. Includes.

[0008] This method, 4) Drive the first control valve using a changed operating value, and / or drive the second control valve using a changed operating value, and / or drive the pump using a determined minimum pump pressure setting. It also includes.

[0009] According to the proposed method, it is possible to relatively lower the pump pressure of a hydraulic drive system and, consequently, to make the operation of the hydraulic drive system more energy-efficient, without causing undersupply of the pressure medium or changes in the allocation of quantity to individual consumption devices due to increases in individual operating values ​​(step 2b) or 3b)).

[0010] In one embodiment, when the pump is driven using a determined minimum pump pressure setpoint, pump pressure control is performed so that the pump pressure of the pressure medium at the pressure outlet is controlled according to a target pressure, where the target pressure is equal to the minimum pump pressure, or equal to the sum of the minimum pump pressure and a predetermined compensation pressure value. Similarly in the following embodiments, according to these embodiments, the pump pressure (corresponding to the target pressure due to pressure control) is relatively low (compared to control that controls the pumping pressure to a constant high pressure sufficient to meet various different load pressure requirements in any case), thereby making the pressure drop through the pressure compensation device and the associated energy loss very small. A predetermined (positive) compensation pressure value can be used to account for or compensate for pressure differences arising from the structure of the hydraulic system (e.g., pressure drops caused by the hydraulic pipeline between the pump and the control valve) and / or pressure differences arising from the arrangement of pressure sensors.

[0011] According to one embodiment, in particular in step 4), if the pump is not driven using the determined minimum pump pressure setting, the pump pressure control is performed so that the pump pressure of the pressure medium at the pressure outlet is controlled according to the target pressure, the target pressure being equal to the sum of the maximum load pressure and the nominal pressure difference of the control valve associated with the consuming device where the maximum load pressure is present, or the target pressure being equal to the sum of the maximum load pressure, a predetermined compensation pressure value and the nominal pressure difference of the control valve associated with the consuming device where the maximum load pressure is present.

[0012] According to one embodiment, at least one control valve, distinct from the first and second control valves, is driven using an unchanged operating value. This is carried out, for example, within the framework of step 4).

[0013] According to one embodiment, the method includes detecting or determining the volumetric flow rate requirement for each consumption device. In this case, in particular, a control signal generated by a user interface (e.g., a joystick) is evaluated to determine the volumetric flow rate requirement.

[0014] According to one embodiment, the load pressure of the consumption device is measured using a load pressure sensor. The load pressure sensor may be provided, for example, on the output side of each control valve, or in each connecting pipe between the control valve and the consumption device.

[0015] According to one embodiment, the first value is 0.2 or less. In particular, the first value may be 0.15 or less, 0.1 or less, or 0.5 or less.

[0016] According to one embodiment, the second value is 0.7 or less. In particular, the second value may be 0.5 or less, 0.4 or less, or 0.3 or less.

[0017] According to one embodiment, in step 2b), the operating value of the first control valve is increased such that the quotient of the changed operating value and the maximum operating value is greater than or equal to a predetermined first value. In this case, the increase (which is performed when the quotient of the original, unchanged operating value and the maximum operating value is less than the predetermined first value) may also depend on the load pressure of the consumer to which the control valve is associated.

[0018] According to one embodiment, in step 3b), the increase in the operating value of the second control valve is performed using flow control, which defines a functional relationship between the volumetric flow rate through the control valve, the passage cross-section of the control valve, and the pressure drop across both ends of the control valve. In this case, first, the passage cross-section corresponding to the (unchanged) operating value can be determined, and then, using flow control, the passage cross-section (in the second control valve) that must exist to satisfy the volumetric flow rate requirement (of the consumption device associated with the second control valve) can be determined from the actual pressure difference (pump pressure minus load pressure), and from this passage cross-section, the changed operating value (for the second control valve) to achieve this passage cross-section can be determined. This results in an increase in the operating value, because in flow control for throttling, choking, or generally narrowing of the flow cross-section, a relatively large pressure drop is associated with a relatively large volumetric flow rate.

[0019] According to one embodiment, in step 3b), the through cross-section corresponding to the operating value of the second control valve is determined, the changed through cross-section is calculated by multiplying the determined through cross-section by the square root of the ratio of the nominal pressure difference to the actual pressure difference, and the changed operating value of the second control valve is determined so that the changed through cross-section is obtained, thereby changing the operating value of the second control valve. This embodiment allows for simple implementation. If the through cross-section is proportional to the operating value, these three steps are simplified into a single step of obtaining the changed operating value by multiplying the (unchanged) operating value by the square root of the ratio of the nominal pressure difference to the actual pressure difference.

[0020] The computing unit according to the present invention, for example, a control device for a mobile work machine or a control device for a hydraulic drive system, is configured to implement the method according to the present invention, particularly in terms of programming techniques.

[0021] The hydraulic drive system according to the present invention comprises a hydraulic pump with a pressure outlet, a plurality of hydraulic consumption devices, and for each consumption device, a control valve and a pressure compensation device associated with the consumption device, each consumption device being hydraulically connected to the pressure outlet of the pump via an associated control valve, and for each consumption device, the associated control valve has a through cross section that is displaceable according to an operating value between a minimum cross section equal to zero and a maximum cross section, the minimum cross section corresponding to a lower operating value, and the maximum cross section corresponding to a larger upper operating value, and for each consumption device, the associated pressure compensation device is configured to limit the pressure drop across both ends of the control valve associated with the consumption device to their respective nominal pressure differences. The hydraulic drive system further comprises a calculation unit according to the present invention, the calculation unit is configured in particular to control the control valve.

[0022] The terms “connected” or “connected” should be understood, unless otherwise specified, in the sense of “hydraulically connected,” that is, in the sense of a hydraulic connection, such as a hydraulic pipeline or passage, which allows for a volumetric flow rate or flow of a pressure medium to pass between elements connected via the hydraulic connection, and the hydraulic connection may be provided with optional control elements, such as valves, which can affect the volumetric flow rate of the pressure medium or affect the volumetric flow rate of the pressure medium in a controllable manner.

[0023] It is also advantageous to implement the method according to the invention in the form of a computer program or a computer program product comprising program code for carrying out all method steps. This is because this causes particularly little cost, especially if the control device for carrying out the implementation is already in existence anyway and is also used for other 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 and the like. It is also possible to download the program via a computer network (Internet, intranet, etc.).

[0024] Further advantages and embodiments of the invention will become apparent from the description and the attached drawings.

[0025] It is self-evident that the features described above and the features to be further explained below can be used not only in the presented combinations but also in other combinations or individually without departing from the scope of the invention.

[0026] The invention is schematically illustrated in the drawings on the basis of embodiments and will be explained in detail below with reference to the drawings.

Brief Description of the Drawings

[0027] [Figure 1] FIG. is an exemplary illustration of the structure of a hydraulic drive system capable of implementing the method according to each embodiment of the invention. [Figure 2] FIG. is a flowchart according to an embodiment of the invention.

Modes for Carrying Out the Invention

[0028] Detailed Description of the Drawings Figure 1 illustrates the structure of a hydraulic drive system that can carry out the methods according to each embodiment of the present invention. A hydraulic drive system is installed, for example, in a work machine, particularly a mobile work machine, to cause the movement of components of the work machine (e.g., boom elements, wheels, or chains).

[0029] A hydraulic drive system has a hydraulic pump 2, which is connected to a tank and pumps a pressure medium (i.e., a working fluid, particularly hydraulic oil) from the tank to the pressure outlet of the pump 2. The hydraulic pump 2 is displaceable, i.e., has a displaceable displacement volume. The expression "displacement volume" (or suction volume or pumping volume) refers to the volume of pressure medium pumped per revolution of the hydraulic machine. This may be specified, for example, as a swivel angle. The pump 2 is, for example, an axial piston mechanism of the swashplate type or swash-shaft type. The pump 2 is driven by an engine 4, for example, an internal combustion engine, particularly a diesel engine, or an electric motor.

[0030] The pressure outlet of pump 2 is connected, for example, to a directional control valve or control valve 22 (e.g., a proportional valve or an electrically proportional valve) via a hydraulic pipeline 12 or hydraulic passage, and the directional control valve or control valve 22 itself is connected to each hydraulic consumer device 20 (also simply referred to as a consumer device). Furthermore, pressure compensation devices 24 are provided, which are, here for example, connected upstream of the control valve 22, i.e., located on the inlet side, or located between pump 2 and the control valve 22. For example, each control valve 22 has a hydraulic inlet 22a (pressure inlet) connected to each pressure compensation device 24 or pump 2, and an outlet 22b (consumer device outlet) connected to each consumer device 20. Each control valve with its own pressure compensation device may be implemented, for example, in a valve module (or valve section or valve disc) of a modularly constructed valve assembly 30 (valve block). The control valves and pressure compensation devices that supply the pressure medium to the consumer devices are also referred to as being associated with the consumer devices. Figure 1 illustrates two consuming devices, a control valve, and a pressure compensator. Generally, a hydraulic drive system may have more consuming devices, control valves, and pressure compensators. Each hydraulic consuming device may be, for example, a hydraulic cylinder or a hydraulic motor, operating independently of the others.

[0031] The control valve 22 (e.g., a directional control valve) has one passage or flow path each with a displaceable passage cross-section (i.e., a passage or flow path for a pressure medium located between an inlet 22a and an outlet 22b, and having a displaceable cross-section or cross-sectional area), the displaceable passage cross-section being able to vary between each minimum cross-section which is equal to zero (i.e., it is impossible for a volume of the pressure medium to flow through the control valve) and each maximum cross-section. For example, the change or displacement of the passage cross-section may be carried out continuously or at least partially continuously. The control valve 22 is, for example, a directional control valve with a longitudinally movable or displaceable (control) piston, the outer surface of which has grooves formed by so-called control edges, so that the longitudinal movement of the piston opens or closes each passage. Displacement of the control valve 22 is carried out using each displacement device 22c of the control valve 22. The displacement is carried out hydraulically, particularly electromagnetically or by electromagnetic pilot control (i.e., an electromagnetically controlled valve controls the flow of a pressure medium that causes the displacement of the control valve, or an electromagnetically controlled valve generates a control pressure from the supply pressure, which then causes the displacement of the control valve against a spring (pressure control)). Each displacement of the control valve 22 (i.e., the size of each adjusted passage cross section) corresponds to an operating value for driving the control valve 22, i.e., the displacement device 22c of the control valve 22, in which case a current is applied to the electromagnet of the displacement device, for example, and the current intensity of this current is determined by or corresponds to the operating value, for example, from the operating value (for example, by multiplication using a proportionality constant).The corresponding control signal may take the form of the current itself with its respective current intensity, or it may take the form of a PWM signal (PWM: pulse width modulation or pulse duration modulation) where the duty cycle corresponds to the manipulated value or current intensity, or, if the control valve or the valve displacement device has a data communication interface (e.g., a CAN (Controller Area Network) interface), it may be a digital signal indicating the manipulated value or equivalent manipulated variable (e.g., the value of the current intensity to be adjusted), in which case the control valve adjusts the current itself according to the manipulated value or manipulated variable.

[0032] The control value is a number greater than or equal to zero (except for its unit), and without limiting generality, the passage cross-section increases with increasing control value, and in particular, a control value of zero corresponds to a passage cross-section of zero. The control value is, for example, a number within a range from a lower control value to an upper control value. For example, in particular when different control valves each have different maximum cross-sections of different sizes, the control value can be normalized to a predetermined range, for example, between 0 and 1, or between 0% and 100%, where 1 or 100% corresponds to the maximum cross-section. The relationship between the control value and the corresponding passage cross-section (i.e., passage cross-sectional area) adjusted when the control valve is driven using the control value is known and may be provided, for example, in the form of a function and / or characteristic map. For example, it is also possible to make the control value proportional to the passage cross-section.

[0033] The pressure compensators 24 are arranged such that the pressure difference or pressure drop across the corresponding control valves 22, to which each pressure compensator is connected upstream, is limited to a maximum pressure drop, referred to as the nominal pressure difference. The expression "pressure difference or pressure drop across the control valves" refers to the difference between the pressure of the pressure medium at the inlet 22a and the pressure of the pressure medium at the outlet 22b, which occurs when the volume of pressure medium flows through the control valve. The maximum pressure drop (nominal pressure difference) is set, for example, by the biasing of the pressure compensators 24, and may be adjustable (statically) using, for example, an adjustment screw, or it may be displaceable (dynamically) using, for example, an electromagnetic displacement device. The nominal pressure differences of each different pressure compensators 24, and consequently each different control valve 22, may be different. In addition to the arrangement in which the pressure compensators are connected upstream as shown in the figure, other arrangements of pressure compensators are possible to achieve the above-described functionality (limiting the pressure drop across the control valves to the nominal pressure difference).

[0034] Given a given (constant) pressure difference, particularly a nominal pressure difference, across both ends of the control valve 22 (and given the characteristics of the pressure medium), the volumetric flow rate, i.e., the magnitude of the volumetric flow rate (e.g., liters per minute), through the control valve to the consumption device 20 connected to the control valve, depends only on the adjusted passage cross-section, i.e., only on the operating value, and not particularly on the load pressure. The pressure compensation device 24 reduces the pump pressure (e.g., selected sufficiently high) to a pressure equal to the load pressure of each consumption device plus the nominal pressure difference of each pressure compensation device. In this process, the hydraulic output is converted into heat via the pressure compensation device, resulting in output loss.

[0035] In Figure 1, the control valve 22 is shown in a highly simplified manner as a displaceable throttle or choke that appropriately controls the individual volumetric flow rates to the consumption device. More generally, for example, multiple volumetric flows in two chambers of a hydraulic cylinder can be controlled by a single directional control valve, in which case, for example, a displacement device acting in the opposite direction is provided. Such a single directional control valve that controls multiple volumetric flows using a corresponding set of operating values ​​may be interpreted as multiple control valves (for example, two in the above example where two chambers of a hydraulic cylinder are provided) in the sense of the present application or claims, each driven by a respective operating value, in which case only a single pressure compensator is provided, and the multiple operating values ​​are generally not independent of each other. That is, multiple control valves (in the sense of the present application) can be associated with one consumption device, in which case, this consumption device is associated with a particular pressure compensator. In other words, each consumption device is associated with at least one control valve and one pressure compensator.

[0036] A hydraulic drive system may be further equipped with pressure sensors. In particular, a pump pressure sensor 6 is provided to measure the pump pressure, i.e., the pressure of the pressure medium at the pressure outlet of pump 2, and / or, for each consuming device, a load pressure sensor 26 is provided to measure the load pressure, i.e., the pressure of the pressure medium caused by the load applied to the consuming device, or the pressure at the outlet 22b of each control valve 22.

[0037] An electronic control unit 8 (i.e., a computing unit, for example, a control device for a hydraulic drive system or a machine incorporated therein) is provided. The electronic control unit 8 is configured to control the control valve 22, that is, to determine and / or generate a control signal corresponding to an operating value and transmit it to the control valve 22 or the displacement device 22c of the control valve 22. Similarly, the electronic control unit 8 may be configured to control the hydraulic pump 2, that is, to control the displacement of the hydraulic pump 2. The electronic control unit 8 can detect an operating signal determined using, for example, a user interface 10 (e.g., a joystick), and control the control valve 22 and the pump 2 using a control algorithm based on this operating signal, in which case the control algorithm implements, in particular, the method according to the present invention. Furthermore, the electronic control unit may be configured to receive or detect pressure measurements from pressure sensors (pump pressure sensor 6 and / or load pressure sensor 26). In this case, the pressure sensors are configured to transmit the measured pressure measurements (pump pressure measurements and / or load pressure measurements) to the electronic control unit 8. Electrical control lines and electrical sensor lines for transmitting control signals or pressure measurements are shown as dashed lines in Figure 1.

[0038] The electronic control unit 8 (or control algorithm) specifically controls the pressure of the hydraulic pump 2 to a target pressure. In this case, the electronic control unit 8 can control or change the displacement volume of the pump 2, thereby controlling the pump pressure (i.e., the pump pressure measurement) to the target pressure. Furthermore, especially if the engine 4 is an electric motor, the electronic control unit 8 can also change the engine speed, and consequently the pump speed, to achieve the target pressure, in addition to or instead of the displacement volume of the pump 2. If the pump does not have a displaceable displacement volume (as shown in the figure) and is a metering pump, the electronic control unit 8 can control the engine speed (especially if it is an electric motor), and consequently the pump speed, to perform pressure control.

[0039] Figure 2 shows a flowchart according to one embodiment of the present invention. For example, it starts with a hydraulic drive system as shown in Figure 1. That is, it starts with a hydraulic drive system comprising a hydraulic pump with a pressure outlet, a plurality of hydraulic consumption devices, and for each consumption device, a control valve and a pressure compensation device associated with the consumption device. Each consumption device is hydraulically connected to the pressure outlet of the pump via an associated control valve, and for each consumption device, the associated control valve has a through cross-section that can be continuously displaced according to an operating value between a minimum cross-section equal to zero and a maximum cross-section. The minimum cross-section corresponds to a lower operating value, and the maximum cross-section corresponds to an upper operating value greater than the lower operating value, that is, the through cross-section increases from the minimum cross-section (when the control valve is adjusted according to the lower operating value or driven using the lower operating value) to the maximum cross-section (when the control valve is adjusted according to the upper operating value or driven using the upper operating value) as the operating value increases. For each consuming device, the associated pressure compensation device is configured to limit the pressure drop across the control valve associated with the consuming device to its respective nominal pressure difference. Pump pressure control can be performed, and this pressure control controls the pump pressure of the pressure medium at the pump's pressure outlet according to a configurable target pressure.

[0040] In step 100, the volumetric flow rate requirement for each individual consumer device can be detected or determined. The volumetric flow rate requirement is derived, for example, from control signals generated based on operator input using a user interface (e.g., a joystick). In this case, the volumetric flow rate requirement is the volumetric flow rate required to achieve the desired motion and / or speed of the consumer device in response to the operator input. In particular, the volumetric flow rate requirement can also be determined at least partially automatically by an automatic function, for example, an algorithm that performs a predetermined motion of the consumer device (e.g., triggered by operator input).

[0041] In step 110, the operating values ​​for the control valve are determined from the volumetric flow rate requirements, assuming that there are nominal pressure differences across both ends of the control valve (or assuming that there are nominal pressure differences across both ends of the control valve), that is, the values ​​required to obtain a volumetric flow rate equal to those volumetric flow rates passing through the control valve or to the consumption device. That is, for each control valve, the operating values ​​required for that control valve to satisfy the volumetric flow rate requirements of the corresponding consumption device (i.e., to obtain a volumetric flow rate equal to the volumetric flow rate requirements passing through the control valve) are determined, assuming that there are nominal pressure differences across both ends of the control valve (determined by the corresponding pressure compensator).

[0042] Subsequent branches in the flowchart, namely steps 120 and 130 on the one hand and steps 140 and 150 on the other, may be performed alternately (i.e., only one of the two branches may be performed), or they may be performed sequentially in any order (indicated by dashed arrows).

[0043] In step 120, a maximum operating value is determined, i.e., a maximum operating value equal to the largest of the determined operating values, and / or a maximum operating value equal to the operating value determined for the control valve associated with the consuming device having a maximum volumetric flow rate requirement. Alternatively or additionally, the maximum load pressure is determined as the largest of the load pressures of the consuming device, in which case the load pressure is measured, for example, using a load pressure sensor.

[0044] Optionally, the sum of the maximum load pressure and the nominal pressure difference of the control valve associated with the consumption device having the maximum load pressure can be used as the target pressure for pump pressure control.

[0045] In step 130, for a control valve, if the quotient (i.e., the operating value divided by the maximum operating value) of the control valve is less than a predetermined first value, the operating value of the control valve is increased to obtain a changed operating value for that control valve. A control valve that satisfies the above condition is referred to as the first control valve (of a set of control valves), and generally, two or more control valves may satisfy this condition, and therefore, there may be at least one first control valve. Alternatively or additionally, for a control valve (similarly referred to as the first control valve), if the (second) quotient (of the load pressure and maximum load pressure of the consumer device to which this control valve is associated) is less than a predetermined second value, the operating value of this control valve is increased to obtain a changed operating value for that control valve. When checking the above condition, only control valves associated with consumer devices having a non-zero volumetric flow rate requirement are considered. In the case of a condition relating to the (first) quotient of the operating value, the operating value of the first control valve can be changed or increased such that the quotient calculated using the changed operating value is greater than (or equal to) a first predetermined value. In the case of a condition relating to the (second) quotient of the load pressure, the operating value of the first control valve can be changed or increased depending on the calculated (second) quotient, in which case the smaller the calculated (second) quotient, the larger the increase. For example, if the quotient consisting of the second value and the calculated (second) quotient increases, the increase can be increased. The first value and the second value are positive real numbers greater than zero.

[0046] A hydrodynamically caused undersupply, i.e., a reduced volumetric flow rate through the first control valve compared to the original operating value, which may occur when the volumetric flow rate through the first control valve should be significantly less than the volumetric flow rate through other control valves (for which the maximum operating value has been determined), can be compensated for by increasing the operating value. An increase in pump pressure and / or pump volumetric flow rate, which eliminates the undersupply but may result in a larger pressure drop through the pressure compensation device and, consequently, a larger energy loss, is not advantageously required.

[0047] In step 140, for each consuming device, a pressure value called the consuming device pump pressure is determined, assuming that the consuming device pump pressure is applied to the pressure outlet of the pump and the passage cross-section of the control valve associated with the consuming device is displaced to its maximum cross-section, in order to achieve the volumetric flow rate requirement for each consuming device. Furthermore, the maximum of the consuming device pump pressures determined in this way is determined as the minimum pump pressure. The latter minimum pump pressure corresponds to the pump pressure required to satisfy at least all volumetric flow rate requirements.

[0048] Optionally, the minimum pump pressure can be used as the target pressure for pump pressure control, or as a target pressure determined from the minimum pump pressure (for example, the minimum pump pressure plus a predetermined compensation pressure value).

[0049] In step 150, for a control valve, if the difference between the selected minimum pump pressure and the load pressure of the consumer to which this control valve is associated is smaller than the nominal pressure difference of this control valve, the operating value of this control valve is increased and a changed operating value is obtained. A control valve that satisfies the above condition is referred to as a second control valve (of a set of control valves), and generally, two or more control valves may satisfy this condition, and therefore, there may be at least one second control valve. When checking the above condition, only control valves associated with consumer devices having a non-zero volumetric flow rate requirement are considered. By increasing the operating value, it is achieved that the volumetric flow rate requirement of the consumer to which the second control valve is associated is satisfied, or that undersupply does not occur even though there is no nominal pressure difference across both ends of the control valve. As a result, the target pressure of the pump (target pump pressure) can be selected to the minimum extent possible, that is, so that there is no nominal pressure difference between any of the control valves, while minimizing the unnecessary energy loss in the control valve itself, even through pressure compensation devices of other control valves where a nominal pressure difference must exist to meet the volumetric flow rate requirements.

[0050] The increase in the operating value of the second control valve is carried out using flow control, which defines a functional relationship between the volumetric flow rate through the control valve, the passage cross-section of the control valve, and the pressure drop across both ends of the control valve. For example, the increase in the operating value is carried out by multiplying the passage cross-section by the square root of the ratio of the nominal pressure difference to the actual pressure difference (pump pressure minus load pressure) to determine the passage cross-section corresponding to the operating value and to calculate the changed passage cross-section, and determining the changed operating value as the operating value to obtain the changed passage cross-section.

[0051] If both branches (steps 120, 130 or steps 140, 150) are performed consecutively, the changed operating value of the control valve (the first control valve if steps 120, 130 are passed first, or the second control valve if steps 140, 150 are passed first) that was changed in the first branch is used for the second branch step. It is possible that the control valve satisfies both the conditions in step 130 and the conditions in step 150. That is, a (single) control valve can be both the first and second control valve so that the operating value is changed or increased in both branches.

[0052] In step 160, the control valves are driven, in which case at least one first control valve is driven using an operating value and / or at least one second control valve is driven using an operating value, and at least one control valve other than the first and second control valves is driven using an unchanged operating value.

Claims

1. A method for controlling a hydraulic drive system, The hydraulic drive system comprises a hydraulic pump (2) equipped with a pressure outlet, a plurality of hydraulic consumption devices (20), and for each consumption device, a control valve (22) and a pressure compensation device (24) associated with the consumption device. Each consumption device (20) is hydraulically connected to the pressure outlet of the pump (2) via the corresponding control valve (22), and for each consumption device (20), the corresponding control valve (22) has a through cross section that is displaceable according to an operating value between a minimum cross section equal to zero and a maximum cross section. The minimum cross-section corresponds to the lower operating value, and the maximum cross-section corresponds to the higher operating value. Each associated pressure compensation device (24) for each consumption device (20) is configured to limit the pressure drop across both ends of the control valve (22) associated with the consumption device to their respective nominal pressure differences. The aforementioned method, 1) For each consumption device (20), determine the operating value for the corresponding control valve (22) such that the volumetric flow rate requirement of the consumption device is satisfied, assuming that the nominal pressure difference exists across both ends of the control valve (110), ●2a) Determine the maximum operating value as the largest of the determined operating values, and / or determine the maximum load pressure as the maximum load pressure of the consumption device (120), and 2b) With respect to a first control valve associated with a consumption device having a non-zero volumetric flow rate requirement, if the quotient of the operating value of the first control valve and the maximum operating value is less than a predetermined first value, and / or if the quotient of the load pressure of the consumption device to which the first control valve is associated and the maximum load pressure is less than a predetermined second value, the operating value of the first control valve is changed and the changed operating value is obtained (130). and / or, ●3a) Assuming that for each consumption device, the consumption device pump pressure is applied to the pressure outlet of the pump, and the passage cross-section of the control valve associated with the consumption device is displaced to the maximum cross-section, the consumption device pump pressure required to achieve the volume flow rate requirement for each consumption device is determined, and the maximum of the consumption device pump pressures determined in this way is determined as the minimum pump pressure (140), and 3b) With respect to a second control valve associated with a consumption device having a non-zero volumetric flow rate requirement, if the difference between the determined minimum pump pressure and the load pressure of the consumption device to which the second control valve is associated is smaller than the nominal pressure difference of the second control valve, the operating value of the second control valve is increased to obtain the changed operating value (150), 4) Driving the first control valve using the changed operating value, and / or driving the second control valve using the changed operating value, and / or driving the pump using the determined minimum pump pressure setting value (160), Methods that include...

2. When the pump is driven using the determined minimum pump pressure setting, pressure control of the pump (2) is performed, and the pump pressure of the pressure medium at the pressure outlet is controlled to the target pressure by the pressure control. The target pressure is equal to the minimum pump pressure, or The target pressure is equal to the sum of the minimum pump pressure and a predetermined compensation pressure value. The method according to claim 1.

3. Pressure control of the pump (2) is performed, and the pump pressure of the pressure medium at the pressure outlet is controlled to the target pressure by the pressure control. The target pressure is equal to the sum of the maximum load pressure and the nominal pressure difference of the control valve associated with the consumption device where the maximum load pressure exists, or The target pressure is equal to the sum of the maximum load pressure, a predetermined compensation pressure value, and the nominal pressure difference of the control valve associated with the consumption device where the maximum load pressure exists. The method according to claim 1.

4. At least one control valve, different from the first control valve and the second control valve, is driven using an unchanged operating value. The method according to any one of claims 1 to 3.

5. The load pressure of the consumption device (20) is measured using a load pressure sensor (26). The method according to any one of claims 1 to 4.

6. The first value is 0.2 or less, and / or the second value is 0.7 or less. The method according to any one of claims 1 to 5.

7. In step 2b), the operating value of the first control valve is changed, and in particular increased, such that the quotient of the changed operating value and the maximum operating value is greater than or equal to the predetermined first value. The method according to any one of claims 1 to 6.

8. In step 3b), the increase in the operating value of the second control valve is performed using flow control, which defines a functional relationship between the volumetric flow rate through the control valve, the cross-sectional area through which the control valve passes, and the pressure drop across both ends of the control valve. The method according to any one of claims 1 to 7.

9. In step 3b), Determine the through cross-sectional area corresponding to the operating value of the second control valve, The square root of the ratio between the nominal pressure difference and the actual pressure difference is multiplied by the determined cross-sectional area through which the modified cross-section is passed to calculate the modified cross-sectional area through which the cross-section is passed. The changed operating value of the second control valve is determined such that the changed through cross-section is obtained. The operating value of the second control valve is changed accordingly. The method according to any one of claims 1 to 8.

10. A hydraulic drive system comprising a hydraulic pump (2) equipped with a pressure outlet, a plurality of hydraulic consumption devices (20), and for each consumption device, a control valve (22) and a pressure compensation device (24) associated with the consumption device, Each consumption device (20) is hydraulically connected to the pressure outlet of the pump (2) via the corresponding control valve (22). For each consumption device (20), the associated control valve (22) has a through cross section that is displaceable according to the operating value between a minimum cross section equal to zero and a maximum cross section. The minimum cross-section corresponds to the lower operating value, and the maximum cross-section corresponds to the higher operating value. Each associated pressure compensation device (24) for each consumption device (20) is configured to limit the pressure drop across both ends of the control valve (22) associated with the consumption device to their respective nominal pressure differences. The aforementioned hydraulic drive system further comprises a calculation unit (8), The computing unit (8) includes a processor configured to drive the control valve (22) in particular, in order to carry out the method according to any one of claims 1 to 9. A hydraulic drive system.

11. The hydraulic drive system further comprises a pump pressure sensor (6) and / or a load pressure sensor (26) for each of the consumption devices (20). The hydraulic drive system according to claim 10.

12. A computer program, wherein the computer program includes instructions to cause the calculation unit to perform the method according to any one of claims 1 to 9 when the program is executed by the calculation unit of the hydraulic drive system according to claim 10 or 11.

13. A computer-readable data carrier storing the computer program described in claim 12.

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